Topic: I have my old cb750 back! Full restoration begins.

[markreimer]

Today is a good day.

I bought back a 1974 cb750k I sold four years ago. It was my first bike and I loved it. I owned it for about 8 years and rode the wheels off it, but I needed the money when we bought our first house. It was a sad day when it left and always wished I could have kept it and done a proper restoration someday.

The bike came up for sale last week by the very guy who bought it from me. We made a deal and it’s back in my garage. Sweet!

Surprisingly there is only a few thousand kilometers more on the odometer. However the bike definitely looks pretty rough. It needs a lot of work to restore it to good working order, which I'll document here.

The biggest issue is a major oil leak somewhere on the left side, likely under one of the rubber pucks or possibly the valve cover. Not sure yet. But the whole engine is covered in caked on oil in the front, and around to the back on the left side. There is a big oily mess behind the countershaft sprocket too. I can't remember if the auto chain oiler was working when I had it, or if this is from a leaking CS seal. The engine case paint is flaking off quite badly and is due for a refresh.

The fork lowers are heavily corroded and there is quite a bit of surface rust on the rims, spokes, steel fasteners, etc. I suspect it may have been parked outside for a while.

The wiring looks pretty bad, but it wasn't great when I had it either. It's mostly all original and just dried out and corroded. There are a few repairs in there, but I think now is a good time to re-do it all.

The carbs are WAY rich for some reason and it belches black smoke. I can start it pretty easily without choke. I noticed the rubber carb linkage boots are missing now, so someone has been in there since I sold it. There is a local vintage bike "mechanic" who I believe had his hands on this bike and carbs at some point. I have seen so many absolute bodges come out of his shop over the last few years, so I'm assuming they need a complete rebuild and stock jetting.

My plan is to do a complete frame-off rebuild. There is a lot of good stuff in the bike so my budget can mostly go to fun things like new paint, maybe some alloy rims and stainless spokes, maybe even some fancy flat slides, who knows. Perhaps some porting and a cam?

My goal is to make the bike a bit more responsive, a bit more power is always nice, but primarily I want it reliable, looking good, and oil tight.

I can TIG weld reasonably well now so I’m going to put in a Gordon frame kit for sure.

Current the good bits of the bike include:
- cycle-x 2nd oversize pistons with maybe 4000km on them
- recent valve job
- pamco ignition
- hindle pipe
- ikon shocks
- new OEM intake boots
- progressive fork springs
- wheel bearings
- tapered steering bearings
- Elan oil pump rebuild

Probably more I’m forgetting. Anyway, follow along if you like!






I’ll start by washing it down, giving it all a once-over and making a to-do list.


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[HondaMan]

Welcome back!
I'd surmise the carbs suffered the same thing mine did after sitting: the tiny air holes from the bell area of the carb into the main emulsifier tube (right below the needle jet) are probably corroded. You'll have to fully disassemble the needle jet and jet needle and then work a soft mechainc's wire thru the hole, from the little brass orifice in the rear carb bell, and push the crud thru and out. It took me about 3 hours to do it to mine. I couldn't ride more than 5 miles before it would foul all 4 sparkplugs, even coasting home on 1 cylinder during the final ride attempt after I started it up from a 5-year sitting session.

Why do you want progessive springs?

[markreimer]

Welcome back!
I'd surmise the carbs suffered the same thing mine did after sitting: the tiny air holes from the bell area of the carb into the main emulsifier tube (right below the needle jet) are probably corroded. You'll have to fully disassemble the needle jet and jet needle and then work a soft mechainc's wire thru the hole, from the little brass orifice in the rear carb bell, and push the crud thru and out. It took me about 3 hours to do it to mine. I couldn't ride more than 5 miles before it would foul all 4 sparkplugs, even coasting home on 1 cylinder during the final ride attempt after I started it up from a 5-year sitting session.

Why do you want progessive springs?

Thanks hondaman!

I know exactly what you’re referring to regarding the needlejets. Years ago I cleaned them up but it’s been sitting for ages now. I always had problems with this bike running rich. I sold it with stock jetting but still had a bit of black soot on the pipe and plugs. Something to look into anyway.


Progressive springs - I actually don’t want these haha. I just meant there is a new set of springs currently in the forks. I installed them ten years ago on the advice of a friend before I understood anything about suspension. A set of appropriate straight rate springs would be much nicer to have now.


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[PeWe]

Do not underestimate progressive springs.
My K6 has Ikon shocks with progressive springs. Handling is good and comfortable.
Classic Cycle City at eBay.de sell them.

My K2 has also Ikon shocks with non progressive springs. Not same handling,  either too hard or too soft. That bike is stock and more like a scooter so slightly too soft is OK when wife is riding with me. Bought them from Andy Cepok eBay.de.

If I knew, I should have ordered another set of the progressive Ikons.

Oversize stock pistons do not have much of a pocket for a hotter cam.
Very mild with not much lift.
I tried a  Kenny Harmon D in my K2 with +0.5mm Cruzinimage K7 pistons and a K6 stock head.
Too close valve vs pistons, light hit. So a stock K7 cam went back in. I guess a CX-1 will work.

If going for ported head and cam, bore bigger and use pistons with pockets for a hotter cam.  Dynoman has 811cc (64mm) JE pistons. This make it possible to use 836 (65mm) next time.

With that DP295 cam, Mike Rieck stage 3 head with 33.5/28mm valves and cast iron guides.
CycleX has 34/28mm valves for a good price. Stainless, hard chromed on stem so cast iron guides can be used.
But all this cost some.

[Stev-o]

WElcome back...following...

[HondaMan]

If the mainjets are Keihin, they should be #105 size. They will have a tiny "K" stamped on them if they are. If not, they are Keyster: use #110 mainjets if Keyster. You can also lighten up the sparkplugs' color by opening up the larger of the emulsifier tube's holes to 0.039" instead of the 0.0375" they were originally. Leave the smaller ones alone, except (forcibly) poke something thru for cleaning well. They oxidize when left sitting with moisture in the bowls, partially blocking their diameters.

[grcamna2]

Good to hear you have your originally owned CBB750 back again Mark.I know you've got some plans for it ahead 

[lash]

Welcome back!
I'd surmise the carbs suffered the same thing mine did after sitting: the tiny air holes from the bell area of the carb into the main emulsifier tube (right below the needle jet) are probably corroded. You'll have to fully disassemble the needle jet and jet needle and then work a soft mechainc's wire thru the hole, from the little brass orifice in the rear carb bell, and push the crud thru and out. It took me about 3 hours to do it to mine. I couldn't ride more than 5 miles before it would foul all 4 sparkplugs, even coasting home on 1 cylinder during the final ride attempt after I started it up from a 5-year sitting session.

Why do you want progessive springs?

What gauge mechanics wire?

[markreimer]

It's been about 10 days since picking up the bike and I've had some time to go over it a bit closer.

First task was just getting the bike clean. The entire engine was covered in thick oily sludge from leaks. I used some diluted Simple Green, some Purple Power, some Dawn dish soap, basically everything I could find I used until it was gone. What a mess! But now I think I've got every bit of sludge, tar, grit and grime off the bike. You can really see how bad the case paint has gotten.







Once cleaned up and left to dry in the sun, I tried to start it up. No dice. It would run on 3 and 4, but 1/2 were dead. I saw gas in the overflow tubes below the float bowls... a clue!




Pulled the plugs and they were very black and smelled of gas. I pulled all four, cleaned them up, and checked for spark. They were all very weak, but did spark. Popped them back in and I got a few stutters, then nothing. More gas in the overflows. This is a waste of time now, carbs need to be rebuilt and new plugs put in. So I rolled the bike back into the garage. At least it is clean!




My shop is getting a bit cramped with three bikes and all this stuff in here.

I think my starter clutch is going as well. I held the throttle wide open and hit the starter to try and clear out the flooded cylinders. That caused a real racket down by the flywheel. Far as I know, it's never been opened up. I'll add that to my to-do list.

So, priority #1 right now is getting the bike to pass highway safety inspections so I can get a license plate and registration setup in my name. I always prefer to do that before opening up an engine and spending money on a bike, if possible. The last thing you want is some kind of registration surprise/barrier after shelling out a few thousand bucks on a bike.

In order to pass the safety inspection here, the bike doesn't need to run. It just has to not leak any gas, oil, or other fluids while parked. Luckily my petcock and carbs do not leak when parked. I only get gas overflowing when trying to start. That should be good enough.

Tires, steering bearings, swingarm bushings, front brake, wheel bearings, fork seals, lighting, horn, side stand and ignition are all working fine. I just had to pull the rear wheel to measure the drum lining and pads and verify they aren't at or past the limit. No worries there - measured 180.04mm and the limit is 181.00mm. Pads are almost new.




With the bike cleaned up best as I can, I have scheduled an inspection for tomorrow morning. I'll trailer it down to the shop and cross my fingers.

If it passes, I'll register it and ride it around to spot where the leaks are coming from.

Then comes the fun part..... ordering parts and taking it apart!

[markreimer]

Little update on my CB750 project.

The bike passed inspection and I've got it registered and on the road again. Winter will put an end to the riding season in about  4-5 weeks so I'm using that time to put a few miles on the bike and get a feel for what needs going through.

First attempt at riding was short-lived as the front brake dragged hard. I made it a few blocks and came home. I pulled the caliper apart and the brake pad was stuck in the housing. It was an easy fix though - remove, clean, lube with high temp brake caliper grease on the back, and back in. The brake is perfect now and the front wheel spins easily when off the ground.

Last night I rode about 100km and there were some positives and negatives.

Positives included the fact that I appear to no longer have oil leaks. The bike came to me covered in grime and oily sludge all over the engine. But I can't find any sign of oil leaks anywhere expect a small occasional drip from the oil filter housing when parked overnight. Must be a bad o-ring or something. Nothing from the valve cover gasket, head gasket, cam carrier pucks, etc. So that's handy. I'm still going to pull the engine apart, but at least this way I can put some miles down before winter without making a mess.

Other positives include nice strong brakes, comfortable suspension, and a pretty smooth feeling engine.

Negatives are mainly in the carburetor and electrical departments. The guys riding behind me told me the bike is blowing a mix of black and white smoke depending on throttle, and it smells like gas strong. I can smell the gas when I come to a stop as well, though never saw the smoke. The plugs confirm - they are very black, as is the tip of the exhaust. And my garage stinks like gas after I park it overnight. There are no gas leaks - the petcock works, no gas in the overflow tubes, and the gas cap is good too. It's just the stench coming from the pipe.

When I sold the bike it had stock jetting and the needle was one clip leaner (second from the blunt/top end). 40 pilot, 105 main, 1-1/8 turns out on the screws. Stock airbox with K&N filter and some small holes drilled in the box per Hondaman's book. I had set the float height manually and checked with the clear tube, confirmed 2-3mm below gasket surfact. I do not know if this is still the case and will need to pull them apart. It always ran rich when I sold it as well though, so something is up. Maybe the floats are off and making everything way rich.

The wiring harness and most electrical is all original with the exception of new spark plug wires/caps spliced into the original coils, and a Pamco ignition. The harness is rather rough. I wouldnt' be surprised at all if I had a decent voltage drop at the coils and a weak spark.

I'm going to start by pulling the carbs and returning jetting to stock with OEM jets, original needle position (even though stock position is actually richer than what I have, just need a baseline at the moment), check all the little passages including that air passage in the intake the runs to the emulsifier tube. I'll check the voltage at the coils, as well as the coils themselves, and check the plug wires. I'm not sure if my jetting is way off, floats too high, if my ignition is weak, maybe all of the above. Most likely all of the above hah.

Also, my exhaust is a slip-fit held with springs design. I have no gaskets or adhesive at any of the joints. I think I'm getting some leaks as a result, which leads to popping on decel. I probably tried to compensate with jetting before I realized I likely had a leak.

Lots to look into this weekend.

Oh, and I've also got a Gordon frame kit in the mail from RRR Tool Solutions. Should be here next week, but I'll wait for winter to weld it in.

[MauiK3]

Following

[markreimer]

Today was a day of inspection and testing which resulted in a some surprises.

So, to recap, bike is blowing nasty gassy black smoke and sometimes white. Just stinks.

I opened up the carbs and much to my surprise they had stock keihin jets. 40 pilot and 105 main. The needles were in the second leanest position, but stock should be second richest position. Strange!










All the passage ways were clean. All the jets and emulsion tube were clean. There was nothing amiss I could find. So I cleaned it anyway, and returned the needles to the stock clip position of fourth from the blunt top.









Next I started testing my ignition stuff. Both coils measured out good. 4.9 ohms and 5.1 ohms. Second measurements were also good. 14.8 and 15.6 ohms across the plug wires (caps removed).

So I moved on to checking power at the coil. Here’s where it got spicy. My batter was showing 12.5v with the key on and kill switch at run. Testing between the coil power supply and any ground gave me 9.5-10v. Up to a 3V drop! That’s no good.

I started looking closer at the wiring and it’s a mess. Tons of corrosion. Wiring with insulation melting. Cracks and splices and all manner of crap




 
I had a 1V drop by the time power reached the main fuse. And another up to the switch. I think it’s best if I junk this harness and start fresh. I might try to hook up a relay straight to the coils to test first, but then it’s out with the old!

These are plugs 1/2/3/4. And a close up of 4, the “best” of them haha.





Last thing I did while I was in there was a compression test. Number two is a hair low compared to the rest, but I’m happy with this. This was with the carbs off, and never checked the valves yet.

1: 162
2: 154
3: 161
4: 164

More to come…


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[RAFster122s]

Things have become much clearer now...
Someone did something nasty & stupid to the bike while you didn't own it.

Agreed that you need a new harness.

Well, your project for the winter became clear. Will run like a new bike when you have it finished. And I must say, those are some clean carbs...

[PeWe]

105 mains with the Hindle 4-2-1 feels too small.

105 works with stock 4-4 HM341 and stock airbox which also need needles in the middle.

My K2 has good flowing Yamiya 4-4 (as HM300).
105 was way too lean, had to use 115, needles at 4th from top. I guess your bike can run on same setting.

The black plugs can be oil residues if you have checked fuel levels in bowls.

Oil residues or way to rich at idle and low lifts can hide way too lean mains.
Pipes will get a bluish tone though. Hindle pipes easy to polish back to shiny stainless, a longer ride later back to the bronze tone.

I have done that a few times due to mentioned reason.

[markreimer]

105 mains with the Hindle 4-2-1 feels too small.

105 works with stock 4-4 HM341 and stock airbox which also need needles in the middle.

My K2 has good flowing Yamiya 4-4 (as HM300).
105 was way too lean, had to use 115, needles at 4th from top. I guess your bike can run on same setting.

The black plugs can be oil residues if you have checked fuel levels in bowls.

Oil residues or way to rich at idle and low lifts can hide way too lean mains.
Pipes will get a bluish tone though. Hindle pipes easy to polish back to shiny stainless, a longer ride later back to the bronze tone.

I have done that a few times due to mentioned reason.

Yes I also thought 105 would be too lean, but doesn’t seem to be the case. Intake is stock and the open pipe alone might have some affect but only a jet size or two I would expect. I have 110 and 115 mains which I’ve tried years ago, but recall it ran poorly. I will have to look into it more.

I checked floats. All four were exactly 26mm. Need to confirm with clear tube still.

It’s been running 105 and leaner needle for at least 4000km I believe. Hindle pipe is a nice bronze, no bluing at all.

The engine has a few thousand km on a cycle-x second oversize piston kit, and new valve guides and seals. I don’t have any oil level drop or burning oil smell. Smoke is black and white, not blue. But I’ll definitely look into it more, appreciate your suggestions.


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[markreimer]

More progress on the 750 last night.

I started off by wiring in a relay to power the coils directly off the battery. I ran a 15A inline blade fuse off the battery positive to a 4-pin relay. Power comes in, then leaves to a female Y-connector, where the coils’ black wire plugs in. The relay low-voltage circuit is powered by the original coil power source, so I retain the killswitch and ignition switch power cut off. Simple and easy to undo.





I tested power at the coils and the relay bumped voltage from 9.5V to 12.1V. Power down at the dyna connection went up 1.5V as well to 11.89V.

I pulled all the old plugs out, lay them on the engine block and turned out the lights. Hit the started and watched the spark. Then I did it again with new plugs, and then again with the original wiring setup for comparison sake.

I’m not actually sure if my spark looks good to be honest. Its a purple colour, not a fat blue. The spark arcs off the edge of the centre electrode and kinda dances around to a different spot each spark. Its very similar to the attached photo.



What do you guys say, is that not ideal? If I’m still not getting a good spark then something is wrong with my testing.

I took some slow mo video to try and capture the spark quality.







I moved on to setting the valves. Seven of the eight valves were loose. Some of them quite loose actually. It took me a minute to remember how to set the crank position for cb750 valves, but it came back soon enough. 0.002” and 0.003” for IN/EX. I adjusted the cam chain statically by rotating 15 degrees past TDC for cylinder #1, then slapped the carbs, airbox and tank back on.




With sparkling clean carbs and fresh ignition, I pulled the choke, opened the petcock and hit the starter…..nothin! not even a puff!

Checked for spark - all good. Pulled a float bowl, dry as a bone! Checked the others, and I had at most 2-3ml of gas. I tapped the petcock with a screwdriver handle and suddenly fuel started flowing. Not sure if that was an airlock or what, but now all four are filling with gas nice and quick, but only in reserve. I don't think my fuel level is low enough to need reserve though. I’ll need to look into the condition of the petcock and filter screen, as well as the fuel line routing. The fuel line is brand new and I’ve cut and routed it so that its downhill the whole way, but something is a bit amiss there. That 1/2 fuel line has always been tricky to get right.

Anyway, with the petcock in reserve the bike fired up quickly and sounded crisp. It didn’t need full choke within a few seconds, which hasn’t been typical. I could shut choke off entirely quite quickly and it purred at idle nicely. There is definitely an improvement here.

Sadly it was 1:15am and too late for a test drive… that will come today/tomorrow after I seal up the exhaust

Final thoughts. I noticed the Honda manual states the Canadian export cb used DR8ES-L plugs (I am Canadian). Not D8EA. Curious difference. I have new D8EA in the bike now and have always used that plug. I don't think the rest of the ignition system is different between US and Canadian bikes, so not sure what that would be. It would be easy enough to switch them around next time and compare. But I also need to verify my bike isn't a US model imported to Canada. It is in MPH, and Canada went metric in '71 I think.

[Prospect]

I don't have anything to add from a technical aspect but your write up is the best I have seen on this forum. Complete details, pictures, a write up of what you have done and results, theories etc. The  ultimate was the picture of the spark. Not easy to take that.  I'm impressed.

[markreimer]

Thank you @Prospect! I think I enjoy sharing progress on this forum as much as the restoration itself sometimes. Glad you are enjoying it. There will be much more to come. I see in your signature you have a ’75 Gl1000. I had one as well! I sold it to buy this cb750 back. Pretty neat bikes.




Tonight it was time to give the bike a test drive after yesterday’s ignition work. I fired it up and was disappointed to see that the pipe was blowing smoke again. Whenever I’d blip the throttle a puff of smoke would follow. It idled nice and clean but with some gas it would blow white/blue smoke. I let it run for a few minutes this way.

I wondered if maybe the pipes were just full of junk from running poorly so long. Maybe it needed a good hard ride before making any final judgements. Before heading out, I checked the oil. It was an inch over the full mark…

Well what the heck, that could produce some smoke. I had checked the oil after buying the bike, before I fired it up, but never actually checked the level. It was more of a “yup, there's oil in there” kinda check. Not knowing if it had been overfilled, or if gas had leaked into the crankcase from leaking floats (remember, I did have gas in the overflow tubes when I first tried to start it) I decided to do an oil change.

This was the first of a comedy of errors for the evening. I removed the filter housing as I was sure I had a filter kicking around, but turns out I did not. No big deal, I’ll just change the oil and reuse the filter. After adding 3L of oil, I fired up the bike and oil leaked rapidly from the filter housing. It was dripping before, but this was much worse. I have a few spare housing o-rings laying around and had to try three different ones until the leak finally stopped. It seems there is a tiny scratch on the sealing face that is letting oil past. I put a dab of Hondabond on it and that seemed to do the trick.




With the bike running, I headed out on my ride. It was about 10:30pm and dark out. 10km in, I stopped for gas. The bike was running GREAT. The stock, richer needle position was a huge improvement. The bike accelerates much better, and also doesn’t pop nearly as much when closing the throttle. I have the IMS at 1-1/8 but I think an even 1 turn might be perfect.

At the gas station, I couldn’t see any smoke from the pipe when blipping the throttle. Could it be? Success already? I filled up with premium and hit the highway.

Then my headlight died…

I pulled over but could not get the headlight to light up again. Bummed out, I turned around and carefully rode back into the city and home with no light, disappointed I couldn’t really give it the beans yet. Once back in my garage, I could again clearly see smoke puffing whenever I blipped the gas. Doesn't seem to have changed at all.

I pulled the 1 and 4 plug. They look almost identical to the plugs I pulled out when I bought it. Black and either very rich, or burning oil. I also noticed the threads of the worst plug was oily. Not looking good for my pistons is it! The worst plug is #1. With the piston at the bottom, I tried to peer into the cylinder. I can see some scratching, but I think it’s just the cross hatching. I need to borrow a borescope.

This is the same plug. White on one side. Black on the other. But if a zebra complex. Not sure what’s up with that?





Ok, back to the headlight. I traced the wiring back from the headlight until the fuse box. Just look at the mess behind the headlight, so many splices, electrical tape, even a spider jumped out of the mess! The fuse box is rough looking as well, like everything else.






I found the 7A fuse that powers the headlight. I started to pull it out and the light came on! The clips were very corroded. And I also found a 14A fuse when it should be 7A! Everything was cleaned up to bright metal and new proper fuses installed. Everything works properly again.

But now it's midnight again and I still haven’t had a chance to ride the bike hard and see if the smoking clears up. If it doesn't, the top end will have to come off, and that's all there is to it. No need to wait for winter. And the job should be pretty easy now, since this arrived today…

[markreimer]

Here is a video of the bike running and smoking. I really need to do a carb sync because the clutch rattle is BAD. I never remember it being this bad before. You can hear it disappear when I pull the clutch lever.

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[RAFster122s]

Do not presume you have an issue that is super expensive or complex. Verify your oil levels again... It is not unheard of to have the anti drain back valve to allow too much oil into the motor and that can cause things to smoke a bit. Doesn't sound like you are having carb issues where you are getting fuel washing down a cylinder and corrupting the oil.
Plugs can foul fairly quickly from idling and plug chops are done with fresh plugs or cleaned plugs operating in the power band you are wanting to check and kill switch is used to cut motor after several minutes of running at that power/throttle position. That gives a more accurate assessment of the fuel being rich or lean.
With all the other issues you mentioned I bet the carb brass needs pulled and cleaned, cleaning any deposits from the jets with a soft copper wire. Carb bodies likely need cleaned too.
Sounds like a neglected bike that needs going through. All the electrical connectors need disassembled and cleaned with dab of dielectric grease used on reassembly. How's your air filter looking? That can affect idle mix if it is dirty/too restricted causing a false rich mix.

[markreimer]

Do not presume you have an issue that is super expensive or complex. Verify your oil levels again... It is not unheard of to have the anti drain back valve to allow too much oil into the motor and that can cause things to smoke a bit. Doesn't sound like you are having carb issues where you are getting fuel washing down a cylinder and corrupting the oil.
Plugs can foul fairly quickly from idling and plug chops are done with fresh plugs or cleaned plugs operating in the power band you are wanting to check and kill switch is used to cut motor after several minutes of running at that power/throttle position. That gives a more accurate assessment of the fuel being rich or lean.
With all the other issues you mentioned I bet the carb brass needs pulled and cleaned, cleaning any deposits from the jets with a soft copper wire. Carb bodies likely need cleaned too.
Sounds like a neglected bike that needs going through. All the electrical connectors need disassembled and cleaned with dab of dielectric grease used on reassembly. How's your air filter looking? That can affect idle mix if it is dirty/too restricted causing a false rich mix.

Hi RAFster122s, the plugs shown in my last post were brand new, but to your point I did not have enough time to stay in a particular throttle position to make for a quality plug chop. Hopefully I can do that this evening.

I totally agree about the electrical comments, it needs a complete going through. Air filter looks good! I checked it when I pulled and cleaned the carbs. It's a K&N unit and appears in great shape, nice and clean and seems recently oiled. I have a new paper unit as well laying around.

I'm pretty confident though that the carbs are good. You can see a few posts back I pulled the carbs apart, removed all the brass bits and cleaned them in carb cleaner, ultrasonic cleaning for the bodies, and I used a soft brass wire to poke through all the passages. I've cleaned a lot of carbs and would bet these are as clean as any.

Your note about the anti-drain back valve is interesting. i'll check the oil level again this morning as I confirmed it was right on the full mark last night after riding. I did rebuild the oil pump prior to selling with one of those 'Elan' kits, so the valve should be good, but who knows.

On that note - how much oil typically drains from the oil pan during a change? I should have measured the quantity last night. I would guess it was around 0.5L or so, just a guess though.

[ekpent]

 The bike would have come with 110's stock. I don't think those mains are Kehin as they do not mark the size on the side of the jet but usually on the face. Was there any other stamps on them ? Are the #40 slow jets stamped with the 'K' ? Might want to make sure whatever is in there for a main has not been drilled larger.  Enjoy the project !

[markreimer]

The bike would have come with 110's stock. I don't think those mains are Kehin as they do not mark the size on the side of the jet but usually on the face. Was there any other stamps on them ? Are the #40 slow jets stamped with the 'K' ? Might want to make sure whatever is in there for a main has not been drilled larger.  Enjoy the project !

K4's switched from 110 mains to 105 mains mid-run. I found the serial number that indicates when the switch happened, and mine is well after. I do have some 110 and 112.5 handy if I need to change, but right now the issue is plug fouling and smoke, so I don't think I want to go richer just yet.

I think these 105's are genuine Keihen, as they have the same stylized "K" logo on the side as the original needle and float valves. Maybe they changed how they brand them? My FCR Keihin on my XR650 has the same side stamping.

But you know what, I don't see the same icon on the slow jets..! They might actually not be genuine after all, great catch! I'm going to look into that and if they aren't, that's an immediate replacement.

[markreimer]

@ekpent, I owe you a beer or something!



The big jet on the left is what I have in my carbs now. The smaller one to the right are old genuine Keihin 40s I found in my parts bin.

I can see the difference in the hole size. The genuine jets seem smaller. The bigger ones in my bike now have no Keihin “K” logo as Ekpent noticed. The smaller ones I found do.

Looks like I have mystery aftermarkets in my bike.

All four genuine 40 jets are getting a soak in carb cleaner and a scrub then back into the carb they go. I’m very curious what effect this will have on running and plug condition.


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[Don R]

 I didn't read it all but be sure the gas is fresh.