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

[markreimer]

Hi Don,

I drained the gas and out fresh premium in it when I picked the bike up. Though funny you should mention gas… I dropped the bowls to replace my pilot jets. Cylinder 2 had deep yellow gas in the bowl with a little bit of sediment in the bottom. Yesterday it was perfectly clean with fresh gas. Kinda…weird?

I put a catch pan under the carb and let gas flow out with the bowl removed. Fresh clean gas flowed as usual. So I’m not sure what’s up with the dark yellow gas. Maybe there was a hint of old gas still left, or some old varnish that new gas dissolved, really not sure.

Anyway, proper jets went in and I took a 45 mile test ride, mostly freeway. It runs really strong! Pulls hard to redline in all gears. Smooth and linear power. I used to have stuttering wide open but that’s gone completely. The idle is a little rough, It purrs then periodically dips down and back up, so the screws need tuning.

But still, smokes like a chimney when on the throttle. Maybe worse even.

Pulled the plugs when I got home. At least they’re all the same level of borked this time hah.

Cylinder one, the worst from before


Cylinder 2, the one that had funny gas in the bowl.




And number four, which was the best before. All evenly black now.



They don’t smell like fuel to me and I don’t smell a gassy smell while riding. I’m thinking this must be oil. Though oil level hasn’t dropped at all, and it doesn’t stink like it either. Maybe the piston rings didn’t bed in, maybe the valve guide clearance is wrong, or seals, who knows. But I am really doubting that messing around with my carb or ignition is going to fix this problem now.  I wish I had a spare carb to A/B test


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[Don R]

 That's pretty evenly carboned for 4 different cylinders. Especially on a bike running well.

[seanbarney41]

Stop running premium.  That is what plugs look like when you run premium in an engine that doesnt want or need it.

[markreimer]

Interesting, I’ll try that. I can see that producing darker plugs. I always ran premium because it has no ethanol here. But that’s changing this year so I have no reason to anymore.

Don’t think that explains my smoking though.


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[scottly]

The "smoke" looks to me like fuel vapor, not burning oil; oil smoke lingers a bit, while vapor dissipates quickly. The black on the plugs also looks like carbon from too much fuel. 

[markreimer]

I hope so!

So, tonight's plan then:

Pick up some new D8EA plugs and some 1/8" clear fuel line.

Verify float level is correct with clear tube. I set them to 26mm via the service manual method. Check and adjust as needed.

Change out the gas for 87 regular. Ride for 20 miles or so to get the engine fully warmed up.

Come home, put the fresh plugs in, setup a fan, and let it idle for 5 minutes with mixture screws in the stock 1-turn out position. Don't touch the throttle. Pull and check all four plugs, adjust mixture screw as needed.

If they're still black and fouled, I'll pull the carbs and have another look I guess. I do have a set of Keihin 35 pilots, but I shouldn't need something so lean.

If they're tan, but it still blows smoke when blipping the throttle, then...I'm not sure.

I rode to work today. I put in a stock paper air filter before I left, just to make the bike as close to stock as possible. I had the mixture screws at 1-1/8 out. It felt like it was missing at low throttle a bit, but cleaned up when I got on the gas. Overall it ran rougher than last night for sure. It doesn't like running cold on those black plugs, go figure!

[scottly]

You are kind of pissing in the wind running the bike with fouled plugs. Try burning the black off with a propane torch.

[Prospect]

Please post a pic of your clear tube float checking method. Curious to see as well.

[markreimer]

Will do guys.

Just got back from the parts store, picked up 8 D8EA plugs and some clear fuel line. For kicks I turned my air mixture screw to 1-5/8 turns out before leaving. When I got back from the ride I blipped the throttle and...no..smoke?? It popped a lot more on decel when riding, but the idle is smoother and settles down to 1k.

I'll post pics and idle plug chop results tonight.

[markreimer]

Today I checked my float levels with the clear tube. I did it on the bike and it worked great if you remove the lower half of the air filter.

I started with 3/4. They came it at maybe 3-4mm below the surface.




I think this ever so slightly low, but decided to check the other two before making changes

1 was identical to 3/4, and 2 was way low.




Using a small right angle o-ring pick I could remove the float and adjust the tang. It took four tries to get it right but they’re all looking good. I think people usually say 2-3mm, but as I’m running rich and blowing smoke I don’t mind running 1mm lower for the moment. I finished the fuel system tasks by draining my premium gas out and replacing it with 87 octane Shell gas.

Next up I decided to seal up my Hindle exhaust. I could see a few spots that were leaking so I used Permatex ultra copper.



Looking into the exhaust ports I can see all four have slight dark spots below the guides. Looks like I have an issue there. Bad seals maybe (only 4 years old), and new guides went in about 7000 miles ago.






I got the pipe back on and was going to proceed with my idle plug chop but realized my exhaust sealant has to cure first. Shoot. Gonna have to wait till tomorrow. 


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[markreimer]

I also pulled my plugs to put new ones in for the morning. These are the same super sooty and black plugs I posted yesterday, but now the IMS is 1-5/8ish out (from 1-turn out before) and I went on a short ride to work and back. Maybe 10km. It’s already starting to clean up! This is the first time my plugs haven't been 100% black soot everywhere.

Progress, I’ll take it.




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[Don R]

 Some good news, awesome. 
  My 78 Goldwing hates Shell premium. It had 90 miles on the tank, I topped it off with 87 no alcohol and it was running better within a couple blocks. It had terrible throttle lag. 
   I did think your plugs looked like ones from a motor I had with a plugged up header. That was going to be my next suggestion, the PO had wrapped the fiberglass packing over the end of the baffle.

[markreimer]

Cleaned my plugs and went on a short city ride. The same ride that resulted in totally sooty fouled plugs a week ago.



Now we’re getting somewhere. 1 is a bit rich. 3 a bit lean. I think it’s time to sync the carbs, recheck, and tweak with the IMS.

Still have smoke puffing out though. Not always, but it’s definitely not gone. Only thing I can think of is guide seals

EDIT.

Six minutes idling on new plugs, hot engine, smelled gassy but it’s also a tiny garage, and I get zero colour. Not run long enough? Maybe it’s the mid range that’s too rich. Would explain smoking when blipping gas but no smoke when idling. Needle is stock, second richest position

I only started getting better results when I set the IMS to 1-5/8 yesterday. I used to have it 1-1/8 with needle in second leanest, but I also had aftermarket pilots then. So there is no way to make educated guesses yet as way too many variables are changing all at once. I think I’ll start by enriching the idle/IMS 1/8 turn and leaning the needle one clip and trying again



New settings: 40 pilot, 105 main, needle clip in the middle. IMS 1.5 turns out. Test ride tomorrow. Did a bench sync while it was off and found 4 was raised a lot higher than the rest. 1/2/3 were quite close.





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[markreimer]

60 mile highway ride followed by city riding to get home. My riding buddies said the smoke is much less, only puffing when rolling on the gas from a stop. That is classic bad valve guide seal symptoms.

The bike ran strong and smooth with the new jetting. I pulled the plugs when I got home and found blacker plugs than before. I had leaned the needle, richened the IMS 1/8 turn.

What’s strange is that 1/2 are black and 3/4 aren’t bad. Sort of a dark grey colour down inside the plug, with some white clean areas at the tip.

Only difference with 1/2 is that they receive fuel from the longer fuel line from my twin petcock. Otherwise it’s same coils, same jetting, carbs synced...

While pondering this strange result I heard a quiet wheezing from my gas cap. I could hear air struggling to enter (or maybe exit?) as though it was breathing through a straw. Strange… I will need to inspect and clean the cap and seal to see if/how this is affecting my carbs. Never had any indication of a fuel starvation though. And I doubt this has anything to do with my black plugs. If anything, a cap restriction would skew things lean.

Anyway.. the top row of plugs are my latest ones. Bottom row was the last jetting - richer needle, leaner IMS by 1/8 a turn.





Any guesses as to what could cause 1/2 to run richer?


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[Don R]

 I would agree a plugged gas cap vent is an unlikely cause of black plugs, but crazier things have happened. 

[seanbarney41]

Did you check for vacuum/carb boot leaks?

[scottly]

Have you removed and cleaned the emulsion tubes and verified they are correct yet?

[markreimer]

Have you removed and cleaned the emulsion tubes and verified they are correct yet?

Yes, I sure did. They’re clean as a whistle!

Also I didn’t check for vacuum leaks. The carb rubber hoses and clamps are pretty new, from Honda, but hey, it’s worth a check!


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[markreimer]

Small update today. I borrowed a leak down tester and checked the engine cold. I had about 10% leakage on all four, +/- one or two psi. I couldn’t hear a whisper out the exhaust pipe. If I plugged the crankcase breather hose I could hear a few gurgles in the oil tank so the minimal leakage I had seems to be at the rings.




So, valves and rings are good. But it smokes a bit. This points strongly at guide seals and/or jetting again.

[markreimer]

More jetting discoveries while I milk the last couple weeks of riding before winter.

I cleaned my plugs and head out on a 100 mile ride. After a long stretch of 70kmh riding I pulled the clutch in while killing the ignition. Pulled the plugs. 1 was wet with gas and dark. This is always my worst looking plug. But it was obviously swimming in gas. The rest were pretty dark but not fouled. This was after ten minutes on holding the same throttle position, roughly 1/8 throttle.
This is 1.




The rest looked like this more or less



Next I hit the freeway and belt 70mph for twenty minutes. That’s roughly 1/4 throttle or more. Same plug chop procedure.

Here is 1 again. Totally cleaned up. A nice off white.



I pulled all four and they were consistent. Clean with a touch of colour forming around the top.



I don’t have a way to do WOT chops. I would be doing 100mph immediately. There are zero hills here as well. But I’m not worried about the main. It’s stock and should be fine. It’s the low throttle positions I need to dial in.

So it seems I’m running rich at closed throttle to 1/8 or so. I know these carbs run rich there to compensate for no accelerator pump, but that doesn’t explain my wet 1 cylinder. Some fine tuning still needed.

I still blow a bit of smoke after stopping, and my pipe is sooty at the back.



I think going to 38 pilot Jets and replacing the valve guide seals over winter will be my next move. Another possibility that comes to mind is if the needle jet and jet needles are worn.





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[MauiK3]

Your wet cylinder might have a bad spark plug cap? Check resistance.

[markreimer]

Your wet cylinder might have a bad spark plug cap? Check resistance.

I have new NGK 5ohm caps and checked them a few weeks back but maybe it wasn’t seated on the wire properly… I’ll take a closer look at it. Thanks!


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[markreimer]

Hi all. It’s been about a year since I posted on this project. Progress had been slow, but it hasn’t stopped.

Over the past few months I’ve been chipping away at a few things here.

First up, I pulled the entire electric harness and various components out. I found so many wires with cracked insulation, connections that were green and fuzzy, signs of burning, you name it. It’s all getting replaced.




With the wiring pulled off, I had a great opportunity to instal the Gordon kit I bought a while back. Cutting the frame was a sick feeling but I’m very pleased with the results. The couplers are a very tight fit in the frame. I TIG welded everything in place and the whole installation process went smoothly.






I still need to drill holes for the little plates but that’s no big deal.

I turned my attention to the engine. I pulled the valve cover as the gasket had a bit of leakage. Glad I did as there was some overzealous application of sealant on the gasket. This is a great opportunity to clean it all up and put an OEM gasket up there.



While cleaning the engine up a bit I decided I should take the opportunity to paint it. The original paint is in terrible shape. I do not have the budget to break the whole thing apart and freshen up the bottom end, so I’m going to paint it assembled. I’ll polish the valve and side covers. That should make it look respectable but cost much less. The downside is I had an endless amount of cleaning to do now.

This was after three hours, two cans of brake cleaner and one container of Grez Off. Not even close to paint ready.





I can’t paint till it’s warm outside anyway, so I’ll just plug away at this over winter.

Debating if I should powder coat the frame while it’s mostly apart as well. The paint is equally as bad on the frame. It would be the smart time to do it. Project creep…


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[grcamna2]

I'm glad you're getting into the project and you have your own space to do it;does your shop have ok heat ?

[markreimer]

It does thankfully. It’s only 12x18 feet, so quite squishy in here. But I can warm it up to 15-20C on the coldest days without issue. I’m planning a new shop for about two years from now that will give more a bit more floor space.


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