Topic: My CB750K2

[denward17]

^Did that fix the wet sump issue?

[willbird]

^Did that fix the wet sump issue?

I think so, before it would drain down overnight from clear full to barely on the dipstick, and 2 days would leave the tank nearly empty. Just checked it now and pretty sure it did not drop much over night.

Bill

[HondaMan]

Bike had a wet sumping issue. Removed header and dropped oil pan hoping to just change the rubber tip of the anti drain back valve. Valve was stuck clear open. Somehow the bore where the piston rests when engine is off seems too small. Submerged a spare pump I had from Ebay and installed it with new O rings. Installed an Ebay K8 oil pan.

The tunnel where that sump valve lives is probably a little bit oval. They sometimes distort like that, making the valve stick open. I have a reamer (somewhere around here) that I run thru those when I get them, fixes it right up again.

[willbird]

Bike had a wet sumping issue. Removed header and dropped oil pan hoping to just change the rubber tip of the anti drain back valve. Valve was stuck clear open. Somehow the bore where the piston rests when engine is off seems too small. Submerged a spare pump I had from Ebay and installed it with new O rings. Installed an Ebay K8 oil pan.

The tunnel where that sump valve lives is probably a little bit oval. They sometimes distort like that, making the valve stick open. I have a reamer (somewhere around here) that I run thru those when I get them, fixes it right up again.

I hear you on that "somewhere" LOL. All my stuff is somewhere LOL.

[willbird]

The bike suddenly started running like crap. It has kind of always had a "weird" spot in the rpm between 2750 and 3250rpm that I just kind of lived with. I have been clear through the ignition, checked advancer operation, one point set was at .009, fixed that, checked both ends of the plug wires. Switched HondaMan out briefly, jumpered out kill switch. I have had the rack on and off I think 4 times now moving needles up and down.

One coil DID have some corrosion where wire plugged into it (ebay 3 ohm coils with towers), swapped it out, was going to swear that was the issue but no. Swapped the other coil too. Put the old KN pods back on and that made it a LITTLE better (I had put on new UNI pods awile back)

Finally said screw it and put my new Delkevic 4:1 on it, thinking about going back to airbox too but have not gotten there yet.

Currently it sits on 130 Kehin main jets and with needles one notch up from the middle.

I have a another rack I bought on ebay for my K3 project, have them all ultrasonic cleaned, going to work on getting them assembled and give them a whirl and see how that goes, had always intended to run them on this bike first.

Bill

[MRieck]

Those oem carbs are very sensitive to needle height. Up or down a notch makes a hugh difference in fueling....probably due to the type of taper. Maybe .020 shims will work....Suzuki has a part number. 130 main is a lot even with K&N's...combine that with raising the needle and that's a ton of fuel. Most times those needles and needle jets are worn out...I don't think oem are avalable anymore

[willbird]

Those oem carbs are very sensitive to needle height. Up or down a notch makes a hugh difference in fueling....probably due to the type of taper. Maybe .020 shims will work....Suzuki has a part number. 130 main is a lot even with K&N's...combine that with raising the needle and that's a ton of fuel. Most times those needles and needle jets are worn out...I don't think oem are avalable anymore

Yes it is a real crap show really as we all know LOL. But it has been on the same setup now since 1995 and overall ran pretty decent. I had the needles all the way up Friday and ran a WOT blast over 100MPH in Mexico ;-), that is with a Windjammer II fairing. I was really hoping to find something stupid like a mouse nest in the Mac muffler that had shifted around when I had it off the bike than put it back on, but nope. Since I got it running again I have had 1/4" tygon fuel lines on it with clamps, had put the "superior" OEM fuel line on it and I think that is an issue right now, did not throw the tygon away, will put it back on. Bringing it back to life I had settled on the Tygon as the only thing that "worked". It was really windy the day I swapped the K&N back on, was thinking the new UNI pods might be even more wind sensitive than the old school K&N.

Did a clear tube test on the flaot level too and tweaked a couple that were maybe slightly shallower fuel level than the other two.

I am really SMH because overall it ran decent up to now. Decided to let the darn thing sit for a day, I messed with it all last week and really did not get anywhere. It was a good thing to go over all the things I did and know they are correct. Cleaned the points too thinking maybe I got something on them using feeler gauges.

Before I swapped on the Delkevic the plugs were pretty white, now they have some color. Have not went out and did a proper WOT plug chop yet. I have a big "kit" of non OEM jets and Kehin 110, and 120 in addition to the 130 that have been in the bike since the 1990's. The 130's I THINK went in when the K&N pods went on, I had an action 4's header on it then, or maybe they went in when I added the MAC header in 1992 or so. I know 1992 MAC install was when I raised the needles up one notch from the middle, it was lean at cruise 60 mph 4krpm or so, plugs bone white.

I have sure gotten practice making needle height changes, have had the fuel tank off more in the last week than on lol.

Bill

[PeWe]

Which CB750 carbs another detail.
The carbs my K2 got last summer are stamped 064A, for CB750F-75.

The needles different than the K6 carbs stamped 086A I used before.

064A has richer needles, thinner taper.
Middle notch is the setting to use.

Same bike had 1 notch richer with 086A carbs.
Main jets 115 for both.
Yamiya no numbers  4-4
Stock air box with K&N filter.
+0.50mm K7/K8 CI pistons give higher compression.

I have had issues caused by fuel delivery.
Adjusted floats, clear tube.
Still got issues after higher speed for a while, 140-160kmh.

I was tricked to use too big main jets (120) Bigger mains gave  sooty spark plugs.
 
Finally fiddled with the fuel hoses.
Probably the rear hose from petcock that has a curved route thru carb rack to carb 3-4. A too bent hose (kinked) reduced flow was my idea.
Also the other hose and how the T pipe is turned, not causing a bent fuel hose.

Now no problem to cruise 160-180kmh for a while without running bad until slowed down the speed for a while.

My K6 with different carbs have stiffer braided fuel hoses made for fuel injection (Gates). All bends via plastic fuel 90* bends. Like a plumber has done it.

My K2's Yamiya not braided and more flexible fuel hoses must be routed correct.

[willbird]

Which CB750 carbs another detail.
The carbs my K2 got last summer are stamped 064A, for CB750F-75.

The needles different than the K6 carbs stamped 086A I used before.

064A has richer needles, thinner taper.
Middle notch is the setting to use.

Same bike had 1 notch richer with 086A carbs.
Main jets 115 for both.
Yamiya no numbers  4-4
Stock air box with K&N filter.
+0.50mm K7/K8 CI pistons give higher compression.

I have had issues caused by fuel delivery.
Adjusted floats, clear tube.
Still got issues after higher speed for a while, 140-160kmh.

I was tricked to use too big main jets (120) Bigger mains gave  sooty spark plugs.
 
Finally fiddled with the fuel hoses.
Probably the rear hose from petcock that has a curved route thru carb rack to carb 3-4. A bent too bent hose reduced flow was my idea.
Also the other hose and how the T pipe is turned, not causing a bent fuel hose.

Now no problem to cruise 160-180kmh for a while without running bad until slowed down the speed for a while.

My K6 with different carbs have stiffer braided fuel hoses made for fuel injection (Gates). All bends via plastic fuel 90* bends. Like plumber had done it.

My K2's Yamiya not braided and more flexible fuel hoses must be routed correct.

I'll have a look at carb numbers, they are whatever round tops Honda used, still OEM. I have a set of DENSO X24ES-U 4099 to swap in as well. The OEM style plugs in it now have about 4K miles on them.

Bill

[HondaMan]

Finally fiddled with the fuel hoses.
Probably the rear hose from petcock that has a curved route thru carb rack to carb 3-4. A too bent hose (kinked) reduced flow was my idea.
Also the other hose and how the T pipe is turned, not causing a bent fuel hose.

Now no problem to cruise 160-180kmh for a while without running bad until slowed down the speed for a while.

I once had to solve a similar issue on a cafe'd 750K6 bike with the Carpy fuel tank that sat so low on the frame that the petcock outlet (only 1) ended at the same height as the float valve in the carbs(!). So, the carbs kept running out of fuel for no downhill flow. The tee didn't work at all, starving the 1-2 carbs (petcock on the right side by 3-4 carbs). After raising the front and rear of the tank with custom-made rubber mounts (i.e., offset discs at the front and raised block at the back, 3/4" each) I did like you, Per, with copper pipe for the sharp bends: rubber to a 90-bend at the petcock, that one line ran from there to the top of the [stock] airbox where I mounted a copper pipe (1/4" ID) across the top of the box and fitted a 1/4" ID tee to feed the 3-4 side, then across the top of the airbox to the 1-2 side. It finally would run, which was problematic before this mod. We found, over time, that accelerating down a 1/4 mile run hard with it would starve the carbs by 4th gear, though in normal riding it never showed a problem. The fuel tank was just too low, IMHO.

I learned this sort of thing from the old 10 gallon BMW fuel tank that we could get in the 1970s. The bottom gallon on both sides wouldn't feed those Bings (metered leaks, in German) in 'deep reserve' hardly at all.

[HondaMan]

Bike had a wet sumping issue. Removed header and dropped oil pan hoping to just change the rubber tip of the anti drain back valve. Valve was stuck clear open. Somehow the bore where the piston rests when engine is off seems too small. Submerged a spare pump I had from Ebay and installed it with new O rings. Installed an Ebay K8 oil pan.

Got these bolts from Belmetric, this is a K3 pan on a K3 engine I have on an engine stand, handy to have a spare engine sitting around to do stuff like try bolts :-). The bolt at 6 oclock was tough to get a socket on the K3, I had to turn a 1/4" drive socket smaller. I lathe turned .04" aka 1mm off the flange dia.



This is what the K8 pan looks like

Yeah, someone at Honda goofed up on the K3-K5 oil pans with that one bolt! I have a 1/4" drive thinwall 6mm long socket, just for those bolts.

Some of the K1 bikes had the issue, too, but not all.

About white plugs: what clamps are you using on those new Honda hoses? Reason I ask: all the modern versions of the hoses are smaller on their OD by almost 2mm. This makes it almost impossible to clamp them tightly. I've used (variously) Honda's 500/550 hoses clamps and the Oetiker 050-9 clamps (be careful with the latter, they are so strong they can cut the hose right off!) on the engine side. I've also sometimes been able to make oval wasjers (4 or 5mm size) to fit inside the old clamp's screw mounts, then flattened out those mounts to snugly nestle the ovalled washers in, to make a straighter, more square closure over the hose. I ran my own K2 that way from 2008 to 2013 before going to the Oetiker clamps - the latter completely solved it. I was getting white plugs on 2 cylinders, totally out of character for this bike in 50+ years(!). It vibrated, too. Now it doesn't.

[willbird]

Bike had a wet sumping issue. Removed header and dropped oil pan hoping to just change the rubber tip of the anti drain back valve. Valve was stuck clear open. Somehow the bore where the piston rests when engine is off seems too small. Submerged a spare pump I had from Ebay and installed it with new O rings. Installed an Ebay K8 oil pan.

Got these bolts from Belmetric, this is a K3 pan on a K3 engine I have on an engine stand, handy to have a spare engine sitting around to do stuff like try bolts :-). The bolt at 6 oclock was tough to get a socket on the K3, I had to turn a 1/4" drive socket smaller. I lathe turned .04" aka 1mm off the flange dia.



This is what the K8 pan looks like

Yeah, someone at Honda goofed up on the K3-K5 oil pans with that one bolt! I have a 1/4" drive thinwall 6mm long socket, just for those bolts.

Some of the K1 bikes had the issue, too, but not all.

About white plugs: what clamps are you using on those new Honda hoses? Reason I ask: all the modern versions of the hoses are smaller on their OD by almost 2mm. This makes it almost impossible to clamp them tightly. I've used (variously) Honda's 500/550 hoses clamps and the Oetiker 050-9 clamps (be careful with the latter, they are so strong they can cut the hose right off!) on the engine side. I've also sometimes been able to make oval wasjers (4 or 5mm size) to fit inside the old clamp's screw mounts, then flattened out those mounts to snugly nestle the ovalled washers in, to make a straighter, more square closure over the hose. I ran my own K2 that way from 2008 to 2013 before going to the Oetiker clamps - the latter completely solved it. I was getting white plugs on 2 cylinders, totally out of character for this bike in 50+ years(!). It vibrated, too. Now it doesn't.

I am using the Oetiker 050-9

Bill

[HondaMan]

I am using the Oetiker 050-9

Bill

No leaks there!

[willbird]

I am using the Oetiker 050-9

Bill

No leaks there!

They are for sure nice clamps. Since I got the new bike and have left the K2 sit the oil level in the tank looks stable so far, it has been 5 days now.

Bill