Topic: Has Anyone Ever Found the 26mm Float Height Spec to be too High?

[Bob Wessner]

I'm struggling to diagnose a running problem, it's a K0. Carbs rebuilt with Keyster kits after two cleanings of the carbs, first in ChemDip then in Yamaha. Floats, brass, in excellent condition, nothing bent, twisted, holed or repaired. I did note that as originally set, the float height was around 30mm and 22 years ago, it ran fine. I reset the float heights to the spec 26mm. Installed the airbox, stock filter and it runs ratty, will not idle and three of the plugs are dry sooty, one seemed to have been slightly washed with gas.

Today I hope to use some tubes attached via the float drains to get a look at the actual dept of fuel in the bowls, but wondered if anyone ever had to disregard the float spec to get it right. Can anyone tell me how far below the gasket seem is pretty much OK for fuel level?

Should have added also, timing is dead on, valves adjusted and idle and air screws set to spec as well. Thanks. Any thoughts would be appreciated.

[MRieck]

Bob  I have disregarded float heights and many of the Factory jet kits mandate new float levels for the exact reasons you have stated (rich running at idle and small throttle openings). Are you using the factory type (Kowa Seiki) float height tool?

[Bob Wessner]

No, been using a small steel sliding "T" measuring in mm. Measured both sides and on 3 different occasions from the gasket base as prescribed.

[Bob Wessner]

Here's a pic of the fuel level in the #4 carb. It seems high, but what do I know. How does it look to others, too high, too low (which I doubt) or just about right?

I might also add that I had the engine running as late as last November, mid month, about the time it got too cold to work on it any more. Even now, it fires right up, but I have to remove vertually all choke within seconds or she stalls. Even though it is quite warm these past few days, I would have expected at least partial choke for a bit longer. Again, any thoughts on the fuel height would be appreciated.

[Jonesy]

I know you've been avoiding this as long as possible , but do you have the carbs sync'ed? There was a post on here about how out-of-sync carbs can show different mixtures on plugs. Ratty running can also be attribulted to sync.

[MRieck]

Looks high to me. Sometimes those aftermarket float needles have weaker intermal springs than OEM which can cause the bowls to overfill. I'd go back to 30mm height.

[Bob Wessner]

Actaully, I've been looking forward to syncing them, or trying to. Right now, it would seem to be running so ratty it would be futile, I would love to at least get it to the point where it would idle without dying. I just finished setting up the tubes on the other three carb bowls and the heights are basically the same, quite close to the gasket joint. Here's carbs 3, 2 and 1, forgot the attachments...

[MotoDave]

Interesting.  I've got a K0 and have always had issue with the bike not running quite right.  I'm about to throw a bank of K1-K4 carbs on it so it'll be easier to tune.  However, my bike idles much better since I put a Boyer Bransden electronic ignition on it.  World of difference. So, perhaps it's spark related and not fuel.

[Jonesy]

One thought from the picture... Was that the original airbox for your bike? I'm asking since it's black and the K0 ones were painted to match. The later airboxes had smaller air intakes... I'm wondering if this restriction is pulling more fuel....?

[TwoTired]

Bob,
Sure seems like you are on the right track for correcting the problems.  You asked for thoughts, though.

Is there any reason to believe that the floats may not be as bouyant as when new?   Are they metal or polymer float material?  Or, for that matter has the present fuel recipe changed so that the material doesn't float as high as it would with early 70's fuel?  (Gasohol?)  

Check your wet plug for spark jump.  Could it have fouled and shorted the insulator?

One cylinder that operates differently than other deserves special focus, I think.  I mean weren't you diligent to keep them all working at the same level of performance?
Are all the exhausts pipes the same as when stock?  Do they all have the same backpressure characteristics?

Do all the exhaust pipes acheive the same temps?

Although, the book calls for one turn on the idle air bleeds, have you tried turning them out a bit more to lean the idle mixtures?

Hmmm...

[Bob Wessner]

Thanks for all the input so far. It is not the correct airbox for a K0, never was, hope to come across one some day, but for now, it is the same airbox from 22 years ago, not right, but not a variable in the context of this discussion. One pipe, the number 1, is a 341 so this is a small, in my opinion, difference, so this would qualify as a new variable. However, even though more restrictive, I can't believe it alone would account for what I'm seeing. The remaining 2,3, and 4 pipes are the same original unmarked pipes of 22 years ago and in very good shape. The floats are brass, in excellent shape, no dents, repairs, etc.

As long as I gave it throttle, it runs, all headers get hot enough to vaporize oil drops. No apparent problems or hesitations as I used the throttle, just at idle.

The points and condensors are new, timing is spot on and I grounded the plugs in pairs (1,4) and (2,3) against the head while my wife hit the starter for a few seconds. After which she said, "so that's all there is to this?"  Good, rythmic blue sparks, no misses apparent.

No special fuel blend in use, plain old unleaded. I did try fiddling a bit with the air screws, but there was not much of a detectible change.

I will be sure to clean and dry all the plugs when I try cranking her again.

So is the collective wisdom that the fuel levels are too high in the bowls, or should I be looking elsewhere?

[Jonesy]

Hmmm.. both the main jet size and needle position were different on the 341-equipped bikes, so I'm not sure how much this can be ruled out. Which cylinder has the plug looking different?

Do you have an in-line spark tester? If you have a weak spot in the ignition system, plugs might fire nicely in the open air, but may not under compression.

Just another stab at what might be contributing....

[Bob Wessner]

No, no in-line spark tester. If I were to try and accommodate the 341 pipe, since it is more restrictive, might I at least drop the needle (raise the clip) one notch? Then again, clearly all are rich, not just the number #1 (341) pipe.

[057 adnoh]

I have spent the last month trying to get my 1969 750 to idle here are a few things I found #1 the plug caps were shot and had to be replaced # 2 the coils did not like the rain I replaced them with cb 750 f dohc coils (big improvement!!!)#3 the carbs cannot be set until you balance them if one is open more than the carb beside, it it has very little vacuam and cannot pull the fuel #4put fresh gas in the tank ,very important as stale gas will not burn properly #5set the dwell and timing with a meter and timing light check these things before you adjust the float height . As I balanced the carbs you could hear r the clutch rattle diminish and the idle smooth out #7 take the bike for a run and blow the carbon out.. good luck!!!

[MikeDeB]

I've just finished going over my shop manuals (factory, Haynes & Clymer) searching for the float height for the K0.  What I have found is that there is no specified float height for the early 750s.  For K1-K6 the specification is 26mm.  In the official shop manual it shows a fixed float gauge for use on the K0s.  This combined with the fact that your carbs have brass floats and the K1-K6 bikes have polymer floats leads me to believe that 26mm may be too low for the brass floats.  Have you tried raising the floats back to the 30mm float setting that you found them in?  It might be worth a try.

[eldar]

I would raise the floats to 30 as well. Brass is likely to be a bit heavier than the polymer floats were. Thus at 26mm for instance, the polymer would float higher from the less weight. I would say to go to 30mm and sine this problem is mainly at idle, turn out you screws a bit and run for a short time and see what happens then.

Exhaust backpressure can cause LITTLE changes but the less backpressure, the leaner your bike would run. Think of how things change when people put on a 4-1 system.

[Bob Wessner]

Thanks for all the feedback. Some how I just knew I was going back into the damn carbs again  . Since checking the fuel depth with the plastic tubes and taking the pics/posting them, I've been getting ready to remove them and reset the height to around 30mm. Getting real familiar with removing, disassembly and reinstallation.. too familiar actually

Hmm, checked the shop manual (reprint) I have for the orig. 750 and you are correct, it does not specify a particular measurement, just illustrates the use of the 'official' float gauge which is no longer available as a part. I never caught that and just assumed the 26mm was the same for all the 750 and K models.

[kaysystems]

Interesting....
I'm still going through the same with my Jan '70 K0. I do know after measuring that the Keyster kits make it a bit rich.

Keyster kits for K0 DO NOT have needle jets, only needles, but later kits have the jet. Needle & Jet kits can be bought for K1 & K2 models. Got mine from http://www.cmsnl.com/ - kit #0499-KHN-NEEDLE at 12 euros each . I bring this up because the needle jets do wear, and cause a rich mixture

Your fuel level looks higher than mine (26mm with brass floats). If you use brass floats, check them for holes by holding them under water. Use hot water in a bowl. Bubbles will appear at any holes. Sunken floats really make it run rich.

David

[Bob Wessner]

David,

So you are saying you are running your floats at 26mm on your K0? I did check the floats visually when I last had them out, but since they are out of the bike and down on the work bench..again.. I will do a float/sink test as you describe just to be sure. I'm fairly confident they are OK, but you never know.

[Jonesy]

Hey Bob-

I have an extra set of the polymer floats. Let me know if you'd like to try them out. If you want, could I offer you a hand with your beast this weekend? (I'm not doing anything on Sunday...) I've got any tools you might need as well.

Just wanted to front the offer....

[kaysystems]

David,

So you are saying you are running your floats at 26mm on your K0? I did check the floats visually when I last had them out, but since they are out of the bike and down on the work bench..again.. I will do a float/sink test as you describe just to be sure. I'm fairly confident they are OK, but you never know.

Yes, I'm running 26mm, but have the needles in the lowest position and the idle mixture screws almost one & a half turns out. I've often wondered if it should be 28 or 30mm.

David

[Bob Wessner]

Dan,

Thanks for the offer, will let you know what happens after I fiddle some more.

David,

Tomorrow I'll reset the float heights to 30mm and let you know what diff. it makes with mine.

[MRieck]

If your floats are leaking you will know- the bike would hardly run and gas would be everywhere.

[Bob Wessner]

Well, everything sort of sucks today. I pulled the carbs, took them to the basement and changed the float heights to 30mm. The result, runs no better, actually worse, as you see, at least all four pipes got hot before under throttle, now #4 is cold.

I shut it down and pulled the #4 plug, it did not appear as though it had been involved in any recent combustion process. Crap! I grounded the plug and determined it was firing though. Then I put a rag under the #4 carb bowl and slightly unscrewed the drain.. hmm, nothing. Unscrewed it more.. still nothing. Removed the screw and not a drop of fuel, the bowl was dry, which certainly would explain the failure of the #4 cylinder to get hot. I know, a brilliant deduction on my part, right?

As a reference, I pulled the #1 plug and frankly, I found it to be as dry/sooty as when the floats were at 26mm. Not sure what in the world is going on or what to do next. This is exactly why I hate carbs. If I were honest though, I guess what I really hate is the fact that I'm not very good at this tuning business and if things don't change, I'm not likely to get much better at it.

Not sure of my next move, go back to 26mm, split the difference and change them to 28mm, put tubes back on the #1 thru #3 drains and see what the height is?? Definitely need to determine why the #4 is bone dry. I pulled the bowl while still on the bike and the floats and valve are free, no sticking so it must be just wrong height.

Dan, if your offer of some time is still open, shoot me an eMail and we will try to set something up.

[057 adnoh]

make sure you are not kinking the fuel line when you replace the gas tank. I did this a couple of times during the many times I removed the carbs on my k0. THe bowls do not fill properly  or run out as you are running the bike.  A guy at cruise night was telling me that modern fuel does not burn the same way as the old leaded gas. He told me the exhaust on his bike ( a Harley) always looks sooty, I noticed most of the bikes looked the same. I am in Canada ,I dont know if they blend differently here!!!