S65 carb woes

Sams65

New Member
Thanks guys, I'll try lapping as the next step - any specific compound/grit? I have the permatex stuff that comes in a jar but it feels very coarse. Not sure if these little heads call for something finer?

As for the liquid fuel you found, are you 100% certain that wasn't a result of fuel slosh + spillage from removing the carb?

Yup, I pulled the intake tube off before touching the carb. With cold starts I'm used to a film of unburnt fuel on the walls but never dripping. I know some bikes/engines act differently when cold so it could well be a non-issue.

As an experiment I again tried to go completely lean by dropping the needle all the way (clip in the top most grove), setting float to the lowest possible position before it stops filling bowl completely, and pulling the air filter. Still guzzles tons of gas and smokes like hell. Mixture screw has no effect unless it's screwed all the way in.
 

Gary

Well-Known Member
I agree it does seem course but in looking I don't see anything other. Might be able to order something on line that's finer,but I do believe the courser stuff will get finer as you use it
 

69ST

Well-Known Member
The "mixture screw" is the pilot airbleed adjusting screw. It controls the amount of air that can be drawn into the pilot (idle) circuit. Turning it CCW (out) allows more air and leans-out the mixture, CW (in) less air, resulting a richer mixture...until you get below ~1/2 turn out from seated. At that point, airflow to the pilot circuit is cut off and the pilot circuit goes dead lean, i.e. it ceases to function.

Almost sounds like the jets are too big, not sealing, or something is missing. I'm unfamiliar with this carb, don't see many s65 bikes, you know? Make sure that the needle jet is in place and fully seated, all O-rings are healthy and installed correctly. Beyond that, it's virtually impossible for me to truly begin diagnosing this carb without seeing it...IOW, educated guesses are the best we have here.

As for valve lapping compound, they all use a diminishing abrasive. There are 4 basic schools of thought on lapping, depending upon whom you ask and how the valve seats are prepped: start with a narrow seat face, then use coarse compound; cut the seats to a width in the middle of the range, then use fine grit compound; cut the seats close to max width spec, no lapping, leaving valve action to use the textured surface instead of lapping compound; CNC machine the valves & seats such that they fit & seal perfectly from the get-go.

In reverse order: #4 only works if you're a manufacturer, with a huge budget and economy-of-scale; #3 I personally cannot buy into...it's controversial, too. That basically means you'll be choosing between available lapping compounds. If you can find fine grit, that'd be preferable. It'll be slower going, giving you more control over metal removal...and I'm talking a handful of minutes slower. The problem is that it's not easy to find. So...you may just want to go to a local NAPA, or equivalent, and pick up a small tube of Permatex lapping compound (a.k.a. lifetime supply), then do the lapping by using light pressure, to minimize the rate of metal removal.

BTW, a Sharpie can substitute for layout fluid but needs to be cleaned away between tests, to keep thickness to a minimum.
 

Sams65

New Member
It’s been a while but here’s a bit of an update to this continuing saga for those still interested. I had the valves/seats recut to guarantee absolutely no leakage (which also bumped up the compression to 140psi) did the solvent leak test and they remained dry. However rich condition continues.

So I turned my focus back on the carb. Here’s the interesting part: the fuel level in the float bowl is doing some weird things... in my attempt to completely lean things out I adjusted the float to barely let enough fuel in to fire up the engine. Here’s what that looked like:
AFA5797D-6822-4DE1-A999-96623E8F5706.jpeg


After firing up the bike and running it for a few seconds, I checked the bowl again and found it looking like this:
7CAFF7FA-4A5C-4BDD-8DB3-F2DC69E1ACBC.jpeg


I then adjusted the float even further lean to barely let any fuel into the bowl:
CBF712D9-B5FD-4ED8-90EA-1CF636BDAD6B.jpeg


To my amazement after a few kicks and some well timed twists of the throttle the bike fired up and what’s more is I could keep the engine running by increasing throttle at the right time. It doesn’t run well like this by any means but logic dictates it’s somehow forcing fuel into the float bowl by engine vacuum?

Maybe it’s not as unusual in an engine this size but I know in other carbs/engines I’ve worked on it wouldn’t even fire up with a nearly empty float bowl.

+ It would definitely explain why it always seems to dump excessive fuel into the engine, floats be damned. (Needle, seats, and floats are all brand new)

If this really is an anomaly the question now is what’s causing it. I double checked that the vent at the top of the float chamber is clear, but would assume any venting issues would have the opposite effect.

Any thoughts?
 

cjpayne

Well-Known Member
This must be frustrating on a high level. I know you've replaced the needle valve, but I'm tending to think that you might have gotten a bad one. I've never gotten a bad new OEM one, but its not impossible. I've got a K3 that NO MATTER what I try, you have to shut the fuel off at the petcock when not running. I've replaced everything inside it TWICE and the bowl itself. It overflows....unless the bike is running.lol. I have a theory, this may be your problem too, that the carb body itself is warped from so many extreme heat cycles. That K3 was rode very hard and badly abused.
 
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Gary

Well-Known Member
CJ might be on to something. I pretty active in boating- it is a common problem with Holley carbs. 99% of V8 oem carbs are/were Holley and once rebuilt have flooding problems. This has been going on for at least 10 years. Common fix is to reuse the old one. Its just like points and condensers for the same engines there is so little call for them anymore that the manufacture of them have been moved and quality control has suffered- either through worn out machinery,don't care attitude or don't understand the concept.
 

Sams65

New Member
This must be frustrating on a high level. I know you've replaced the needle valve, but I'm tending to think that you might have gotten a bad one. I've never gotten a bad new OEM one, but its not impossible. I've got a K3 that NO MATTER what I try, you have to shut the fuel off at the petcock when not running. I've replaced everything inside it TWICE and the bowl itself. It overflows....unless the bike is running.lol. I have a theory, this may be your problem too, that the carb body itself is warped from so many extreme heat cycles. That K3 was rode very hard and badly abused.

CJ might be on to something. I pretty active in boating- it is a common problem with Holley carbs. 99% of V8 oem carbs are/were Holley and once rebuilt have flooding problems. This has been going on for at least 10 years. Common fix is to reuse the old one. Its just like points and condensers for the same engines there is so little call for them anymore that the manufacture of them have been moved and quality control has suffered- either through worn out machinery,don't care attitude or don't understand the concept.

Hmm interesting... I suspected a defective carb body at the beginning of this whole mess but gave up on that theory after trying 2 other carbs that gave the exact same results. But not sure, could be a common issue with these?

(I’ve tried the needle and seat from both a keyster kit as well as OEM)

Been scouring for an after market/new chinese repro carb for a while but pickins seem slim compared to CT70s/90s etc. If anyone has any leads, please let me know.
 

cjpayne

Well-Known Member
I had a '86 Gran National at one time. If you ran it hard and didnt run it for a few minutes at idle afterwards, it would cause turbo problems later. A freind of mine had bought that car from his brother in law after it was stolen/recovered. I had learned that when the car was being chased by the police, it was being driven VERY hard for awhile, but then ran out of gas. The motor was fine, but the rear end was screwed up, the tranny was slipping, and....you guessed it,....the turbo/induction....was warped. I, Later, and after things were rebuilt/replaced, bought the car and learned it was very mean, but finicky about cooling down for a few.
 

dirtbkr188

Active Member
Just my 2¢ on this, but, if you've had the exact same issue with 3 separate carbs all doing the same thing, I'd be looking upstream, maybe a clogged gas cap that is causing the fuel tank to pressurize and pushing the fuel into the carb? Just a thought...
 

Sams65

New Member
Just my 2¢ on this, but, if you've had the exact same issue with 3 separate carbs all doing the same thing, I'd be looking upstream, maybe a clogged gas cap that is causing the fuel tank to pressurize and pushing the fuel into the carb? Just a thought...

Thanks - I have tried that, running without gas cap makes no difference. (Currently have a simple auxiliary tank hooked up for troubleshooting)

Considering it’s drawing enough vacuum to pull fuel out of a nearly empty float bowl looking up (or down) stream for some sort of air related issue is where I’m also currently at...
 
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