6hp 1960’s rich at high speed

[johnyrude200]

Weird one here. I’ve rebuilt the ignition, cleaned and thoroughly checked over the carb, and set the timing with a link n sync. The motor appears to be getting way too much fuel as soon as it switches over to the high speed jet.

At about 1/3rd throttle it starts to bog down, shakes like hell, and smokes like hell. It doesn’t stall out, but it is showing all the symptoms of running way too rich at the mid to top end.

I checked the fuel pump and it is not leaking fuel into the cylinders, it appears to be a front end issue. The carb is not flooding (the float valve shuts off when the bowl is full) and I installed a new boss gasket to be sure it was OK. I pulled the high speed orifice and it appears OK.

Beginning to suspect perhaps something going on at the manifold? Does this sound like the next logical step?

Fortunately, it looks like these 6hp motors can have the manifold removed without taking the powerhead off.

Thoughts?

[chris-p]

Someone bore out the high speed orifice when they cleaned it? Did you pull it to inspect it for damage?

[johnyrude200]

It appeared OK when I pulled it. I may put another 6hp carb on the motor from a parts motor to rule out the carb. I mean, there’s only 2 places that fuel can get in…the wrong way. The carb, or the manifold. The fuel pump does not appear to be leaking through the intake hole (I removed the pump and pumped the primer bulb and no fuel came out through that intake hole).

[frankr]

I’ll bet somebody cleaned the jet with a drill. "Appeared" to be ok doesn’t get it. That is a precision hole, not to be messed with. I don’t see how anything with the manifold would affect it. It isn’t inhaling smoke, is it? I think you are experienced enough to recognize that.

[chris-p]

Wonder if at that throttle position, 1/3 throttle, a plug wire is worn and it is only running on 1. Have you pulled the plugs after noticing this condition>>? Is 1 of them overly wet? I have had a motor that rubbed at a certain throttle setting and would ground that cylinder at that exact spot.

I would run it with neon spark testers inline, and watch them to see if the spark is consistent as you throttle up to rule that out. If all is well there, you know its fuel related. Just a thought before you pull the carb.

But try a different orifice as well in case its bored out by a previous owner.

[johnyrude200]

Both plugs are pretty consistently wet and dark. Not the worst I’ve seen, but the motor is shaking like hell (like what happens if you set the slow speed needle way too rich) at anything much beyond 1/4 throttle.

I’ll report back tomorrow once I have another go at it. I’m sure it’ll get figured out by end of day. A little disappointing right now, I already replaced gearcase seals, rebuilt the ignition, and fixed the manual recoil today, after rebuilding the carb, the fun is seeing them run the right way again!

I will say on this one that when I pulled down the gearcase the lower main bearing oil recirculator pin, that was missing. Thankfully there was no rod knock on this motor. So perhaps the terrible condition it was in when I started the day in fact saved if from being destroyed, because since it couldn’t be run by the last owner or two, the bearings weren’t run lean and destroyed.

These 6’s seem to be prone to rod knock.

[johnyrude200]

Frank! It’s good to see you back on the forums! I was asking last week about you, wanted to make sure you were OK. My first order of business tomorrow will be throwing another carb on and seeing what happens.

The nice part about it is swapping out the bowl from another carb is a cinch, no rebuilding or transplanting parts off of the original carb. I run all the motors with a fan blowing on them to avoid the exhaust inhalation issue.

I reached out on this one because I swapped out the cam follower and the cam from some parts motors (the original was pretty worn, both pieces), and I played around with the pickup and adjusted it to be both late and early, and basically saw no significant difference with the problem.

If there’s anything I’ve learned in the last year, is to stop repeating the same steps hoping for different results in the repair process. To your point and the other forum ‘tenders,’ experience is the best teacher. Thanks again for saving myself and so many others time by sharing your knowledge!

[Michael]

Think this carb has a gasket around the main nozzle – is that in place and in good condition?

[johnyrude200]

Yes, mentioned that in the earlier post

[fleetwin]

I know you replaced the nozzle gasket but your problem is the classic symptom of a missing/worn nozzle gasket. I guess you will know more when you swap carb bowls, unless the carb nozzle casting is flawed/cracked/porous.
I don’t think there is anything in the intake manifold that would cause it to run rich, so I would rip into that. The only other thing that comes to mind is a plugged exhaust/intake, but you have already been there and would have seen nests, mud dobbers, etc.

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