Intake Leak or???

[rousseau]

you wrote " Air stops sucking in the carburetor and fuel and air starts blowing out of the carburetor" There is only one thing that causes this. An intake valve is open when it"s not supposed to be. So your problem is in the valve train.

[50Panhead]

Bike was doing it before but not bad. It also had several intake leaks. The old bike was just plane sick before I started. I repaired the intake leaks and I freshened up the top end because the compression was getting low. Honed the cylinders installed new rings. The exhaust valves were showing signs of galling. So I had the valves and guides replaced and Intake valves dressed up. Compression is back to where it should be. After having done these repairs this problem is shows up. I'm sure it was there before but not as bad and mask because of the intake leaks.

I know the statement in the shop manual refers to FLH but I think it was a typographical error. As everyone knows FL came out with the Knuckleheads and ran up to a point in time when they upgraded the panhead engines somewhere in the late 50's

Back in 1975 when Yeagers HD rebuilt my motor the first time the Owner told me they built the bike with FLH parts, They also had to Bored it 40 over. The exhaust valves that were installed were 5/32 Oversize. (I still have the paper work.) Valves are part number 18082-60. I had a hard time finding replacements but I found NOS. Valve seats are Bronze

I have some other bikes scheduled to come in the shop for tire replacement and one getting ape hanger handle bars installed. So I'll have to put my problems aside for a while. When I get my panhead back on the lift I'm going to pull the heads off and I'm going to replace the valve springs. When I do I'll post the results here.

Thanks Herman

[duffeycycles]

Is the ventury in backwards?The nozzle in right?Who did the carb?

[50Panhead]

Is the ventury in backwards?The nozzle in right?Who did the carb?

I did I never took the ventury out.

[duffeycycles]

If you took the bowl off you can mess up the nozzle & ventury.If there is crap around the nozzle/ventury it needs to be cleaned

[50Panhead]

If you took the bowl off you can mess up the nozzle & ventury.If there is crap around the nozzle/ventury it needs to be cleaned

I don't think this is my problem but I'm listen to you. I had the low speed nozzle out and cleaned it. Ventury was - is, in tight and I saw no reason to knock it out. I have had the carburetor apart many time over they past 40 years.

[duffeycycles]

The nozzle is high speed circuit and transition from low to high,not low speed.From here you are on your own

[T. Cotten]

50Panhead!

The erratic strobe reminds me of when points "bounce".

I doubt the carb is the problem too,
but beware that removing the venturi is the only way you can clean its air correction "void", and inspect where the nozzle spigot goes. If it is worn, then some of the "accelerator sump" charge just drools out below the spigot. (There's a band-aid for that.)
And please inspect the idle bleed slot under magnification for obstructions; Often they are transparent.

Patience, and Good Luck!

.....Cotten

[rousseau]

Let me try this again. If fuel and air is blowing out of the carb (as you stated) the ONLY thing that causes this is an intake valve not sealing during the compression stroke. From what I could tell from the video the bike starts easily and runs ok at idle and low speed. The problem starts at higher RPM's. I agree the problem could be a valve spring. I'll go as far to say you may have a broken spring or a failed keeper.

[50Panhead]

Let me try this again. If fuel and air is blowing out of the carb (as you stated) the ONLY thing that causes this is an intake valve not sealing during the compression stroke. From what I could tell from the video the bike starts easily and runs ok at idle and low speed. The problem starts at higher RPM's. I agree the problem could be a valve spring. I'll go as far to say you may have a broken spring or a failed keeper.

Thats what I'm thinking. I'm betting I'll find weak springs. I'll start pulling the heads back off next week. I'll let everyone know what I find.
Thanks.
Herman

[T. Cotten]

I broke a valve spring once, Rousseau!

It was immediately after I put 70wt Castrol in my Lake Shore stroker Pan, about 1978 or so...
It did not affect running at all, but reverberated like a Silvertone guitar amplifier.

Another mystery is why the MOCO tried to go back to very weak springs in the early 80's.

Reversion out the carb during the circuits' transition can can be aggravated by wide cam overlap and cam gear timing, combined with general motor wear: I found out the hard way.

....Cotten
PS: I still have seven bottles of the Castrol on the shelf...

[rousseau]

Herman. This probably doesn't apply to your situation because you changed back in 75. However---- Some of the solid lifter "conversion " kits are supplied with light weight alloy(aluminum) push rods which were much larger in dia/circumference that stock. Because of this they would (sometimes) Bind/rub against the top of the push rod tubes where they go into the rocker boxes. It wouldn't be noticed when adjusting because it happens at lift. When you look at the push rods and they have a shiny/wear mark near the top, this is whats happening. Most of the time it isin't bad enough to effect performance,but if they are really binding a lot it's a different story. And here's the deal. If this is happening the symptoms are the same as a weak/broken valve spring.

[T. Cotten]

I, think.. I can remember '75,.... or so... ... . . .

It seemed common for "performance" aluminum kits to have 'idiot springs' beneath the 'slugs'.

Oh wait, that was for later hydraulic Pans, although you never know what you will find.... nevermind.

.....Cotten