Engine only runs at full or partial choke

[sastanley]

Art, yes, like that, or also around the flange where the carb & manifold meet, etc.. Especially those of us with the Indigo or Moyer PCV kit, we have double the spots for air to leak in. If there is an air leak, when you spray the WD-40 or similar (carb cleaner works too..any petroleum based spray really) the petroleum temporarily blocks the air leak, ritchens the mixture and the engine surges, helping to pinpoint the air leak.

I personally wouldn't use WD-40 since it is kind of oily & messy..I'd use a carb cleaner that would evaporate quicker with less mess.

[ArtJ]

Art, yes, like that, or also around the flange where the carb & manifold meet, etc.. Especially those of us with the Indigo or Moyer PCV kit, we have double the spots for air to leak in. If there is an air leak, when you spray the WD-40 or similar (carb cleaner works too..any petroleum based spray really) the petroleum temporarily blocks the air leak, ritchens the mixture and the engine surges, helping to pinpoint the air leak.

I personally wouldn't use WD-40 since it is kind of oily & messy..I'd use a carb cleaner that would evaporate quicker with less mess.

So it wouldn't bubble like gas grille leak checks do with soapy water?

[sastanley]

Art, I think it's the other way around...gas grill leaks bubble because the LPG is pressurizing the system...once you get passed the carb, the manifold is in vacuum, pulling air & fuel into the cylinders. This is caused by the intake valve being open and the piston moving down in the cylinder creating vacuum. Except for the brief moment when the pistons are at TDC, or BDC (i.e. changing direction) there should always be one cylinder drawing in air at any given time.

This is all my theory & personal understanding, so don't take it for fact.

[Dave Neptune]

A differant tak!

Gary, it does sound like a possible fuel problem however the poping doesn't seem consistant with the fuel problem. You are getting clean fuel to the carb and the pump is working. You have cleaned the carb and the problem persists. Just for the sate of argument pull the dist cap and give it a good look inside for a carbon trail and or moisture, or just put on the spare if you have one. The ignition sounds ok as you have spark however moisture and or a carbon trail can cause the spark to wander to a lug that the rotor is not pointing at~~~~pop.
As for the surging have you plugged the PCV if you have one?

Dave Neptune

[ArtJ]

Art, I think it's the other way around...gas grill leaks bubble because the LPG is pressurizing the system...once you get passed the carb, the manifold is in vacuum, pulling air & fuel into the cylinders. This is caused by the intake valve being open and the piston moving down in the cylinder creating vacuum. Except for the brief moment when the pistons are at TDC, or BDC (i.e. changing direction) there should always be one cylinder drawing in air at any given time.

This is all my theory & personal understanding, so don't take it for fact.

I was thinking of the input side fuel pump etc.

[Marian Claire]

Posting this for clarity not to be argumentative:
I thought he said he had not opened the carb to clean it just removed it and shot in some cleaner.
Shawn: I also use carb cleaner. But there has been debate about safety so I suggested the WD-40. My theory is that the spray, which ever one you use, basically gets drawn in and replaces the air. My engine actually bogged down when I was searching for my air leak.
Art: I have only used the spray to check the carb to manifold connection, throttle shaft and the joint between the carb body halves. Dan S/V Marian Claire

[gary gerber]

Dan was correct " the smallest piece of crud can mess things up ". The problem is solved and the engine is running perfectly under normal conditions.

This morning, first I checked for air leaks, there were none so even though I had removed the two year old carb the other day, had clean fuel draining from it and blew air through the orifices I decided to remove it again and disassemble it. I found the problem right away...the very small brass vent fitting was blocked, I removed it and cleaned it with a paper clip. Reassembled the carb, refitted it to the engine and started her up.

The engine is running like new.

Initially, should I have just taken the carb off right away and disassembled it? Well I'm from the school of check the easy things first advancing step by step. However, since I went to the trouble to remove the carb the other day and seeing clean fuel being delivered I suspected an air leak "somewhere", I didn't take that next step and just take the carb apart. My big fear was an internal air leak at the exhaust manifold gasket, which would have involved partial disassembly of the exhaust system just to get the manifold off.
A project I wasn't looking forward to.

I only offer this lengthy explanation because maybe it will help the next person. I want to thank you all for your input.