Running on one cylinder

lazyeye6

lazyeye6

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My ’74 Interstate is running on only one cylinder. Two months ago it ran fine on both cylinders. It starts and runs quite easily on one cylinder.
I have a TriSpark EI. Both plugs spark nicely using it’s diagnostic test..
I changed plugs. No difference. I switched plugs to opposite sides. No difference.
I changed HT wires. No difference.
I switched the HT leads from coils to opposite plugs. No difference.
The non-running cylinder plug is wet when pulled.
The carbs are Amal Premiers and synchronized
The coils are Lucas type and test within the correct Ohm range.
The cylinders each have in excess of 150# compression
It would seem that I have a carburetor problem, so I will remove it for a clean and inspect.
Anyone have thoughts of other things I should look at?
 
Is it always the same cylinder with the wet plug? I would start by pulling the bowls and checking float levels.
 
lazyeye6 said:
My ’74 Interstate is running on only one cylinder. Two months ago it ran fine on both cylinders. It starts and runs quite easily on one cylinder.
I have a TriSpark EI. Both plugs spark nicely using it’s diagnostic test..
I changed plugs. No difference. I switched plugs to opposite sides. No difference.
I changed HT wires. No difference.
I switched the HT leads from coils to opposite plugs. No difference.
The non-running cylinder plug is wet when pulled.
The carbs are Amal Premiers and synchronized
The coils are Lucas type and test within the correct Ohm range.
The cylinders each have in excess of 150# compression
It would seem that I have a carburetor problem, so I will remove it for a clean and inspect.
Anyone have thoughts of other things I should look at?
Click to expand...
What happens if you open the throttle while running to 1/4 throttle or more?

It sounds flooded and as @Cuppy says, check the fuel height in the bowls.
 
Has the bad side got a helicoil repair to the plug hole, if so it could be breaking the circuit. Solid insert needed.
 
Pull the rocker covers and verify the valves are operating properly. My 850 was running fine and went to running on a single cylinder pretty much instantly while running at interstate speeds, one exhaust valve lobe failed.
 
No helicoil repair to the plug hole. I’m leaning towards the carb float level needing adjustment. At high rpm and close to WOT that
cylinder does fire intermittently. I’ll report back.
 
lazyeye6 said:
No helicoil repair to the plug hole. I’m leaning towards the carb float level needing adjustment. At high rpm and close to WOT that
cylinder does fire intermittently. I’ll report back.
Click to expand...
So, I pulled the float bowl off, Trimmed the gasket which was overhanging the float pivot rod, slightly tweaked the float level.
It started immediately firing both cylinders and settled into an easy idle. Thanks to all for the helpful suggestions!!!
 

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