Topic: Low RPM Engine Miss


joe b    -- 06-03-2012 @ 4:35 PM
  My '41 needs to crank a lot to get started if it sits for more than a week. Starting every few days no problem. Now it has developed a surging and miss at low RPM such as starting from a stop and going through the gears. Once up to speed it settles down OK. At speed if I floor it I get a short bucking and then all is well.Running the electric fuel pump I have back at the tank does not help. Last night after a 10 mile trip I smelled gas when I pulled into the garage but really didn't see anything. I think my first look should be the "power valve." I have a new Echlin part from NAPA.
Your comments please.


supereal    -- 06-03-2012 @ 9:05 PM
  As your booster pump doesn't clear it up, I'd suspect the gas line is partially clogged between the tank and the firewall. It is also possible that the flex line at the firewall is collapsing inside. Alcohol fuel will cause that as the rubber liner softens.. Remove the gas line at the carb and place it in a container. Run the booster pump and see if you get a strong, full stream.


joe b    -- 06-04-2012 @ 6:57 AM
  Super: I disconnected the flex line from the fuel line from the tank. Ran the electric pump and got a good strong stream. Then re-attached the flex line and got a good strong stream through it. The flex line is only a year old so it looks like it is OK.
What do you think-replace the power valve?


supereal    -- 06-04-2012 @ 3:15 PM
  Joe: If you recently replaced the economizer (power) valve, that may be at fault. The replacement valves being sold now have a rounded base that doesn't seal to the carb body correctly. That could account for the gas smell you report. Unless the power valve is not fuel proof, and the diaphragm isn't breached, I wouldn't be quick to blame it. Almost always, the last thing you did to an engine is more likely to be the culprit. Check your spark plugs to see if they show evidence of running rich, which is a sooty appearance. I use Champion RJ14YC plugs instead of the stock H-10's, which tend to foul easily. Also, check the float setting of your carb, and be sure the float isn't leaking. If you need a float gauge, I'll post one.


sturgis 39    -- 06-04-2012 @ 7:25 PM
  A sticky needle valve will make the speed up and slow down when idling.

IF IT CAN NOT BE FIXED WITH BLASTING WIRE, DUCT TAPE OR JB WELD - IT CAN NOT BE FIXED


joe b    -- 06-06-2012 @ 8:26 AM
  Well, I removed the carb and checked the float level. It was OK. I replaced the power (economizer) valve since I had one in stock. The engine runs fine now.
The economizer valve was replaced in 2010 and probably had 2531 miles on it.
Thanks all, for your help.
This new gas sucks!!!


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