My engine has almost always had a little surge in the idle since I put in this engine. I have changed carb gaskets and just recently changed the manifold and it still does it. Could there be a vacuum leak in the carb? It’s a 750 Demon that is about 4 years old. It runs perfect when the engine is really cold and really hot. Also if the air temp is above 80* there is no surge. I’ve plugged all other vacuum lines and it still does it. Do I just need to rebuild the carb?
Surging at idle
- Thread starter 1969mach1351
- Start date
69Rcode_Mach1
Active Member
Buy a vacuum guage they are only $20 and will help you determine the problem. If it's not a vacuum leak then atleast we know that's not the problem.
krash kendall
Active Member
I have the exact problem at similar conditions. When idling at at stoplight in gear it runs fine with an occasional momentary burp as if one cylinder fired with a little more power every3-5 seconds. I've vacuum checked it and ignition checked it and just can't find a solution. It isn't causing any problems what-so-ever, I just expect perfection.
Pbum5
Member
If it is a vacuum leak
Try spraying some carb cleaner around the carb, intake, etc while it’s running and it might help you find the vacuum leak.
Try spraying some carb cleaner around the carb, intake, etc while it’s running and it might help you find the vacuum leak.
I've seen such a problem on a vehicle where the power valve was opening due to a drop in vacum. Once the additional fuel was dumped in... the idle and vacum picked up for a second and so the power valve closed. Only to have the idle and vacum drop and cause the power valve to open again.
Could be your power valve, could be a vacum leak.. could also be the wrong power valve to run with your cam.
Could be your power valve, could be a vacum leak.. could also be the wrong power valve to run with your cam.
84convertablegt
New Member
heres a weird story. i had my engine recently rebuilt. they installed a ford factory 4v spacer with the pcv hookup. well i had a crazy surge going on. first thing i did was hook up a vacuum gauge, and it read a steady 15 lbs, no surge. i was very confused. then by just feeling around i managed to stick my pinky finger under the spacer and barely got it to fit down into the intake where the carb mates up. i couldnt believe it. i bought a jegs phenolic carb spacer and a new gasket and the problem was solved. the moral of the story, the vacuum gauge didnt tell me squat! weird isnt it!
2nd Mustang
Founding Member
84convertablegt said:
The vacuum gauge can help, but is not always the only thing to help trouble shoot. I had many carb related problems, even some minor vacuum leaks, but the vacuum gauge always read a steady 14 inches at idle, even with a brand new carb, it still reads 14 inches due to my cam.
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