I have a 360 with a 727 trans, 3.23 gears. I was using a vacuum gauge to adjust the carb. The vacuum reading was 12 mm Hg. I tried adjusting the mixture screws, no change in the vacuum level. I checked for vacuum leaks around the base of the carb, using carb choke cleaner. No change in the idle. I had the engine rebuilt about 2 yrs ago. I'm not sure what cam is in it. The builder said he was going to use an RV cam to get more torque. Could the cam be the problem with the low vacuum. I'm measuring the vacuum off the port for vacuum advance for the distributor. If I rev the engine, the vacuum does go up. Thanks
Low Vacuum
- Thread starter money pit
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Challenger RTA
Well-Known Member
Gauge stay steady? just rises and decrees? I would check vacuum at manifold brake booster port.same result? may be obstruction in carb. then check compression.read spark plugs.
Look at the charts see what fits you findings. I know you don't wan;t to hear it Worst case cam maybe not set right.Hope for something simple! Pvc valve ok?
Look at the charts see what fits you findings. I know you don't wan;t to hear it Worst case cam maybe not set right.Hope for something simple! Pvc valve ok?
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The needle pulsates. the compression is good. The plugs look a little lean. I'll check the vacuum at the booster. Thanks
Chryco Psycho
Well-Known Member
You are reading the ported vacuum to the dist so it should be zero at idle & rise with rpm as the vacuum is above the throttle plates & yes the idle mixture will not affect it at all .
You want to be reading manifold vacuum Below he throttle plates , this works in reverse & is highest at idle & drops as you increase throttle opening .
You want to be reading manifold vacuum Below he throttle plates , this works in reverse & is highest at idle & drops as you increase throttle opening .
I have the vacuum to the distributor wrong. The installation instructions says to use the port on the rt (facing the engine) That port has high vacuum at idle. I'll switch it and check the timing and vacuum. Thanks
Chryco Psycho
Well-Known Member
Dist should connect to zero vacuum at idle & rise with RPM , [even tho others will argue that] so that you have no advance @ idle & rising with rpm , the way you have it now will kill mileage as the mechanical advance & vacuum are working opposite so as one is increasing the other is retarding .
This is great info. Thanks
That's probably why my MPG sucks. I thought something was wrong when I pulled the vacuum hose from the distributor and the idle really dropped,. There was no change in the low idle when I capped this port. As always, you're a wealth of knowledge. Thanks
Challenger RTA
Well-Known Member
Is this why you called it a money pit? You can change it back to get that old time feeling again!hope every thing works out ok. Use to adjust carbs by placing and over carb. would speed up or slow down depending on rich or lean.would be fairly close. when your on the road.Hand job works good when you only have you hand.better when you have the tried and true comforts of home. why is it I think there is some humor in between the lines!
As usual, Chryco is a wealth of information and spot on. Although I believe the cause has been diagnosed, I will mention one other thing that can cause idle screws to lose affect. If your float level is set way to high I have had it pour fuel right by and make idle screws ineffective. Always good to check on a carb you don t know well.
Chryco Psycho
Well-Known Member
always check float levels , they can be way off in any carb .
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