Thread: vaccum leak

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i sprayed carb cleaner down both primarys on my
4 barrel carb,when i sprayed it down the driver side
primary the engine smoothed out and sounded good
when i sprayed down the other primary nothing happened.
i was told if it smoothed out and sounded good that means
i have a vaccum leak. then i sprayed around the carb and
intake manifold i did not find any leaks. i only have one
vaccum line running to my mallory distributor that is ok.
i still think its a manifold leak but maybe my carb is dirty.
the engine is a 350 sbc with 3500 miles and still under
warranty. the engine started running rough when i got
off the freeway. the compression read 140 each cylinder.
what got me was when i sprayed carb cleaner down the
primary only one made a difference.

Originally posted by dotgone
i sprayed carb cleaner down both primarys on my
4 barrel carb,when i sprayed it down the driver side
primary the engine smoothed out and sounded good
when i sprayed down the other primary nothing happened.
i was told if it smoothed out and sounded good that means
i have a vaccum leak. then i sprayed around the carb and
intake manifold i did not find any leaks. i only have one
vaccum line running to my mallory distributor that is ok.
i still think its a manifold leak but maybe my carb is dirty.
the engine is a 350 sbc with 3500 miles and still under
warranty. the engine started running rough when i got
off the freeway. the compression read 140 each cylinder.
what got me was when i sprayed carb cleaner down the
primary only one made a difference.

if you have blocked the dist. off theres only a couple places it can leak, one would be the carb. and or carb gasket, and the intake gaskets. i have seen the intake gasket leak from the bottom side which makes it all most inpossible to prove, but would come down to pulling the intake because you couldnt find it anywhere else. you need to put a vac. gauge on the motor then you would know for sure what you have. if it has a e.g.r. valve they give a lot of trouble. check the vac with a gauge and let me know what it reads.watch the gauge hand and see if it moves around a lot

the vaccum read 15 at 750 rpm 21 at 2000 rpm
the engine has a mild crane cam i changed the plugs
and wires i also changed the fuel filter, i talked to the
engine builder today he said bring it in tuesday no charge
if its there work,he said i could try spraying carb cleaner
down the carb and if it smoothed out it probably is a
vaccum leak,but it only smoothed out when i sprayed it
down the driver side primary when i sprayed it down the
other primary nothig changed thats strange or is that
normal? i was thinking maybe the carb is dirty.

when i sprayed carb cleaner down the driver side
primary the the engine smoothed out but it did
nothing when i sprayed it down the passenger
side primary,what do you think about that?

Originally posted by dotgone
the vaccum read 15 at 750 rpm 21 at 2000 rpm
the engine has a mild crane cam i changed the plugs
and wires i also changed the fuel filter, i talked to the
engine builder today he said bring it in tuesday no charge
if its there work,he said i could try spraying carb cleaner
down the carb and if it smoothed out it probably is a
vaccum leak,but it only smoothed out when i sprayed it
down the driver side primary when i sprayed it down the
other primary nothig changed thats strange or is that
normal? i was thinking maybe the carb is dirty.

15 in. lb. is not bad with a mild cam. 15 to 17 is about normal. most of the time if you have a vac. leak and spray carb. cleaner anywhere near the top of the carb it should pick up the rpm. a vac. leak leans the motor out so if youre spraying the cleaner into the carb. it has nothing to do with where the leak is, what you are doing then is richen the motor back to normal. hope this makes sense

what i cant figure out is why when spraying carb
cleaner in the primarys it only makes a difference
on one of them it should rev up when sprayed in either.
oh well i can always let the builder fix it but i hate
dropping the car off and leavingit.

Originally posted by dotgone
what i cant figure out is why when spraying carb
cleaner in the primarys it only makes a difference
on one of them it should rev up when sprayed in either.
oh well i can always let the builder fix it but i hate
dropping the car off and leavingit.

what kind of carb. and intake do you have and is the vac hand study whe the motor is running?

if you have a vac leak and it was below the carb. then it should speed up anywhere you spray in the carb. so it sounds like it would be in the carb, but id let the man check to be sure

i have a edlebrock carb and manifold and the
vaccum is steady

Originally posted by dotgone
i have a edlebrock carb and manifold and the
vaccum is steady

im not sure you have a vac. leak but let the man check it and let me know what he says.

thanks for your help,i will let you know what the
problem is.