vacuum issues?
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vacuum issues?
How much vacuum should there be on the carb side at idle? Should it be enough to advance the dist?
I have a 240 1Bbl
Having a hard time getting the idle to smooth out, and to accelerate smoothly. Once the rpms are up, the engine runs very smoothly.
Any suggestions?
I have a 240 1Bbl
Having a hard time getting the idle to smooth out, and to accelerate smoothly. Once the rpms are up, the engine runs very smoothly.
Any suggestions?
Fleet Mechanic
Joined: Aug 2007
Posts: 1,806
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From: Piney Woods of East Texas
Manifold vacuum should run between 18-22. On some carbs you have 2 ports. One indicates manifold pressure, while the other port increases vacuum as throttle increases. If you are below this start checking for loose manifold bolts. Others have reported on the six cyl the screw the hold the carb loosen up's. Something else to check.
Check timing, it can greatly impact vacuum.
Not real knowledgeable on the sixes. But yes. The reason you remove and plug them when you set the timing.
Adjust carb for max vacuum with timing advanced connected. If it's sluggish you may have the idle stop too high, so your not completely on the idle circuit. back off if needed.
Check timing, it can greatly impact vacuum.
Not real knowledgeable on the sixes. But yes. The reason you remove and plug them when you set the timing.
Adjust carb for max vacuum with timing advanced connected. If it's sluggish you may have the idle stop too high, so your not completely on the idle circuit. back off if needed.
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The PVC valve seems to have plenty of vacuum. It is coming directly out of the manifold. The only vacuum coming from the carb is the one running to the distributor. There doesn't seem to be any vacuum at all at idle. If i apply vacuum to distributor it smooths out nicely. Could the bushings in the throtle body be wore enough to cause this problem.
When I spray carb cleaner at the shaft running through the throttle body, you can hear the rpm's rise. Is this normal?
It is currently at 5 to 600 rpm idle and smooths out at about 1500 to 1800 when driving.
When I spray carb cleaner at the shaft running through the throttle body, you can hear the rpm's rise. Is this normal?
It is currently at 5 to 600 rpm idle and smooths out at about 1500 to 1800 when driving.
Fleet Mechanic
Joined: Aug 2007
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From: Piney Woods of East Texas
Do you have the throttle position opened up to much?
Try backing the idle off, then see if you start getting any fuel/air adj screw. The pickup should be below the butter fly in the carb.
Adding cleaner will increase rpm. but most the time the butter fly is closed that it will flood it out.
If you have initial timing of 8, then you connect the vac adv it should (rpm) pickup some more.
Try backing the idle off, then see if you start getting any fuel/air adj screw. The pickup should be below the butter fly in the carb.
Adding cleaner will increase rpm. but most the time the butter fly is closed that it will flood it out.
If you have initial timing of 8, then you connect the vac adv it should (rpm) pickup some more.
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there is no increase or decrease in rpm's whatsoever whether the vacuum is hooked up for the distributor or not when I am at idle. I cannot get it to idle any lower than 500 and keep running.
I am using the carb cleaner around the outside of the carb to see if there are any vacuum leaks that I can find. I don't know the correct terminology, but the shaft that the butterfly is connected to is the one that sucks the carb cleaner in. I am not sure how tight that should be, but it lets the carb cleaner get by and the rpm's go up.
The air/fuel adjustment screw is out about 3 turns...starts to choke it down at about 2 1/4 turns.
the vacuum pickup is above the butterfly in the carb. I could rig it up straight from the manifold?
I am using the carb cleaner around the outside of the carb to see if there are any vacuum leaks that I can find. I don't know the correct terminology, but the shaft that the butterfly is connected to is the one that sucks the carb cleaner in. I am not sure how tight that should be, but it lets the carb cleaner get by and the rpm's go up.
The air/fuel adjustment screw is out about 3 turns...starts to choke it down at about 2 1/4 turns.
the vacuum pickup is above the butterfly in the carb. I could rig it up straight from the manifold?
Fleet Mechanic
Joined: Aug 2007
Posts: 1,806
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From: Piney Woods of East Texas
Adjust your air fuel at max rpm. Increase your idle speed to book, ~650.
Connect the vac adv up.
Now when you move the throttle quickly do you see raw fuel being squirted in the top of the carb. This is accelerator pump. If it is not squirting there is a problem with the accel pump. This will require a carb rebuild or inspection of the accel pump.
It's been a long time since I have done a 1 vent carb. So this is all from memory, so I could be wrong on your carb.
The accel pump consist of a piston (or diaphram), should have a ball check in the bottom of the pump. There may be a spring loaded lever. If the pump seal is bad or the check does not hold it will not squirt. Without the accel you will be flat off of the throttle.
Connect the vac adv up.
Now when you move the throttle quickly do you see raw fuel being squirted in the top of the carb. This is accelerator pump. If it is not squirting there is a problem with the accel pump. This will require a carb rebuild or inspection of the accel pump.
It's been a long time since I have done a 1 vent carb. So this is all from memory, so I could be wrong on your carb.
The accel pump consist of a piston (or diaphram), should have a ball check in the bottom of the pump. There may be a spring loaded lever. If the pump seal is bad or the check does not hold it will not squirt. Without the accel you will be flat off of the throttle.
