Working on my 72 chevell can not get it to idle properly, I noticed when i removed the vacumm hose from the carb going to the brake booster it run alot butter but the rpm also went from 950 to about 1300 rpm. Any help would be great
AVOSSLER
AL, you'll want like 18° initial with that cam. another 18° mechanical advance will give you 35° total, if your distributor has a vacuum advance another 10° vacuum would be good.
From your PM I see that you have a 4 corner idle carb. I recommend you warm up the engine completely and start tasking 1/4 turn at a time out of all 4 mix screws. That is, screw in all 4 a quarter turn see what happens to the idle. before starting run them al in to seat and count the turns. average the turns to seat and set them all at that number, then start leaning them out. pay attention to the idle quality, if it starts bogging down or idling rougher you're close to the end.
look at the throttle plates, see if you can tell if the front and rear are open about the same.
Let us know what happens.
From your PM I see that you have a 4 corner idle carb. I recommend you warm up the engine completely and start tasking 1/4 turn at a time out of all 4 mix screws. That is, screw in all 4 a quarter turn see what happens to the idle. before starting run them al in to seat and count the turns. average the turns to seat and set them all at that number, then start leaning them out. pay attention to the idle quality, if it starts bogging down or idling rougher you're close to the end.
look at the throttle plates, see if you can tell if the front and rear are open about the same.
Let us know what happens.
18 initial, 18 mechanical, 10-12 more vacuum. You're pretty close there if you've got 16 initial.
Is this a 4 corner idle carb? all 4 are 1.25 turns out? if so, try it with them all at 1/2 to 3/4 turn.
Is this a 4 corner idle carb? all 4 are 1.25 turns out? if so, try it with them all at 1/2 to 3/4 turn.
base
traditional sign of a blown PV is that the engine keeps running even if you turn the mix screws all the way in. fuel leaks by the diaphragm of the PV and enters the manifold via the vacuum passage to the PV back chamber.
So the question remains, if a 3/8" vacuum leak causes the engine to speed up instead of die where is it getting all that fuel?
Can you turn in the mix screws equally until it drops a couple hundred RPM, IOW, lean it out and pull the PB hose again?
What is the timing at? Usually if the timing is not advanced enough for the performance cam the throttle will be jacked too far open to get the idle speed up to where it won't die all the time. then the engine will idle off the idle transition system which are not affected by the mix screws.. So, how big is the cam and what is the timing set at?
Also, when did this problem start? always been like this? or started after some other work/upgrade was done to the engine?
So the question remains, if a 3/8" vacuum leak causes the engine to speed up instead of die where is it getting all that fuel?
Can you turn in the mix screws equally until it drops a couple hundred RPM, IOW, lean it out and pull the PB hose again?
What is the timing at? Usually if the timing is not advanced enough for the performance cam the throttle will be jacked too far open to get the idle speed up to where it won't die all the time. then the engine will idle off the idle transition system which are not affected by the mix screws.. So, how big is the cam and what is the timing set at?
Also, when did this problem start? always been like this? or started after some other work/upgrade was done to the engine?
Power valve blown? with the PB hose hooked up can you kill the engine by turning the idle mix screws in?
is the carb dripping from the booster venturiis? It's massively too rich if it speeds up when given a 3/8" vacuum leak. It should die more or less instantly when you do that.
what is the timing set at?
what is the timing set at?
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