i'm having trouble with my 65' 352. once the truck reaches it's normal operating temp. it idles really fast. i checked for leaks in the carburetor base, manifold and couldn't find anything wrong. so i thought it could be the distributor, so i got a new cap and an accel points eliminator kit. that didn't work either. so i bought a carb rebuild kit thinking the problem was with the carb. the first thing i tried was setting the timing and idle mixt. screws. nothing seems to work. anyone have any ideas.

thanks in advance

 

I'm just thinking a weak or broken vaccum line, could be the problem. Have you attempted to spray a product like wd40 on your lines while running?
Just a thought to your situation.

Mitch

 

ya i have tried spraying carb cleaner fluid around the base of the carb, around the manifold and lines to check for leaks. one thing i have noticed since this problem accurred was a increase in suction in the vacum line. when i set the timing with the vacum line disconected from the distributor and re-attach the line, the timing jumps up by like 5 degrees. the engine runs fine when it is first warming up with the choke on. then when it is at it's normal temp it starts acting up.

 

Have you got a dashpot? If the carb is a later replacement most of them had a dashpot, under the rubber boot is a spring loaded piston, that may be stuck.

 

At idle there should be no vacum on the line. Idle should be set at operating tempature in (D) if auto appr 650rpm. Mixture "should" be set using a vac gauge for best results. http://www.centuryperformance.com/vacuum.asp my guess is that the vac advance unit is dirty and needs cleaning and lube. Gunk combined with cooler temps are making a slightly noticable problem worse. But thats a guess...still good practice to keep these parts clean and in good working order.

 

no my carb does not have a dash pot. so the problem could be in the vacum advance unit on the distributor. could that be why when you rev the engine up it doesn't idle back down.

 

thanks for the link to the website. can you find a vacum gauge at a local auto parts store are do you have to order it online?

 

harborfreight.com $9.00

 

Have you removed the throttle linkage from the carb to test the cables travel ease ? Squirt some pb blaster into the sleeve if it's tight.. that may be the whole issue ?

 

It may be that your base idle is set to idle too high when warm.
If the cold idle screw is not set correctly on the choke linkage to make it idle high when cold, then the base idle may have been set too high in an attempt to compensate fo rthe cold idle not working correctly.
Or, the choke linkage is not releasing the cold idle, to let it idle correctly.
The base idle is set on the right rear (driver's side) of the carb.
The fast cold idle is set on the choke linkage, on the left (passenger) side of the carb.

As Redmanbob pointed out, the vacuum advance should be getting no vacuum at idle. If it is, then it is connected to the wrong port on the carb, or the base idle screw is in too far.

Do this:
1. Get the engine warmed up.
2. Unscrew the base idle screw a half-turn at a time. Be sure to blip the throttle after every turn, to make sure it returns to the new position.
3. If it doesn't drop after 1 or 2 turns, stop. Screw it back in the number of turns you back it out. Your problem is elsewhere, your linkage is binding somewhere, most likely at the choke.
3. If this drops the idle speed, continue doing this until the speed drops to normal, about 500 RPM for a manual and 600 for automatic. These may not be just right, but they will do.
4. If you cannot get it down to 600 or so, you may have to adjust the idle mixture screws.

(After this, we'll need to figure out how to adjust your cold idle speed at the choke linkage.)

Pay attention to the way the engine responds to your adjustments.
1. If it goes down gradually, and seems to idle sort of OK at each step to the way, then the general system is probably OK as well.
2. If however, after you make only a turn or two, and then the engine suddenly dies (especially if it makes a kind of sucking, gasping sound in the carb), you most likely have another problem, such as a major vacuum leak.

Post back and let us know how it goes!

 

all these engines draw vacuum at idle.thats why they tell you to unhook the line when setting the timing.is your choke open fully when hot. i mean 100 percent open.if its not the fast idle will stay on.if you have booster brakes clamp of the hose and see if that helps.and as someone said unhook your gas linkage from carb.your dist,could be sticking but it takes only minutes to try this stuff.

 

thanks for the ideas,

after i first noticed the problem i imediatly thought the throttle linkage was sticking, but it worked fine and that is one of the parts i lube regularly. i rebuilt the carb and tuned it to the factory settings which always worked before. i bought a new vacum advance for the distrubutor and hopefully that works. i haven't had a chance to let it run and warm up. if that doesn't work i am going to take the carb to a place called the "carburetor specialists". supposivly they do really good work, so hopefully they can help me out.

thanks again for all the replies.

 

No sir these engines do not draw vacuum through a ported vac source at the proper rpm ..read up on it. The manifold open source has a vac constant but not the ported vac for the advance mechanism on the carb. If that were the case you wouldnt need a vac advance it would all be done via mech.

 

WHY??? Wrong forum.

 

And a 15 year old thread.