truck wont stay on

[69heavychevy]

i have been having trouble getting my truck to stay on while idling. it first started when i put on a new distributor. i havent timed it using a timing gun yet, but i marked it according to my old one. in order to keep it on, i have to just put my foot on the pedal lightly. if i let idle by itself it idles at around 200rpm and eventually turns off.

[69heavychevy]

by the way i upgraded the cam (212/.447 int; 218/.454 exh). everything on the ignition side is new. except for the plugs, they look good but i will be replacing them soon. it sounds great, doesnt sound like its missing or anything, but it just wont stay on. i have a couple friends telling me the carb is trashed or that the timing is completely off. i think the carb may need to be adjusted for the new cam. thats just my guess, im new to the carb world. any help would be great, thanks!

[rwgregory]

My GMC does that from time to time when the floats stick. Just tap on the side of the float bowl a couple of times with the handle of a screwdriver and see if it go's away...

[69heavychevy]

ill try it, i kind of thought about that too. also if it matters, when i was trying to get it running after putting it back together the carb was backfiring really bad. turned out some of the rocker arms came loose. thats why my friend told me i could have trashed it.

[tsetsaf]

You moved alot of stuff around during the switch. Are you sure the cam is aligned properly?

Were you having problems with the carb before the switch? If not, I would look elsewhere first.

[HoupPhotography]

It sounds like your timing is a little off, NOT COMPLETLY, just barely. loosen the dist. bolt, have a buddy or someone start the motor while you, very slightly, turn the distributor. I don't know what motor you have, but as you turn the Dist in one direction the idle will decrease, turn it the other way and it will idle higher. A sort of trick to tuning, trurn the dist. whichever way makes it idle higher, try to determine where that fine line is from the idle peaks then goes flat, once you get it right at that peak, turn it back just a hair and you will be very damn close to spot on.

[69halfton]

bigger then stock cams require a higher idle. if your idle screw is still set the way it was with the stock cam, the engine would slowly die down as the butterflies aren't open enough to support the motor running. if your cam timing was off, the truck would run very good, regardless of the rpm. if the dizzy wasn't timed i would think you would hear some popping of pinging at another perticular rpm.

my truck with a big cam idles at 900 rpm in park, and may creep down to 800 when in drive & warm.

200 rpm is too low even for a stock motor.

[AGRV8D]

I was thinking the same thing as the above poster: adjust the carb a little on the idle screw

[67ChevyRedneck]

I actually read a good post yesterday:

The simple answer to the question is that if you have a stock or near-stock cam, you should connect to ported vacuum as no additional vacuum advance is needed at idle. Ported vacuum is taken above the throttle butterflies, and so is less than manifold vacuum at idle.

If you have an aftermarket cam that's a little warmer, connecting the distributor advance to manifold vacuum will provide additional vacuum advance at idle which can improve idle quality.

Once the butterflies are open to any extent, manifold vacuum and ported vacuum will be virtually identical and so there is no performance/fuel economy/etc. difference - the only reason for additional advance at idle is to smooth out a lumpy cam.

Of course, if you swap to manifold vacuum, don't forget that you need to block it off when you set your initial timing.

[69heavychevy]

well new plugs on today so thats out the way. i have a edelbrock 1405, which screw is the idle screw, left or right. sorry like i said before im new to carbs. the cam is timed right i made sure of that, i made sure the dizzy went in at tdc. i have tried moving the dizzy around but with no success. also when i put the new dizzy in at tdc 0 degrees. should i have had advanced or retarded the timing any with the new cam.

[67ChevyRedneck]

The two screws at the base of the carb are the mixture screws. The screw on the DS side of the carb with the spring on it is the idle screw. It should be parallel with the top of the motor and kinda stick past the front of the carb just a hair. Turn counterclockwise to take fuel away, turn clockwise to increase the fuel at idle (it's possible I've said that backwards...) Turn one way, truck will die, turn the other, truck should run better

In the pic, the screw on the side is the idle screw.

[69heavychevy]

finally! thanks alot guys. i had to adjust my idle a bit, now i just have to dial it in. unfortunately i the same time i realized i have an exhaust leak at the header collector on the passanger side. im telling you, if its not one thing its another. oh well, thats what makes everything interesting.

[roughedup72]

your luck sounds like mine. Keep at it and you will get it right. Readjust your mixture screws if you moved them before. I'm running mine about 1 1/2 turns out on each screw. to do this turn them in clockwise untill they stop ( DO NOT OVERTIGHTEN THEM) then turn the counter clockwise 1 1/2 turns or untill it sounds like its running smooth. Good Luck