Engine Won't Idle--been workin on this for a week

[americanmusc1e]

When I installed a new 350 in my truck we pulled the old one and pullled the pan and timing cover and replaced the oil seals, and timing chain and adjusted the valves, then we put it in my dads '72 K20 Suburban. the motor runs OK but it won't idle(i think its flooding)

we Pulled my HEI, wires, spark plugs and my 4160 Holley off my '70 and put them on the engine, the Holley flooded badly at idle and i checked the pump and found 10PSI (might be more, my gauge only goes to 10PSI)at idle, my dad had a generic electric automotive fuel pump laying around so we put that on it (It put out 3PSI) and the engine still wouldn't idle, pulled the Holley and HEI off and put them back on my '70 and it idles just fine.

We picked up a new fuel pump(puts out 10PSI too), coil, a set of points and a condenser today and installed them and checked dwell and ignition timing and the thing still won't idle

P.S. carb is Quadrajet

[maddog1331]

I really don't know if this will help any, you probably don't have this problem, but...

I recently had similar trouble. My truck would idle, but contantly flood out at idle. Had Holley on it that was constantly leaking, so I bought an Edelbrock. Same thing was happening.

ANyway, what I ended up doing is replacing all the flex fuel line, and flaring out the end of the metal hose where it came up towards the engine. I don't know if yours is like that or not, but I think since mine had been hacksawed off it was getting pieces of rubber up in the carb, enough to keep the carb messed up.

Hope that helps, I doubt that is your problem but it is something to check.

[americanmusc1e]

anybody know what the fuel pressure is supposed to be on a Q-jet

[ed2552]

I would guess 5-8. I'd try a fuel pressure regulator, and see if that makes a difference.

[STOCKISH]

Fuel pressure should be about 7 psi. Sounds like a vacuum leak or valves adjusted too tight. Hope it helps.

[americanmusc1e]

Originally Posted by 1972SuperCheyenne

Fuel pressure should be about 7 psi. Sounds like a vacuum leak or valves adjusted too tight. Hope it helps.

valves adjusted too tight??

I tightened them until the pushrod stopped turning, then 1/2 turn more

[americanmusc1e]

bump.

guys i need your help with this one!!!

[bdydrp97s10]

check how many inches of vacuum the engine is pulling.. it should be pulling around 16-20".... if its not you have a vacuum leak and that will cause bad idle..

and 10lbs of fuel to a carb is another problem.. with that much pressure the fuel will overpower the needle and seat in the carb and cause flooding. get your fuel pressure down to around 5 or 6 lbs, and then check your plugs because im sure they are fuel fouled now.. if they are fuel fouled get 8 new ones..

but the first thing i would check is how many inches of vacuum it pulls,and then get your fuel presssure under control

[steelhorse]

Ditto on to much fuel pressure.I would also recheck you valve adjustment.

[americanmusc1e]

I should have checked the vacuum a week ago. Its pulling 10inches I think i got a vacuum leak

[Tynee]

When you installed the front disks, did you add a booster? It could very well be the source of your vacuum leak. If this truck is an auto, the leaking booster could also manifest itself in poor shifting...

You wouldn't necessarily be able to hear the leak either. A quick check would be to pull the vacuum hose from the booster and plug the end with your thumb. If the idle improves, you're on the right track.

Of course, this is a shot in the dark, not knowing for sure if you have either power brakes, or an auto tranny.

Edit: Just realized this may be in your dad's burb, but the theory holds, brake boosters are a common source of vacuum leaks, in my experience.

[americanmusc1e]

Originally Posted by Tynee

When you installed the front disks, did you add a booster? It could very well be the source of your vacuum leak. If this truck is an auto, the leaking booster could also manifest itself in poor shifting...

You wouldn't necessarily be able to hear the leak either. A quick check would be to pull the vacuum hose from the booster and plug the end with your thumb. If the idle improves, you're on the right track.

Of course, this is a shot in the dark, not knowing for sure if you have either power brakes, or an auto tranny.

Edit: Just realized this may be in your dad's burb, but the theory holds, brake boosters are a common source of vacuum leaks, in my experience.

yeah its my dads burb i'm working on but i'm going to plug all vacuum ports on the carb and intake and see if i can get it to idle

[stockish shawn]

you can spray brake clean around vacume ports and throttle shafts to locate vacume leaks. But 10 lbs. of vacume could be caused by a larger than stock cam an may not be the problem. check the vacume gauge and if it dances than the problem could be your valves. also check the timing and firing order real well. good luck

[QKENUF4U]

no more than 7psi and 10lbs could be TIGHT VALVES or timing as metioned above.....

[spinning wheels]

Originally Posted by americanmusc1e

When I installed a new 350 in my truck we pulled the old one and pullled the pan and timing cover and replaced the oil seals, and timing chain and adjusted the valves, then we put it in my dads '72 K20 Suburban. the motor runs OK but it won't idle(i think its flooding)

we Pulled my HEI, wires, spark plugs and my 4160 Holley off my '70 and put them on the engine, the Holley flooded badly at idle and i checked the pump and found 10PSI (might be more, my gauge only goes to 10PSI)at idle, my dad had a generic electric automotive fuel pump laying around so we put that on it (It put out 3PSI) and the engine still wouldn't idle, pulled the Holley and HEI off and put them back on my '70 and it idles just fine.

We picked up a new fuel pump(puts out 10PSI too), coil, a set of points and a condenser today and installed them and checked dwell and ignition timing and the thing still won't idle

P.S. carb is Quadrajet

Before pulling the engine from your truck it ran fine? The only thing you changed was the timing chain, and re-adjusted the valves. I would check those two items again. Cause this motor isn't running right, even when you installed the set up it had in your truck.

Was the timing set a multi timing sprocket type? Some sets you can retard or advance the timing. If it is, you may have changed the cam timing by accident.

Last would be, that the valves need to be readjusted. After you check the timing gear set.

I would also add a fuel pressure regulator. A stock to mild carbed SBC can idle off of 5 psi. of fuel pressure.

[kwplot34]

Originally Posted by americanmusc1e

valves adjusted too tight??

I tightened them until the pushrod stopped turning, then 1/2 turn more

When you adjusted the lifters did you make sure that the lifters were pumped up first? and did you make sure that the lifter was on the base circle of the cam,valve closed. you might of over tightened them.
If you have an old set of valve covers laying around you can cut the top out to gain access to the rockers (this will keep oil from spraying everywhere) and the loosen one lifter at a time and re tighten just till it's quiet and then give another 1/4 turn. Good luck,keep at it you will find the problem.

[americanmusc1e]

sorry guys, I haven't been working on the burb, my transmission went out in my '70 and I'm swapping to a 700r4, i should be able to get back on it next week

thanks for the suggestions, greatly appreciated

[americanmusc1e]

Finally yesterday I fixed It.

I tried everything but suggested above but adjusting the valves. It turns out I had all the valves too tight on the burb and on my truck. It didn't hurt the burb, just made it run bad. It killed a couple of lobes on my truck.

I had adjusted the valves by turning them in until the pushrod stopped turning and then 1/2 turn more. When I took my truck in to the transmission shop last week the guy there heard a loose rocker on my truck and he showed me that I had most of the valves on my truck too tight but two too loose. He showed me how to adjust the valves when it was running.

I couldn't adjust the burb when it was running so I modified it, I used an old piece of tape measure blade and adjusted them in until I couldn't fit the blade between the valve and the rocker and then a 1/4 turn more after it started I checked the valves with it running and found they were right where they should be.

THE MOTOR RUNS BETTER THAN IT DID IN MY TRUCK

thanks to all who helped with suggestions, sorry I didn't listen about the valves earlier

[soba_03]

Ok, I have to say that valves to tight is a possibility. I just dumped a motor in my 68 and adjusted them just as you discribed and had two off their seat and it would not idle.

Do a compression check, it will let you know if valves are to tight. I had #3 & #4 set to tight and was completely convinced it was an intake leak.

Good luck...