GM 250 Inline six NEED HELP!

[Longley428]

Hello! I am restoring my 1969 C10 with the 250 straight 6. It has a recently rebuilt Rochester Monojet carb on it. I have recently replaced:

plugs, plug wires, coil, distributor cap, rotor, new breather, alternator, radiator, hoses, rebuit carb, im sure im forgeting a few things...

Had it running pretty good but when I would take off down the road after about 5 minutes of driving it would just stall out. Then would have to wait around 15-20 mins for it to cool back down and then it would start right back up and then repeat. So I thought it could be a vacuum/carb adjustment problem but now I have everything all screwed up. I have the carb adjusted the best of my ability but now truck will start up almost instantly, idle at 1,000 rpm but it is not a perfectly smooth idle, it is a mild rumbling idle with an occasional pop, as soon as you give it gas it has a hard sucking sound then will rev up with a popping/backfiring action then after a few seconds will idle back down, sometimes will only come back down to 1500 rpms and you have to quickly pat the gas to get it to idle back down. So I am at a loss on what it could be. Also I may not have the vacuum lines hooked up correctly if someone could post a picture of how they are supposed to be that would be great. Could it also be he accelerator pump in the carb causing the trouble? Please help!!

[CST10]

Idle Rpms should be set at 700 Rpms with the vacuum advance disconnected and capped. It might be a vacuum leak either on a hose or even carb itself. You can check the carb by spraying carb cleaner around the joints and seams of the carb. If it's leaking there the Rpms will increase.

[franken]

First, connect or plug vacuum lines. On an old 6, you don't need much. Connect a slamm line to the vac advance on the dist and the big one to the brake booster.
If it won't start when warm, describe exactly what it does, sounds, etc. when it won't start.

[Longley428]

I sprayed around the manifold and base of the carb with no change in idle while running. So are you saying plug the vacuum advance off and leave it that way? or just plug it off for test purposes?

[cadillac_al]

I don't see points and condenser on your parts list.

[Longley428]

I have not done points or condenser, would it be best to just buy a whole new distributor? Not wanting to go with the HEI distributor, would like to keep it all old and original with points type distributor.

[TJ's Chevy]

A new dizzy is in expensive. What is your valve adjustment? You could have some valves hanging open. Could be something in the carb to. Whats the float level set at? In correct float level will cause problems as well. If your A/f mixture is to lean that will cause stalling and backfiring. Alot of these single barrel carbs have a tendency to leak through the throttle shaft. Your timing might be off as well. Another thing to consider would be the points and condenser as mentioned. As points where down the gap gets wider and that starts causing similar issues.

[GRX]

The cutting out and running fine after cool off is a classic coil and/or condenser overheating issue. I would start by buying a new coil. A quick test for coil strength is to observe the spark color. Should be bright blue not yellowish.

[chevy_mike]

I know you don't want to change to an HEI but when I did with my 250 in my wagon, it was like I had a new engine. It ran so much smoother, started easier and eliminated any slight misfires it would get.

Best $100 I spent, http://www.langdonsstovebolt.com/sto...ategory=361515

[TJ's Chevy]

Another good one would be pertronix. Use the stock dizzy and cap all you do is swap the points for the pertronix and use their coil(available in black) and only you would know the difference.

[burnin oil]

If it has been sitting a long time it could be a clogged up fuel filter in the tank. Most people call it a sock filter. On a tank full of junk the truck will run until the junk clogs the filter then the motor will die from a lack of fuel. Once it sits for a little bit of time the crap falls off the sock and it will fire up and run again. This cycle will run indefinatly. Just one more thing to check. It is at the bottom of the fuel line on the sending unit. Pretty easy to check.

[88Ironduke]

100% agree on the HEI conversion. Its like a whole new engine. While the Pertronix is super cool if you have a problem with it parts are not readily available off the shelf at NAPA unlike a stock GM HEI. Either option will dramatically change your engines operation. You will love it the conversion and its easy.

Paul

[GRX]

Like a whole new engine if you are replacing a worn out points system with a new HEI.

[rockridgemike]

I've had coils and condensors cause those exact issues.
they get hot and it just shuts off.
start there.

[CST10]

Originally Posted by burnin oil

If it has been sitting a long time it could be a clogged up fuel filter in the tank. Most people call it a sock filter. On a tank full of junk the truck will run until the junk clogs the filter then the motor will die from a lack of fuel. Once it sits for a little bit of time the crap falls off the sock and it will fire up and run again. This cycle will run indefinatly. Just one more thing to check. It is at the bottom of the fuel line on the sending unit. Pretty easy to check.

I did have this same issue with the sock filter. Easy to check, just pull the sending unit. If it's really dirty that could be the issue.

[rockridgemike]

yup, had a 67 impala years ago, the sock would plug up and the car would die.
when that happened it would crap out slowly as it starved for fuel.
I guess the first thing to check when it does it, is whether it's spark or fuel.

[Longley428]

Thanks for all the help guys! I have replaced the coil already, I am going to replace all the vacuum lines tomorrow and then on to points and condenser, then if still no help then onto the fuel/sock filter. I will post what I find out!

[Longley428]

well installed new vacuum lines and it ran allot better!! But when now when I put it in gear and let out on the clutch it feels like I’m dragging a house behind my truck???? It tries to die and go dead... you can give it gas and will go but it still feels like a big drag is holding it back?? Any suggestions??

Also I still feel I need help with the vacuum line set up, I have a new PCV valve but the hose is not connected correctly I don’t feel, I have a 1 barrel mono jet carb with one small port on the base right front of the carb and one bigger port maybe a 3/8 hose would fit?.. off the manifold (almost directly under where the carb mounts on to the manifold.) And one on the back of the carb that is hooked up to my vacuum advance. Thats all the ports I can find. The truck does have power brakes and I can’t figure out where the hose for the brake booster goes?

[TJ's Chevy]

Originally Posted by Longley428

well installed new vacuum lines and it ran like a champ!! But when now when I put it in gear and let out on the clutch it feels like I’m dragging a house behind my truck???? It tries to die and go dead... you can give it gas and will go but it still feels like a big drag is holding it back?? Any suggestions??

Sounds like your parking brake is on. lol I had that happen with my GMC....be giving it the gas and you get that weird dragging feeling....turned out my brake pedal was sticking so the front brakes were on just enough to cause issues......this is 50 year old power brakes mind you. lol As I have been driving it everything has gotten better. So it never felt that way before and it does Now?

[Longley428]

It has felt like it since I’ve had it but I’ve also only got to drive it around the neighborhood a couple times lol I thought of that too but Ive tried pulling my release and nothing happens.. any other way to disengage it?

[burnin oil]

Block it up and lift the rear off the ground. Put it in neutral and see if the tires will spin. That should tell you if the e brake is hanging. This will not work if you have a trans mounted brake. You would have to drop the driveshaft to check that the rears are spinning free. It might be a good idea to just pull the drums and check everything out and replace the shoes if it is needed. Your problem could be as simple as someone over adjusting the shoes to the drum and causing excessive drag. If that doesn't fix the problem I would double check your work. I cant tell you how many times I made a what was I thinking mistake when working tired. One last thought is you may have a bad wheel cylinder. I have seen more than one corrode from sitting and cause as kinds of headaches.

[TJ's Chevy]

Originally Posted by Longley428

It has felt like it since I’ve had it but I’ve also only got to drive it around the neighborhood a couple times lol I thought of that too but Ive tried pulling my release and nothing happens.. any other way to disengage it?

Jack the rear end up and see how easy each wheel is to spin. The ones that are really hard are the ones where something is wrong. You do want Some drag, but not a ton. Enough to feel a bit of it. If your brake fluid was low and you refilled it That can cause those types of issues as well.

[Longley428]

Thanks! I will try that, can someone post a vacuum line picture or a diagram of how they are supposed to be hooked up?

[SiCk_DiAbLo]

Sounds like a fuel problem..My 72 used to to that, found out it was the inlet sending unit hose, was filled with rust..

[ViviensTractor5110]

Had a similar issue with my 250...turned out to be that stupid filter on the inlet of the Rochester...ditched that and I was golden.