engine trouble!!! grrr

[BoeJaker1976]

OK, so with all the work ive done with truck, the engine is still running like crap. The engine use to work fine before the carburator went out. I relpaced it with a rebuilt qjet. I used a chiltons to figure out the vacuum diagram. I timed the engine to 8b, and turned the screws on the mixture to 4-4 1/2 out.
The truck is a 76 with a 350 and a 350t tranny and a 4b quadrajet. The HEI distributor was replaced with an MSD. The airpump and supporting emissions equipment have been removed except for the canaster. There must be something i missed some where or maybe something is in the wrong place. Here are the symptoms: During temp of 70 degrees or lower, the engine will start fine, but will soon die after. After it does start, it takes some time to warm up. After the engine warms up or when the tempurature out side is about 85+, it starts fine. Another thing it always does is, when im able to drive, and i put load on the engine (puting into drive or rev.) when i lay the pedal down lightly, like when i pull out of the drive way or slow driving, the engine bogs down and will die if i hold it there. But when i mash on the pedal its like theres no problem at all except at WOT. It'll bog a little there too. And today, it started back firing.
So i would really appreaciate any help or advice anyone can give me. Ive gone through the chiltons trouble shooting guide and i cant figure anything out!

p.s. Please dumb what ever advice down and be as specific as you can. Im not to engine savy.
thanx

[bowtiecb]

have you checked the choke

[BoeJaker1976]

i know that it has a manual choke. i dont know how to adjust that even if i can adjust that.

[old Rusty C10]

as to the choke when it is pulled out is the butterfly completely closed? when pushed in is it completely open? thats how you adjust a manual choke you make sure it opens and closes fully

[LONGHAIR]

I used a chiltons to figure out the vacuum diagram.

The airpump and supporting emissions equipment have been removed except for the canaster. There must be something i missed some where or maybe something is in the wrong place.

These two statements seem contradictiory? If everything is removed, the manual isn't goning to help you much....

First things first:
1) Be sure that there are no vacuum leaks.
Check the carburetor base, all fittings, all lines.

2) Check firing order....18436572

3) Timing set with vacuum advance disconnected and plugged?

4) Vacuum advance reconnected to "Full vacuum" fitting.

5) Idle speed set.

Manual choke on a Quadra-jet?

[BoeJaker1976]

So i had the car quest guy swing by my house and i had him look at everything and he said the the q-jet wasnt put together right or something is very wrong with it. He noticed that the secondaries werent opening infact the secondaries were actually becoming very stiff and didnt even try to open. so i guess. im gettin a new carb unless someone has any ideas

[Kixwy2]

Do you mean that the choke is automatic, but not electric? This is what mine looks like:

I still have the air rails and the canister, as well as the pcv valve. In my experience with my old engine (and swapping the new one) the backfiring meant my engine wasn't timed properly and the exhaust was coming back up through the engine and into the carb...

Also, once I started fiddling with non-stock additions and taking off the egr valve, I couldn't really go by the timing or diagram that the Haynes manual suggested. At the moment, I have one line going from the carb to the pcv valve, and one line to the vacuum advance. That's it. Everything else is plugged.

Adjusting the choke is real high tech - not. If your choke is like mine, you adjust the choke by bending that little vertical rod... your chilton's guide should have an illustration that will help you out.

Edit: Just saw your update - this happened to me too! I ended up taking mine to a rebuild shop and they gave me a good core and rebuilt my q-jet for $150. My secondaries didn't open because the core was bad... there should be some air holes in front of the secondaries that allow for air flow and push them open. Yeah, those didn't exist on my core. Still, it was one more thing in a sequence of faulty bits, including a flat cam.

[BoeJaker1976]

yup, thats what mine looks like. Anyways, my vacuum routing looks like yours and has been. now, for the secondaries not opening. as far as i could tell, them things never opened. Do you think its possible that when you buy a rebuilt carb from an autoparts store and not an actuall carb shop, that they could never test it? I just ran it up, and it looks like that the diaphragm that connects to butterfly valve for the secondaries, its always sucked in? Is it supposed to do that?
and just for my knowledge, again stateing that i hardly know anything about carbs. How do they open, what makes them open?

p.s. what did you end up timing your engine too? when you remove all that stuff, do you have to go up? or do you have to go more toward 0?

[LONGHAIR]

You probably will not get them to open just "free-reving". It is a vacuum drop that makes them open. If you have an "open element" style air cleaner, you should be able to hear it when they open. I you have a stock "snorkel" type, you may not. Intake noise is pretty loud, unrestricted.

If you are rolling along at a steady cruise, say 35-40 MPH and "floor it", you should hear and feel it when the secondaries open.....but trying to do it in the driveway, not good.

[BoeJaker1976]

i guess that makes sense. i really could never hear them tho, even when i had my old carb. Now is it a vacuum drop in the entire system or just in the carb?

[Kixwy2]

Originally Posted by BoeJaker1976

yup, thats what mine looks like. Anyways, my vacuum routing looks like yours and has been. now, for the secondaries not opening. as far as i could tell, them things never opened. Do you think its possible that when you buy a rebuilt carb from an autoparts store and not an actuall carb shop, that they could never test it? I just ran it up, and it looks like that the diaphragm that connects to butterfly valve for the secondaries, its always sucked in? Is it supposed to do that?
and just for my knowledge, again stateing that i hardly know anything about carbs. How do they open, what makes them open?

I doubt a place like Kragen or Autozone checks their stock. I got a distributor from Kragen and had to take it back within 2 months because the springs were faulty and the weights didn't work like they were supposed to.

I tried rebuilding my carb myself, and did ok - found some missing parts and went to the carb guy for help. He gave me a new metering spring for free and some good advice. When things still didn't work the way I thought it would I went back to the carb shop. He told me I did a good job but I had a bad core - it was like a Frankencarb. That's when he told me about the air holes in the secondaries. It was cheaper to have him do it than buy a new one, he re-dipped everything for me, plus he guaranteed his work.

Originally Posted by BoeJaker1976

p.s. what did you end up timing your engine too? when you remove all that stuff, do you have to go up? or do you have to go more toward 0?

At the moment I am at 10.5* BTDC. Hood sticker for the original 350 said 12, Haynes said 8, and the new crate engine spec recommended 10. Power and response is good without much stumble off idle (and this is only when cold), and fuel economy is decent-ish considering the vehicle.

If you can, take the carb back and get another one, especially if there's a warranty on it.

[84 400]

Here this video might give you a better idea of what goes on inside the carb. Disclaimer: I don't agree with this guys mehoids but it does have some info in it.

YouTube - part 2, 77 gmc 4x4 truck fix to start

[MylilBowTie]

That guys defiantly different, seems sober in this one.

[LONGHAIR]

That video is an almost perfect documentary....of what NOT to do.
Starting with doing any of that work with the carburetor still on the manifold.
The exposed 5-gallon plastic bucket fuel tank is illegal everywhere.
He is so worried about the plastic gasket on the inlet fitting, yet ties an electric fuel pump to the side of the engine, right over the exhaust manifold?

If he had even one scrap of good information, it is so buryed in bad practices, you wouldn't gain anything. It is far easier to pick-up bad habits than to glean the good from it.

[84 400]

Yeah i posted that vidoe just for the fact that it showed the inner workings of a Q jet.

And yeah He may think he is smart but the guy half A$$ everything. You should see one of his other vidoes where he puts a new starter on his 427 powered chevy dump truck..... puts all that money into it but runs it with no oil breather nor air cleaner and it sits out in a feild so mice and what not have all winter to crawl all around........

As mentioned in my Orginal post I don't agree with anything he does. Sometimes it is comical others downright dumb but mostly dangerous.

[babyJay]

that vid was funny, Longhair hit it right on the nose....

[Kixwy2]

Oh, my god - that would be hysterical if it wasn't so sad...

Totally ignore what that guy did!

[Kixwy2]

oops - double post?