The Stovebolt Site Forums The Shop Area Engine Shop This Truck's Killing Me - Help

We've been here before but this ole girl (57 3100) is still giving me fits. What are your thoughts?

What I have: 235 newly rebuilt .030 over with stock parts. Offy 2x intake. Fentons with dual exhaust and Flowmaster 40's. Langdon's HEI distributor. New wiring harness. Alternator. All parts are new.

Problem: The truck will start and run ok; although it's running rich. I have the timing on the mark and I've tried to adjust the air/fuel mixture but I'm not getting much variation on the vacuum guage. It's at about 14" right now and that's the best I can get. (I've RTV'd all the gaskets to prevent vacuum leaks, but...) The truck will run all day in the garage but if I take it out and put it under load, it will die. It acts like it's starving for fuel. However, my tank is full and my settlement bowl are full. Funny thing is that I can't see or hear fuel spraying in the carbs when this happens. After a short time (5-10 minutes) I can start the truck and the cycle repeats itself. However, it gets harder and harder to start over time. The chokes are wide open.

My exhaust tips are covered with dried gas. Sometimes when I start it, she bucks and pops like it's all carboned up.

What have I done? Someone suggested the problem is in the coil pickup in the distributor so I replaced it. No difference. I had the control module checked and it was ok. I replaced it anyway. I was running a water line along the fuel line at the top of the engine for heating the intake. I was afraid that was creating a vapor lock so I relocated it. Nothing has changed.

What are your thoughts?

Just some things to check off the list.

Is the timing right?
Are the plugs hooked up right?
Is the cam / crank gear installed correct (i.e. in the correct tooth)?
What is you cylinder compression (measured not calculated)?
Is the fuel pump running at high enough pressure?

Don't really have an answer for you, but I know where I'd start investigating. Good Luck!

Are the carb pumps spraying gas when you depress the peddle.

With two carbs, you might not see any vacuum difference when adjusting, just set them where they idle best and forget the gauge for now. How does it idle, smooth? rough? quiet? lots of air noise? rock solid?

Your next problem, during a test drive it dies? This sounds like dirt in the fuel tank blocking the pickup tube. Try mounting a fuel gauge, temperary, where you can see it when driving. I bet you find it loosing pressure, after it sets a bit, the dirt falls off the pickup tube and it runs again. Under driving conditions, the fuel requirement is much greater then setting in the garage idling.

Here are few more things to check.....

Is your fuel cap vented, try a test drive with the cap a little loose

have you done a search around the intake flange using a hose, with the other end in your ear, checking for any leaks?

Fresh fuel? old gas runs like crap,

Timing, would have to be way off not run,

low compression, would run, just have no power,

coils, would run till they get hot, takes a while for them to cool back off,

How are the valve adjustments, do you hear any poping out of the carb or exhaust? is the vacuum gauge steady or is it bouncing?

Joe

This is not the problem but I think you will find it will run alot better if you advance the timming more than the stock setting.

I didn't see mention of what kind of carburetors you are running. Does the mini-HEI have an external coil, and does it use a vacuum operated advance.

Have you put a timing light on the engine and checked to see what the marks do when you pop the throttle a bit...do they move around as they should.

If the truck actually gets harder to start as it warms up, the problem is obviously tied to temperature.

Tight valves could do this, as well as an electrical/electronic failure.

Does the HEI require a full 12 volts at all times.

Sorry to answer your questions with my questions!

Stuart

My guess is that you have either fuel or spark starvation. After driving and condition exhists is the coil to hot to touch? If so is there a ballest in the power line? Some HEI ignition systems require a ballast resistor on the 12V feed line.
As for fuel well like Joe H said, install a fuel guage and look at fuel pressure after condition exhists.
Adjusting idle mixture. Do you have a Uni-sync to sync the carbs.? You should adjust the carb.'s so that they both pull the same vacuum at the intake of the carb.'s. This device measures the suction at the carb. for each carb.
They both need to be the same before you adjust the mixture screw. Then forget the vacuum guage and screw in (one at a time) the idle mixture screw untill a noticable drop in engine rpm is noted, turn it out to its best idle and add 1/2 turn. Do this on both carb.'s one carb at a time.

This sounds like a fuel vent problem to me. First have you replaced the gas cap, perhaps with a non-vented cap? What type of carbs are you running, do they have fuel bowl vents, are they closed off?

I had a similar problem with mine. As irt turned out, it was the timing. Once it was advanced (15 degrees in my case) the popping and dying under a load want away. I'd suggest advancing it abou 5 degrres ant a time , until the engine sounds happy. You'll want to follow Toyvo's advice, too, as the RPM will increase with the advance, so the idle will have to be reset.
I recall from your other posts that you have a hydraulic cam, so that should eliminate valves, though you might check them just to be certain.
I should mention that my truck does not have a vacuum advance.

Hello Jerry, sorry to hear the conditions still exists. I dunno man, you've sure paid your dues on this truck. Well, you asked for some thoughts and here's one that occured to me:
I've never read that the cam was changed upon the rebuild but if it was did your guy degree it in and do you have the valve timing spec's that should have come with the cam?

Probably the timing would be different than the stock ball on the mark timing you've indicated.
Good Luck.
Dave

Jerry,

Put a vac guage on the intake manifold and adjust timing to highest vac reading ~ on a new engine it should be easy 19-22. If not then drop back and adjust the valves, then go back and adjust for highest vac again. I would also open up the carbs and check float drop and level settings and trim the gasget if they are hanging up. Is there junk in the bottom of the fuel bowls maybe the fuel pump is worn out from a dirty gas tank. Put a clear inline filter somewhere before the fuel pump and one between the pump and carbs. Try running on one carb at a time, disconnect the linkage one at a time. Contrary to popular belief I found that a 235 with properly set up 2x1 bbl carbs don't like a lot of ignition timing. Good luck.

Sounds like a fuel problem to me too. Replace the fuel pump & blow out the fuel lines. Put a filter between the tank & pump. Drill a little hole in the gas cap. I,ll bet this will solve it.

The popping seems to indicate your timing is too retarded. What is your timing at idle? Most engines like about 12 degrees BTDC for a mild engine, but I like to add a degree per 1000 feet altitude. This is kind of a general rule of thumb.
So when it's idling, check it with your timing light and see where it's at. If you're not equipped to check timing, then advance your distributor a bit at a time.

So back to your problem. You open the throttle when you try to drive it, and it dies. Yet it idles okay. Your idle circuits work. But how about your accelerator pump? (Depending on what carbs you are using). When you are idling the engine, what happens when you suddenly open the throttle by hand? It dies, right?
Okay. Is there a strong smell of gas when that happens? If so, probably too much fuel out the squirters.
Otherwise, perhaps it's exactly the opposite. Not enough fuel will cause it to die also, especially under a load.
I suspect your accelerator pump circuits.

But why are your plugs sooty? Well, at idle, you're definitely rich. Of course, you've got two carbs, so twice as much fuel is going to your engine at idle. I'd cut the air fuel mixture way back to bring that back. With two carbs, you might try about 1 turn out from completely closed on your idle mixture screws, and if that idles, bring each idle mixture screw more closed a little bit at a time. Like maybe an eighth of a turn. If you're on the right track, your idle speed should pick up. If you've gone too far, the idle will start stumbling and might die.

Sorting out your engine with a single carb first is a very good idea. I think it'll still run on all cylinders on a single carb. This is simple. Just leave the second carb on there, and disconnect the throttle lever to it temporarily.

One thing that really concerns me is, if this is a new rebuild, did you even break in your cam yet? All this fartin' around at low rpms can ruin a brand new cam. It's imperative that you immediately pop the rpms up to a fast idle of 2000 rpm for about 20 minutes. If your engine can't support that, your cam could be flattening its lobes. So if you haven't broken your cam in yet, as soon as you can get it to take a fast idle, worry about that first. Your idle circuits work, so that should be possible.

Jerry, you say it is running rich when it runs. Can you tell us how you determined that? It is almost impossible in my experience to get an engine to idle well if the idle jets are set to rich. If it is really rich, like black smoke at idle, that has to be float or need and seat problems. The discolored tailpipes are most likely due to water, just normal condensation as a result of never getting the pipes hot enough to dry them out.

If you do decide to disable one carb, be sure to run the idle speed screw out far enough to completely close the butterfly and seat the idle fuel screw.

The low vacuum could be any number of things, retarded timing, couple with butterflies to far open will do it. So will tight valves.

I would double check float levels and accelerator pump function first. Set idle fuel mix screws and close the idle speed setting. Then set timing as far advanced as possible and still start without kickback. Then start it and turn the idle speed screws in a little at a time, on both carbs until it will run. Then warm it up and back the idle screw on one carb down until it slows, move to the other carb. Keep that up until you reach the speed you want, probably around 650-700. Then adjust the mixture That will probable require a tweak of the speed again. Then back to the timing. Keep up this dance until you get were you need to be.

Let us know how it works out.

I forgot, info on the cam and carbs you are running would help.

Good points.

But don't ignore breaking in the cam if you haven't yet.

Ok; I spent some time with the ole girl today. I pulled the sending unit and there was no sock on the bottom. Strangely enough, there's evidence that there was one once but I don't find it in the tank (wonder if it's in my fuel pump). I blew air through the pickup and it seems that there was some yuk in there but nothing that would have blocked it completely. I blew air through all lines and they seem clear. I had installed a clear plastic filter at the bottom of the tank. I swear I doubled checked it but it was in backwards. My guess is that was the problem.

I ordered a new pickup from Chevy Duty and I'm going to replace that rubber line between the line coming out of the sending unit and the line going along the frame (it's threaded on both ends).

I'm going to clean up and paint the floor and the lower part of the cab rear wall; paint the tank and replace all rubber componenets. And then I'm going to go for a nice long cruise and finally enjoy my new engine.

I'll let you know how it turns out.

If it has solid lifters, make certain that they are adjusted properly.

I had this problem because my exhaust manifold heat riser was rusted in the open position.

After installing an HEI distributor in my small block, turned out that I should have bypassed the ballast resistor. It seems the new distributor needed the full 12 volts to operate properly. No wonder it ran like crap. After that, much better.

Ok; I may have solved part of the problem. I replaced the fuel pickup and sending unit in the tank and removed the filter (yes, the one I had in backwards) and the truck runs like a champ. I still need to synchronize the carbs but it seems to be fine now. It must have been the backwards filter that was causing my troubles. Thanks for your help.

I bought a UNI-SYN to help me synchronize the carbs. I may work on that this coming weekend.