dies on acceleration

[nachoman]

After a long period of a few years of my car running mostly good, lately has been one thing after another. I've got a 200 with a large bore Holley 1940 carb, 1968 distributor with Pertronix and 12v coil. My problems lately have been thus:

When I try to accelerate after an idle, the car sputters, bogs down, and sometimes dies. Low RPMs it dies, but at higher RPMs, it is okay. Yesterday driving to work it was real bad and I stalled a few times coming off of lights. I opened up the hood at work, fiddled a few spark plug wires, and at lunch tested it out (even on the freeway) and all seemed great. But when I went to go home, the stumbling problem happened again, now even worse than before.

Last night, I rebuilt the carburetor just to see if the accelerator pump was bad. I also replaced the inline fuel filter. I put it back on, things seemed better, yet on the way to work again this morning, same thing again.

Here are some things that I have noticed recently: After a hot day, the car is very hard to start a few hours later after the engine has cooled. I crank and crank and crank as if the fuel bowl is out of gas. When I do get it started, It usually dies again the first time I try to accelerate, but after that it is okay. But I don't have this problem if I just run into a store. I only have this problem after the car has sit for awhile. The spark plug wires and distributor cap and rotor are new.

I'm thinking fuel pump going bad. Thoughts? I could also pull the plugs and wires again and see if I can find one that is not right...

 

[nachoman]

Should also add that I have had issues lately with dieseling. That could be a function of idle speed too high.

Now I am also thinking about the new plug wires I bought. I bought the cheap duralast autozone wires, and the coil wire doesn't seem to snap into the cap very well. It feels like it isn't pushing in far enough. Are the cheap wires even acceptable for use with a 12v system and pertronix?

 

[rbohm]

it sounds to me like you have a fuel boil issue to start. the dieseling is caused by a hot spot in the cylinders though. you can try a colder plug to see if that solves that problem. as to a possible fuel pump issue, its possible, so do this;

1: run the engine so you know there is fuel in the float bowl

2: disconnect the fuel line from the inlet at to the carb

3: stick that end of the hose in a bottle and have someone start the engine

the bottle should fill fairly quickly, about half way in about 2-3 seconds or so depending on the size of the bottle you use. if you dont get a nice stream of fuel coming out, then i would suspect the fuel pump.

 

[nachoman]

I do have another fuel pump in the trunk of my car. I could swap it out relatively easily and see if it makes a difference. I'm thinking that the fuel pump is not my problem, though. Like I said, it seemed to run fine yesterday at lunch. I think it would be strange to have an intermittent fuel pump problem. Plus, since it idles okay, and the problem is at low RPM, I now think that is not a fuel pump because I would expect a worn fuel pump to falter at higher RPMs when the fuel demand is greatest. The stumble is as soon as I crack the throttle...

 

[bubba22349]

How is the condition of your fuel tank, the fuel line from tank, and fuel pickup tube? Was there any signs of rust and grudge or trash in the carb when you rebuilt it?

 

[66stang84]

I second bubba22349's response. I had similar issues with my 200. I did the glass jar trick suggested by rbohm and found I was getting adequate fuel vol/pres but it was filled with a lot of rust sediment. The tank was in fact the problem. It was completely rusted on the inside with no evidence outside, the sending unit filter had completely eroded also. Easy check and good place to start.

 

[nachoman]

Well, the fuel tank was new as of about 3-4 years ago. I suppose trash or water could have gotten into there.

 

[nachoman]

On lunch break I replaced the pcv valve (cheap enough to replace) with no success. I also trimmed away at the coil wire boot so that the coil wire could snap in place better - again no success. The problem seems to be less when the engine is cold(er) for the first minute or two. I also disconnected the fuel hose downstream of the fuel pump, and it was under pressure and fuel sprayed out. That leads me to believe it is not a fuel pump or fuel line issue - there is apparently plenty of fuel available to the carburetor. That is unless the pump is supplying plenty of pressure but not enough volume? Is that possible?

I think before I leave I will pull the spark plugs for a look, and if all okay just limp home and replace the fuel pump tonight simply because it doesn't take long and because I have a spare.

 

[rbohm]

it is very possible that the pump puts out, but not enough. that is why i recommended the volume test. no need to replace a fuel pump that is working.

 

[nachoman]

Well, I had convinced myself that it was the pertronix going out after I found a discussion on another website that basically described my problem. So, I figures what the heck, I can put the points back on, put the stock coil back on, and see. And it fired right up, so I test drove, and same problem again. At least I know it's not the pertronix, not the coil, probably not the new plug wires... I guess I am back to the fuel pump, should pull and check all plugs to see if one is fouled, and after that - I guess a carburetor problem that I did not solve in the rebuild.

 

[rbohm]

i still say its a fuel boil issue.

 

[JackFish]

Stuck choke?

 

[bubba22349]

X2 might be fuel boil get a thick carb base gasket or make a plastic insulator is a low cost fix and general a good idea anyway. I am also leaning more towards your carb adjustments. Have you tried adjust the accelerator pump shot? I.E. The timing and duration! Is your fuel float level set to correct spec? X2 on JackFish suggestion make sure the choke is opening fully and operating as it should for the most part these old engines need a choke when cold, rbohm is right too you really need to test the fuel pump volume it's a quick and easy test that's costs nothing and then you know if fuel pump is working right. Good luck

 

[nachoman]

Well, I spent time cleaning the spark plugs and re-gapping. i also replaced the fuel pump with another good one I had on hand. It runs better, but still has the same issue. It's pretty apparent the issue gets worse as the engine warms, but I think it is between the time of it coming of of fast idle and before it actually gets up to temp. I adjusted the accelerator pump to spec when I went thru the carburetor, and it had been way off (too rich). I'm baffled now. I'm thinking of replacing the spark plugs. They are cheap and quick, and it's possible I have one that has a cracked insulator down inside. Other than that - I guess I need to tear back into the carburetor in more detail. Perhaps there is a speck of dirt that I didn't dislodge the other day.

Another thought is that i have bad gas or got water in the gas.

 

[nachoman]

Gee, I think I found the problem. I replaced the spark plugs, tried adjusting the carburetor a little bit (accelerator pump and idle screw) and things were better, but still not good. I then fiddled with the plug wires again, just to make them ore orderly, and as I pushed one of them back into the distributor cap, the distributor cap snapped down just a wee bit more. I took the cap off (new as of a few months ago) looked at the terminals, and I saw a groove worn in several of them. Aha. I guess the cap may have been a teeny bit crooked, and the rotor had contacted the terminals. How much clearance should there be between the rotor and terminals when installed? looks like not much, and if the cap is a tiny bit crooked, it will make contact!

 

[nachoman]

Well, I replaced the distributor cap - no change. So, I tore down the carburetor again, did a real deep cleaning (read online to soak in pine sol, and that worked awesome!) I found that the main jet was not completely snug, a few areas that were gunked up, and a gasket that did not fit well. But now it's clean, I found a gasket that fits better, the float level was double checked, and the accelerator pump was double-checked for the correct stroke. I put it on this morning, and same problem. One issue with the carb, the accelerator pump goes when I open the throttle, but slowly. Like maybe I have installed the spring upside down, or there is too much drag between the rubber cup and the cylinder. I will look at that tonight, but I don't think this was my original problem. Also, I noticed the car revved better with the air cleaner removed. The air filter is dirty, but not horrible. Probably not causing my problem, but I guess it needs replacement.

But, in the process of trying to diagnose things this morning with the engine idling, I tried moving the plug wires around, and got myself zapped when I grabbed the coil wire. I don't think that is normal for a brand new wire. This is the wire from the new set that had a 90 degree end that did not fit into my coil far enough, so I cut away at the boot and bent the terminal straight. It fits into the coil now, but the boot does not completely cover the connection. Also, when I grabbed the wires 1-3, I did not get zapped, but could feel a rhythmic "vibration" in the wire, almost as if I could feel the electricity. I didn't feel this on wires 4-6. Not sure if I was just feeling the vibration of the engine or distributor through the wire, or this was indicating some other kind of issue. Nonetheless, I'm about out of ideas, so I am thinking of buying ANOTHER set of plug wires of a different brand (hey, 30 bucks, can't hurt), and if that doesn't work, I'll just scratch my head straight through my scalp!

 

[bubba22349]

You can get the correct new coil wire boots separate or a new coil wire at most good Auto parts stores try NAPA etc. have you done a compression test on the engine yet? One other thing that can cause an acceleration stumble is a faulty vacuum advance can on the distributor test it to see if it holds a vacuum. Good luck

 

[nachoman]

No compression test yet. I lost my "compression tester" when my dad moved out of town last year That will probably be my next step if a new coil and a few carb adjustments don't solve things. I can't imagine that it's an engine mechanical problem. It idles fine, does fine at higher RPMs. Unless I have a valve that may be sticking open when warm. Plugs look fine, no oil. I've had burnt exhaust valves before, and it runs like crap at all RPMS.

This is a mechanical and vacuum advance distributor. I suppose there could be issues with the mechanical advance, but again this is something that is changing as the engine warms. If a spring had broken or fallen off, I would think the issue would be all the time. It's not hard to pull up the breaker plate to have a look, though. Perhaps a little bit of trash is blocking an advance weight. The vacuum canister seems fine. No leaks there.

 

[nachoman]

Well, I've fixed the accelerator pump issue. Not sure if I just didn't have the rubber cup inserted properly or maybe the discharge hole was slightly clogged. I ran a tiny drill bit through the discharge hole, just to be sure. Now the spring fully discharges the pump when the throttle is opened. I also replaced the plug wires with a set that seems to fit much better. Also put on a new air filter.

The car runs 90% better now. I drove it to work this morning with little problem. There was still some slight hesitation at low RPMs, but it wasn't trying to completely quit on me just off of idle. I've had some low RPM hesitation issues before and I just lived with it for awhile. The idle was a little rough, but maybe that can be smoothed by adjusting the mixture screw.

I'm thinking this was just one of those issues where in the process of trying to solve the original problem (it may have been the distributor cap or a coil wire that did not fit well) I created another issue when I took the carburetor apart. In re-reading the carb rebuild instructions this morning regarding the float level, it says the TOE of the float should be level with the top of the fuel bowl. Well, I have a brass float, and the top of the float is higher in the center, and I set it to where the center of the float is level with the fuel bowl. If I went with the toe of the float, the fuel level would be about 1/16" higher. I think the instructions were written for a plastic float. Thoughts here?

 

[bubba22349]

Congrats on getting it to near drive able condition! Float level is quite important for drive ability using the measurements usually gets you very close though on some carbs I set them by the wet fuel level if they list a spec then it's the most accurate way. If you have a Tach / Dwell unit or a vacuum gauge that would help you get the mixture screw and curb idle set to the correct specs. Your almost there good luck