I need help diagnosing a problem

[*MJF*]

I want to get my truck running better for a trip I'm taking in a few days.

It idles rough. It stutters & backfires at highway speeds & during mid to hard acceleration. I thought it was the carb or it was starving for fuel, but now I'm laening more towards timing/vacuum advance.

Here's a link to another post that explains the problem better: http://www.norcalbigdawgs.net/phpBB2...pic.php?t=2161

Please make some suggestions that I can look into to try to fix this thing. I am going to have my alternator checked out when I get home from work. If that checks out, I will rig up something to make a good ground from the frame to the block. If that doesn't fix it, I am going to just replace everything in the distributor that I can get to, but the parts for that are over $100. I don't want to spend $100, if it's not the problem.

[mtdave2]

did this all start all at once? what did you change b4? if anything.
9 times out of 10 a back fire has been timing for me. have you checked the pluggs as well? you may have a combo of things going on.

[jamie72]

when you changed over to hei did you run a new wire with 12 full volts to it???
if you used the coil wire you are only getting about 9.
good luck i`m fighting a gremlin myself
but its at low rmp.

[*MJF*]

I thought the carb went tits up. It started spewing fuel out of the accelerator pump rod & flooding itself out. I rebuilt it & reinstalled it & it still spewed fuel out the top. I then bought a cheapy fuel pressure regulator & installed that. The rebuild on the carb wasn't successful. It would run but I couldn't adjust anything. And it would idle but wouldn't drive. Kept cutting out when I would load up the engine.

I finally got pissed & pulled the carb off my wife's truck & it did the same thing. I thought my fuel pump was bad so I replaced it. Still the same thing. Found out the fuel pressure regulator was bad & not letting fule pass through. I removed it & ran the truck for a day or two & then it started spewing fuel & flooding again.

I go & get another regulator & put it in there(still with the wife's carb) & it seems to be ok. I decided to put my rebuilt carb back on since it seems to work perfectly on my wife's truck. The truck was still running, just rough & idle is sparatic(sp?). AT a stop light, sometimes it would be at 600rpm & other times at 1200 rpm.

So I finally get pissed again & put the wife's carb back on. The timing is right, it idles right, but it still runs rough & is now starting to cut out under acceleration & highway speed driving.

That's where I am now. it idles rough, cuts out & backfires, & generally runs like ****.

In the last few days I have put an inline filter on, replaced the spark plugs, tried pulling out the filter inside the carb in case it was plugged & it had no affect. That's why I'm leaning toward the distributor since both carbs are acting the same.

Someone suggested teh alt may be bad. I will check that out tonight. I went out at lunch & started the truck & pulled the pos cable off. The idle went up & the gas gauge & tach started surging wildly. Now I don't know if I have a shorted/dead cell in the battery that's loading things down.

My plan of attack tonight is: make a good ground between engine & frame, check out the alternator, put a different battery in. If that doesn't fix anything, I will then go buy all the tune up parts for the distributor & try that.

[*MJF*]

Yes I used a new wire connected to ign unfused.

[cdowns]

you could check the strainer on the fuel tank pickup

[Class of 69]

Take a plastic spray bottle, and spray water around on the distributor while it's running. May show a short, or voltage leak. Hook up your timing light on each cylinder, and watch for eratic flash from a bad wire. Keep your fingers crossed that the cam isn't gong flat on a lobe!

[HennyM]

Let's assume (and you know what that means!) you've already done a compression test, checked plugs, ign wires, firing order, and a good fuel supply, you have an HEI dist & 12 volts to it, and there are no vacumm leaks. Check the pickup coil in the distributor. An ohmeter across the two leads should read 750 to 1200 ohms ? (or something like that) and should not change when you wiggle the wires. Sometimes the copper inside the little wires breaks and the insulation remains intact. This causes backfiring whenever the vacumm advance moves the pickup assy.
You can also reach in & give the wires a little tug, if the wires are bad they will break right off. It sounds as if you may have more than one problem. Double check for vacumm leaks; brake booster?, pcv hose burned?, Good Luck! H.

[jewels.]

i had the EXACT same problem a few weeks ago. turns out the bracket for my manual choke had wiggled loose a tad, and the choke was not adjusted correctly. the engine wouldn't run correctly at all. it was idling hard, and not accelerating correctly. i would have sworn it was an electrical problem. but, i checked the plugs, distributor, fuel lines, etc. etc. i finally found the choke bracket and about kicked my ass cross the parking lot! i was mad at myself for missing such a simple problem.

bottomline, if you have a carb, and you have having idling problems, seriously make sure EVERYTHING is adjusted on that carb before you start replacing anything else. they are old, and can act funky very easily. check your choke.

good luck!
jewels.

[Canadian694x4]

...ya what she said

[Don Smith]

I agree with HennyM. Sounds like the pickup coil wire is shorting or disconnecting when the timing is advanced as during acceleration.

[*MJF*]

SOmeone suggested the alternator & it did check out bad on the tester so i bought a new one. That wasn't the problem. I bought all the tune up parts & was about to try that when I had an idea. I removed that POS, cheapy($20) kragen fuel pressure regulator & hooked straight to the carb & it works fine now.

So my initial evaluation of starving for fuel was right. I think it's time to go with an electric fuel pump & a good regulator.