Misfire @#$!@$

[farside847]

My truck started running a little rough, wanting to stall at idle, and jumpy in low rpms. So, I looked around and checked the plugs. They looked good but I found a melted spark plug wire so I thought it was time for a basic tune up. I proceded to replace the plugs, spark plug wires, cap and rotor. After doing this it does run a bit better, but not much. It is still rough. Unfortunately that is the limit to my "tune" up knowlege. I just thought I would check to see if anyone had any suggestions before I have a pro fix it....

thanks!

PS - its a stockish 307 with the 2bb carb and an ignitor ignition.

[70rs/ss]

Originally Posted by farside847

My truck started running a little rough, wanting to stall at idle, and jumpy in low rpms. So, I looked around and checked the plugs. They looked good but I found a melted spark plug wire so I thought it was time for a basic tune up. I proceded to replace the plugs, spark plug wires, cap and rotor. After doing this it does run a bit better, but not much. It is still rough. Unfortunately that is the limit to my "tune" up knowlege. I just thought I would check to see if anyone had any suggestions before I have a pro fix it....

thanks!

PS - its a stockish 307 with the 2bb carb and an ignitor ignition.

It could be a vacumme leak, so look for old brittle vac lines or unplugged lines as well as a leak around the base of carb. The easiest way to fin em is to have truck running and spay carb or brake cleaer arounf the carb (not in it) and if it effects the idle quality you have founf the leak. could be crud in th carb as well (change fuel filter).

[tomatocity]

Cooler fall temperatures bring denser moist air which should ceate a more lean situation though the cooler temperatures should create a more rich situation which should equalize the fuel mixture. My 4.3L TBI S10 started stumbling in the mornings and I am waiting to see if the computer catches up with itself.

I agree with checking for a vacuum leak. Use a water bottle (like a restaurant ketsup bottle) and not a spray bottle. If you see any dry or cracked vacuum hoses replace them all. If you are using a stock air cleaner housing there probably is a vacuum line that connects to the carb and you have probably removed it more than any other vacuum line.

What coil are you running and what is the gap of your spark plugs? If you have a good HEI (50,000 volts) you can get away with a lot. If you have a stock coil (25-35,000 volts) you need to be more accurate with you settings.

Try to keep your spark plug wires separated. Indisction can cause mis-firing. This usually affects weaker engines. If all the engine major components are good it is easier to garage tune an engine.
Make sure your spark plug wires have a good connection, use dielectric grease, and that they are in the proper firing order 1-8-4-3-6-5-7-2. 5 and 7 are the common problems.

Do you have an automatic choke on your 2bbl carb? If so, you might want to reset it.
Can you see any carbon buildup on the top of the carb where the butterfly contacts the opening. If so, clean that area with carb cleaner and a shop towel. This will allow the butterfly to contact the opening properly.

To get some of the annual services out of the way.
* Have you run your gas tank very low recently?
* Have you replaced the inline fuel filter lately?
* If there is one, have you replaced the fuel filter in the carburetor?
* Check your battery terminal connections.
* Check your thermostat.

Hope this helps.

[farside847]

Originally Posted by tomatocity

I agree with checking for a vacuum leak. Use a water bottle (like a restaurant ketsup bottle) and not a spray bottle. If you see any dry or cracked vacuum hoses replace them all. If you are using a stock air cleaner housing there probably is a vacuum line that connects to the carb and you have probably removed it more than any other vacuum line.

I did look at the lines, they are old but they are all plugged in where they should be. They are a bit dry though. Think this really could be it?

Originally Posted by tomatocity

What coil are you running and what is the gap of your spark plugs? If you have a good HEI (50,000 volts) you can get away with a lot. If you have a stock coil (25-35,000 volts) you need to be more accurate with you settings.

I have the stock coil. So my plugs are gapped to the recommended .35

Originally Posted by tomatocity

Do you have an automatic choke on your 2bbl carb? If so, you might want to reset it.

Yes, I do, but it doesnt seem to work. It never seems to engage. How do you reset or test it?

Originally Posted by tomatocity

* Have you run your gas tank very low recently?

I do almost every time.

Originally Posted by tomatocity

* Have you replaced the inline fuel filter lately?

Yep did it about a month ago with a new air filter too.

Originally Posted by tomatocity

* If there is one, have you replaced the fuel filter in the carburetor?

No, I havent. I thought that everything would have been caught by the inline filter though.

Originally Posted by tomatocity

* Check your battery terminal connections.

They look good.

Originally Posted by tomatocity

* Check your thermostat.

I didnt check it but I kinda ruled it out. The roughness is when the engine is hot and when its cold...


Hope this helps.[/QUOTE]

[tomatocity]

---I did look at the lines, they are old but they are all plugged in where they should be. They are a bit dry though. Think this really could be it?
*For the price I would not take the chance. I have seen guys rebuild carbs only to find it was a vacuum leak or bad point condensor in the distributor. These items were less than $2 each and simple to replace.
***Does your distributor have points and condensor? If so, makes sure these are in good condition and adjusted correctly before you do anyhing else. The thickness of a match book cover is a good starting point for the point gap.

---Yes, I do, but it doesnt seem to work. It never seems to engage. How do you reset or test it?
*If it is a manual choke: On a cold morning, loosen the fasteners holding the round black plastic piece on the side of the carb. If you look inside there should be a coil of flat metal. Actually it is two metals pressed together. The different metals contract and expand at different rates. With the round black plastic piece in place, rotate it until the choke butterfly starts to open, then rotate it to where it just touches the carb opening, then snug the fasteners down. There should be a tube, copper maybe, that goes from the exhaust manifold to the round black plastic piece. To release the choke all you have to do is tap the throttle.
**If it is an electric choke: read the manual but the settings should be similar. Make sure the electric wire is connected. Hope this helps. I know you live in the Bay Area with moderate weather but you must have had problems starting and driving in the cooler mornings.

*Make sure the throttle plates and butterflies are cleaned and the area around them. This is darn near free to do.


---No, I havent. I thought that everything would have been caught by the inline filter though.
*I would check it anyway. If you have a carb filter it might be a ceramic filter.

*If you have a rubber fuel line, make sure it does not leak and is in good condition.

*Check the tightness of the nuts on the base of the carb. They don't need to be very tight. Check your manual for torque specs.

*Generally check your carb for gas or air leaks. Use the household catsup bottle filled with water to check for the air and vacuum leaks. You would notice an increase in RPM if you find a vacuum leak. The water help plud the vacuum leak but does not create fumes that could be drawn into the carb an increase the RPM's.

[farside847]

For all those that helped, I thought Id post the solution. It was my carb. Had it rebuilt and now it puuuuuuurrrrs.