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Topic Review (Newest First)
09-29-2011 05:26 PM
2old2fast Crap in the gas 'could be causing the needle & seat to leak intermitently , check a manual for the correct fuel pressure , Many GM products spec 5-7 as correct, also Q-jets are notorious for having 2 lead plugs in the bottom of the float bowl , accessable by removing the base plate, that leak . Their used to be a rubber plug that came in the carb kits to remedy this, but J_B weld works too.


dave
09-29-2011 04:04 PM
techinspector1
Quote:
Originally Posted by nanmer
So what are you saying to just replace the fuel pump like from an auto parts store and i should automaically get 5 psi. At least in theory.
Just out of curiosity the truck was sitting for 2 yrs. Wonder if trash in gas tank would have anything to do with it.
Choose from one of these Carter Muscle Car pumps, they seem to do a good job on a street motor. Trash in the tank would restrict flow. That does not seem to be your problem. Install a good quality fuel filter in the line and rebuild the carb. There could be some junk in one of more of the passages or in the fuel bowl, where it could restrict flow into the main jets.
09-29-2011 03:04 PM
nanmer
Quote:
Originally Posted by techinspector1
Regulators work well on systems using a steady pressure, like that provided by an electric fuel pump, but not so well on a mechanical pump system due to the pulsing of the pump. Try it though, you have nothing to lose.
So what are you saying to just replace the fuel pump like from an auto parts store and i should automaically get 5 psi. At least in theory.
Just out of curiosity the truck was sitting for 2 yrs. Wonder if trash in gas tank would have anything to do with it.
09-29-2011 02:48 PM
techinspector1
Quote:
Originally Posted by nanmer
Ok thanks.I think i have a regulator. Ill try it out and go down to 5psi.
Regulators work well on systems using a steady pressure, like that provided by an electric fuel pump, but not so well on a mechanical pump system due to the pulsing of the pump. Try it though, you have nothing to lose.
09-29-2011 02:32 PM
nanmer
Quote:
Originally Posted by techinspector1
It's just natural for hot rodders to think that more is better because it's true in many aspects of car building. In the case of a carburetor, it is not the truth. Your motor will operate better at 5 psi max using a Quadrajet, Carter or Edelbrock carb. Holley's will tolerate another 1 psi, for a max of 6.

More pressure will not make more horsepower. It will over-ride the needle and seat and blow raw fuel into the intake manifold, creating a tuning nightmare.

Find a way to drop the pressure to 5 psi at the carb inlet and you will be rewarded with a system that functions properly. If I had a mechanical fuel pump and it was delivering 7 psi, I would either replace it with a pump that delivers the proper pressure or I would rig up a bleed back to the tank, with an adjustable screw to limit or allow more fuel to be returned to the tank.

The Carter muscle car mechanical pumps spec a little higher than 5, but seem to work well on a street application....
http://www.summitracing.com/parts/CRT-M6624/
Ok thanks.I think i have a regulator. Ill try it out and go down to 5psi.

@cobalt327 What i meant to say in the quote was that My SPARK PLUGS keep fouling out out on me. It doesnt drip fuel while at idle. Ill have to check if it does after i shut if off. Also just curious How would one check the primary and secondary igniton.

P.s. Tried to multi quote but i didnt have the multiquote option unless i missed it. All i saw was the quote button.
09-29-2011 01:04 PM
techinspector1
Quote:
Originally Posted by nanmer
Ok.i purchased a oiled filled gauge. It reads 7 psi. A little confused. Some say 5-7 psi is good readings for a mechanical pump while others say 5 psi only.
It's just natural for hot rodders to think that more is better because it's true in many aspects of car building. In the case of a carburetor, it is not the truth. Your motor will operate better at 5 psi max using a Quadrajet, Carter or Edelbrock carb. Holley's will tolerate another 1 psi, for a max of 6.

More pressure will not make more horsepower. It will over-ride the needle and seat and blow raw fuel into the intake manifold, creating a tuning nightmare.

Find a way to drop the pressure to 5 psi at the carb inlet and you will be rewarded with a system that functions properly. If I had a mechanical fuel pump and it was delivering 7 psi, I would either replace it with a pump that delivers the proper pressure or I would rig up a bleed back to the tank, with an adjustable screw to limit or allow more fuel to be returned to the tank.

The Carter muscle car mechanical pumps spec a little higher than 5, but seem to work well on a street application....
http://www.summitracing.com/parts/CRT-M6624/
09-29-2011 12:31 PM
cobalt327
Quote:
Originally Posted by nanmer
As for the vacuum. Can i check it with that miss. Or will it give me a bad reading.Ill try to clean the plugs and get it as steady as possible to get a good reading. Their is no nozzle drip at idle.Let me see if there is any after i shut it off.
You can still check the vacuum, the miss will cause the needle to bounce but you'll still see where it would be normally.

I'm a bit confused. You responded to this post:

Quote:
Originally Posted by 355Nova
I figured it out by taking air cleaner off first and looking into carb when someone shut off the car for me. The carb was just literally dropping the a little bit of gas for about 15sec after car was turned off.

I hinted carb when I had pulled out a spark plug and smelled gas on them. Reason I pulled spark plug was because I had no start. I also noticed that If I kept cranking engine it would start in long run but hesitated when I accelerated.

I bought a fuel pressure regulator at autozone and walla! I also took time to tune carb while I was at it.
With the following:

"I know this thread is old but i have the same problem. Only thing is i have a mechanical fuel pump. Is that what you have as well. I didnt think one would need a fuel pressure regulator with a mechanical fuel pump."

What is the same problem you have? If it's not the carb dripping fuel, it must be the wet plugs?

There are a ton of things that can cause the plugs to foul w/fuel- carb, anything on the primary or secondary side of the ignition, fuel pressure to name a few.

Besides the fuel pressure, you need to rule out the ignition and carb float level, or blocked air bleeds, stuck power valve, internal leaks from warpage, bad well plugs, etc.
09-29-2011 11:46 AM
nanmer
Quote:
Originally Posted by cobalt327
Because of the design of a OEM-type mechanical pump, it will have a fluctuation on the gauge- this is considered normal. The psi you are seeing- while borderline high- is still within specs.

You said there was dripping fuel entering the engine. What you need to be aware of, is the Q-jet will exhibit "nozzle drip" if the idle isn't right. And the idle is tied to the timing. Also check to see if there's any dripping happening right after you shut the engine off.

So, to start with:

What is the initial timing?

What is the vacuum is at idle?

Have you checked for vacuum leaks?

Is the vacuum advance working and if so, is it connected to ported or manifold vacuum?

If the float level is off either because the adjustment is wrong or the float has soaked up fuel and has become heavy, this will cause a too-rich condition. If the idle vacuum is insufficient to fully seat the power piston, this can cause a too-rich condition.
What is the initial timing? Its set at 10 btdc

What is the vacuum is at idle? Havent checked it. Since the engine fouls the plugs . Figured i would have a bad reading. Due to the slight miss.

Have you checked for vacuum leaks?Yes,but ill check it again.

Is the vacuum advance working and if so, is it connected to ported or manifold vacuum?Yes its working,ported vacuum.Above the throttle plates.

It has a metal float. Already checked it. It has not fuel in it when i shake it. As for the vacuum. Can i check it with that miss. Or will it give me a bad reading.Ill try to clean the plugs and get it as steady as possible to get a good reading. Their is no nozzle drip at idle.Let me see if there is any after i shut it off.
09-29-2011 08:06 AM
cobalt327 Because of the design of a OEM-type mechanical pump, it will have a fluctuation on the gauge- this is considered normal. The psi you are seeing- while borderline high- is still within specs.

You said there was dripping fuel entering the engine. What you need to be aware of, is the Q-jet will exhibit "nozzle drip" if the idle isn't right. And the idle is tied to the timing. Also check to see if there's any dripping happening right after you shut the engine off.

So, to start with:

What is the initial timing?

What is the vacuum is at idle?

Have you checked for vacuum leaks?

Is the vacuum advance working and if so, is it connected to ported or manifold vacuum?

If the float level is off either because the adjustment is wrong or the float has soaked up fuel and has become heavy, this will cause a too-rich condition. If the idle vacuum is insufficient to fully seat the power piston, this can cause a too-rich condition.
09-28-2011 10:55 PM
nanmer Ok.i purchased a oiled filled gauge. It reads 7 psi. A little confused. Some say 5-7 psi is good readings for a mechanical pump while others say 5 psi only.
09-23-2011 10:14 PM
nanmer Here is an interesting read. Its sounds like the fluctuation is normal and to use a oil filled gauge for more accuracy.
http://www.hotrodders.com/forum/fuel...nd-145058.html
09-23-2011 09:54 PM
nanmer You mean results while driving and monitoring the gauge.Ill see if i can scrounge up fittings. Im still wondering why the gauge is bouncing so much. I dont think it should be doing that. Its brand new. Wondering if its the spring in the fuel pump by the rocker arm.
09-23-2011 09:49 PM
sqzbox Sorry I thought you had one on there. I needed to read back to the first post I guess. It didn't come with a reg, though. Get back with results tomorrow ok?
09-23-2011 09:42 PM
nanmer I don't have a regulator on it. Its a mechanical pump from the parts house.Didn't think i needed a regulator. Not hi performance. As for how many lines. I need to check it again tomorrow. Its 2 or 3. Its a 83 1/2 ton Pu.I didn't think these trucks came with regulators originally,correct. Thanks.
09-23-2011 09:35 PM
sqzbox At idle it shows your pressure regulator is working. Really need to take it for a ride and monitor pressure at cruise and WOT. I'm guessing you have a 2 line fuel pump?
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