Weak Ignition??

[Shawn]

Ok, I have a built 327 in the jeep and I have been running this Mallory Pro Comp 9000 for many many years. If I need to get into the engine spec's I can but, this is my problem. When I'm heading up to work (Snowbird) I usually fly up the canyon. When I want to pass or give it some gas, right about were the 4 barrels would kick in it starts to act like it's flooding out and or a bogging feeling. I have noticed black smoke coming out the rear. I can let off a bit and it goes away.

It really doesn't do it in the lower elevation, but the again I really haven't tried it going up hill.

Carb, Bran new Holley Truck Avenger. The plugs show it is running just right, not to rich and not to lean. Yes, I did change the jets and pump.

I think it is not getting a hot enough spark and when I give it too much gas it is just washing the pistons. I was going to take the HEI out of the cruiser and drop in there to see if made a difference.

So, I thought I would see what you all thought.

Bobdog, I know you are an engine master... Input??

 

[bobdog]

Not an engine master, but I do run a mallory distributer and at one time had a problem similar to yours. I added a MSD 6A box trigered by the mallory distributer and it solved my problem.

 

[BCGPER]

I'm not that familiar with your set up, but let's try the easy stuff first. The black smoke indicates too rich. Opening the four barrlels shouldn't change air/fuel ratio at all, it simply allows more air and fuel at the same ratio to enter the engine.

When you rejetted, did you do both primaries and secondaries? Are there two sets (upper and lower) of butterflies on your secondaries? Are the uppers opening?

Air filter is good? (I know you're smarter than that)

Vacuum advance (if you have it) hooked up to venturi vacuum and not manifold vacuum?

Centrifugal advance working (only effects higher RPM's)?

Any lifter noise in the past? (a flat cam acts exactly like this, but should act up at all elevations)

Cam Timming correct?

Since it seems to be related to the secondaries, I'd start my search there and assume the ignition is ok.

 

[kowe69]

It sounds like it could be a number of possible problems. It very well could be flooding like you said, especially if it only happens at higher altitude where the air is thin. I would checked your plugs for fuel fouling and wires for arcing to ground somewhere. I also had a problem like this recently on my 383 Vortec. At approx 3000 rpm at cruise it would start to misfire and backfire. It went away with more or less throttle or RPM. I finally traced it down to a worn distributer gear causing erratic ignition timing. Replaced the gear, good as new. If none of these things, maybe try putting slightly leaner jets in your carb. I admit I'm no expert on carburetors though...I'm a fuel injection kind of guy. Hope this helps. Let us know what you find.

 

[Shawn]

I'm not that familiar with your set up, but let's try the easy stuff first. The black smoke indicates too rich. Opening the four barrlels shouldn't change air/fuel ratio at all, it simply allows more air and fuel at the same ratio to enter the engine.

When you rejetted, did you do both primaries and secondaries? Are there two sets (upper and lower) of butterflies on your secondaries? Are the uppers opening?

Air filter is good? (I know you're smarter than that)

Vacuum advance (if you have it) hooked up to venturi vacuum and not manifold vacuum?

Centrifugal advance working (only effects higher RPM's)?

Any lifter noise in the past? (a flat cam acts exactly like this, but should act up at all elevations)

Cam Timming correct?

Since it seems to be related to the secondaries, I'd start my search there and assume the ignition is ok.

ya, this stuff is all dialed in. I rejetted like 4 time to get the proper jetting.

 

[Shawn]

It sounds like it could be a number of possible problems. It very well could be flooding like you said, especially if it only happens at higher altitude where the air is thin. I would checked your plugs for fuel fouling and wires for arcing to ground somewhere. I also had a problem like this recently on my 383 Vortec. At approx 3000 rpm at cruise it would start to misfire and backfire. It went away with more or less throttle or RPM. I finally traced it down to a worn distributer gear causing erratic ignition timing. Replaced the gear, good as new. If none of these things, maybe try putting slightly leaner jets in your carb. I admit I'm no expert on carburetors though...I'm a fuel injection kind of guy. Hope this helps. Let us know what you find.

no fouling, new wires

Not really and miss, more like a wash. Kind of like you took a can of gas and dumper it down the card... kinda. I can tell it is not burning all the fuel because of getting on the gas and backing off washes it.

 

[BCGPER]

You want to run it over here over the weekend? It sounds like the carb to me. I have a funeral to hit for a couple hours tomorrow, otherwise I'll be here all weekend.

 

[Shawn]

Not an engine master, but I do run a mallory distributer and at one time had a problem similar to yours. I added a MSD 6A box trigered by the mallory distributer and it solved my problem.

What is a 6a box??

I have really never been sold on the Pro Comp... But I hate to lay down a few hundred to find out that is not the problem.

 

[Meat_]

Did it kick down a gear when you stomped on it? Maybe you just aren't turning enough rpms for the fuel.....

 

[Shawn]

Did it kick down a gear when you stomped on it? Maybe you just aren't turning enough rpms for the fuel.....

It is a stick and I can light them up in second & third

 

[Shawn]

You want to run it over here over the weekend? It sounds like the carb to me. I have a funeral to hit for a couple hours tomorrow, otherwise I'll be here all weekend.

Let me see how the weekend goes.

Thanks B

 

[Meat_]

It is a stick and I can light them up in second & third

hmmm I thought I remembered it being an automatical

 

[Shawn]

hmmm I thought I remembered it being an automatical

nope, SM420

 

[waynehartwig]

6al is MSD Ignition. MSDP is the parent company of MSD, Edge , Superchips and RacePak.

I agree; definately carb related. Is your Holley vacuum or mechanical secondaries? To me, it sounds like maybe the metering blocks or the power valve? If they are mechanical, it's an adjustment. If they are vacuum, then it's a different weight of spring. Could also be secondary jets are too big...

The power valve works off of vacuum. When the vacuum drops below x amount, the valve opens, dumping more fuel. The power valve only works at WOT, so maybe not. But if it's too light maybe? They come in different spring/vacuum stages. ie 3.5, 4, 4.5 inch of vacuum. If you're cracking the 4 barrel open, it might be dipping too low and causing it to open up? See...It's been too long away from Holley's and I don't remember this crap now.

Put a vacuum guage on the motor so you can watch the vacuum. Cause it to do what you are talking about and see what the vacuum is at. Also when it starts loading up, see if by giving it more gas if it smooths out or just gets worse. More throttle will drop the vacuum and if it's a vacuum issue, it should make it worse. If it's jets, it will stay the same.

 

[Shawn]

6al is MSD Ignition. MSDP is the parent company of MSD, Edge , Superchips and RacePak.

I agree; definately carb related. Is your Holley vacuum or mechanical secondaries? To me, it sounds like maybe the metering blocks or the power valve? If they are mechanical, it's an adjustment. If they are vacuum, then it's a different weight of spring. Could also be secondary jets are too big...

The power valve works off of vacuum. When the vacuum drops below x amount, the valve opens, dumping more fuel. The power valve only works at WOT, so maybe not. But if it's too light maybe? They come in different spring/vacuum stages. ie 3.5, 4, 4.5 inch of vacuum. If you're cracking the 4 barrel open, it might be dipping too low and causing it to open up? See...It's been too long away from Holley's and I don't remember this crap now.

Put a vacuum guage on the motor so you can watch the vacuum. Cause it to do what you are talking about and see what the vacuum is at. Also when it starts loading up, see if by giving it more gas if it smooths out or just gets worse. More throttle will drop the vacuum and if it's a vacuum issue, it should make it worse. If it's jets, it will stay the same.

The carb is vacuum, I did change the power valve to a lower setting (it has been a while so I don't recall which one) I have changed the spring, and the rear jets.

So the power valve needs to be stiffer? I went off of the instruction for the carb when I bought it.

 

[waynehartwig]

The carb is vacuum, I did change the power valve to a lower setting (it has been a while so I don't recall which one) I have changed the spring, and the rear jets.

So the power valve needs to be stiffer? I went off of the instruction for the carb when I bought it.

Why did you change it all? What would happen if you put it all back to factory? Same thing?

Jet's work all the time, regardless of vacuum
Power valve is vacuum sensitive
The vacuum secondaries are vacuum sensative

I'd really be curious what a vacuum gauge shows when you have problems. And how do you know the secondaries are opening when you are having this problem? Typically they don't open unless you are about 3/4 throttle? If you aren't sure, put some grease on the linkage and drive it. See if the grease has been messed with after the problem starts. Maybe the power valve is opening before the secondaries??

 

[Shawn]

Why did you change it all? What would happen if you put it all back to factory? Same thing?

Jet's work all the time, regardless of vacuum
Power valve is vacuum sensitive
The vacuum secondaries are vacuum sensative

I'd really be curious what a vacuum gauge shows when you have problems. And how do you know the secondaries are opening when you are having this problem? Typically they don't open unless you are about 3/4 throttle? If you aren't sure, put some grease on the linkage and drive it. See if the grease has been messed with after the problem starts. Maybe the power valve is opening before the secondaries??

It was running way rich.... black fouling, pukey..

Keep in mind, this happens when I'm driving and the motor is under a load. Checking the vac could be kinda hard while driving...

 

[NE_Utah]

I had a truck that did it when I was going up to Snowbird. To fix it, stop going to Snowbird and get a job in the valley like the rest of us



Now the serious part. When mine did it, it was low spark just by a little bit. It had enough to run when I ran the primaries but when the secondaries opened there was not enough spark to ignite the fuel. It looked like a diesel for a second.

It did it when pulling also. anytime I had to ad more fuel it fell on its face. I went with the MSD ignition and went with bigger wires. After that i had problems with a empty tank and bald tires.

 

[waynehartwig]

It was running way rich.... black fouling, pukey..

Keep in mind, this happens when I'm driving and the motor is under a load. Checking the vac could be kinda hard while driving...

Yeah, you'll have to run a long vacuum line and put the gauge inside or ?

When was it running rich? Changing those items might have only band aided the true problem - main jets or etc.

The idle circuit only works at idle and a little off idle, then it relies on the main jets.

Fuel level being too high will cause a rich condition, too. More pressure on the jets and easier for them to pull fuel.

The accelerator pump works all the time when the throttle is moved. So if it's fine while the throttle is stationary, but loads when the throttle is pushed, then it could be out of adjustment.

But if it's running rich while you are driving down the highway at 60, then you have a jet issue.

 

[Shawn]

after doing some reading I think I will try and lean out the secondaries some more and see what happens.