Ok guys/ladies, I have a situation that recently developed. As some of you know I've had my share of motor problems over the past several months. Once I switched to a roller cam, lifters & rockers it solved my problems. Well, some of them anyway. I now have a bogging, backfiring issue. I am running a Q-jet, Ignitor II ignition & stock intake. I've put about 3k miles on the car since the last rebuild and just recently have felt confident enough to get on the car a bit.

First gear, no issues, idle no issuse, second gear and nail the gas, bogs down, backfires and after a few seconds it recovers and takes off like mother! Hit third gear no issues, go to fourth all is well until you get up to the higher revs. Let's say I am on the thruway doing 60mph, everything is great. Now, let's put the pedal to metal as they say, bogs down, backfires etc. and just about stalls.

Also, on ocassion you will smell gas when it does the bog down backfire routine then goes away and all is well. One last detail, tail pipes have a fair amount of black soot inside them. Run your finger around the inside of the pipe and it's all jet black soot type crap.

Can't think of any other symptoms to offer. My next step just for starters I am going to put a new fuel filter and new plugs as I have changed the oil several times since the last rebuild, but not the fuel filter and plugs and I know have almost 3k on the last rebuild.

Any ideas and or suggestions you all may have to offer would be greatly appreciated!

Might want to double check with a timing light , also Make sure you have correct vacum at your advance and its working correctly!

That's why I love this site. Post a question at 1am and get some responses. Love it. Will put the timing light on the car first thing tomorrow and will check the vacuum as well. Thanks for the suggestions...

No problem...Anytime buddy!

Sounds like you are a little rich. You could try backing out your mixture screws on the carb.

He says it idles fine and drives fine at low rpm. The idle mixture screws should not be an issue. It sounds like it occurs when it transfers off idle.

Jets/rods, power piston, accelerator pump, secondary air valve should be isolated and tested.

Does it happen only when you stomp on it, or also when you gradually go to high rpm?

I didn't say 'idle screw'. I said 'mixture screws'. He said that his pipes were black and sooty..... And before he 'digs in' to the carb, I thought external adjusts were in order.

Could be his plugs are getting fouled from having the 'too rich' condition....

My friend Stacy just had that same problem , it really bogged down....his plugs were very fouled up, black from being too rich, changed plugs ,ran fine, then leaned it out...

Like Vikki said, some testing and clarification of the problem is in order. That will point to the solution. At first glance, I'd say it is a fuel delivery issue but the info so far isn't sufficient to rule out the fuel pump or maybe ignition or possibly several circuits in the carb that need addressing.

Backfiring is almost always caused by a lean condition unless there is so much fuel that raw fuel gets into the exhaust and then is ignited when the cylinder refires.

The soot may be caused by excess fuel in another circuit of the carb. Richening up the idle mixture screw adjustment in an attempt to compensate for a bad or nonexistent accelerator pump shot, or richening up the main jets when the fuel pump is at fault are examples of chasing the wrong things to fix the problem.

Have someone follow you (if they can!) while you test each phase of the carb to see if you get black smoke at any time. If you don't have smoke when the problem arises, you are having a lean spot. Either way, figure out what circuit(s) in the carb is/are working when the problem shows up or post the results and we'll all pitch in!

If you need a few ideas on how to test any part of the carb function just ask.

Ok too clarify it does it when you really nail after second gear. If you get up to speed gradually, no problem. I was going to change the plugs & fuel filter just as a start but it is pouring out today. The only other symptom is at the top end of any gear (let's say 4800-5100 rpm) the car does begin to break up almost as if it had a rev limiter type of thing. But I would usually shift well before that high of an RPM anyway so I havn't really worried about that part of it, but I am guessing it is related. I am also running a stock fuel pump as well...

Personally, I would look at the cam and springs. What cam and springs are installed?

You said you have a roller cam? As in? You could have a spring issue. Your symptoms sound alot like mine. Had bad inner valve springs and replaced them all with the correct springs, fixed a vacuum leak and ran like a raped ape.

I'll go into more detailed effects regarding mine later.

What heads, cam, springs, compression..etc. I agree with the fuel matter being rich, but a spring issue and vacuum leak will cause the same symptoms in the upper RPM band.

I will look into the carb, vacuum, timing issues first as I am fairly confident in the cam, springs etc. due to all the previous issues my builder really went all out to ensure the correct cam, springs were all dead nuts.

I am leaning towards a carb set up due to the fact that last spring when I bought my Q-jet from 69firebirdman, all I did was take it out of the shrink wrap, set it on the intake & hook everything up. I never touched a screw or anything as I have no clue what I am doing when it comes to carbs.

I really need to look at my vacuum lines as well as I am using a stock vacuum switch and I can't say for sure that the thing even works...

I have a brand new Performance Years PY68 vacuum switch still in the package if you are looking. I ordered three cause I had some change in the jar. My old one works fine, but like to have a spare or two around. Distributor Vacuum Control Valve, manual only.

Well, mine is new so I think it's most likely fine. I am just saying that I don't even know if the thing is working as it should, not sure if the advance is getting enough vacuum etc. So this is why I am leaning towards this being the problem...

Ok, changed the plugs. To say they were shot would be an understatement. Four of them were blacked out, the other four were clean but somewhat "white", I guess from heat? Anayway, changed them all and the car fired right up and idled great. Took if for a spin and at first seemed fine. Then began to get on it just a little and backfire and running like crap. Even stalled twice but fired right back up.

Tomorrow I will check the timing. Also, I did not smell ANY gas at all this time. I'm begining to wonder if I am getting enough fuel. The vacuum line looks fine, although I have to be sure that it's actually getting enough vacuum as well.

So, 4 fouled plugs(rich), and 4 white plugs(lean). What the...?

Which four were fouled and which 4 were lean? Normal plugs are tannish on the electrode insert.

Could be that his carb is running way too rich on one side and the other is lean or normal. The idle circuit could be fine or not (depending on idle) and the secondaries could be real fat on one side.

Primary circuit feeds both sides fine. On hard acceleration, one side is so fat or gaskets dried where vacuum or a hard part is not seated properly or is missing. If only one side of the secondary is "good" and the other dumping fuel, it would only foul one side of the motor, either even or odd plugs because the intake is divided in half..if stock. Correct?

you might have a problem in side the distributor where the springs inside the distributor underneath the rotor is weak. this could cause the rotor to advance too much when you floor it. try different springs.

The dual plane intake has a divided plenum but I don't recall which cylinders are fed on each side. I'll dig one out and take a look.

Even if the idle circuit is really rich, the plugs should clear up with normal driving and be clean when pulled immediately after.

Yes, if you know which plugs were black, and oily or carbon, and which were lean/white, it would help.

Distributor could be a contributor to performance issues, but not to differences in plug color.

You know, I beleive it was every other plug. I know for a fact the the two front plugs were the black/oily & worst if that tells you anything. If I were to go out and take the car for a ride right now it would start with NO problem, idle perfectly and would drive/run great if I were too just drive around very casual.

Then, if I were too take off from a light and hit it fairly hard (not crazy) it would get through first no problem, soon as you hit second and give her the pedal, it would bog, put & backfire and run like total crap. Then back off, let the car "recover" and give it some gas nice and easy, back to running fine...

Oily is not good. How many miles are on your new engine?

Black, dry, dusty = carbon
Black, shiny = oil, or raw fuel on carbon (smell)

I would do a compression and leakdown..

I had one plug with a bit of oil on it, passenger side front.

Almost 3k miles on it for this last build...

I may be nuts but this does sound like a fuel delivery problem... Plain and simple. One cause could be that your float is set a little low.

I was wondering about the floats. Again I have not done a thing with this carb since I bought it. I opened it up and bolted it down and hooked everything up and that was it.

I figured that the floats should have been adjusted etc. I've never done them so I wasn't sure exactly how to go about it.

Someone that I spoke with last night at Old Town cruise night mentioned that I could use a fuel pump for a 455? Supposedly it has a cansister and hold some fuel? Would it work with my stock setup (fuel line) etc.?

You'd have to make changes to the lines. The Carter has a bigger body than the AC, and the ports don't line up the same.

It could be one of many possibilities, or a combination of issues. You've done the first, to swap the plugs. Next check the firing order. They run surprisingly well with a few wires swapped. Then timing at idle, and at part throttle, and at 3/4 throttle (you'll need an adjustable timing light).

If all checks out on the ignition side, isolate carb functions. Make sure you don't have a vacuum leak (hollow stud uncapped, loose base nuts, bad vacuum line, etc.) Use a vacuum gauge. You should get 15" or more at idle. If not, find the leak. The idle speed screw should be in just a small amount, if it's open too far to compensate for a vacuum leak or late timing you'll get the stumble.

Step by step. Keep notes of what you find, what one item you test, and what the results were.

Sounds like the main problem is a major bog with backfiring after a few (or more) seconds at full throttle. That points to the fuel pump like I mentioned on the first page of the thread, especially with the description that was quoted by Jim (thanks, Jim!).

Having it happen at the top of each gear could be a fuel pump that is at its limits for your combo. I'd start the testing with a fuel pressure gauge hooked into your fuel line to the carb.

The stock intake (dual plane) has two plenums and each feeds the outside two plugs on one bank of the engine and the inside two on the other bank. If you can remember which ones were where like Vikki said or check the new ones for colour, you may be able to isolate which side of the carb may be dumping fuel like Tom said. Could be a pump problem and a carb problem at the same time.

Just a note, with leaded fuel a tan colour on the plug is about right but with unleaded you have to look down inside near the base of the centre electrode to see the slight tan residue. The main part of the electrode will appear white.

Ok, went out this morning and looked at the old plugs. Amazingly I put them in order of how I took them out. It was the four corners (so to speak) that were the very black plugs and the center four that were more of a white (clean) look.

Can you post pics of your clean and fouled plugs?

You're welcome. Someone needed to bring to discussion back down to Earth. It was obvious to me that he was 'running out of gas'. Which could easily be a low float. But this would depend on how the problem 'presented' itself. Which I haven't heard yet. Did this problem come up all of a sudden or did it manifest over time? Or was it something that came up when you pushed the engine a little harder than usual?

Good question on "when" this happened. Ok, after this last rebuild I was very leary as you can imagine after wiping out so many cams. Given that, it was quite some time before I dared to goose the ole girl. I would say that after putting around town with the car for the first 1k miles I began to feel a bit more confident so I slowly began to push her more and more. At about 2k I felt pretty good. This was around Thanksgiving and we weredriving back and forth every day at least once a day from our house to Daytona Speedway. It was during those trips that I really began to push the car up towards the top end (5k).

The car would run PERFECT up until I would get it up around 4500rpm and higher, it would begin to break up much like a rev limiter. I thought maybe the Pertronix unit had one built in, but later found that not too be true.

Howeve, even though it would "break up" it never backfired and never stalled. Now it seems this problem is happening more often at lower rpms but only when you go to give it a quick slam of the gas pedal. That's when she bogs, spits, sputters and backfires like a mother, then if you back off and let it "catch up" so to speak then it's fine.

Again, the car starts, idles and through first gear all is perfect. It's when you hit second gear all goes down hill if you are really getting on her.

So all in all it's kinda hard to answer the original question about when this all started based on the fact that I baby the crap out this car for the first 2k miles.

Hope this helps a bit more and yes I will post pics of the plugs as well...

It helped a lot. I think your next step should be to isolate your fuel delivery problem. See if you can tell if it's delivery to the carb or low float. I would go back over what you have done in terms of your fuel delivery. Has the tank been flushed? Are all the fuel lines new? What components have been replaced? Is this a car that had all new parts installed as far as tank, lines, pump ect?

Original tank (cleaned and flushed 3 winters ago), new sending unit (works perfectly), original fuel line (one line), NO leaks anywhere, stock fuel pump (brand new as of last rebuild), stock Q-jet.

My next step will be to replace the fuel filter (I figure start with the easy stuff first). Then I will check the floats. Think I may need a book on Q-jet carbs as I have no clue how to check these things.

The fuel filter is the best bet first. There is just one float in a quadrajet. The manual will provide the adjustment measurement. If you aren't really familiar with carbs then you might want to get a gauge in the fuel line to make sure you have sufficient fuel to the carb before you tear into it. Believe it or not, this could also be as simple as bad gas....

In dyno testing I have found that a Pertronix does act like a rev limiter, reducing power noticabley in the upper rpm. This is usually around 5500 rpm but yours may be coming in early. More on that part later.

It sounds to me like you have two separate problems, the first being a bog/backfiring issue at lower/medium rpm (right at the shift recovery rpm into second gear or about 3500 rpm) and the second, the engine breaking up above 4800 rpm without backfiring. Is this right? Or can you tell at this point?

Okay, try this test: with the car in second gear bring the engine rpm to 2500 rpm and let it stabilize for a couple seconds then press the pedal down at a medium rate. Do this several times, increasing the speed that you get the pedal to the floor until you are essentially stomping on it. Does this result in the bog/backfiring that you're talking about? Does it get worse if the engine rpm is lower? Do you feel that the engine bogs as soon as the pedal moves or could you feel it more once the pedal is past halfway to the floor? This is testing how well the carb is handling the transition from light load to heavy load at different transition rates.

The second part that may be confusing the issue is the breaking up at higher rpm. To test this, start your testing at 4000 rpm in second gear, again letting it stabilize for a few seconds then getting on it. Concentrate on what is happening at the 4800-5100 rpm that you mentioned before. If the engine is still breaking up at the same rpm each time with no backfiring, then it is very likely that it is an ignition problem, possibly because of the Pertronix. If it doesn't break up, lower the starting rpm and try it again, repeat until you are starting below about 2300-2400 rpm. If you have the appropriate roads do this test in third gear. Watch your engine temp during the test and if it starts cutting out earlier (bog) than it did when starting at 4000 rpm, get out of the throttle, you're running very lean! This is testing how well the fuel system is working to keep the carb supplied with fuel, and also whether the ignition system is limiting your upper rpm. As I said earlier, a fuel pressure gauge in your line to the carb will also show whether the fuel system is keeping pressure to the carb during this kind of test. If you have it, bring a friend so they can watch the gauge while you drive.

The essence of good testing is to be able to repeatedly make the car have the problem with the least amount of other things happening at the same time. For instance, if you can make the car bog without having to rip through first and hit the gear change into second, that can eliminate several other possibilities for the problem. Make careful notes as to the results of the tests, it's very easy to get things confused after the tests!

It should only take about ten minutes to do these tests and you'll have fun at the same time! If anything is unclear just ask!