Hi all

Hey, I went to the track yesterday and had a couple wierd things happen. Hopefully you guys can give me some insight.

I went to GLD yesterday, and I got two runs. Weather was hot as hades and humid to boot

First run car ran pretty well despite the heat. I clocked 13.4 at 104 mph. Yet, at the end of the run as I let off it seemed to backfire more then usual. I run open exhaust at the track and it does this from time to time.

First question:
What causes it to backfire like that?


Ok second run I tried to adjust my launch by getting out of the hole at 2500, this did not work as well. I ended up redlighting . Now despite the redlight car seemed to run ok, i shifted slightly higher then usual to try. 1st shift 5800, second shift 5800 , but when i shifted into third it started off llike a hitch all the way up too 5000 rpms, where it just fell flat! It wouldn't go beyond it! I typically shift this car St 5600 or so. Anyway run finishes up and again more backfire! Worst run I've had in the coronet in years.

Ok second question: Why do you think it just seemed to run out of gas at 5000 rpms like that?

Info on car 440 9:1 stealth heads, 274xe comp cam, 770 Holley avenger carb, street dominator intake Hedmam shorty headers. 727 with 3:91 gears. I run msg digital 6 with msg distributor 4000 lb with me in car.


Any idea guys?

I hope that give some info to help with this question, thanks racing guru's

Mike

Is it back firing through the exhaust or intake...
question 2... you could be running out of fuel, maybe
a low float level... also it could be boiling the
fuel on these HOT days

Mike

Thanks for the help! I believe thru the exhaust, it only seems to happen when I uncork the headers, but let's say for argument it is exhaust side.

Mike

And..... on the chance I hear it wrong and the backfire is thru the intake?

I've just had some bad luck this year , so just a tad paranoid

Mike

Ok that makes sense, would too much timing cause it to pop thru the intake? Now, that you mention it I did run it at 36 all in by 3000, and it did have a half second struggle to start.

Mike

No vacuum advance i take it??

I wou;ld bet that the popping is too fat. It is possible that when you reved higher either you had a little valve float or it was running out of gas. Are you running a stock pump with 5/16 stock fuel line? LOL

Well it is a good question the pump is the bigger pump, but I can't verify the lines all the way back are NOT 5/16" perhaps I should check it out. car ran well up to 5800 in first and second gear, so me thinks not valve float , but running out of gas at top of third quite possible

You really need a guage mounted on the cowl so you can see what the fuel presuure is running down the track.

Gosh, that I guess is an option, but man I'm not sure I want to go that far with this car, it is mostly a street car.

Thanks for the help too guys.

Mike

All engines use more fuel in high gear at WOT than they do in either 1st or 2nd gear due to gear multplication in the lower gears, the motor accelerates quicker using less fuel If it is going to run out of fuel it will usually do it in the last half of the track, around 900 ft and beyond

Cab

Well it does make sense, except I'm a little bit down. I thought I fixed this issue last year, bigger mechanical fuel pump. I got the big carter one on it and I guess the only thing would be to look at that fuel lines. I can't verify that they are not 5/16, but I doubt it, at least 3/8's on it.

mike

If it is going flat at the big end it is most likely running out of fuel with the looks of that fuel system. I would add atleast a small elect fuel pump back by the tank . We install alot of the small carters with a micro switch on the secondaties so that when they kick on so does the pump. That way you do not have to remember to turn on or off the pump. Now on the back firing on decell it sounds like you have a header leak and that will back fire in decell. Jake

The only time it backfires like this is when I'm on it at the track with the headers fully opened. I've done a few closed header spirited runs on a country road by our house

I like the small electric fuel pump idea, the question I have is what size of fuel lines are people running in their cars? I mean should I be upgrading to 1/2 in or bigger?

Mike

You could get away with the stock 5/16 if you put the pump on. 3/8 is not a bad idea. 1/2 is way over kill. Ron Mancini went 8.98@155 with 5/16 fuel iline and 2 carter pumps. Everyone told him he would go faster with a better fuel system. So he goes and spends $1200. on a complete fuel system and never went any faster. Now back to your back fire I still say it is a header leak. You would not hear the back fire with closed exaust.

Jake

That is a good point about the exhaust I never thought about it. I'll look at the headers. I might be spoiled, but since I've run copper gaskets I haven't had a leak since high school, might be my luck ran out.

How difficult is it to set up this electric pump?

Recommendations of what you would use?
Mike

Piece of cake. Buy a no2 switch that mounts on carb. Use that to control the ground for the pump. Run a fused 12v to pump and your done. Now everytime you nail it it will come on and when cruising its off. No need to remember after the fact to turn on pump or remember to turn it back off when done. ready to go 24-7 Jake Oh finished reading your post. I think the mechanical pump is fine for the driving around etc. I put on the carter pump that is 6lb. and does not require a regulator. It worked in my car that could go 11.40's in street trim .

As always you folks are very helpful!

Mike

do you have any header extensions? how long?
Without any ext i belive there will be some backfire.
If the backfire has gotten worse its either an exhaust leak or the carb has gone fat when coasting in some way.
One reason could be butterflies opened too far.

If you have the stock fuel pick up in the tank you might want to test it to see if it is plugged up with gunk You can hook a flexable fuel hose to the steel line at the pump and blow back into it, if you have to blow really hard to put air into the tank it may be plugged I've seen that more than once, hard gunk gets into the stock pickup in the tank and sometimes in the line between the tank and the front of the car If your car is a early 1960s to mid 1970s and a non Hemi or 440 car it will a have 5/16 O.D.(1/4 inch I.D. ) line stock, even the Max Wedge cars did My 1963 Max Wedge stocker had the 5/16 lines, I added a Holley Blue pump into the line at the rear of the car, I decided to bypass it at a division points race in Las Vegas one year as I had a alternator on the car that was stripped out and not charging, the car ran faster with that pump disconnected I was running a MSD 7 race box and coil I was using the old Carter NASCAR race hemi mechanical fuel pump, the one that has three valves inside instead of two like the other Carter mechanical race pumps had I used that pump per instructions from Mike and Dick Landy That car low elevens with that mechanical pump only after that BTW, I had added another 3/8 pick up in the tank and used a Moroso Y fitting to feed both lines from the tank to the stock steel fuel line going to the front of the car