Carb Or Ignition Problems??

sparks · #1 (**permalink**) 02-20-2003, 08:01 PM

Took my cobra out today here in chicago...about 50 degrees today. Car ran great for about 50 mi. or so. Some stop and go and some hwy. And a couple of burnouts, fish tails etc. While getting on the hwy.(a long right hand sweeper) just after the sweeper rpm about 5k the car started to sputter(thought i mite of hit rev limiter) Let off gas and slowed down then a.o.k.. Got off hwy and hit a couple of lights. While cruisin at 40 mph? went to accelerate and nothing. Car seemed to die. Coasted to shoulder then car started going again. Drove down about 1/2 mile, car quit again. When I let off the gas, heard popping sound out of exhaust. Pulled over again. Let car idle for a minute and was a.o.k. After getting home, called Eric at Performance Engineering and he told me to inspect the float levels (he said sometimes the floats will stick and either under- or over-fuel the motor). He said it could be a temporary problem and would most likely fix itself. He also pointed out the coil pick up in the distributor ? From your experiences, would you think this would be carb or ignition related? Carb is a demon 850,msd ign.,w/a 460 boat anchor. Should I wait and see or just relace coil pickup or just drive around area to see if it happens again.

KobraKarl · #2 (**permalink**) 02-20-2003, 08:22 PM

My money is on your carb,sound like fuel starvation, and modern ignition is usually either on or off. course it never hurts to pop the bonnet and look around for a loose wire or???????????/

Rick Parker · #3 (**permalink**) 02-20-2003, 08:29 PM

Usually if the primary side of the ignition is faltering the tachometer will fluctuate as the sytem intermitantly breaks the circuit, causing it to fluctuate. It will also have instant power as the ignition cuts in and out. If it is fuel related the response will be more "flat" like running out of gas.

Good luck.

Rick

George Snyder · #4 (**permalink**) 02-20-2003, 08:37 PM

Sparks,
I had almost the same thing happen to My Car the 1st time out.
Ended up it was the Holley Fuel Pump was assembled wrong. Pressure by-pass.

If it is the floats, it is easy to see fuel level thru site glasses. The gas should be close to the middle in the glasses.

If the are too high the fuel will be dumping into the engine at idle. If too low the engine will die at higher RPMS, but will recover after you let off the gas and the fuel bowps have time to recover.

I can not really comment on if it could be the coil pick-up.

Just a thought! I would guess fuel. Pump or floats.

George

sparks · #5 (**permalink**) 02-20-2003, 09:25 PM

Checked site -glasses and level was just less than 1/2 full. Do u think this kinda problem could correct self? Put in fresh gas yesterday,100 octane (10gal)and 93oct(5gal). Come to think it did have that no gas sound,but would that cause poping on decel.Also what would be the most comon cause of low fuel level in carb?

fw209 · #6 (**permalink**) 02-20-2003, 09:58 PM

I would say you have a float problem. How long did it sit? If it has been sitting all through our cold spell or longer here in Chicago without running odds are it's the floats. Do you start her up and let her run a while during the winter? If not you should. just another opinion... Good Luck

sparks · #7 (**permalink**) 02-20-2003, 10:01 PM

Just got car about 1 1/2 mo. ago . New motor, hasnt sat much w/o running yet.

Excaliber · #8 (**permalink**) 02-20-2003, 10:12 PM

Popping is generaly associated with a rixh mixture. BUT, that puts you back to square one. Rich mixture can be caused by a weak spark, Oh no! Fuel or spark is ALWAYS the first question to ask, and is not always easy to nail down.

Myself, being very mechanically inclined, would look at my ignition system first, just to rule it out if nothing else. Carb diagnosis is tough, eliminate other possibilities as you proceed. You got "points" or electronic ignition? If points, the capacitor is suspect, replace it, a "weak" one will give these symptoms. While your in there make sure the points are "gapped" properly.

Check the underside of the "rotor bug" (electronic or points) and look for indication of "burn through" where it might be shorting to the metal by "burning" through the plastic.

If electronic make sure you got GOOD volts at the dist. and coil, use your digital volt meter. If you don't have one, buy one! This is THE most important diagnostic tool you can own! Check the coil wire for signs of burn through. If all looks good, proceed to "fuel diagnosis".

Indeed, the floats may be OK for now, and just waiting for your "next cruise". Fuel filter, pump, hoses are also part of this picture to look at.

Ernie

decooney · #9 (**permalink**) 02-20-2003, 11:26 PM

Sparks,

in addition to resolving any float or sticky needle/seat issues first...

experienced the exact same situation with a friends newly built car last year. It would run, stop, start right back up... go for an hour... then stop again for no reason. Turn the key two times, and it would start. No consistency. We tore the carb apart, played with the floats, and it seemed like it was flooding. Had to be fuel, right? We were sure it was the carb, until running out of choices.

The Result:
a bad pickup coil in the brand new MSD distributor. Ordered a new one from Summit for $17. Cured, no problems since. Its an easy check. Check for recommended resistance across the two wires in the plug - per you mfg specs if you are running this type of distributor / pickup setup.

Excaliber · #10 (**permalink**) 02-21-2003, 12:29 AM

Sparks,,,,,yup,,,,I been there! LOL

Ernie

Bob Putnam · #11 (**permalink**) 02-21-2003, 04:52 AM

Possible if it was a humid day: Carburetor icing

Excaliber · #12 (**permalink**) 02-21-2003, 06:51 AM

Eewwwwww,,,,,,carb icing, good call! I haven't seen that since I moved to Hawaii, lol. But it DID happen to me once in Michigan, in another life, long long ago........

The intake manifold heat crossover for the carb had been blocked off. Icing was a problem even on a "relatively" warm day!

Ernie

Cal Metal · #13 (**permalink**) 02-21-2003, 07:47 AM

Check your fuel filter

flipper35 · #14 (**permalink**) 02-21-2003, 11:45 AM

The popping can also be caused by a lean condition where there isn't enough fuel to burn and it builds up until it lights off.

Steve Kirkham · #15 (**permalink**) 02-21-2003, 12:24 PM

I would check for carburetor icing. This has happened in exactly those conditions.

Air outside is close to freezing. When the gasoline vaporizes, the air cools tremendously. Moisture in the air and gas freezes on your venturies, in effect 'choking' the carb, same way a choke valve does.

Then you sit, the carb heat soaks, the ice melts, and all is good.

Check: next time it dies, quickly pull the air cleaner and look for ice in the air intakes.

sparks · #16 (**permalink**) 02-21-2003, 03:33 PM

Talked to Eric at Perf. engineering today and he instructed me to raise bowl level. Seemed to make it alittle better, but still happened when driving hard. Took out rev. limiter, my idea but still happened. Leaning towards fuel pump and or filter. After today(55 deg.) its supposed to get cold again plus the neighboors are getting ready to call cops so things will be postponed for a few wks......This 460 that Eric built pulls like a frieght train on nos. ... Thanks for help guys......

SPARKS

decooney · #17 (**permalink**) 02-21-2003, 04:57 PM

Sparks,

here at work and saw your comment about the "neighbors getting ready to call the Cops"... Hilarious! Man, it took me a few minutes to stop chuckling when I read this.

I was in the garage last weekend too late doing some carb/timing adjustments for full-advance; and was thinking it just about happened to me. Between custom Harley's, 2-stroke Shifter Karts, and Cobras over the last few years, I think my gentle neighbors were just about ready to have us shot or impounded. Layin low now... respectfully.

aumoore · #18 (**permalink**) 02-21-2003, 09:05 PM

I will step out on a limb and make a few suggestions

1. Is your Fuel tank vented properly? If not it can cause a vaccume that will overpower the fuel pump.
2. If you have a electric fuel pump it could be mounted too high. Most electric pumps need to be mounted so the pump housing is at or very near the bottom of the fuel tank.
3. Could there be any silicone in the fuel tank that was used for sealing? I sealed the top plat e of my aluminum tank with RTV blue which allowed some to get into the tank. This stuff turns into an automotive version of the blob and will stop up the fuel line. This will cause the fuel pressure to be very erratic or none at all.
4. There are electronic gizmos in the new distributors that can kind of short out when they get hot, or when you are trying to impress your friends with a smokey burnout. My son has a Mazda and his car would run find and then the engine would just die. Took it to a local import doctor and he said right away it was probably the distributor as that is common on Mazda's and Hondas. He was right and I was almost $400 poorer after the surgery.

Mike I · #19 (**permalink**) 02-22-2003, 09:42 AM

Sparks,
Statistically, more than 75% of driveability problems (stalling, backfiring, etc..) are caused by faulty electronics, not fuel. Make sure your ignition system is working properly before looking at fuel solutions. When I switched over to Weber induction last Spring, I also switched to MSD 6AL ignition at the same time, including a brand new set of Accel wires. After a few weeks of driving the car with no problems, the engine began to misfire severely as though it was starving for fuel. It turned out to be the Accel wires which were breaking down under the hotter spark from the 6AL. I could actually see the wires arcing at night. Good luck.

~Mike

sparks · #20 (**permalink**) 02-22-2003, 03:38 PM

Aumoore, Fuel pump is mounted under tank, As far as venting ? when I open gas cap to put gas in I hear a sound like the tank itself is full of pressure(escaping presure?) The temp was about 50 outside and fans did not even kick in yet.
Mike I,
Have the msd ign. with taylor wires. Everthing is routed cleanly. Only backfired on deceration 1 or 2 times. Raised float levels a bit and it helped alittle. Even took rev. limiter out but still happened. Raised bowls to much so I now have oil that smells like gas. Should prob. change oil before I take it out again. Eric at per. Eng. will prob. senb me out a pump and filter and maybe some plugs.(hint hint if your seeing this Eric) Thanks again for advice, Been helpful........................................
SPARKS