Major Backfire!

SDPintheLBC · Post by **SDPintheLBC** » Sat Oct 28, 2006 6:51 pm

I've put my pinz away for 6 months because of a problem I had. I went to start it while in a parking lot and it cranked and cranked then a HUGE backfire and major flames ahot out the exhaust.

I mean this was LOUD. So I went home to get my truck to tow it - I wanted to check to see if it would start, tried and it started right up.

: I drove it home. Later that day I drove it about a mile and it started to act up - hesitating, couldn't put the accelerator down without it stalling. Then it just stopped.

I got my truck and tried to pull-start it and nothing, just hesitation, backfireing and stalling.

This also happened when I first got it, then it just went away - like I threw a switch and everything was fine!

The only thing I've done is electronic ignition and set the float level and it's run perfect until now.

Can anybody help?

Thank you.

Jim LaGuardia · Post by **Jim LaGuardia** » Sat Oct 28, 2006 8:45 pm

See if the distributor came loose and is popping up resulting in timing 180deg off

Have found this on a few trucks

SDPintheLBC · Post by **SDPintheLBC** » Sat Oct 28, 2006 9:22 pm

OK - just charged the batteries - as soon as the carbs filled she started right up - drove it around a few miles - got some fresh gas - still running great - starts at just a touch of the button.

I want to drive it to the Wing, Wheels & Rotor Expo at Los Al tomorrow, but I'm afraid that it'll act up again and I'll be stranded and embarrased......again. Last time the police came because the backfire was so loud - everybody came out of the stores and stared at me - really embarrasing.

Jim - Thanks for the reply. I checked the distributor and all is good - nice and tight.

I'm really confused - lots of gas smell when it's happening, definitely flooded - Is it possible that the float valve can stick open?

Floats can't be sunk because it's intermittant.

Thanks again.

M Wehrman · Post by **M Wehrman** » Sun Oct 29, 2006 12:17 am

I would be inclined to suspect the ignition switch,I've had an issue in the past with crank and no start. I turned the key off and on a few times and all was good. The same proceedure works for a intermittent t-signal, just run the lever up and down a bunch of times. If you are old enough to remember the old TV's, they would get crappy and you had to crank the tuner knob a bunch of times to clean the contacts and get a good picture. Possibly the same issue as the Pinz was designed during that era. For you young'ns we actually had to get up to adjust our TV's

, as there were no remotes. Man those were the days!

TTFN , Mark

SDPintheLBC · Post by **SDPintheLBC** » Sun Oct 29, 2006 12:24 pm

Thanks Mark. I have had issues with the ignition and fixed them, but it still did it after. Also, when it's doing it, it does run, just real bad and I can't even touch the pedal or it stalls. If it was the ignition, would it still run?

Anyway, got in it this morning and fired right up, no problem. This is frustruating me - I really don't wan't to get stranded with my whole family.

By the way, I do remember the TV's - I also have some old amplifiers in my bar that I have to do that to once in a while - I'm going to try it in the Pinz and take my chances.

Thanks again.

hrafn · Post by **hrafn** » Sun Oct 29, 2006 4:25 pm

Something similar happened to me this weekend. We took a 150 mile trip to
West Virginia. Three hours of driving in very hard rain. The truck ran great.
We stopped for an hour after the rain quit. When we were ready to go
again, the truck was hard to start and was missing very badly, backfiring,
and any attempt to give it gas would result in it stalling. I pulled the
distributor cap off and it has some condensation inside. I dried out the cap
as best I could and we got underway again but the truck was running very
poorly. We managed to limp into the nearest town and there it died
completely. I tried to get it running again to no avail and to make a long
story short, I had the truck trailered home. Glad I had AAA.

Once home, I replaced the distributor cap and rotor and it fired right up and
ran perfectly. My theory is that any amount of moisture in the distributor cap
will cause arcing to the other plug wires causing the missing and backfiring.
Both the stock coil and the coil sold with Scott's civilian conversion develop
enough voltage to kill an elephant, and I can easily see how arcing
to an adjacent terminal could happen.

The design of the distibutor, with the vacuum that sucks out (or in)
moisture has been previously discussed. Moral of the story is to always
carry a spare distributor cap and some WD-40

SDPintheLBC · Post by **SDPintheLBC** » Sun Oct 29, 2006 6:58 pm

That's interesting, Jay. I'll definitely check that out next time it does it. It'll be nice if that's the problem.

Thanks.

Charles · Post by **Charles** » Mon Oct 30, 2006 3:52 pm

Hey There,
I know you said you checked this, but maybe you want to check your float level / needle valve again... Sometimes if you're dribbling raw fuel into the cylinders, you can get this exact symptom on startup.
Also, when you got that "bang" did you notice a backfire in the carbs (a big "pop" under the doghouse lid) at the same time. If so, maybe check the carb float again.

hrafn · Post by **hrafn** » Mon Oct 30, 2006 5:18 pm

I had a few more thoughts on the subject. As long as the truck is running the
engine heat probably keeps the moisture in a gaseous state, but once the
engine is stopped, and the distributor cools, any moisture in the distributor
will condense on the coolest part (the top of the cap). This is exactly what I
observed.

Since both the stock coil and the Pertronix coil are very high voltage (I have
observed a 3/4" spark !!!), any moisture in the cap will short out adjacent
terminals and cause very rough running, backfiring, and stalling.

Seems to me that the distributor should be slightly pressurized with dry air
rather than using vacuum that just sucks in moist air. I'm not quite sure how
that could be accomplished, though.

Anthony · Post by **Anthony** » Tue Oct 31, 2006 3:53 am

hrafn,

I guess you could have a line running to a breather hole on the distributor with a filter at the end and a small container with Silicone crystals in it, this would dehumidify the air as it is sucked in. Every now and then dry out the crystals or replace them.

Of course this could be mounted high to enable immersion without ill effects.

russ · Post by **russ** » Tue Oct 31, 2006 10:00 pm

Mine used to backfire a bit, well a lot... Biggest problem was that it blew up the old muffler. Had it rewelded but finally replaced it with something that hugged the body a bit more to avoid rock damage.

Mine had a few ignition problems. Fixed all of them but the last was related to the vacuum line. I would wind up with condensation in the cap after a good run followed by storage. Wouldn't run well and backfired. Cleared it out by unclogging the vacuum line. No problems since.

SDPintheLBC · Post by **SDPintheLBC** » Wed Nov 08, 2006 8:23 pm

Thanks alot for the tips. I don't think it's backfireing through the carb, just the exhaust - big flames too! So it must be flooding.

It seems to do it when sitting for 10min - 3 hours. If I turn it off it starts right back up. If it sits a little bit, won't start. If it sits a few hours or overnight, it starts.

Thanks.

milesdzyn · Post by **milesdzyn** » Thu Nov 09, 2006 1:33 am

Mark...Have you checked the exhaust valve clearances. If there is a gap the compression stroke will force air fuel mixture thru the exhaust and create a back fire. Could also be some debris at the exhaust valves. A compression test should reveal the problem, backed up with a leak down test with the cylinder at top dead center with both valves in the closed position. It just so happens that Harbor Freight has a leak down tester for sale $39.99 this month.

Miles