66GL on fire!

[durableswedish]

I finally got everything back together on the car, was cranking it to prime the fuel system and trying to get the car started. It was cranking and it finally started up but was backfiring pretty bad. I just thought the engine had some crap in it, so I kept cranking and giving it throttle. I saw a drip on the exhaust manifold, but I just thought it was water or a cleaner from me cleaning the engine. I kept cranking it to get it to idle on its own then i see a nice big 1' flame shoot out of the carb. I had 2 thoughts at that moment, "cool, fire!" then "oh F**K! the bottom of the carb is on fire!!!" I ran over to the fuel line on the other side of the engine to yank it so the fire doesn't go down the car to the gas tank then grab the 1 gal bucket of coolant on the ground from when I drained the radiator. After about 8 bucket fulls of water all over the carb the fire went out. Now I have 2 problems:
1. The carb needs to be rebuilt because it was on fire and probably burned all the gaskets.
2. Why is the car shooting flames out of the intake?

Seeing the carb on fire just about gave me a heart attack, I'm still all juiced up on adrenaline from putting the fire out. The whole situation reminds me of when the Kee bird B-29 up in the arctic caught on fire after they got it up and running again.


:grrr:

[spunkymonkey]

Ouch! That's a lucky escape by the sound of it! In relation to your two problems:

1) The carb probably won't have been too badly damaged. It's amazing how much heat gaskets can take - bear in mind they're sandwiched between the metal of the carb which is a very good heatsink. There's an old pub bet that works on a similar idea. Place a banknote on the back of their hand and bet that they can't keep their hand there while you burn a hole in it with a cigarette. Do NOT try it yourself - your hand will blister before the paper even starts to scorch!

The biggest worry on that one is, why was it leaking in the first place?. That's probably going to mean either finding or making a gasket set anyway.

As for flames out of the carb. Assuming you're not running some really OTT tuning mods on it (?) the normal cause comes down to one of the following:

1) Very weak mixture causing it to still be burning when the inlet valve opens, igniting the mixture in the manifold.

2) Firing order wrong. For example, should be 1-3-4-2 but plug leads put on as 1-2-4-3. Will cause some of the plugs to fire at the top of the exhaust stroke rather than compression. The remaining charge ignites, and is still burning when the inlet opens, also igniting the mixture in the manifold.

3) Badly burnt / sticking inlet valves so that burning mixture blows back and ignites in the manifold.

There are other causes but they tend to happen after fairly major work (such as cam timing wrong) so it's likely to be from the above list. Given your description of how it was trying to fire, I'd put money on number 2 - plug leads being in the wrong order. It's an easy mistake to make, especially at the end of a long assembly session when they're similar lengths!

[Bob Scrivens]

I agree with what Joe has suggested, if it is not the timing or plug lead firing order, it might be worth doing a compression check just in case an inlet valve is sticking, has a burnt seat or spring broken, could also be that the valve inlet clearance has closed up? on one cylinder.
It sounds as though it could have been a lot worse!
let us know how you get on.

Bob

[durableswedish]

^ how much did that new carb run you? a rebuild kit looks like it's going to run me $50+ shipping from Germany.

Also, I'm going to check the spark plug wires tomorrow. They were all unplugged and I didn't double check them when I replugged them back in. I have a feeling that there is one plugged backwards. This time, I will be standing by for fire control

[daf44]

hi there.

the first thing i would check are the two simplest.

1. is the timing right. if the dizzy has moved, the spark could just be early enough to ignite the fuel before the valve is shut (backfiring). could be as simple as retiming the car.

2. is the float valve stuck in the carb. this is the most likely cause of fuel dripping from a carb. the float chamber overfills and fuel comes out from the overflow pipe. especially if the carb has been dry for a while andcan often be cured by sharply tapping the carb body with the wooden end of a light hammer.

if the fire was put out quickly then there it should not have caused any problems. Many weekend bikers that I know have had the same problem at some time or another - INCLUDING setting fire to the carbs as the fuel hits a hot exhaust and after putting out the fire and eventually finishing swearing just cary on driving with no further problems.

Good luck and happy (flame free) motoring

paul44