Almost a fire! Will my carb problems never end?!?!?

[Sluggo]

Been driving the Bus around today. No problems until.....

I started her up after a 1/2 hour sit. Had just driven about 15 miles. Bus won't idle for some reason. I give her some gas and hold it for a few seconds and then the idle rests at 2000 RPM. I get out to see if the accelerator cable is stuck or something and all this smoke is coming out of the tail pipe and engine compartment. I shut her off immediately and open the hood. I can hear the gas sizzling in the 3/4 carb. It's way too hot to touch. Some smoke is coming from the Air Cleaner. 1/2 side is fine. CHT shows no abnormally high temps. Pulled the cover off my Webers and even the air cleaner covers are hot as hell. Too hot to touch. The inside of the a/c cover for the 3/4 side is black on the inside. The filter has melted to the base. The inside of the a/c is black! I felt the heads, exhaust, heater boxes & pushrod tubes and they are not too hot. Not even close to as hot as the carbs. I can rest my hand on the exhaust. I jumped the fuel pump for 1/2 a second to see if it's a delivery problem. I can hear the gas sizzle as it hits the carb. I pulled the negative cable from the battery and took the Toyota instead.

What the hell just happened?

[Amskeptic]

What the hell just happened?

Carb fire. If they are out of synch you get backfires, you have experienced them before.Every 1,000th one will be the perfect little spark that catches the carb on fire. Usually the fire goes out because the engine is drawing in fuel and air.
Look around carefully so you can see the extent of the fire. Did it invade breather hoses? Did it get into the fuel evap lines?
Colin

[Sluggo]

What the hell just happened?

Carb fire. If they are out of synch you get backfires, you have experienced them before.Every 1,000th one will be the perfect little spark that catches the carb on fire. Usually the fire goes out because the engine is drawing in fuel and air.
Look around carefully so you can see the extent of the fire. Did it invade breather hoses? Did it get into the fuel evap lines?
Colin

Over at Samba they think it's a stuck valve.

They are in synch (or damn close). It looks like it could have been a fire though. Contained completely in the carbs. I checked the vac hoses to the manifold and they were fine. Breather lines are copper and look to be unharmed. By fuel evap lines do you mean the breathers from the tank? If so, it doesn't seem like it got there. I'll take a look.

[Amskeptic]

What the hell just happened?

Carb fire. If they are out of synch you get backfires, you have experienced them before. Every 1,000th one will be the perfect little spark that catches the carb on fire. Usually the fire goes out because the engine is drawing in fuel and air.
Look around carefully so you can see the extent of the fire. Did it invade breather hoses? Did it get into the fuel evap lines?
Colin

Over at Samba they think it's a stuck valve.

Sticking intake valves will cause backfires, yes, but that begs the question, who did your valve guides? How many miles on the heads at this point?
Colin

[Sluggo]

Over at Samba they think it's a stuck valve.

Sticking intake valves will cause backfires, yes, but that begs the question, who did your valve guides? How many miles on the heads at this point?
Colin

This is the head that was done when I dropped a seat. Guides are new. Just a few hundred miles.

Would I be able to see it with the valve cover off? Just rotate the engine and see which one doesn't move.

[chitwnvw]

Leakdown test would be best. Compression test would probably be enough...

Are fires in the carbs common?

[Sluggo]

Duh. I was thinking of the valve being stuck open. But obviously it would be closed and keeping the gas in the manifold.

I'll do compression test before I remove the carb.

I'm looking at (and seriously considering) a set of 36 IDFs.

[vdubyah73]

If it's a sticky valve the valve would have to be stuck open when the cylinder fires for that to happen. Colin made a great point that I didn't think of Carb sync' however It wouldn't necessarily be the adjustment screws on the carb. It could be a linkage sync' issue. If your linkage is opening one carb ahead of the other because your angles aren't equal on the down rods or your down rods are unequal lengths the carb that is behind will be lean. There is more to sync'ing carbs than just makeing them idle evenly. Do you have a hex bar linkage they are easier to sync than the round bar type. The arms that come off the bar have to be equal. they have to be in such a position that the rods are at as close to straight up and down as you can, and the left and right should be as close to a match as you can as far as the angle that they are at thru the range of motion. Did that make sense? Could be that is what your whole problem has been all along as far as getting it to run rite. Good luck with it. Matbe the carb will be fine just clean it and put it back together.

Bill

[chitwnvw]

Did you hear it backfire? Would a little fire in the carb be enough to cause all that smoke coming out of the exhaust?

[vdubyah73]

Did you hear it backfire? Would a little fire in the carb be enough to cause all that smoke coming out of the exhaust?

Yes it could smoke out the exhaust too. Even if there are no issues with the exhaust valve. You're not gonna get full compression with a sticky valve( which by the way may not show up with a straight edge check because the valve may only be fetching up for a split second and then closing.) The combustion can't happen efficiently with out good compression. thats why he's got a blackend carb the rest of the poorly burnt black exhaust goes out the exhaust when it's supposed to.

Bill

[Sluggo]

Colin has shown me how to balance the carbs twice. First I balanced them static then at 2500 RPM. It's a Hex Bar and the arms are straight.

[vdubyah73]

Man, your having trials and tribulations with your bus.Good luck to you, I hope you figure it out. When frustrated just walk away from it and come back later. Don't give up, you'll figure it out eventually.

Bill

[Sluggo]

Man, your having trials and tribulations with your bus.Good luck to you, I hope you figure it out. When frustrated just walk away from it and come back later. Don't give up, you'll figure it out eventually.

Bill

Except for the dropped seat and oil pressure, all of my problems have been carb related. And only half were mentioned on this or any other site. Bottomend and I are convinced these carbs are cursed and that something else is seriously wrong with them.

[Sluggo]

Tore it down yesterday. I have some pics I'll post later.

Fire was in the #4 barrel. The Air Cleaner Cover was black on the inside. So was the #4 Velocity Stack and carb barrel. This was the valve that was just replaced along with the guide & seat. You can see where the fire got sucked down the #3 stack. No hoses or anything else melted. Just the filter. Checked the valves by removing the valve cover. They all rotate in & out.

I'm waiting for Bottomend to come by with his compression tester. If it turns out I don't have a stuck valve and that it was just my crappy luck to get that 1 in a million pop that turned into a carb fire, can I just clean the carb up and use it till I get another system? Or is it out of commission till then?

[vdubyah73]

If the compression checks out, I'd clean 'em up, check out the float adj., the needle and seat and all O rings. I read in muirs book you can run a quart of diesel or Bardahl in your oil for a few hundred easy miles to free up a sticky valve. I think I'd look for an additive that says it can help sticky valves before the diesel though.

Bill