Fire in the carb air intake

[joshuapfitzpatrick]

1976
Just bought the bike. Charged the battery, fixed the carb caps and tried to fire it up. Well it took that too literally and it FIRED UP on top of the carburetors. I put it out quite quickly since I had everything open already. There was no air filter on there just because I was only going to run it for 20-30 seconds. The fuel pump diaphragm is also bad and throwing fuel all over the damn place. That is going to get replaced this weekend.
So the question is:
What would cause the air intake to catch on fire? Do I need to rebuild the carburetors?

[seabee_]

When was the last time they were rebuilt?

[joshuapfitzpatrick]

Since I just bought the motorcycle its hard to tell. I'd say its been a while based soley on the outside dirt buildup.

[virgilmobile]

FIRE.....
Don't blame the carbs.....They deliver fuel mixture to the engine....The engine and timing determine when it's time to ignite the fuel.
Possible causes that really should be triple checked before you crank it again.
This will take a couple of hours..
1st...Remove the timing belt covers....The cam timing MUST be perfect and the belt tension just right.
The "Hot-To Articles" goes over this.
2nd....Get the ignition timing done exactly right.It's the "split the difference" method.
I can't stress this enough..You gotta get it exact.
3rd...Pull the valve covers off and set the valve clearance.This is done with a cold engine.

Do these things in this order and as long as the valves aren't burt or bent and the compression is OK the bike will run fine.
Don't forget to sync the carbs .

[scotterichmond]

FIRE.....
Don't blame the carbs.....They deliver fuel mixture to the engine....The engine and timing determine when it's time to ignite the fuel.
Possible causes that really should be triple checked before you crank it again.
This will take a couple of hours..
1st...Remove the timing belt covers....The cam timing MUST be perfect and the belt tension just right.
The "Hot-To Articles" goes over this.
2nd....Get the ignition timing done exactly right.It's the "split the difference" method.
I can't stress this enough..You gotta get it exact.
3rd...Pull the valve covers off and set the valve clearance.This is done with a cold engine.

Do these things in this order and as long as the valves aren't burt or bent and the compression is OK the bike will run fine.
Don't forget to sync the carbs .

What he said exactaly dead on, if you need the how to "split time" I can send it to you .

[thrasherg]

Also check that you have the correct coil lead connected to the correct spark plug as that can cause back firing and flames in the air box.. Don't ask me how I know this!! My eyebrows did grow back!!

Gary

[joshuapfitzpatrick]

Yes please send me a link on "split-time". I'm kind of new to working on motorcycles so any help is much appreciated! I am going to follow all of these steps this weekend with the addition of a fire extinguisher. I found a great how-to on cam timing but I'm still questionable on the rest.

[Fred Camper]

Here is the split timing technique courtesy of Randall Washington's Tech Tip #7

http://www.randakks.com/TechTip7.htm