Backfire Under Acceleration

I'm trying to troubleshoot a problem with backfires under acceleration/throttle increase. What typically causes this? I think the bangs are coming out of the intake rather than the exhaust, but I'm not positive.

On a possibly related note, I have been trying to get good fuel delivery after the motorcycle sat for 8 years or so. Has anyone tried the Kreem product that Z1 Enterprises sells? Is there a better solution? My problem right now is a lot of rusty sediment that is coming out of the tank even after trying to rinse it out. Here's a link to the product I'm refering to: www.z1enterprises.com/detail.aspx?ID=435

so you're saying you used the Kreem to strip and reseal your tank? I've used it and had good results, but I also got a new petcock just for good measure. I also cleaned my carbs plenty once the switch was done.
I am not sure about your backfire problem... could it be carb jets? Have you done any other mods to the bike?

DoubleDub wrote:

I'm trying to troubleshoot a problem with backfires under acceleration/throttle increase.

I'd check timing and the timing advancer first.

Thanks - it was a two part question.

1.) What generally speaking causes backfire under increased throttle (I don't even make it to WOT).

2.) Has anyone tried the Kreem - I think I need to rinse and reseal my tank.

I'll start there! Thanks!

I don't know much. Nothing at all in fact about kreem.

About the backfires, only experience I have to pull from is my 650. It sat out in the yard for a few years. When I decided to start riding it would back fire, incredibly loud, when I would take off. I don't know if it was while increasing throttle or at the point of letting off. To resolve I had to clean my carbs and put in all new rubber parts.

SO you might have the same thing going on since 1 your bike sat for eight years, and 2 your tank is putting yucky stuff into your carbs.

SOrry I can't be all technical and tell you the magic bullet answer.

Best wishes.

Backfiring out the intake suggests one of two things - or both

1) Lean AFR - Not enough fuel. It could be wrong jetting, dirty clogged jets, or a bad vacuum leak. If it was running fine before you let it sit for a long time then there's a good chance you have clogged jets. Also sounds like you might be getting rust from the tank in your carbs or possibly restricted fuel flow from the tank due to rust in the petcock screen (if there is one) Definitely worth removing the fuel line from the tank and switching the petcock valve to PRI (PRIME) and see if fuel flows freely. If fuel just trickles out of the tank, you'll have problems under acceleration though the bike might idle fine.

2) retarded ignintion timing will also produce backfiring out the intake.

DoubleDub wrote:

...What generally speaking causes backfire under increased throttle (I don't even make it to WOT)....

If not already done, would check valve clearances, especially intake valve clearances.

Insufficient clearance might be preventing complete closure of the intake valve against its seat, thereby allowing leakage through the valve seat during combustion. When this happens, some of the combustion may get past the leaking seat of the supposedly closed intake valve and go back through the carb (backfire).

As to restoring the fuel tank interior to pristine condition, could do a search on this site for numerous excellent methods and detailed instructions for various techniques such as BB's in dryer, electrolysis, acid, etc.

Am not a fan of Kreem or any other coating inside the fuel tank, unless needed to prevent leaks through pin-holes or seams. If applied strictly according to directions, Kreem will perform well for many years. Failed Kreem may be removed with acetone.

Good Luck!

DoubleDub wrote:

Thanks - it was a two part question.

1.) What generally speaking causes backfire under increased throttle (I don't even make it to WOT).

2.) Has anyone tried the Kreem - I think I need to rinse and reseal my tank.

I'll start there! Thanks!

like Patton said, a well done Kreem job will last a long time. A bad one (not thorough) will leave rust on the inside of the tank and compromise the strength of the coating and leave you screwed.

You have pretty much all the information from the other posts, and if you Search the "Filebase" found under "KZ Information" at the top of the page you'll find a few methods to clean a fuel tank. My favorite is to use a mild acid called Phosphoric Acid and a length of chain to remove the rust. I leave the tank bare with no coating other than what the Acid leaves behind.

I don't like the Kreem method either, but I think the POR-15 product would be good, it leaves a hard coating that should last a long time. Yamaha sells a tank cleaner too, haven't heard anything about it...

The backfiring will probably go away when you tune this engine up, adjust valves, and replace cracked hoses, and hard rubber airbox boots and cracked intake manifolds. Not getting to WOT has it's root cause in the engine not being tuned too, and the carbs being very dirty, etc.

Good luck and have fun.