Yamaha Big Bear Backfiring Problems

[ajblank]

I have a 91 big bear.I have put a brand new carb on it but am still having problems. It idles fine, but when you throttle it spits and backfires. It also does it sometimes when it is trying to start. I have a Clymer book on it and it leads me to believe that it could be a timing problem which would lead to an electrical problem.....just wondering if anyone has seen this before and what the problem could be. Thank you for your time.

[hondajoe]

Originally posted by ajblank@Aug 11 2005, 12:36 AM
I have a 91 big bear.I have put a brand new carb on it but am still having problems. It idles fine, but when you throttle it spits and backfires. It also does it sometimes when it is trying to start. I have a Clymer book on it and it leads me to believe that it could be a timing problem which would lead to an electrical problem.....just wondering if anyone* has seen this before and what the problem could be. Thank you for your time.
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It could be a timing problem or a electrical problem and a host of others, but unless it was doing it before the new carb I would look at that first.

Be sure the float isnt too high or any jets clogged, and also that there is a proper seal around the intake (a big cause of backfiring) between the carb and the engine. The carb could also need to be rejetted.

If it was doing it before then start with what internal work or other things were done to it recently before the problem started.

Also think of starting fresh, fresh gas, air filter, oils, and a good general clean up so you can see what your working on. Nothing better than working on a clean machine.

If none of these easier to fix things correct the problem then you can start looking at valve adjustment, timing, piston and rings, and any of a number of electrical problems.

[EMTJeepers]

Typically backfiring is caused my unburnt fuel entering the exhaust... It could be that your plug is not gapped right or the right temperature plug and causing a inproper burning..

Pull the plug and take a look at the condition.. See if it is burnt or fowled in any way...

Other than that, I'd go with the timing issue...

Just a thought...

[ajblank]

Originally posted by hondajoe+Aug 11 2005, 12:15 AM--><div class='quotetop'>QUOTE (hondajoe @ Aug 11 2005, 12:15 AM)</div>

It could be a timing problem or a electrical problem and a host of others, but unless it was doing it before the new carb I would look at that first.

Be sure the float isn't too high or any jets clogged, and also that there is a proper seal around the intake (a big cause of backfiring) between the carb and the engine. The carb could also need to be rejetted.

If it was doing it before then start with what internal work or other things were done to it recently before the problem started.

Also think of starting fresh, fresh gas, air filter, oils, and a good general clean up so you can see what your working on. Nothing better than working on a clean machine.

If none of these easier to fix things correct the problem then you can start looking at valve adjustment, timing, piston and rings, and any of a number of electrical problems.
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we adjusted the float according to the book and no jets were clogged i haven't checked the seal yet. The problems started after i had let it sit and the carb got all varnished up....one reason why i put a new one on. since then it hasn't ran right

[ajblank]

Originally posted by EMTJeepers@Aug 11 2005, 10:41 AM
Typically backfiring is caused my unburnt fuel entering the exhaust... It could be that your plug is not gapped right or the right temperature plug and causing a inproper burning..

Pull the plug and take a look at the condition.. See if it is burnt or fowled in any way...

Other than that, I'd go with the timing issue...

Just a thought...
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I have changed the plug and have gotten a little bit hotter one. I gapped it according to the book but its not saying its perfect. i got a timing light today and will probably try that tomorrow. Thanks

[hondajoe]

If your problem started with the replacement of the old gummed up carb I would be looking at the carb before anything else.

Make sure that the seal from the carb to the engine is good and then start looking at the carb itself for the cause.

Just because its a replacement does not mean its the same carb, and it could be jetted different or even a larger or smaller carb too.

I have to think that since that is the only change you made from when it ran good that it most likely is the problem, but dont discount that you could have moved or disconected a wire too.

good luck