BRAVO HELP?? ( Back Fire) ANY IDEAS??

kking32

kking32

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Jan 30, 2010
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Age
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moncton canada
just picked up an 85 bravo for the kids, i was missing a few things like the recoil , got it all together , i didn't get a chance to clean the carb yet, pulled the choke and gave it a couple primes, i flooded it the first try then replaced plug and it started up, let it warm up then put it up on then stand to get the track turning, seemed to bog a little, but works ok wide open , shut it down and went to restart it and it back fired and blew the vacuum fuel line off the base, hooked it back up and it started up again, i restarted it about 10 different times and id say it back fired about 3 of the 10 times and blowing the vacuum line off one other time, does this sound like a dirty carb? also the fuel is probably old . any ideas?? thanks for any help
 

Make sure there are mouse houses in the air box or exhaust after cleaning the carb and replacing all the rubber lines. I had one of those Bravos for my kids and I wish I never got ride of it, best sled I ever owned....... except for my Nytro!
 
well i just cleaned the carb was a little dirty but not real bad , drained fuel, added fresh fuel, started right up but still the same , not running 100%, still back fires when you start it up, tried another coil -plug -wire- cap- plug, i'm also gonna try another fuel pump, the engine seems noisy but i think its coming from the clutch, ( i hope) i ran it back and forth across the field wide open a few times and it didn't blow up, lol . i read some wheres that the crank bearings go bad and the flywheel sags and starts to rub?? oh and no nice nest!! any ideas??
 
have you tried bypassing the tors? I think it was around there Yamaha started installing it on sleds.
 
it doesn't have TORS,,, it only backfires when trying to start it, once running it doesn't, pulled the clutch off and everything is worn out, so i'll be looking for weights and collars for the bravo, i pulled it over with clutch off and it started up ,just let it idle for a few seconds and noise was gone, so that's one problem, now just to figure out the backfire problem, oh also checked compression 120 ish, any ideas?
 
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back fire after start up can be a few things ...........unburned fuel in the exhaust .....preignition .....try letting it idle for a bit before you shut is down .....also as a 85 it should have Tors as this was the first year it was introduced from Yamaha if it does not have the TORS it should have a tether .....or it is a 84....................

just looked it up yep 85 does have TORS ........so if it does not have it you have a 82-84 machine
 
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i never checked the serial number to make sure, no wires on the carb, i was told it was an 85 buy may be a 84, it has a red Cab, Transporter decal on the tunnel , Canadian model?? i did get a box of extra parts with it, and i saw a cdi , should i try swapping that out?
 
What is your air or fuel screw set at? Does it fire up with just a couple pulls? Or does it take 4-5? I would agree with Yamaha Nutz and say it may be unburned fuel.
 
went into garage today to play around a little with it, air screw was set at 1 1/4, and today it started in one pull, no back fire. i gave it one shot of prime, what are causes of unburned fuel?
 
running the sled hard and shutting it off ....or having a high idle and shutting it off as you kill the ignition the motor is still pumping and the excess fuel is forced into the exhaust upon startup the first flame front from the exhaust ignites the raw fuel in the exhaust
 
ok thanks, also would having a Mikuni fuel pump on it rather than the original Keihin make any difference,(cause too much fuel) i have a spare Keihin that i never tried.
 
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