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Backfire vs Misfire

Started by Fuzzlewump, June 16, 2013, 03:28:36 PM

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Fuzzlewump

Working on dialing my carbs in so I can give another try at passing emissions, and I'm kind of stumped.

I can tune the carbs so that I have proper synch and idle, but I've always got either misfire or backfire.

If I tune so that there is no misfire or backfire, then either my synch is way off or my idle is way too high. Adjusting synch or idle at this point throws everything off completely.

In other words, when I have good synch and idle, it's like there's no middle ground between misfire and backfire.

Is it possible that my backfire is being caused by something other than carb settings, and if I eliminate that problem then I will have the elusive, holy trinity of proper Synch, Idle and Mixture?
Know ye not that ye are a gremlin?? Thou hast no quarter here- flee now from me!!

QBS

Not sure if this will help, but pretty sure it can't hurt, check everywhere for vacume leaks and verify that the correct jets are in the correct holes.

Rick G

The main air jets and the main jets are the same configuration. be sure they aren't switched.
Rick G
Go soothingly on the grease mud, as there in lurks the skid demon
'82.5 Yamaha XZ550 RJ  Vision,
'90 Suzuki VX800, 1990 Suzuki DR350.
'74  XL350   Honda , 77 XL350 Honda, 78 XL350 Honda, '82 XT 200 Yamaha, '67 Yamaha YG1TK, 80cc trail bike

Fuzzlewump

I've checked all over for vacuum leaks and so far I haven't found any, but I do have an exhaust leak at my y-pipe....

The jets in the top of the carbs are 135 on the front and the rear. Could this be my problem, or will it cause some problems?
Know ye not that ye are a gremlin?? Thou hast no quarter here- flee now from me!!

QBS

An exhaust leak won't cause the problem you describe.

treedragon

........ an exhaust leak can cause a backfire under ride conditions though. It is one of the first things we look for in similar cases. 

On my original exhaust system when I had a leaking rear Y pipe I would often get backfires when riding, (as different from misfires), I let it go for a while because it was a pain to fix, then I got a really bang and had to fix it  ;D 

On my current system I would occasionally get one and have subsequently found a faulty seal where the new muffler fits on.



Talking about emissions...... apparently it is a common trick to put a bit of acetone in the fuel for more efficient burning to pass tests. I can't attest to this aspect at all but I do know it gives me 2 to 3 of K's per litre of better fuel economy, thoroughly tested over 1000's of k's..... The amount is important and it is a SMALL amount, 1ml per litre of fuel. YMMV  ;D

 
There is always a way

fret not

Are your valve clearances correctly adjusted?
Retired, on the downhill slide. . . . . . . . still feels like going uphill!

Fuzzlewump

I haven't had the time yet to check my clearances, or my compression. I really need to do both of those.  :-[

I can move the backfire from one cylinder to another, which had me doubting whether the exhaust leak was related or not. This might not make much sense, but I just kind of feel that's a carb tuning related problem.

In about a week I'm going to take the bike on her first "long distance" run, about 200 miles on the interstate roads. She'll be treated with kid gloves, and I think it'll be good to see what that kind of a trip will do for her. This gives me a week to try and find a happy place with the carburetors.

I've finally found the culprit for a blown fuse on my signal circuit, and aside from improperly tuned carbs she's running very strong and healthy. Starts well, no leaks, smooth shifting and solid braking, suspension feels good. I'm very pleased with all this!
Know ye not that ye are a gremlin?? Thou hast no quarter here- flee now from me!!

sunburnedaz

When you want to hit the road hit me up I can come down from the north valley and there can be two visions running a pack.
1982 Yamaha XZ550 - Almost bone stock
2005 Honda F4i - Nothing stock
98 ZX-6R Track Bike
1998 Chevy truck - AKA recovery truck

Rikugun

QuoteI've finally found the culprit for a blown fuse on my signal circuit
Soooooooooo, what was it?  :)
It is far better to grasp the universe as it really is then to persist in delusion, however satisfying or reassuring.  Carl Sagan

Fuzzlewump

Quote from: sunburnedaz on June 19, 2013, 04:13:58 PM
When you want to hit the road hit me up I can come down from the north valley and there can be two visions running a pack.

That sounds like a great time! My own V is the only one I've ever actually seen "in person" and it would be cool to see and hear another. I'm heading down to Mexico for some dental work on Tuesday. It may not sound like a very exciting ride, but you're more than welcome to join if you'd like. I've been thinking of sending you a line sometime soon, considering how close proximity we are to each other.

Quote from: Rikugun on June 19, 2013, 04:42:54 PM
QuoteI've finally found the culprit for a blown fuse on my signal circuit
Soooooooooo, what was it?  :)

Turns out it was the rear brake switch all along. The V presented me with another lesson in being thorough and patient. (she's good at that ;))

I had previously checked all the wires, grounds, and units and found nothing. I mean disassembled switches, applied multimeter, removing and replacing units, everything I could think of. I checked them again, and still saw nothing wrong. Totally confused and very aggravated, I pulled the wiring harness off the bike and unwrapped it.

Over two days I completely disassembled the entire thing and checked every wire in the harness for the second time, then replaced every connector....checking every wire again each time a new connector was put in place. Putting the harness back on, I again sanded my ground-to-frame spots for clean connection. Still blowing a fuse!

Finally, I just sat on the bike and wiggled and jiggled everything, pulling levers and flipping switches, and one of the times that I pressed the rear brake pedal the fuse blew instantly. Pulled that switch out of the circuit and now the problem is gone! Crazy, you can check something thoroughly more than once and still not see the problem.

Very humbling, to say the least. But not near as humbling as the time I called my boss to ask if he could pick me up when I broke down at a gas station on the way to work. He drove thirty minutes and helped me load the bike into the truck, then took it back to my place. We were two hours late getting that work day started because he's such a good guy. Later that night I disassemble the starter switch, clean everything completely and test it all with the multimeter. Put it all back together and just before starting the bike I realize what the problem was....I had forgotten to flip the engine kill switch back.  ::)
Know ye not that ye are a gremlin?? Thou hast no quarter here- flee now from me!!

Re-Vision

Anyone admitting that he "forgot to reset the engine kill switch" can't be all bad. Glad you found the problem.     BDC

Rikugun

When I got to the part about removing the harness and unwrapping it I started to feel lightheaded.  :o Thankfully I recovered by the time I got to the kill switch story! Classic!  :D
It is far better to grasp the universe as it really is then to persist in delusion, however satisfying or reassuring.  Carl Sagan

sunburnedaz

Quote from: Fuzzlewump on June 19, 2013, 07:06:49 PM
Quote from: sunburnedaz on June 19, 2013, 04:13:58 PM
When you want to hit the road hit me up I can come down from the north valley and there can be two visions running a pack.

That sounds like a great time! My own V is the only one I've ever actually seen "in person" and it would be cool to see and hear another. I'm heading down to Mexico for some dental work on Tuesday. It may not sound like a very exciting ride, but you're more than welcome to join if you'd like. I've been thinking of sending you a line sometime soon, considering how close proximity we are to each other.


Well I have to work tuesday. But if you are not busy tomorrow I will be at the pavilions car show at Indian Bend and the Loop 101 in the Home Depot parking lot.

Hit me up if you can find your way over there,  hit me up at 602-410-7961
1982 Yamaha XZ550 - Almost bone stock
2005 Honda F4i - Nothing stock
98 ZX-6R Track Bike
1998 Chevy truck - AKA recovery truck

Fuzzlewump

#14
Quote from: sunburnedaz on June 21, 2013, 11:23:08 PM


Well I have to work tuesday. But if you are not busy tomorrow I will be at the pavilions car show at Indian Bend and the Loop 101 in the Home Depot parking lot.

Hit me up if you can find your way over there,  hit me up at 602-410-7961

Ok will do. I work tomorrow but I should be off by noon. I'll give you a call then and see if you're still there. 
Know ye not that ye are a gremlin?? Thou hast no quarter here- flee now from me!!