so, I've had this annoying backfire since I put on slash cut & changed jets. started to think it might be an exhaust leak. checked & re torqued one of bolts where header goes into head & tightened down the muffler clamps (well, one of them).

still pop & bang.

so sceptic that I am thought I'd try Lancer's simple carb tune (how can anything so simple cure a backfire, I thought).

I did the first part & turned the screw in until engine started to slow down, counting turns in. then went back to where it was originally & started to turn it out. did not seem to matter after a turn or two - did not seem to speed up & then slow down.

so  what the heck - I twisted the throttle & let it go.

no backfire! repeated twisting throttle & letting it go - still no backfire!

put on coat, helmet & gloves (today is maybe a record here - in the mid 70s but I still dress for the job) & went for ride around town, stopping & starting @ lights (still no backfire & seemed to pull strongly) & went to see Lon (Thumperclone) to tell him news (he was not in but know he'll read this!)

so gosh knows what I did - like I said did not follow Lancer's instructions through to conclussion but arrived at same result.

so much for mechanic @ local shop who said after I asked his advice "Once you mess around with aftermarket mufflers it can screw up the bike for smooth running for good."

thanks to Lancer for putting me on right track & person who posted the instructions on the site.

me - a happy camper (doubly so - Ferrari won the first race of the Formula 1 season - my wife & I are fanatics!)  

LANCER wrote on 12/31/69 at 16:00:03:


I was "chomping at the bit" to say it, but you beat me to it.  What an idiot, and they get premium labor rates to pass out such crap too.

You are right on.

wasn't the header bolt or tightening the muffler clamp, Greg - I did them a week ago & it still banged. no it was definately just unscrewing out the idle mixture. still seems weird that was all it was - makes me want to kick myself for not working with it ages ago. as I said, did not find Lancer's mid spot, just unscrewed it about 2 turns & twisted grip. another unseasonably hot one tomorrow - can't wait to go out on bike again  for longer twisty ride!

(by the by Greg - mechanic did not try to fix it - just gave me "advice" when he said I might be stuck with misfire)

I am over the moon! (makes me more confident about tackling plug leak when worse weather kicks in next winter)

thanks for your words of support, Lancer & Greg!

It's good that it worked out for you.
In my state, the proffesional mechanics are prohibited from doing this by an environmental law.
If they get caught doing anything that changes the exhaust emissions, it is a 5,000 dollar fine.
I have not yet heard of anyone being charged with this offense but just the threat of it deters most mechanics from trying to richen up a carb to get it to run better.
I don't know how many motorcycles would have to richen their carbs to pollute as much as one black cloud producing public bus, but I notice a lot of busses fogging up the air we breathe without anyone doing anything to correct it.
It must have something to do with who can afford to rent the most public officials.

Phelonius

Phelonius wrote on 12/31/69 at 16:00:03:



For benefit of those who may not have seen it; as I posted on another thread:

It is against Federal law for individuals as well as pro mechanics to tinker with that screw. The civil penalty for an individual is up to $2500 per occurrence! A dealer or shop can be fined $25K per !!!  OUCH !!!  

http://www.epa.gov/compliance/resources/policies/civil/caa/mobile/engswitch.pdf

Shhh....

thumperclone wrote on 12/31/69 at 16:00:03:


No doubt about it, with the stock carb even the best setting you can get is going to be susceptible to even very slight clime/elevation changes. I think I've tinkered with mine till it won't get better at any one setting; and like you, I feather the throttle at times to aviod excessive popping. Sometimes I just let it pop, and wish my pipe was louder!