Suddenly running very rich.

[Guest]

A couple weeks ago I finally got around to adjusting the air screws as I was running rich on one cylinder. I got 'er running really nice for about 2 weeks and then suddenly backfiring, smell of gas after turning the bike off, and poor mileage[well poor compared to before:close to 40mpg], and high idle once warmed up.
Will this happen from switching from warm weather fuel to cold weather fuel, or is there something I may have adjusted wrong? I have been filling up at the same 2 gas stations since I got the bike, both are Shell I think.

When it backfires is usually when I close the throttle after a quick blip like at a stop sign, and it smells faintly of carb dip and unburned fuel.

[BassCliff]

Hi,

I've noticed a little drop in my fuel mileage lately too, just the last few tankfuls. It seems I'm switching to reserve about 10-15 miles sooner. I've changed nothing on my bike so perhaps it is the "winter formula".

What are you calling "air screws"?



Are you referring to the "idle mixture screw"?


Thank you for your indulgence,

BassCliff

[JCSkokos]

yeah, the mixture screws. I actually used the method outlined on your website.
Have you had any problems of backfiring or misfiring?

[BassCliff]

Hi,

No, my bike is running the same, just slightly degraded fuel economy. I was thinking of synching the carbs, using the "highest idle method" adjustment on the idle mixture screws, and cleaning the air filter just to see if that helps. But I think it may be just the crummy gas we get in the winter.

Could water have gotten in your gas? Perhaps from condensation? Is there any rust in your gas tank? Have you tried some Sea Foam or BG44K or similar? Is your air intake system still sealed up tight?

I've also heard of weird things happening, like main jets coming unscrewed and falling down in the float bowl.


Thank you for your indulgence,

BassCliff

[janner]

Another possibility could be that one of the float bowls is leaking or a pet cock problem maybe !! or just a float sticking ?

[tom203]

When it backfires is usually when I close the throttle after a quick blip like at a stop sign, and it smells faintly of carb dip and unburned fuel.

Time to check petcock operation! Your problem sounds similar to mine last summer- turns out that my petcock was leaking fuel down vac hose during running. Didn't leak when off- just when vacuum was applied and #2 plug would foul and unburned gas would backfire especially at low speed.

[chef1366]

Sounds electrical to me. Check battery and spark.

[JCSkokos]

Time to check petcock operation! Your problem sounds similar to mine last summer- turns out that my petcock was leaking fuel down vac hose during running. Didn't leak when off- just when vacuum was applied and #2 plug would foul and unburned gas would backfire especially at low speed.

this is entirely possible considering its the original 30 year old petcock w/o even a rebuild.

Good news is though that I went on a nice 50ish mile ride yesterday and burned down past reserve about 15 miles, refilled tank and haven't had a backfiring issue yet. maybe just a bad batch of gas?

[bwringer]

Time to check petcock operation! Your problem sounds similar to mine last summer- turns out that my petcock was leaking fuel down vac hose during running. Didn't leak when off- just when vacuum was applied and #2 plug would foul and unburned gas would backfire especially at low speed.

Bingo! Time for a petcock.

[mcycle-nut]

Hey! This sounds similiar to my ESD problems! High idle, sucky gas mileage, fouling plugs. Backfiring not so much though. I'll have to track down a petcock now.