Carb cough .....

fmbeach · #1 10-26-2006, 11:05 AM

Finally EVO's get some respect with our own forum!

Having a little problem with my '97 FLSTC. Had the scoot rejetted a month or so ago. Original owner self-installed a Dyno-jet package and of course picked the largest jets. Bike was running way fat/rich and was getting crappy (<30 MPG) mileage. Had my local indy shop (Circus City Custom Cycle) rejet the carb. Reduced the main jet 2 sizes. Performance and mileage both are now great. However, I am getting a occasional carb cough or fart after a quick decel and start from a dead stop. Ususally one fart and its over but occasionally two or three and it almost quits.

Any expert EVO advice would be most appreciated.

Hackd · #2 10-26-2006, 03:32 PM

Find a good independent that has a dyno and get the bike tuned there. Any carb is gonna have a 'flat spot' (when you transition from the idle circuit to the main circuit). Sounds like you've got a doozie. A good dyno guy can minimize that to where it is virtually un-noticable. It could be something a simple as adjusting the idle mixture screw.

You will also find that there are many different ways it seems to get the desired results from the CV carb. Sportster needles, washers to raise the needle, different jets, lightened slides, weaker springs, etc. And everyone has their own favorite method and combo. But unless you get it dyno'd you'll never know what the carb is doing at different rpms.

cornell · #3 10-26-2006, 03:40 PM

Do you know if the slide vacuum hole was drilled larger?

If it was, the slide could be raising too fast and leaning things out with the smaller jets in there now.

Also you could readjust the idle mixture to the highest / smoothest idle which may correct this issue.

fmbeach · #4 11-01-2006, 03:54 PM

Thanks Hacked and Cornell,

Started with something very simple first. Cleaned and reoiled my K&N air filter. Seems to have helped. I have a dyno sheet from a run just after the rejetting. Will be taking it and the scoot back to my indy next week for the flat spot adjustment. Might have been simply a crap tank of gas. Will be putting enough miles on this weekend to see if a clean filter and several tanks of fuel make any difference.

Hackd · #5 11-02-2006, 08:15 AM

Keep us posted.

Babs · #6 11-20-2006, 07:36 PM

[sm=popcorn.gif] Yeah I'll be interested in how this one turns out as well.. Ain't tuning an art. No pc's to plug into, no downloads.. it's you the carb, some tools and a handful of jets. Scares the bejeevies out of me but I know my bike needs some expert love as well.. crappy gas mileage and bad stutters occassionally when pulling in low RPM's.

Gutman · #7 11-21-2006, 03:18 PM

fmbeach, Try increasing the slow jet from a 42-45. Re-adjust air fuel screw for highest, smoothest idle.

fmbeach · #8 03-16-2007, 10:47 AM

Update .....

Had it in for a new rear tire and finally found and fixed the carb fart problem. Leaky intake seals. To quote my mechanic "they look like original wiper blades from a '57 Chevy".

Runs like a new scoot. Much better performance,easier start andsmoother cold idle. Still pop on decel but much reduced.

'97 bike = anythingrubber is suspect

Also, had the trans gear oil changed to Red-line shockproof heavy. Hugedifference in shift smoothness, gear noise and typical harley bang when shifting gears. Much smoother and quiet. Thestuff isvery thick ....pours like cold honey.