coughing bike

[mchaous]

Hi,

I have a 1998 EG I just purchased. It has 69000 miles on it. I believe the motor was gone through and it seems to be fine. My problem is the carb spits/coughs back at low throttle like when you rev the engine at idle. I put a rebuilt carb “CVO” in with enhanced jets. Bike has screaming eagle ignition and breather. Has better pipes too. The bike runs fine except the cough every once in a while and I do get a lot of popping from the pipes when backoff in gear going down hills and such.

What else….The plugs are a little black but not too bad just a little. Funny the front plug is worse then the back. You would think it the other way. By the way I checked the compression and both are 93psi.

Any thoughts on how to get rid of the coughing?

thanks

[harley92]

back fire on decell could be a leak in the exhuast , black on the plugs means it running to rich , for the poping check for vacum leaks , float level , excel pump . take the air cleaner of and with the bike not running look down the throught of the carb and give it throtle see if you have a good stream of fuel being sprayed . also have the timing ck

[rickr01]

Mine has the decel pop which is just associated with free flowing exhaust. It also occasionally spits back through the carb mostly when cold on low easy throttle. It's a 1998 Evo. It has no leaks in intake or exhaust. My plugs are a light tan ash color. I don't believe you have any problem. It's the nature of your free flowing exhaust a CV carb design Etc. If it runs good ride it! Oh and my two evo riding buddies all experience the same thing and our bikes are all very well maintained. When you check your plugs you should really get going down the road and run for a bit in a higher gear at medium throttle then just shut her down and coast to the side of the road and check. To many people just pull plugs at any old time and check them. For the inexperienced plug reader this usually leads to one thinking a bike is too rich. You have to find a happy medium. the best CV carb modification for good all around speed and gas mileage performance on a mild stage 1 upgrade like yours is to keep the stock main and intermediate jet Purchase and install a 1988 Sportster needle, and drill out and crank out the idle mixture about a 1 turn. In your situation, I would leave it alone and ride it if it runs good.

[harley92]

i have a free flowing exhaust and it never pops on decell there true duels with vance &hines mufflers. as far as the poping yes if its once and a while but if i read his question write his seems to be all the time i do agree with what you sad thou on all of it . did i mis read or am i just missing some thing

[lml1340]

If you fit a free flowing exhaust, you would usually want to go larger (richer) on the jetting.

Popping under deceleration is indicative of a lean mixture.

To check plugs do three tests. Mark throttle grip with tape or similar and do plug chops at 1/4, 1/2 and full throttle. By this I mean ride the bike with the throttle in the positions indicated and kill ignition. Coast to stop before attempting to remove plugs (lol)

The 1/4 throttle reading adjust with your fuel mixture screw/pilot jet
the 1/2 throttle adjust with your needle
Full throttle is main jet

[rickr01]

Removed my exhaust for some work and found the rear flange gasket leaking like crazy! It had a Screaming Eagle gasket in there. The front gasket was not leaking and was stock crushable.

[harley92]

did your poping go away after the fix on decel

[rickr01]

Originally Posted by harlet

did your poping go away after the fix on decel

The down hill burbling is still there. I just found out this morning as it's the first time in a week that the rain has let up enough to ride it. It does not pop and never really did pop on decel. It burbles and still does. Interestingly though the minor cold weather carb cough I had is gone and in fact I had to lean out the idle mixture about 1/2 turn. I had richened it up awhile back due to the cold weather occassional carb cough. May be my imagination but it seems much smoother! Always was pretty smooth but it just seems even better. After 10 years I know her pretty good ...yep smoother!

[harley92]

a leak in the exhaust can cause some problems due to uneven back pressure. when there cold they do pop thru the cab due to a lean condition which is normal after warm up it should go away

[Hillside]

Originally Posted by mchaous

Hi,

I have a 1998 EG I just purchased. It has 69000 miles on it. I believe the motor was gone through and it seems to be fine. My problem is the carb spits/coughs back at low throttle like when you rev the engine at idle. I put a rebuilt carb “CVO” in with enhanced jets. Bike has screaming eagle ignition and breather. Has better pipes too. The bike runs fine except the cough every once in a while and I do get a lot of popping from the pipes when backoff in gear going down hills and such.

What else….The plugs are a little black but not too bad just a little. Funny the front plug is worse then the back. You would think it the other way. By the way I checked the compression and both are 93psi.

Any thoughts on how to get rid of the coughing?

thanks

Your low speed jet is too lean.
If it is a 42, go to a 45, and/or more, drill the welch plug out for your air idle and begin by setting the air idle screw at three turns.
This should help.

[harley92]

that's good advice that should take care of the coughing