2500-3000 rpm engine is rough!

Energy One
midwest

midwest

Member
Last fall I had the compression increased on my S&S 117 06' K9, in addition to a 650 Woods and Thunderheart installed. Carb also has a ThunderJet. Performance is where it should be, no complaints. My question though is related to tuning the G carb...

Following the build, jetting has been adjusted a few times, most recently last week. Anyhow, acceleration is now smooth, seamless and fast, however, cruising in the 70mph-range, between 2500 and 3500rpm, the motor is hesitating or stumbling...in other words - it's having a surging effect as though it's looking for more fuel. When I twist the throttle - it smoothes out and accelerates. During 70/75mph cruise speed I pulled the enrichener (choke?) and the stumble reduced, a little. If the engine is cruising sub-2500rpm there's no surging from the engine.

I run a mixture of 106/93 octane nearly the entire time, from the same station I've used for years, so it's VERY UNLIKELY a fuel quality issue.

Thoughts?
 
W

woodbutcher

Mr. Old Fart member #145
Staff member
Do you have an inline fuel filter? Pingle seems to be the only one that doesn't cause trouble.
 
Utopiapga

Utopiapga

Active Member
Typical Cone Intake issue! Getting all that air rushing down into the carb causes it to stall and starve for fuel. Re-jetting will work, turning cone upward instead of forward will work, and or make sure you have removed the bowl vent screw.
 
midwest

midwest

Member
D&M cone is what's on it now...

Not running an in-line fuel filter on it, using only the screened petcock...

And the D&M is in the forward direction.

Utopiapga, what effect should I expect when removing the bowl vent screw? Sorry boss, I'm unfamiliar with what to expect in doing so.

Corey
 
Utopiapga

Utopiapga

Active Member
This will allow it to breath properly and not choke out when you are getting that extra rush of air from the D&M Cone. I actually liked the look of mine in the up right position but when I installed the 2 1/2" extended forward control I had to turn it back in order to have the leg room.

You can try that first just to see if that is indeed what it is. When in forward position it acts almost like a forced induction system when going at those speeds so this is why it will spit and sputter and be hard to maintain one speed. There are only 3 small bolts to take out and turn it upright just to see if that's it.

Here is an attachment to give you the breakdown of the carb to help you with tuning and finding the bowl vent screw...........
 

Attachments

aspen874

aspen874

Well-Known Member
I had the same issue with the spike, I would turn it upright and see if the problem goes away before doing anything else.
 
midwest

midwest

Member
Seems an overwhelming concensus to turn the D&M vertical...will try today and report back to everyone.

Thank you all for the input.

Corey
 
midwest

midwest

Member
Well, as suggested, pointing the spike air cleaner vertical took care of the surging...you boys are great...thank you all for the advice here!!

Corey
 
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