Decel backfireing on big inch motor

zoo-mon · May 25th, 2009, 02:13 PM

121" TPE motor, 45mm mikuni carb, supertrap exhaust, I can't seem to find any way to stop the backfireing on decel. I have changed the pipes, adjusted the main jet, and the pilot air screw. What cause's backfireing anyway?

Hobbit · May 25th, 2009, 02:16 PM

it might not be back fire as in the lean back fire it might be after burn, this is the stuff you see on race car when they lift off you know the flames out the exhausts.
My Dyna suffers after burn due to the free flowing baffle so i have removed fuel from the EFI map and it has got better, it does not hurt the motor as it under no stress and the O2 sensors keep it at a steady 14.6/14.1 so its not going run lean or completely stop.
with a carb its a little more difficult, dose you supertrapp have the disc system?

zoo-mon · May 25th, 2009, 02:37 PM

Disc system? The baffles are in. would be a major job to remove or change out.

Hobbit · May 25th, 2009, 02:40 PM

is the baffle like a load of metal disc's or a normal baffle

zoo-mon · May 25th, 2009, 02:48 PM

It is a normal one and spotwelded in very tight.

Hobbit · May 25th, 2009, 02:50 PM

Quote:

Originally Posted by roygregory

It is a normal one and spotwelded in very tight.

ok if had been the Disc system you may have been able to tune it out a little by altering the number of discs on the rear.
try going the other way on the main jet say 1 size smaller and see if this helps with the back fire.

Hobbit · May 26th, 2009, 03:31 AM

also check here for correct tuning on the mikuni carbs
http://www.hdtalking.com/members_tip...rb_tuning.html

zoo-mon · May 26th, 2009, 11:42 AM

I have a mikuni tuning manual. I think the afterburn is some if not all of it. I will try the next size smaller jet. Then see what that does. Thanks Hobbit

zoo-mon · Jul 11th, 2009, 01:04 PM

Found it. The throtle stop start wasn't set right. The start was holding the slide open. When the throtle was released the slide didn't shut all the way allowing fuel to flow at deceal. After a lil adjustment. no problem. No nead to rejet. Thanks for the info it caused me to look at it closer.

May 25th, 2009, 02:13 PM	#1
zoo-mon Warming The Wheels Ride: 2009 Custom Join Date: Apr 12th, 2009 Location: Cincinnati Ohio Posts: 80 My Mood:	Decel backfireing on big inch motor 121" TPE motor, 45mm mikuni carb, supertrap exhaust, I can't seem to find any way to stop the backfireing on decel. I have changed the pipes, adjusted the main jet, and the pilot air screw. What cause's backfireing anyway? __________________ Build it Ride it Roy"Zoo-mon"Gregory

May 25th, 2009, 02:16 PM	#2
Hobbit Moderators Ride: 2009 FAST 103 Street Bob Join Date: May 18th, 2007 Location: The Shires UK Posts: 7,625 My Mood:	Re: Decel backfireing on big inch motor it might not be back fire as in the lean back fire it might be after burn, this is the stuff you see on race car when they lift off you know the flames out the exhausts. My Dyna suffers after burn due to the free flowing baffle so i have removed fuel from the EFI map and it has got better, it does not hurt the motor as it under no stress and the O2 sensors keep it at a steady 14.6/14.1 so its not going run lean or completely stop. with a carb its a little more difficult, dose you supertrapp have the disc system? __________________ Please stop by the "self help section" for maintenance tips, diagnostic codes and much more. >>Self Help Information and Tips<< click me!

May 25th, 2009, 02:37 PM	#3
zoo-mon Warming The Wheels Ride: 2009 Custom Join Date: Apr 12th, 2009 Location: Cincinnati Ohio Posts: 80 My Mood:	Re: Decel backfireing on big inch motor Disc system? The baffles are in. would be a major job to remove or change out. __________________ Build it Ride it Roy"Zoo-mon"Gregory

May 25th, 2009, 02:40 PM	#4
Hobbit Moderators Ride: 2009 FAST 103 Street Bob Join Date: May 18th, 2007 Location: The Shires UK Posts: 7,625 My Mood:	Re: Decel backfireing on big inch motor is the baffle like a load of metal disc's or a normal baffle __________________ Please stop by the "self help section" for maintenance tips, diagnostic codes and much more. >>Self Help Information and Tips<< click me!

May 25th, 2009, 02:48 PM	#5
zoo-mon Warming The Wheels Ride: 2009 Custom Join Date: Apr 12th, 2009 Location: Cincinnati Ohio Posts: 80 My Mood:	Re: Decel backfireing on big inch motor It is a normal one and spotwelded in very tight. __________________ Build it Ride it Roy"Zoo-mon"Gregory

May 26th, 2009, 03:31 AM	#7
Hobbit Moderators Ride: 2009 FAST 103 Street Bob Join Date: May 18th, 2007 Location: The Shires UK Posts: 7,625 My Mood:	Re: Decel backfireing on big inch motor also check here for correct tuning on the mikuni carbs http://www.hdtalking.com/members_tip...rb_tuning.html __________________ Please stop by the "self help section" for maintenance tips, diagnostic codes and much more. >>Self Help Information and Tips<< click me!

May 26th, 2009, 11:42 AM	#8
zoo-mon Warming The Wheels Ride: 2009 Custom Join Date: Apr 12th, 2009 Location: Cincinnati Ohio Posts: 80 My Mood:	Re: Decel backfireing on big inch motor I have a mikuni tuning manual. I think the afterburn is some if not all of it. I will try the next size smaller jet. Then see what that does. Thanks Hobbit __________________ Build it Ride it Roy"Zoo-mon"Gregory

Jul 11th, 2009, 01:04 PM	#9
zoo-mon Warming The Wheels Ride: 2009 Custom Join Date: Apr 12th, 2009 Location: Cincinnati Ohio Posts: 80 My Mood:	Re: Decel backfireing on big inch motor Found it. The throtle stop start wasn't set right. The start was holding the slide open. When the throtle was released the slide didn't shut all the way allowing fuel to flow at deceal. After a lil adjustment. no problem. No nead to rejet. Thanks for the info it caused me to look at it closer. __________________ Build it Ride it Roy"Zoo-mon"Gregory

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Decel backfireing on big inch motor

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