Engine cough on quick rev occasionally ... why?
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Cruiser
Joined: May 2018
Posts: 139
Likes: 45
From: Okanagan, BC
Engine cough on quick rev occasionally ... why?
2018 Ultra Limited, Stage 1 with EFI flashed. The bike has always run like a top and I have changed nothing. I'm on my third season however the bike has developed the very occasional cough (maybe even a slight backfire) if you give it throttle really quickly like when taking off from a light when you rev before engaging the clutch ... happens when warm or cold ... once it does this cough it takes right off like normal ... and as I say very occasionally, like once a week. I have checked for exhaust leaks, re-flashed the EFI, air filter is clean, gas always 91 octane ... like I say, the bike has been flawless, I have changed nothing but this has developed starting with this riding season. 20,000 miles on the bike.
Your thoughts and ideas to try?
Your thoughts and ideas to try?
Extreme HDF Member
Joined: Jan 2017
Posts: 10,790
Likes: 19,651
From: On the move
My 2017 with a stage 2 occasionally did this is and so does my 2020. I notice it when I give the throttle a quick blip before down shifting. When it happens it almost feels like the engine wants to shutdown but it doesn't. I just ride with it the way it is as it only happens once in awhile.
Both models have different tuners, cams etc so that probably isn't the issue.
Both models have different tuners, cams etc so that probably isn't the issue.
Last edited by RET_SCPO; Jul 17, 2020 at 11:34 PM.
Seasoned HDF Member
Joined: Jan 2007
Posts: 5,624
Likes: 4,078
From: Virginia
I wouldnt worry about it too much, remember you have 20k worth of carbon deposits on the fuel injectors, intake valves and combustion chamber. If if you use premium gas with cleaning additives, you can get hesitation in accelerating just from that. It shouldnt get too bad till you get many more miles on the motor.
2018 Ultra Limited, Stage 1 with EFI flashed. The bike has always run like a top and I have changed nothing. I'm on my third season however the bike has developed the very occasional cough (maybe even a slight backfire) if you give it throttle really quickly like when taking off from a light when you rev before engaging the clutch ... happens when warm or cold ... once it does this cough it takes right off like normal ... and as I say very occasionally, like once a week. I have checked for exhaust leaks, re-flashed the EFI, air filter is clean, gas always 91 octane ... like I say, the bike has been flawless, I have changed nothing but this has developed starting with this riding season. 20,000 miles on the bike.
Your thoughts and ideas to try?
Your thoughts and ideas to try?
HDF Community Team
Joined: Nov 2012
Posts: 6,190
Likes: 2,419
From: USA
My 04 does it also. I describe it as a sneeze. Stock cam, stage 1 or 2 intake, unknown stage ecu. Every once in a while, at low rpms, usually with some on and off of the throttle, theres a sneeze into the intake.
It happens so rarely, and so singularly, that I really suspect its a mapping failure on the ecu. Where the combination of rpm and throttle motion/position throws it way off for one single premature ignition firing.
It happens so rarely, and so singularly, that I really suspect its a mapping failure on the ecu. Where the combination of rpm and throttle motion/position throws it way off for one single premature ignition firing.
Seasoned HDF Member
Joined: Dec 2005
Posts: 19,921
Likes: 8,027
From: poway
My 04 does it also. I describe it as a sneeze. Stock cam, stage 1 or 2 intake, unknown stage ecu. Every once in a while, at low rpms, usually with some on and off of the throttle, theres a sneeze into the intake.
It happens so rarely, and so singularly, that I really suspect its a mapping failure on the ecu. Where the combination of rpm and throttle motion/position throws it way off for one single premature ignition firing.
It happens so rarely, and so singularly, that I really suspect its a mapping failure on the ecu. Where the combination of rpm and throttle motion/position throws it way off for one single premature ignition firing.
Seasoned HDF Member
Joined: Dec 2005
Posts: 19,921
Likes: 8,027
From: poway
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HDF Community Team
Joined: Nov 2012
Posts: 6,190
Likes: 2,419
From: USA
Ive seen plenty of backfires from lean mixtures, which are actually afterfires in the exhaust. As well plenty of glowing exhaust manifolds from the slow burning mixture combusting in the exhaust manifold instead of in the chamber.
Usually when Ive seen intake and carburetor fires its an ignition timing problem. Rotor position in a distributor, arcing wires, crank/cam sensor problems, etc.
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Road Master
Joined: Jun 2007
Posts: 774
Likes: 21
From: Florida
When you say cough are you talking about a slight hesitation? If thats the case your fuel flow rate is inconsistent. I had an issue with dirty injectors once that caused that.
Last edited by stevepacman; Jul 19, 2020 at 08:53 AM.
Seasoned HDF Member
Joined: Dec 2005
Posts: 19,921
Likes: 8,027
From: poway
Not sure how itd be doing this though. The exhaust opens about 180 degrees earlier, and the contents go down the exhaust. Then it opens the intake and pulls in the next charge.
Ive seen plenty of backfires from lean mixtures, which are actually afterfires in the exhaust. As well plenty of glowing exhaust manifolds from the slow burning mixture combusting in the exhaust manifold instead of in the chamber.
Usually when Ive seen intake and carburetor fires its an ignition timing problem. Rotor position in a distributor, arcing wires, crank/cam sensor problems, etc.
Ive seen plenty of backfires from lean mixtures, which are actually afterfires in the exhaust. As well plenty of glowing exhaust manifolds from the slow burning mixture combusting in the exhaust manifold instead of in the chamber.
Usually when Ive seen intake and carburetor fires its an ignition timing problem. Rotor position in a distributor, arcing wires, crank/cam sensor problems, etc.