Misfire under load. 85 FLHTC
Cruiser
Joined: May 2012
Posts: 184
Likes: 2
From: Nor-Cal
Replace the cheap stuff first. I know you say you replaced plugs and the plug wires but I've had the same problem twice. First time it was my spark plugs from using the enrichiner and the second time it happen it was my plug wires.
Road Captain
Joined: Jun 2012
Posts: 533
Likes: 2
From: Virginia
One other thing to check (assuming you have a CV carb, and not the old butterfly type) is that you don't have a stretched or torn vacuum diaphragm on top of the carb slide. That can result in the symptoms you've described.
Seasoned HDF Member
Joined: Mar 2010
Posts: 38,593
Likes: 6,435
From: Honah Lee
Just reading you post it appears to me it just is not getting a rich enough mixture. At idle and not under load sitting still it can briefly rev up OK sitting still that way even with too much air from the opening up of the air passage but of course under load the fire goes out and it sputters and misses. Like the others say it can be other things that mimics this.
If I were you and you know all the simple stuff is good. plugs and their wires (good spark) good fuel and clean and open tank and vacuum peacock working (fuel pores out and vacuum pot does not leak and good vacuum line) I would get Denis Kirks $19. overhaul kit and go thru carb once more if all you did was clean and not overhaul. I would completely screw the low speed and medium speed jets out to spray thru from both sides. I have a fine spring wire about .012 thick about 5" long. I slide it slowly thru them (do not force or enlarge) and then respray again. I use Gunk carb cleaner. Test yours to insure it cuts deposits and not just grease. Find a dark red spot in bowl and spray a tad on and rub with finger. A real popular brand will not do the job.
Different animal but I went thru 3 carbs off a Yamaha 2 stroke that even has screw in jet even for the idle system and rubber plugs hiding some where they screwed in since they picked up from the side . It had set couple years. I went thur those carbs 3 times before getting them right. Went from would not run to only idle to half power sputter to like brand new.
hope below are sponsors. Harley is probably best place to get parts however in my opinion.
your overhaul kit I THINK??
https://www.denniskirk.com/carb-rebu...06.ph49196.prd
your carb I THINK OEM Kline 27006-76 Ronnie requires a human verification now and below may not work for you
until you type it at his home page.
http://www.shopronniesharleydavidson...110048-H060017
If I were you and you know all the simple stuff is good. plugs and their wires (good spark) good fuel and clean and open tank and vacuum peacock working (fuel pores out and vacuum pot does not leak and good vacuum line) I would get Denis Kirks $19. overhaul kit and go thru carb once more if all you did was clean and not overhaul. I would completely screw the low speed and medium speed jets out to spray thru from both sides. I have a fine spring wire about .012 thick about 5" long. I slide it slowly thru them (do not force or enlarge) and then respray again. I use Gunk carb cleaner. Test yours to insure it cuts deposits and not just grease. Find a dark red spot in bowl and spray a tad on and rub with finger. A real popular brand will not do the job.
Different animal but I went thru 3 carbs off a Yamaha 2 stroke that even has screw in jet even for the idle system and rubber plugs hiding some where they screwed in since they picked up from the side . It had set couple years. I went thur those carbs 3 times before getting them right. Went from would not run to only idle to half power sputter to like brand new.
hope below are sponsors. Harley is probably best place to get parts however in my opinion.
your overhaul kit I THINK??
https://www.denniskirk.com/carb-rebu...06.ph49196.prd
your carb I THINK OEM Kline 27006-76 Ronnie requires a human verification now and below may not work for you
until you type it at his home page.
http://www.shopronniesharleydavidson...110048-H060017
Last edited by Jackie Paper; Sep 14, 2018 at 11:14 AM.
Road Master
Joined: Jun 2007
Posts: 842
Likes: 47
From: New Hartford CT
I had a similar problem with my '89 with the stock butterfly carb and compliance fittings. My solution was to upgrade to a CV carb and a newer manifold.
The bike has been upgraded to a rigid mount for the carb so no rubber to crack. I guess it could possibly be leaking at the gasket. I will have to check. Carb doesn't have a vacuum diaphram.
At this point I am sure of nothing anymore, but I have thoroughly cleaned the carb and am pretty sure it is as clean as it will get.
After reading everyone's post (Thank you all very much by the way, this has been a great place and couldn't ask for a better group for help from) and doing a little research on my own I have decided to change the ignition module and upgrade to an aftermarket system. Not the cheapest route but I believe the best. Even if it turns out not to be the problem, with my recent electrical problems it will give me piece of mind.
I will keep everyone posted on how it turns out.
God Bless!!
At this point I am sure of nothing anymore, but I have thoroughly cleaned the carb and am pretty sure it is as clean as it will get.
After reading everyone's post (Thank you all very much by the way, this has been a great place and couldn't ask for a better group for help from) and doing a little research on my own I have decided to change the ignition module and upgrade to an aftermarket system. Not the cheapest route but I believe the best. Even if it turns out not to be the problem, with my recent electrical problems it will give me piece of mind.
I will keep everyone posted on how it turns out.
God Bless!!
Road Captain
Joined: Jun 2012
Posts: 533
Likes: 2
From: Virginia
The bike has been upgraded to a rigid mount for the carb so no rubber to crack. I guess it could possibly be leaking at the gasket. I will have to check. Carb doesn't have a vacuum diaphram.
At this point I am sure of nothing anymore, but I have thoroughly cleaned the carb and am pretty sure it is as clean as it will get.
After reading everyone's post (Thank you all very much by the way, this has been a great place and couldn't ask for a better group for help from) and doing a little research on my own I have decided to change the ignition module and upgrade to an aftermarket system. Not the cheapest route but I believe the best. Even if it turns out not to be the problem, with my recent electrical problems it will give me piece of mind.
I will keep everyone posted on how it turns out.
God Bless!!
At this point I am sure of nothing anymore, but I have thoroughly cleaned the carb and am pretty sure it is as clean as it will get.
After reading everyone's post (Thank you all very much by the way, this has been a great place and couldn't ask for a better group for help from) and doing a little research on my own I have decided to change the ignition module and upgrade to an aftermarket system. Not the cheapest route but I believe the best. Even if it turns out not to be the problem, with my recent electrical problems it will give me piece of mind.
I will keep everyone posted on how it turns out.
God Bless!!
If you are looking at ignitions, the Ultima single fire units are a decent buy, and mine's working well so far.
Road Master
Joined: Oct 2011
Posts: 957
Likes: 2
From: Carlsbad Springs Ontario
I have never seen an ign. modual in any application actually deteriorate to a point were they cause missfire under load. My experience is that they either operate or dont with no spark as a result. The modual wiring connectors could also be a culprit.
I would check for leaking current whether primary or secondary by starting the bike in a dark area and spraying water onto the coils , wires , plugs etc. If arcing is seen , replace the affected components , if a miss develops but no arcing then check for loose connectors or worn wiring.
I would check for leaking current whether primary or secondary by starting the bike in a dark area and spraying water onto the coils , wires , plugs etc. If arcing is seen , replace the affected components , if a miss develops but no arcing then check for loose connectors or worn wiring.
Seasoned HDF Member
Joined: Aug 2007
Posts: 8,200
Likes: 3,089
From: NW AR
I'm going with carb/fuel related. Sounds like the idle and/or slow speed circuit is gunked up.
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Okay I ordered a used ignition module off ebay for $35. It came in today and i put it on at lunchtime. Same problem. So thats that. I tried it at lunchtime and it seems that under a load it stalls and sputters between 1800rpm and 2500 rpm once it hits 2500 it takes off and accelerates hard. Any ideas?
Outstanding HDF Member
Joined: Oct 2010
Posts: 2,706
Likes: 14
From: Near Frankenmuth, MI
By your description it might be timing. The voes trigger the ignition module. The voes is not activating due to either a bad switch or leaking vacuum. It can idle well but miss under load if leaking vacuum. Typically it actuates at high vacuum draw and advances the timing /spark for higher rpms. So the opposite might happen if it's not returning / responding to low vacuum, this offsets the idle timing which can be smooth until under load.
May be as simple as just trimming the expanded ends of it's vacuum line or replacing it.
You may even need to set the timing module to adjust the timing correctly
The slow speed jet is still clogged.
Intake air leak. It can idle well but miss under load. It can temporarily seal with high vacuum at faster engine revs.
But the easiest consideration would be another set of fresh plugs.
The compression test may point to bad rings but the odds are low.
Take out your plugs and read them. Then put one more fresh set in.
May be as simple as just trimming the expanded ends of it's vacuum line or replacing it.
You may even need to set the timing module to adjust the timing correctly
The slow speed jet is still clogged.
Intake air leak. It can idle well but miss under load. It can temporarily seal with high vacuum at faster engine revs.
But the easiest consideration would be another set of fresh plugs.
The compression test may point to bad rings but the odds are low.
Take out your plugs and read them. Then put one more fresh set in.