Engine cutting out on acceleration
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Joined: Apr 2007
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Engine cutting out on acceleration
1991 EVO (FXR)
24,000 miles
Andrews EV3 cam
Screamin Eagle adjustable pushrods
Screamin Eagle igintion coil (New)
Screamin Eagle Ignition module (New)
Magnecor Wires (New)
stock ignition
Just installed a thunderslide kit (175 main jet, 42 slow, needle in #7). Been going to/from work which gets the bike up to around 75mph with no problems. Then this weekend I opened it up to 100-ish mph and when I got back to town the thing has started to cut out really bad on acceleration. It cuts out at all speeds (putting around town at 25-35 mph and on the highway at 55-65mph too).
I checked the plugs and they seem to be fine. they look a little "fat" but still have a nice tan going on too.
Any ideas?
Gunk in the carb/jets?
Float situation?
Intake leak?
Could it be a damaged intake/exhaust valve?
Valve springs?
24,000 miles
Andrews EV3 cam
Screamin Eagle adjustable pushrods
Screamin Eagle igintion coil (New)
Screamin Eagle Ignition module (New)
Magnecor Wires (New)
stock ignition
Just installed a thunderslide kit (175 main jet, 42 slow, needle in #7). Been going to/from work which gets the bike up to around 75mph with no problems. Then this weekend I opened it up to 100-ish mph and when I got back to town the thing has started to cut out really bad on acceleration. It cuts out at all speeds (putting around town at 25-35 mph and on the highway at 55-65mph too).
I checked the plugs and they seem to be fine. they look a little "fat" but still have a nice tan going on too.
Any ideas?
Gunk in the carb/jets?
Float situation?
Intake leak?
Could it be a damaged intake/exhaust valve?
Valve springs?
Road Warrior
Joined: May 2009
Posts: 1,945
Likes: 3
From: Victoria, Australia
The first place I would look would be the simple stuff. Maybe check your new coil/module/wires for loose connections or broken strands in your connections.
Could be a bad ignition module or coil (or wires) but my money is on a vibration or installation induced wire breakage. Maybe the vibes running at 100MPH nearly broke a wire.
My logic for this is you say "it cuts out at all speeds". I would think if carb related more likely to cut out at a specific rpm/speed than at all speeds, but just my thinking. I suppose it could be a chunk of crap dislodged and blocking your float inlet.
Please let us know what you find
Regards,
V2Evo96
Could be a bad ignition module or coil (or wires) but my money is on a vibration or installation induced wire breakage. Maybe the vibes running at 100MPH nearly broke a wire.
My logic for this is you say "it cuts out at all speeds". I would think if carb related more likely to cut out at a specific rpm/speed than at all speeds, but just my thinking. I suppose it could be a chunk of crap dislodged and blocking your float inlet.
Please let us know what you find
Regards,
V2Evo96
Road Captain
Joined: Jun 2008
Posts: 640
Likes: 13
From: Hickory, NC area
It does sound like it is starving for gas, which could be something in the tank or float bowl. I would start there as it is easy to pull and clean everything out. As V2 says, if it isn't in there, it is probably electrical in nature and I can honestly say I have no good advice for you there!
HDF Community Team
Joined: Dec 2005
Posts: 5,375
Likes: 2,570
From: NC USA
Could be any number of things as mentioned in previous posts, not the least of which could be the diaphram leaking. They're easy to mess-up and don't always show up a problem on install, I mean they can get a hole (tear) after being flexed a good number of times....
But running the needle that "short" on a road bike doesn't sound good to me. Or was that a typo? (#7 ? I thought there were only 6 anyway .. been a while, can't remember) I realize with the plugs looking good, you'd think all is well, but 175/42 especially with your cam sounds really lean for jetting. Raising the needle that far would compensate for lean condition in the mid range but it'd still be lean at WFO. And sometimes pulling the carb out of the intake grommet more than a few times -- they don't want to seal well even if they look good.
Difficult to "feel" one "cutting out" over the internet, so just throwing this out here - I'd suggest new plugs (they're cheap) check the diaphram and drop the needle to 3, 4 at the very highest, replace the grommet and go 180/45 as a minimum for jets. You can check fuel flow while the carb is sorta off. And I don't remember exactly when they started using the vacuum control petcock, but if you have one check it and the hoses closely.
Couple more things that came to mind with the thunderslide kit - a bad accelerator pump can cause the symptoms you mentioned. Also, if the kit came with the new pump nozzle (pedestal) the destructions tell you to aim it at the overflow pipe in the bowl. That isn't the best direction as it will spray and splash on the front side of the carb throat. Twist it toward the opposite corner to the bolt hole and it will spray directly at the needle giving a much better pattern...
But running the needle that "short" on a road bike doesn't sound good to me. Or was that a typo? (#7 ? I thought there were only 6 anyway .. been a while, can't remember) I realize with the plugs looking good, you'd think all is well, but 175/42 especially with your cam sounds really lean for jetting. Raising the needle that far would compensate for lean condition in the mid range but it'd still be lean at WFO. And sometimes pulling the carb out of the intake grommet more than a few times -- they don't want to seal well even if they look good.
Difficult to "feel" one "cutting out" over the internet, so just throwing this out here - I'd suggest new plugs (they're cheap) check the diaphram and drop the needle to 3, 4 at the very highest, replace the grommet and go 180/45 as a minimum for jets. You can check fuel flow while the carb is sorta off. And I don't remember exactly when they started using the vacuum control petcock, but if you have one check it and the hoses closely.
Couple more things that came to mind with the thunderslide kit - a bad accelerator pump can cause the symptoms you mentioned. Also, if the kit came with the new pump nozzle (pedestal) the destructions tell you to aim it at the overflow pipe in the bowl. That isn't the best direction as it will spray and splash on the front side of the carb throat. Twist it toward the opposite corner to the bolt hole and it will spray directly at the needle giving a much better pattern...
Last edited by t150vej; Jun 22, 2009 at 04:44 PM. Reason: additional info
6th Gear
Joined: Jun 2009
Posts: 11
Likes: 0
From: Maine
It does sound like it is starving for gas, which could be something in the tank or float bowl. I would start there as it is easy to pull and clean everything out. As V2 says, if it isn't in there, it is probably electrical in nature and I can honestly say I have no good advice for you there!
Hope this helps...
Stellar HDF Member
Joined: May 2005
Posts: 2,137
Likes: 17
From:
Those dyno-slide thunder-jet type kits are known for dumping a whole lot of fuel into your cylinders. Enough to put out the fire? Is your fuel mileage way down? On the other hand, I agree your jet sizes sound real lean. So, frankly, the first thing I'd suspect is your carb is way screwed up. I would get rid of what ever "kit" parts you have and get the stock TC88 jets (44, 180?) and the '88-'89 Sporty 1200 idle jet needle, or something similar to that setup, and see how it runs then.
Here's a link http://www.ridermagazine.com/output.cfm?id=217441 about carb tuning.
Here's a link http://www.ridermagazine.com/output.cfm?id=217441 about carb tuning.
Road Warrior
Joined: Nov 2006
Posts: 1,699
Likes: 2
From: Deltona, FL
Here's something I ran into once that you might want to check. You could be vapor locking your gas tank. Check to ensure your vent tubes are not clogged or blocked by your gas caps. I had this happen on a sporty.
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Thanks for the replies!
Sorry to get back to this so late. Finally got the carb torn off............disassembled.....cleaned.......reas sembled..............put in new plugs. Something I did in the process fixed the problem for the most part.
I still think it's cutting out a bit............and the back plug looks "sootier" and "blacker" than the front. The front looks like it's starting to tan up a bit.
Like I said before, I just installed a "thunderslide kit". A local shop owner told me that it was the way to go. When I first put it on I had the needle in groove #2 or #3 (it does have 7 grooves...........#7 being the "lowest" which makes the needle sit highest). I then took it for a spin...........it backfired and popped like crazy on deceleration.........so I dropped it a slot.........etc. until I finally got it cleared up in the lowest groove (#7).
I asked my guy if I should switch to a 180 main jet and possibly upsize the pilot from 42 to a 45............since I was running my needle on the last notch........and he said no.
I'm thinking I SHOULD switch to a 180 main and a 45 slow and then drop the needle down to notch #3 or #4.
Any suggestions???
By the way, I didn't state that I'm at about 4,500' elevation (Carson City) and travel up to Tahoe quite a bit (8,000' ish).
I still think it's cutting out a bit............and the back plug looks "sootier" and "blacker" than the front. The front looks like it's starting to tan up a bit.
Like I said before, I just installed a "thunderslide kit". A local shop owner told me that it was the way to go. When I first put it on I had the needle in groove #2 or #3 (it does have 7 grooves...........#7 being the "lowest" which makes the needle sit highest). I then took it for a spin...........it backfired and popped like crazy on deceleration.........so I dropped it a slot.........etc. until I finally got it cleared up in the lowest groove (#7).
I asked my guy if I should switch to a 180 main jet and possibly upsize the pilot from 42 to a 45............since I was running my needle on the last notch........and he said no.
I'm thinking I SHOULD switch to a 180 main and a 45 slow and then drop the needle down to notch #3 or #4.
Any suggestions???
By the way, I didn't state that I'm at about 4,500' elevation (Carson City) and travel up to Tahoe quite a bit (8,000' ish).
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HDF Community Team
Joined: Dec 2005
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From: NC USA
I am assuming your idle mixture plug has been removed and screw adjusted? And you've not mentioned whether you're running straight pipes? And have you properly checked your float level? That is very important on the CV. If the idle circuit is way lean, it would take a LOT of midrange action to overcome that to the point of sooting your plugs at all but low RPM.
You could have an intake leak at the grommet, the manifold o-rings or VOES hose. The VOES could be bad or loose connection (not advancing the timing) I'd look about that too, since the ignition was recently replaced, and it must be grounded properly.
No matter what, 7 is way too high for any CV on a harley for the street and until you remedy "whatever" until you can run it on 3 or 4, it ain't gonna be right....
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I'm running stock exhaust (baffles still in).
I've recently replaced the VOES hose leading from the switch to the carb. Should be no leak there.
I have removed the idle mixture plug and adjusted mixture screw.
Float level looks right when I do the "angled gravity test thingy"
I'm running stock ignition but screamin eagle module and coil.
I've sprayed brake clean onto the intake manifold while the bike was running to see if it would 'cut out' indicating an intake leak...............no problems there.
When I had the needle at #3 or #4 it was popping at decel.
Should I go ahead and drop the needle back to #4 and check other things??
I've recently replaced the VOES hose leading from the switch to the carb. Should be no leak there.
I have removed the idle mixture plug and adjusted mixture screw.
Float level looks right when I do the "angled gravity test thingy"
I'm running stock ignition but screamin eagle module and coil.
I've sprayed brake clean onto the intake manifold while the bike was running to see if it would 'cut out' indicating an intake leak...............no problems there.
When I had the needle at #3 or #4 it was popping at decel.
Should I go ahead and drop the needle back to #4 and check other things??