High Idle - Carb Binding?
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Cruiser
Joined: Jul 2016
Posts: 241
Likes: 33
From: Syracuse IN
High Idle - Carb Binding?
Months ago I removed and thoroughly cleaned the Bendix carb on my '75 FXE to remedy what seemed to be a fuel starvation issue. Cleaning fixed the fuel issue, but on 90-degree plus days I would pick up a few hundred rpms at idle.
Pressing on top of the throttle arm would bring the correct idle back. Thinking that the rod that the butterfly is mounted on might be binding, I've tried lubricating it with spray chain oil, spray graphite and a few other concoctions.
Most of the time the bike settles right into idle with out issue. But on the really hot days, the higher idle shows up, and pressing down on the throttle arm is the remedy. There is slack in the throttle cable. My guess is there is a temperature-related expansion and binding issue?
Pressing on top of the throttle arm would bring the correct idle back. Thinking that the rod that the butterfly is mounted on might be binding, I've tried lubricating it with spray chain oil, spray graphite and a few other concoctions.
Most of the time the bike settles right into idle with out issue. But on the really hot days, the higher idle shows up, and pressing down on the throttle arm is the remedy. There is slack in the throttle cable. My guess is there is a temperature-related expansion and binding issue?
Seasoned HDF Member
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From: la la land jerzey
question -- did you remove the throttle blade to replace the side seals with the tin covers
it goes in only one way and can be turned back wards making it a 3 way wrong one correct
is the cable tight the throttle receiver needs play while on the k stand
is the cable bunched up in the end and or is the inner cable dry and or fraying
it goes in only one way and can be turned back wards making it a 3 way wrong one correct
is the cable tight the throttle receiver needs play while on the k stand
is the cable bunched up in the end and or is the inner cable dry and or fraying
Road Warrior
Joined: Sep 2015
Posts: 1,447
Likes: 463
From: USA
The same question as John?? Did you remove the the throttle shaft/ plate? If you can loosen the plate screws allowing the plate to find its home that the housing has over time made for it then retighten the plate screws may work. Removal of the carb safest way to not having a runaway plate screw. Good luck.
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Cruiser
Joined: Jul 2016
Posts: 241
Likes: 33
From: Syracuse IN
Didn't take anything apart, just sprayed the dickens out of it with carb cleaner and scrubbed the bowl and internals with a toothbrush. Same thing I do with my teeth in the morning ;-)
There is slack in the throttle wire, and everything works smoothly, no sharp bends and no binding on the cable itself.
Maybe I knocked some grit loose and it found its way between the butterfly rod and carb body. Possibly I can add a small helper spring somewhere. It's a minor annoyance, but just one of those things that I hope to figure out at some point.
There is slack in the throttle wire, and everything works smoothly, no sharp bends and no binding on the cable itself.
Maybe I knocked some grit loose and it found its way between the butterfly rod and carb body. Possibly I can add a small helper spring somewhere. It's a minor annoyance, but just one of those things that I hope to figure out at some point.
Last edited by Rusty Axle; Jan 3, 2018 at 09:26 PM.
Seasoned HDF Member
Joined: Jul 2014
Posts: 8,590
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From: Cental, MI
Didn't take anything apart, just sprayed the dickens out of it with carb cleaner and scrubbed the bowl and internals with a toothbrush. Same thing I do with my teeth in the morning ;-)
There is slack in the throttle wire, and everything works smoothly, no sharp bends and no binding on the cable itself.
Maybe I knocked some grit loose and it found its way between the butterfly rod and carb body. Possibly I can add a small helper spring somewhere. It's a minor annoyance, but just one of those things that I hope to figure out at some point.
There is slack in the throttle wire, and everything works smoothly, no sharp bends and no binding on the cable itself.
Maybe I knocked some grit loose and it found its way between the butterfly rod and carb body. Possibly I can add a small helper spring somewhere. It's a minor annoyance, but just one of those things that I hope to figure out at some point.
Seasoned HDF Member
Joined: Nov 2006
Posts: 12,878
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From: la la land jerzey
the cleaner you used has swollen the rubbers on the ends of the throttle shafts and causing it to be slow in returning to rest
get in the ends with WD 40 and see if its starts to work
get in the ends with WD 40 and see if its starts to work
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Road Captain
Joined: Jan 2007
Posts: 645
Likes: 215
From: Minneapolis
My 71 Superglide does the exact same thing. It's annoying when riding, as it doesn't want to drop rpms fast enough when going through the gears quickly. My bike had a piano wire (internal throttle) stock, so it helps push the throttle closed. However, I thought it was too hard to turn the grip with the wire, so I replaced the piano wire with cable. On the bench, it snaps back quick/perfect, but just not quite good enough once it's all together. Like you, I have slack in the cable.
I might try and rebuild it again in the spring, and possible find a new return spring and blueprint the shaft. I don't really want to add another spring like you mentioned (I did consider that), as this is a big buck show bike (all stock Boattail).
I also have a 74 sportster with a Bendix, but that one is a newer replacement Zenith with the adjustable main, and that thing works mint.
I might try and rebuild it again in the spring, and possible find a new return spring and blueprint the shaft. I don't really want to add another spring like you mentioned (I did consider that), as this is a big buck show bike (all stock Boattail).
I also have a 74 sportster with a Bendix, but that one is a newer replacement Zenith with the adjustable main, and that thing works mint.
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Road Captain
Joined: Jan 2007
Posts: 645
Likes: 215
From: Minneapolis
Now that I started thinking about it and remembering the last time I had it apart... the issue is in the accelerator pump assembly. It binds ever so slightly and the return spring doesn't have enough ***** to close the butterfly and zero out the pump completely. Wish somebody made a non leather pump....
Now I'm going to take the carb off and modify the pump to use a brake cylinder style rubber u-cup seal, or machine a tiny piston and use an oring. That way there won't be any pump binding and it should fix the problem. Thanks for reminding me I need to fix it!
Now I'm going to take the carb off and modify the pump to use a brake cylinder style rubber u-cup seal, or machine a tiny piston and use an oring. That way there won't be any pump binding and it should fix the problem. Thanks for reminding me I need to fix it!
Last edited by mrlexus; Jan 10, 2018 at 07:48 AM.
Seasoned HDF Member
Joined: Jul 2014
Posts: 8,590
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From: Cental, MI
Now that I started thinking about it and remembering the last time I had it apart... the issue is in the accelerator pump assembly. It binds ever so slightly and the return spring doesn't have enough ***** to close the butterfly and zero out the pump completely. Wish somebody made a non leather pump....
Now I'm going to take the carb off and modify the pump to use a brake cylinder style rubber u-cup seal, or machine a tiny piston and use an oring. That way there won't be any pump binding and it should fix the problem. Thanks for reminding me I need to fix it!
Now I'm going to take the carb off and modify the pump to use a brake cylinder style rubber u-cup seal, or machine a tiny piston and use an oring. That way there won't be any pump binding and it should fix the problem. Thanks for reminding me I need to fix it!
Problem with most Bendix Accelerator Pumps is that the Rebuild Kit is Crap from anyone out there... except O.E.
Or, Experience problems with the Pump.
If you think the Pump is a Problem, removing the Pump plunger is no problem... run without it to see if that is the problem. I have run my '77 Sportster without acc pump "guts" since the Early '90's..
Remember that to Properly tune a Carb. the Pump needs to be disabled anyway!!!!