V-Twin Forum banner

1 - 16 of 16 Posts

·
Registered
Joined
·
33 Posts
Discussion Starter #1
My bike is a 1992 fxlr with the evo and an s&s super e with an intake, all stock other than that. Bought the bike a year and a half ago from the second owner who lived in VT, and brought it down to MA. Bike always ran decent except when you whack the throttle or you have it below 2000 rpm's it studders and pops like it's running on one cylinder. I've gone through the carb with a rebuild kit and spent endless hours tuning it. I feel pretty confident that my pilot and main jets are the correct size.
I've checked timing and adjusted the curves, the module is a compufire 21835 for high comp Harleys, it is a single fire ignition. The problem seems to get better and worse and I can never really track it down. The thing I hate the most is when this happens to me in a corner.
I've also sprayed for leaks all around the intake manifold and there were no changes in idle. Does anyone have a direction they can point me in to fix this problem?
 

·
Registered
Joined
·
16,955 Posts
Look at the cam sensor for melting.

Sent from my SM-A102U using Tapatalk
 

·
Registered
Joined
·
33 Posts
Discussion Starter #3
No melting there, but I may be on to something. I took the VOES hose off the manifold and plugged both connections and took it for a ride. From what I hear the motor should act differently but it performed almost identical, is this true the motor should perform differently? It had the same hesitation at 2000 rpms and below and still performed good at full throttle after.
 

·
Registered
Joined
·
168 Posts
No melting there, but I may be on to something. I took the VOES hose off the manifold and plugged both connections and took it for a ride. From what I hear the motor should act differently but it performed almost identical, is this true the motor should perform differently? It had the same hesitation at 2000 rpms and below and still performed good at full throttle after.
Disconnecting VOES puts ignition on same curve you run when you crank open the throttle so you won't see much difference.

Take a look at your accelerater pump adjustment. Sounds like it isn't coming in quick enough.

Sent from my SM-T350 using Tapatalk
 

·
Registered
Joined
·
33 Posts
Discussion Starter #6 (Edited)
I took apart the carb and blew out all the passages with compressed air, and still no luck. I tried to retime the accelerator pump and the only thing I noticed is the pump spray even after blowing it out doesn't always spray the same, not sure if its the way I'm twisting the throttle or not, but after 1 1/2 turns out the spray starts to hit the butterfly.
 

·
Registered
Joined
·
560 Posts
I'm guessing the bike came to you with the Super E already installed. If so, did you get any idea from the prior owner how long it had been on the bike? It could just be worn out.

It's been a long time since I rebuilt one of those. Did the kit come with a new shaft and butterfly? Or maybe some sleeves or bushings for the body? I think they have 3 different levels of rebuild kits. Also, compressed air might remove some dust or other particles, but it's not much of a solvent for any dried fuel that could be hiding in the tiny passages.

I think you should keep looking for some sort of intake leak. Did you check the VOES line for a leak?
 

·
Super Moderator
Joined
·
20,423 Posts
What kind of shape is the motor in? Whacking it at under two grand is asking a lot out of it.
 

·
Registered
Joined
·
33 Posts
Discussion Starter #9
My guess is the carb is made before 2004 due to not having an air bleed on it, but even still I cleaned it with carb cleaner and blew compressed air through that nozzle. I still find it odd that the accelerator pump spray hits the butterfly even though I have the o ring on the sprayer and everything seems in its correct place. The motor has 58,000 on it and starts and runs strong other than that issue. It even happens if I go to half throttle too quick, and it will not accelerate at all it just continues to studder until I let almost all the way off the throttle.
 

·
Make me use my bullet?
Joined
·
12,998 Posts
You should not be "whacking the throttle" while under 2000 RPM. Are you not able to downshift?
 

·
Registered
Joined
·
33 Posts
Discussion Starter #11
No problems down shifting, even tho it does do it when you whack the throttle wide open which I can understand having issues there due to not being able to pull the fuel in. But it happens when I'm trying to take a easy corner around town around 1800 rpm and even a easy roll to half throttle will cause it to do it. If this is normal operation for an S&S carb then I'm fine with that, but this isn't my first motorcycle and I've never had an issue like this that I cant tune out.
 

·
Registered
Joined
·
16,955 Posts
But it happens when I'm trying to take a easy corner around town around 1800 rpm and even a easy roll to half throttle will cause it to do it.
Ah. I misinterpreted your initial post. I thought you were just taking off in 1st gear.

To solve your problem, keep the rpms around 2500.

Sent from my SM-A102U using Tapatalk
 

·
Make me use my bullet?
Joined
·
12,998 Posts
No problems down shifting, even tho it does do it when you whack the throttle wide open which I can understand having issues there due to not being able to pull the fuel in. But it happens when I'm trying to take a easy corner around town around 1800 rpm and even a easy roll to half throttle will cause it to do it. If this is normal operation for an S&S carb then I'm fine with that, but this isn't my first motorcycle and I've never had an issue like this that I cant tune out.
I may be misunderstanding the problem, but if your issue has to do with rolling on the throttle while the engine is cruising at under 2000 rpm, you will always have a stutter and it isn't an issue with the carb, it is lugging the engine.

Just curious, have your other motorcycles been Harleys?
 

·
Registered
Joined
·
33 Posts
Discussion Starter #15
As long as you consider a sportster a harley then yes this is my second harley. Every other 4 stroke carb i've tuned has been a cv carb. I'll have to try plugs and wires next. I still find it odd the accelerator pump nozzle sprays at the butterfly
 

·
Registered
Joined
·
560 Posts
....I still find it odd the accelerator pump nozzle sprays at the butterfly
Well, since the nozzle is upstream of the butterfly, I don't know where else it would spray, unless it was backwards and pointing to the A/C.

I extracted these instructions from the carb instructions. I hope S&S doesn't mind. If you don't have a copy of their instructions, pretty simple to go and download a copy of whatever particular model that applies

F- Adjusting Accelerator Pump - Function of accelerator pump is to improve throttle response when rapidly opening throttle at low rpm and
to aid cold starts. Pump travel screw regulates volume of fuel delivered by accelerator pump.. During assembly, S&S sets
screw for maximum volume to aid during initial start-up after installation. Turning screw inward or in clockwise decreases delivered pump
volume. Turning screw outward or counterclockwise increases delivered volume.
1- Warm engine to operating temperature.
2- Turn pump travel adjusting screw inward or clockwise until screw contacts pump actuator arm. This limits actuator arm travel and shuts
off pump.
3- Perform intermediate and high speed jetting tests to determine proper jetting.
4- With engine warm and at idle, blip throttle and note throttle response.
5- Turn pump travel screw outward or counter clockwise about 1⁄4 turn at a time and recheck throttle response until engine no longer
hesitates. This is usually about two turns out.
6- Road test motorcycle noting throttle response at idle and at levels in 500 rpm increments from idle to 3000-3500 rpm.
7- Set pump travel screw at point where best throttle response is noted with minimum pump travel. Minimum pump travel is recommended
to conserve fuel, prevent spark plug fouling, and curtail black smoke from pipes when “blipping” throttle. Black smoke from pipes is
usually an indication of a rich condition or excessive accelerator pump travel.
NOTE: Final accelerator pump adjustment should be confirmed by riding motorcycle and noting throttle response with motorcycle underway. Because of displacement, compression ratio, cam timing, exhaust design and other, related factors, many engines will stumble or bog if throttle is abruptly cranked fully open with engine at idle. If correct carburetor (E or G) is installed and engine properly tuned and equipped with appropriate exhaust and cam, stumble should disappear under normal riding conditions.

Maybe you'll find something in here that will help.

Are you sure there aren't other modifications you are dealing with. Near 30 year old motorcycles have a lot of time to have forgotten stuff done to them. Especially after changing hands more than once.
 
1 - 16 of 16 Posts
Top