Mikuni VM38 trouble
Road Warrior
Joined: Sep 2006
Posts: 1,605
Likes: 82
From: nj
I 'm Sorry your right I should start a new thread,but that we are talking about problems witha idle I thought I could throw in a twister for help because we are having problems and I know pinion that you have alot of info and maybe you had a similiar problem. I will try the cables but everything looks good as the linkage goes back but I will loosen everything up and see what happens Thanks again
Stellar HDF Member
Joined: Feb 2006
Posts: 3,035
Likes: 17
From: Houston Texas
I 'm Sorry your right I should start a new thread,but that we are talking about problems witha idle I thought I could throw in a twister for help because we are having problems and I know pinion that you have alot of info and maybe you had a similiar problem. I will try the cables but everything looks good as the linkage goes back but I will loosen everything up and see what happens Thanks again
Now I feel like I should apologize to you. I meant nothing by my suggestion other than it may get a better and faster answer to the question if you were to start another thread.
As I said, I have no experience with an S&S, but a lot of guys here do have. Maybe a post titled 'Have a question on my S&S' will draw an immediate reply.
For your idle speed to not return to normal after giving it some gas makes me think something is binding.
If your butterfly is returning to a hard closed position, then binding is not the problem.
At the same time, I really think a closed butterfly is not going to idle fast either.
Hope someone has a comment on this problem and you get a good answer soon.
pg
Road Warrior
Joined: Sep 2006
Posts: 1,605
Likes: 82
From: nj
Pinion, I know what you meant, you want me to get as much help as i can get for trying a new thread. But i am going to take the air cleaner off and look at the butter fly and try your sugg first Thanks for your help
Stellar HDF Member
Joined: Feb 2006
Posts: 3,035
Likes: 17
From: Houston Texas
The part of the butterfly that has a slash cut out of it is sized to provide the proper mix of air coming in and fuel needed to obtain a proper idle with the butterfly shut tight. If you need a bit faster idle, that is where the idle stop screw comes into play....opening the butterfly just slightly. Once set, this should be constant from that point on.
pg
Stellar HDF Member
Joined: Feb 2006
Posts: 3,035
Likes: 17
From: Houston Texas
Glider.........
You may have this info but if not check this regarding adjusting your carb.........
http://www.millerscustomparts.us/san...tuningtips.htm
pg
You may have this info but if not check this regarding adjusting your carb.........
http://www.millerscustomparts.us/san...tuningtips.htm
pg
Thread Starter
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Novice
Joined: May 2009
Posts: 15
Likes: 0
From: Long Island, NY
I do have it but thanks.
I've tried running lean but that does not seem to help, however if I give it just a bit of the enrichner lever it smooths out. Kind of like you would with a choke. Could I be that lean?
I'm leaning toward a blockage of some type. I guess I'll be giving it a good cleaning.
I've tried running lean but that does not seem to help, however if I give it just a bit of the enrichner lever it smooths out. Kind of like you would with a choke. Could I be that lean?
I'm leaning toward a blockage of some type. I guess I'll be giving it a good cleaning.
Although I believe what was causing my problems may be different, I had THE EXACT symptoms you have. I prayed to the Harley gods every time I downshifted to a light.
When my motor was tight I could pull the enricher up, kick it and push the enricher down immediately(cold motor on a 70 degree day) with an idle of about 900 if I wanted the pitter patter sound with out stumbling to a stall.
I took my VM apart and cleaned it so many times I could win a prize on a game show while cleaning it drunk and blind folded. Check gas tank pet **** for full flow. Soak the carb body submerged in cleaner, pull the orifices out (check on the stamp for the right sizes), soak them, pass gas through the passages and check for flow, check the gas inlet neddle valve isn't stuck. If it has flow when your done, step away from the carb, it's gotta be something else (your VM is used so of course get the idle needle length straightened out, then recheck for the vm-9 set up for orifices and needle selection).
I re-read the thread but I don't see what kind of pipes your running. Putting golf ball baffles in my 2" drags made a tremendous difference with maintaining low idle rpms without taking away from the sound that my suburban neighbors love so much.
Unlike the S&S there really isn't much to do or set up with the VM 38 in my opinion. Check for the VM-9 set up, set pilot circuit screw, set idle screw, done.
I still think you have a push rod out of adjustment holding open a valve after the bike gets hot, or an intake or exhaust leak, maybe not through the valves themselves but the rubber spigot connector or however youre mounting the carb. If the enricher is up to keep you running than your have a lean condition.
I forget is it hard to kick it over and get her started before you head out or it starts acting up after riding awhile?
Danny
Cruiser
Joined: Jun 2008
Posts: 200
Likes: 39
From: Assonet MA
Cleaning
Have not done the cleaning thing yet.
Pipes are just a stock type. nothing special. Same pipes for the last two years. No changes.
If there is a leak it is not showing itself. Check and rechecked.
Set the push rods a couple of times. No rocket science there so I think I am on the money.
What do you thing about a cracked lifter that could be expanded after it hets up? I once had a 73 that would fire on first kick when cold, but after she warmed up kicking became an adventure. I swapped out the lifters and she began to start fine all the time. Problem is I don't recall why I swapped the lifters, it was about 30 years ago, but I remember the problem going away.
Compression is 123-125 lbs both cylinders.
I keep returning to the VM because I do not have same condition when I put the S&S on her.
Bike starts great. Hit the button and she fires. That is biggest differance from the S&S.Let her warm up with the enrichner. When I disengae the enrichner she will idle but as I said it is very inconsistant. As you said at a traffic light sooner or later I have to give it a twist to keep her running. When the idle drops it just falls almost completely away. What does your bike idle at? I am keeping her at 1300 or so. It sounds high but less than that it is really uneven.
I may play with it today as the rain is flying today up here in New England.
I will stay in touch.
Bucaman
Pipes are just a stock type. nothing special. Same pipes for the last two years. No changes.
If there is a leak it is not showing itself. Check and rechecked.
Set the push rods a couple of times. No rocket science there so I think I am on the money.
What do you thing about a cracked lifter that could be expanded after it hets up? I once had a 73 that would fire on first kick when cold, but after she warmed up kicking became an adventure. I swapped out the lifters and she began to start fine all the time. Problem is I don't recall why I swapped the lifters, it was about 30 years ago, but I remember the problem going away.
Compression is 123-125 lbs both cylinders.
I keep returning to the VM because I do not have same condition when I put the S&S on her.
Bike starts great. Hit the button and she fires. That is biggest differance from the S&S.Let her warm up with the enrichner. When I disengae the enrichner she will idle but as I said it is very inconsistant. As you said at a traffic light sooner or later I have to give it a twist to keep her running. When the idle drops it just falls almost completely away. What does your bike idle at? I am keeping her at 1300 or so. It sounds high but less than that it is really uneven.
I may play with it today as the rain is flying today up here in New England.
I will stay in touch.
Bucaman
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Stellar HDF Member
Joined: Feb 2006
Posts: 3,035
Likes: 17
From: Houston Texas
The shape is probably not a great thing. All the end of the needle does is force the slide to come up. Rounded is most likely preferable to pointed.
Let's just call your screw 1/8 inch short compared to what mine measures.
That may be enough to coil bind the spring before it raises the throttle slide.
(It's not much shorter though.)
Get the ring nut and see if that helps maintain the idle speed.
You want a speed of approx 900 rpm, and..... smooth and consistent. It it stumbles at 900 then look for clogging in the carb on the low speed circuit.
Of course let us know what happens..... pg