New Mikuni
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Cruiser
Joined: Jun 2008
Posts: 200
Likes: 39
From: Assonet MA
New Mikuni
Need some help folks.
Just put a new VM38 on my 74XLH. Can't get her to fire. Seems to be fuel where it should be. Just won't start. Any suggestions?
Needle set in third position. Backed off 1.5 turns on the screw.
Whats next?
Bucaman
Just put a new VM38 on my 74XLH. Can't get her to fire. Seems to be fuel where it should be. Just won't start. Any suggestions?
Needle set in third position. Backed off 1.5 turns on the screw.
Whats next?
Bucaman
Stellar HDF Member
Joined: Feb 2006
Posts: 3,035
Likes: 17
From: Houston Texas
Well I must say I am shocked to hear that. That is the best carb you will ever find for a Sportster.
So you have the clip in the middle slot on the needle (3rd up or 3rd down). That is correct.
The only other thing I can suggest on setting the carb for starting is to turn the air screw out ž to 1 turn rather than 1˝ turns.
You will always have to use the enricher when starting a Mikuni in my experience. Even with the engine warmed up I have to use it. That is the lever gizmo in front of the slide. Down is on.
So, my question: Have you been using the enricher when trying to get it started? This is not a choke, but rather an enricher.
Let me give you some information about this important Mikuni feature.
The way it works:
The enricher system has it's own independent jets in the bottom of the float bowl.
For starting the fuel and air mixture is metered entirely by these independent jets.
The fuel flowing through the starting jet is mixed with air and is broken into tiny particles in the emulsion tube (where the needle sits) The mixture then flows into (beneath) the plunger area (located where the lever goes into the carb body).
At this point, the mixture mixes again with air coming in from the air intake port for starting.
The mixture is now at the optimum air-fuel ratio and is delivered to the engine through the fuel discharge passage.
Now...... and be sure to get this: The enricher is constructed to utilize the vacuum of the inlet passage (located around the plunger).
Because of this, the throttle valve (slide) must be closed when starting the engine.
That is how it works and perhaps you can now better understand how important using the enricher lever is when starting.
A Bendix just uses a choke plate to close off part of the intake. All that does is throw the air-fuel mixture out of balance and make things on the rich side.
Then if you are lucky the bike may start.
The Mikuni is a much more complicated set up, and as a result it works much better than a Bendix.
Let me know if this gets your bike popping............... pg
So you have the clip in the middle slot on the needle (3rd up or 3rd down). That is correct.
The only other thing I can suggest on setting the carb for starting is to turn the air screw out ž to 1 turn rather than 1˝ turns.
You will always have to use the enricher when starting a Mikuni in my experience. Even with the engine warmed up I have to use it. That is the lever gizmo in front of the slide. Down is on.
So, my question: Have you been using the enricher when trying to get it started? This is not a choke, but rather an enricher.
Let me give you some information about this important Mikuni feature.
The way it works:
The enricher system has it's own independent jets in the bottom of the float bowl.
For starting the fuel and air mixture is metered entirely by these independent jets.
The fuel flowing through the starting jet is mixed with air and is broken into tiny particles in the emulsion tube (where the needle sits) The mixture then flows into (beneath) the plunger area (located where the lever goes into the carb body).
At this point, the mixture mixes again with air coming in from the air intake port for starting.
The mixture is now at the optimum air-fuel ratio and is delivered to the engine through the fuel discharge passage.
Now...... and be sure to get this: The enricher is constructed to utilize the vacuum of the inlet passage (located around the plunger).
Because of this, the throttle valve (slide) must be closed when starting the engine.
That is how it works and perhaps you can now better understand how important using the enricher lever is when starting.
A Bendix just uses a choke plate to close off part of the intake. All that does is throw the air-fuel mixture out of balance and make things on the rich side.
Then if you are lucky the bike may start.
The Mikuni is a much more complicated set up, and as a result it works much better than a Bendix.
Let me know if this gets your bike popping............... pg
Road Warrior
Joined: Aug 2008
Posts: 1,306
Likes: 865
From: Sheboygan, WI
is it a new carb or a good used carb new to you? it may have been sitting around and the jets may be full of gunk, or the float or inlet needle may be stuck. did the bike run before you put the carb on, or did you do anything else to it between the last time it ran and now? is it electric start or are you trying to kick it? just a few thoughts/questions...
I would also verify that you have spark, and pull the plugs to see if they are wet or dry as a bone. If they are dry as a bone, it's most likely the carb causing you grief.
I would also verify that you have spark, and pull the plugs to see if they are wet or dry as a bone. If they are dry as a bone, it's most likely the carb causing you grief.
Last edited by d_slat; May 23, 2009 at 04:08 PM.
Thread Starter
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Cruiser
Joined: Jun 2008
Posts: 200
Likes: 39
From: Assonet MA
I will have at it again tomorrow. Putting a full charge to the battery. PG I think I may have the "choke" lever back asswards. I was pulling lever up, pushing plunger down. Debated that with a friend and I am still not so clear. Pull lever up or push it down?
This is a brand new carb. Like I said I will be back at it Sunday.
Will advise,
Bucaman
This is a brand new carb. Like I said I will be back at it Sunday.
Will advise,
Bucaman
Stellar HDF Member
Joined: Feb 2006
Posts: 3,035
Likes: 17
From: Houston Texas
Bucaman......
The enricher lever should be pushed down for starting (this raises the plunger) and then pull the lever up (horizontal position and plunger is down) for running. There is a lock made of strap spring steel to hold the lever level for running.
Let us know if this makes a difference. I am betting it does........ pg
The enricher lever should be pushed down for starting (this raises the plunger) and then pull the lever up (horizontal position and plunger is down) for running. There is a lock made of strap spring steel to hold the lever level for running.
Let us know if this makes a difference. I am betting it does........ pg
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