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Ironhead Sportster Motorcycle Talk (1957-1985) For all those that wanna talk about Ironhead Sportster Motorcycles

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  #41  
Old 4th October 2011
bhakakha bhakakha is offline
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PG,
It looks like the pilot jet in your picture. I may be mixing my terms. but I am calling something else the air jet. When looking into the carb from the air filter side there are 3 little holes on the bottom of the opening. They start at the center and go towards the right. From the right going to left, the first hole I can see the air screw, the second hole is completely closed off, and the hole further to the left (in the midline of the carb) had what I am calling the air jet. I am going based on the picture in the VM manual I downloaded. Of note, I spoke to a Mikuni rep and he told me that based on the application this "may" need to be closed, and either way it should not affect starting. And yes, I meant to type I could NOT remove it.
Ben
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  #42  
Old 4th October 2011
MegaDON MegaDON is offline
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I think you are taking about the passage ways in the front in the venturi i believe. I dont think you should remove those...if you can
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  #43  
Old 4th October 2011
bhakakha bhakakha is offline
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Hopefully this picture will clarify.

I am referring the three holes at the bottom of the opening, specifically the one to the left. Also, this is how far the slide goes down. Is that the proper place for throttle completely off?
Thanks
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  #44  
Old 4th October 2011
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piniongear piniongear is offline
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Quote:
Originally Posted by bhakakha View Post
PG,
It looks like the pilot jet in your picture. I may be mixing my terms. but I am calling something else the air jet. When looking into the carb from the air filter side there are 3 little holes on the bottom of the opening. They start at the center and go towards the right. From the right going to left, the first hole I can see the air screw, the second hole is completely closed off, and the hole further to the left (in the midline of the carb) had what I am calling the air jet. I am going based on the picture in the VM manual I downloaded. Of note, I spoke to a Mikuni rep and he told me that based on the application this "may" need to be closed, and either way it should not affect starting. And yes, I meant to type I could NOT remove it.
Ben
Opps! My mistake.
I showed the pilot jet, not the air jet because I thought we were talking about the pilot being hard to remove.

The air jet I just removed using an Xcelite #R181 screwdriver..............



The air jet is a bit harder to remove than the pilot jet.
Again, use a proper fitting screwdriver and it takes at least 6 full revolutions to remove it.
The air jet has a single hole through the length of it that a #61 drill bit fits. That is .039 inch diameter hole for the #2 air jet.............



If you cannot remove the jet in your carb I would leave it alone.
It has to have a .039 hole through it however and if this hole is stopped up you need to open it up.
The air screw works with this passage to meter the amount of air going to the pilot jet.
So the pilot jet is more important in my view than the air jet.

Inside the main bore of the carb there are two holes downstream of the slide.
The hole closest to the slide is the pilot outlet and the other hole closer to the manifold end is the bypass.
Looking into the carb bore from the manifold end both holes should appear to be open.

There is another version of Mikuni carb which has only one hole rather than 2. That is used for smaller carbs than the 38mm, so it is no concern to us.

OK, so where do we stand?
Your reference to the carb at the shop having an open hole and yours being not open...... Was that in reference to the air jet or the pilot jet?

Sorry about the induced confusion on my part.
pg
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  #45  
Old 4th October 2011
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Ben,
I just saw your pic of the end of the carb and yes, the slide looks to be closed down.
The air jet does go in the left hole.
The middle hole is closed off.
The right hole does allow you to view the end of the air screw.
So everything in the pic is as it should be.

On the side we are looking at the slide has the cutout which shows.
On the other side of the slide.....that face should be 'almost' all the way down. The idle screw adjustment screw elevates the slide just a bit depending on how far it is screwed in.
Too much and the result is a fast idle because the slide has been raised too much.
But yours looks about right in the pic.
Sometimes the Mikuni slide will hang just a bit when you first install the slide back in the carb.
A couple of throttle twists will seat it down should this occur.

So if the jet holes are clear you are about ready to start it up.
How is the points adjustment coming along?
Maybe you have not done that yet because you want to do only one thing at a time. Otherwise you have loose ends everywhere.
pg
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  #46  
Old 4th October 2011
bhakakha bhakakha is offline
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PG,
It is the air jet I was referring to. Will see if I can open the hole as soon as I get some time. Have not tried doing points yet. Won't have a chance before you head off to New Mexico. Next chance I get will be for air jet then try to start bike. Have a good and safe trip.
Ben
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  #47  
Old 4th October 2011
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Quote:
Originally Posted by bhakakha View Post
PG,
It is the air jet I was referring to. Will see if I can open the hole as soon as I get some time. Have not tried doing points yet. Won't have a chance before you head off to New Mexico. Next chance I get will be for air jet then try to start bike. Have a good and safe trip.
Ben
OK, if the air jet appears to be clogged up....... try to remove it.
If you cannot get it to turn, don't use force on it.

Contrary to what I said before, if you can obtain a #61 drill bit (you may have to buy a set of #61 thru #80 bits for $7 or $8) take the #61 and gently feed it into the air jet while turning the bit.
You never want to use a drill to clean out a jet but here we will make an exception because (a) you need it opened and (b) it is only an air passage, not a fuel/air passage.

I would certainly do all of this at a work bench with the carb removed from the machine. You do not want any junk from the air jet to fall further into the carb passages.

I will check back in if I can access a computer while away. Otherwise I will continue when I return.
pg
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  #48  
Old 5th October 2011
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Home made carb stand based on an idea from PG. Angle aluminum, about 1/8" X 1" ...



Original idea in flat steel - a bit wobbly but works well ...

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  #49  
Old 5th October 2011
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Just an FYI, I soaked my Mikuni in Pinesol for 24 Hours, used a guitar string through all the passages and Jets followed by Carb Cleaner and Compressed Air. I reinstalled the Carb and Turned the Air Screw out 2-1/4 Turns, Started on First Kick. I Finally got it to Idle. With the enricher on, I had to set the Idle screw A little higher then I normally had it once it warmed up, turned the enricher off and Stayed on. I have some pictures of the process, let me know if you want to see them.
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  #50  
Old 5th October 2011
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The guitar string is a very good idea. They are real stiff in comparision to wire or other thing's to poke through the small passages. I, for one, would like to see the pictures.
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