Variations in VM20 Carburetor Ace 100/B/B+

[mycle_g]

I have an ACE100 B+ (Frame number A68261) my father was "restoring" before he passed. I am wondering if he didn't acquire an earlier carburetor.

I have a copy of the Hodaka 100-B Workshop Supplement Manual. In Figure 25C, it shows an air port in the air horn Inlet, on the left side (adjacent to the fuel line connector). Whereas the carburetor I have is like that shown in the complete workshop manual for the Ace 90. In that, the incoming air is in the top of the air horn inlet and travels at about 45 degrees to the slide (Fig. 82). There appears to be a port on the left side but it is plugged with a brass plug.

All the pictures I can find showing the 100B+ seem to have the former carburetor, with the air port on the side of air horn inlet.

Yet, all the specification sheets I have found for the ACE 90/100/100B say that they used the same VM20 SH 10.

Do I have the wrong carburetor for my B+? I'm thinking the VM20 SH 10 came in sub-variations.

[dirty_rat]

Every 20mm carb I have has the air port on the left side (see photos). Could you post a photo of your carb. and list the jets, needles, slide numbers etc. too see if anyone can identify what carb you have?

[Dale]

Well I can only add to the confusion! Hopefully someone with more experience will chime in with more history here.

There are certainly 2 different versions of the VM20 carburetor. I believe that the one with the 45 degree angle on it was the earlier of the two. When they changed, I have no idea. Did they both exist all the way to the B+?

What is really confusing is that the Ace 90 Workshop manual shows both versions just pages apart. This leads me to believe that the carb version was changed mid-Ace90 production. However, there is nothing listed on the update section of the workshop manual.

Here are my pictures:

[mycle_g]

Thank you.

I think I was successful uploading the image. Notice there is a port on the left side of the inlet but it has a brass plug. Instead the air passes through a port on the top of the inlet, up the 45 degree passage to the slide area.

My carburetor looks like the last one Dale posted.

[Dale]

I belive the one you show to be correct for the B+. As Dirty Rat mentioned, check all of the internals against the B+ specs.

[taber hodaka]

A side note. Hodaka changed the mixing chamber body, also called the carburetor body die casting. The change was on the ace 100, June 6th 1968 on engine 26120. The ace 90 and earlier engines the choke only worked with a closed throttle. Dirty_Rats pictures show the new version ----------------------- Clarence

[mycle_g]

I appreciate all the input.

The main jet is 90. The pilot jet is 25. The needle is 4F6. I could not see a way to pull the needle jet out. It looks like someone has tried. The casting's threaded stub that main jet screws into has a small portion chipped away. Almost like someone was trying to lift the brass part (pilot jet?) out with a small screwdriver.

Also, I notice that the brass that sticks up into the carburetor throat has an opening. And that opening is not in line with the air flow direction. It appears to be rotated about 45 degrees. Picture attached (rotated, ugh). Is that normal? I don't see it in the parts diagram so I figure it is pressed into the carburetor and the needle jet butts up against it.

Clarence, I saw reference to changing the mixing chamber change in the 100B workshop manual supplement. "...to eliminate starting carburetor activations on closed throttle body only." There it shows the carburetor with the side air port. That made me think that the 100B and 100B+ should have the other design.

Thank you all again. Michael.

[dirty_rat]

Sorry to say, but your carb seems to be somewhat out of kilter. Your second photo, the one of the carb's throat showing the top of the needle jet (the needle jet is the entire brass part that both sticks up into the throat and that the main jet screws into at the bottom) shows the spray bar (the part that sticks up into the throat), turned at an angle. The opening on the spray bar should be pointed straight toward the front of the carb. There is a pin in the carb body that aligns with a slot in the needle jet to keep these parts orientated properly. It looks like either the pin is missing or someone forced the needle jet into the body misaligned. The needle jet is removable, so if your's isn't, it was probably forced back together with the parts misaligned. To remove it, the needle jet goes up, out the same bore as the slide. Sometimes using a small soft drift (like a wood dowel or soft metal rod) can be used to gently tap the needle jet out. Don't use anything hard as it can easily deform the end of the jet and make it impossible to screw in your main jet.

[mycle_g]

Dang. The needle jet will not budge.

Appears I will be needing a different carburetor.

Thank you for all your help.

[viclioce]

What needle jet does it have in it now? Every version I see when I look up the Ace90/100 VM20 uses an N6 needle jet with a 4F6 needle. Victor

[dirty_rat]

To get the needle jet out, the main jet must be out (as it holds the needle jet in place). Then, you can usually use a soft drift to punch/tap it out (going from bottom, pushing it out through the slide bore).

[Bullfrog]

But that needle jet will have to be "clocked" to the proper position prior to any effort to tap it out. This situation may not be "savable".

[viclioce]

If you need a 20mm Mikuni carb for an Ace, I have a few in my tool box. I typically don’t sell them but consider trades for other parts with other Hodaka Club members. If you don’t have an item to trade, we can talk. I would be interested in a functional Ace 100 stator! Victor