Introduction and 94 Wombat carb question

[ncwLoren]

Hi everybody. I'm new here but not necessarily new to Hodakas. My habit has seemed to come and go over the years. I thought I was over it when I watched Greg Watkins and his wife pull out of my driveway in Wenatchee with their motorhome stuffed with a garage full of bikes and miscellaneous parts about 12 years ago. But old habits die hard. Five years ago I picked up an early 94 Wombat that was really pretty complete with very little rust. All in all a really nice starting point. The top end was bad however so I took it to Hodaka Days and Hodaka Dave took it to Missouri I think, and redid it. Which leads to my question. When I got the top end back I had already replaced the points and condenser as well as seals and bearings but it never ran well at all. Now I think what happened after reading on this forum is that I fried the condenser when I soldered it. New condenser and points and it seems to be running pretty well. After more reading I have determined that I have the bad carburetor. So... since it seems to be running ok is there a chance of damaging this pristine top end with this bad carb ? I will eventually replace it with a good one but I just am curious if it should be priority #1 or if it can wait.

Thanks if you were able to get through that, Loren

[hodakamax]

Welcome Loren, As I sold several Model 94 Wombats as a Hodaka dealer at that time, I'm not aware of any "bad' carbs, but I suppose I could be missing something as I sold my dealership shortly after that period. Only lean conditions could damage your new top end such as obstructed or too small of jet as far as carbs go. Actually, I'm going to use that carb on an ongoing trail bike project with a reed valve. Maybe the Gang knows more about this "bad' carb but for now that's my opinion.

Max

Hmm, after looking at the charts, I see that 94As had VM2400B carbs (which I have, I think, as there are no markings) instead of VM2400 on the 94. I wonder what the difference is? (Or if it's visual.) Here's the mock-up.

[hodakamax]

OK, a bit more info, I looks as though most of the changes addressed a leanness problem. From the charts I see a different body, throttle valve, jet needle, 160 to 180 main jet, different main nozzle and 15 to 25 pilot jet. I'd check the main jet and up it to a 180 or larger to start with to protect your new top end.. (This all started to be an easy answer!)

Maxie

[Dale]

There is indeed a "bad" carburetor. The early 94 Wombats were shipped with a carb that was not right for a 2-stroke motor. There is quite a bit of documentation on this including pictures. I will have to search for some examples. The bad carb is known as Type A while the correct carb is Type B.
The best way to tell is to look into the throat of the carb and observe the needle jet (nozzle). The Type A carb does not extend into the venturi of the carb while the Type B carb has the nozzle splash protruding up into the venturi.

[Dale]

Update: Check the Resonator March 2010 for details. Non-club members can use the search feature at the top of the forum page. Try searching for "pencil holder"

[hodakamax]

Thanks Dale, seems as though I learn something every day. Mine is indeed a "B" model.

Maxie

PS--I,m looking it up as we speak!

[Zyx]

If the carb you have isn't damaged or blocked with crud in passages too remote to see, I don't see how your carb or any carb could cause damage per se. The best carb, poorly tuned, can be a problem, and I would expect that regardless of the version of the carb you have, if the jets can be replaced, you can tune it. Unless, of course, someone here knows for a fact that correct jets won't fit into the type A carb.

So, you need to do some baseline investigating. Remove the carb and photograph it for future reference. Then take it apart, and write down the numbers on every jet, needle, and the slide, as you take them out. When you are done, you should have a lit including the main jet, needle jet, jet needle, pilot jet, starter circuit (assuming it will come out - I find them hard to remove after 40 years in service), and if you have one, the air jet. Basically, if it is removable, take it out, look for numbers, write down what you find.

Compare the list of jets and slide with the standard list for your model, which you can find on the Strictly Hodaka website. None of your jets should be leaner than stock unless or until you decide they need to be to run at your altitude. The slide and needle should be stock and so on. The idea is to start where Hodaka started. It doesn't guarantee a result, but gives you the best chance of getting where you need to be in the shortest time.

If all your parts are stock, as compared. To the stock build list, you aren't going to hurt your bike even if it doesn't run right. Rather, if everything is stock and it runs funky, you could have anything from bad gasoline to air leaks to a leaking crank seal. But before changing anything, you need to know what you have. I would start with the carb, but keep an open mind.

The other th it you can do without spending a bunch of time and money is check the plug color, and for that matter, the plug itself. Verify it is correct, and replace it if you want to start diagnosing issues of most any kind. Plugs foul easily, and sometimes it is hard to see just by looking at a plug, so get a few new ones, and start with a fresh plug before tuning the carb or making other changes. As with any scientific problem, isolate one variable at a time of your want to know what the problem is.

No Hodaka has to be perfect to run well. They have a very broad window of acceptable combinations, even though only one combination leads to optimal performance. First get it running nicely, then you can try to find perfect.

[hodakamax]

Ah, The Resonator, nice article from Ed. Take notes all you non-Hodaka Club people! Everyone with a Hodaka should join.
Thanks again Dale! (and Ed.)

Maxie

[Zyx]

Did a bit of research in the old posts on the question of the type A carb, but what I don't see is a discussion of replacing the needle jet in that carb. Are they pinned in place? Are they built with one-off jets that fit nothing else in the product line? If not, why would the carb be "bad" when it appears that it is just the needle jet that is weird? What else is going on that the type A is just a paper weight?

[hodakamax]

AZ, Ed's article in The Resonator said that the entire body needs to be replaced. I looked at the schematic and the list of parts below for a 94A on the SH site and it shows several changes including the body and jets which was helpful to me.

Max

[ncwLoren]

Thanks everyone for the replies. It seems the consensus is go ahead and use the type A carb that I have. The bike seems to be running okay. It is just so long since I've ridden a 125 or any for that matter any two stroke that my frame of reference is pretty much gone.

I am attempting to attach a photo that a friend took at Badrock that appeared in the East Oregonian. I wanted to go watch and when I picked him up his father who worked for the paper told him to take his camera. I should see if I can get the rest of the pics he took.

[Dale]

Loren,
No, I would not run the bike with the Type A carb. It will never run well over the full range of the throttle and it will have lean spots. At least that was my experience with that carb. I would not run it much without getting a replacement carb. Paul has replacemenths and I will say that the one that I purchased made a whole new bike out of my Wombat.
Dale

[Zyx]

I take it that no one has ever identified what it is about the early carbs that is the problem. I understand the needle jet didn't have a shroud. Frankly,mthat can be fixed if the jet comes out, even if other needle jets don't fit.

So what is wrong with the "body" that makes it not useable? Anyone have any "why" answers?

And, Loren, have you verified that you have the Type A carb, or is this an assumption?

[ncwLoren]

Yes I have verified that I have the bad carb. The pictures somewhere on this forum show the difference quite well. The frame number on my bike is c00195 and that's pretty early so it makes sense that I've got the bad one. The thing that's curious to me though is that the bike as near as I can tell is all original and the odometer has 1200 miles on it. So I would infer that it ran with that carb for that many miles.

[hodakamax]

AZ, I was just about to ask the same question; what was the problem? The reason I'm asking is that I took an early 94 out of the crate and drove it lotsa miles without any problems. I had a couple of racers at the time and didn't put any severe demands on the 94. Obviously something was wrong or all of the changes wouldn't have been made. Maybe under performance demands it was not ideal but at the time I had no complaints. After reading all these reports from credible people I think I would probably consider sizing the main jet up a bit just to be safe.

As Dale and Ed said the "B" model has the needle collar protruding into the venturi as shown.

Max

PS--Good discussion, I've learned a thing or two about VM2400 carbs that I didn't know.

[Zyx]

I understand the difference in the needle jet as described. Question is, why can't the old carb be successfully modified? Is there something that isn't remediable? Jets not available or whatever. There is no such thing as a "bad body" unless it is cast wrong. So, for those who have had these carbs, what is it about them that can't be changed?

It may be that 40 years ago it was cheaper just to change it out, but that doesn't address the issue its the older carb.

Can the jetting be changed in the type A carb, yes or no?

[Bullfrog]

The "A" type body also has different passages in the body than the proper "B" type carb body. The "A" type body is best used as a paper weight. If I had time to do it, I'd dig into both bodies to explain the full differences to inquiring minds . . . but I don't, so I won't.

Several expert tuners have tried and failed to make the "A" type (four stroke specific) carb run properly on a two stroke engine and I've not heard a success story out of the attempts. Did I mention that the "A" type carb body makes a fine paper weight?

Ed

[hodakamax]

I must say if I was designing an update for the "A" carb from a performance standpoint, I'd think about not taking up so much venturi area with the nozzle. Of course I'm not a carb designer but it does take up several percent of the intake area. Just an observation.

Max

PS--Ed, now what is it that you don't like about the "A" carb?

[Bullfrog]

Maxie:

You are well aligned with the thoughts of Harry Taylor about the shroud sticking up in the throat area of the carb . . . and HT did some tuning on that item. By trimming off the top of the shroud about 2mm at a time and testing, he found that some positive effects could result -- improved throttle response and increased peak hp in particular. Though the proper amount to trim varied across several machines - probably due to differences in all the things which normally have an influence on carb jetting (carb size, compression, porting, exhaust system, etc, etc.)

You have to be sort of dedicated to the proposition of tuning this specification, since it you can't simply put material back on the top of the shroud if you go too far. Still, 4 needle jets in your inventory would set you up for tuning to your specific situation. Sorry, but I have no information on the magnitude of the potential improvement.

Ed

[hodakamax]

Good report Ed, I suppose the "B" carb did what is was supposed to do for a street/trail bike and for race performance a bigger carb was fitted to the 95 CW model. (and my 94A based cross-country bike.)

Thanks,

Maxie

[racerclam]

Harry had taught me that cutting the needle jet down to 4mm should be a standard on all carbs , it really does crispen the off idle response , I do alot of carb mods and this is standard especially when using a UFO since it shrouds the needle jet so much and pulls in the main circuit way sooner . I even do 4 stroke carbs that way. My own 125 I cut down to 3mm it works great. Also Yamaha Banshee carbs I have seen do not have the needle jet nozzlle sticking up at all just like the type one 24 mm wombat

Rich

[Zyx]

In which case, perhaps the lack of a shroud on the type A isn't the problem.

Specifically, what makes a given carburetor a two-stroke versus a four-stroke unit? I am not aware of any design differences.

[Bullfrog]

I don't think anyone specifically said the lack of the shroud is the problem . . . it IS the easiest way to identify whether or not a given chrome tank Wombat carb is an "A" or a "B" type carb.

I've forgotten which is which - but one of the carbs is a "bleed type" and the other isn't.

Ed

[Zyx]

The only difference between a bleed typ needle jet and a primary needle jet are the bleed holes in the jet body. This is not a difference in the carburetor, just one of the jets. Even if the jets don't swap between a bleed and primary carb body, the jet itself can be changed back and forth by drilling or soldering the bleed holes. Yet, talented tuners tried and failed to get the type A carb to work? I try not to allow myself to be limited by the failure of others.

If the collective simply doesn't know what the differences are between type A and type B, just say so. But frankly, both primary and bleed styles of jetting are used on both two and four stroke machines, so that isn't it.

[Bullfrog]

Well then, we'll wait for your report on how to make the "A" type carb work properly on a Hodie. I'm going to work on other things.

Ed