Combat Wombat Mystery

[drbridge]

I have a Model 95 that I have recently restored that has me completely puzzled and I am looking for help figuring out this mystery.
Symptom: Bike starts easy and idles perfect. It wont transition from idle to mid/top throttle unless choke is on. If choke is engaged it will ramp up to top end and runs very strong at mid to full throttle.
To me that would point to a carburation issue, but no matter what I do to the carb it runs the same.

History: engine has been completely rebuilt. New bearings, seals, rod kit piston and bore. Carburetor is brand new Hodaka Parts 28mm spicket mount conversion set up for Model 95 of which they have sold many with no issues. Gas cap vents correctly and exhaust and baffles have been cleaned and are clear. Timing has been double checked. Engine compression is 150psi. Motor has been pressure tested twice and when pressurized to 6psi takes 9 minutes to bleed off 1 pound. I am running freshly mixed ethanol free premium mixed 32:1

I have gone up one size on pilot jet and then up 2 sizes. I have Raised the needle all the way up and even one size bigger on main Jet. And of course. I have fiddled with the air adjustment screw. All done one change at a time. It runs the same no matter what I do. I talked to Terry about it and we decided that perhaps it is defective carb. He was nice enough to send me another brand new carb. It does the exact same thing.

I have had a lot of 2 strokes over the years and this is the fourth Hodaka I have restored and never had a bike act like this.
Lost and Looking for clues.

Doug

[olddogs]

I always start with the basics. Air goes in. Air goes out. In between is spark. Try running down the road with no air cleaner. Then run it with no pipe. I like to put a longer fuel line on and remove the carb and float bowl. Open the petcock. Is the petcock itself and needle and seat flowing enough fuel to keep the bowl full. When you lift the float does fuel stop flowing. Eliminate enough things and only the problem area will be left.

[viclioce]

I had a similar problem with a Wombat motor. The issue with mine was too big a pilot jet. It had a 40 pilot in it with a 24mm carb. When I changed the pilot back to a stock 25, the issue resolved itself!

I suspect you may have too small a pilot jet, or possibly main jet, in your 28mm carb. Here is the stock jetting info for a Combat Wombat with a 38mm carb. Double check everything! Hope this helps! Victor

[Dale]

Two new carburetors with the same result. You certainly have described checking and eliminating the right things. I run this same carb setup and it is great. Mine is actually set up a little leaner than how it is equipped but yours seems to already be too lean. Did your carbs come with new slides or are you using an existing slide? What size is it?

With it only pulling with the choke on indicates a lean condition. I think Olddogs has a good suggestion of checking for good fuel flow. Have you checked the petcock filters?

[drbridge]

This Carb I got from Hodaka parts came with the stock jetting that Victor describes.
The carb is an all new 28mm mikuni spicket (including slide) that comes with a flange adapter from Hodaka parts and is supposed to be set up for model 95. I know for sure that there is plenty of fuel to the carb and the float valve is not leaking. The motor is not loading up at all. The floats are adjusted paralell to the carb body and that is the only adjustment spec that I know for these carbs and they both came that way. I have gone up from a 25 pilot to a 27.5 and then a 30 I have not tried going leaner than stock because it already seems to lean. Also went up from the 190 main to a 200, although I don't think the main jet has a lot of influence to the part of the power band I am missing. It runs great at the top of the power band. Also, I am at near sea level for altitude.
Maybe the float level is too low and pilot system is having trouble picking up fuel. Maybe I will try raising the level tomorrow.
Thanks Guys.

[Bullfrog]

You say that pilot jet changes have no effect. That MAY mean that the pilot circuit PASSAGES are somehow plugged (in which case, jet changes would have no effect because the passages are not letting any thing flow thru). Check with squirts of carb cleaner while watching for flow at the pilot fuel delivery holes near the down-stream side of the slide.

Ed

[Bullfrog]

PS: 2nd carb having the same symptoms suggests that a double check for a plugged exhaust might be worthwhile.
Ed

[taber hodaka]

Has it ever been ported, exhaust port raised? That can really get things off kilter. How about a smaller thinner needle? Clarence

[viclioce]

Didn’t ask, but the intake isn’t reeded is it? Just asking to eliminate possibilities. I agree with Ed. There should be notable changes in how she runs as you increase the size of the pilot jet. If it isn’t, something may be effecting your pilot circuit. Victor

[drbridge]

So this morning I tried raising the fuel level in carb. Raised it quite a bit but was still not overflowing. Made no difference at all.
This is a piston port engine. As far as any porting work that had been done on it I could not say. Nothing appeared to be polished or anything but I did not take measurements so at this time that is an unknown factor. I will say though that the thing seems plenty fast when you get it wide open for a 125. I would think that if it were a plugged exhaust issue it would not run like that wide open and I have cleaned the spark arrestor. The spark arrestor has been partially cut away to make it breath better by PO and is no longer really a spark arrestor. it has the flame thrower exhaust. I have never ridden another model 95 so have nothing to compare it to.

Since nothing I do on the carb seems to make any difference I am starting to think again about other things, even though it does seem like a fuel issue since it does run with the choke on.
- I discovered that I do not have the right Spark plug in it. It calls for B9HS and I have a B8HS 10 from my model 94. I will probably order the B9HS tomorrow.
- the other thing that I did different on this bike is I mounted the condenser remotely. on my other bikes I did this and mounted them under the tank. On this one I mounted it under the seat for easier access and this required an extension wire to make it reach the black wire from coil. I used a Malory 400 condenser
-I checked the jets on the original carb that came with this bike and it had stock 25 pilot and 190 main in it. I don't know for a fact that this motor ever ran with this carb though.

i Will be leaving on a trip next week, so will have to put this project to rest for a couple of weeks. Out of ideas for now.

[olddogs]

I mentioned air cleaner and exhaust removal just so you could eliminate these from the equation. Removing the pipe completely eliminates puddled fuel and wasp nests. Exact carbs showing same symptom should eliminate this. Unless your making the same error on each. Needle retainer washer under spring? Gasket under carb cap seating when top tightened. Throttle cable long enough, Is the slide going all the way up and making a thunk when you release it.? Generally they shut down when a coil or condenser go bad and restart after cooling. I have had coils break down in cars and cause a phantom miss at load, but never heard of it on a bike. Swapping it would be an easy elimination. Since it starts and idles you have timing and spark. Spark plug wire or cap would not care what rpm it bogged down. We are assuming seals are in correctly and the piston is not in backwards. That's all I got in my bag of tricks.

[ossa95d]

Just a thought from previous experience. If a vent hose on the carburetor is plugged or crimped it can cause very erratic symptoms ranging from lean to rich.

[Dale]

The B8HS plug is just fine for the Combat Wombat. Actually recommended by Harry Taylor.
You said the pipe was a flame thrower style. Is it the correct cross over pipe for a model 95?

[taber hodaka]

Only two hodaka manuals cover carburetor tuning, that I know of. The ace 90 manual page 99. It shows the fuel flow route for choke and non choke. The pilot jet influence up to 1/8 throttle that combined with the slide cut away, only influenced up to a 1/4 throttle. The needle and needle jet covered the range of 1/4 to 3/4 throttle, this is the broadest range and the one that has the problem, The main jet covers 3/4 to wide open. This is covered on pages 99 - 108. The second official shop manual that covers carburetor tuning covers the Combat Wombat model 95 and includes the Wombats models 94 and 94A. This manuals carburetor tuning starts on page 62, it is the same as for the ace 90 air screw idle to 1/8 throttle. Slide cut away 1/8 to 1/4 throttle. Needle and needle jet 1/4 to 3/4 throttle and 3/4 to wide open the main jet. It also states it would be impossible to set the carburetor at the factory. Reading the manuals on this could be everybody"s starting point? ------Clarence

[drbridge]

You said the pipe was a flame thrower style. Is it the correct cross over pipe for a model 95?

This bike does have the correct through the frame early model 95 flame thrower pipe

[drbridge]

I mentioned air cleaner and exhaust removal just so you could eliminate these from the equation. Removing the pipe completely eliminates puddled fuel and wasp nests.

I have another pipe that has been roasted in the bonfire. It has small corrosion holes in header and needs repair. When I get back from my trip I will put it on and see what happens. Air filter is brand new.

[drbridge]

Slide cut away 1/8 to 1/4 throttle. ------Clarence

This is where the bike won't run. Starts and idles fine. As soon as you crack the throttle it wants to die. If you leave the choke on It will run and ramp up to 3/4 to full throttle and it runs strong there. Slide is 2.5 and that is what stock specs call for. The original carb also had 2.5 slide. However, it is a bigger body carb and the slide will not fit in the new carb.
The reason I did not use the original 28mm Mikuni is that it needed a rebuild and the float bowl is no good since the insert with the threads that the main jet holder screws in to is gone . By the time I purchased all the things the carb would need I was more than half way to to the price for the new one, so opted for new.

[Dale]

Well, I went back to my notes on my current carburetor settings. I have 2 Combat Wombats with OEM carbs and they both run the 2.5 slide. However, my track Combat Wombat, with the replacement carb setup, runs a richer 1.5 slide! In my notes, I was chasing an off idle lean condition as well. Hummm, I think this is your issue!!!

[drbridge]

Well, I went back to my notes on my current carburetor settings. I have 2 Combat Wombats with OEM carbs and they both run the 2.5 slide. However, my track Combat Wombat, with the replacement carb setup, runs a richer 1.5 slide! In my notes, I was chasing an off idle lean condition as well. Hummm, I think this is your issue!!!

This is encouraging news to have a direction to go in. It will be a couple of weeks before I can get to it. When I get back I will try to find one and try it out. I will report back with results.
Thanks for taking the time to look that up.

[Dale]

We will be anxious to hear your progress.
I do keep good notes but then have to remember to look at them!
My notes showed that I had also tested 2.0 and 1.0 slides. The 1.5 was the ticket.

[drbridge]

We will be anxious to hear your progress.
I do keep good notes but then have to remember to look at them!
My notes showed that I had also tested 2.0 and 1.0 slides. The 1.5 was the ticket.

I could only find a 2.0 so far so I ordered that. It should at least make some difference.

Does your track bike have modified porting and or a reed valve?

[Dale]

My track C/W is stock piston port. Also has the early flame thrower cross over pipe.

[taber hodaka]

In the racing years we cut the slide ourselves. Just made it happen. ----- Clarence

[Dale]

In the racing years we cut the slide ourselves. Just made it happen. ----- Clarence

Right, but at $25 to $50 per slide, I can not bring myself to start grinding on one! I have come across a number of used slides that have been modified though. I'm always checking for that when I am selecting one to use from my parts stash...

[taber hodaka]

But in the day, when we modified our race bike and the race was tomorrow, you did what you needed to do in that moment in time. I would not recommend it to any one. We were good tuners and to me Harry was among the very best, of the best. ------Clarence