Hodaka experts needed

[budpat105]

I race a stock Combat Wombat. I rebuilt the motor 9 races ago. After reading here and watching videos I realize I am not an expert motor builder. But It has been a good motor. It has developed a miss at high RPM's so I have been short shifting to avoid this. I replaced points and condenser, set timing with a timing light, did not change. Second problem- today it stared to kinda jump into gear when I shifted, now I push down for first-nothing, pull up and shifts fine.Where did first go? Where would be a good place to start checking? Thanks bud

[taber hodaka]

The inside left control shift spring has mushroomed and will not let the control shaft recess into the counter shaft. Any hard shifting without clutch can do this. Me $.02 worth --------------Clarence

[matt glascock]

If the bike is truly stock (no porting mods, stock carb and induction, transmission gearing, etc), what main jet are you running? Have you made any jetting runs to get a read on the plug? Could you be a little more specific in describing the high RPM "miss"? That would help in zeroing in on the issue.

[Bullfrog]

Clarence may have nailed it on the shifting . . . or it could be that the spring on the right side of the ball receiver has collapsed, so now it can't "push" the ball receiver far enough to the left to engage 1st gear. Question - do you "snick" your shifts . . . or stomp 'em? Is the shifter mechanism in good condition?

Like Matt, I need more information on the "miss at high RPM's" - his questions were good ones.
Ed

[budpat105]

Okay, I do try to "snick shift" but have stomped also so I will install new springs and see where that goes. The motor porting is stock,no reed valve, stock bottom end. I did put a spigot mount 28mm carb from Hodaka parts before season. It has stock jetting, I have run a 190 main jet also. Just feels like it cutting out when at high RPM's.

[Dale]

My track Combat Wombat is notorious for breaking up at full throttle (not a miss, but richness). I also run the 28mm spigot carb and typically run a 175 main rather than the original 190. I also run a slightly larger pilot jet 27.5 or 30 rather than the original 25 (it feels and sounds better on hard decelerations).

If you pull the exhaust pipe tip, does it make any difference?

What plug are you running? Per Hodaka legends "the stock B9HS is too cold and B8HS is a better choice for the Combat Wombat." I have found this to be the best advice for my Combat Wombat.

My last question is what oil are you treating your air filter element with? I use Bel-Ray and it is exceptionally thick. I do remove all of the excess oil, but I believe that it does contribute to my bike running on the rich side.

Just my thoughts...

[matt glascock]

I too have had difficulty expressing various behaviors when posing questions on this forum because the real experts here are met with the challenge of long-range diagnosis and can base their advice solely upon the symptoms we describe. Having said that, and with all due respect, "cutting out" at high RPMs doesn't add much light to the situation. How does the bike idle and take off from idle? Does it accelerate smoothly? Remember, the pilot jet supplies fuel throughout the throttle range so before any tuning efforts are undertaken, a good carb cleaning is the first move. Not a "squirt a little carb cleaner here and there" cleaning, but rather a complete disassembly, inspection, confirmation of the JN, NJ, MJ, PJ sizes and integrity, replacement of any worn parts, and chasing all passages (including the pilot circuit) with fine copper wire and carb cleaner. After that, its time for some speed runs to take a plug reading or three. My hope is that a bit of crud in the pilot circuit may be disallowing the last bit of fuel delivery at WOT, but remember, there is little - make that no - significant overrev on a nonpumped up CW motor. How does it run in the midst of the power band?

[budpat105]

You guys ask tough questions, but I know I am going to replace springs on control shaft, first time in bike! Then I will do complete carb teardown, cleaning and jet verification.I'm also going to check exhaust pipe. I will do some plug chops (B8HS)and will get back with you then. Thank you!

[budpat105]

I messed with the combat today, cleaned air filters and tried 2 different air filter oils, no change. Put a 190 jet in it, no change. Did a plug chop, looked good. Tried a 180,190,200 and 210 jet. Same with all.Still sounds like it's breaking up at high RPM and I could go more. Checked exhaust and its open, I do have a silencer made up that replaced the spark arrester. Put the original flange style carb bad on, still does it but seems to rev higher before it happens(just a seat of pants feeling). Maybe just expecting to much from the 125? Maybe coil? crank not true? Any help is welcome. Thanks

[Bullfrog]

If changing the main jet 4 sizes makes no difference . . . well actually, that seems hard to believe. There should (must?) be some difference between a 210 and a 180.

Um, my own CW (piston port, stock carb with vanes at half throttle, custom expansion chamber) jetted in with a 170 at about 1,000 feet of elevation.
Ed

[budpat105]

Ok, I may have misled you with my "still the same" I did not do a plug chop with all the jets, I just tried bigger jets to see if it would help with the "breaking up". I will get more plugs this week and start with a 190 and work down to see what happens. I am at about 650 feet of elevation. You didn't hit on the crank or coil, I just put that out there for bait to get any thoughts. Are you running stock ignition? Looks Like I am just chasing carb settings, I will keep trying. Thanks

[Bullfrog]

Yup, standard points ignition. But if you didn't feel/hear something different between a 210 and a 180 . . . well, something is just wrong.

- overly oiled air cleaner foam
- weakened ignition (dirty/burned points, failing condenser, other)
- ignition timing not set to spec
- exhaust system problem (partial plug)
- carb problem - ? hard/cracked O-ring at bottom end of needle jet?

Ed

[olddogs]

When you can keep going up on main jet size and it makes no difference in high rpm performance, you have reached the capacity of the needle jet and the needle to flow fuel. With these 50 year old bikes it is sometimes hard to tell how many different carbs were used by someone to make a whole one. Start by confirming these 2 items. Guys hate tuning with these because needle jets and needles are much more expensive and main jets are just plain easier to understand than needle tapers. Check that all these numbers are stock CW so you aren't on a wild goose chase. I raced a Super Combat for years and the needle jet and needle taper is where the real performance changes were found. Not the same carb as a non reed CW, but some things are constant with Mikuni carbs.

[Bullfrog]

Excellent point Olddogs! However, since the problem "developed" while the machine was in use, it seems like something else is probably the root of the fault.

IF the carb is indeed still fully stock, the needle jet is an O4 and the needle is a 5EJ13 (info provided for reference) - and those specs will certainly flow well enough to show a difference between a 180 and a 210 main jet. But, like Olddogs says, confirming what is actually in the carb is a good idea.
Ed

[olddogs]

I see this now that I read the post again. The variables from the point the bike started running different than before are a rebuild with new rings and seals?? and 9 additional races. Since it is a consistent miss regardless of carb alterations, I would also try using a different coil with a new plug cap. Corrosion or frayed wires where the plug cap screws into the coil lead could cause spark scattering and continuity breakdown as rpms get beyond the connections ability to handle the resistance. I have chased that demon more than once. It may sound silly, but also make sure if the plug cap requires the top be left on the plug, it is in place.

Checking that the engine itself, and the coil mounts are grounded well to the frame should also be looked at. If it were a 4 stroke I would suspect weakened valve springs are causing valve float. In a 2 stroke I would take a good look at ignition system if the carb has been ruled out.

[budpat105]

Great thoughts, been busy and haven't worked on bike. I will keep you informed. You are "teaching me how to fish" thanks

[budpat105]

Back with more information, I put new shifting springs in my bike (that was a major victory for me), new clutch plates and did the "blueprinting" of the clutch. Assembled it on a drill press so I could make it work. I never knew a Hodaka clutch could work this good.Now back to the miss- I was convinced it was ignition since I had changed so many jets. Swapped coil, new sparkplug cap, redid all wire connections, unhooked kill switch - all no change. Had a experienced friend listen to it- he said "your way rich" start dropping your needle, it that doesn't work put needle back to center and install next smaller main jet, continue until fixed- Well 2 sizes down and 2 clips up and this bike is back to life! Plug chop looks good. I think I can answer Ed now, how can there be no change on all of those jets- all were tooo rich, I can't believe mow much a difference every change made when I was getting close(the needle really impressed me)- you all are a great help and I not on got bike fixed but have learnt soo much in the process. thank you all!