The Hodaka Club Forum

How much low end torque do you have? You could have bom spec porting that would fall off completely. ----------Clarence

Hi Clarence. Low end grunt is not anything to write home about. In fact, it is not as strong as the low end pull of my bone stock Wombat and compared to the reed valve induction Combat Wombat, essentially non-existent. This bike was owned and set up by a man who was a dedicated desert racer and was ported for same. Unfortunately, the port mapping specs were lost in the shuffle and the previous owner can't communicate following a stroke a few years ago. I bought the bike from his son as he was tasked with dispositioning his father's posessions. I would consider trying to take some measurements, but it has such an awesome piston/cylinder right now I can't bring myself to tear it down. That is probably overly superstitious, but I believe that a piston/cylinder combo that works this well is just this side of magical. When the time comes for a new top end, I'd like to send the entire engine to Rich for a detailed exam and possibly refinement.

Rich, thanks for the advice. I'll stick with regular NGK plugs. That's what it was tuned for. Why change now? I have the tach ordered. Should be here tomorrow. Weather permitting, I should be able to accrue some performance data.

PS - Rich, maybe I'll pull the Hypercharger off my Sportster, slap it on the Wombat, and check your theory

Using either a standard or iridium plug isn't a tuning choice. They are both spark plugs, and basically fungible. There are benefits to using the rare metal plug that have more to do with spark stability at high rpm due to lower voltage demands. Since you say yours runs on the high side for an iron bore, the iridium plug is simply an upgrade in the spark plug department, not something that would demand a change in jetting. If it runs fine with a standard plug, it isn't a mandatory change issue, just a matter of money and preference. Both plugs will foul in the wrong environment, either will give you good spark under normal circumstances, and the iridium will tend to resist blow out at high pressure. I don't think spark blow out is the issue with your engine, but at this point, who knows.

Hi Jack, I was unclear with regard to rejetting. I brought richer main jets along because the air temperature was approximately 40 degrees F colder that the last time the jetting was set and not with regard to changing to HIX plugs. I run them is my bikes with PVL ignitions but was merely wondering if there would be a performance advantage with this Wombat set-up. I'm hoping for a decent day before the show flies but for tight woods riding, the racing points performed well.

The advantage would be slight. It is a cost/benefit question. I don't think it will cure whatever is going on. But I have never had a time when changing plug styles within the same family and heat range caused a need to retune.

OK, back to this. For whatever reason, last Saturday gave us temps in the low 60's F. Not bad for December in Iowa. All day riding. Heaven!! Anyway, I installed the tach. The racing points and new air cleaner were previously installed. I also cooked and repacked the silencer insert. Additionally, I replaced the in line fuel filter and cut off the little screen stand pipe filters off the pet cocks and increased MJ to 240. Actual improvement appreciated. There is no 'fall off" as I previously described. The motor spins to 10,200 RPM at WOT in 3rd gear. Now though, it gets there and STAYS there. It definitely hits the "wall" but doesn't bounce off it. I'm thinking of changing up to a VM28 just to try and wring an extra pony or three out of the mill, but then, the other 99.9% of what's left of my brain screams 'Are you a moron? Don't mess. The bike rips!' I'm not sure which adjustment did the trick, and at this point, who really cares? The trick was turned and I thank you all you your input.

Am I getting this right? You are grumbling 'cuz your engine won't rev past 10,200RPM . . . and its a dirt bike, not a road racer?

Ed

The problem now as I understand it is that when you release all throttle from WOT the engine will not idle back down, but hangs there at high rpm.

This is probably the pilot jet being too lean. In think Harry Taylor did a write up on the question years back.

Hi Captain. I placed an addendum to my last post where I realized how absurd it is to be Bi+ching about this set-up. Its really breathtaking listening to the motor work. Now, I'm thinking about this Wombat in the Southern California desert ripping past a tire fire pinned in 5th gear

Hi Jack, I wasn't clear. There is no problem. I was referring to the fact that it will now sustain max RPM with no perceived fall off of power. It just keeps pulling. The motor shuts down fine. If anything, I have to blip the throttle a bit at idle which is no biggie. I'm used to it with my 78.5 RM250s. They don't idle worth a crap.

I thought I might be pushing it to use the b_ _ ch word in my previous post, so I went with "grumbling". But now you know what I really meant.

Just out of curiousity, where in the heck on the RPM band is your shift point??

Ed

You're a much classier person than me, Captain. In this case, I thought it was the only worthy verb option to describe a guy "fussing" about a 10K+ bike he bought as a "play bike", and for about a nickel per RPM. Shifting at 7200 - 7400K. BTW, I did check the motor mounts. All A-OK.

Glad to hear that the problem has been rectified. I guess we can assume that one or all of the changes that you made collectively addressed the issue, but in summary it seems that the problem was either fuel delivery (addressed by the mods that you made) or point float (addressed by the racing points). Doesn't matter at this point as long as it's running great!

Thanks Pop. You are correct in that I didn't adhere to any scientific process in the set-up. A 60 degree day in December means seat time and more seat time. I would not be surprised if all maneuvers played at least a bit part role in sorting out the fade issue. Its one of those situation where I'm happy to accept success without question to the method . Thanks for your input.

10,200 rpm from an iron bore Wombat isnt science, its amazing. As far as lacking low end, I am not surprised given the top end. But you might be able to have both worlds. I would contact Rich Gagnon at Rich's Taylor'd Porting and discuss a Venturi vaned 28mm Mikuni. He posts here as Racerclam. Might very well get some of your low end grunt back as well as a solid high end. The Venturi vanes do work when using a larger carb on a ported cylinder. We didn't know this stuff back in the Hodaka days, but we do now. Might also ask about torque grooves on the cylinder head. (Edited. Not the piston. Pop is right, and I wasn't thinking. Must have been late.)

Jack, I have seen torque grooves on a head but never on a piston. Is that really a thing or did your typing fingers get ahead of your thoughts?

Jack, I do have a VM 28 (no vanes). Maybe Rich could fabricate and install the vanes. I'm a bit concerned about running lean right now although if that was the case I would likely have blown the motor by now. I also considered a VM32 but it runs well with a stock carb. The 28 is probably the way to go. I'll look into it.

Rich can modify your carb, and I think he usually works with your equipment rather than starting with an off the shelf carburetor. He has a website showing his many services. Note, carb vanes look simple, but they aren't. It is easy to do wrong, and not easy to do right. It would be nice if this were an inexpensive modification, but it takes literally hours (all day or more) to do carb vanes. On the other hand, they work. Largest benefit would be getting back bottom and mid range torque while not affecting top end.

If you are worrying about running lean, you could consider an Intelajet, which allows adjustment of main jet mixture while running. Find out if they can be mounted on the VM28 but I think they can.

thanks jack for the vote of confidence. I do mods to existing carbs as well as new. Most will go to bigger carbs since the dividers make a big carb behave small. Intelajet can be used on any carb. AS for venture dividers there has even been gain in top end , verified on dyno , one of my road race customers with RD400 had noticeable improvement in out of the corner acceleration and when he ran on dyno had a one hp gain all the way up

Rich

Perhaps I should have said the dividers will not sacrifice anything on the top end (I don't doubt the gain but don't have a dyno).

What I do know is that the dividers on a stock 32mm Mikuni on a stock Super Combat took an MX bike with no guts in the mid range, unrideable in the woods, and made it a terrific woods bike that will also pull third gear berm shots in MX without fanning the clutch, with no other modifications to the engine. I can't say that the low to mid range is more than your average woods bike would have, but it is now totally usable, pulls hills without screaming, and does what it needs to do. Wish I had this set up back in the early 70's when I was racing Hare and Hound. The Bad Rock trail ride at Hodaka Days was no problem at all with no changes to gearing or jetting, even though I was set up for the MX event.

Hey Rich and Jack, This carb mod really interests me. The big question now would be if the VM28 or VM32 would be the best candidate. Mind you, it is currently running a stock carb with a 240 MJ. This bike performed well in a hare scrambles this fall but looking back, I made all my hay on the MX track integrated into the course and the woods riding was relatively open including about a half mile of sand along a river bank where the bike was right at home and just flew. I can predict that the current set-up would totally suck, right up until the motor explodes, on a tight/hilly single track course which is pretty standard around these parts. Thoughts? Thanks fellas!

Rich will have a better idea of which carb will best fit your needs. My thoughts are that the 28 might do everything you want. If I was faced with constant tight stuff, hills and sand, I would probably drop back to an 03 cylinder mildly ported with the 28 Mikuni to try to get more midrange and low end power, even if I gave up some on top. Since you have the 28, I would start with that.

If you get to the point of pulling the cylinder, map out your porting. Use a rolled up sheet of paper and trace your port openings with your finger. This will leave impressions in the paper. Then firm up the impressions on the paper with a pencil or pen. Beats trying to measure things down inside.

Something else that will help with mid range power would be reed valves.

Agreed Reeds are always a good thing as long as your allowed them in your class. I do have Reed to fit the Iron wombat cylinder. And yes an o3 cylinder would be better , but I can do much to help the Iron cylinder. I would Like to know if anything is done to your currant cylinder and what you are using for a pipe?

Rich

Hi Guys, That's what I was thinking, Jack. The 28 would be my guess as it runs well with the 26. I think adding a reed cage would give me more usable power. Most likely, the bike will be used for enduro/hare scrambles unless I completely redo the suspension although a couple MX tracks I run basically use a supercross style track bypassing the do-or-die doubles/triples, rhythm section, etc. I have a piston port CW for classic class, but since there are no AHRMA events around here, I mostly race in open class vintage events around here where year and displacement are the only qualifying features. Rich, the jug was modified. The owner of the bike had it set up for desert racing - H&H and some hare scrambles according to his son. He PO can no longer talk because of a stroke. His son who sold me the bike told me it was ported, but the PO did his own work the build/spec sheets are long gone. Just looking with an untrained eye, The exhaust posts were raised and the transfer ports have had work as well. The cylinder looks like it has maybe one overbore left as the piston crown is stamped +6. The pipe is manufactured by "JR Powerpipes" which is a long defunct SoCal power house that I can not find any information on. It looks like your typical vintage aftermarket performance pipe. It has a nearly worthless glass pack silencer. I can easily map out the dimensions if you'd like. Thanks for all the help/input guys!!