M94 Transmission issues

[Hydraulic Jack]

Point gap sounds correct, or in the range anyway. You can always change the timing to match point gap, so the gap isn't critical as long as it is wide enough to allow coil saturation, which it should be. Actually, 0.38mm is on the upper end of the spec range, so dwell time should be okay.

The Wombat was rated for around 7,800 rpm with a 24mm Mikuni. Certainly one can get more than that, but at some point, any points actuated ignition can be driven past its ability to track the cam, just as valves can float if rpm is driven above what the valve springs can handle. Nothing mystical about Hodaka points, and they can float. The question here is whether they are or not. Since points float would be a question of inertia, any time rpm got to the point where the spring could no longer keep the cam follower on the cam, timing would go out the window, dwell time would drop, and spark would suffer. If this engine is pushing 9K or 10K, that's a whole lot of opening and closing for a simple set of points. There is more than one reason high rpm applications use CDI. Not saying that's what is going on here, just suggesting that it is possible given the symptoms.

[matt glascock]

I appreciate your insight on this Jack. I'm wondering which way I want to go with this bike. Part of me wants to see how much I can wring out of it. I agree that a CDI ignition is in order if that becomes the final plan and I've been very happy with the Penton PVL systems I'm currently running on the CW and SR. I'd like a piston port assault weapon for classic class eligibility. I like the bullet proofness of the CDI package. I replaced the points with the "racing" points as the spring did feel stiffer than the stock points and have regapped to 0.38mm. Hopefully that will allow the follower to hug the cam with more integrity at extremely high RPMs. I'd like to install the VM 28 but that might be a spring time event as weather and time will not provide for what I'm anticipating will be an epic jetting event. Funny, this started out as a basket case that was going to be a play bike but it turns out it has the makings for a fairly serious piston port racer. I also tossed the old filter and have a brand new UNI with UNI aerosol filter oil installed. I really appreciate you help with this bike Jack. I'll let you know how the high speed performance pans out. Thanks again.

[Bullfrog]

Matt,

Sorry it has taken me so long to return to the thread. Here are a few thoughts after reading all the comments (a time or two).
1. In your response to my first question - you clearly confirmed "loss of ground speed with no loss of RPM". Is there any chance you want to reconsider that statement? (um, can you tell that I'm guessing that may be a misinterpretation of what is really happening? )

2. On the concept of fuel starvation . . . causing the same symptom when you hit peak RPM in 2nd, 3rd, 4th and 5th (unkown in 1st). I have doubts that it is possible to starve on fuel in the itsy bit of time required to accelerate to full rpm in 2nd, then things are OK while accelerating in 3rd . . . and it starves again . . . repeat in 4th and again in 5th. That just doesn't seem reasonable for a simple fuel flow problem . . . regardless of how "pumped up" the engine is. However, since the problem happens at about the same RPM in every gear . . . mayhaps vibration at that high RPM point is causing a problem with either fuel or ignition. Have you checked engine mounts for cracks/breaks? Engine bolts? Does this bike have the head stay which came out on the later 94 models? (there was a reason for the head stay) All that having been said . . . I don't really think vibration is the problem either.

3. Point float could be the problem . . . but there were (are!) a bunch of high revving Hodies with standard points - both mags and total loss battery ignitions. So I have my doubts there too.

4. Would you re-analyze what happens when as you approach maximum RPM? Is it mayhaps more like the arm-stretching acceleration on this fire-breather just falls off so fast that it almost feels like you are being thrown forward? Does it REALLY slow down (ground speed), while engine RPM remains constant?

5. I've ridden some after-market pipes which had some strange characteristics . . . and which were not nearly as good as a stock Combat Wombat pipe in the dirt (for MY purposes). Some folks who designed pipes back in the day were happy with gobbies of power between 9,100 and 9,900 RPM . . . and would be happy to sell you one too. So far, I've seen nothing in this thread which would cause me to remove the pipe from being the prime suspect as the cause of what you are experiencing.

6. Too much oil on the air cleaner element? Nah, it would be running rich and wouldn't get you to the rev range where you are having problems.

my current 6 cents,

Ed

[racerclam]

Jack the 97 and 98 CDI limits revs to 12,000 RPM exactly

Rich

[matt glascock]

Hi Captain, I'll address point by point. 1) I'm doing a poor job of describing the symptoms. I might be able to better explain the sense of loss of ground speed perception by an attempt at analogy. Imaging riding in say 3rd gear and pouring on the coal. Revs climbing through the power band. All of the sudden, it feels as though the bike just slows suddenly such that your bodies inertia would slide you right up onto the tank if it was more severe. While this is happening, it doesn't seem like you closed the throttle. There might be a minimal loss of RPMs. Then if you back off the throttle for a short interval (a couple or three seconds) and roll it back on, the engine will rev back to the same spot and the process will repeat. 2) I don't spend enough time in 1st gear to have a good idea of peak engine performance. I usually hit the gate in second. Where it has happened in second is during loooong and steep hills and on deep sand chacane. I will check the engine mounts and do have one of those engine head stays on my streetable 94 which I can easily install. In fact I think I have another set in the parts stash. 3) I did install a set of "racing" points but have not had a chance to test for effect yet. I will report. 4) Good point. See my response to #1. This may be result of a sudden decrease in acceleration more so than slowing rapidly from peak velocity which could be perceived similarly on the arm-o-meter. I have to confess that there is a lot going on at this point in the performance curve most of which is focused on not killing myself so I may not be giving the best account, but the sensation is like hitting a compression release/engine braking action with a minimal change in engine RPMs. 5) I might try and figure a way to mount up my CW pipe for testing purposes. My only other option is a stock 94 pipe but my impression is that they were not necessarily designed to performance - especially at the 9K+ rev level. I also have a spare Torque Engineering "Competition Only" I might cobble together a mounting system for. 6) I have replaced the air filter with a new UNI with UNI aerosol oil just to take that issue definitively out of the mix. If time (and weather - currently 19F- cooperate, I am going to try to make a few speed runs this weekend in front of a video camera so everyone can see and HEAR what my feeble power to describe with text ain't cuttin'. Thanks Captain.

[Hydraulic Jack]

Jack the 97 and 98 CDI limits revs to 12,000 RPM exactly

Rich

Good to know. Not that many of us spend any time at 12K, but still. That's probably at or above the engineering limit of the piston and crank assembly in stock trim anyway. Would you have any input on the rpm limitations, if any, of the magneto based system with or without the flywheel?

[Hydraulic Jack]

Matt,

The more you describe the symptoms, the more I tend to doubt it is a fuel issue, simply because of the repeatability, but I wouldn't take any ideas off the table yet. It could, I suppose, be a combination of low fuel level in the bowl and frothing from high rpm vibration. But the way it just hits a wall at a given rpm, and you can back away from it and go right back and get the same reaction is a substantial clue.

It sounds to me more than just reaching a top rpm or a flat power curve. I would expect those things to be less abrupt. Now that you have changed some parts, take it for a run and let us know if that parts swap changed the situation.

[matt glascock]

Will do Jack. Somewhere up in the rafters above the Hodaka Test Kitchen I have an old Airguide 2-stroke tach. I'm going to do a temp install to get more objective performance data. My CW will spin just under 11K and my ear tach says this one does 9 and change but maybe a bit more real data can help sort this out. Thanks again!

[Bullfrog]

I certainly agree with Hydraulic that backing off and coming right back to the same symptom is a substantial clue. But a clue to what . . . is still a bit of a mystery.
Ed

[matt glascock]

I'm going to get you some real data to crunch, Captain. What I'd really like to do is audio/video record a few speed runs and will do so if the weather holds out. As Always, thank you Captain.

[racerclam]

Jack I have no info on rpm limitations of a normal Magneto system since I havnt run one in years and had no tach when I did , but I know my Hodaka flat tracker would scream like crazy and never miss a beat even when I went to no flywheel total loss system , the only problem is that with no flywheel to help absorb shock it broke two crankshafts off at the clutch so then went back to a shaved down flywheel . And Matt you can buy a Trail tech inductive tach forabout $40 that will tell you the highest RPM that you had during its last run cycle as soon as you shut the engine down , its handy since you don't have to stare at the tach while riding

[matt glascock]

Great suggestion, Rich.That looks a lot sleeker that the enormous Airguide. Its about the size and twice the weight of a standard Wombat Speedo. What I really like is the recording feature so I can concentrate on the machine and taking care of biz thereon. Nice. Apparently it does double duty as an engine run time hour meter. (There's probably a slicker name for that. ). Thanks for hipping me to it.

[racerclam]

your welcome

Rich

[matt glascock]

Well...39 deg F today. Took a handful of main jets out to the track. Then it started to drizzle. Now 19 deg F with windchill. So, I said skrew it and went woods riding. Tight course. Blipped the throttle a few times but no room to get on it. Response was great on these sporadic hits but no room to push the envelope. The results of the racing point set and air filter foam swap remain to be seen. Quick question - would there be any advantage to switching to iridium plugs? This bike at least flirts with 10K and probably kisses it.

[racerclam]

Iridium plus are always a good thing with a concentrate spark higher rpm and higher cylinder pressures have less affect on spark delivery. But I'm sure it wont fix your issue . The good news is you can put a blower on it and still get the spark to jump 8o)

Rich

[taber hodaka]

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

[matt glascock]

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

[Hydraulic Jack]

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.

[matt glascock]

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.

[Hydraulic Jack]

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.

[matt glascock]

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.

[Bullfrog]

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

[Hydraulic Jack]

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.

[matt glascock]

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

[matt glascock]

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.