Flabbergasted

[JackM]

OK, I had my Ace 100b+ all ready to fire up, but not being sure of my set-up, and not willing to sacrifice a brand new piston, I tore it all down and will start over. Can anyone explain to me, in laymans terms, the differences in pistons for these bikes? Mind now, that this bike was set up when I got it, using a reed valve, with a model 93 head and 24mm carb. The new piston that came with it has 4 holes on the intake side and two rings and the proper type for a 93 head. The new pistons that I've seen on the Hodaka websites show a piston with no holes for the super rat 93. I want to go back to the way it was originally. Stock. I need a new (or used) 92 head, piston kit, and 20mm carb. I don't see the 92 piston kits on the Hodaka sites. Am I being too wary in thinking the above setup may not work? The 4-holed piston is what has me confused. Thanks for any input. JackM

[Bullfrog]

If indeed you have a reed valve, then you NEED the piston with holes in the skirt to work with it.

The stock chrome tank Super Rat did not have a reed induction system, so the piston did not have holes in the skirt.

Ed

[JackM]

Ed, that's good news. If I can't come up with the parts in the near future to make it stock, I'll put it back together and give it a try. Should have ask about this before I took it apart. Thanks.

[racerclam]

why would you want to not have reeds ? Way more fun to ride way more power and trail and attitude friendly

Rich

[Hydraulic Jack]

I'm with Rich on that question. I started with an Ace 100B in 1971 and about the first modification was to change from piston port to reeds. Even if you don't get more power (which generally you will) reeds make the bike more rideable. Efficiency increases, response to throttle increases, ability to chug along slowly increases, resistance to stalling is improved. It is simply a far more efficient intake system. It isn't harder to tune, the reeds last a lifetime, and none of this decreases longevity of the cylinder and piston.

So the question really is "why"? If you are building a vintage presentation piece, going back to original spec makes sense. If you are building a riding machine, changing back does not make sense. Not to mention that leaving it be at this point cost you nothing, and changing back will cost money. Depending on whether the cylinder was ported for reeds, changing back could cost a serious chunk of the value of the entire bike to replace cylinder, head, intake, and piston, and possibly the carburetor and air cleaner assembly.

The choice is yours, of course, but curious folks will want to know.

[JackM]

Well, you guys have me convinced. Ill have to admit that its my ignorance about reed valve induction that made me think that going back to stock would be better. You see, I haven't owned/ridden any 2-strokes since my Husky days back in the '70s. Not much riding since then except my xr Hondas and even then, not recently. It's just been my hobby, mostly, in the years since I retired, to rescue older bikes that I can find locally, that would otherwise probably go in a junk pile. The problem is, after I fix them up, I tend to hang on to them, which is starting to limit my garage space. (kept 7 sold 1). I may not even ride this bike much, once I fix it up, but just the fact that I'm preserving it means a lot to me. Besides, it keeps me occupied and out of trouble. Thanks for your input. JackM

[JackM]

Since I began putting everything back together, I re-examined the carburetor to see how the original owner had it jetted. After looking through the various schematics, I discovered the carb is a VM-24, but it was off of a model 94 125 Wombat. The jetting was 220 main, 15 pilot and 215-04 for the nozzle. According to the schematics, they call for a 170 180 190 main, 15 pilot and vm2433a04 nozzle. Looks like the pilot jet and nozzle are correct, but what about the main jet? L to R pilot, nozzle, main.

[Dale]

Double check your standard jetting for the model 94 Wombats. There are two different setups depending on whether you have the type A or type B carb. The parts listing shows them by frame number.

If you indeed have the type B carb then the listed pilot is 25 and main is 160 with a BN8 nozzle.

[bobwhitman]

Um, Dale, remember he's working with a reeded cylinder, so standard setting are out the window. He'll need larger jetting.
Bob

[Bullfrog]

What Bob said.

Changing from piston-port to reed induction REQUIRES richer jetting (so published jetting specs for toaster tank Super Rats and Wombats are useless because they were piston port induction).
Ed

[JackM]

So Ed, what would you recommend? Apparently the above jetting with 220 main 15 pilot and 04 nozzle worked for the previous owner, but since I haven't had a chance to start it, due to the tank issues, would this still be a good starting point? I'll tell you, I had no idea that this motor/carb etc was such a conglomeration of different parts when I bought it. I do hope to get it running one day though. Thanks






















s o

[thrownchain]

Theoretically if it ran for the last owner it should run for you if you can get everything clean enuff to flow fuel. How well it runs is an entirely different idea. But if it will run you can tweek it from there.

[Bullfrog]

I simply don't have any notes regarding "ball park" jetting for the sort of set up you have . . . but . . . there are some foggy memories. BUT FIRST - one of the most important rules of jetting two strokes is: "Find rich, then work leaner . . . to 'just right' "

So, (from the foggy memories) 220 is a good starting place (it MAY be big enough to be rich). The 15 pilot jet is almost certainly wayeeee toooo leeeeeean. 35 or 40 would be a way better starting place.

You haven't mentioned the throttle valve (slide) cut-away number. You will likely end up needing a half step (.5) or even a full step richer than stock in a toaster tank Rat or Wombat. You also haven't mentioned the needle. A "rich" clip position is highly recommended for starting out. You might be able to stick with the O4 needle jet.

Look up Mikuni jetting procedures. The very first step is tuning/selecting the proper pilot jet - and the process will "tell" you if the 15 pilot is too lean. And since the whole pilot jet selection process happens at idle speed in the garage . . . it is relatively easy, safe for the engine and quick. But you have to get it "right" since the pilot jet delivers fuel at ALL throttle openings - and it, therefore, has an effect on proper jetting at ALL throttle openings.

Ed

[JackM]

Ed, the throttle valve is a 1.5 and the needle is a 4J13 with the clip in the middle setting. Both the throttle valve and needle numbers are consistent with an early framed model 94 wombat carb. I'll hunt for the Mikuni jetting procedures. Thanks for the advice. JaclM
P.S.
Standard specs for new vm24 carbs indicate a 210 main jet and 40 pilot jet while other settings remain the same, so I'll give those jets a try starting out.

[Hydraulic Jack]

From what I gather, you have a bike that you haven't personally run yet, but you are trying to sort out jetting numbers on a carb and intake system that isn't stock......

Several folks have mentioned that reed setups need richer jetting but no one really has a database for reference, probably because no one bothered to keep records. Not to mention that when Hodaka was still being sold and ridden regularly, there were no social media or internet means of sharing data. All this suggests that you simply have to start somewhere, and respond to what you find about how it runs. You already have a carburetor that arguably works on the bike you bought. So I have to ask, why are you worrying at this point about jetting? There is as much likelihood as not that what you already have is perfect. But until you run the bike, there isn't a way to know.

This isn't like building a 350 Chevy crate motor from a pick list. There are a number of possible combinations that will work, yours being one of them with the possible exception of the pilot jet, which I agree sounds a mite lean. But if it is, you will know about it as soon as you get it running, and it isn't likely to kill the bike even if it is on the lean side. Most serious risk occurs at high rpm where the pilot is no longer part of the equation. The 1.5 slide sounds okay. The needle sounds okay, and the main jet is close. So why not get it running first, then worry about tuning the carb as needed?

By the way, what is it that keeps it from running now? "Tank issues" covers a lot of ground. Besides, you can start and run the engine without a fuel tank. The bowl holds a couple of minutes work of idle time fuel, and a length of fuel line attached to the carb and tied to the backbone of the bike with the tank off will provide another minute or so. That's enough to find out if it starts, even if not enough to test ride it.

[JackM]

Jack, your first sentence is right on the button, but after finding out that the pilot jet is a 15, I'd at least change that since the carb was already off the bike. Plus, I agree with Ed that the 15 pilot jet may be too lean. The tank is clean inside now, so there's no problem with it. Chances are it will start and run with the original set-up, but at least I'll know now if I do need to re-jet it, I'll have a few extra jets around just in case. No hurry. Winter is coming and I won't get around to riding it until spring anyway. Thanks for your input.

[swcaudill]

Here is what I ended up with my early rat motor. I added the reed valve, the jetting that worked was 190/200 main, 25 pilot and needle clip on the top groove. The bike ran OK, but was too rich in the middle range. I gave up several times trying to get it right.
Finally I found out the needle and needle jet for the 93B was different. I bought those parts, installed them and promptly seized a piston. After fixing the damage I went up to a 440 MJ, needle clip in the middle and 30 pilot jet. Ended up with a 420 MJ, clip in the middle on the needle and 30 PJ. The bike lifts the front wheel with no clutch help. Idles good thru the entire throttle range.
Maybe previous owner had the same problem I did.
The reed valve your Hodaka article stated at least a 400 MJ, but mine would not run right until I changed the needle and needle jet.
Sorry, I don't know the part number for those items.

[Hydraulic Jack]

Working off of recollection only on this, the reason richer jets and needles are needed for reeds is the reduced intake reversion allowed by reeds. Air travels back and forth through a carburetor, even though we might think it only travels one direction. If you have ever watched a carburetor in action, there is a fog of fuel that stands or dances outside the carb when the engine is running. This is caused by air flow reversal associated with port timing overlap.

The air pulsing back and forth creates a signal of sorts in both directions, and causes fuel to flow into the venturi from flow in both directions. Piston port engines have a stronger back flow due to port overlap and a lack of anything other than the piston skirt to stop back flow, and get a sort of double dip per stroke. Reeds, however, respond much faster to the drop in pressure caused by piston movement and reduce greatly the amount of back flow across the needle jet area. Because with reeds there is now far less air flowing out and then back in, there is less fuel offered per stoke, all other things equal, because there is little if any double dipping. This requires more fuel to be delivered during the primary air flow, or first time around, so larger jets are needed to do the same job as before. This doesn't necessarily change the total fuel consumption per stroke, it just changes when the fuel needed is provided, i.e., when air is first drawn into the engine through the carb.

Perhaps someone with more technical experience in this area can confirm or clarify, but I think this is why reeds need larger jets.

[JackM]

Mr Caudill, that's some interesting info. Where did you read the article about using at least a 400 main jet? The last thing I want to do is seize a new piston. Thanks, JackM

[swcaudill]

I think it can be found on the Strictly Hodaka site. Maybe under articles concerning Hodaka. The Rat motor does have a larger intake manifold and probably transfer ports.
Sterling

[JackM]

Thanks, Sterling. I found an article about jetting in the Resonator, but it didn't mention anything about jet sizes or jetting with a reed valve motor. I guess it will be trial and error until I find the right combination. I just don't want to have to buy a lot of jets. BTW, I had a good buddy in the service from southern Jersey. He was from Salem, I believe.

[Bullfrog]

Sterling,

Were those typo's? 440? 420? Are you sure that shouldn't be 240 & 220? What size carb were you working with?

(When I get some time I'll try to find the "Reed This" publication.)

Ed

[Bullfrog]

PS: Yes, effective control of reverse flow through the carb is the main reason adding a reed system calls for richer jetting. The engine "sees" the same fuel/air ratio - but richer jets are required in order to deliver the "same" amount of fuel.
Ed

[swcaudill]

Jack,
I'm only about 20 minutes from Salem. Its a very old, founded in the 1700's, interesting place.
Sterling

[swcaudill]

Jack,
Found the article. Strictly Hodaka, FAQ, technical articles. Says 300 to 400 MJ. If you would like I'll send you some jets, just send them back when you find the right one. I'll check what I have. I should have from 200 to 440, the 420 is in my bike. Nice thing about those carbs, its easy to change the main jet.
Sterling