carb reed help

[bronco70]

i just bought 95 combat engine code j which should be stock motor but carb and intake dont match stock
intake has reed vavles and rubber slip fit carb .i assume from road toad or later wombat since rubber intake
has oil injection port ?bike will start and run if i shoot fuel into back of carb .so i am cleaning carb and fuel tank
before i try running again,but i would like to know if i should remove reeds or not i dont see any extra holes in piston
so i dont know what the advantage of reeds would be unless piston and clyinder were set up for it.i think so parts were
just slapped on bike to sell the guy who owned bike died and his wife and kids are selling off his collection im thinking carb
came from toad since rear fender on my bike is also green but not sure he had tons of frames and parts .just want to know
what i should do? right now i have bike apart for cleaning and painting before going part together iwas going to put motor
and wheels on 100 frame but i think i am liking the 125 frame size better
thanks for any input

[viclioce]

If there is not porting for the reed valve it's pretty much useless. Your guess that it was just thrown together is a good one. The Model 95 is piston port, not reed valve, by design. So the porting in the cylinder is not there for the reed valve to work.

It is possible that the DPO couldn't find a flange mount carb to fit the Model 95 cylinder, and opted for the carb which is on there now because it was all they could find. So you could use the intake w/o the reeds and still get a functional carb & intake but it won't work as reed valve intake without the piston and cylinder porting. At least that's my understanding of it. I'm sure someone who knows more than I do about it will jump in!

If you want to configure it accurately, then go for a traditional Combat Wombat piston port configuration. If you want to get the adddd benefits of the reed valve, then consider acquiring a Super Combat head, cylinder & piston. But, you didn't say what size carb it has on it now either and may need to upgrade the carb as well for a proper running reed valve assembly. Vctor

[olddogs]

Take another look down that intake track. Could there be an extra set of windows in that cylinder? It may be that you have an entire later model 03 cylinder on the bike with the regular non reed CW piston. This is a likely swap as the 03 piston would not have worked, so they put it together with the parts on hand that didn't require machine work. Putting the 03 cylinder on is a direct bolt on for the CW with no extra work.
It is more than a little work to make a later model reed cage bolt onto a CW cylinder as the stud spacing is different. The reed manifold would show signs of hogging out the holes, or the cylinder would have had to come off and the studs moved. The 03 cylinder would have a flange mount exhaust manifold that the CW manifold and pipe would bolt directly to. The oil injection port tells you its from an late model setup, but not Super Combat or late Super Rat as these rubber intakes did not have oil ports in them. I would look further into it. You may just be able to add a SC piston and get a nice running mx bike or great trial rider.

[Bullfrog]

The next thing I want to know is whether or not there is still a "roof" or "ceiling" in the intake port. With the intake manifold removed, can you look "up" through the top of intake passage - or is there still a "ceiling" there? This bit of information will tell us whether or not the cylinder is "reed ready".

If the "ceiling" is still there (you CAN'T look up through an opening there) . . . then the cylinder is still "piston port" - and you'll need to remove the reeds (and the piston should not have holes on the intake side - other than the ONE rectangular "window" right in the center just below the ring).

If you CAN look up through the top of the intake passage (where the "ceiling" used to be), then the cylinder IS reed ready - and you can keep the reeds - BUT the piston must have holes on the intake side in order to run well.

Ed

[bronco70]

i will take a closer look at everthing tonight to see what i have and i will post back tonight or in the morning
but just to make sure im clear about cylinder head if i take off the intake that bolts on to head i want to see
if there an open port looking up towad top of clyinder head corrsect?

[Bill2001]

Take pics. Report back with pics.

[Bullfrog]

No, the intake manifold bolts to the cylinder - nothing bolts to the head. OK, the spark plug threads into the head.

The carb attaches to the intake manifold, which attaches to the cylinder.

Ed

[dcooke007]

All good advise.

But....I am beginning to question the traditional wisdom of drilling holes through the victory port to connect directly to the intake passage on the combat wombat cylinder. Seems to me with the horizontal slot at the top of the combat wombat piston and the matching blind victory port in the cylinder... a passage / port already exists. Just not connected directly to the intake tract.

With out the connecting holes drilled.... piston moving down bore after tdc, pressure starts to build in crankcase, intake port closes, transfer ports and victory port open and allow fuel air mix to flow into combustion chamber. Fuel air mix flowing through victory port flows under piston and through piston slot to victory port.

With cylinder intake port connecting holes drilled and traditional four 1/2 diameter holes drilled in piston intake skirt two paths exist to feed fuel air mix to the victory port. Not sure so many paths for flow is a good thing. Tubulance, velocity loss, lower possible crankcase pressure. Just thinking out loud.

Danny Cooke

[viclioce]

Remove your carb and the intake manifold from the rear of the cylinder for the inspection Ed is requesting. This is where you will, or will not, see the "ceiling." And yes, pics would help those giving you advise the ability to be more accurate. You do not have to pull the cylinder head for this inspection. Victor

[bronco70]

ok i see 2holes in clyinder afetr removing intake and it looks as if sombody sloted holes in
intake so it could fit the clyinder how should i proceed
thanks for all the input and sorry if i ofended any one calling clyinder head

[bronco70]

[Hydraulic Jack]

Your original question was whether you should remove the reeds, since it didn't appear at first blush that any modifications had been done to make the bike what was referred to otherwise as "reed ready." Answer, no, not necessarily.

If the cylinder and piston have been modified for reeds, you can't really take them out and expect it to run because the gamut of reed modifications make full use of the reed intake valve system, but make piston port function no longer possible. If your engine hasn't been modified as such other than sticking reeds on, you could take them out, but the question is whether you should or must. I don't think so. Even if you are not really making full use of the reed potential, still they are not (sorry Vic) about useless. Actually, the reeds will close any time intake pressure goes neutral or negative, such as when the piston starts back down from the top and before the piston skirt closes off the intake port. That brief period of time traps a bit of intake charge that would otherwise revert, and gives you a little bit more push than you would otherwise have. Could you do better with mods? Sure. But are they useless? No. Do they hurt anything? Not that I can think of.

Instead, if you don't have reed mods I would mod the cylinder to make full use of the reeds. You already have half the stuff needed to make a reed valve engine, and what is missing is just some Dremel work on the piston, and maybe, maybe some port work on the cylinder. The boost ports in the intake ceiling are nice, but not necessary to make reeds work. My Webco conversion doesn't have them and has worked fine for 40+ years. Boost porting was a later increase in modifications needed to make reeds work best, but they aren't critical at all. There are many modifications you can do to get another half ounce of power out of the engine, but they aren't critical by any means.

If you want a Combat Wombat purist bike, take them off. Your choice -- as long as there are in fact no mods to the intake other than the reed assembly. The reed manifold without reeds might not be the ideal piston port intake manifold (maybe a bit big volumetrically) but I would expect it to work. Or you could source a correct manifold and carb.

You mentioned the slightly slotted manifold mounting holes. Not a problem. They were needed to make a part fit your cylinder that was not intended to fit there. Hurts nothing.

[dcooke007]

Bronco,
The two holes drilled in the upper part of the intake tract is one step of modifying a combat wombat for a reed valve. With these two holes "open" you can not go back to a piston port arrangement. However, you plug those holes and then go back to piston port if desired. Personally I prefer the reed valve arrangement.

You definitely have a late model Hodaka reed assembly and carb that has been adapted to your cylinder. Either a Road Toad or 03 Wombat. Both use the same reed assembly but different carbs. Suggest measuring carb bore on engine side of carb to see what size it is. Some port blending needs to be performed as the reed valve port opening is larger than your cylinder intake opening.....port matching.

Need to see picture of intake skirt. Are there any holes drilled in the piston?

Danny Cooke

[bronco70]

i dont see any holes in piston also the carb has #26 stamped on side so i assume is a 26mm
another ? is everybody saying those 2 holes were not in factory clyinder??
they seem to line up with slot in piston almost perfect

[taber hodaka]

Well I kinda think the holes are stock but are they??? I have a cylinder with the same holes. Hopefully we will get the word shortly. ----------Clarence

[viclioce]

Jack. No need to apoologize to me. I said my knowledge was limited! And suggested those who knew more to jump in! So in his case, the Celing has been partially removed, as shown in the picture. What else does he need to make everything work effectively? Danny? Jack? Anyone? Bueller? LOL! Victor

[taber hodaka]

Well I kinda think the holes are stock but are they??? I have a cylinder with the same holes. Hopefully we will get the word shortly. ----------Clarence

[Hydraulic Jack]

For (probably) age related reasons I didn't note that the photo of the upper intake boost ports were on the OP's machine. Changes my answer slightly, but Danny already got there. You can't just take the reeds out without plugging the boost ports, which is easy to do with 24hr epoxy.

But that still leaves the "should you" question. I still think, and concur with Danny, that reeds beat piston port, and you should stay with what you have. I am not sure I would trust numbers stamped on a carb as indicative of size, but could be. Trust but verify. Simple to do, and you already have the carb off, so just look in the engine side of the carb and measure the diameter. Done. If it is a 26, or even a 28, that would be a good, mild mannered woods carb for your bike with reeds.

Next step is to modify the rear of the piston skirt to best advantage. There are diagrams on the Strictly Hodaka website, and I am sure others here could post a photo of a properly modified piston to go with reeds. Opening the piston skirt in the back will only enhance the whole reed experience.

No problem Vic. Putting on reeds but making no mods seems a bit pointless, but every bit helps. I have never known reed valve conversions, no matter how primitive, to be a disadvantage over piston port. Perhaps they wouldn't make much difference on a land speed record machine, but for general use, they rock. That's why they were used.

[matt glascock]

Great thread fellas. Good info all over the place here. Thank you!

[Bullfrog]

bronco70,

Here is your photo with confirmation notes that your cylinder has indeed been modified to work with reeds. It sort looks like it might be an "Enduro/Cross" reeded cylinder. Back in the day, PABATCO/Hodaka offered a "hop up" kit for the Combat Wombat. It had a stock Combat Wombat cylinder with simple 1/2" holes drilled through the bottom side of the "Victory Port" (which you haven't seen yet bronco) through the "ceiling" of the intake passage. Those holes allow the reed induction system to work well.
[url=http://s1165.photobucket.com/user/Bullf ... 2.jpg.html][

I'm sure no one was offended by the use of the word "head" when you meant "cylinder". I brought focus to it to be sure we were talking about the same thing. (Sometimes it is difficult to separate mis-use of mechanical names from typos).

What to do next? Add the holes to the piston, make sure everything else is ship-shape . . . and run the reeds.
Ed
PS: On the carb size questions, in case you are a metric measurement novice. 25.4mm equals 1 inch. So if the engine side of your carb has an inside diameter of just a hair over 1", it is a 26mm carb.

[Bullfrog]

. . . and . . . I don't see any "windows" (holes) in your piston. Here is a diagram from a tip sheet for reed valving the Combat Wombat. There are other hole patterns which are more popular with tuners these days - but this hole pattern worked fine wayeeeee back in the 1970's.


Ed

[bronco70]

so if my carb is a 26mm and i dont drill holes in piston am i ok with running as is ?
this is just going to be trail bike. also if anyone can tell me if the holes were drilled
by somebody and not stock how did the hole in piston work before since at bottom of
stroke it seems to line up perfect with the 2 holes in clyinder? this has me confused


thanks again to all for the help

[Bullfrog]

26mm carb is OK . . . IF (repeat IF) it is properly jetted. (a doubtful proposition considering the things we see).

The single rectangular window in the piston does its job by aligning with the "Victory Port" (which you haven't seen yet). When operating as a piston port engine, the "window" and the "Victory Port" allow some of the fuel/air charge to flow up past the wrist pin, across the under-side of the piston crown and through the "window" and "Victory Port" to transfer to the volume above the piston . . . where it gets compressed and fired.

But now that the engine is reeded and has the holes through the ceiling of the intake port -- an additional capability has been added to the engine. With the reed set-up, the engine can "draw in" fuel/air mix anytime the pressure inside the engine is lower than the ambient air pressure. Having the holes in the piston provides for increased flow area and flow time for that intake function to happen. So, while your engine will run in its current condition, it will run better with the addition of the holes in the piston.

Given the relatively "slap it together" situation exhibited by the engine as you found it, and what seems to be not a lot of experience with two-stroke engines on your part, I would highly recommend that you find someone who is experienced at tuning Mikuni carbs (specifically Mikuni round slide carbs) and have them check your jetting. If the jetting is lean, the engine will seize . . . and that will take a whole lot of the fun out of this adventure.
Ed

[bronco70]

again i thank you for the help bullfrog could you give input on recommended jet size to start with

[dcooke007]

I took some pics of an unmodified combat wombat cylinder and piston. Hopefully that will help.

Danny Cooke