Gears Not Engaging!!!

[Bullfrog]

OK! 27.5mm slide OD makes it NOT a 28mm carb from a Combat Wombat. Combat Wombat 28mm carb slide is about 31.5mm OD.

So it appears to be confirmed that you have a 24mm carb.

Can't discuss further right now . . . I've got places to be. Will be back on line later.

Ed

[viclioce]

Thanks Ed! I think it's a VM2400 from a model 93 Ace 100 Super Rat. The picture for this model matches up and it has the same shape bowl gasket too. At least now I know what bowl gaskets to order!!! ; D Victor

[rlkarren]

Wombat specs at sea level call for:

Pilot 25
Main 140 or 160
Slide 2.5
Needle Jet N-8
Needle 4E1

I am not an expert on jetting, but I have learned a lot by reading. One of those things I learned is to follow the instructions in the manual closely. To summarize, tune the pilot first. Then tune the Main, then adjust the needle position to fine tune. Another important factor I learned was that in all throttle ranges, the pilot jet is delivering fuel. Which makes tuning the pilot critically important. I would suggest that a 40 Pilot is way too big at 7000 ft. I'm at 4000 ft and still use the standard pilot. But you also don't have a stock Wombat engine. If it were me, I would back up and start from the beginning with a smaller pilot. Everything else you have indicates a stock setup for the 24mm carb.

When I saw your photo, I thought it was a 24mm Carb. Looks just like my Super Rat carbs. But I wasn't sure so I kept silent.

$0.02

Roger

[admin]

Service Bulletin from Recreational Sports July 10th 1974 titled Altitude Jetting Guidelines
By Jim Noble service MGR Recreational Sports Idaho Fall ID

[viclioce]

So this is a VM2400 carb. This chart doesn't say anything about the pilot jet. Should I assume still a 25 pilot jet and change the main to a 170 or should I assume the 140 was sea level and go down to the 100 main?

These figures don't tell me enough because nothing on this bike motor is original to anything. And I don't even have a 25 pilot jet. A 30 is the smallest I think I have. I will dig around some more and report back. But I'm thinking of trying a 30 pilot, a 100 or 95 main and my current needle at position 2 with my 2.5 slide. Does this sound like it might get me close?

Also, can you tell me how to move the choke lever so it runs in the front of the carb like stock? It currently is on the right side and my hand hits the exhaust gong in to set & release the choke. Not bad when the pipe is cold, but hot...... : ) Victor

[Pep]

Victor, I'm coming in on the thread late, but here's my 2 cents.
Tune the carb following typical Mikuni protocol (easy to find on the internet). Short story: start with the pilot jet FIRST. Warm engine, tune pilot using the idle and air adjustment - that will dictate what size jet to use. Do this first, no point fiddling with the other stuff until this is right.
Then work your way through the other jets.

I will say that if the bike runs nicely until it gets warm or hot, you may have ignition issues (namely, condenser) clouding the issue.
As for high altitude tuning (in my experience hauling Hodakas from Texas to Colorado) all you really need to do is change out the main, maybe adjust the needle a little. Seems like the rule of thumb was a change for every 4,000 feet. Unless your racing, there's not a lot of fine tuning to do for altitude shifts.

I've had a sea level Combat Wombat and Dirt Squirt happily pull along through 12,000 ft passes with very minor jet changes once we got to CO.
Many of us have hybrid bikes with mixed engine, carbs, pipes, ignitions, etc. They all vary a little when it comes to jetting. Remember that all the parts of the carb work in concert (lots of overlap, lots of ways to achieve the same end with different combos of jets).

One other tip I have (from running in circles myself) - if that carb has a lot of miles on it - check for wear on the needle and needle jet - these things can give you tuning fits. A few bucks for fresh ones is worth it.

[Bullfrog]

1. Which of the two carbs in the following photos looks like yours? The answer to this question is very important BEFORE spending time tuning the carb.


2. Let's not worry about main jets for a moment. The first step is to get the right pilot jet installed -- and picking the right pilot jet is not as simple as giving you a number.

Ennneywayeeee, answer to Question #1 please.

Ed

[viclioce]

Well, it doesn't look exactly like either one! It does have the brass tube inside where the needle drops down but it appears to be a bit shorter. And the air hole (for the choke?) on the intake collar is not at 12 o'clock like in your picture. It's more like at 2:30 in position. Also mine has the choke on the right side towards the intake manifold, and it appears that airway leads to the choke. It also has a hole to the right at 5:30, and your two don't. Here's a photo. Sorry, but I can't answer a simple A or B because it's not an exact match to either. The left flange says 248 with an A1 under the 248. Don't know if that helps or not. Looking at the schematics, it looks like the carb on the Model 93 Ace 100 Super Rat. It even has the same bowl gasket. That's the best I can describe it to you. : / Victor

[viclioce]

Ed. So you know, I changed the pilot jet to 30 and I dropped the main jet from 140 to 100. I have the air screw at one full turn open and the idle screw at 1.5 turns. I'm still using the 2.5 slide and the same 4E1 needle I posted earlier with the clip in the #2 position. It almost starts but not quite. I think it may be too lean now. I don't have main jet between 100 & 140. At least not one that is marked! Victor

[Zyx]

Your photo looks like my 24 from a 93 Super Rat. When I suggested measuring the throttle bore, perhaps I needed to explain what that was. It isn't the slide. The slide runs perpendicular to the bore. Your photo is taken looking down the bore. Easiest to measure from the back side, toward the engine, because that is very close to bore diameter, whereas from the front, you have the Venturi bell which is much bigger than bore diameter. Carbs are generally sized by the size of the hole that passes air. The slide is always larger than the bore by several millimeters. If it is still off the bike, turn the carb around and measure across the back side. That should be around 24mm give or take a half.

After that, it is still a quiz which you have but you are right that your looks different than the other two shown, and more like an old Super Rat carb. I ran mine on a Webco 125 conversion for many years, so they do work.

The ISO markings are Mikuni typical, but don't identify the carb by size or model. I don't think any of them had model or size markings. They were specified by application by Hodaka and made to order or picked from a pick list accordingly. Some had flanges, some were spigot carbs, some had wider bolt spacing, and some were jetted differently, all according to application. Just as you can put a Carter carb on a Ford if you want to and make it work, it was originally designed for a Chevy. In the end, a carb is a carb, and can be configured as needed. But that makes you a design and research engineer so it takes some doing. Yours will work. No question. And it could just as easily be something other than the carb.

What oil do you use and at what ratio for premix? These things can affect tuning. Air filter clean? Some things seem obvious, but everything affects something else, so on this end of the problem we can't make assumptions about things only you would know. Is the plug new? Timing right? Not being cranky, just trying to get a handle on the problem.

[Bullfrog]

Victor:
1. You Won! You do NOT have the "A" type carb shown in the previous photo I posted. That is a very good thing.
2. Your recent photo of the intake mouth of your carb provides 90+ percent proof that you have a 24mm unit from a Model 93 Super Rat (chrome tank, 100cc). This is a good carb and CAN be tuned for your application.

3. Have you ever heard the comment, "Slow down. You'll go faster." It is an important concept. You should follow it. I know you are excited and want to get the machine running right but . . . . . . slow down, you'll go faster.
4. You may not have the information on Page 64 of the Workshop Manual, but I am under the impression that you do have Page 63. Read it. If you are not very good at reading and understanding technical information . . . I can't fix that. But you can. Slow down, you'll go faster. I recommend Workshop Manual in one hand, carb in the other ( . . . and brew of your choice at the ready). Read. Look at carb. Figure out what each sentence means. Re-read and re-look as needed. (sip brew as needed) Slow down, you'll go faster.
5. You are currently executing Step 2 AND Step 3 (on page 63) at the same time. Do not do that. No. Do one thing at a time so you'll be able to identify the effect of each SINGLE change. (If you change two things at a time . . . how do you tell what change had what effect?) Slow down, you'll go faster.

Now, lets go to work.
1. Check float level (item 1 on page 63)
2. Pilot Jet Selection and Pilot Air Screw Adjustment (item 2 on page 63)

When you complete step 2 you'll have the engine idling happily. AFTER COMPLETING STEPS 1 and 2 . . .

. . . report back here to tell us about it. We'll want to know which Pilot Jet you installed which allowed things to "tune in" with the Pilot Air Screw setting near 1.5 turns "out".

AFTER that, we'll move on to Step 3 "Find proper Main Jet"

Ed
PS: Did I mention, "Slow down. You'll go faster."?

[BrianZ]

Before you go too much farther, check item 31 in the carburetor fiche, the needle jet o ring. If this o ring is damaged the engine will run too rich.

Brian

[viclioce]

OK Ed. I have the pilot jet reduced from the 40 that was in there to a 30, which was what came with this carb initially according to the schematics. Carb float tab is at approx. 17mm and appears to be level and square with the base of the gasket surface and not putting pressure on the needle. Carb is back together and on the bike, WITH the 140 main jet in it so I "slow down" and only make one change at a time and can know what he change causes.

I am hoping the bike will start now & idle and I can adjust the idle speed screw and air screw, in that order. I also put a new throttle cable on, with the hopes that if the old one was stretched, that the new one I'll eliminate any issues that might have caused. I will report back what happens and if she starts & idles and then we can go from there. ; D Victor

[Zyx]

I guess it is a dumb question but when your bike warms up and runs poorly, is the starter lever up or down?

[admin]

Not a dumb question at all Greg!! I get asked this very question a lot.
Paul

[rtboone]

Victor

Did you clean the inside of your pipe? If not, check out the post "New Video-Whats in your pipe" to show you how to burn out the accumulated oil and carbon. (I've used a hand held propane torch to do this job, it just takes a bit longer than if I had a torch like the one used in the video)
This will make your engine breath a whole lot better. Brand new engines will run like crap if the pipe is restricted.

Tom

p.s. I've seen photos of pipes and cylinders packed with seeds and nuts by some busy rodent. So, no telling whats inside yours.

[viclioce]

Greg. I was always starting it with the plunger in the down position. This was my biggest indicator that it was too rich. If it starts not choked when cold and dies when it warms up, that to me says that the carb is set too rich for my elevation. But now, she is not starting at all again. I have kicked and kicked until my leg is sore! I've confirmed the plug is getting some spark but I can't tell if it's often enough for it to run because I don't know how many revolutions the crank makes when I kick it. So.....

A couple of folks talked about the condenser giving me some issues. I am beginning to suspect that possibly running the motor for the first time in numerous years, that it is quite possible the condenser has now failed on me. To remedy this possibility, I have purchased a new condenser and also a new set of points. No, the old points didn't look bad, but I figure since I'm opening the magneto cover and pulling the wheel, I may as well replace the points as well, so that I can say I know for certain that they aren't contributing problems. I know condensers are usually an all or nothing proposition, at least it always was with my Kawasaki. So replacing it will eliminate that possibility.

I have changed the carb from the #40 pilot jet to a #30 pilot jet, which also was the stock pilot for this carb. I don't have one smaller, but it had a #40 pilot jet so I am sure that was a part of the reason it was running too rich. I returned the 140 main jet so I am only dealing with one change at a time. But I'm kicking and kicking and not getting any start. I have pulled the plug and confirmed that there is spark, but if the condenser is working intermittently, it would certainly keep me from being able to start the bike. And, I certainly can't set/tune anything if I can't get the bike to start and idle at any speed.

Ed says "slow down" you'll go faster. So I am slowing down, a lot. Confirming that I don't have possible condenser issues and points issues eliminates those problems from the equation. I ordered the parts this morning so it will take probably 3-4 days from Monday before I see them arrive in the mail. So I won't be posting again until after they arrive and I have had a chance to install and determine whether or not they were causing any issues. Keep your fingers crossed for me! ; D Victor

[viclioce]

No Tom. I wasn't aware. I watched the video and will see about doing it while I wait for parts to come in. I wish I had known to do this before I sandblasted and engine painted the whole exhaust! But one more can of engine paint isn't that costly. And I bought new springs, which were a pain in the A$$ to get back on the pipe! So I will give it a try.

Are you saying it can be done with a propane torch, or should I seek out a more powerful one? I can take it to my son in law's brother over at Meineke and maybe use one of their torches to burn it clean. I understand from the video to get the pipe red but not to "Over Do It!" So I will be careful and just try to get it to smoke! ; D Victor

[viclioce]

Ed. The bike is not starting at all now. I am beginning to think that maybe the condenser failed? I did ride it before trying all this effort to rejet the carb. It started cold, without the choke. I went around the block, maybe 1/4 mile and she died on me. I couldn't get her to start again and had to push her home a short distance. The following day, when she cooled off and sat over night, she fired up briefly until getting warm again. Then she died while idling and has not started since. Not even a rough start with a poor idle.

So I bought a new condenser and figured a new set of points too. I am going to have to "slow down" and wait for them to arrive which since I ordered them today (Saturday) means they won't even ship until Monday. So, I should have them Wednesday or Thursday next week. I will replace them and see if either of these has caused the non run situation. If she then starts, I will see what she does with the #30 pilot jet in place and the #140 main jet. If she starts, I can then report to you how she is running. But since she doesn't want to run at all right now, I have to "slow down to a stop!"

I will report back once I have changed out the condenser and see if I have any new news to report. Thanks for your help and for your patience with me. And have a Happy and Blessed Easter! ; D Victor

[Zyx]

The condenser won't stop it from sparking. Once the condenser fails it causes arc across the point gap too actively and erodes points, but it will spark and run with no condenser. Suppressing point arcing is about all a condenser does.

I would put in a new plug. You have been loading up pretty regularly. It won't take long to oil foul a plug. That is more likely to give you intermittent spark than a bad condenser. Keep a good plug handy for testing for spark. Once fouled, a plug will re foul quickly even if it starts to work again. There are other ways to check for a visible spark. Used to be able to find tools for this with an adjustable gap. There were even plugs for oil burning autos that had a gap built into the plug housing to boost voltage.

Also I don't remember if you told us what oil and mix ratio you use ( or is yours an oil injection model I don't recall.)

[viclioce]

Greg. I'm using a Castor oil based oil an I think I mixed it around 24-28 to 1. The cap on the gas tank said to go 20:1 but the guys at the local shop who gave me the oil for free said I'd be better off not mixing it 20:1.

I appear to be getting some possible problems with spark. It doesn't look like its firing on every up stroke. So I'm still going to change it to be sure. You Know how it is. I don't know how old it is and want to be sure it's not a problem. So That's the reason. On my Kawasaki F6, it worked or it didn't and the when it didn't the bike didn't run. So better safe than sorry.

I also found out when looking at the schematics that there is a rather large spacer washer in the shifter mechanism which is missing. Only 95 cents so it was worth ordering. I'll have everything back together in a few days and will go from there. ; D Victor

[ossa95d]

Victor,
Looking at your carb, if the choke lever is down the choke is on (not really a choke but the enrichening circuit). Again down is ON, up is OFF.

[Zyx]

The cap says 20:1 because it is circa 1970-something. Oil has come a long way in 40 years. I used to run castor oil for racing with mixed results. Castor seeks heat, which is a good thing. It can also leave gummy stuff behind which isn't so good but for a race bike that gets overhauled regularly, not a problem, and most of the old castor based oils yielded a bit extra power because they ran leaner, and smell like model airplanes. Cool factor high.

There are a variety of synthetics these days that are first rate, most mixing around 32:1. For general riding they may be a better choice, and they stay blended better longer. Never mix castor with petro based oils. They do not all mix correctly. If you need to change, dump the tank, dry out the carb, then refill. I killed a bottom end in 73 during a race by mixing castor on top of petro. The oils coagulated and I burned up the big end bearing in about two hours. Finished eighth but then could not restart the engine. Knocked like a diesel.

Have you checked your pipe and silencer? The video recently posted shows what a funky mess they can be. If in doubt, remove the pipe entirely and fire it up. I don't recommend running this way for long, but if you can warm up and run okay without the pipe, it is the pipe. If nothing changes, it isn't the pipe. Noisy but simple test.

If you have been struggling with a super rich mixture or clogged pipe and now can't start the bike, replace the plug. Check the old one for color and wetness. Black and wet is not good. If it is brown and dry, it likely isn't the carb that is giving you problems. But either way, you can load up a new plug really fast with the symptoms you describe. Until you get this sorted, I would keep new plugs on hand. We used to clean spark plugs in the shop years ago, but it was never cost effective because the cleaned plug would foul again quickly. A good working plug could stand cleaning but an oil fouled or lead fouled plug not so much. These days lead isn't an issue but oil still is.

What is your bike making in the way of compression? Might want to test it just to check one more thing off the list. If you don't have one you can find them at a Auto Zone or wherever, not expensive and they last forever. While dealing with the condenser is a good time to reset the timing so you know that is right as well. A leak down test would be good as well but harder to do.

[viclioce]

I bought 2 new plugs. A new one is in it right now. Unless you're telling me that cranking the bike will flip a new plug, I don't think it is. If you say change it again, I will. But I do not think it has had the opportunity to be fouled just from attempting to start the bike. If this is a wrong assumption, let me know and I will change the plug with the condenser & points. ; D Victor

[Zyx]

No, you should be okay. Use the new plug for checking for spark rather than a used one if in doubt at all about the plug. I was thinking more of the kicking till you leg was tired. That plug, who knows. Weak spark coupled with rich mixture, it doesn't take long so I was just saying use the new one as a tester. Any doubt about the plug, change it.

If you have a stock pipe, at least take out the silencer and spark arrester. The pipe itself is hard to clog to the point of choking the bike unless something is nesting in there. Just looking for ways to give the bike every chance of running.

Compression, spark, fuel. Everything else is a matter of degree but you have to have all three. To avoid potential flooding, drain the carb so you know it is empty, open the cock until the bowl is basically full, and turn off the cock so no more fuel gets in. There should then be enough fuel to start and run for several minutes. This will minimize the potential for flooding due, for example, to a leaking float valve. You can even start with no gas in the carb, put a squirt in the spark plug hole, and kick that a few strokes. If everything else is hunky dory, it will start for a brief moment or at least sound like it is trying to. Then you can open the fuel and go for it. These are ways of sneaking up on run testing without flooding out.

If you think that the crankcase may be flooded, which it could be if you tried to start for quite a while without success, turn off the gas off, drain the carb, check for a dry plug, kick it a couple times and check for a wet plug. If it is wet, the crank is full of gas, which can happen. Another sign of a flooded crankcase is excess fluid at the cylinder/pipe joint. In which case, pull the pipe, leave the gas off, leave the plug in, and kick vigorously or give it a push start. The idea is to pump excess fuel out of the crankcase using the natural function of the piston.

At some point or other in the past, we have all had such issues.