Back to reed valve jetting on a Super Rat

[viclioce]

OK. So how do you make a buzz box? And how do you use it? Victor

[Bullfrog]

I don't have the formula for making a buzz box, but they work by sensing the change (electrically speaking) when the points open. They ARE really a nifty timing aid! Then use the cheapest timing light you can find from the local NAPA store to confirm that spark is happening exactly "when" you want it to. Timing lights with dwell or advance knobs are overkill for this situation. They will not be used - and cost more. Pop the hood on the family soccer van to connect to 12V power and put the spark sensor unit (usually a "clamp" looking sort of thig) on the Hodie spark plug wire. Use the timing light to see if the lines are truly lined up when the Hodie engine is running.

[viclioce]

Well, been on the phone & texting with Dale regarding this no start issue. First of all, I want to thank Dale again for being so helpful!

While we were discussing issues, Dale mentioned Ed’s article in the Resonator. Volume 1 - 3, wherein the Captain’s Mast covers the ins & outs of Mikuni carbs and the pilot circuit specifically. Now Ed used a 28mm Combat carb for the discussion & illustrations. I’m using a 24mm on the Super Rats.

In the photos, with heavy descriptions, there’s three holes in the bottom of the intake side. The left hole has a ball stop in it. I noticed my 24mm carb was missing the ball stop. I looked at the 2 other Super Rat carbs on the bikes I have and they both have ball stops in them.

This means the air screw on the pilot circuit is sucking way too much air, even at only 1 1/4 turns open, because the air is being pulled thru the hole with the missing ball stop!

With the bike not starting, the spark plug still never got wet, because it was sucking too much air & not pulling enough fuel. Here’s a couple of photos. The first is the carb with the missing ball stop. You can actually see the needle end of the air screw through the hole!

The second is the carb off the second Rat I’m building. The 3rd is from Ed’s article which helped me figure out it was missing. Is there a way to replace the ball stop? Or should I try a bit of lead? Maybe some JB Wrld? You can see the difference!

P.S. Lee Fabry suggested I try one of the steering head bearings and see if one fits. I have a bunch of those... Victor

[Bullfrog]

Vic, don't do anything to your carb that you can't easily reverse. I just took a peek at a stock Road Toad carb . . . and you can see the pilot air screw through the passage (just like one of your photos). So . . . at least on the stock Toad carb, if you put a "ball block" in that passage you will totally block the ability to "tune" the air with the pilot air screw. This is an interesting situation - but I won't have time to look into it further till at least Monday (possibly later).

I'm still thinking you are putting wayeeeee to much blame on the failure to start on the pilot system . . . the starter circuit should allow it to start . . . THEN, you tune the pilot jet. (IF all the ducks are in a row, the engine WILL start even with an extremely lean pilot jet)

Ed

[Stever]

I just want to echo what Ed said, and especially the last line "IF all the ducks are in a row...". A person can guess themselves crazy trying working on carburetion before the ignition is working just right. That duck needs to get in line.

You are certainly correct that there are two circuits that operate at closed throttle, the choke circuit, aka starting, aka enriching, (if it is activated), and the pilot circuit. And activating the choke does not disable the pilot circuit. For cold starts, the choke is overwhelmingly the important one, and the pilot has little effect, maybe not even necessary in a lot of cases. It would be interesting to plug up a pilot and see what effect it has on cold starting any given bike. In 1977 there was a Kawasaki service bulletin for some KZ650s that were EXTREMELY difficult to start cold. The KZ650 was a brand new model, so Kawasaki jumped right on the problem. I had labored unsuccessfully with the problem myself at the large dealership where I worked. The bulletin called for simply drilling out the pilots with a certain number wire drill bit. Once that was done the bikes cold started almost instantly (Kawasaki changed the carbs soon after that). So, the pilot is not meaningless, but that's the only example I ever saw and I'm guessing it was actually due to the design of the choke circuit being too limited. I think that if the smart guys at Mikuni had miscalculated on the choke/pilot interaction for any Hodaka that it would be well known by now.

It is always a good idea to clean the pilot circuit if a bike is had to cold start, but mainly because it won't hurt an it might help.

Sorry to be so long winded. I just realized I was talking about service bulletin from over 40 years ago, so take this advice with a grain of salt. Classic quote from olddogs recently, "I used to know this stuff". Amen, brother.

-Stever

[MTrat]

I will put a complete, illustrated, instructional article on how to make a buzz box in the next Resonator.

[viclioce]

Well, I swapped out the carbs. I put another 24mm carb from another Super Rat on this one and for the first time I actually got a wet spark plug. In fact it looks like it fouled the plug. So a new plug will go in tomorrow. The no spark issues have been resolved. It was both the points needed cleaning with Acetone, even tho they were new to me from Terry, and the Super Rat coil was not firing consistently. I put a rebuilt Ace coil on the Sup Rat coil mount and got really good spark! So I may have to tinker with this second carb a bit, but I think I’m getting close now. Victor

[viclioce]

Ed. I’m not blaming one particular thing. It seems to have been small things adding up to a BIG FAILURE. Spark issues? Tested entire circuit from the points to the coil. Everything worked with an alternative 6 volt power source, so stripping the points clean with Acetone cleared one problem. The original coil only gave intermittent spark, so replaced coil.

Carb missing check ball AND not delivering fuel? Replace carb with an identical model. May need to find a replacement for final disposition of second bike.

Eliminating issues one by one, until she finally sings, is the only way I know to eliminate possible problems. I only have 5 days left to finish. ,Victor

[viclioce]

For those of you keeping up, I have started the Super Rat! Turns out the problem was two fold! The first was the missing check ball in the carb. Switched carbs and started getting fuel to cylinder.
However, there was still an electrical issue. Seems, for some reason, the DPO reversed the wires on the back of the stator plate!!! So it was grounding out. Reversing the wires to the correct positions solved the dilemma.

Have more time to work on it. Buyer won’t be here Saturday! Whew! Just when I thought I was going to have some late nights!!! Victor

[olddogs]

Good piece of trouble shooting. Solve one problem, then move on to the next. Solve enough problems and you get to ride.

[viclioce]

Well I put the second 24mm on Super Rat #1. No missing check ball.

Today, after trying numerous small ball bearings, all of them too large in diameter, I bought some JB Weld Steelstick!

Cut off a small amount, trying to get even amounts of both. Mixed it together by hand as directed, & placed a small amount over the hole.

Then I added an additional small amount & applied it over the first & smoothing it around the side of the opening.

Here are a before & after pic! The first photo is a carb with the correct check ball in place. The second is the carb with the missing check ball & the third is the fix in place! Victor

[Bullfrog]

I sure hope you haven't ruined that carb.
Ed

[Antique 1]

I can see that JB Weld loosening up and getting sucked in to your intake and trashing the top end.

[matt glascock]

Impossible to imagine any set of circumstances where a shot plug could get dislodged. Never.

[viclioce]

All I can say is this:

1. I haven’t checked the JB Weld yet to see if it’s holding.
2. Antique1 it’s a valid concern IF it’s not holding.
3. Ed. Really? You know of a better way of fixing it since I have confirmed that at least 4 other VM2400 Super Rat carbs all have check balls in that location? And, that I’ve confirmed with Sudco that check balls are not a resale item from Mikuni.

I’m afraid what’s going to happen is the surface is too smooth and the JB Weld won’t properly adhere. If that’s the case, I may try using some tire weight lead to make a ball which I can then press fit into the carb.

And I don’t see anyone volunteering a VM2400 Super Rat carb. Going once, going twice..... Victor

[taber hodaka]

Victor Really! We all hope you don't screw up your super rat carburetor. !258 people have read this post and we would not want to mislead them or lead them astray. I will look at my stack of rat carbs and see how they are. I do not think what you are refering to is a check valve. I will cut one open and look. ---------- Clarence

[Bullfrog]

Yup, concerned. I don't have a known stock carb from a toaster tank Rat to look at . . . but I do have a single owner, un-modified Road Toad carb . . . and the Pilot Air Screw is visible through one of the passages. I don't have any way to independently confirm the view in the throat of a Model 93 Super Rat carb.

Model99 26mm carb1 copy.jpg

Sorry you took offense. Hope it all turns out well.

Ed

[Bullfrog]

Hopefully the photo will show up this time.

Ed

[viclioce]

Not taking offense, just explaining my position from what I’m observing. It seems you’re comparing apples to pineapples. Almost the same name, but vastly different tasting.

I have 2 26mm carbs. One is a Toad & one is a Modrl 03. Both of those have no check balls as well.

The difference is, with the first Rat carb the plug was staying dry, aka no wet fuel getting to plug despite not having spark because of the reason explained. However, with the second Rat carb, with the check ball, the plug got wet, and when the stator wires were corrected on the back, the bike started.

All things considered the same, the carb missing the check ball wasn’t sucking enough fuel because the loss of the check ball created maybe 5-6 times the air flow opening.

I even stated that Dale thought there was a possibility that there might be some air flow around the check ball. And I reminded him that if air could flow around the check ball, then the ball would be too small to stay in the hole. Victor

[viclioce]

Clarence. I’ve discussed this with Lee Fabry, a technician at Sudco and a few other people. They have all confirmed it to me. The check ball is like a cork. The hole is drilled to provide access during construction. Then the brass check ball is pressed in to stop the air flow. The air for the pilot jet is controlled by how far the end of the air screw protrudes into the small hole in the Venturi into which the needle on the end of the air screw goes in & out of. The hole is much smaller than the opening normally covered by the check ball. Without the check ball in place, too much air goes into the pilot circuit. So there’s way too much air to fuel in the mixture which is supposed to be controlled by the needle and the small hole in the Venturi. That’s the best way I can explain it.

As far as Ed’s Toad carb with no check ball? It isn’t a 24mm Super Rat carb. I have 2, 26mm carbs(pictured below), which, like Ed’s photo, (even tho one of mine has not been cleaned) and both of those ARE like the carb Ed shows. But they aren’t 24mm Super Rat carbs. Not trying to cast any aspersions. He only said he had a Toad carb with no check ball in the hole in contention. So do I. But we aren’t discussing a 26mm Road Toad Carb. We are discussing a 24mm Super Rat Carb. I have 3 of those. Alan has 3 more. Every one except the first has the check ball. Lee confirmed it & so did the technician at Sudco. I’m not guessing.

Now, if someone shows me a functional 24mm Super Rat carb, with a check ball missing from the pilot air jet, that works on a running bike, we can discuss it further. Clarence, I’m told you have, to my understanding, about 6-7 Super Rats. Do all of those carbs have a check ball in the left hole? Are they all functional? These are the questions which need answering.

Now. The JB Weld appears to be secure enough that it won’t accidentally come loose, but, I can pry it off if needed. I will test this carb on the second Rat I’m about to finish, and if it works & the bike runs properly with the JB Weld in place, we will have our answer. Victor

[Bullfrog]

There you go. Background research has been done. You are on target. (A situation which was not known when I posted my earlier comments urging caution and noting that there ARE carbs which do not have the blocking BB in that location).

Ed

[Stever]

Peace, love and understanding to all. Just one small nit to pick, forgive me.

Matt has the terminology right, as far as I've always heard, it is a shot plug, cheap and easy in the manufacturing process, often swagged (spelling?) or peened in place.

A check ball is found in a check valve or something akin, often spring loaded, but responding to pressure in both directions.

-Stever

[viclioce]

Thanks Stever! I really didn’t know what they were called. Someone else told me check ball. So for lack of a better term.... Victor

[taber hodaka]

Well how is it running with all the issues sorted out? ----------------- Clarence

[viclioce]

The motor is still really tight. Not sure if the crank is warped or if something else is binding it inside. When you grab the flywheel it is very hard to turn manually. And it won’t idle because something is binding.

I drained the oil and will be pulling the motor, most likely tomorrow. I have a couple extra cranks I can try if needed. I’ll let you know as soon as I get it opened up & figure it out. Victor