I like carbs. Your bottom pic showing the slide, block thing the cable hooks to, needle and plate. So first put the needle in the slide then you need to get a screw and attach the block thing into the top of the slide then you put your cable through the spring and through the thin plate. Squish the plate and spring up so you have some cable to work with to put the end into the block thing (I gotta look that up so I know the name of it) and slide it over to the center of the block/slide then let the plate and spring go down and the spring pressure holds the plate down in the slide on the block thing so the cable can't slide over and fall out. Whew that's a mouth full. So basically you need to attach the block thing into the slide first, get a screw. Now some of the mikuni's have litle plastic washers on each side of the needle clip and some do not, but I bet you'll get it running. Good luck.

 

Thanks 72EXT. That's kind of what I figured. I guess that my real question is how the throttle attaches to the slide on the carbs without the tall top cap? And if you DO find the name of the part, could you reference a diagram so I can see?

I was told that the tall top cap was for creating an easier throttle pull. So my carb looks like my competitors, I want to use a normal top cap, rather than the tall one. This carb is legal, but it is a near-spec class, and it would raise suspicions. . .

Chris

 

O BOY!!! Do I have some good reading material for you. It'll give me time to find the name of that block thing. I googled "mikuni carburetor vm38" and I found a 20 page site about Super Tuning Your Mikuni. http://www.mikuni.com/pdf/vmmanual.pdf There ya go. O by the way you don't need the block thing to go with the short top. I THINK all you'll need is a short cap, a different thin plate, a shorter spring and different length throttle cables. You'll see what I mean when you read the pdf. They have a pic exploded view of a short top. Cat happy

 

Thanks! Doing a bit of reading myself - I found service manuals for the Arctic Cats and some Ski-Doos. The cylinder is called a "magnet block". Strange, as being aluminum it is neither magnetic nor ferrous (able to be grabbed with a magnet). And blocking a magnet? What magnet? Who named these things???!!! :angry2:

So I went to the Ski-Doo manual, and looked at a carb with a flat cap. There is something called a "needle retaining plate" that the throttle cable hooks to, that screws onto the slide. One piece, no flat washer with a hole in it. But it connects using TWO screws according to the diagram. . . Are AC slides different than SD slides? Be kinda silly if they were. . .

Neither of which part is shown in the diagram in the manual you reference (that is the diagram that has been confusing me). And so, the diagram also shows what seems to be a third style of flat plate (also called a "needle retainer plate"), with no obvious way to connect the throttle cable. In the diagram a flat plate with a hole or two and a cutout. Gah!

Seems like what I need is a new needle retaining plate for a Ski-Doo. And maybe a new Ski-Doo slide. . . (which is likely needed for tuning anyway, so no biggee)

Chris

 

Ah, a pleasant Sunday surfing the net trying to answer just one question. . . It would be more pleasant with a good measure of vodka in me, but I'm doing it sober. I dunno

More info, and I think the solution. There seem to be two possible solutions. Length of cable may be an issue, but in my machine won't be (attachment of throttle cable to accelerator pedal is different on each car).

First: A Ski-Doo Needle Retainer (flat to sit on the top of the Throttle Valve, but a three sided box on top to slip the throttle cable end into) - 404 122 900. A Needle Retainer Cap - 404 154 800. Two screws - 404 121 300. And a Throttle Valve (what I would call a slide) that has a center hole for the top of the needle and two threaded screw holes.

Second: Not sure of the application or part numbers, going from pictures and descriptions in various places. A Needle Retainer Plate (flat washer, center hole for top of Needle, offset hole for screw to go into Throttle Valve, and cutout for the throttle cable to go through). A screw to attach this to the Throttle Valve. And a Throttle Valve with a center hole for the needle, and an offset milled depression that has a large hole and a slot for the throttle cable to go through, then slide over and lock.

The diagram that is in your referenced manual, the one that confuses me still, shows a third style of Needle Retainer Plate: A flat washer with a center hole for the Needle, a cutout for the throttle cable to go through and go into the hole/slot in the Throttle Valve, then an offset hole for a screw to attach it to the Throttle Valve - which is unnecessary in my understanding (the screw), as the plate is held down by the spring.

And, of course, most of these parts will be different for different sized carbs. . .

So, determine the size Throttle Valve I need, be sure it has one of the two sets of holes as described above, and is the correct size and has the correct side of slot, then buy the appropriate pieces. I'm glad that I'm not in a hurry.

Whew! And all I wanted was a Mikuni VM38 carb! :blink:

Chris

 

I think you would need a different style slide(throttle valve). I'll look when I get home tonight hopefully or at least this week. Are you in need of hurrying I will look tonight for sure. The other style slide the cable can hook in it like on that block thing and then that plate in the PDF is different but it's what you'ld need. I'll talk tonight.

 

I think that I need a different style throttle valve as well. And that will determine what throttle-cable-attachment stuff I need. I guess I need to buy the stuff from a place where a sales guy can hold the throttle valve in his hands with me on the phone. Well, it's going to be a large-ish order, I'll likely need all new jets and needle and such for my application, as well as a variety of other jetting so I can tune my carbs. I run an O2 sensor during the tuning phase, and run my engines VERY lean (only possible with race gas from cans). And usually re-jet the morning of the event based on weather (temp, humidity, barometric pressure).

No hurry, I won't even install the new engine in my car until late winter. Winters are brutal here in Atlanta, and we all just hunker down until warm weather arrives again. . . :lol: Though I am glad that I started this process early - it would have been very unpleasant if I had waited until the week before my first event to get the engine running!

Chris

 

There's a number on your slide inside you'll see it in the top where the cable goes or in the bottom where the needle sticks out. That's your slide size. Let me know that number I may have parts you need: slide, plate and cap. I think that's all you need. I have to look over the post again. I also have needles and needle jets tubes. I use these terms compared to the PDF term. Slide=Piston valve. Needle=jet needle. Needle jet tube=needle jet. Are you running 1 carb or multiple and how many would that be?

 

I'm here, my computer was slow. Got some pics of a slide, cap and cable retainer I think you need. Let me know if you think it'll work. If not or if you have questions I can PM you my phone number, it may be easier talking. I think the number on the slide has something to do with the diameter or the slope of the bottom of the slide, someone may jump in and HELP ME OUT (THANK YOU).

 

PM sent.

Chris

 

well... we have seen the carbs... how about the car? ics; :needpics:

 

<div class='quotetop'>QUOTE (I Ride Sand @ Oct 26 2010, 09:32 AM) <{POST_SNAPBACK}></div>

well... we have seen the carbs... how about the car? ics; :needpics:[/b]

X2. I tried calling him but I'll try at noon. He PM'ed me this(below) but I don't know if I'll have the ski doo parts. It sounds different than the AC Mikuni but I'll know more when I talk to him. I'll tell him WE NEED PICS.
Thanks for your help! I just spoke with the guy who did the dyno runs we needed to get this engine approved, and he says that I'll need a 2.5 slide. The smaller number means that the angle cutaway is smaller, and this makes the carb run richer.

So I need the 2.5 throttle valve for a VM38, and (from my research):

"A Ski-Doo Needle Retainer (flat to sit on the top of the Throttle Valve, but a three sided box on top to slip the throttle cable end into) - 404 122 900. A Needle Retainer Cap - 404 154 800. Two screws - 404 121 300. And a Throttle Valve (what I would call a slide) that has a center hole for the top of the needle and two threaded screw holes."

If you have these parts as spares, I'd be happy to buy them from you. Even if you only have parts for one, that would be a step in the right direction.

The engine is a two cylinder Rotax 593, the plain-jane version. So I have two carbs. He said 45 pilot jets are likely, I have 40's now. All of the other stuff will be determined once there is a custom pipe made for us - hopefully mid-winter.

 

OK, OK. Here's a pic of my "snowmobile." Some descrip after the pic:

I can out-accelerate just about anything but a high powered sport bike, out-corner anything without wings, and out-brake just about anything (except at very high speeds against something with wings). With me in it, my minimum weight (which I am at), is 800 pounds. I am geared low, for acceleration, and top speed is likely about upper 80's.

I autocross the car. Medium speed (40-75mph), high precision driving. When going through a slalom that is good - say, 20 paces between cones - I'll be going about 50. And need to be within an inch or two of the base of the cones to get a good time. . . hmy_old: We set up in large parking lots, runways, airport aprons, and the like. It is a very large sport, run by the Sports Car Club of America (SCCA). Most large cities have groups that do it.

You can take your street car and do it - it will make you a much better driver! My car is essentially custom made for this application. You can't run a 4WD pickup, but some folks have run pickups (but because of weight distribution aren't very fast), some even with race tires.

On a normal parking lot I pull about 1.6 g's lateral. On high quality asphalt I have SUSTAINED 2.0 g's. On high quality, high grip concrete I have hit 2.4 g's. :super_happy:

edit: Oh, and a 5-point harness, so when I'm strapped in, I can only move my head, hands, and feet. Roll cage keeps me from moving arms much, or legs at all. Snowmobile clutching gives me just a GO pedal (right foot) and a STOP pedal (left foot). No room to take feet off the pedals, just depress them. And size 12 feet, so I need racing shoes to move both feet on the separate pedals. . . And at max steering, my left hand goes from 9:00 to noon. And I sit on the floor that is 1.5 inches off the pavement. . .

It is "quite entertaining."

I will be posting a "parts wanted" for some Arctic Cat low top Mikuni VM38 slides (Throttle Valves), size 2.5. Two. Plus the attachment parts to connect the throttle cable to the slides. And some 45 pilot jets.

Chris

 

Holy Sweet, I had to be the first to say it's awsome. Ok now I gotta go back and read the post, ok done reading sounds like a BLAST. Thanks for posting, nice talking to you on the phone and here. Good Luck. Cat happy Rockerdude :chug:

 

<div class='quotetop'>QUOTE (MCoupeAtlanta @ Oct 24 2010, 10:22 AM) <{POST_SNAPBACK}></div>

Thanks! Doing a bit of reading myself - I found service manuals for the Arctic Cats and some Ski-Doos. The cylinder is called a "magnet block". Strange, as being aluminum it is neither magnetic nor ferrous (able to be grabbed with a magnet). And blocking a magnet? What magnet? Who named these things???!!! :angry2:

So I went to the Ski-Doo manual, and looked at a carb with a flat cap. There is something called a "needle retaining plate" that the throttle cable hooks to, that screws onto the slide. One piece, no flat washer with a hole in it. But it connects using TWO screws according to the diagram. . . Are AC slides different than SD slides? Be kinda silly if they were. . .

Neither of which part is shown in the diagram in the manual you reference (that is the diagram that has been confusing me). And so, the diagram also shows what seems to be a third style of flat plate (also called a "needle retainer plate"), with no obvious way to connect the throttle cable. In the diagram a flat plate with a hole or two and a cutout. Gah!

Seems like what I need is a new needle retaining plate for a Ski-Doo. And maybe a new Ski-Doo slide. . . (which is likely needed for tuning anyway, so no biggee)

Chris[/b]

The magnet block is for a magnet that is read by an external sensor the forms part of the Throttle Safety Switch (TSS) system. The TSS is there to prevent the engine from starting if the throttle valves are stuck open, which could result in a run-away machine.

There are a number of online parts microfiche for Arctic Cat parts, Alpha Sports and brown's Leisure World, so there must be similar sites for Ski-Doo parts.

That project sure looks like fun.