Single carb conversion thread...

[yamaman]

TC, be prepared to go as low as a 180 main jet to get it right! Yeah a 36 should run a tad higher main than a 34, but all conditions are never equal. 7 a 180 WILL deliver fuel in a very close amount. So to sort the difference between a 180/ 190/ 200 will require some leval of dedication!

 

[Travis]

I was kind of wondering how much more fuel, if any, a single carb setup needs vs dual carbs of the same variety.. Maybe it has something more to do with intake length??? Anyone care to explain?

 

[TeeCat]

Guys, thanks... will take this on board.

I'm trying to get the bowl off this brand new 36mm VM, and it won't budge. I have the four screws out, but I don't want to pry or hit it. What am I doing wrong? There should be nothing but a gasket, so what's holding it on there? I don't want to ruin this carb or the gasket, so help appreciated.

TC

 

[HionHiFi]

TeeCat nice carb setup. I may do something similar to yours. Was the adapter difficult to make? Can a piece be purchased RTU (ready to use)?

I'd be interested in the very setup you have. If it fits my drop seat six fiddy. :b

 

[weekendrider]

Try tapping it with the end of rubber handled screwdriver.
If it was an old carb I'd say spray carb cleaner around the lip but....

 

[pumps]

+1 on yamamans comment!

 

[Tech7]

I was kind of wondering how much more fuel, if any, a single carb setup needs vs dual carbs of the same variety.. Maybe it has something more to do with intake length??? Anyone care to explain?

Well, in theory, it shouldn't require any more fuel. The engine is still going to need a certain amount of fuel to produce power. Optimal air/fuel ratio is generally 14.7 to 1 on internal combustion gasoline engines. And I use the word generally because we are talking theory. Sound reasonable?

 

[Hooligans]

TeeCat... nice to see a walk through on this setup. I have been interested in a single carb conversion for a while now. I'll be keeping an eye on this to see the complications (if any) you run into on this setup.

 

[TeeCat]

I'll keep you posted, Hooligans et al.

Got my recommended jets in, and got my cable today. It's a one-into-two, which I knew. It will be ideal in length, but do I HAVE to remove one of the two cables at the junction, or can I just leave it unattached and put it out of the way? Just kind of hate to cut it if I don't have to. It's from Mikes, btw, with a metal junction tube and a little nylon insert inside, with a slot for each midpoint cable nipple.

 

[5twins]

You should be able to just remove the 2nd cable if the junction comes apart. Still, I'm not sure this is going to work right. That set-up was designed to have a cable pulling equally on each side of the disc, keeping it straight in the tube. Now you will be only pulling on one side. It may cock the disc and bind it in the tube.

I would search for a single cable off a dirt bike that used a VM carb. Then all you'd need do is match up the ball on the throttle grip end.

 

[TeeCat]

twins, I think I see how that might happen, depending upon how the particular cable is built. In this case, the little nylon disk is more like a "plug" that's tapered toward the bottom, so binding seems like less of a possibility. Might have to cut one cable, though, because the housing seems pressed or otherwise attached to the base of the metal tube. I'll examine it more closely.

joe-wiseguy has indicated that this works. If it does not, I'll try your other suggestion, though my local bike shops never fail to disappoint me, even when I am looking for something as simple as a cable.

 

[TeeCat]

Just a brief update... I did get the cable attached to the carb. Not as hard as it seemed it would be, though the idea of it is really a bit cumbersome. Direct pull makes sense, though. I did remove one cable and it seems to be fine off the bike. Tomorrow, I'll install the whole single carb setup and hopefully get her running. I'll update in the thread dedicated to that.

TC

 

[TeeCat]

TC, be prepared to go as low as a 180 main jet to get it right! Yeah a 36 should run a tad higher main than a 34, but all conditions are never equal. 7 a 180 WILL deliver fuel in a very close amount. So to sort the difference between a 180/ 190/ 200 will require some leval of dedication!

yama...

To start, I have gone with joe-wiseguy's recommendation of a 200, and I have a 210 as well, based on his recommendation. I installed a 25 pilot in there based on his rec, too, with a 27.5 still sitting in the bag. But you're suggesting that I may need to go lower than 200. What would I be looking for? Dark plugs?

Tomorrow, I plan to assemble everything, start with the air screw at 1 1/4 turns out, it;s screw backed off to just barely touching, and try to start her up and see where I am.

And this is ONE carb... just to remind you, right?

 

[TeeCat]

Update:

Why did I think this would be easy?

25 pilot, 200 main, air screw 1 1/4 turns out. Fuel on.

The bike started on about the second hot kick on the choke, ran on both cyls for about 30 seconds to a minute. As I tried to come off the choke gradually, it lost the left cyl, stalled, and will not restart. There is raw fuel at the mouth of the carb. I tried to kick it with and without choke... no luck.

I pulled the left plug and it seems/smells wet. But now the additional fear is that I kicked it three or four times, having forgotten to reconnect the left plug wire. So I hope I didn't damage my (I'm running a Pamco) damned coil.

I need a tuner looking over my shoulder. I'm just taking somewhat educated guesses and wasting my time (and money).

And I'm out of beer.

Getting really tired of this puffed up paperweight, and carburetors. Quitting for the day. Maybe for good.

TC

 

[TeeCat]

Curious and not fond of being defeated, I went out there again about an hour later. I went IN on the air screw about a quarter turn, so nor its about a turn out. I just kicked it with the gas that was in the bowl, and it fired up right away on the choke, ran (on both cyls, so I know my coil's not hurt) for about a minute, then died. There was still fuel in the line but I opened the petcocks and tried again. Would rarely restart but backfired loudly through the right pipe and stalled. Now will not restart. Raw fuel at the inlet.

So, it's a fuel issue (flooding?), but I have no idea what to do at this point.

TC

 

[TeeCat]

Oh, and I should add that I have not yet done anything with the idle speed screw. It's backed off all the way, I believe. Maybe I should adjust it so that it is just starting to lift the slide by itself. Do I need SOME throttle opening even at startup when the choke, but no throttle, is being applied?

 

[JasperLP]

TeeCat,
I think they say start with the smooth end of a 5/32 drill bit under the back of the slide, I use a 3/16, didn't have the other. It's just a starting point. It's not gonna idle with that slide all the way down. Just remember most of us running VM's have two of them to work with. Clean that thing out real good, I found an aluminum shaving in one of mine after the sixth cleaning. They don't clean them at the factory.

 

[TeeCat]

Jasper, thanks very much. I have been reading some online manuals, but never came across that info. I'll try that tomorrow. Now, when you say "back" of the slide, do you mean to insert the bit in the intake and under the slide?

Also, could this be causing the "flooding" if there is not enough air being admitted? I thought that on VS the starter circuit was completely separate from the others. So I thought the throttle valve was supposed to be closed, and the slide all the way down.

TC

 

[JasperLP]

TeeCat,
By throttle being closed, they mean down on the idle screw. After using the drill bit, you will adjust the idle screw to get desired idle speed. Don't use any throttle when starting, hot or cold, choked or not.
Have you checked the float level.

 

[TeeCat]

Jasper -

I went out there and used the idle screw to set the slide so that I can just friction fit a 5/16 drill bit under the slide from the intake side. Is that the right starting point?

Also, I had the bowl and cap off to install the jets and the cable, but I did not "check" the float height because this is a brand new, out of the box carb, and I don't have those specs. Frankly, I think the fact that they sell these carbs with no literature whatsoever is pretty abysmal.

One web manual warns against messing with factory (predetermined) float settings, so I'm really concerned about making a bad situation worse, especially with no literature/specs. But it seems odd to me that a brand new carb would flood to the point of fuel dripping out the inlet.

TC