Flat slide carbs! Are they for you???

[mrsg]

Hello everyone,
As most of you know i have been trying like mad to fit a flat slide mikuni carb 28mm on my bike and fine tune it.
These carburetors are very finicky and extremely frustrating.

Some of the bonus to these carbs, requires no vacuum to operate. When you are at WOT the slide is out of the way, which equals no resistance to air flow.

Negatives and the thing that bothered me the most. You have to baby the throttle. You can not go from idle to wot or you will stall this puppy out. Huge negative in my eyes. I always had to chock it to get the bike to start, even though people claims you do not have too.

My personal feeling towards this carburetor is do not buy one! I had such great hopes for this carburetor, was bragging to all my scooter buddies how awesome it was going to be. Now i have my tail between my legs.

I would buy a high performance cv carburetor next time. Benefits, when u give it throttle it goes!!lol
Once you have them fine tuned you will love the cv carb over the slide trust me!! Everything about them are easy. Plus they are very cheap to buy vs flat slide carbs.

In my belief i would stay with the cv carb and only switch to a slide carb for racing purposes.

Best of luck, please heed the warning about flat slide carbs, if you run WOT and nothing else flat slide is the way to go. If you use it in town and highways cv is the way to go!

Ray

[Rebel]

Sorry you had such a frustrating experience. Your last post about the holes in the intake manifold identified were most probably the problem was, you might find it much easier now to just replace that rubber pipe with another and see how it goes.

[felliott]

I know you are breaking new ground and have a jetting nightmare. You are proving why 4 stroke scooters have a diaphram carb. Keep up the good work and you will get it to your liking. It is very easy to over carburetorize an engine using a flat slide due to the amount of air it flows.

[kliff]

Flat slides are not for everyone, whereas a CV type carb may be. The CV, with it's vacume variable needle position, makes it a very forgiving instrument to tune, especially when traversing the throttle position up or down, fast or slow.

The Flat or "D" slide carbs are precision instruments of mixing fuel and air, and are not intended as a "Plug and Play" piece, at least they weren't when introduced, back in the day, I haven't followed advertising hype on carbs in years. I just use whatever I have available nowadays, or whatever fits the budget. Just when starting with a F/S, I allow about 5 times more "jetting time" just to get it roughed in. Just comes with the territory.

Would I suggest an F/S or "D" to a noob tuner....HELL NO! They can be a tough nut to crack. But with a "power Jet" as factory installed on an OKO, or a dial-a-jet installed on A Mik.... life gets easier. Loose the P/J on the OKO, and install a D-a-J, and life starts getting easier, much quicker.
With the P/J or D-a-J, the FIRST thing you want to do, is lower the main about 10 points, and raise the slow jet about 2 points. Be CERTAIN, it is correctly plummed, and like usfmarine says...fuel, fuel, fuel.....gotta keep the bowl full on these jewels. NO vacume leaks....NONE.

Set up your exhaust, and intake, and do each and every jetting run with all equipment installed, every time.

A properly done FS is a thing of beauty, a half-assed one is just that, a half-assed sado-masochistic attempt at self abuse. If you don't have the time or patience, and basic understanding of system overlaps...then get a CV. If you want ALL and everything your engine can produce at idle to WOT, and anywhere in between, and are will to pay your dues, then go for an OKO or Mik.

You done good usfmarine, just don't be surprised to see a little interrim tuning as seasons change, not much, usually a teak on the mixture scew, possibly a better flowing pilot in Winter, but that's about it. sually just a tweek on the mixture every now and again.... That's the way we did 'em way back when...it don't seem to have changed much.

[rhettbutler]

Kliff, that was a beautiful post. I like my CV carb for puttering around. It does a good job.

Until the Chinese scooters, the only CV carbs I've seen were on later model Japanese motorcycles, Harleys, and some cars from the late 70's and early 80's. Early pollution control. AAARRGGHH! What a nightmare. At least on our scooters, the number of vacuum lines are limited.

I always liked having control through my hand to the slides. I don't like giving that away to carb venturi vacuum and that rubber boot. You learn how to use the throttle.

But my experience is mainly with ROUND slides. I have some experience with two cycle flat slides, but not four cycle.

I don't hear much about round slides mentioned for Chinese scooters. I've seen gobs of round slides on similar CC Japanese small stuff from the 80's.

I've not searched. Are manually operated round slides available for our scooters?

[kliff]

Jul 18, 2009 7:28:52 GMT -5 rhettbutler said:

Kliff, that was a beautiful post. I like my CV carb for puttering around. It does a good job.

Until the Chinese scooters, the only CV carbs I've seen were on later model Japanese motorcycles, Harleys, and some cars from the late 70's and early 80's. Early pollution control. AAARRGGHH! What a nightmare. At least on our scooters, the number of vacuum lines are limited.

I always liked having control through my hand to the slides. I don't like giving that away to carb venturi vacuum and that rubber boot. You learn how to use the throttle.

But my experience is mainly with ROUND slides. I have some experience with two cycle flat slides, but not four cycle.

I don't hear much about round slides mentioned for Chinese scooters. I've seen gobs of round slides on similar CC Japanese small stuff from the 80's.

I've not searched. Are manually operated round slides available for our scooters?

OKO and Mikuni both make round slides, and if one in the size I think I'll use one day, crosses my path, I'll scarf if up. As long as it uses a "push on" spigot ytpe mount, manifolding will be a snap. If it a 2 bolt flange mount, just a little improvising and adapting.

Don't be afraid to think outside the box, if it's in the size range you want or need, and that range is compatible with your engine displacement...then it can most likely be done. Probably time consuming, little advice to fall back on, but a carb is a carb. Once you disassemble it, identify the "circuits," and jetting or adjustments for those circuits, it's just a matter of going for it.

That's why my best advice is to always have a "test bike" and your daily rider. Work all the bugs out on the TB, before incorporating them on the DR.

[mrsg]

Well kliff after your write up i decided to give it one more go. Bought some hydrolic hose to replace the intake rubber which was ripped. Fired it all back up and i get back fire coming from my bike when i accelerate. Idle is fine. It is weird and i do not get the back fire with my cv carb, wish i did then i would know it is not the carb.

But i do not have a second bike to play with right now so i am going to save it for the winter.
I would not go with a slide carb again i would stay with cv.
Mind you if i had great success with this i would be praising it.

All in all i would stay away.

Ray

[kliff]

That's really what I meant Ray. I like 'em, but I don't recommend them, especially to noobs, because they can be discouraging. Every now and again, someone like usfmarine will come along, get real close, right away, and with a little logic, and a handfull of jets finds a sweet spot. Those guys are hooked for life. He may own another dozen bikes with CV's and F.I., but he'll never be afraid to tackle another flattie.

Then there's guys like you, that just run into wall after wall. And, well, get discouraged. It happens. No shame there. Experience is best gained on the easiest path. The tougher trails can be explored later on, when you have some experience to fall back on. Afterall, this IS supposed to be fun, right?

Do it the way YOU most enjoy it, and don't worry when your buddy rolls out a triple progressive carb, 14mm flattie, 24mm CV, 32mm round top, on a 206cc fire breather, he, "just slapped together this past weekend," that purrs like a kitten....
Cause he may have neglected to tell you how many Tumms, Tylenol, beers, busted knuckles, sleepless nights, and months of development he put into that "weekend build." LOL

KISS, it'll all start to fall together and make sence....

PS....what were you saying about quitting Ray? I ain't quit, I just figurred I'd take on some of the tougher projects, and let some of y'all noobs 'sperience the trenches full of mud, bloodand OIL!

DOUBLE PSPS.....the acceleation backfire is usually a sign of a lean needle. The flattie doesn't have an accelerator pump like the CV does. Raise the needle one clip position, try a 122 main, and screw the pilot adjustment in. On the OKO, it adjusts air, not fuel. Screwing it in, will make it ritcher, not leaner.
Just see if that gets you closer. If it does, then you've got a path....go for it.

[usfmarine]

Sorry you're not having good luck mrsg. My mikuni 28mm flatslide was a breeze to install (except the throttle cable that took forever to modify). It sounds like you're having the opposite experience that I had. Mine is not finicky and has been rock solid since day 1.

You sure yours is jetted correctly?

Bogging at 3/4 -> WOT sounds like a specific jetting issue.

I find the more sensitive throttle exciting. No, you cannot jack the throttle from idle to WOT and expect the engine to take that. If you know how a flat slide works, why would someone expect that to work? With terrific throttle response comes the obligation to not jack it around like a 14 year old on his first quad. If you want the most forgiving carb that will allow you to ride strictly at idle and WOT, use the CV. If you want to have fun with the throttle, get a flat slide. That is of course if you can get it to work with your scoot.

Anyone can PM me if they have specific install questions, I've walked many dawgs through the process of installing these bad boys.