cv Mikuni carburators any good?

[awayatc]

My aprillia pegaso 650 has 2 Mikuni bst 33 CV carbs (identical to the old BMW f650) I pulled them apart today and gave them a good clean, but wonder about the whole CV concept.
Would I be better off with regular slide type carbs? Has anybody got any experience with "recarbing".... What are the advantages /disadvantages CV/regular slide carbs....
My fuel consumption is about 15 km to the liter which is a lot more then the carbed BMW f650 is reputed to do. Since I only have a 15 liter tank that is a bit of an issue...
The Aprillia has 5 valves , the BMW has 4, but the rest of the rotax engines is nearly identical. The carbs are the same.
I am a bit puzzled, and would appreciate some input.....

[FruitLooPs]

From what I hear about Mikuni CV's (on older GSXR's like mine) they're good for streetable use, smooth power delivery but have less go than equiv sized flat slides (you've got stuff in the way of the airflow, at the end of the day)

Not sure if you would get better fuel economy with flatslides though... I'm going with a set for my gsxr, power reasoning - but they're not cheap

[xwhatsit]

Overseas it's very popular to retrofit Hinckley Triumph twins (which have Mikuni CVs -- 33mm too, off the top of my head) with Keihin CR Specials. I know this because I want a Keihin CR33 myself, so just Googling around

The Keihin CR is a smoothbore round-slide. The Trumpies make more horsepower, but become less smooth; gone is that CV `cushion', instead apparently it's a more direct feel. Being a roundslide sans accelerator pump, one needs to match throttle input to engine speed; you can't just snap open the throttle and let the carb adjust for you. All standard roundslide stuff.

The alternative is to fit Keihin FCR33s instead, for even more performance (but serious outlay). The FCR is a flatside with accelerator pump; you can snap open the throttle and the bike wants to escape from underneath you. Again, supposedly less smooth, but the bike will really howl. FCRs are usually used on MX bikes, they're optimised for that sort of instant snap.

Anyway, this is all second-hand information from Trumpy forums, and none of it speaks about fuel economy.

I, personally, with very limited experience, don't like CV carbs. They're designed to make decisions about slide position that the rider normally makes himself with a roundslide; and usually the decisions the CV carb makes are all wrong. Just ends up feeling soggy and plush like a bit automatic.

[FilthyLuka]

If you are cack-handed, stick with the CV.

You open the throttle and the CV's slide goes up and down when it feels like it, the slide on a flat/roundslide carb goes up when you tell it to.

Keihin FCR is good, I've had good experiences with Mikuni's VM series too (i like mikuni's , don't ask why, just do)

@fruitloops, if you got a GSXR that was one year older you would've had flatslides already :P

Oh, and flatslides rattle like fuck, but you get used to it.

[FruitLooPs]

Yeah but there were VM29SS or some bollocks, either way i'd probably still have taken 'em.

My bike came with 91/92 CV slingy carbs - and yeah they would make everything quite 'plush' and smooth. But nothing too exciting about them, my RG150 comes with a flatslide and if you whack the throttle full open you'll just stall or bog heaps unless you're up to speed.

I still prefer that though, since i've been riding on it for years.

[Crisis management]

When I had an 86 GSXR1100 I looked at the flat slide option but all the info I got was that it made sod all difference; the CV's were more economical, there was negligible power difference but the flat slides had street cred.....

I don't see an advantage to flat slides unless you're going racing and would suggest you're better off to spend the money on suspension if you actually want to make an improvement to the bike.

[awayatc]

I don't see an advantage to flat slides unless you're going racing and would suggest you're better off to spend the money on suspension if you actually want to make an improvement to the bike.

The Pegaso is great fun, and I thoroughly enjoy taking it out for a spin.
But since it is not as economical as expected, I thought that I might as well try to up the performance a bit.......
Also I like tinkering.... and have only done some minor mods so far.
Been Fiddling with the carbs a bit :
One float level was to high, the air/fuel screws were not wat the manufacturer reckoned they should have been, and not the same for both carbs.
The Choke brass tube thingy was broken off and needed brazing....The choke plunger never fully retreated when off.....

As a result the bike runs smoother, idles better and is less jerky at lower revs...
Not sure if i get a bit further on a full tank..... try that tomorow.
Would like to get a bigger range- like the F650's.......still don't get it

What do you mean about upgrading suspension?
( once again, I like to tinker....am a reasonable handy home mechanic)

[Crisis management]

What do you mean about upgrading suspension?
( once again, I like to tinker....am a reasonable handy home mechanic)

Sorry, been meaning to get back to this.....

Generally, in my far from humble opinion the best things you can do to any vehicle are ranked as follows (most effective highest ranking):

Improve rider skill.
Improve suspension
Improve tyres / traction
Improve power output.








Add bling.

Basically a good rider will outride almost anything else, good tyre contact (compound, design & suspension) will have the greatest effect in improving cornering, acceleration and braking and adding power is usually a compromise of some sort ie; better top end at the detriment of the mid range etc...

I think you only need more power when there is nothing left that will make you go faster.

Mind you, I can crash almost anything so I may not be the worlds greatest expert on this.....

[awayatc]

Sorry, been meaning to get back to this.....

Generally, in my far from humble opinion the best things you can do to any vehicle are ranked as follows (most effective highest ranking):

Improve rider skill.
Improve suspension
Improve tyres / traction
Improve power output.








Add bling.

Basically a good rider will outride almost anything else, good tyre contact (compound, design & suspension) will have the greatest effect in improving cornering, acceleration and braking and adding power is usually a compromise of some sort ie; better top end at the detriment of the mid range etc...

I think you only need more power when there is nothing left that will make you go faster.

Mind you, I can crash almost anything so I may not be the worlds greatest expert on this.....

I appreciate what your saying, and am not disagreeing....just that since economy isn't there, I thought I may as well up the power to justify fuel consumption.
The skill thing is not easy, being away from bike riding (or land for that matter) half my life....you just have to re-adjust every time.....
Suspension at the moment is definitely not the limiting factor....