48mm flat slide carbs?
04-14-2009, 08:36 AM
#1
Junior Member
Squid
Thread Starter
Join Date: Aug 2007
Location: Toronto
Posts: 19
48mm flat slide carbs?
Anyone try Mikuni's 48mm flatslide carbs on their VTR? I've added slip-ons, stage 1 cam, hi comp piston, oversized valves and ported the head a bit and can't get the dynojet carb kit to work as well as I'd like with the std CV carbs.
Also, when ever I use a free flow airfilter I always get a lean spot around 4-5k (modified motor or not) that I can't re jet with a change in clip so I'm guessing I need a richer needle. Anyone experience or resolve this?
Unitl then I'll still stick with the stock filter (wire mesh removed) which works better low to mid.
Tx!
AB
Also, when ever I use a free flow airfilter I always get a lean spot around 4-5k (modified motor or not) that I can't re jet with a change in clip so I'm guessing I need a richer needle. Anyone experience or resolve this?
Unitl then I'll still stick with the stock filter (wire mesh removed) which works better low to mid.
Tx!
AB
04-14-2009, 08:45 AM
#2
Senior Member
MotoGP
Join Date: Apr 2005
Location: Montreal
Posts: 5,631
First of all greetings to a fellow Canuck 
Traditionally, going from a CV type carb to a non-CV carb requires going down in venturi size. In other words, a 48 mm flat slide may be too much.
In terms of the filter situation, there is much debate on the merits of aftermarket vs stock filters (even amongst respected tuners who have worked on the VTR). Bob Hayashida (?) of Big Valley Honda (who built a serious VTR in the late 90`s, full of Moriwaki parts) recommends against aftermarket filters, saying there is nothing to be gained and some to be lost (precisely in the area you speak of).
Hope this helps.
P.S. Did you remove the fine screen only or the screen and the holed metal part from your filter? Need to do any jetting changes as a result?
Traditionally, going from a CV type carb to a non-CV carb requires going down in venturi size. In other words, a 48 mm flat slide may be too much.
In terms of the filter situation, there is much debate on the merits of aftermarket vs stock filters (even amongst respected tuners who have worked on the VTR). Bob Hayashida (?) of Big Valley Honda (who built a serious VTR in the late 90`s, full of Moriwaki parts) recommends against aftermarket filters, saying there is nothing to be gained and some to be lost (precisely in the area you speak of).
Hope this helps.
P.S. Did you remove the fine screen only or the screen and the holed metal part from your filter? Need to do any jetting changes as a result?
04-14-2009, 07:07 PM
#3
Senior Member
SuperSport
Join Date: Dec 2005
Location: Sunshine Coast, Australia
Posts: 963
I had the same problem with a bigger airfilter. The CV carbs just don't like it, and the slides won't work properly giving that flat spot.
I tried a lot of things to fix the problem, including some HRC needles (lot richer than stock) I borrowed, but nothing fixed the problem except going back to a standard size filter. The only thing I did not try was changing the springs in the slides. Perhaps some experimenting might find a spring that will do a better job. I gave up on it, as I am going to EFI eventually.
In regards to the carbs, I have seen a few flat slide set-ups for VTR's using 41mm FCR Keihins. So I would have to agree with Mikstr and suggest that 48's will be too big.
I tried a lot of things to fix the problem, including some HRC needles (lot richer than stock) I borrowed, but nothing fixed the problem except going back to a standard size filter. The only thing I did not try was changing the springs in the slides. Perhaps some experimenting might find a spring that will do a better job. I gave up on it, as I am going to EFI eventually.
In regards to the carbs, I have seen a few flat slide set-ups for VTR's using 41mm FCR Keihins. So I would have to agree with Mikstr and suggest that 48's will be too big.
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