Carbs

[dopeshots]

Thanks guys, I ave learnt loads from yor posts.

So am I correct in thinking that the carb of choice for a fast TS1 is gonna be a TMX35?

[nelson pk]

Thanks guys, I ave learnt loads from yor posts.

So am I correct in thinking that the carb of choice for a fast TS1 is gonna be a TMX35?

Its still down to personal preference. I would still choose a Delly VHSH 30mm over a mikuni 35 tmx.
Some tuners like the mikuni tmx, some dont.
It also depends on what you mean by a fast TS1? top speed or good response low down. The bigger venturi size you go say, 35mm, would probably be best for top speed but you will lose a bit lower down compared to a 30mm generally.

You may put a 35mm on and have no top speed gain and still lose lower down, it all depends on other factors like exhaust etc as well.

[GP Kevo]

Mikuni TMX 35 has excellent throttle response for it's size, certainly better than my old Dellorto VHSA (?) 32 mm.

[victor]

Best carb? I'm 'graduating' to Keihin PWK for the responsiveness and fuel efficiency: 1 x 28mm and 1x 33mm, phasing out Dell PHBH30 and VHSB34

Waiting for the chosen top end kit to be produced in the meantime I've gotten the pipe and the carb.

So on a standard Tv175 with Gori exhaust I slapped on a PWK 28mm with blocked PJ.

Due to the engine's limited performance I constantly ride it WOT everywhere.

For the first few tanks while still running (way) too rich I couldn't see any noticeable difference in fuel consumption from the standard SH1/20, whereas I was expecting it to get worse :O

Further to this, after having jetted it up correctly I believe the scooter to now consume less than previously but since my speedo currently is out of order I can't verify this, but definitely filling up less frequently than previously...

[shocky]

ive used several large bodied pwk/koso/stage6 carbs these are khelin copys very compact oval bore D slide and are able to be ored out to 35mm if needed i prefer the large body ones over the small 30mm because the fuel flow was nearly twice as much with the float bowl off allowing a greater safety margin they used to be very well priced for spares but as they have got more popular SAT has been added to the cost the carbs can still be got for about £50 and theres some info on the scootrs site re jetting and some on here who will trade sel or swap parts for jetting ohh and SAT is scooter added tax

[fairspares]

i ran a 34 koso pwk for many years, shocky is right about fuel flow being better on the larger bodied ones but i have found the float to play up and stick now and again , the new koso,s on ebay from extremeimport2 are s**t quality and look like copys of koso,s copy so its twice as s**t, i sent one back i bought a couple of months ago apparently the oko version is better. i bored the 34 out to a 37mm and ran on my sprinter for 2 years but ive now gone over to keihin pwk 39, i have done quite a bit of dyno testing against dellortos and found them to give much better results but ive never tested against a mikuni.

[victor]

i ran a 34 koso pwk for many years, shocky is right about fuel flow being better on the larger bodied ones but i have found the float to play up and stick now and again , the new koso,s on ebay from extremeimport2 are s**t quality and look like copys of koso,s copy so its twice as s**t, i sent one back i bought a couple of months ago apparently the oko version is better. i bored the 34 out to a 37mm and ran on my sprinter for 2 years but ive now gone over to keihin pwk 39, i have done quite a bit of dyno testing against dellortos and found them to give much better results but ive never tested against a mikuni.

And I got the BGM version which both in price and finish seem to be inbetween Keihin and OKO.

Did you do anything to avoid the float sticking...?

[fairspares]

the bgm version looks like the early good quality koso type , i tried many things to get over the floats sticking but never really found a solution they just seem to be cheap and flimsy you just have to be very careful when taking the bowl on and off. i do like the clear bowls but had 1 buckle once when i was parked in the sunshine one hot summers day.

[Yanker]

Think we have summarized same opinions there Mr Piquee.

Basic Vacume in the venturi = (DisplacementxRPM) / RPM x (inlet tract minimum id in sq mm - crank chamber volume below BDC)

This factor can be added to in direct figures by (inlet tract length x diameter (mm) / 343.2 metre per second

Factored of course by sub BDC chamber volume and exhaust efficiency (Blair et. al.)

But most importantly "when you increase the revs or opening the throttle the powerjet cuts in to supplement the leaner main jet": just think of all the overlap and possibilities for lower than desirable venturi vacume when the PJ ought still to be working eg. at 875 rpm and WOT is the power jet working?

[nelson pk]

Think we have summarized same opinions there Mr Piquee.

Basic Vacume in the venturi = (DisplacementxRPM) / RPM x (inlet tract minimum id in sq mm - crank chamber volume below BDC)

This factor can be added to in direct figures by (inlet tract length x diameter (mm) / 343.2 metre per second

Factored of course by sub BDC chamber volume and exhaust efficiency (Blair et. al.)

But most importantly "when you increase the revs or opening the throttle the powerjet cuts in to supplement the leaner main jet": just think of all the overlap and possibilities for lower than desirable venturi vacume when the PJ ought still to be working eg. at 875 rpm and WOT is the power jet working?

At wide open throttle the power jet will be at its highest flow rate, thats the point of it.
When you shut off from wide open to cruise at lower throttle positions the needle atomiser is more important to let enough fuel through the bleed hole there (this is where most seizures and holey pistons occur because the needle/ atomiser setting hasn't been properly set up for this), granted you cant go too low on your main but at the lower throttle positions you don't need as big a main jet, its the needle atomisr bleed hole thats more important so you can go down a few sizes on the main.

The idea is that with a power jet you go down on your main a bit and this therefore cleans up the carburation lower down because less air is delivered at lower throttle positions so you dont need a whopping great main although the bleed hole between atomiser and needle is important and needs setting correctly.
When you reach half throttle and above, you need a bigger main because more air is being delivered so your power jet starts to kick in to supplement the leaner main jet and flows progressively more (like the main jet) up to WOT.
When you roll off the throttle to cruise at say just under half throttle the power jet starts to cut out but as long as needle/atomiser setting is good you dont need the whopping great main.
All jets overlap otherwise you would have lean spots all over the place.....books etc say the main kicks in at this point and needle at this point for illustration purposes but they all overlap a lot, its just that at the positions quoted its when they are making the biggest difference to the carb.
For example....books etc say the main delivery system does not kick in to 1/4 throttle......i think you'll find there is even overlap from the main at tickover......not a lot, but its there although the jet operating the most is the pilot/idle jet.

You can also do a very simple test fot lean peak, low revs at wot, by having the scoot at tickover on the stand and a quick snap of the throttle to wide open. If your lean, it will cough and die....if its safe the scoot will respond quickly but this can mean your too lean at any point in the throttle range.