24 or 30mm carburetor??? By imnts2 (Read 3,940 times)

[imnts2]

I am of the opinion that a 24mm carburetor properly tuned is the best alternative on a stock 150CC GY6 in ordinary street use with a stock or near stock clutch engagement RPM. A stock engine just does not pull enough air through it to make a 30mm work well, particularly a low rpm- even with a free flowing exhaust/intake.

On the other hand, a BBK with a big valve head, an A9 cam and a free flowing exhaust just about begs for a 30mm carburetor?

Am I correct or am I missing something?

Thanks for the expertise.

[Deleted]

correct. A stock engine works great with the stock carb. but once you go to a BBK and all the works a 30mm+ carb is a very nice upgade!

[imnts2]

thank you.

[tvnacman]

I have seen someone post that 30mm carbs are very hard to tune or to get to work at all . imnts2 slow down don't rush into anything , see what others have to say .

John

[Deleted]

Feb 4, 2012 11:21:21 GMT -6 tvnacman said:

I have seen someone post that 30mm carbs are very hard to tune or to get to work at all . imnts2 slow down don't rush into anything , see what others have to say .

John

That is also true. It is not easy tuning them. My 30mm carb took a few days to tune perfectly.

[tvnacman]

Feb 4, 2012 11:25:48 GMT -6 @scooterelements said:

Feb 4, 2012 11:21:21 GMT -6 tvnacman said:

I have seen someone post that 30mm carbs are very hard to tune or to get to work at all . imnts2 slow down don't rush into anything , see what others have to say .

John

That is also true. It is not easy tuning them. My 30mm carb took a few days to tune perfectly.

so when you say a few days , how many hours spent ?
Has it been ok since ?
Would you recomend someone that does not work with carbs on a regular basis to try this them self ?

John

[sprocket]

Even a GY6 with a 63 mm BBK has borderline vacuum for a 30mm carb... I go 24mm and a larger jets..still have high vacuum and plenty of fuel/air...

The only difference in a 24mm carb is the air flows faster than in a 30mm. I have never seen a GY6 suffer from lack of air...

If you do go 30mm on a 63mm BBK you need also to change out to a free flow exhaust or it defeats the purpose.

There are probably lots of scooters sitting in garages with 30mm carbs that the owners can't tune...they run like crap...

[Alleyoop]

Got that right Sprocket, as you know i am running with a 62mm and 60mm crank and I am running with the 24mm carb and a 122.5 main jet and a #38 pilot and K&N Filter and a Free Flow exhaust. With a 125 main it would start to pop (to much fuel) at high rpms put in the 122.5 and runs like the wind.
Alleyoop

[jct842]

Higher speed air seems to work better than the same volume of lower speed air. I believe the higher speed air gets a better fuel mix. I prefer vacuum fuel pumps too and the larger carb is not going to have much vacuum if any at WOT. When at WOT the fuel mix percentages will stay pretty much the same with the smaller carbs where the larger carb after loosing vacuum the mix will change. It is vacuum that pulls the fuel through the main jet. john

[imnts2]

very good thread

That is I was thinking. Sometimes it takes a bit or reading between the lines. No-one wants to remind a dealer that he may be a bit optomistic what his performance stuff will do. Stick with stock.

thanks

[sprocket]

>.Higher speed air seems to work better than the same volume of lower speed air.

Right on...it has to do with optimum fuel atomization and there are all kinds of formulas. Basically the fuel molecules are more evenly distributed among the various air molecules and this gives a better 'BANG'

The pilot jets on a CV carb also use side holes which does the same thing... atomizes the air fuel mixture better...on idle...pretty cool.