24mm carb is pathetic even for a bucket!

**F5 Dave** · 21st August 2006, 18:28

So whaddayareckon? The F4 125 aircooled 2-stroke rule to limit carb size to 24mm is quite a limitation. Probably why there aren’t any fast aircooled 125s.

I mean compared with a water cooled hot 100 that may be running a 34 (RS 125s run 39 & bigger) the 24 has an area of 452mmsq compared to a 34 of 907mmsq. That’s half the size for a piddly extra 25cc & aircooled to boot!!

So who wants to front up to the next MNZ doodacky & give those poor 125 guys a boost, say 28mm might be better? (615mm).

Actually there are some guys I believe who are running 28s & none of them seem to be cleaning up.

**Ivan** · 21st August 2006, 18:32

Originally Posted by F5 Dave

So whaddayareckon? The F4 125 aircooled 2-stroke rule to limit carb size to 24mm is quite a limitation. Probably why there aren’t any fast aircooled 125s.

I mean compared with a water cooled hot 100 that may be running a 34 (RS 125s run 39 & bigger) the 24 has an area of 452mmsq compared to a 34 of 907mmsq. That’s half the size for a piddly extra 25cc & aircooled to boot!!

So who wants to front up to the next MNZ doodacky & give those poor 125 guys a boost, say 28mm might be better? (615mm).

Actually there are some guys I believe who are running 28s & none of them seem to be cleaning up.

Yeah mate that size is gutless as considering you can change carbs on 150s and clean up a 125 aircooled puppy aint winning

**k14** · 21st August 2006, 18:32

if you got it sorted perfectly on a 125 twin then a single 24mm carb can be made to be identical as 2 24mm carbs. would just need to get the timing and porting sorted. then you'd have a weapon me thinks.

i reckon they should increase the size limit to say 180cc too. let people bore out their FXR150's, seeing as they aren't very competitive...

**steve k** · 21st August 2006, 18:39

Originally Posted by F5 Dave

So whaddayareckon? The F4 125 aircooled 2-stroke rule to limit carb size to 24mm is quite a limitation. Probably why there aren’t any fast aircooled 125s.

I mean compared with a water cooled hot 100 that may be running a 34 (RS 125s run 39 & bigger) the 24 has an area of 452mmsq compared to a 34 of 907mmsq. That’s half the size for a piddly extra 25cc & aircooled to boot!!

So who wants to front up to the next MNZ doodacky & give those poor 125 guys a boost, say 28mm might be better? (615mm).

Actually there are some guys I believe who are running 28s & none of them seem to be cleaning up.

Sounds like a job for ya dave to go and lobby the rule makers if you want to run a bigger carb.....

On a different note you dont have a spare cdi that I could test my mb100 motor with. The one I have got is dead!!!!

cheers

**Jantar** · 21st August 2006, 19:13

Originally Posted by k14

if you got it sorted perfectly on a 125 twin then a single 24mm carb can be made to be identical as 2 24mm carbs. would just need to get the timing and porting sorted. then you'd have a weapon me thinks.

i reckon they should increase the size limit to say 180cc too. let people bore out their FXR150's, seeing as they aren't very competitive...

Absolutely correct. Everyone seems to think that you must have one carb per cyclinder. Although that means that each cyclinder can be at optimum tune, you can get the same results from a single smaller carb feeding two cyclinders. Just look at what Burt Munroe did with a single carb on his V-Twin Indian.

K14, Didn't we discuss this very thing at work a ferw days back?

**WINJA** · 21st August 2006, 19:24

Tr50 Has 12mm And 14 Mm Carbs , So Shadup

**stanko** · 21st August 2006, 19:39

Im not sure I agree with this 100%, while that may be true for diesels, 2 stroke are quite a different beast and we are talking about 125 cc aircooled 2 strokes arent we? In a 4t the inlet opens and atmospehric pressure pushes fuel air into the cylinder valve closes it stops , simple eh? In a 2 stroke its a bit different as the suction caused by the pipe can suck the reed valve open again so the carb can fuel the cylinder twice in the same engine revolution, if there are 2 cylniders sharing this carb it would be crap as the pulses would be uneven. Thats my take on it.
Im all for 28mm carbs on 125 aircooled , mainly cos they are easy to get

**Jantar** · 21st August 2006, 20:12

Yes, reed valves do add a complication to tryting to tune the inlet tract. What K14 and I were talking about was the simple piston ported engine such as a T125 stinger. A single 24 mm carb with a properly tuned and shaped inlet manifold would allow up to 80% more fuel/air flow than the two standard 17mm carbs.

**jonbuoy** · 21st August 2006, 20:24

Didn't the V Boost system on the Vmax have one cylinder sucking from two carbs?

**TygerTung** · 21st August 2006, 21:16

If the 125 2 stroke has a massive carby on it won't this make it a bit unfair the the fulla's on there 4 strokes? I mean it's hard enough as it is without them having to contend with a 125 2 stroke with a huge carby?

**Ivan** · 21st August 2006, 21:23

Originally Posted by TygerTung

If the 125 2 stroke has a massive carby on it won't this make it a bit unfair the the fulla's on there 4 strokes? I mean it's hard enough as it is without them having to contend with a 125 2 stroke with a huge carby?

Nah maybe on ya standered CG125 but someone like RG100!! who has a hotted up FXR 150 with Different carb and exhaust system on it ends up producing more power and speed than the 125 2 stroke with 24mm carb.
I have been at the last few meets and no 125 aircooled is near the front

**Motu** · 21st August 2006, 21:42

Just consider yourself lucky you aren't feeding a V8 through 50mm like the NASCAR guys.

**Sketchy_Racer** · 21st August 2006, 21:53

Originally Posted by Ivan

Nah maybe on ya standered CG125 but someone like RG100!! who has a hotted up FXR 150 with Different carb and exhaust system on it ends up producing more power and speed than the 125 2 stroke with 24mm carb.
I have been at the last few meets and no 125 aircooled is near the front

Hotted up aye?

oh you mean the XR250 carb.... that was jetted in my bck yard....

oh and that exhaust system... I thought you said it was shit? you know with the sharp 45 cut and weld .... then the home built muffler

I admit that it does go very well.....

What is hotted up is the CBR 150 with the full race sytem ... very nice that bike!