Is a 30mm Dellorto too much for 195 RT Kit with Big Bore

[shocky]

Flow modified jettex for me stg4 harry Barlow 200 scootrs pipe goes well I have a 30 dellorto and a pwk oval D slide to try im going to dyno each and see relative benifits if any

[bristolmod]

whats a "flow modified Jetex" please

[mawso]

Will that not pull a 16 tooth?

[shocky]

whats a "flow modified Jetex" please

The passage way that comes from the fuel bango has been enlarged and it runs a modified atomiser ,again central passage way and holes have been enlarged to give richer mid range also the carb didnt have a gasket on the slide top it has now and tbh its been very reliable and easy to set up harry barlow did it and actually only charged me £10 becouse I had other work done

[cev]

Unless you are two up a lot you wont have any problem using a 30mm carb but you might get a bit fed up with 15/46 if you are going to use it for distance work.

[Adam_Winstone]

Small carbs work well on reed motors, which have extended inlet periods (often 360 degrees), whereas piston port motors have a much shorter inlet duration (less than 180, therefore less than half of the common reed motor's 360). If you need to get a similar final volume into the combustion chamber then you need an induction stream that is twice as fast of a carb that can supply twice the volume in the same time... therefore, piston port motors typically run bigger carbs than reed motors. Yes, I agree that we could go into even greater detail but that's probably more than enough for now.

The above is simply stated to stop people confusing piston port and reed motor carb requirement, they are not the same and any comments relating to reed motors have no place on this thread... if we are talking piston port RT 195 (?).

Going small carb on a piston port motor often limits the power that the motor will make so it all depends what you are looking for; performance on fuel economy? You may find that going for a halfway house simply gives the worst of both worlds.

I personally don't care what carb size is used but the question of, "Will I have any problems running a 30mm?", should be answered with 'No, you will not have any problems running it, in the same way that I and many others have run 30mm PHBH carbs on 175s.' Is it the 'best' carb choice.... that requires a better understanding of what is better for the individual asking the question and what they intend to do with the bike.

Providing you know how to jet a carb and gear it correctly for the motor spec (rev range and pipe power delivery) then you should be able to run a piston port 195 on anything from a 20mm (as per standard SX/TV200) to a 36mm (race porting and rev range). As so much depends on the porting/pipe/gearing/usage/etc. then it would probably make sense to give us these details or simply to ask MB what he would suggest for the specific RT spec kit that you are trying to sort a carb for.

I still stand by my initial comment that the 30mm will not give problems if jetted in correctly.

Adam

[Livi- Graeme]

Got a 30mm phbh on mine. Av266 x7 needle2nd clip 55 pilot 122 main.40slide With a filtered trumpet fitted runs great. 15x46 primary gears with a jet 200 gear box. And a taffy copy pipe

[Adam_Winstone]

^... sounds like a good setup

[Livi- Graeme]

I like this set up. Got the same in my avanti. No need to jump down to third against the wind or going up hills.

[LittleBritishCar]

Thank you for all the answers. I have three new carbs on the shelf; a 24 TM Mikuni, a 30 PHBL, and a genuine 28 PWK Keihin. I have eliminated the Mikuni so it's between the Dellorto and the PWK. Some people swear by the oval bore PWK but I've had good luck with Dellortos, although the smaller variety. The good news is they use the same manifold so I can play around with both once the engine is in.