TT250 Keima Carb Numbers

mtiberio · 06-17-2020, 09:59 AM

I wanted to know what the dimensions on the stock TT250 Keima carb were in case I want to replace it. After measuring it, I believe these bikes come with such small carbs as a pollution measure. Smaller carbs run higher vacuum and carburate more cleanly. The numbers I was able to glean:

carb to manifold stud holes: 48mm center to center (no surprise here)
carb exit to manifold ID: 29.5mm
manifold intake ID: 30mm
carb intake OD (snorkle i'face): 42mm
Venturi: 21mm by 28mm

It is the last number I find most distressing. An Aermacchi 250. An Italiam 250 pushrod single from the 60's had a 28mm round bore carb stock. I find it hard to believe that a stock 229cc CG motor could not have decent drivability and a better top end with nothing less than a 28mm smooth round bore carb. Right now the only carbs I see out there that look promising are the PWKs that all have the power jet attachment. Does anyone know if they are round bore or oval bore?

**JerryHawk250** · 06-17-2020, 10:05 AM

Quote:

Originally Posted by mtiberio

I wanted to know what the dimensions on the stock TT250 Keima carb were in case I want to replace it. After measuring it, I believe these bikes come with such small carbs as a pollution measure. Smaller carbs run higher vacuum and carburate more cleanly. The numbers I was able to glean:

carb to manifold stud holes: 48mm center to center (no surprise here)
carb exit to manifold ID: 29.5mm
manifold intake ID: 30mm
carb intake OD (snorkle i'face): 42mm
Venturi: 21mm by 28mm

It is the last number I find most distressing. An Aermacchi 250. An Italiam 250 pushrod single from the 60's had a 28mm round bore carb stock. I find it hard to believe that a stock 229cc CG motor could have decent drivability and a better top end with nothing less than a 28mm smooth round bore carb. Right now the only carbs I see out there that look promising are the PWKs that all have the power jet attachment. Does anyone know if they are round bore or oval bore?

The PWK is a round Smooth bore.

Wild Dog · 06-17-2020, 12:04 PM

Quote:

Originally Posted by mtiberio

It is the last number I find most distressing. An Aermacchi 250. An Italiam 250 pushrod single from the 60's had a 28mm round bore carb stock. I find it hard to believe that a stock 229cc CG motor could not have decent drivability and a better top end with nothing less than a 28mm smooth round bore carb. Right now the only carbs I see out there that look promising are the PWKs that all have the power jet attachment. Does anyone know if they are round bore or oval bore?

You should try a PE28 or if you can find an OEM PWK that doesn't have the powerjet. Pretty much useless on a 4T.
Also i found the PE28 much easier to jet than the PWK.

mtiberio · 06-17-2020, 12:57 PM

Quote:

Originally Posted by Wild Dog

You should try a PE28 or if you can find an OEM PWK that oesn't have the powerjet. Pretty much useless on a 4T.
Also i found the PE28 much easier to jet than the PWK.

PE28 is an oval bore? Max venturi width, what? 26? With a choke plate to eff up the flow? No thanks

**JerryHawk250** · 06-17-2020, 01:07 PM

Quote:

Originally Posted by mtiberio

PE28 is an oval bore? Max venturi width, what? 26? With a choke plate to eff up the flow? No thanks

The PE is a round smooth bore just like the PWK. The difference is the PWK has a flat slide and the PE has a round slide.

Wild Dog · 06-17-2020, 04:21 PM

Quote:

Originally Posted by mtiberio

PE28 is an oval bore? Max venturi width, what? 26? With a choke plate to eff up the flow? No thanks

The PE don't have a choke plate, they have an enrichment circuit.

The ones with a choke plate are the PD and the PZ(clones of the PD)

The PE are mostly a PWK but with a round slide and no power jet.
Plus you have the PE30 with has a bigger venturi.

mtiberio · 06-17-2020, 06:44 PM

Good stuff, thanks. I ran PWKs on my Guzzi, so i'm familiar. The powerjet can always be defeated.

Wild Dog · 06-17-2020, 08:18 PM

Yes of course that the powerjet can be disable.
I love PWK, so i tested them on various CGs (125 to 229), i like them a lot they performance great from 1/4 to WOT but they always seems to struggle at idle, no matter what pilot jet i use. So i did got a PE, they idle just fine but yes the PWK fells much better at near wot.

06-17-2020, 09:59 AM	#1
mtiberio Join Date: Jun 2016 Location: Arlington, VA Posts: 258	TT250 Keima Carb Numbers I wanted to know what the dimensions on the stock TT250 Keima carb were in case I want to replace it. After measuring it, I believe these bikes come with such small carbs as a pollution measure. Smaller carbs run higher vacuum and carburate more cleanly. The numbers I was able to glean: carb to manifold stud holes: 48mm center to center (no surprise here) carb exit to manifold ID: 29.5mm manifold intake ID: 30mm carb intake OD (snorkle i'face): 42mm Venturi: 21mm by 28mm It is the last number I find most distressing. An Aermacchi 250. An Italiam 250 pushrod single from the 60's had a 28mm round bore carb stock. I find it hard to believe that a stock 229cc CG motor could not have decent drivability and a better top end with nothing less than a 28mm smooth round bore carb. Right now the only carbs I see out there that look promising are the PWKs that all have the power jet attachment. Does anyone know if they are round bore or oval bore? __________________ 4 time WERA SuperVintage Roadracing National Champion, SCTA Land Speed Record Holder, 3rd AMA Motorcycle GP of Miami Last edited by mtiberio; 06-17-2020 at 10:30 AM.
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06-17-2020, 06:44 PM	#7
mtiberio Join Date: Jun 2016 Location: Arlington, VA Posts: 258	Good stuff, thanks. I ran PWKs on my Guzzi, so i'm familiar. The powerjet can always be defeated. __________________ 4 time WERA SuperVintage Roadracing National Champion, SCTA Land Speed Record Holder, 3rd AMA Motorcycle GP of Miami
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06-17-2020, 08:18 PM	#8
Wild Dog Join Date: Dec 2016 Location: Argentina Posts: 756	Yes of course that the powerjet can be disable. I love PWK, so i tested them on various CGs (125 to 229), i like them a lot they performance great from 1/4 to WOT but they always seems to struggle at idle, no matter what pilot jet i use. So i did got a PE, they idle just fine but yes the PWK fells much better at near wot.
	1