Boring the 250r

[subxero]

if you are going that far I see no reason to stick with the stock carbs, seems kinda silly

JMO

[bruce71198]

Originally Posted by subxero

if you are going that far I see no reason to stick with the stock carbs, seems kinda silly

JMO

I only discussed the internals of the engine as far as the build is concerned. The carbs will add another $400 to the build and although not necessary will most likely benefit the package. If I had the fuel curve graph from the dyno runs you would be able to see that in the upper RPM range the stock carbs went rich. I attribute that to the air bleeds in the carb mouth being to small. You still have to be impressed with what was done with the stockers, or not. If the latest version makes it past the overheating issues it will get different carbs. Stay tuned.

[bruce71198]

Originally Posted by corksil

Changing to ninja 300 head = bigger valves, more flow.

But if the 250r carbs I will be using will still be "the" restriction, it's probably not smart to bother trying to find a 300 head ($$$).

Your biggest restriction is the intake valve. I think with a little more developement the stock carbs would be fine. Dyno tuning the air bleed as stated above. The stock carbs are good all around carbs and the small bore will benefit intake velocity so dont write them off completely. I think if I spend about an hour with them I could see over the 42hp mark.
Add to the list stronger clutch springs. Although they don't advertise it Barnetts replacement springs are stiffer.

[sharky nrk]

Originally Posted by corksil

2mm overbore it is. 315cc ninja 250r, here we go.

Do you believe (based on your experience with these motors) -- that changing to a 300 head will have a sizeable performance gain?

Keep in mind I'm doing crower "race" cams, and paying for a port and polish on whatever head I decide to use (250 or 300.)

List of mods currently will include
-300 crank
-300 con-rod
-weisco/JE 2mm overbore piston
-250r cylinder/block (2mm overbore)
-crower "race" cams
-port/polish on head (intake and exhaust valves)
-K&n pod filter (all over intake stuff removed)
-PCV delete
-250r carbs w/jetting
-area P full race exhaust
-kevlar clutch friction plates

What am I forgetting?

Man when this build thread opens up

[subxero]

Originally Posted by bruce71198

I only discussed the internals of the engine as far as the build is concerned. The carbs will add another $400 to the build and although not necessary will most likely benefit the package. If I had the fuel curve graph from the dyno runs you would be able to see that in the upper RPM range the stock carbs went rich. I attribute that to the air bleeds in the carb mouth being to small. You still have to be impressed with what was done with the stockers, or not. If the latest version makes it past the overheating issues it will get different carbs. Stay tuned.

absolutely, I followed your engine thread, very impressed with what was done with the stock carbs.

my comment was more directed at Corksil

[bruce71198]

Originally Posted by subxero

absolutely, I followed your engine thread, very impressed with what was done with the stock carbs.

my comment was more directed at Corksil

My point was that you can always install carbs after the build with relative ease. What I think in my head never seams to make into my post.

[Bigballsofpaint]

Or just switch it over to the 300's EFI while your at it

[Racer x]

I was amazed what I got from the stock carbs. I absolutely love my CR specials but unless you are pulling so much fuel and air the carbs are the restriction there is not much to gain. Except the ability to change jets and needles in seconds. One thing also with the special carbs a good set of needles and pilot main and air jets will add up to 300 dollars real quick.

[bruce71198]

Originally Posted by Bigballsofpaint

Or just switch it over to the 300's EFI while your at it

I haven't made that leap yet. On the ninja anyway. I think it's coming.

[cuong-nutz]

Originally Posted by Racer x

The Weisco pistons hit the cylinder head. I bought the pistons and the bored cylinder cheap on E bay. The guy thought the engine had a knock. It did but not from the bearings. Anyhow I put it all together and have adjusted the cams. The compresson is fine so I will run it. But I am not confident with it.

I think I saw who you bought it from

[choneofakind]

So... Are weiso pistons of quality that should be worried about? I've read conflicting things and can never remember who on ninjette has had what experience with them.

[bruce71198]

Originally Posted by choneofakind

So... Are weiso pistons of quality that should be worried about? I've read conflicting things and can never remember who on ninjette has had what experience with them.

I used the Wiesco pistons in mine and had the same head interference issues that Racerx did. I just used a die grinder and surface prep disc to remove the necessary material.

[corksil]

Originally Posted by bruce71198

I used the Wiesco pistons in mine and had the same head interference issues that Racerx did. I just used a die grinder and surface prep disc to remove the necessary material.

The weisco piston was hitting the underside of the cylinder head? Did you need to remove much of the piston or was it a minimal amount of material that had to be removed?

Thanks.

[bruce71198]

Maybe .030". There is an excess of material in the area that hits.

[corksil]

Careful hands with a dremel and a scale to double check that the same amount of material/weight has been removed from each piston to keep the crankshaft balanced?

This build is becoming a reality, almost ready to order parts.

[liberpolly]

Originally Posted by Bigballsofpaint

Or just switch it over to the 300's EFI while your at it

And add a turbo.