Yamaha TTR125 Rev Limiter

ACS

Member
Joined
Apr 17, 2001
Messages
242
Likes
0
#1
Does the TTR 125 have a electronic rev limiter and can it be bypassed? The TTR seems to pop and go flat when reved really hard. Its heavily modded, cam, carb, pipe etc. Jetting is well sorted. Bike is fast but faster would be better.

The only other thing I can think of is valve springs need to be heavier. If its springs are there any USA sources for better valve springs?

Any ideas?
 
Joined
Jan 12, 2001
Messages
60
Likes
0
#2
I would check with one of the specialty shops and get their advise. BBR has a championship winning TTR that really hauls and Frank at XR100.com would be a good resource also.
 
Joined
Aug 22, 2000
Messages
527
Likes
0
#3
Don't forget, Powroll builds the parts that go into the BBR race-winning engines. I'd give them a call, or check out their website at

www.powroll.com

BTW, EVERY major Minibike m/x in the last 4 years has been won with bikes running Powroll parts. Langtown, White Brothers World Minis... Jimmy Lewis, Lance Smail, Rich Taylor, Brad Hagseth, Bob Langin, Guy Cooper, Rick Johnson,etc, etc. All these guys run Powroll mini engines & parts!

Anyway, I just thought you might like to go directly to the source!
 
Joined
Jul 27, 1999
Messages
22,683
Likes
503
Location
Chicago
#4
That isn't really answering the man's question PJ but it does have a nice SPAMMY smell to it.

ACS - I haven't had the opportunity to really dig into the ignition on the TTR, but it doesn't appear to have a rev limiter. The valve train does seem to get a bit unstable over 8000 rpm. The rocker shafts are just simple pressed in steel tubes and I think they may be contributing. BBR is in the process of producing their own billet cam and spring package. Im not sure if any other changes will be required to run it.

I've seen some evidence that the TTR overheats the piston crown fairly easily when run hard, requiring a much richer main than would normally be needed to keep it from misfiring.
 

ACS

Member
Joined
Apr 17, 2001
Messages
242
Likes
0
#6
Thanks Rich

I played around with the main jet and went up to a 320 mukini. Its happy at 180 - 200. Thats in a 26mm carb with a big nossle and thin needle. Cant remember the actual sizes at the moment and dont have my little black book with me.

Rockers and shafts as well as cam is much better design than a XR motor and I think the XR80/95/100 etc rev harder esp the 95cc ones so I'm not sure that they are the problem in the TTR. The shafts are a very tight press fit. I think it is the springs but I will keep an eye on the jetting and fiddle around a bit more.

It does have a Powroll cam in it. I think the Powroll one is the only modified cam available in the world. Its done by Webcam according to a email I recieved from Webcam. It is an exclusive. Powrolls new cam is for their stroker engine. I'm running stock bore due to class restrictions in Juniors over here. Powroll couldnt confirm that the cam would work. Actually they canned it with a standard bore. They were wrong. Its really good but it does need carb and exhaust. In a stocker it would be pretty bad.
 
Joined
Jul 27, 1999
Messages
22,683
Likes
503
Location
Chicago
#7
I believe Powroll's cam recommendations are actually spot on with the mild cam in their current catalog. Given the amount of testing they have done you can count on the fact that they didn't draw their conclusions without ample supporting data.

The cylinder head on this engine is the major sticky point in the quest for performance. You can bolt parts on till you're blue in the face but it's an (expensive) excercise in futility till you improve the dismal airflow numbers.
 
Last edited: