Struggling to get past 6500 revs

[davewills4]

Hi all,  after having got the no spark problem sorted put bike back together and went for a run starts first kick and seem to run nice. But when I tried to get past 6500 revs the engine struggles as though starved of fuel eventually will go past 6500 and then revs cleanly to 9000  if i knock it down a gear or 2 it happily revs freely its just trying to get it past 6500 if i stay in the gear im in.  Is this something to with carbs,or as i read somewhere i had to adjust oil pump a long way to get it to line up as per manual compared to how it was set up over the last couple of years. Has anyone have any suggestions.

Cheers Dave

[claw74]

Hi Dave,

Checking the oil pump settings wont hurt and it only takes a minute.  It did make a difference on mine.

If you can I would get it dynoed as it will show you where the problem is.  I should have done it years ago.  it would have let me enjoy the bike more instead of guessing what was wrong with it.

John

[teezer250]

6500 is about where the powervalve starts to open and if you are in too high a gear,it will struggle and if you are sort of tootling along around those revs,the powervalve kind of can't make its mind up to open or not.You will feel the bike sort of hesitating.
You need to ride it in a sporty kind of way with the revs up and not too high a gear.
You really cannot ride it lazily in a high gear and low revs and expect it to pull,it will bog down until you drop down a gear or two, unlike with your Suzuki 750 4 stroke which will pull from low revs in a high gear.

Hope this helps,Phil.

[davewills4]

Hi Phil, this is different to the feeling of where the power valves are deciding to open  it really can take 4 or more seconds to pull through and past 6500 revs in any gear and feels like it is struggling to get fuel  for a few seconds then will go on to near red line quite easily. When I put the engine back in and reconnected the oil pump I had to o really adjust it a long way to get the markers to align on the oil pump so was just wondering as claw74s post about it affecting his performance. Cheers Dave

[teezer250]

Hi Dave,the breather in the fuel cap might be partially blocked preventing good fuel flow.
If you take the tank off (again unfortunately) you could try a few tests to determine fuel flow.
Connect the vacuum pipe onto the fuel tap and a pipe to the fueltap outlet into a container.
Then suck on the vacuum tap to see if fuel flows freely in the "on" and "res" positions and also try the "prime" position without sucking on the vacuum pipe.
If you try the "prime" position first,it should flow quickly,but if it shortly after starts to come to a trickle,then the breather in the cap is partially blocked.

The other possibilities may be the oil pump setting or even the ypvs box settings.(the dip switch settings done by the 2 stroke race lab in Greece).
Turn ignition on and let the powervalves cycle,then open the throttle fully and the dot mark should line up with the pin.
Repeat the process again to ensure the dot mark and pin line up.

Here's a link to some dip switch settings for the 1KT from the 2 stroke race lab,scroll down just past half way:
http://www.2t-racelab.com/search/label/YPVS%20reprogrammable%20controller

And a little bit more settings info further down regarding the 1KT.
It sounds like my favorite setting for the Tzr250 1KT will suit the early Rd350 bikes as well.
The suggested setting is 1-2-3-6-7-10-12. This setting while used on the early RD models will pump up some more midrange and still retain an aggressive and quick opening at 9.000rpm... just to retain the old school two stroke spirit.