RD125 - Down on speed & power

[sav0r]

So many potential issues. You have to cross your t's and dot your lower case j's.

Does it run better if you back off the throttle to like 70%?

[John Ritter]

A compression test and then a pressure test might point to something.
I would have to look but I think I have engine parts laying around, I was going to sleeve a 125 twin to 100 for land speed because the LS1 cylinders are impossible but like so many projects oh well so if you need cylinders or bottom end stuff let me know.

[SoCal250]

A compression test and then a pressure test might point to something.

I did a compression test last week.
Right: 122psi cold
Left:   116psi cold

For a pressure test I'll need to fab up some block-off plates for the intake ports, and see if my leakdown kit has small enough exhaust plugs or source some new ones. This has been on my to-do list for a while. Too many other things going on lately.

[SoCal250]

Does it run better if you back off the throttle to like 70%?

No change really at just off WOT when running at max speed, after that it starts to slow down with less throttle input.

[rodneya]

A lot of jetting issues turn out to be ignition issues. Id recommend to double check timing and change plugs, or maybe even put the old points back in there. The set in there may be doing something weird when they are opening and closing at warp speed but seem fine at lower speeds.
Stock jetting should really be lean with modern fuel.

[SoCal250]

see if its better with headlight off. 

This is with the headlight off. I've been running with Ignition switch in #1 position (headlight and tail light off)

see if its worse with headlight on. 

Roger that. Next time I'm out on it I'll run a few comparison tests on the small hill near me

I was able to do a little comparison testing with the ignition switch in both positions (#1 lights off & #2 lights on). Also on position #2 I compared with light on (high-beam) and light off (burned out low-beam). There doesn't seem to be any discernible difference with any of the settings, but I'm going to do some more testing just to be sure.

[RustyRD]

What about vent in gas cap, not venting properly causing poor fuel flow. ( starving )

[SoCal250]

What about vent in gas cap, not venting properly causing poor fuel flow. ( starving )

Don't think that's an issue because it's a brand new OEM cap and it seems to vent pretty well. In fact it doesn't seal very well and kind of makes my garage smell like fuel. However, I can try twisting off the cap next time I'm out ripping around and see if there's any change.

I was also considering replacing the inline fuel filters with straight hose to see if there's any difference.

I plan to swap in some new plugs just for giggles even though the "old" ones have less than 500 miles on them.

And I'm probably going to swap in some new OEM points when I get the time to test if there's any change there.

[RustyRD]

Another thought, resistors in the plug caps degrade causing weak spark. Sounds like you are about to cover it all, my next thought would be leak down test.

[Gil Gallad]

being as nobody has mentioned it, i will. just one thing to cross off your list is binding brakes  when a bike is slower for whatever reason i always check for brake binding first - if it's out on the road.
cheers, gil.

[pidjones]

being as nobody has mentioned it, i will. just one thing to cross off your list is binding brakes  when a bike is slower for whatever reason i always check for brake binding first - if it's out on the road.
cheers, gil.

Yup!