Scooterotica

Hi,

I have a new build, still riding in with only 25 miles on the clock. Revs out with good power in 1st, 2nd and 3rd. Power drops in 4th. Revs drop by about 2000 revs.

Rapido Race 225 with Harry Barlow piston,
Li150 gear box + 46/16 = 4.9 gear ratio.
Tameni 60/110 racing crankshaft
JL4 exhaust
BGM stator with AF Light flywheel (AC)
5 plate clutch
81 link chain with LTH pull down tensioner.
Dellorto 30PHBH carb with LTH reed valve
Kytronik smart booster 2.5
Boost port by Scooterotica

Can't remember the jetting set up, I will have to strip it and look at what I put in it. I based it in an average TS1 set up from memory, but I am thinking it might not be getting enough fuel or something when it is getting up there in the power range, Seems to be great up until the end of the rev range in 3rd. Then I change into 4th and power just goes?

Help please!

Have you checked petrol flow rate?

or

stuck or worn rings ? What's your piston/bore clearance ?

The petrol tap is a brand new SIP high flow tap, there is no extra in line filter or anything, so that should be Ok. The Piston and bore is unknown, But I had the barrel off only a month ago and they were not seized. Only about 15 miles on it since then, slow riding around town. Only in 4th for the first time this week. They won't be seized.

i had this with a jl3, changed gearing, carb , coils etc etc etc, fitted a bgm clubman and it pulls great in top, might not be your problem but mine would die a death in 4th,,

You have a pretty torquey top-end and a decent gear ratio but that JL4 is pretty high-revving and it might add to your problems in 4th. The Fran Race is a good alternative and offers more low-end torque than the JL4 and starts to pull hard by ~5500 rpms. For even more low end pulling power the Fran SuperTourer comes in at ~4500-5000 rpms and hits hard.

Hi,

Clarify how you have set-up Smart Booster variable ignition unit.
It could simply be that you have not enough timing at mid to high-RPM.
Piece of advice: setup your engine with Smart Booster on Curve 0 (strobe ignition to confirm static timing). Then only, once jetting is fine, enable variable ignition timing

With reference to your fuel tap, you say it's new and "should be ok" have you actually taken the pipe off and checked it? The reason I ask is I had a new tap supposedly high flow, well I can tell you not one drop of petrol flowed through it haha.....worth checking before you dig any deeper.

If it is pulling well at high revs in 3rd then it is unlikely to be retarding too far in 4th as it'll be running higher revs at the top of 3rd. It could be a combination of a number of things. Depending on the port timings of the top end, it could well be that it wants to be running 5.2 4th ratio, rather than 4.9. If you consider the JL4 to be a revvy pipe and look at AF's recommendation for gearing with various pipes (also printed at the back of Sticky's manual... nice one Sticky) you'll see that they recommend 5.2 for the revvier pipes in the list. It certainly sounds as though you're bike is happier in 3rd than 4th, which is typical of a bike that has been over-geared for the state of tune.... or over-tuned for the gearing that you want to run.

Adam

With just 25 miles on a rebuild things will still be a bit tight and not yet run in. I'm sure that if you give it a few more miles then it will loosen up and run much better. Besides AF Rayspeed recommend staying below 35mph for the first 100 miles and 45mph for the next.

ming wrote:You have a pretty torquey top-end and a decent gear ratio but that JL4 is pretty high-revving and it might add to your problems in 4th. The Fran Race is a good alternative and offers more low-end torque than the JL4 and starts to pull hard by ~5500 rpms. For even more low end pulling power the Fran SuperTourer comes in at ~4500-5000 rpms and hits hard.

+1

Stick a JL3 on it.