Port Timings Changed

[GP240]

I have a TS1 225 which has ran great for the last 3yrs,

Get it set up at Chiselspeed to match a Fat Mamba, and runs spot on for another 1,500mls then pops the piston.

The barrel and head had silicone joints but decided to change to gaskets thinking holed piston was due to air leak.

I've now got a 0.5mm head gasket and base to suit to gain a 1.3mm squish.

Runs great upto 3/4 throttle but if i go to full it pings (ting ting ting) really loadly.

Have tried up-jetting (142-152) but still the same.

So the question is by altering the barrel height by 0.5mm, has this now upset my port timings to cause it to run weak at full throttle.

just another thought, does anyone know what the fuel output is on the fast-flow tap, ie how long to fill a 1ltr bottle, just to check i'm getting enough fuel.

please help, Dave

[chris2470]

Hi Dave
I'd check the squish again as it sounds like the piston could just be hitting the head a high revs. Take the head of and you will soon see if it has, its best to be sure.

[Diablo]

Did you have a new head when you changed to gaskets or was your old one skimmed to achieve squish clearence?
Also what was your old exhaust. I've found PMs generate more heat due to a smaller diameter baffle pipe and stinger(which also makes more power). This can be a problem and so I've always set bikes up with pms slightly richer than I normally would and also make sure the timing is no more than 17degrees.
You really need to know what your compression ratio is and also check and if neccesary adjust your timing. Niether of these things would neccesarily show up on a dyno unless the motor was loaded likey wouldn't show up until road tested.
You may find retarding your timing is enough to cure the problem. With the PM the motor will respond well to retarded timing at high revs.

[GP240]

Will check cyl-head clearance and squish,

Same head as before but reduced the 3mm base packer (110 rod) to allow for the 0.5mm head gasket.

Static timing set at 19deg.

I had a bit of a play about with the carb and raised the needle to the bottom clip (rich) which made it unridable, 4 stroking in all rev range, raised clip 2 notches (lowered needle) and its running best it ever has, me n mrs do a 50mile ride round b roads and she cant believe how much better it is.

So now thinking, is it worth leaving carb has it is and putting a black box on the ign to retard at higher revs.

[Diablo]

Well yes they do work well and will suit the pm pipe. Whatever you do I'd start by backing of the timing to 16 or 17 degrees.
To be honest I'd be surprised if reducing the port timings has caused it to run weak at full throttle.

[GP240]

cheers for the info Diablo,

i've changed the timing to 17degs and put carb setting to what it was.

me n mrs are off to cheeky northern monkeys tonight so will see how we go from here.

thanks again and much appreciated for your advise (priceless), Dave