F5's 300 head mod thread

Well I went to the dyno last night (in a lockup). But with two other bikes to go on. The upshot however is I scored a 130x18 road tyre in the process. It should just squeeze on good enough for a few runs. When I get keen I'll swap it on & dyno it (have a new selection of jets), but I do have a bit of work for a large race coming up.
 
Weather forecast for sunday is clear light breeze 23 deg so don't be surprised if one of me mates twists my arm into just getting out for a ride.


That said I have to get a knobbly back on before the 23rd or my next ride will be a bit of a struggle.
 
Faultless day here. Should have gone for a ride on the road bike, but decided to go to the dyno after all. Wasted my time. Tyre wasn't beaded properly. Looked ok in the garage, but not quite. Couldn't bead it with the foot pump. Went to the servo to try bead it with forecourt pump. Went to three but they all failed. Tried a few runs, but they were all over the place and looked like 3 different bikes. You need a round tyre. Arse.

Bad luck (preparation) continued with my 500 ( RZ350 with a Trinity Banshee 496kit). Was going ok but stator bolts started backing out with a resulting burning wire smell. Double arse.

Have to try bead this tyre and get back this week and then fit another S12.
 
That sounds like an awful day! I always fit tyres using loads of WD40, far better than tyre soap I find :). I'd love to get mine on a dyno but there aren't any too close and I've just put a fresh set of knobblies on by hand!
 
You know, I'm beginning to dread trips to the dyno, or rather I have for a while. With development you often find the great idea of something to try that will def add power often doesn't. Moreso on the small cc racebikes which are modified commuters so have many compromises, but sometimes just weird stuff happens. . . . Or payback for my laziness or lack of time.
 

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Ok this sucks. Tyre beaded ok (Yamaha tyre spray), but now I have another problem. Won't rev out worth a damn. And won't run consistent up top. Fine at lower revs.

Tried a 2nd hand plug, no real diff. Put a bigger main in it and maybe better. Put a brand new plug in and it was better for one run, but still not good. Seems to run fine at low revs.

I might have to borrow a mates bike and play swapsies with cdi etc.
 
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Well its all pretty bizarre. Measured the stator coils & ign coil. All within spec when cold.

Went & grabbed a mates 07 EC300 same as mine. Swapped out the cdi & coil & ran the bike up. Revved out to 9500. Still not fantastic power but at least its revving out. Swapped back to my cdi. Even better. Eh?


But now I'm finding that I can influence the power curve by where I start the run. There is a pretty nasty hole from 5-6000. If you start the run above it, it provides a better run. If you have to pull through it it loads up a bit & affects the run higher up.

Swapped over muffler, pipe (in case my de-cat'd pipe was an issue) & even another coil off another bike. Pulled off the PV cover & pipe & checked PV moves freely. Pipe on & start it up & PV operates.

But it does swing open pretty quickly. I wonder if on the dirt it spins though quick enough that this dip doesn't happen vs turning a heavy dyno roller. If it still does its asking for a heavier PV spring to delay PV opening I'd say.

Tried a 175mj (down from 178 I'd put back in the day before & it preferred the 178 (this is NZ gas so don't draw conclusions).

I have the rare opportunity to put my mates bike on to compare. But I still have to put his parts back on, pull the wheel off mine & onto his & I don't have any stands at the dyno lockup.

I've had two past midnight evenings so I load up. I'll ride it sunday. Maybe we'll do a drag race or three.

Still sounds & pulls real fine down low. But I'm concerned how variable it has been on the dyno and I've found no smoking gun as to why it wasn't revving out. Perhaps my ign coil, but I wanted to leave my cdi & stator on for the night so if it ever played up again I didn't have another suspect in the mix. I'll swap my coil on after a loop & try it when hot. Its a 5min swap & easy to do in the field.

Had the
 
Go leaner on the main. My head mod pushed me from 180 to 168. I thought the bike was fucked when I'd put it all back together, but eventually came to the jetting in my sig. I have about 30 main jets, 15 pilots and 4 needles. I did not copy and paste my jetting from anyone. Go down mate! 2 strokes always require leaning out after mods like this as the velocity through the carb increases and draws more fuel through!
 
motopsycho87 said:
Go leaner on the main. My head mod pushed me from 180 to 168. I thought the bike was fucked when I'd put it all back together, but eventually came to the jetting in my sig. I have about 30 main jets, 15 pilots and 4 needles. I did not copy and paste my jetting from anyone. Go down mate! 2 strokes always require leaning out after mods like this as the velocity through the carb increases and draws more fuel through!
Click to expand...

I would not say "always" but more often than not mods lead to leaner jetting. If your mods have increased the efficiency of the motor at "X" rpm then a jetting change will be in order. It all boils down to charge density vs flow vs blowdown vs resonance vs trapped volume , a little simplified but you get the idea.
 
Dyno sez 178 over 175 or 172. Well for now. Bike runs fantastically off closed throttle low to mid revs. Didn't think there was a stumble but the course opened out and I became aware of it.

I'll pull the PV to clean and check both ends. But other bikes have queue priority till mid next month. I'll test for main when that's sorted. I've gone down to av38 pilot which is ideal.
 
Did you raise you barrel much? if you didn't that may explain it? Am at sea level, air is almost freezing and I'm running 28:1 at 168, technically I should be jetting richer but have found the opposite!
 
Also I do remember a friend "looping out" his jetting on an X7, jetting so rich it started getting better again, obviously it didn't run great, but later he went the other way and that thing sang!
 
My barrel is in std position height wise. Also Our Gas will be somewhat different.

It could be that if the PV is miss-operating it is requiring a different profile to get through the dip.
 
Hey I've been racing small roadrace motorcycles. I got 2nd in our national 50cc class yesterday. That saddened me as I wanted to win,

Worse I got duffed up by a 19yr old. . . . Which I suppose isn't as bad as getting a 19yr old up the duff, but makes you feel old nevertheless.

Trail ride on next weekend so back on the GG - I'm pulling the pv out before that if all goes well & can inspect, clean, repair, compare in short order. Next step is PV mods for more preload but lets get back to std.
 
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