rattle rattle rattle

[shelpi]

I will put money on the combstion chamber, put in another head gasket and the only spark plugs to use are NGK and the only ngk to use in 2 bangers is the EV ie B9EV woops sorry thats old school, now B9EGV, THEY MAKE THE ES look like glow plugs, differant heat range may be needed. and do the process of elimination, ive been stuck in ever increasing circles, prove it right prove it wrong move on, start with the simplest and cheapest 1st. i had a DT250C that was great cold and pinged and fluffy when hot, so cooled down the whole show, richened, coolder plug and oiler than useul air filter the damn thing wanted to run rich, but i was just a snoty nosed kid, so did'nt bother finding out why, didn't even know what a engine pressure test was back then.

[paco]

Could the octane rating be to high?.In the old days,you had to use standard fuel with two stroke oil.paul.

[Freakshow]

If the noise is detonation, then the problem is that your compression ratio is too high relative to the fuel you're running.
Or, the compression ratio is too high relative to how crappy the combustion chamber shape is...

I went down this path with my AT1 and had exactly the same symptoms as you. It was great for a couple of laps from stone cold, but would then ping like mad when it was fully warmed up, no matter what you did with jetting or timing or riding style.

Its a particlar problem for the early xT1 Yammies - a reed valve head on a piston port barrel (or visa versa, I can't recall) will do this every time.

Both Bikes are YZA 250s............... one is mine the other i got from the states.  they both do the same thing.

[PRITCH39]

Had the same problem with my RM250A it was the fuel. The bike absolutley hated Shell and Bp wasnt much better I went back to Caltex vortex and have had no problems since. I also went through similar problems with a mildly worked SR500 years ago, the only fuel it wouldnt ping on was the Vortex.

I hope it is as simple as this for you Good Luck

Brian

[jimg1au]

i am with you brian i only use caltex 98.
no pinging with this on any of the bike i use it on

[Lozza]

Used BP98  from various locations (including a control fuel out of a 200l drum) found it to be very consistent and great to tune to the point of detonation with. The 98's like to run with iridium plugs.

[Freakshow]

one had irridiem the other had a EGV.

BAring any other confirmed fixes,
I'll change to a 100* ethonol blend, try a colder plug, try to knock back the timing to 2mm( currently 2.3), then try a bigger needle tube.
and probally eliminate in that order for operator simplicity.  Any success and ill report back at which point it went normal.......

[jimg1au]

FREAKY
you prob know this but 1 change at a time
good luck
jim

[Freakshow]

YEP,   that just my elimination schedule.
Try one onto the next............
if nothing out of above works, i start stabbing people at the bowser.

[shelpi]

GOOD LUCK FREAKY, I TRIED ETHENOL IT WAS GREAT BUT MIX IT WITH ORANGE JUICE @ 20:1 , MAKES ALL THE PROBLEMS GO AWAY, UNTIL YOU WAKE UP THE NEXT DAY

[090]

One thing I have just found out while jetting my Maico. A proven motor that runs sweet. Only change was a brand new Mikuni and a top end freshen up. It rattled bad in the first part of the throttle, up to the first 1/4 say. All good after that. I put bigger pilot, bigger main,dropped the clip. No change. Had the carby off 100 times, had the top end off four times second guessing myself. Re did the timing, all good. Went through the jets etc with Les ( this is where it's handy to buy locally) and found it had the wrong needle. I know I never take the needle into consideration when jetting and it is just as important as the other jets. Same as the needle jet. I had also had the same issues with my twin port but never considered changing the needle. I am now more confident of fixing that pinging issue as well.

[Freakshow]

I was going to change the needle jet or whatever that tube it in the carb is called, if i had to push the issue any fiurther.

IN My last6 retest - i ran a retarded timing, dropped the clip down 2 and ran the heigher 100 octane juice.  cant hear the pining anymore so think thats got it out.

It was a little flat to 1/8 th throttle though now and when it winds out it drops off in the higher revs, so i have put the timing back to where it was and put the clip back up to the middle slot (just back up one)   but i might still pop in a colder plug/ or little more main jet just incase its still holding heat, but a dam site better than where it was at, man that rattle was annoying.

I point it squarley at the Shell votex from 1/8 to 3/4 throttle and the BP was  marginally better but still
rattled 1/4 to 1/2.

It has liberty 100 max 5% blend in there ATM and there is no pining at all.  I

I guess BRad you have proved the same point the fuels are going backwards if the previous set up is moving away from a standard area of OK.   To have to change a needle to fix a rattle seems a big move, when it makes such a big noise and heats up and yet you have to go to that small a variable to fix such a big issue, the fuel cant be normal anymore and must be clashing with all the other shit they are padding  out there petrol with, polishers, britners, solvents, cleaners, stretchers and what ever.  I used to think octane was the stable, but its seems not anymore cause that seems to change between brands on the same listed oct number. 

I might start going back to the Avgas cans again if it happens again,  to be sure it dont keep  happen.

[chrisdespo]

have a thought that may help, you don't get the same plug color with this new shyte fuel even on the fourstrkes the plug should look a bit richer. on a 2 stroker try jetting till it fourstrokes and then start to reduce main jet size better running a bit rich on top and will help keep these old bikes a bit cooler.