OzVMX Forum
Clubroom => Tech Talk => Topic started by: Freakshow on April 11, 2011, 12:27:29 pm
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so here's the thing.
i have 2 x 250cc bikes now both making the same rattling - deto noise......
1 has a PVL - set at 2.3 BTDC
1 has a standard yamaha ign set at factory BTDC
one has a 36mm carby
1 has a 34mm carby
1 rebuilt motor
1 original motor
NOw here's the thing, they were jetted seperately and by differant people and with a plug chop there looks to be tan and plenty of gas on the main jet on BOTH.
And they both sound clean and crisp off idle on the stand.
NOw this is where it goes pear shaped, after the first FT lap or 30 sec, they both rattle from what sounds like in the head/ barrell like a can of spray paint. and i mean rattle ugley although it seems to get noisey as they warm up and is only under riding throttle.
I have stuffed about with the timing and main jets and results stay prity much the same. There must be a common denominator as the bikes are unrelated so there is no duplication of a mechanical error.
Although they were ridden seperately, and 6 months apart , the fuel came from the same bowser outlet , as i happened to have a empty can on me at the time. It was shell V power or what ever they call there 98 at both times. LAter yesterday after we had a tune up day bike 2 displayed the same characteristics as its brother had 6 months earlier at a race day. Later in the day i drained the tank and used a mix of BP 98 and TTS the pinging/ rattle had moved from across the range under load to just the bottom to mid under load and went away at full revs, throttle. so i suspect its in the Fuels burn or the timing of the burn.
The motors are stock so the amount or style of fuel is my problem i suspect. What does my head in is, both the bikes are displaying the same issue. "Rattle can in the motor' albeit now i have got it down to the low end - loaded. Late in the day After about 6 laps i think it nipped up So i pulled in , (will pull it down this week to see what was going on there) as it warmed up, and maybe up the pilot incase its leaning off the gas. But these bikes are to far removed to be displaying the same fault based only on set up. iT has to be a fuel related issue in quality or quantiy characterised by the Shell or BP 98 that has changed the previous baselines that worked.
Question anyone else seen this change and if so what correction did you make to move or solve the issue ?
What concrete ( not guesses please ) adjustments should be made to chase out the problem.
I plan to pull them both down in the next week or so and record them separately to see what is mechanically the same and what if anythign is differant in the barrel and head, squishes and comp etc. Incase there is a need to refer to this data and make changes.
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definately do not use the shell fuel it will cause problems
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had the same thng but both my motors failed . it was a blocked feul tap they would run good for about 2-3 laps then sh88 them selves.It seems that those motors will run very lean and detonate befor seizing.
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You can try BP 100 then at least you will know if it's the fuel or not.
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But why on a plug chop was the plug tanned out ? at some point it was getting Juice in.
Only one has a Fuel filter, but in saying that i actually checked it was flowing on at least two occasions.
cant beleive both have had blocked fuel taps. both were on 25:1
Its strange its worse on the shell and only 25% better on the BP. IM yet to try i higher octane again, but i would have thought the timing and flow would have made a differance there but not that i could notice. Standard heads so its not over compted.
if i had the chance i was going to strat messing with needles. ITs just weird that both are dipsplaying the same issues so there is a common issue.
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Float level setting, it could be that the fuel level is to low resulting in not enough fuel at FT ?
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Hi whats spark plugs are you useing and what heat range? can you get your hands on some AVGAS as it still has lead in it ANTI PING AND KNOCK (just to test for fuel sake) , have you tried other fuel additives and other 2 stoke oils ? recommend belray MC-1 or PENRITE TS40C ,what happens when you richen the fuel ratio? start at 30:1 then 25:1, 20:1 even 16:1, are they running cdi or points? did you use a battery powered timeing light to see what the timeing curve is doing in real time? have the heads been modified or are they stock? try lowering compression ratio (2 head gaskets) are both the port timeings the same, have they both been modified from std (ported) WHAT AIR filters are you useing? HOW much back pressure? have you done a engine pressure test to see that they are not sucking air from a seal, gasket or crankcase join, all the best and hope they come good and soon.
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NOT float as both Carbs do it.
As i said HEads barrels are standard.
2 differant timings/ bikes shelpi they cant both be out.
one motor has new seal other ran fine a few years back so the seals were fine.
Its got to be something in the way the fuel is or isnt going bang its the only common denominator and the relations ship it is having on the spark and the delivery of fuel. In 2 differant, but otherwise identical models and cc bikes.
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Freaky ... I normaly run caltex fuel, this weekend I ran shell in My Rm 125 and it was running like shit at high RPM changed 2 plugs and still the same so o the trailer it went . In my case it's either the High speed coil ( stator ) or fuel.
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Start with fuel change. Check float and fuel tap. Let us know when you find answer.
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i changed fuel like i said went from the shell to the BP ( drained tank and refilled) as it was the only thing i could think to try off the top of my head.
went better on only rattle its face off up to half throttle but the nise is still inthere at low to mid revs and under load. increasing with heat...............
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I just did a search on Shell 98 pining its guts out and it had more hits than * insert politically incorrect stament here*
I suspect more an more its a definate fuel issue. I just have to figure out how we can tune around it.
If a harley complains of pingin there must be issue with te juice itself
http://www.hdforums.com.au/Default.aspx?tabid=71&view=topic&postid=312592&forumid=27&tpage=1
THEre was a write up that all feul comes out of BP qld and then each state blends it out ? so if that the case Shell SA may be way diffeant to another state at the pump. iSee that have added inhibitors to increase economy ? what ever you need that for ????
I had had a lot of success with a batch of that ethonal stuff in the TM and it went like a cut snake, but i never had the can with me in the car when i was going that way. Might be worth me making a special trip to get a can filled to suss if it makes any differance in these bikes.
and as such if its true as they say that ethanol based fuels have "a natural tendency to resist compressive precombustion in engine combustion chambers." Its probally worth me testing an outing to see if the inherant 'effect of lifting octane and allowing exposure to greater heat and compression in engines without 'pinging' (precombustion)." actually does anything to move this problem away.
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It sounds like they are detonating through too much compression or the timing too advanced and you may need a higher octane fuel or add an extra head gasket or base gasket and try that.
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Lift the head and look for signs of deto on the head and piston. If you can see signs of sandblasting the fuel per se will not be the issue more the O2 content of the fuel.
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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.
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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.
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Could the octane rating be to high?.In the old days,you had to use standard fuel with two stroke oil.paul.
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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.
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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
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i am with you brian i only use caltex 98.
no pinging with this on any of the bike i use it on
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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.
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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.......
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FREAKY
you prob know this but 1 change at a time
good luck
jim
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YEP, that just my elimination schedule.
Try one onto the next............
if nothing out of above works, i start stabbing people at the bowser.
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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
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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.
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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.
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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.