1990 Yam Exciter 570 - Missfire ???? - Snowmobile Forum: Your #1 Snowmobile Forum

Dave · 02-21-2005, 02:14 PM

Hi Folks, New to the board, could use some help, at the start of this season I bought a 1990 Ex570, beauty shape, PST pipe, jetted etc....was running great.. till recently..

I think ive got a missfire (i say "think" not sure if im now only just noticing the nuances of the way this piped and jetted machine runs)..any way.. It Idle's great, but at just over 3200rpm as the clutches engage, i detect a miss, once she's over 5500 - 6000 and really on the pipe...its fine, goes like a scared cat... its just that mid range where i hear/ feel it..

Changed the plugs already, no difference..

could it be too much oil in the mix, i tend to add a wee splash of oil to the tank each time i fuel up (just for that bit of extra lube)..

-plugs are same colour, wee bit black form oil,
-it doesnt bog at all
-throttle response from idle to full is great.

any other thoughts on what it is or what to do to narrow it down?

thanks in advance for the help

**smallengineguy** · 02-21-2005, 06:22 PM

Is it a constant miss or occasional?

Dave · 02-21-2005, 07:50 PM

its constant (if im getting what you mean), as soon as it hits just over 3000rpm and the clutch engages, its starts missing , the miss firing engine tone doesnt go away, its constantly misfiring (almost like throwing a switch).. now as i said when im ove 6000 rpm, i dont notice it, i dont know if thats because its goes away or the engine is firing so fast i dont notice ....

thanks for any help

**smallengineguy** · 02-21-2005, 08:13 PM

Maybe it's a little lean in that RPM range? Did you try moving the slide needle clips down one notch to richen the mid range a little?

Dave · 02-21-2005, 09:06 PM

No, didnt change any carb settings, it wasnt doing that when i got it, so i figured something had failed in some way...ie bad gas, too much oil, plugs, dirt in the carb, bad witres, coil etc....????

maybe i should go over everything again,

ill try dropping the clip one notch down if that doesnt do it...

Dave · 02-22-2005, 07:09 AM

What if i remove the Drive belt and try revving it to 3500-4000 or so, ie see if only miss fires under load....?

what would that point to if it misses only weh the clutch is engaging ?

**smallengineguy** · 02-22-2005, 04:34 PM

You have an inline spark tester? Might want to try it on each plug when it's running to try to determine which side is misfiring. May be something as simple as the coil for that side.

Dave · 02-22-2005, 06:49 PM

no, maybe ill go get one, may save me alot of trouble...

one other question,, what does the carburator switch do ? ie the electrical connection thats attached to the carb? what would be symptomatic of that being buggered,?

Just in from the garage - More info on my problem...

-Removed the belt, it still misses but not as bad - put belt back on.
-Seems to be worse after it gets hot (electrical?)
-Ive confirmed that it misses right thru the rev range over 3000, ie it doesnt go away over 5 -6000 (carb? ie low speed circuit ok , other not?)
if i pull the plug wires off while its missing, i still get a huge difference on both sides, so, both sides are firing.

for some reason while on the jack stand, it wont rev past 6500 rpm or so ...that normal ? i typically dont ride it beyond there (ie im not one to thrash it alot) so im just noticing this.

**smallengineguy** · 02-22-2005, 08:50 PM

Stator going bad....

Dave · 02-23-2005, 07:02 AM

ok, thanks smallengine guy...sounds like this one is out of my league...is that a pull the flywheel off type of deal, reset timing etc...?

sounds expensive...

time to call my Yammi dealer for some quotes i think

**smallengineguy** · 02-23-2005, 09:02 PM

Pull the flywheel, it'sright behind it. I'm just suggesting it from many other high RPM miss posts I've read here. Turned out to be the coil or stator most of the time...

shaggydog · 02-27-2005, 06:10 PM

hey this doesn't have to do with your current problem, just wanted to say thank you very much for your reply!!

Dave · 02-27-2005, 08:48 PM

Well Problem Solved...took it to the dealer

the disconnected all the electrics, tested everything (coils, stator , cdi, throttle swithces etc..)

everything was in spec

reconnected it all....bingo...problem gone....bad connection of some sort.

twenty dollars later, im truckin' the sled home ....now...thats service!!

phazedout · 03-04-2005, 09:27 AM

dave, when your sled started to miss did it take you a while to get over 6000 in order for it to start pulling like normal? did it keep missing for a while? just curious i got a phazer acting almost like that and cant figure it out. and i cant get it on a long strait enough to know. small town

Dave · 03-21-2005, 07:07 AM

Didnt really take long to get to 6000, it was just hard getting past 6000. it missed all the way thru the revv range, just got harder to notice as it Revv'd higher,