replaced silencer = no start?

[breakdirt916]

So I replaced an FMF shorty with the stock silencer on a '98 RM125, 144 kit, stroker kit, with maybe 20(?) hours on the top end.

The bike started first kick as usual, but after about 30 seconds of running/revving as usual, it stalled.

I checked the tank and the gas looked low, but not empty, so I made more 32:1 and tried again. No dice.

I tried the roll start, but it didn't work.

I kick started it over again, and it started (and revved), but then stalled within 15 seconds.

I tried the roll start again, and had it roll about 20 feet in 4th gear, but it didn't sound like there was a fire in there at all.

Could the stock silencer affected the way that it runs (back pressure?), so much so that it won't start?

It was smoking slightly the last 2-3 times I rode it, so I was thinking it could be the plug, but I called 3 motorcycle dealerships, 2 auto shops, and nobody stocks the plug. Apparently it's also a $36 spark plug

any ideas?

[Sheppo]

I can't imagine that's the issue. I've never had a silencer do that. When was it last run? is the carb needing a clean? Spark even when it wont start?

[seth399]

there is a rat stuck in the silencer...remove and enjoy riding


aha but seriously, there is no way that should be related unless it is actually plugged, but it wouldnt have started in the first place.

[Ericthejet]

Remove plug and inspect.
Very soft wire brush to clean if it is gunky or burn carbon off.
Confirm fuel delivery to the carb.
Air filter free and clean?

[Cerberus]

2 strokes are very sensitve to back pressure, but as said, i doubt that is the cause.
sounds like fuel starvation regardless of any indicators to the contrary.

fuel line pinched?
getting flow out of bowl drain?

petcock on?

[lrrs313]

After checking all of the above, if it still won't start:

Pull spark plug, pour a little oil (tablespoon or so) into the cylinder, replace spark plug, attempt to start.

If it starts and runs briefly, replace piston and rings. 2 strokes are very sensitive to compression and refuse to start when it's too low. And usually it happens very suddenly. The bike will run great, you shut it off, and it won't start again.

[breakdirt916]

it was the plug

I pulled it (came out black), tied some speaker wire between the plug and the cylinder head, kicked it over, and saw NO spark.

Got a new plug from peformance cycles a few minutes before they closed and swapped it out: started first kick

I even took this opportunity to turn the air screw in 1/4 turn increments until it smoked the least and was smoothest with mid throttle: 2-1/2 turns was the magic #

As it turns out, the OEM plug is a $36 plug that will last awhile, but is only available as a special order item. OTOH, there is a cheaper version available for $6 that the previous owner was using, but it won't last as long (5? tanks worth). I went ahead and bought 3 of them and will keep 2 on when hitting the trails

[Paul_E_D]

OK, but turning the airscrew IN richens the setting even more. Turning it OUT leans it up.

2-1/2 turns out indicates that your pilot jet is too rich and you should go to the next smaller number. 48 to 45 for example. You want to be somewhere between .5 and 2 turns out.

btw, I somehow missed that your bike is a 144 stroker. I've always wanted to try one of those!

[breakdirt916]

OK, but turning the airscrew IN richens the setting even more. Turning it OUT leans it up.

2-1/2 turns out indicates that your pilot jet is too rich and you should go to the next smaller number. 48 to 45 for example. You want to be somewhere between .5 and 2 turns out.

oops, I can't count. I just checked and it's 1-1/2 turns out from being screwed all the way in.

btw, I somehow missed that your bike is a 144 stroker. I've always wanted to try one of those!

you riding this weekend? this is my first 125 2-stroke and I'd like some feedback from the pro's on what I bought

[Paul_E_D]

Saturday, Crow Hill!

[Fast_Eddie]

Bhavesh, You should be able to run a B7ES plug in your bike for the woods.

[breakdirt916]

Saturday, Crow Hill!

hmm...unlikely for me, but we'll see

how about Franklin sunday?

Bhavesh, You should be able to run a B7ES plug in your bike for the woods.

sweet, cheap alternatives rock

also, even with 1-1/2 turns out, after a quick warm up run and a couple full-throttle rips, the spark plug still comes out black.

It's not oily/wet, but it's still black. Should I be turning the air screw out a little more?

[Fast_Eddie]

Go another 1/4 turn out on the air mixture screw and lower the needle 1 clip position. you probably will end up re-jetting at some point, but this should be enough to keep you going without fouling flugs.

[Paul_E_D]

And no to franklin on sunday. I'm hittin the Hill tomorrow. Day on the lake Sunday.