JCL MP250A still stalling, timing question By wheezy (Read 699 times)

[wheezy]

My scoot has been stalling now for over a month.  Each time I think I got her running good, the next day it proves me wrong.  So far I have:

-adjusted the valves, checked them two more times.
-cleaned and tuned carb.
-replaced all fuel and vacuum hoses.
-replaced fuel pump and filter.
-replaced charcoal canister with hose and fuel filter to eliminate tank vacuum.
-removed a ton of grease from the roller cavity, cleaned variator and clutch.
-checked brake pads and master cylinders for locking up.

It will stall the most close to 6000 rpm or higher now.  If I keep it around 55mph or lower, it runs rough, but doesn't stall.

So here's where I am now.  I removed the timing cap on the crankshaft and checked the timing with a good old fashioned inductive timing light.  The timing is supposed to fall between the two timing marks on the crank.  But, it's all over the place.  When it's off, the bike runs rough.  When it actually hits the mark, it sounds good.

It looks like I'm down to replacing the CDI, coil, or pickup.  But I don't want to guess if I don't have to.  Anyone out there had a similar issue? 

[Barnie]

wheezy,,chances are your fuel pump is getting weak and not putting out enough volumn at higher rpm. I have same scooter u have and 4 years ago I installed an electric pump and eliminated all problems. Still runs like a dream or did at least last fall when I put it away for winter but it is still in storage yet. If you stay with a vacumn pump just make sure you get a good one and not a cheap one. Make sure u don't have a vacumn leak to the pump also.. Barnie

[alleyoop]

I think your on it, one of those is the culprit, so replace the easiest first the COIL then the CDI then the PICKUP last since you have to tear into it for that one.
Alleyoop

[wheezy]

Mar 30, 2014 9:21:46 GMT -6 Barnie said:

wheezy,,chances are your fuel pump is getting weak and not putting out enough volumn at higher rpm. I have same scooter u have and 4 years ago I installed an electric pump and eliminated all problems. Still runs like a dream or did at least last fall when I put it away for winter but it is still in storage yet. If you stay with a vacumn pump just make sure you get a good one and not a cheap one. Make sure u don't have a vacumn leak to the pump also.. Barnie

Thanks, Barnie. I replaced the cheepie fuel pump a month ago with a Mikuni. I also replaced all the fuel and vacuum lines to it.

[wheezy]

Mar 30, 2014 16:31:17 GMT -6 alleyoop said:

I think your on it, one of those is the culprit, so replace the easiest first the COIL then the CDI then the PICKUP last since you have to tear into it for that one.
Alleyoop

Thanks, Alley. I will change them in that order if it keeps up. I worked on it again all weekend. I did find the timing marks. It appears they were just outside the window, maybe two degrees or so. I cracked open the crank cover to see if you could adjust the stator/pickup like you can on some GY6's (you can't  ). 

But, I did find a couple more things since then that all add up to the trouble.  I opened the air box, removed the filter, and placed my hand over the intake port.  Believe it or not, it not only didn't die, it idled better.  Just damn.  May have been too lean across the board.  I temporarily sealed off the two inputs to the air box from the charcoal canister and the camshaft cover.  Then I closed the airbox back up and placed tape over it's intake opening.  It still idles!!

Wow. Just wow.  I redid the clamp on the intake from the airbox to the carb.  It's nice and tight.  With the tape on, it idles but stalls when I open the throttle (I expected that.)  It's not a vacuum leak, but an air leak on the input to the carb.  I did test a vacuum leak and it stalled immediately.  Maybe I've been running lean throughout the whole throttle range because of this.

I rode it 15 miles yesterday and 45 miles to work today.  Seems to run better.  I have had it up to full speed a couple times with no stall.  We'll see.  But, I still gotta find where that extra air is coming from.

[alleyoop]

If it is all sealed no cracks which sometimes are hard to see try a 1/4-1/2 turn RICHER on your Fuel Ratio to match it up with the amount of air coming in. It could just be like you said it has been running lean all this time and their are no air leaks.
Alleyoop

[ellpee]

Not a nitpick, just a question from the Still-Pretty-Clueless: If you run lean, don't you get white residue on the plug? Hope I have that right, as I'm dealing with lean/rich issues on my Magnum in the summer months.