Harley Aermacchi x90/z90 help needed. Runs like crap.
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Road Captain
Joined: Jan 2007
Posts: 645
Likes: 215
From: Minneapolis
Harley Aermacchi x90/z90 help needed. Runs like crap.
I have an old 70's 90cc Aermacchi/Harley minibike I'm trying to get going. It's a 2 stroke and probably hasn't run for 20 years. I cleaned it up and got it started. It would run at idle with the enrichener out, but as soon as you tried to give it any throttle, or take if off the enrichener, it bogs down. I have a perfectly running bike just like it, so I swapped the carburetors, thinking that was the issue. Made no difference. I deduced it must need new crank seals, so I pulled it back apart and installed the new crank seals, head gasket and barrel gasket. Put it back together and I still have the same issue. I seem to have good spark, I tried a different coil, but it made no difference. I cleaned up the points and have adjusted the timing and points gap, I've tested the voltage of the alternator, and I'm getting 13+ volts at the coil, so that's not the issue. The only things I haven't tried are replacing the points and condensor. Could this be the issue?? It starts very easy and will stay running, except when you try to rev it. I'm convinced it's not a carb issue, but there isn't much to a 2 stroke.... I did a compression check and it looks to be about 80-85 psi. The service manual has no spec for a compression test. Would this compressionl level be low enough to affect how it runs?? I also did a compression test of my running X90 and found it to be 85-90 psi. Obviously parts aren't easy to find for these things, but I can get points and a condensor. New rings will be another thing..... I'm running out of options at this point, and would just appreciate some oppinions. I will also mention I am using a Ricky Stator Regulator/rectifier wired directly to the coil positive, with the neg going to a bolt on the engine. No additional lights-etc at this time. Thanks.
Elite HDF Member
Joined: Dec 2009
Posts: 4,598
Likes: 14
From: navarre ohio
i wrenched on 2 stroke bikes for 10 years.. it sounds like a dirty carb.. make sure the intake isnt cloged,cracked, or leaking at the mount.. is the air filter clean, or present, and is there oil,or some thing else under the piston (crankcase)that isnt suposed to be there??that will block the intake flow
Stage I
Joined: Sep 2010
Posts: 1
Likes: 0
as long as the jets and carbs are the same and you put a carb off a perfect runner on and compared compression to the runner the only other thing is exhaust I suggest to bake it or the insulation on the plug wire to test start the bike and spray a mist of water really lightly on the wire from like a used windex bottle and see if it kills it if it dies it means the plug wire insulation is going to crap and grounding out through the body/frame the water just makes it easier if not that then bake the exhaust and check if its partially clogged.
Ultimate HDF Member
Joined: Jan 2008
Posts: 6,532
Likes: 132
From: SoCal
Does it have a reed valve? Underneath the carb manifold? Pull it out if it does and inspect it, looking for cracked reeds or reeds not laying down flat. I don't have any experience with those motors so I dont know if it is just a piston port or a reed valve, case reed, or rotary valved 2 stroke.
Stage I
Joined: May 2019
Posts: 1
Likes: 0
From: Fayetteville, GA
I just ran across your post from 2010 about the x90 running problem. Did you ever figure out what was wrong with it not running without the starter valve on? I have the same issue. Thanks, Jim
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Seasoned HDF Member
Joined: Aug 2008
Posts: 5,052
Likes: 993
on the road so no access to my library.
does this thing have lighting although not present?
a lot of these types of machines have two coils, one ignition and the other charging.
the capacitor can cause issues as it can fail open, short or change of value. if this were a battery ignition, it would run without the capacitor but at the expense of the points.
on the rectifier, if it is bad, a lot of ac ripple will be present and can cause issues with coil saturation.
when i get back, i'll see what the books have to say.
for a coon-a$$ test, if it is 12v system, remove wire to points and jumper in a 12v lantern battery (limits current) with other battery lead to engine case and see if it will run.
if it does not have mechanical advance, it is timed at full advance but flywheel marks should make this easy to set.
does this thing have lighting although not present?
a lot of these types of machines have two coils, one ignition and the other charging.
the capacitor can cause issues as it can fail open, short or change of value. if this were a battery ignition, it would run without the capacitor but at the expense of the points.
on the rectifier, if it is bad, a lot of ac ripple will be present and can cause issues with coil saturation.
when i get back, i'll see what the books have to say.
for a coon-a$$ test, if it is 12v system, remove wire to points and jumper in a 12v lantern battery (limits current) with other battery lead to engine case and see if it will run.
if it does not have mechanical advance, it is timed at full advance but flywheel marks should make this easy to set.
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