Suzuki FA50 Moped - "The Bumblebee," or, my first two stroke

hillsy said:
If you still have the carb uncovered put your hand over the end while you kick it over to help suck in some gas.
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Thats how I diagnosed a no-start after a rebuild on my MB5. Covering carb enabled it to catch so checked out carb and turns out I totally forgot to set the idle and air screws after cleaning the carb. I just screwed them back in after the cleaning and said I'd set them later. After setting them correctly it fired right up.
 
HerrDeacon said:
Thats how I diagnosed a no-start after a rebuild on my MB5. Covering carb enabled it to catch so checked out carb and turns out I totally forgot to set the idle and air screws after cleaning the carb. I just screwed them back in after the cleaning and said I'd set them later. After setting them correctly it fired right up.
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I had to do that with an FZR250 after a carb rebuild. It had a fuel pump and everything but it still needed the carbs covered to suck the fuel in to get it to fire. Weird but true...
 
Re: Suzuki FA50 Moped - "The Bumblebee," or, my first two stroke

No luck with starter fluid through the carb or directly into the head, or covering the carb with my hand. It still sounds like it doesn't have spark, but the spark looks great when the plug is out resting on the head. I am going to swap out the coil from the XL tomorrow and see if I have any luck.


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I'd stop at this point and check for bottom end leaks and rings to see if the problem is basic and mechanical. I seem to recall a very low compression number but if that was on an HF compression tester, that reading might be inaccurate. I have thrown 2 of them out.
 
Re: Suzuki FA50 Moped - "The Bumblebee," or, my first two stroke

Plug has been slightly wet, but barely fuel - it usually seemed a bit oily.

Compression read in at 90psi before I replaced the crank seal and gaskets, then 60 afterwards. I am going to put a set of rings in and give the cylinder a light hone.

Where should I be looking for leaks in the bottom end? The mating surfaces all looked to be in decent shape, and the reed valve rubber was nice and pliable when I reinstalled. I installed a new base and head gasket.

The mating surface on the carb was not flat from the factory - the center was cupped about 1mm from the edges. I shaved it flat with a honing block before reinstalling.

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Re: Suzuki FA50 Moped - "The Bumblebee," or, my first two stroke

adventurco said:
The mating surface on the carb was not flat from the factory - the center was cupped about 1mm from the edges. I shaved it flat with a honing block before reinstalling.
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Why did you do that? Are you using a gasket?
 
hillsy said:
Why did you do that? Are you using a gasket?
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Yeah. The gasket that was on there was fairly thick, maybe 1.5mm. The one in the kit/the gasket material I had was not as thin. It would not have sealed to the intake with the thin gaskets.

I figured it couldn't hurt. I wasn't getting fuel to the plugs before I did it, or after.
 
You could do a leak down test with a fancy leak down test kit or get plugs for intake and exhaust to seal them and then make an adapter out of an old plug and pump in some air (6-8 psi and no more than 10psi) and listen for air hissing out of anywhere. It's not as s subtle as a 250 buck MotionPro leakdown tester but it works.

More that 8-10 psi blows out the seals.

60 pis is really low and probably too low to actually fir and I wonder why it dropped by 30 PSI. could be new rings are not sealing. I have been known to run a piston up and down the bore with Brasso as the lubricant to get a recalcitrant set of rings to seal but It's a huge mess to clean up afterwards and just as likely to snap a ring getting it off to clean it.

Just out of interest, I wonder how far it can throw that spark. I use a cheap spark tester from Autozone where I can adjust the gap to see how wide a gap it can jump. It's a crude measurement of the HT lead output and if it struggles in fresh air to jump 3mm, it will probably fail to fire inside the cylinder.
 
Re: Suzuki FA50 Moped - "The Bumblebee," or, my first two stroke

I will give that a go, teazer. I can make up a couple plates to seal the intake/exhaust and JB weld an old Schraeder valve to one of them.

I didn't put on new rings (yet), so It probably dropped 30 psi since the rings hadn't had time to reseat after I put the head back on.

My original thought was that the rings weren't creating enough compression to draw mix down. The PO mentioned it may have needed rings from the get go, maybe I should've started there


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If the problem is worn rings, then a squirt of oil in the cylinder should raise the compression the same as it would with a 4 stroke.
 
Re: Suzuki FA50 Moped - "The Bumblebee," or, my first two stroke


hillsy said:
If the problem is worn rings, then a squirt of oil in the cylinder should raise the compression the same as it would with a 4 stroke.
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Doh. Here I am thinking a 2 stroke is a different animal altogether

I went back and dry tested compression. 60 psi, same as before. A few squirts of oil later, and there's no compression. I mean, none at all. Gauge flips up to about 60 psi with one kick over, but drops immediately down to zero.


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That sounds like a harbor freight tester. Please tell me it's not and if it's not, then let's fix the compression. The compression should be at least 100 even on a l,ow powered low compression motor or else it won't run. Not 100% sure that 100psi is an actual limit to combustion but it must be in the ball park. Old motors back in WW2 ran on 80 octane fuel with 6:1 compression which is still 90psi.

But before you go tearing it down, try the spark plug tester just so you know if it has enough spark to fire.
 
teazer said:
That sounds like a harbor freight tester. Please tell me it's not and if it's not, then let's fix the compression. The compression should be at least 100 even on a l,ow powered low compression motor or else it won't run. Not 100% sure that 100psi is an actual limit to combustion but it must be in the ball park. Old motors back in WW2 ran on 80 octane fuel with 6:1 compression which is still 90psi.

But before you go tearing it down, try the spark plug tester just so you know if it has enough spark to fire.
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It isn't a harbor freight tester. I can't remember the brand but it's from an auto parts store or the internet somewhere. I have had successful readings before after adding oil (increased compression) - on other motors. I can check it against another gauge but I won't be able to get ahold of it until next week sometime.

I have one of these spark testers somewhere in a box, I will dig it out tomorrow and give that a go. If I can't adjust the gap I'll run to the store and grab the right one.

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This is acting really weird. if it were a 4 stroke I would think the came was out 180 or something but since it is a 2 stroke there has to be something simple that is just not set/installed right or missing.
 
probably a valve stuck open or something like that ;)

possible that you broke a ring putting the barrel back on??
 
I got some like this from Autozone not too long ago. There are a couple of similar designs at low cost.

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Re: Suzuki FA50 Moped - "The Bumblebee," or, my first two stroke


teazer said:
I got some like this from Autozone not too long ago. There are a couple of similar designs at low cost.
Click to expand...

Grabbed one of these and tested today. Throwing a good blue spark well up to 7mm, probably past. So I think we can rule that out.

I'm about 99% sure neither of the rings are damaged, I've had the barrel off and on a few times. When I get a little extra cash I will grab a piston and ring set and hone the cylinder.

I need to set the timing with a light as well.


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is the spark plug in the center of the head. if so and you wanted to we could mess around with some squish stuff on the lathe. ;)
 
Re: Suzuki FA50 Moped - "The Bumblebee," or, my first two stroke

Also, this is rad....
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