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- Apr 16, 2023
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Warning, I'm cross posting from other forums so this is a LONG post.
So I have this SXLAO that I picked up a few months ago. It came to me running, but not well. Previous owner replaced the fuel line, filter, duckbill valve, and if I remember correctly, did a carb refresh. Since then I found the p+c was scored and the flywheel side seal failed a vacuum test (passed pressure interestingly). I swapped the p+c with an aftermarket set from Traverse Creek, changed the seal, and did my own carb kit.
I got it running but it idled erratically. Coming down from WOT it would get stuck at a high idle for a few seconds (enough that the clutch engaged), and then come down. It also raced when tilted to the flywheel side, and shut down tilted forward. After I changed the flywheel seal it passed a pressure and vac test so I was fairly certain it wasn't that, but sprayed some brake cleaner on both sides anyway. It didn't shut down with that. Then I thought maybe the fuel line is too short or leaking and it's sucking air, but both seemed fine. But I did find the carb (Zama C2-20-02) wasn't holding pressure, a really slow leak existed, which is weird since it held when I installed a new carb kit.
I thought maybe the inlet needle was leaking, but when I took the metering side apart the needle looked fine. I took apart the pump side, and found the pump diaphragm looking like this:
This diaphragm came from a brand new OEM carb kit from Zama, and after less than a tank of fuel through it. I run ethanol free VP fuel with Amsoil Saber at 40:1. Regardless, the diaphragm was replaced.
Today I had some cleanup work after a 70 foot piece of pine decided to split from the main trunk. Figured it would be a perfect time to finalize the tune and run this thing. Well, I had the same symptoms as last I described in the original post, but also developed some concerning things on top of that. I still had the erratic idle, idling high coming down from WOT, shutting down when tilted down, racing when tilted sideways, but then today I also developed at WOT it would come to about 9.5-10k RPM, and suddenly race to 11K.
So I figured I must have a vacuum leak. So frustratingly (seriously taking that carb off is huge PITA, curse those engineers), I took it apart AGAIN expecting a leak and tested. Nada. Zilch. Passed with flying colors, and I even kept it pressurized/vacuumed over 30 minutes. Needle didn't budge at 10 or 5 psi pressure or 15 mmHg vacuum. I had it sealed between the reed valve and the carb, so to me it must be the carb.
Could this be a bad check valve (it held vacuum when tested for what it's worth)? What other carb specific issues could cause these symptoms? What am I missing?
So I have this SXLAO that I picked up a few months ago. It came to me running, but not well. Previous owner replaced the fuel line, filter, duckbill valve, and if I remember correctly, did a carb refresh. Since then I found the p+c was scored and the flywheel side seal failed a vacuum test (passed pressure interestingly). I swapped the p+c with an aftermarket set from Traverse Creek, changed the seal, and did my own carb kit.
I got it running but it idled erratically. Coming down from WOT it would get stuck at a high idle for a few seconds (enough that the clutch engaged), and then come down. It also raced when tilted to the flywheel side, and shut down tilted forward. After I changed the flywheel seal it passed a pressure and vac test so I was fairly certain it wasn't that, but sprayed some brake cleaner on both sides anyway. It didn't shut down with that. Then I thought maybe the fuel line is too short or leaking and it's sucking air, but both seemed fine. But I did find the carb (Zama C2-20-02) wasn't holding pressure, a really slow leak existed, which is weird since it held when I installed a new carb kit.
I thought maybe the inlet needle was leaking, but when I took the metering side apart the needle looked fine. I took apart the pump side, and found the pump diaphragm looking like this:
This diaphragm came from a brand new OEM carb kit from Zama, and after less than a tank of fuel through it. I run ethanol free VP fuel with Amsoil Saber at 40:1. Regardless, the diaphragm was replaced.
Today I had some cleanup work after a 70 foot piece of pine decided to split from the main trunk. Figured it would be a perfect time to finalize the tune and run this thing. Well, I had the same symptoms as last I described in the original post, but also developed some concerning things on top of that. I still had the erratic idle, idling high coming down from WOT, shutting down when tilted down, racing when tilted sideways, but then today I also developed at WOT it would come to about 9.5-10k RPM, and suddenly race to 11K.
So I figured I must have a vacuum leak. So frustratingly (seriously taking that carb off is huge PITA, curse those engineers), I took it apart AGAIN expecting a leak and tested. Nada. Zilch. Passed with flying colors, and I even kept it pressurized/vacuumed over 30 minutes. Needle didn't budge at 10 or 5 psi pressure or 15 mmHg vacuum. I had it sealed between the reed valve and the carb, so to me it must be the carb.
Could this be a bad check valve (it held vacuum when tested for what it's worth)? What other carb specific issues could cause these symptoms? What am I missing?
