Post by toplessfc3sman on Nov 27, 2020 21:23:09 GMT -5
Hello Everyone,
I've had this Razz for about 8 years now, bought it for $50 in non-running, rough shape and patched it up, cleaned the carb, and it provided reliable transportation for about 2 years. Well, after living outside one winter it refused to start in the spring. No amount of cleaning the carb or adjusting things made it better, so it got parked in the corner until this summer when I started tearing into it. The compression seemed low, and the carb & tank were quite gummed up after sitting for 6 years, but I think the real culprit was the exhaust pipe was completely plugged with mud... some bugs may have made a nest in there or something.
Anyway, my nephew and I took it apart to fix it up for him, replaced the piston & rings (what I suspected was the problem prior to finding the mud - we found that the skirt was cracked in 2 places too), cleaned out the muffler, thoroughly cleaned the carb, gapped the plug, and went through basic maintenance. Once it was all back together, it started up fine, seemed to run well and have about as much power as I remembered... for about a total of 10 minutes. Then it started getting harder to start until it would barely catch & sputter for a few seconds before dying.
Thinking it was deposits in the tank that had been loosened up and were plugging the carb, we pulled the carb, drained the tank and flushed more gas through it, cleaned the carb (didn't find anything of note in there, it seemed fine), put it all back together and... it started and ran well for 30 seconds before dying and refusing to do more than sputter for a couple cycles at a time. We tried this a few more times with more tank flushes, carb inspections, a new vacuum fuel shut-off valve (the old one started leaking), and a separate fuel filter, but the same result happened each time. Definitely smelled like fuel when cranking, spark was strong (once the plug dried out), just no dice on it running for more than 30 sec without dying. We checked that the carb was getting fuel and the vacuum shut-off valve was working properly.
Worried that something was wrong with the new piston & rings, I did another compression test (cold, just cranking with the starter but with a fresh battery) and was only getting 30 psi, vs 54 psi minimum in the manual. Ok then, apart it all comes. The piston & bore looks fine, piston slides well in the bore without snagging, rings look like new, reed valve appears normal... hmm. So I lather the bore, rings etc up with some petroleum jelly to help things seal and not scuff when dry, re-assemble the motor on the bench without the carb or exhaust (but with the reed valve), and jump the starter from the battery - 32 psi. Next step, remove the reed valve and check again - 30 psi. Disassemble the reed valve, check to make sure the reeds appear straight (they do) and are clean (they are), put some petroleum jelly on the reed valve to help it seal up better if something is slightly warped, re-assemble, and compression-check again - 32 psi. What the heck?!? I could see one of the two flaps of the reed valve getting drawn in and pushed back into place when doing the compression test, and there is a significant puff of air out the exhaust with each revolution, so things appear to be working fine except low compression.
During the same tear-down, I took the carb apart too to inspect everything as closely as I could, chase all the passages with carb cleaner and thin copper wire, and inspect each piece. The only thing that seemed off was the float height when measuring with the carb upside-down and the bowl off. Spec is 15-17mm, and the most optimistic measurement I could come up with was 13mm (no gasket, highest point on the float etc). If I lifted the float so that it was barely touching the needle, it was still only about 14mm, however the needle appears fine, the valve end is still rubbery and the other end that goes in the float is still springy, and it does seal up well as I move the float (at least against me blowing air through the fuel line). The float itself is still air-tight and does not appear deformed in any way. The manual mentions a needle valve seat, but I can't find a part listing for that and it's hard to tell if its a separate, pressed in part or just machined into the aluminum carb body.
So, after that little novel, now the questions:
- I'd expect more than a 2 psi difference in compression pressure with the reed valve vs without, but the reed valve does appear to be working and I'd think that the petroleum jelly would seal any small gaps between the reed and the rubberized flange. I'd rather not just throw parts at it hoping that they'd work, but do these fail or go bad in ways that aren't apparent?
- Is the needle valve seat a separate piece of the carb that could be removed and replaced or shimmed to get the float height correct, or is it machined into the body?
- Similar to the reed valve, I don't see any obvious failure of the float needle and would like to avoid just replacing things and crossing my fingers. Anything else I can check that I may be overlooking?
- One last one, the float bowl has a screw at the bottom that I presumed was for draining the bowl, and it does work for this. However, there is a long hollow needle that reaches up from the inside of the bowl at the location of this screw and just about touches the under-side of the carb. When the screw is removed, you can see clear through the needle out the bottom of the bowl, but there is also another hole near the bottom of the bowl that gets uncovered. It's not the fuel overflow (that is a separate hole), it is plugged when the screw is tightened, and loosening the screw even by 1/4 turn causes fuel to start to leak. What is the purpose of the needle here? Is this just a drain?
I expect that I should just suck it up and replace the reed valve & the float needle and hope one of them solves it, but I cannot find any new or aftermarket reed valves for the SH50. The closest I can find is for the PW50 that it looks like the right size & shape, but they aren't cross-referenced. The float needle is available new, but for $20 + $10 shipping its a bit of a gamble when I can't tell if anything is wrong with the original.
I've had this Razz for about 8 years now, bought it for $50 in non-running, rough shape and patched it up, cleaned the carb, and it provided reliable transportation for about 2 years. Well, after living outside one winter it refused to start in the spring. No amount of cleaning the carb or adjusting things made it better, so it got parked in the corner until this summer when I started tearing into it. The compression seemed low, and the carb & tank were quite gummed up after sitting for 6 years, but I think the real culprit was the exhaust pipe was completely plugged with mud... some bugs may have made a nest in there or something.
Anyway, my nephew and I took it apart to fix it up for him, replaced the piston & rings (what I suspected was the problem prior to finding the mud - we found that the skirt was cracked in 2 places too), cleaned out the muffler, thoroughly cleaned the carb, gapped the plug, and went through basic maintenance. Once it was all back together, it started up fine, seemed to run well and have about as much power as I remembered... for about a total of 10 minutes. Then it started getting harder to start until it would barely catch & sputter for a few seconds before dying.
Thinking it was deposits in the tank that had been loosened up and were plugging the carb, we pulled the carb, drained the tank and flushed more gas through it, cleaned the carb (didn't find anything of note in there, it seemed fine), put it all back together and... it started and ran well for 30 seconds before dying and refusing to do more than sputter for a couple cycles at a time. We tried this a few more times with more tank flushes, carb inspections, a new vacuum fuel shut-off valve (the old one started leaking), and a separate fuel filter, but the same result happened each time. Definitely smelled like fuel when cranking, spark was strong (once the plug dried out), just no dice on it running for more than 30 sec without dying. We checked that the carb was getting fuel and the vacuum shut-off valve was working properly.
Worried that something was wrong with the new piston & rings, I did another compression test (cold, just cranking with the starter but with a fresh battery) and was only getting 30 psi, vs 54 psi minimum in the manual. Ok then, apart it all comes. The piston & bore looks fine, piston slides well in the bore without snagging, rings look like new, reed valve appears normal... hmm. So I lather the bore, rings etc up with some petroleum jelly to help things seal and not scuff when dry, re-assemble the motor on the bench without the carb or exhaust (but with the reed valve), and jump the starter from the battery - 32 psi. Next step, remove the reed valve and check again - 30 psi. Disassemble the reed valve, check to make sure the reeds appear straight (they do) and are clean (they are), put some petroleum jelly on the reed valve to help it seal up better if something is slightly warped, re-assemble, and compression-check again - 32 psi. What the heck?!? I could see one of the two flaps of the reed valve getting drawn in and pushed back into place when doing the compression test, and there is a significant puff of air out the exhaust with each revolution, so things appear to be working fine except low compression.
During the same tear-down, I took the carb apart too to inspect everything as closely as I could, chase all the passages with carb cleaner and thin copper wire, and inspect each piece. The only thing that seemed off was the float height when measuring with the carb upside-down and the bowl off. Spec is 15-17mm, and the most optimistic measurement I could come up with was 13mm (no gasket, highest point on the float etc). If I lifted the float so that it was barely touching the needle, it was still only about 14mm, however the needle appears fine, the valve end is still rubbery and the other end that goes in the float is still springy, and it does seal up well as I move the float (at least against me blowing air through the fuel line). The float itself is still air-tight and does not appear deformed in any way. The manual mentions a needle valve seat, but I can't find a part listing for that and it's hard to tell if its a separate, pressed in part or just machined into the aluminum carb body.
So, after that little novel, now the questions:
- I'd expect more than a 2 psi difference in compression pressure with the reed valve vs without, but the reed valve does appear to be working and I'd think that the petroleum jelly would seal any small gaps between the reed and the rubberized flange. I'd rather not just throw parts at it hoping that they'd work, but do these fail or go bad in ways that aren't apparent?
- Is the needle valve seat a separate piece of the carb that could be removed and replaced or shimmed to get the float height correct, or is it machined into the body?
- Similar to the reed valve, I don't see any obvious failure of the float needle and would like to avoid just replacing things and crossing my fingers. Anything else I can check that I may be overlooking?
- One last one, the float bowl has a screw at the bottom that I presumed was for draining the bowl, and it does work for this. However, there is a long hollow needle that reaches up from the inside of the bowl at the location of this screw and just about touches the under-side of the carb. When the screw is removed, you can see clear through the needle out the bottom of the bowl, but there is also another hole near the bottom of the bowl that gets uncovered. It's not the fuel overflow (that is a separate hole), it is plugged when the screw is tightened, and loosening the screw even by 1/4 turn causes fuel to start to leak. What is the purpose of the needle here? Is this just a drain?
I expect that I should just suck it up and replace the reed valve & the float needle and hope one of them solves it, but I cannot find any new or aftermarket reed valves for the SH50. The closest I can find is for the PW50 that it looks like the right size & shape, but they aren't cross-referenced. The float needle is available new, but for $20 + $10 shipping its a bit of a gamble when I can't tell if anything is wrong with the original.