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/cgi-bin/YaBB.pl General Category >> Technical Documents/Reference >> HELP! MY BIKE WONT RUN (ISSUE AND FIX) /cgi-bin/YaBB.pl?num=1758340880 Message started by MrMangoTime on 09/19/25 at 21:01:19 |
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Title: HELP! MY BIKE WONT RUN (ISSUE AND FIX) Post by MrMangoTime on 09/19/25 at 21:01:19 PART 1 Greetings! This thread will serve as my documentation relating to the diagnosis and repairs regarding starting/running issues I was having with my s40 around a year ago. Before I discuss the issue and fixes, I will recap how my issue started back last year. The Issue Starts So, I bought my 07 S40 back in mid September of 2024. Although it needed a bit of TLC visually, everything looked ok and it ran fine. I bought this bike as a starter bike for me. I've ridden dirt bikes since I was little (I'm 22). I needed to take my written test and then do my motorcycle skills test via my dmv (exempt from MSF since 21+) to get my license to ride it on public roads. The day after I brought it home I rode it around my neighborhood a few minutes to get used to the way the bike handled. I noticed that it had gassy smelling oil coming out of the airbox (this is an important key for later). This resulted in me taking a look at the oil level and realizing it was overfilled. I realized that the previous owners had left the fuel petcock on prime rather than just the normal "on". This caused the crankcase to fill with gas as well as oil, and made this concoction belch out of the crankcase breather hose and into the airbox. I ordered a new air filter and a new oil filter, and then bought some new synthetic motorcycle oil. I did the oil change and all seemed fine. It needed new front brake pads and I wanted to change the mirrors. I also went ahead and changed the drive belt because it had a suspect rip on the outside that I didn't want to chance. It was borderline on tires so I decided to put new tires on it as well. After I received all of these parts and installed them (everything but tires), I took another test drive around my neighborhood. As I was riding, the bike felt like it lost almost all of its power. Once I came to a stop at a stop sign it died and wouldn't start. I thought it was just out of gas, so I pushed it home and filled up the tank with enough gas that I new it would start. Well, it didn't. It was getting late so I parked it for the night. It still wouldn't start the next morning. I thought it was either a bad fuel petcock (the stock one) or the carburetor needed cleaning. Turns out that both of these items were working properly. Being in college and such limited my time to work on the bike, and then on November 5th I was in a terrible freak car accident that resulted in me needing left shoulder surgery and a lengthy recovery (physically and mentally). Needless to say I shelved the bike project for a good while. Fast forward to this summer (around june) I ordered a new carburetor kit from Murray's carbs and install it (still thought carb was issue). The bike started and ran (HOORAY!). I take it down my street and it dies again. Needless to say, I'm quite perplexed and frustrated at this point. The last thing I needed to test was compression (I was going to test this and then had my wreck). Turns out I was only getting around 85psi in compression. I checked the valve clearance and it was fine. I also put a bit of oil in the spark plug hole to see if the rings were bad (oil seals for a short bit in cylinder and makes compression jump if rings are bad) and compression was still bad. So I pull the motor out of the bike and put it on my workbench. I begin tearing it down from the head and then find something that legitimately made me go "huh!?". THE ISSUE Turns out a piece of the iron wire mesh that sits in the top of the breather passage in the head cover had broken off when the crankcase was overfilled from before. It travelled down the breather hose into the airbox, and the engine vacuum sucked it through the carburetor and then it lodged itself into the left intake valve :o. I have attached and image of the mesh as I found it when I was tearing the motor down. I went ahead and gave the motor new rings, new valve oil seals, lapped the valves, did the cam chain tensioner mod, and cleaned pretty much all carbon and other junk from the piston and combustion chamber since I had it apart anyways. I'll leave some info and images below regarding some of my encounters/difficulties along the way for someone who may end up having this issue in the future! ;) |
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Title: Re: HELP! MY BIKE WONT RUN (ISSUE AND FIX) Post by MrMangoTime on 09/19/25 at 21:04:40 WIRE IN VALVE AND MESH IMAGE Valve+mesh |
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Title: Re: HELP! MY BIKE WONT RUN (ISSUE AND FIX) Post by verslagen1 on 09/19/25 at 22:05:25 access denied easier to upload 1 pic at a time or reduce its size 640x480 is good or attach side by side wow, never heard of the wire migrating like that. |
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Title: Re: HELP! MY BIKE WONT RUN (ISSUE AND FIX) Post by MrMangoTime on 09/19/25 at 22:19:05 PART 2 STRANGE ENCOUNTER So the disassembly went rather smoothly other than the two nuts that fasten to the studs which sit under the intake and exhaust ports. These were so seized that I had to split them to remove them. Obviously I had to get new studs for reassembly. After I removed the head, the gasket looked fine (bought all new gaskets anyway). The head itself (combustion chamber) had quite a bit of carbon buildup, but I was able to clean off the majority of the buildup pretty easily with some carb cleaner and a soft bristle brush. DIVINE PROVIDENCE??? I was sure that there was going to be carnage in the cylinder from the mesh wedged against one of my valves. BUT, believe it or not, there was nothing out of the ordinary inside the cylinder, or on the piston itself. The only reason I can explain this is because the mesh wedged at the top of the valve instead of the bottom, which was keeping the piston from making physical contact with the mesh. When I removed the head, the mesh was pushed up against the curve of the dome of the combustion chamber where the piston wouldn't have hit it. Luckily enough, the piston, cylinder, and head were all in really good condition, and looked brand new after cleaning them with some gumout spray carb cleaner and a nice soft bristle brush. Valve Grinding, Honing, and Ring Seating, Oh My! After I removed the valve springs and cleaned the combustion chamber, I used valve grinding compound (the Permatex stuff you can get at any major auto parts store) and lapped them. I was surprised the intake valve that had the mesh stuck in it was not dented or hurt. They cleaned up well. I bought a good ball flex hone (240 grit I believe) and honed the cylinder to prepare it for new rings (45 degree crosshatch). After I did this, I gave the head, cylinder, and valves a nice bath in warm water made soapy with dawn. I cleaned all of these parts twice (just out of paranoia lol :P) The ring installs on the piston is relatively easy. Just use the Clymer manual for your ring orientation (important for compression/lubrication) and make sure that your ring gap is ok. The gap service limit for the 1st and second rings are 1.00 mm (0.039 in). Feeler gauges are cheap and you have no reason to not have any. Go and buy some. Main thing is double-check your work and take your time :). Cleaning Aside from the major stuff, I took the time to clean all the various nuts and such I was re-using. The previous owner had this bike sitting outside so some of the nuts and bolts had some pretty gnarly surface rust. This is easy peasy. I actually had an almost-full tube of red Wenol that I used on the shiny chrome bits. This made many of the parts look almost new (including the rest of the chrome/shiny bits on the rest of the bike). Cam Chain Tensioner Not much to say here. I have a friend who is a welding instructor at my local Tennessee College for Applied Technology (trade school). I had him weld me an extension to the stock tensioner. Re-assembly Once I was satisfied that I replaced everything I needed to, I re-assembled everything back opposite the way it came apart (duh lol). Make sure you have a torque wrench, you're gonna need it I promise. Honestly, getting the camshaft lined up with the sprocket and the piston at TDC was the hardest part for me. The cam has two lines at the end of the shaft that attaches to the upper sprocket that have to be parallel with the journal edges. This is the easy part. The hard part is keeping the cam and the piston lined up while putting the sprocket back. This just takes trial and error (and a few choice words each time you have to re-do it :P). Make sure you give the valve landings, cam lobes, and rocker pads a healthy dose of assembly lube to avoid unnecessary wear the first time you crank it. Also, I chucked that little wire mesh thingy in the trash and installed a standalone spectre crankcase breather filter from auto zone at the end of the hose (no more mesh breaking off 8-)). I got a little vacuum port cap and put it over the airbox port that the breather usually connects to as well. I finished the assembly with a fresh valve adjustment and a few new head cover bolts. Be careful with old head cover bolts. I had a few that wanted to stretch, so I had to replace those. I also used some extra RTV gasket for the head plug leak fix (just as a precaution, I wasn't having this issue). I also bought a 16" slash cut Delkovic muffler to cap things off. After putting everything back together, I am happy to say the bike runs like a top, sounds amazing, and should be as reliable as it could possibly be. I did a bunch of extra cosmetic work too, and it honestly looks almost brand new. I hope this helps someone down the road at some point. If you have any questions, please don't hesitate to ask. I will try my best to answer! |
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Title: Re: HELP! MY BIKE WONT RUN (ISSUE AND FIX) Post by MrMangoTime on 09/19/25 at 22:21:52 4A594E4F505D5B59520D3C0 wrote:
yeah super strange. Pics are too large to upload even separately. I guess they're too high-res since I took them with my iPhone. :-/ |
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Title: Re: HELP! MY BIKE WONT RUN (ISSUE AND FIX) Post by MrMangoTime on 09/19/25 at 22:36:20 THE MESH IN QUESTION |
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Title: Re: HELP! MY BIKE WONT RUN (ISSUE AND FIX) Post by MrMangoTime on 09/19/25 at 22:41:51 HONE The odd colors are just the reduction of the image quality because of the forum limitations |
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