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Post by stellarfoxy on Jun 24, 2015 22:26:49 GMT -5
Hello everyone! I a 157qmj and appear to have the somewhat common "won't start when hot" issue. i think I've done most of the diagnostics, but everything seems to be right. Valve lash is .004 intake and .006 exhaust cold, compression is 125psi warm, no oil leaking on the cdi (or anywhere for that matter), strong spark in all conditions, and the timing is correct. i finished a complete rebuild on the engine a couple months ago, replacing the crank, piston and rings, gaskets and seals, head, timing chain, cam (a9), plug, coil (orange), cdi (orange), carburetor, intake manifold (aluminum), intake pipe and filter (uni), exhaust (header and free flow muffler), i have a breather on the pcv, fresh upgraded vacuum and fuel hoses/ filter, i can't remember anything else right off. i honed the cylinder also since i was already in there. carb main jet is 130, idle jet is whatever the carb came with, it idled best with the gas screw being like 2.5 turns out or so. it can idle around 700rpm without dying but i have it around 1000.
tl;dr, this thing gets weird when it's warm. it almost left me stranded yesterday but after it cooled off for a few minutes i fiddled with the idle screw, it cranked and i rode it home, it pulled hard all the way. i rode it around the hood today for about half an hour, not going hard but not babying it. when i got back to my driveway it dropped to idle fine but when i opened the throttle and it died and wouldn't crank. i quickly checked compression, spark, etc while it was warm, everything seemed ok, but maybe 125psi is on the low end?
the plug was brownish but dry and didn't smell of gas. however, the oil kinda does have a gassy smell, so i might need a manual fuel valve soon, but i don't think that would be related?
anyway, if anyone has any ideas what to check, I'm extremely open to ideas. i will say that i had a 125 main jet in before and it went for hours with no issue but the plug was white-ish so i took it to 130. also this is my second ebay carb and they both might be complete crap, but this one ran better so its what i'm using. so that might be something to try if someone can recommend where i can get a not-garbage carb for reasonable money. most keihin are knockoff, even the oko and hoca ones have knockoffs now, my eye isn't keen enough to tell the difference.
... and uh, if i missed anything, don't hesitate to ask.
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Post by geh3333 on Jun 24, 2015 23:30:36 GMT -5
Here is what I'd like for you to do . first your idle rpms are way too low , even at 1000 rpms. The norm is around 1700 for these scoots.
Start the scoot , let it warm up. Next turn the idle screw up until you rpms are near 2000 rpms. Next adjust the air fuel until you get the highest rpms possible. Please remember , you don't want the clutch to engage, so at some point you may need to back the idle screw down " if they get too high, turn the idle screw back down so the scoot is back to 2000 rpms ". Then u can return the the air fuel screw to keep adjusting for the highest rpm. After you hit that point , you will then turn the idle screw back down so your scoot idles around 1700 rpms. Now the carb will be tuned properly. Let us know if this helps.
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Post by stellarfoxy on Jun 25, 2015 9:58:58 GMT -5
wow, I was way low. I get off work at 6, I'll drive it around and try tuning it that way. Thank you for pointing me in a direction man. will it not be harder to start with the screw set to idle at 1700 though? or will the af screw being turned correctly help that?
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Post by ricardoguitars on Jun 25, 2015 10:57:36 GMT -5
A 130 jet is too big, try with something smaller, the lean condition could be the A/F mixture or a clogged jet
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Post by geh3333 on Jun 25, 2015 16:53:30 GMT -5
wow, I was way low. I get off work at 6, I'll drive it around and try tuning it that way. Thank you for pointing me in a direction man. will it not be harder to start with the screw set to idle at 1700 though? or will the af screw being turned correctly help that? We usually say to set the Idle around 2000 because when the carb is not tuned correctly it is sometimes hard to get the scoot to idle even around 1700 rpms. Your case is kind of odd , considering you can get the scoot to idle a 700 rpms. The reason you will want to tune to the highest rpm with the air fuel screw , is because this is the only way you can get the air fuel mixture perfect. To be honest, you may already be there , so if you want to try just raising the idle with the idle screw and see if that works first. Now that i think about it ,I'd don't see the scoot idling at 700 rpms if the airfuel mixture was off. If for some reason it doesn't work , try the carb tuning process I stated above. Let us know how it turns out. |
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Post by stellarfoxy on Jun 25, 2015 18:22:12 GMT -5
ricardo- i thought so too, but the carb is new and I've always had a filter on it. how should i check if it's clogged?
geh- i thought that same thing about it idling so low. i was kind of proud of the little thing for doing it really. the tach is kind of slow on mine and i assume accuracy is relative but I'll get it to 2k then tune. i just got a set of slow jets in today, i think 32-45, should i try upping that first and going back to the 125 main before i warm it up?
thank you again for the help guys, your patience and knowledge is greatly appreciated.
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Post by geh3333 on Jun 25, 2015 20:00:51 GMT -5
ricardo- i thought so too, but the carb is new and I've always had a filter on it. how should i check if it's clogged? geh- i thought that same thing about it idling so low. i was kind of proud of the little thing for doing it really. the tach is kind of slow on mine and i assume accuracy is relative but I'll get it to 2k then tune. i just got a set of slow jets in today, i think 32-45, should i try upping that first and going back to the 125 main before i warm it up? thank you again for the help guys, your patience and knowledge is greatly appreciated. I do suggest going back to the 125 . if you want to up the pilot jet , just go up to your next closest size. Its usually not necessary to up the pilot when only switching to a uni and a free flow exhaust. Most mainly have to up the main jet. But all setups are different so you will have to make that decision. |
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Post by stellarfoxy on Jun 25, 2015 20:49:06 GMT -5
just got back in from a 15 minute ride with a 38 pilot and 125 jet. set the idle to 1800ish then backed the screw out, tightened it, but no change until it dropped from being too lean. took the screw back out to about 2.5 turns again and drove it a bit, it still wants to cut off when i give it a sharp twist on the throttle when its warm, then not start for a few minutes and will onl start if i drop the idle screw back to where it would idle at 700-800rpm.
it may not matter but i have an a9 cam also, apparently that designation can mean a lot of things, this one was roughly double the lift and a bit more duration than stock. also, are the pilot jets numbered backwards from main? my sizes were 42<40<38<35, smallest to largest holes. the stock ones were smaller than the 42. i may switch it back out with a 40 or 42 but it didn't seem to change anything anyway. I'll let it idle tonight and check the plug.
also, could overheating cause this symptom? my fan shroud intake hole is missing the grate thing, might not be pressurizing the air properly to cool everything but I'm pretty sure that's secondary to the carb being wrong.
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Post by geh3333 on Jun 25, 2015 20:59:16 GMT -5
just got back in from a 15 minute ride with a 38 pilot and 125 jet. set the idle to 1800ish then backed the screw out, tightened it, but no change until it dropped from being too lean. took the screw back out to about 2.5 turns again and drove it a bit, it still wants to cut off when i give it a sharp twist on the throttle when its warm, then not start for a few minutes and will onl start if i drop the idle screw back to where it would idle at 700-800rpm. it may not matter but i have an a9 cam also, apparently that designation can mean a lot of things, this one was roughly double the lift and a bit more duration than stock. also, are the pilot jets numbered backwards from main? my sizes were 42<40<38<35, smallest to largest holes. the stock ones were smaller than the 42. i may switch it back out with a 40 or 42 but it didn't seem to change anything anyway. I'll let it idle tonight and check the plug. also, could overheating cause this symptom? my fan shroud intake hole is missing the grate thing, might not be pressurizing the air properly to cool everything but I'm pretty sure that's secondary to the carb being wrong. At what rpm does the scoot clutch seem to engage ? The cam should have no bearing on what rpm you idle at. Its strange how you can get the scoot to idle so low. I wonder if your rpm gage is off " that's why I asked at what rpm the clutch seems to engage ". I don't see the pilot jet needing to be any larger. Have you checked the float level ? When your scoot acts up , shut it down quick , do not try to start it again. Open the drain on the carb bowl and see if any gas comes out. You may be running out of gas if the float is not set right. So give it throttle and when it sputters shut the scoot down quick. Then check the bowl. |
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Post by stellarfoxy on Jun 25, 2015 21:47:09 GMT -5
the clutch is being kind of chattery at the moment as if it's glazed, but I'd say maybe 2500? i checked the bowl yesterday after it died and refused to start again. i have a manual gas cut off now so i dont think i can check it anymore because the bowl will fill up immediately.
i was thinking the cam would have an effect on jetting not idle rpm, like since more air is being pulled in more gas would be required. in regard to idle speed, I'd think low rpm would be worse with a bigger cam. can i upload a video here? i can show you the low idling and maybe my tach is just off
i going to check the plug to see what color it is, I'll make a short video and try to put it on youtube for you to see
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Post by nimajneb on Jun 25, 2015 21:50:03 GMT -5
just got back in from a 15 minute ride with a 38 pilot and 125 jet. set the idle to 1800ish then backed the screw out, tightened it, but no change until it dropped from being too lean. took the screw back out to about 2.5 turns again and drove it a bit, it still wants to cut off when i give it a sharp twist on the throttle when its warm, then not start for a few minutes and will onl start if i drop the idle screw back to where it would idle at 700-800rpm. it may not matter but i have an a9 cam also, apparently that designation can mean a lot of things, this one was roughly double the lift and a bit more duration than stock. also, are the pilot jets numbered backwards from main? my sizes were 42<40<38<35, smallest to largest holes. the stock ones were smaller than the 42. i may switch it back out with a 40 or 42 but it didn't seem to change anything anyway. I'll let it idle tonight and check the plug. also, could overheating cause this symptom? my fan shroud intake hole is missing the grate thing, might not be pressurizing the air properly to cool everything but I'm pretty sure that's secondary to the carb being wrong. At what rpm does the scoot clutch seem to engage ? The cam should have no bearing on what rpm you idle at. Its strange how you can get the scoot to idle so low. I wonder if your rpm gage is off " that's why I asked at what rpm the clutch seems to engage ". I don't see the pilot jet needing to be any larger. Have you checked the float level ? When your scoot acts up , shut it down quick , do not try to start it again. Open the drain on the carb bowl and see if any gas comes out. You may be running out of gas if the float is not set right. So give it throttle and when it sputters shut the scoot down quick. Then check the bowl. I had this problem sometimes with my float. I fixed the float and the bowl stayed full and fixed it, also removed my evap canister, because it was making it flood out when trying to start it. |
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Post by geh3333 on Jun 25, 2015 22:08:20 GMT -5
the clutch is being kind of chattery at the moment as if it's glazed, but I'd say maybe 2500? i checked the bowl yesterday after it died and refused to start again. i have a manual gas cut off now so i dont think i can check it anymore because the bowl will fill up immediately. i was thinking the cam would have an effect on jetting not idle rpm, like since more air is being pulled in more gas would be required. in regard to idle speed, I'd think low rpm would be worse with a bigger cam. can i upload a video here? i can show you the low idling and maybe my tach is just off i going to check the plug to see what color it is, I'll make a short video and try to put it on youtube for you to see Yes , after downloading a video to YouTube , copy and paste the address here. Your right about the manual shutoff . I have one also. The only thing you can do if you suspect the float is to adjust it and give it a shot. |
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Post by stellarfoxy on Jun 25, 2015 22:45:46 GMT -5
first thing ive ever edited on a cell phone or uploaded to the tube. how do i adjust the float? and the clutch grabbed at around 2k on the throttle, didnt check how high it had to idle to grab
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Post by geh3333 on Jun 25, 2015 23:00:42 GMT -5
Right off the bat I can tell your rpms are not correct. I can hear the engine when the idle drops below 1000 , and it is not idling that low. I'll watch more and get back to you.
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Post by geh3333 on Jun 25, 2015 23:08:00 GMT -5
Right off the bat I can tell your rpms are not correct. I can hear the engine when the idle drops below 1000 , and it is not idling that low. I'll watch more and get back to you. It sounds like your rpms are about 1000 rpms off. I can get mine to idle around 1500 , even as low as 1300 at times , but I usually keep it around 1700. What does it say on your tach ? Mine has x1000 . I'm sure yours is the same . your tach redlines the same as mine so it just must be off. |
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