jack667
Scoot Enthusiast
Posts: 190
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Post by jack667 on Nov 17, 2018 18:45:10 GMT -5
Hey 49cc'ers, I got some new boppers on the Zuma today, and on the ride home, it was running amazingly well, but then the temp started rising. The gauge was reading 300 and going up and up. I was looking to pull over, but there wasn't a good spot and quite a bit of traffic. I backed off on throttle and it still kept rising. 420 something and then some dashes --- and then 520 something and then it just konked out and I pulled over. Maybe I have A/F and/or jetting messed up. I brought it home in the truck, let it cool down, replaced the plug, still no start. Pulled off the intake and reed block and looks good. I'm still a total newbie but I guess I need to pull the cylinder head? I don't have a leak tester but I see in the threads about making one. Or I could buy one... Looking for ideas. Doing searches but no luck so far. I need to get better at reading plugs, etc. Please let me know if you have any ideas, suggestions, etc. plug:  Click here for YouTube video of rocker (Intake off)Some possibly useless additional info: I drained my oil and replaced it with Malossi 7.1. It's still a pump, ie not a pre-mix. I had to drop it off in the truck for the tire change, and I hadn't ridden it at all since the oil change, bc it had a flat. My son rides it almost exclusively, and the temp may have been running high for a while. I need to ride it more to get a sense of this stuff as I don't think I can trust the boy to be diligent and aware. I installed the temp and tach gauges, both Trail Tech TTO. The tach has been acting up, and it must be reading low. Maybe 1/2. The tach was running at about 4500-4750 during the ride when it konked out. I said it was running really well. The speedo was pinned, probably going 50+. The slowest was 42 up a really big hill, at the end, but mostly I was cursing along perfectly in the 45mph zone, probably speeding for most of the time. I recently tuned it a bit, playing with idel and A/F, and I thought I had it set pretty well, based on what I've been reading on how-to's, etc. It has been having some issues starting when warmed up. Like last Saturday, I took it about a mile to the neighborhood club for tennis and I needed to spray some quick-start into it to get it going on the way home - after about 2 hours sitting, but it started cold on the way to the club, no problem. |
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Post by tsimi on Nov 17, 2018 19:34:04 GMT -5
One more thing to check is your oil pump. Does it still work? Was there sufficient oil inside the oil tank?
You might have soft seized the top end.
Pull off the head once and turn the crank slowly and check for scratches on the cylinder wall or any other kind of damage.
The scoot having problems starting when warm but no issues when cold is kinda weird. Most of the time it is the other way around.
What is your current carb jetting and what air filter do you use?
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Post by 'O'Verse on Nov 17, 2018 19:42:58 GMT -5
Never ever heard of a cylinder making to 520 degrees before. Usually a soft or hard seize presents itself way before that. Like in the 350-400 range. Anyway if your temp gauge was reading correctly I'd say your piston expanded to much inside the bore of your cylinder and shut it down. I'd give it a compression test before anything. See what you got. Then +1 on pulling the head and piston to see if there's any large metal debris floating around in there.
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jack667
Scoot Enthusiast
Posts: 190
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Post by jack667 on Nov 17, 2018 19:54:31 GMT -5
Oil is full. All new. Just changed. Not sure on pump.
Current main jet is 95
Air box is 70cc Sport. Looks like stock. Its pretty new and would have stock (? for it) filter in it but I should check. I never cracked it open
I need to do some searches on soft seize. I have no idea what that is.
Thx so much for the reply. You guys are great
Jack
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Post by tsimi on Nov 17, 2018 19:59:17 GMT -5
Sorry for asking, Sunday morning over here and my brain isn't fired up yet, what is your scoot setup?
Stock cylinder?
Stock carb?
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jack667
Scoot Enthusiast
Posts: 190
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Post by jack667 on Nov 17, 2018 20:06:15 GMT -5
It’s supposed to be in my sig. Sorry. Need to figure that out but watching a movie with fam now and I appreciate your help
It’s a 2008 Zuma 2t with a dellorto 17.5 carb with electric (stock type) choke. Sport airbox per above. Stock intake and Malossi reed block. NCY pipe.
Also has Malossi MultiVar and NCY clutch. Malossi Kevlar belt
Thx!
Jack
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Post by tsimi on Nov 17, 2018 20:08:55 GMT -5
I see, i was browsing with my phone and couldn't see your sig. Thx
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Post by 'O'Verse on Nov 17, 2018 22:58:51 GMT -5
Soft seizes are mostly caused by heat or lack of lubrication. Heat entering the cylinder from an air leak or as Tsimi pointed out lack of lubrication. Oil or gas not aiding in the cooling of the piston or cylinder. If you can still kick it over with the kickstarter than its soft seize. If you can't move the kickstarter and the bore seized up it's a hard seize. Hard seizes can end up with a locked up back tire as it's shutting down. From what you said it just shut down. Which if I'm correct is from a lack of compression.  Usually if a piston expands too much it has nowhere to go. So unfortunately the metal of the piston and the metal of the cylinder suffer during the expansion. Usually pieces of the piston (softer material) end up gouging the cylinder walls creating a gap. Hence the loss of compression.  |
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Post by niz76 on Nov 18, 2018 2:37:37 GMT -5
From the sounds of the high temp story I agree with the good fellas above- probably gonna find a ring smeared into your aluminum piston upon inspection. Once you get the piston/cylinder squared away then time to figure out why it (may have) seized up on ya. Sounds like a whole lot of scoot experience coming your way!
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jack667
Scoot Enthusiast
Posts: 190
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Post by jack667 on Nov 18, 2018 8:43:51 GMT -5
OK - great info, thx Niz, OV, and ts.
I have a Malossi sport bbk ordered and on the way for my other scoot. Should already be here. grrr. Once that comes in (hopefully in a day to two), I'll pull it apart. I'm thinking that with my lack of experience, I'd rather try and get the whole job done in one session if possible.
(I'm noting that once I get the probable cyl/piston/ring problem sorted, that I'll still need to figure out the hi-temp issue, probably oil delivery)
If the rocker arm seems like it works well enough, per the video above, then I'm guessing bbk parts are all I should need? Is there any reasonable expectation that the damage would be beyond that?
Thx again!
Jack
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jack667
Scoot Enthusiast
Posts: 190
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Post by jack667 on Nov 18, 2018 8:47:54 GMT -5
Soft seizes are mostly caused by heat or lack of lubrication. Heat entering the cylinder from an air leak or as Tsimi pointed out lack of lubrication. Oil or gas not aiding in the cooling of the piston or cylinder. If you can still kick it over with the kickstarter than its soft seize. If you can't move the kickstarter and the bore seized up it's a hard seize. Hard seizes can end up with a locked up back tire as it's shutting down. From what you said it just shut down. Which if I'm correct is from a lack of compression.  Usually if a piston expands too much it has nowhere to go. So unfortunately the metal of the piston and the metal of the cylinder suffer during the expansion. Usually pieces of the piston (softer material) end up gouging the cylinder walls creating a gap. Hence the loss of compression. It still kicks over and the rocker arm looks functional, from the view when the intake is removed. While driving, the engine just cut out and I coasted to a stop on the side of the road. |
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Post by snaker on Nov 18, 2018 15:21:11 GMT -5
You mentioned a couple times that you just changed oil. Was that before or after your breakdown?
If before, how through of a job did you do bleeding the oil pump. I don't know about all but many pumps require a very precise bleeding, any air in the pump and it won't pump.
Whoa I just reread the thread. You talking about a 2 stroke or a 4 stroke? |
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Post by ryan_ott on Nov 18, 2018 18:27:10 GMT -5
The “rocker arm” your looking at is the crankshaft. If you had temps that high I’d think the motor would be locked solid. Maybe just a fluke with the gauge and you just happened to shut down not sure but check for the basics first spark, air and fuel. Make sure that intake is sealed properly or you will end up with a lean condition. The plug tells me your jetting is fine. You may be looking for a ignition problem.
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Post by 'O'Verse on Nov 18, 2018 20:08:16 GMT -5
Next step after checking for compression would be to run an air leak test. Definetley two essential gauges to add to anybody's 2 stroke arsenal for sure. Let's say you run an air leak test and your system is air tight. That leaves lubrication. The best case scenario would be to switch to premix anyway. That way lubrication of the cylinder and piston is guaranteed. Our Moderator 90gtvert has YouTube videos for all kinds of information pertaining to 2 stroke scooters in our tech section. Videos and step by steps on switching to premix, making a air leak tester, and compression testing.
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jack667
Scoot Enthusiast
Posts: 190
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Post by jack667 on Nov 19, 2018 9:13:19 GMT -5
3 great comments - thanks again guys.
Snaker - On the oil change, it is a 2-stroke and I did not do any bleeding. This could be my issue.
Ryan - yes - you guys might be on to something. The temp went up super quickly. Maybe it is a gauge fluke. Maybe it did get high bc of a lack of oil, but maybe not as high as the reading. When it konked out, it seemed like it ran out of gas. I replaced the spark plug and checked everything over, but I'll put it all back together and see if I can make some magic happen. It does seem like a spark or fuel problem, and sounds like it wants to fire up. (maybe that's just wishful thinking). I did spray in some quick start, but that's not helping, so not sure if it could still be a fuel problem. I've also had this type of non-start scenario with vacuum leak. But everything looks tight. I'll check again.
OV - I'm pricing out these tools and they're not too bad. (Looking at OTC stuff, $73 for 5605 Deluxe compression kit and $66 for 5609 Leak Tester) I agree that I should have these for doing work, both on scoots and on cars. I guess I need an air compressor, too (Excell Sac22HPE). I've been holding off on that purchase for a long time. I've got $335 worth of kit (including hoses and accessories) in my Amazon cart and working up the energy to pull the trigger on it...
I'll post back when I do that work above. Also, seems like I need to figure out the oil thing, whether a bleed, or convert to pre-mix. I really didn't want to do that, since this scoot is in the care of my son. I have 3 sons and it will get passed down as they age up into cars, etc. Seems easier on them to add gas and oil separately. If it was just me, I wouldn't be as concerned.
Thx again!
Jack
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Usually if a piston expands too much it has nowhere to go. So unfortunately the metal of the piston and the metal of the cylinder suffer during the expansion. Usually pieces of the piston (softer material) end up gouging the cylinder walls creating a gap. Hence the loss of compression. 
Usually if a piston expands too much it has nowhere to go. So unfortunately the metal of the piston and the metal of the cylinder suffer during the expansion. Usually pieces of the piston (softer material) end up gouging the cylinder walls creating a gap. Hence the loss of compression. 