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Post by backwoods on Dec 23, 2010 19:15:43 GMT -5
I'd like to start at the end, then let everyone know what happened. I wondering if someone else has had a similar experience.
I had been riding around for about 10 minutes with the scooter running awesome, then switched to let a buddy drive it while I followed in my truck to see what kind of speed it was getting. He had been driving for a few minutes, then said it felt like it didn't have as much power or pick-up. Cruising at about 42mph, I saw him slow down to about 35 and stay there, then just get slower and slower til he signaled me to pull over which I did. Then as he pulled up to me, the bike cut off.
Now it won't start, and it feels like there is little compression. The kick starter pushes through much smoother than it should. He said he heard a noise that was like spark knock, but no metal grinding or smashing or anything.
Since I got the new 83cc running good, it only had a handful of miles on it, but I had let it run for hours in the parking lot going out periodically to take it for a few laps just to try to break it in better.
The only thing I can think of that would make it have so little compression would be the rings going out. But if that happened, I would think it would be more sudden and noisy, instead of a gradual loss of power. I don't think the valves adjustment could have backed of causing this, but I don't know what else to consider.
Just wondering if anyone has any ideas before I get around to taking it apart and looking inside.
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Post by larry001964 on Dec 23, 2010 19:29:47 GMT -5
I think i would do a compression test, and go from there. As you say it's now turning over much easier than before.
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Post by backwoods on Dec 23, 2010 19:38:55 GMT -5
Yeah I planned to do that once I get a hold of the gauge again. It doesn't feel like there's no compression - just less. I don't know what would cause this sudden fall off and loss though. I'm really hoping there is no problem with the rings.
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Post by larry001964 on Dec 23, 2010 19:50:58 GMT -5
Yeah I planned to do that once I get a hold of the gauge again. It doesn't feel like there's no compression - just less. I don't know what would cause this sudden fall off and loss though. I'm really hoping there is no problem with the rings. Are you using the stock CDI ? if so do you have another to check with ? Some CDI's have a rev limiter, when they go bad I em not sure how they act. |
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Post by Enviromoto on Dec 23, 2010 19:53:20 GMT -5
Where did you get the kit? What was your jetting?
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Post by erictheviking666 on Dec 23, 2010 20:09:45 GMT -5
but I had let it run for hours in the parking lot going out periodically to take it for a few laps just to try to break it in better. You let it sit and run for hours? If that's so you overheated it! An air cooled engine has to be moving to keep cool. You should not let one sit still and idle more than 10 to 15 minutes max. If what your saying is true you may have cooked that motor. Sorry to be the bearer of bad news, but that does not sound good at all. |
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Post by backwoods on Dec 23, 2010 20:27:05 GMT -5
I am running the performance CDI from scrappy. The rebuild kit was the big bore top end assembly, also from scrappy, and there is a 95 main jet in it.
I could throw the stock CDI back in just to see if that makes any difference, but because the compression feels lower on the kick-start, I don't think that would make a difference.
Yes it ran for about 2 hours, going out periodically to run it around the parking lot. It seemed to run totally fine after this, when I drove it around regularly.
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Post by backwoods on Dec 23, 2010 20:29:39 GMT -5
Oh I also forgot to add, when the other guy was riding it and signaling to pull over, I got beside him and in my headlight could see a cloud behind him. Couldn't tell if it was burning oil, unburnt gas, or what.
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Post by tomcas on Dec 23, 2010 20:39:21 GMT -5
Until you get the compression tester you could pull the valve cover for a look see.
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Post by buiditright on Dec 23, 2010 20:39:49 GMT -5
it ain't the CDI, you sound like you have a major issue inside. You are going to need to do a compression check first. then go from there. But the if what you say is true you are going to have to pull the top of the motor.
That is if your lucky.
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Post by backwoods on Dec 23, 2010 20:44:44 GMT -5
I'll do the compression check soon. I just went outside and looked at it, and it looks like there's more oil than there was on the ground after I re-parked it. Compression very low and it almost sounds like it's breathing. I wonder if I have a hole in my cylinder or something...
Is there any way the valve lash could have backed out causing a problem with compression? If the bolts weren't tight enough, the last could have gotten bigger, but I would think if anything, this could cause more compression as they wouldn't open fully.
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Post by erictheviking666 on Dec 23, 2010 20:44:59 GMT -5
Yes it ran for about 2 hours, going out periodically to run it around the parking lot. It seemed to run totally fine after this, when I drove it around regularly. Yeah and if I'm not mistaken (someone please correct me if I'm wrong) but with an 83cc kit the larger piston means the cylinder walls are thinner, which would make it even more susceptible to running hot. |
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Post by backwoods on Dec 23, 2010 20:51:59 GMT -5
You are correct about that erictheviking... we will see what is in store when I take the cover off and check things out.
Most air cooled motors can stand to run at an idle for extended periods and be fine, like lawn mowers. I would bet that a stock scooter wouldn't have any issue with it either. Perhaps with the larger displacement, it didn't particularly like sitting still. But I still feel like at an idle, it should be fine.
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Post by erictheviking666 on Dec 23, 2010 20:56:39 GMT -5
You might be right since it was only idling. Actually I had my 72cc idling for quite some time today because I was trying to figure out why my headlight quit working. I noticed that it was getting kind of warm sitting there so I shut if off. After I figured out what was wrong with it I took it out for a little ride and everything was fine. Got home let it sit a couple of hours and now mine won't start. I probably won't have time to mess with it until after Christmas now, so I'll figure it out later.
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Post by lshigham on Dec 24, 2010 3:14:38 GMT -5
Guys, you must remember that these are forced cooling motors not passively cooled Harley's.
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Post by rockfish on Dec 24, 2010 9:27:54 GMT -5
it doesnt matter the temp!! they are FORCE COOLED!!! leaving it run at an idle for hours probably cooked the motor....especially with an 83cc kit in it!!
they run hotter with larger bore kits in them anyway
not a great thing to do dude......you should have been driving it to break it in a bit not letting it sit and overheat
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Post by erictheviking666 on Dec 24, 2010 11:20:38 GMT -5
Yeah that's what I was afraid of, with the plastic cowling on these motors they have to be moving to force through and keep it cool.
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Post by lshigham on Dec 24, 2010 11:24:52 GMT -5
Yeah that's what I was afraid of, with the plastic cowling on these motors they have to be moving to force through and keep it cool. There's a fan  I'm not saying leaving a scoot idling for a long time is a good idea, it isn't. However, it probably won't cause catastrophic damage. |
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Post by erictheviking666 on Dec 24, 2010 11:37:01 GMT -5
Yeah true there is a fan, but it doesn't move a lot of air. It all depends on outside temperature of course. I try to never let mine idle for more than 15 minutes at a time.
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Post by buiditright on Dec 24, 2010 11:51:48 GMT -5
The fan does not move enough air to cool the motor while it is idling. Eric your so right about that. But either here not there you have other problems to fix here, It is best after you do the compression test if it is low then you have to pull it which is what it sounds like your going to have to.
Bill
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Post by lshigham on Dec 24, 2010 11:52:02 GMT -5
Yeah true there is a fan, but it doesn't move a lot of air. It all depends on outside temperature of course. I try to never let mine idle for more than 15 minutes at a time. That's wise. It's also a big no-no letting a newly rebuild engine idle for a prolonged period of time. |
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Post by larry001964 on Dec 24, 2010 12:22:37 GMT -5
Well I know the CDI is a stretch when it comes to his problems. I was just thinking of things that may also cause a lack of power.. Everyone here has come to my aid when I needed it, I just try to be helpful and give back when I can..
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Post by mopedmedic on Dec 24, 2010 12:51:18 GMT -5
The big bore kits for the QMB139 engine fail a lot. We have found one okay one, but it's only a 70cc kit. The 80 and 100cc kits usually last 200-600 miles, if they are put in right, before they destroy the bottom end of the motor.
If you want go fast in a 50, get a 2T engine. The stock 50cc 2T motor will usually outrun the QMB139 with a 100cc kit and all the other crap people put on it, and last tens of thousands of miles longer. And when you put a 70cc kit on it, or replace the motor with a 100cc engine, which is a bolt in swap, the thing flat out flies. And lasts.
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Post by backwoods on Dec 24, 2010 12:58:18 GMT -5
No worries, thanks Larry  I sure hope the bottom end isn't hosed. I'd be fine if it was something like a cylinder or rings I suppose. Only compression test and dis-assembley will tell. |
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Post by mopedmedic on Dec 24, 2010 13:35:26 GMT -5
That's wise. It's also a big no-no letting a newly rebuild engine idle for a prolonged period of time. If it's a new or rebuilt 4T engine, you want to warm them up to operating temperature, ride them really hard for 20 minutes with a lot of Wide Open Throttle, full speed and then deceleration under load runs, preferably on a Dyno or long stretch of road where you can open it up and slow down without getting rear ended, and then change out the oil for a good synthetic. that is how you break in a 4 stroke motor. |
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Post by buiditright on Dec 24, 2010 18:47:40 GMT -5
Larry,
I was not trying to jump on you. It is just the totalitary of the cercumstances show that he has major problems inside his motor.. Please to not take it that I was hiting to you it was not meant that way.
I did not want to see him jump up and o buy a new one when the way he discribed it that was not an issue here.
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Post by larry001964 on Dec 24, 2010 19:19:25 GMT -5
Larry, I was not trying to jump on you. It is just the totalitary of the cercumstances show that he has major problems inside his motor.. Please to not take it that I was hiting to you it was not meant that way. I did not want to see him jump up and o buy a new one when the way he discribed it that was not an issue here. I didn't feel jumped on, I actually felt like an idiot for even saying it. I knew from my own experience that the likely hood was pretty much slim to none... I just hated giving him the bad news like that after he put so much work into it. But I didn't feel jumped on. just stupid on my own part, I really em a better mechanic than that. |
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Post by buiditright on Dec 24, 2010 21:12:55 GMT -5
good I am glad bud
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Post by Bluefront on Dec 25, 2010 6:16:53 GMT -5
Add up the circumstances......83cc BBk, too short/problematic break-in period, loss of power w/excessive smoke from the exhaust, lower compression, etc. If you reused the stock head, your compression was raised=more heat. If you got a head designed for a BBK, you still raised the compression somewhat. If you check the spark plug, you'll probably find metal deposits on it. Sounds like a partially seized piston and damaged rings, along with score marks on the cylinder walls. The ring end gaps may have been too little.....that can cause all sorts of problems. These gaps need to be checked before you install the piston. You might also check the piston clearances.....could have been too tight. Good luck with the re-build.  |
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Post by tomcas on Dec 25, 2010 10:41:01 GMT -5
Guys, you must remember that these are forced cooling motors not passively cooled Harley's. I agree 100%. These guys are worried unnecessarily. As long as the shrouding is properly in place, the bike isn't sitting in the hot sun with a 110 degree air temp, AND the bike as already been properly broken in, then the engine should be fine. Of course you should never let a bike idle to break it in. The most important thing is to vary the engine speed and put it under at least a moderate load to create pressure on the back side of the piston rings. The piston rings get 90% of their radial loading from the pressure differential and without this loading the rings can't seat it from just the expansive fit of the rings themselves. |
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