KDX80 won't idle low
Posted: 08:50 am Aug 01 2011
Hi folks,
I recently picked up a 1980 KDX80 for my kids. At the seller's, it was hard to start and idled, but at a high idle. I didn't think too much of that at the time, but when I got it home I found that it was near-impossible to start with the kickstart, and that, once push started, it would run for about a minute before dying.
I checked the carburetor, and it was actually very clean (not even any sediment in the bottom of the bowl). I cleaned it again, anyway, though, and checked the reeds, which were fine. After playing around with it a bit more, I found that, if it were warm, and I set the pilot pretty rich, and the idle kind of high, I could keep it running at the high idle. But cold it still has to be push started. If you reduce the idle to a normal speed, it will idle OK for 20 or 30 seconds, then start missing a little bit, then just die. Once it's running, it has decent power and throttle response, but has the issue idling, and blows some smoke when the throttle is pulled.
I did a compression test, cold (and, BTW, I'm at 6500 feet elevation), and came up with 91 PSI. The service manager at the local dealership told me, under 90, at this elevation, would be a problem. Well, it's not under 90, but it's close.
The question is, do you think this slightly low compression would account for the symptoms I'm seeing, or might there be an issue with ignition as well?
I have a service manual on order, hopefully should get it in a day or two. Also, I do plan to rebuild the top end anyway, since the compression is marginal. I pulled the cylinder yesterday and it looks pretty good... no scratches that I could feel, just the ring of carbon at the top; so I'm hoping (since it has that electrofusion bore) that all it'll take is a new piston and rings.
Thanks,
Paul
I recently picked up a 1980 KDX80 for my kids. At the seller's, it was hard to start and idled, but at a high idle. I didn't think too much of that at the time, but when I got it home I found that it was near-impossible to start with the kickstart, and that, once push started, it would run for about a minute before dying.
I checked the carburetor, and it was actually very clean (not even any sediment in the bottom of the bowl). I cleaned it again, anyway, though, and checked the reeds, which were fine. After playing around with it a bit more, I found that, if it were warm, and I set the pilot pretty rich, and the idle kind of high, I could keep it running at the high idle. But cold it still has to be push started. If you reduce the idle to a normal speed, it will idle OK for 20 or 30 seconds, then start missing a little bit, then just die. Once it's running, it has decent power and throttle response, but has the issue idling, and blows some smoke when the throttle is pulled.
I did a compression test, cold (and, BTW, I'm at 6500 feet elevation), and came up with 91 PSI. The service manager at the local dealership told me, under 90, at this elevation, would be a problem. Well, it's not under 90, but it's close.
The question is, do you think this slightly low compression would account for the symptoms I'm seeing, or might there be an issue with ignition as well?
I have a service manual on order, hopefully should get it in a day or two. Also, I do plan to rebuild the top end anyway, since the compression is marginal. I pulled the cylinder yesterday and it looks pretty good... no scratches that I could feel, just the ring of carbon at the top; so I'm hoping (since it has that electrofusion bore) that all it'll take is a new piston and rings.
Thanks,
Paul