Hi all. I bought a 78 DT178 this summer that's practically new (1400 miles). I really enjoy this bike, and I've put around 500 miles on it already. However, starting recently the engine wants to die once the bike gets hot.
Hopefully these symptoms will ring a bell with you experts. I have to ride the bike pretty hard (winding it out on-road) for a good 5 minutes or so before it acts up, which is what makes me think its temperature related. I can ride it around the yard, wind it out up and down the street, and it's fine until I get out on the road and push it harder for a while.
The problem is the bike will suddenly cut out, or just barely run. If I can keep it running the engine sounds muffled - it doesn't have the normal crisp bright sound. Something else that makes me think it is overheating is today it died about a block from the house, and I couldn't get it started. So I pushed it home, and when I tried it again 30 minutes later it fired right up.
One other thing is I hear a rattling sound that I've not noticed at any other time, that starts up just before it dies out. It sounds like it comes from the combustion area of the engine, but its hard to tell.
The spark plug looks good, and I'm pretty sure it's getting gas (I cleaned the carb a couple times just in case).
Electrical in general seems to be fine, because the headlight stays nice and bright even when it is running like crap (and I don't have a battery).
Oh, one other thing. The first time I noticed this problem was when I was on a long 20 mile off-road ride on a mountain. The last 8 miles was all downhill, so the bike basically idled the whole time, and I'd let the engine hold me back a bit with the RPMs around 4-5k. Well, it didn't like that at all after a while. That's when it first started running bad and dieing. Even if I held the clutch in it still didn't want to idle right. At one point I swear the thing must have started dieseling. If I held the clutch in the RPMs would shoot up to 8-9k, and even after I killed power it kept running (but sounded really muffled) at those RPMs until I let out the clutch and stalled it.
I'm pretty sure this bike has a reed valve, and the rattling makes me wonder if that could have anything to do with it? Can a reed valve get too hot, or get to the point it can't tolerate heat like it should? Would it rattle, and cause the bike to run like this, or am I barking up the wrong tree?
Any help would be greatly appreciated!
Dan East
Hopefully these symptoms will ring a bell with you experts. I have to ride the bike pretty hard (winding it out on-road) for a good 5 minutes or so before it acts up, which is what makes me think its temperature related. I can ride it around the yard, wind it out up and down the street, and it's fine until I get out on the road and push it harder for a while.
The problem is the bike will suddenly cut out, or just barely run. If I can keep it running the engine sounds muffled - it doesn't have the normal crisp bright sound. Something else that makes me think it is overheating is today it died about a block from the house, and I couldn't get it started. So I pushed it home, and when I tried it again 30 minutes later it fired right up.
One other thing is I hear a rattling sound that I've not noticed at any other time, that starts up just before it dies out. It sounds like it comes from the combustion area of the engine, but its hard to tell.
The spark plug looks good, and I'm pretty sure it's getting gas (I cleaned the carb a couple times just in case).
Electrical in general seems to be fine, because the headlight stays nice and bright even when it is running like crap (and I don't have a battery).
Oh, one other thing. The first time I noticed this problem was when I was on a long 20 mile off-road ride on a mountain. The last 8 miles was all downhill, so the bike basically idled the whole time, and I'd let the engine hold me back a bit with the RPMs around 4-5k. Well, it didn't like that at all after a while. That's when it first started running bad and dieing. Even if I held the clutch in it still didn't want to idle right. At one point I swear the thing must have started dieseling. If I held the clutch in the RPMs would shoot up to 8-9k, and even after I killed power it kept running (but sounded really muffled) at those RPMs until I let out the clutch and stalled it.
I'm pretty sure this bike has a reed valve, and the rattling makes me wonder if that could have anything to do with it? Can a reed valve get too hot, or get to the point it can't tolerate heat like it should? Would it rattle, and cause the bike to run like this, or am I barking up the wrong tree?
Any help would be greatly appreciated!
Dan East