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'78 DT 125e woes


78dt125e
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Recently aquired a 1978 DT 125e. It has been sitting for at least 20 years. So I knew it was going to take some doing to get it on the road again.

Here is a list of the things that I have replaced:

1. Battery

2. Air filter

3. Coil

4. Points (I didnt replace the condenser because in my experience they usually dont go bad, plus it was hard wired in an looked to be a PITA)

5. Fuel and Oil lines

6. Removed the carburetor and rebuilt it leaving the float set at were it was when I removed it.

I checked:

1. cleaned the gas tank and the fuel switch, including the strainers. (it drains fuel at about a half gallon/min now)

2. had to free up the stuck clutch disks.

3. reprimed the oil pump and resealed the clutch cover. (I started it with premix fuel just to be safe.)

4. has good hot spark.

Kicked it over and.....Horray! It seemed to run great. So I thought...

It ran just fine for about 5 minutes and then it was just like someone reached up and turned the key off.

I did some more adjusting on the carb and kicked it over after working on it for about 10 minutes.

It fired right up just fine, returned to idle. A slight crack of the throttle and it winds up great. So I decide to take it around the block for a quick spin. Get half way around and it dies again...no stuttering, no amount of twisting on the throttle or messing with the choke will keep it running. Again, it was just like you reached up and turned the key off. I kicked and kicked on it to restart it to no avail. I checked the spark right after it died and it had great spark. Reinstalled the spark plug and kicked it and kicked it and kicked it. No startey. Must be a fuel problem right!? Wrong. Removed the carb again. Everything was in order and functioning as it should. Reinstalled carb, kicked it over. It runs. like it always did; great. It runs great for about 5 minutes then it dies again. No restart until it sits for about 5-10 minutes and then it runs just fine....for five minutes. You get the picture. What am i missing? Thanks for reading and any help would be much appreciated!

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Hi there how's it going,

If you have spark and from what you wrote it sounds to me like the fuel might be running out in the carby so check the inlet needle and seat? Check the the float height too.

Hope that helps,

Gordo

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............ No startey. Must be a fuel problem right!? Wrong. Removed the carb again. Everything was in order and functioning as it should. Reinstalled carb, kicked it over. It runs. like it always did; great. It runs great for about 5 minutes then it dies again. No restart until it sits for about 5-10 minutes and then it runs just fine....for five minutes. You get the picture. What am i missing? Thanks for reading and any help would be much appreciated!

I would say right myself, runs for about as long as it takes the carb float bowl to empty.!?

You may have a very slow fuel supply either because of blocked filter screen in the float bowl...or within the tank.

Pull off the pipe from the carb and check the flow is fast

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I would say right myself, runs for about as long as it takes the carb float bowl to empty.!?

You may have a very slow fuel supply either because of blocked filter screen in the float bowl...or within the tank.

Pull off the pipe from the carb and check the flow is fast

Thanks for the replies!

It runs out of the tank at a rate of about a half to 3/4 gallon per minute. It seemed sufficient to me? I just rechecked all the screens and strainers to make sure they were free of contaminants and everything was clean.

Also, while it is running it doesnt seems to make any difference if i have it running at a constant 2,500 rpm or if I am out riding it and speeding the engine up. It seems to die +/- 15 seconds no matter how fast or slow I run the engine. I would think that riding it would empty the bowl faster than a sustained 2,500 rpm would?

Usually if it is a float level adjustment it will stutter and try to continue running for a while before dying. Not just, bam, im dead and you're not getting me started again without waiting for 5 minutes. It just seems odd.

Would a bad condenser do that? Heat up and quit working? I've tried everything else. I even polished up the tangs that the coil mounts to thinking it was somehow losing a ground? But that didn't fix anything.

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Thanks for the replies!

It runs out of the tank at a rate of about a half to 3/4 gallon per minute. It seemed sufficient to me? I just rechecked all the screens and strainers to make sure they were free of contaminants and everything was clean.

Also, while it is running it doesnt seems to make any difference if i have it running at a constant 2,500 rpm or if I am out riding it and speeding the engine up. It seems to die +/- 15 seconds no matter how fast or slow I run the engine. I would think that riding it would empty the bowl faster than a sustained 2,500 rpm would?

Usually if it is a float level adjustment it will stutter and try to continue running for a while before dying. Not just, bam, im dead and you're not getting me started again without waiting for 5 minutes. It just seems odd.

Would a bad condenser do that? Heat up and quit working? I've tried everything else. I even polished up the tangs that the coil mounts to thinking it was somehow losing a ground? But that didn't fix anything.

good you have a fuel flow so the screens ank tank venting must be good. Sounds electrical now doesn it, can you quickly test for a spark at the point she quits?

Perhaps something is going open circuit or short circuit with heat.

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My old V8 land rover would do exactly the same when the condenser was past its best. To the point i kept a spare mounted next to it on the dissy mount. Once i felt the telltale missfire i'd swap.

I would definately swap out the condenser, it is a bit of a pain but you really cannot fault find something like this without correcting something so likely to be the cause.

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