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1975 DT400--hard starting and other odd things


turrican64
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I couldn't pass up on it after seeing it on Craigslist since it was complete, in decent shape and it's a 400! That ought to be an upgrade from the 175! :D After having it for a few days, I discovered issues the seller kept his mouth closed about:

--The bike is quite hard to start. I have to jump on the kicker and give it some gas in order for it to start within a reasonable amount of time. It takes about 6 kicks if I'm feeling lucky, but I've seen lots of these which start within one kick!

I'll also add that it makes a loud hiss exactly like the sound of removing an air tool from a compressor if I hold the throttle open. Sometimes it backfires too.

--Idle speed is quite high at 2,000 RPM. Trying to adjust the carb following the manual results in very hard starting and it stalls frequently when warm.

--It runs somewhat spotty between 3-5,500 RPM. It sounds like it's firing every other stroke and power feels jerky/mushy but it's very very subtle.

--Neutral is not easy to find. Takes a few tries.

--It really likes to burn its lights.

I've done a compression test and I got 120PSI cold. I put some oil in, the compression went up to 130 and it got very hard to kick over. I cleaned the carb out, and put fresh gas in. Petcock allows gas to flow freely. Spark seems OK.

My guess is that it just needs a new top end. It does have 6,100 miles on it. I've been pulling my hair out trying to outsmart this thing...what do you guys think?

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I couldn't pass up on it after seeing it on Craigslist since it was complete, in decent shape and it's a 400! That ought to be an upgrade from the 175! :D After having it for a few days, I discovered issues the seller kept his mouth closed about:

--The bike is quite hard to start. I have to jump on the kicker and give it some gas in order for it to start within a reasonable amount of time. It takes about 6 kicks if I'm feeling lucky, but I've seen lots of these which start within one kick!

I'll also add that it makes a loud hiss exactly like the sound of removing an air tool from a compressor if I hold the throttle open. Sometimes it backfires too.

--Idle speed is quite high at 2,000 RPM. Trying to adjust the carb following the manual results in very hard starting and it stalls frequently when warm.

--It runs somewhat spotty between 3-5,500 RPM. It sounds like it's firing every other stroke and power feels jerky/mushy but it's very very subtle.

--Neutral is not easy to find. Takes a few tries.

--It really likes to burn its lights.

I've done a compression test and I got 120PSI cold. I put some oil in, the compression went up to 130 and it got very hard to kick over. I cleaned the carb out, and put fresh gas in. Petcock allows gas to flow freely. Spark seems OK.

My guess is that it just needs a new top end. It does have 6,100 miles on it. I've been pulling my hair out trying to outsmart this thing...what do you guys think?

Ok, i'll admit i'm a lot better with the 175's but 120psi from a stroker aint so bad and it only went up 10 with the oil so i'd say the top end isnt where the problem lies.

My 175 was performing a lot like this, got a couple of things for you to try.

Take off the LH cover and with the engine running at whatever its happy to on tick over try and blast a good amount of wd or similar behind the flywheel, use one of the straw things that always gets lost, and see if it affects the idle speed.

While you have the WD out soak everything carb side, the rubbers everything again monitoring the idle speed.

If that makes no difference then get a glass of water and dip the crankcase/gearbox breather in it and see if you have a constant steam of bubbles, OR it tries to suck the water up. Finally check the gearbox oil i would expect it to smell of fuel if i'm right.

I would bet that one of the above tests will have an effect, everything you have listed above is what you would expect for a crank seal failure. Hard to start,high idle, 4stroking (thats the spotty running at 3-5000) the backfire. If the tests above prove to have no effect then it may be a leak somewhere else but that wouldn't generally give all the stated symptoms just a select few.

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