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1981 dt100 tuneup help

12 Jun 2019 08:35
Hrspowr
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1981 dt100 tuneup help #1
Hi All, first post.

I have a pretty extensive 4 stroke background (cars and Honda 3 wheelers). But am new to two strokes.


My son and I bought a 1981 Dt100 for him to start learning on, that had been sitting since parked in 1999. It has a little under 2000 miles on it.

We cleaned the fuel tank ( had to remove the failed Kreme liner) and coated with por15’s system. New petcock, lines and inline filter.

New spark plug.

We cleaned and rebuilt the original carb, air screw two turns out per service manual, changed all the fluids and verified the autolube system is working.

New air filter (in stock air box)

Put in new clutch frictions.

New battery

It starts and idles great now. We are able to ride it, but it is VERY slow to rev. Before I start throwing parts at it I thought someone here might have ideas to start with.

Out of gear, if you stab the throttle, it takes almost 5 seconds to come up to high rpm.

I was going to replace points, condenser and coil, as well as order some Boysen reeds for it. (Do reeds stiffen with time?)


Anyone have suggestions on where to start?


Thanks in advance for you help!

Dan

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12 Jun 2019 10:12
yamahahaha
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1981 dt100 tuneup help #2
When you cleaned and rebuilt the carb did you replace the jets? If so did you use Mikuni jets ?

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12 Jun 2019 12:46
Wheel mad
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1981 dt100 tuneup help #3
Sounds like the exhaust could be blocked
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12 Jun 2019 13:53
Hrspowr
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1981 dt100 tuneup help #4
All the original jets were cleaned and reinstalled.

What’s the best way to check exhaust? It looks like it’s not a good idea to run 2 stroke without the exhaust to see if it runs better?

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12 Jun 2019 14:24
Blackhat250
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1981 dt100 tuneup help #5
Remove the tail piece first, and try it,, as for the front pipe, it may need burnt out,

If you aint mixin gas " you aint haulin Ass
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12 Jun 2019 15:12
Hrspowr
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1981 dt100 tuneup help #6
I’ll try it tonight, and report back.

Thanks for the help.

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12 Jun 2019 15:19
RT325
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1981 dt100 tuneup help #7
Run it minus the tail section & if ojk then check the spark arrestor down in the tail bit. If no better then remove pipe & check the exhaust port right up to the piston as carbon 'can' grow across the port in an extreme case. Look into the front of the pipe & poke something full size int where the tail muffler engages. Have very rarely seen reeds stuck shut with our crap fuel in nz & your bikes been sitting since "99--so!!. Have seen home made base gasket where the maker has omitted to cut out for the transfers--that killed the performance lol. Have see pistons back to front with reed holes to the exhaust--goes all flat & gaspy. If left crank seal has popped out you have the choke on constantly to keep it going. If right side got out it'd smoke the village out & also be gaspy & choke on. Think they were still points ignition so 15 thou gap for close to right timing & enough advance--no more than nipping 15. Thought idle mixture would be i.5 out but if 2 is ok & not lean then no worries, not the issue anyway. I had a cylinder of one of those we replaced at work under warranty as was porous in one transfer & kept getting fuel mix running down the fins. Didn't affect its running though. I'm thinking the smaller wheeled, smaller bike DT100SD we called them--great learner bike. The more i think the more it sounds exhaust. Run i minus the complete system, won't hurt for a rev down the drive, only hurt everyones ears.

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12 Jun 2019 15:43
Midlife Motor
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1981 dt100 tuneup help #8
I have a 1980 DT100 and it has a CDI. The parts diagram for the 81 has a CDI also. Have you had the flywheel off yet to see if someone put points ignition on it?

It's better to remain silent and be considered a fool than to speak and remove all doubt.

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13 Jun 2019 12:21 13 Jun 2019 12:27 by Hrspowr.
Hrspowr
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1981 dt100 tuneup help #9
Pulled the muffler (silencer?), seemed to run a little better, but had to have the choke on for it to run. Still slow to rev. CLeaned out the muffler at car wash with high pressure hot water. A little black chunky came out but not bad. Pipe flows air freely.

Put it back on, bike seems to run worse then before, still needs choke to run. Unbolted the exhaust from the head, other then really loud, ran the same.

I also pulled the carb again, and checked the reeds. Clean, not stuck, no issues there.

Just a thought, would the position of the clip on the needle affect this? I put it in the middle spot when I rebuilt the carb, because I didn’t pay attention where it was when dissasembling the carb.

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13 Jun 2019 12:50
JordanCook
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1981 dt100 tuneup help #10
Sounds silly to ask this but did you pull the pilot jet right out when you rebuilt/cleaned the carb?
The orifice in there is suuuuper small. Any time I've ever had to run a carb with the choke on, it's been because that little suckers been plugged. And then runs like crap until the main opens up.
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