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Makotosun

‘76 DT100 starting issue.

  • johnny340
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‘76 DT100 starting issue. was created by johnny340

The issue is, it won’t.
I now have:
Large, bright blue spark.
New points set as per the manual at 1.8mm before TDC.
The carb is all clean with a new float valve and seat.
The reeds look fine.
The kill switch is currently not wired into the system.
Compression is fair with no noteworthy scratches or blow-by on the piston as viewed from the intake or exhaust.
Not sure where to go from here but it will not start despite a big spark and a clean carb (or even with starting fluid, or gas mixture down the plug hole).
Thanks for your suggestions :)
31 Mar 2019 14:11 #1

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Replied by Blackhat250 on topic ‘76 DT100 starting issue.

Take off the Exhaust ,make shure its clear,, . and i usually fire brake cleaner spray at the rear of carb [ boot off ] to get an offer, from a troublesome engine,
If you aint mixin gas " you aint haulin Ass
31 Mar 2019 14:32 #2

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Replied by johnny340 on topic ‘76 DT100 starting issue.


I’ve tried starting it with and without the exhaust. The air box is not on it but I can feel suction at the carb. Spraying starting fluid in the carb didn’t help either.
31 Mar 2019 14:38 #3

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Replied by Blackhat250 on topic ‘76 DT100 starting issue.

Bump start it , sometimes it need it for a first start , Oh ,try another Plug ,Some dont work under compression ,,
If you aint mixin gas " you aint haulin Ass
Last edit: 31 Mar 2019 15:03 by Blackhat250.
31 Mar 2019 15:02 #4

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Replied by Mothersbaugh on topic ‘76 DT100 starting issue.


Help me out here, guys. Aren't we creating a deadly poisonous gas if we are heating and/or igniting chlorinated brake cleaner? Best be using starting fluid rather than brake cleaner. Correct me if I'm wrong, gentlemen.
31 Mar 2019 16:23 #5

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Replied by RT325 on topic ‘76 DT100 starting issue.

gosh i dunno, has to go. Not flooded in the crankcase in which case hold the throttle wide open & kick or push. Bright blue spark could indicate a faulty condenser but chances are you'd still get a backfire once in a few kicks. If its sucking to the feel of your hand over carb then crank seals left & right must be in place. Start fluid would have to get it excited, hell i just use CRC5-56 which is just penetrating fluid spray & everything here lights up & even had a derelict quad running fully on it with a continual spray for a minute in the carb mouth. Drop the pipe & must give a sign if ya push it. If plugs getting wet then fuel off then drain carb then hold throttle open & kick or push away. Can hear it running now. Get an aftermarket condenser & just tuck the wire into the coil wire--black wire--heading to the spark plug coil from the magneto then earth it best way you can & see if spark looks more concentrated rather than a blue flash.
Last edit: 31 Mar 2019 17:03 by RT325.
31 Mar 2019 17:02 #6

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Replied by johnny340 on topic ‘76 DT100 starting issue.

Thanks for the replies!
I do have a new condenser on it and a new spark plug, which I suppose could not be firing under pressure. I too thought I’d at least get a backfire or any sign of life. There is no chain on it so bump starting isn’t an option till I get a new chain and sprockets. Maybe that’s what I’ll try next if another spark plug doesn’t help.. it’s like the spark plug isn’t firing when it’s tightened down and under compression??
Good to know that the carb suction should indicate that the crank seals are good enough.
31 Mar 2019 18:48 #7

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Replied by johnny340 on topic ‘76 DT100 starting issue.

Ok so new spark plug didn't help. Lots of spark but nothing when the plug is tightened down.
Here are picks of spark and residual staring fluid igniting. What next? It will not even sputter..
17 Apr 2019 15:07 #8

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Replied by Wheel mad on topic ‘76 DT100 starting issue.

I've always figured that if you've got spark and fuel and it won't fire at all, then it Has to be crank seals BUT the last 2 stroke to give me this sort of brain damage turned out to be the spark plug cap. The one before that, it was a crankcase full of fuel. With bone dry carbs and no fuel at all, I manage to get it to fire by holding it wide open throttle and kicking forever and it finally started and ran for 10 minutes , just running off the fuel in the crankcase.
Thinking maybe that crank seals can work OK on suction but not under compression when they're meant to be transferring ? Guessing.
Try the plug cap .....
17 Apr 2019 15:45 #9

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Replied by johnny340 on topic ‘76 DT100 starting issue.

Thanks for the quick reply. Plug cap ordered. As well as chain & sprocket to push start it.
17 Apr 2019 15:55 #10

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