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'75 DT 100 Runs one day not the next

04 Jul 2019 21:25
MarkT
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'75 DT 100 Runs one day not the next #11
Sometimes a petcock won't shut off so that's something to check too.

Not likely that just leaving the plug out one night will cure a badly flooded engine. Excess gas in crankcase might take weeks to evaporate.

Leave gas off. Put plug in. Kick it a couple times. Pull out plug. Wet?

I flooded my LT2 a bunch of times by leaving the petcock on when I was a kid. Pipe on LT2 was really easy to take off. Often there was gas in the bend in the pipe. So I'd take it off and dump it out. Then with pipe off and plug out and ignition OFF, I'd put it in gear and push it down the driveway and down the street holding the throttle wide open and pushing as fast as I could. (It was nice that the street went down hill from our house.) BWAAAAAAAAH.... all the way down the street spraying the gas out the open exhaust port and open plug hole. Then I'd take it out of gear and push it back home. Put plug back in and pipe back on. Gas still off. I'd kick it a couple times with the throttle wide open. If I was lucky, it would fire... barely running with throttle still wide open. Might die a few times. Sometimes plug would foul and I'd have to change it. Then... sometimes sooner rather than later if I was lucky it would start to clean out and rev normally. I'd reach down and turn on the petcock and ride away.

A shortcut if it wasn't flooded too bad was keep gas off, pipe on, good plug in, ignition on, throttle wide open, in gear... friend would help push down the driveway, pop clutch (bounce on seat at the same time for extra traction or tire would just skid) and keep pushing as fast and far as we could... If lucky, a couple houses down it would start to catch and I'd just keep holding it wide open until it would clear out to where I could jump on and ride and turn on gas all at the same time. Turn around, pick up friend... go riding.

1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

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04 Jul 2019 23:14
Wandwuff
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'75 DT 100 Runs one day not the next #12
must be flooded then, eh?

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05 Jul 2019 00:52 05 Jul 2019 01:03 by Wandwuff.
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'75 DT 100 Runs one day not the next #13
So i did what you did with the plug and the exhaust and getting the gas out, and it started up but it absolutely refuses to run with even the slightest amount of choke. To start it i have to put the choke off and then full throttle and 3 or 4 kicks it starts. is that cause of flooding or something else?

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05 Jul 2019 04:12
bluntz465
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'75 DT 100 Runs one day not the next #14
Check your float level also the spark should be blue,check all grounds.

1957 Cushman Eagle 1969 Honda 90 ATC 1969 Honda CB250
1973 Yamaha AT3 1974 Kawasaki KH440 1974 Honda XR75
1975 Suzuki TS75 1975 Kawasaki GreenStreak 90 1975 Suzuki GT550
1975 Suzuki TS250 1976 Suzuki GT550 1976 Indian Chief
1976 Yamaha YZ80 1978 Yamaha IT175 1980 Suzuki GS550
1982 Yamaha IT465J

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05 Jul 2019 05:55
MarkT
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'75 DT 100 Runs one day not the next #15

Wandwuff wrote: So i did what you did with the plug and the exhaust and getting the gas out, and it started up but it absolutely refuses to run with even the slightest amount of choke. To start it i have to put the choke off and then full throttle and 3 or 4 kicks it starts. is that cause of flooding or something else?


No choke! If it's flooded, and it sounds like it is, you need to hold the throttle wide open (maximum air) until it clears out. It may die a few times and won't rev up very much even with the throttle wide open.... it kind of "chugs"... when it starts to rev up, that's when you back off the throttle... you don't want to over-rev.

The engine in this video is not flooded too bad... clears out pretty fast and starts to rev normally... but you can kind of get the idea Important to note he keeps the throttle wide open until it starts revving. Fast forward to 5:11 in the video to see him actually start it.


1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

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05 Jul 2019 17:32 05 Jul 2019 17:39 by DT100K.
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'75 DT 100 Runs one day not the next #16
So if chronic flooding is your boggle then, what I would do:

- drain crankcase and put new oil (no more gas in crankcase!)
- install working spark plug
- take carb apart: check needle valve condition/function and replace needle valve gasket
- verify float integrity and float height
- verify petcock function - if leaky, tighten the nut behind the lever, or better yet, replace the valve inside.

Maybe then the flooding will stop, and the bike will start, either choke on or off, with a closed throttle.

If not, you're into checking the spark and electrical.....

Good luck, you have a very cool lookin' bike.

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05 Jul 2019 20:11
hd395a
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'75 DT 100 Runs one day not the next #17
Hi, just chiming in on your post. Did you say it had good spark?

1977 Yamaha 250 Enduro kid

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05 Jul 2019 22:25
Wandwuff
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'75 DT 100 Runs one day not the next #18
yup it has good spark now, unflooded the engine and it runs fine so far, thanks for your input everyone! <3

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