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TOPIC: She runs...WAY TOO FAST

She runs...WAY TOO FAST 04 Jun 2019 16:24 #1

  • DreddwardElric
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So, I got the bike to start! The downside is, it seems the thing is stuck at full throttle, maybe? It is revving what sounds to be very high, and I hit the kill switch when the idle screw and throttle grip had no effect on engine speed. Any ideas on how to check if the throttle is stuck. Is there some kind of tension spring that I need to check or anything? My manual doesn't really tell me how to address the throttle other than the handlebar adjustments.

Also, I think that the one mounting thing that keeps the cable against the chassis broke off. Does that effect throttle position?

P.S. You guys are WONDERFUL! I started this knowing nothing about anything, and in a few short weeks, am on the cusp of having a bike that hasn't run in 35 years back on the road. THANK YOU!

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She runs...WAY TOO FAST 04 Jun 2019 16:26 #2

  • Scottddove
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First thoughts. You can check that the slide is going all the way down. I would also be suspicious of crank seal.
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She runs...WAY TOO FAST 04 Jun 2019 17:58 #3

  • RT325
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sounds like you've missed the guiding pin in the side of the carb & its either on full song or if slide is around to the cutaway & sitting on the pin it'd be 3/4+ throttle. Take the air filer hose off & have a look or use a mirror. Should hear it click down to the bottom. Gotta be a bit careful that the slide needle finds its way into the needle jet too.

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She runs...WAY TOO FAST 04 Jun 2019 18:24 #4

  • MarkT
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Topic is well covered.... not much to add... Habit I know many share is to twist throttle and release listening for the satisfying "click" or "clunk" of the slide closing completely. If it's doing that, and not responding to the idle speed screw, likely it's an air leak.

With the troubles you've had, air leak is a very distinct possibility.... monoshock 175's often have the ignition-side seal leaking in my experience. Pulling the plastic ignition cover off might reveal oil/gas leaking in the flywheel area.


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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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She runs...WAY TOO FAST 04 Jun 2019 19:21 #5

  • DreddwardElric
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So, getting the carb on and off with the boots on the airbox and engine sides was really difficult. Well, actually, getting it back on was really hard, off was a little easier. Is there a trick to getting it to all fit back together, maybe a particular order in which the parts attach or something?

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She runs...WAY TOO FAST 04 Jun 2019 19:37 #6

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Soft new boots makes it easier. No matter what it's a bit of a pain on that model... Great job getting it done!
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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

She runs...WAY TOO FAST 04 Jun 2019 20:55 #7

  • Midlife Motor
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Also check that the slide adjustment or "idle" screw is not excessively loose on the side of the carb. Carb can suck in air this way. How do I know? This happened to me tonight on my DT100 and resulted in a "runaway" engine. Operator error.

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

She runs...WAY TOO FAST 04 Jun 2019 23:17 #8

  • liferbiker
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I agree w/Mark, the slide clunk is the most important noise on any bike. I'll tell you about a novice rider's error after dropping (Maico 400) he just had to have. We were at Hollister in northern Ca. after starting drill, I told him if he drops it to check for that throttle clunk b 4 starting (Maico's will run away) he didn't, bump started down the hill I was at top, bike literally left him like a cartoon, full throttle crashed about 100 ft further down, it was spinning around I ran down the hill to bike pulled the clutch in to stop rotation, tried kill button, nothing, pulled plug wire, nothing, it was dieseling rpm was so high, turned off fuel eventually stopped motor runaway. That cost him crank rebuild, Just to be safe (I did all the labor for free good friend) wanted him to pay something(for crank rebuild) he sold it and bought a bike (as I suggested first) more suited to his newbe skills, a 250 yamaha enduro!
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She runs...WAY TOO FAST 05 Jun 2019 03:16 #9

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Yes the throttle shutting right off is the most important thing but i'd also back out the idle speed screw so you don't get a clunk on that & think its shutting right off. That's especially important if someone has screwed the idle speed right home not realising what it's doing.

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She runs...WAY TOO FAST 05 Jun 2019 07:38 #10

  • Scottddove
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A trick that works for me on disassembly and reassembly where the rubber boot is a tight fit is to use a heat gun to soften up the rubber boot. Assuming yours is hard.

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Last Edit: by Scottddove.
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