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Makotosun

Good Ol Stalling - however strange.

  • Thrashpipe
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Good Ol Stalling - however strange. was created by Thrashpipe

Hey guys! I come to you with a question that stumps me and can't seem to find an answer to anywhere. 
My bike: 1970 AT1-b. 125
New or already checked: New battery, just rebuilt the VM24SH carb due to the stalling, float is at 25.5mm and not full of gas, all passages cleaned (Sept one that seems to go no where from the mouth of the carb?), A/F screw out 1 1/2, new o ring for the main jet and carb to head, fuel is flowing great from petcock, no gas is dribbling out from bowl after rebuild, new plug gapped to 0.23, great spark. Idle set to just above 1000rpm.

Problem: Bike will start and idle fine, but if I compress the front shocks or hit a bump, it will bog out and die. Sometimes I can feather it and keep it running but usually it will stall right out. I can replicate the issue by pushing the front forks down or lift the front of the bike real quick, and also by sitting down aggressively. Traced all wires and there are no wears to body. Acts as if it flooded because it takes a few kicks and some throttle to start afterwards. 

Does anyone have any ideas as what I should check next? 

Thank you in advance! This site is a god-send. 
Last edit: 16 Jul 2022 11:57 by Thrashpipe.
16 Jul 2022 11:43 #1

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Replied by Tom P on topic Good Ol Stalling - however strange.

Did you look at the underside of the ignition switch to see if all the wires are soldered on securely?
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16 Jul 2022 14:03 #2

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Replied by RT325 on topic Good Ol Stalling - however strange.

Sounds like the fuel level in the carb is way too hight & compressing the forks--just the pushing forward motion--is enough to tip the ballance & flooding the needle jet. That's a wild guess.
Last edit: 16 Jul 2022 21:13 by RT325.
16 Jul 2022 16:13 #3

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Replied by Thrashpipe on topic Good Ol Stalling - however strange.

Thanks guys, I'll take a look as soon as I can. It has me so confused. Old needle and new one have the same outcome.
16 Jul 2022 16:55 #4

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Replied by MarkT on topic Good Ol Stalling - however strange.

Idle speed spec is 1200 to 1300...  about halfway between 1000 and 1500.  Mikuni carbs sometimes do weird stuff if idle is set low.  Makes no sense at all but I've seen turning up idle speed slightly fix issues. 

Are float arms pretty much parallel to float bowl gasket surface when float needle just closes? 
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
16 Jul 2022 17:30 #5

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Replied by yamahoper on topic Good Ol Stalling - however strange.

 
True story
Shortly after this picture the late  Kevin smokin Duby on his way to the Grand Canyon had the bike stall.
The pictured Yamaha DT360 had developed an intermittent stall problem. It would usually start back up but not this time. I rode back for the truck and loaded the bike. After hours of looking for the problem (no spark). I put a different ignition on and it fired up. The cause... The wire was loose under the solder joint on the condenser. 
Electrical gremlins are sometimes hard to diagnose. Until the bike failed to restart I didn't know it was an ignition problem. The connection at the condenser appeared good , it wasn't. 
A spare running bike is usually how I find the problems after logic fails. Putting on a known good carb would send you in the right direction.
Good luck
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17 Jul 2022 03:05 #6

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Replied by Thrashpipe on topic Good Ol Stalling - however strange.

Yeah, I set the floats according to the Service Manual at 25.5mm. can't tell if it is flooding or starving when it dies, could check the plug I suppose.
17 Jul 2022 04:54 #7

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Replied by Thrashpipe on topic Good Ol Stalling - however strange.

Thanks for that yamahoper. I like to do that to and honestly I would just put a new one on but they are impossible to find. My stocker appears to be almost mint though so idk. I will keep checking. Thanks alot everyone so far!
17 Jul 2022 04:57 #8

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Replied by MarkT on topic Good Ol Stalling - however strange.

Manual specs are sometimes wrong.  Or parts like carbs get swapped to one from a different model/year that will work.  That's why I asked about float arms being parallel to gasket surface.

"Just over 1000" might be too slow an idle too.  Not sure what that means or even if tach is accurate.  Easy and cheap to turn up idle or make sure speed is at spec. 

Simple stuff first.  I tend to be the guy that is certain it must be something major and tears out the engine and completely rebuilds it...  only to find out the problem was I ran out of gas. 

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   So experience talking here. 

Good luck and hope you figure it out soon. 

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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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17 Jul 2022 05:06 #9

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Replied by yamahoper on topic Good Ol Stalling - however strange.

Belly laugh, me to Mark
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17 Jul 2022 05:29 #10

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