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Old 07-14-2018, 09:24 PM   #1
notyou83
 
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Bike won't stay running after warm up

So I have a 1981, Yamaha SR185 Exciter. I love the little thumper, but I can't get it running longer than about 10 minutes before it shuts itself down/off. The engine revs just drop for no reason that I can find and I have to downshift while revving a bit high to keep it on.

2 coworkers said it sounds like a regulator/rectifier issue. I had assumed it was carb/fuel/air related.

Anyone got any ideas?
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Old 07-14-2018, 09:27 PM   #2
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Re: Bike won't stay running after warm up

You can easily rule out the RR failing by Short and causing that type of issue

Start bike and unplug the RR
If the issue does not happen you have a shorted RR you can confirm that by testing with a volt ohm meter

If by warmed up you mean just off choke and will not run
That would be a common carbed pilot jet plugged issue
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Old 07-14-2018, 09:34 PM   #3
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Re: Bike won't stay running after warm up

not the off choke kind of warm. I can start it without choke already. Warm Texas DFW weather and all. not quite oil change type of warm as it makes it 7-10 minutes or so before shutting off. I ran around my block 1 and a half times in first gear at about 10-15 MPH.

I'm willing to accept I have the air/fuel idle mix adjusted wrong or that the float is adjusted wrong. Or both of those things may be the case. Maybe even a clogged passage in the carb itself. those things can be picky.

I'll see if I can start it again and see if after 2 minutes when I pull the RR if the bike stays one or not. Thanks for the suggestion.
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Old 07-14-2018, 09:49 PM   #4
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Re: Bike won't stay running after warm up

ok. Started the bike for about a minute. disconnected the RR plug connection. Idle changed to more "steady", not really in speed. some of the minor rpm fluctuations went away it seemed, but I only left it disconnected for about 20 seconds. Bike stayed on the entire time.

I guess this means teh RR is shorted somewere/how. Can I use a generic one to replace it? I doubt I can find a factory version.

maybe I disconnected the wrong thing?
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Last edited by notyou83; 07-14-2018 at 09:51 PM.
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Old 07-14-2018, 09:53 PM   #5
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Re: Bike won't stay running after warm up

If it is electrical you should be able to just check for spark with a spare plug after it dies.

A restricted fuel intake flow could cause these symptoms. Check if it does this with gas tank open. Then open the drain line on the bottom of the carb with the bike running and see how much fuel flow you are actually getting through the petcock. If it doesn't have a vacuum operated petcock just check that when the bike is cold and see if eventually it stops flowing gas.

Spark, fuel
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Old 07-14-2018, 09:56 PM   #6
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Re: Bike won't stay running after warm up

so if it does spark after it dies with the spare plug, then I am guessing that leads to the fuel side of the issue.

too little gas getting in carb = restricted fuel intake flow. This could be my issue. the float is not quite factory so I've had to be creative with it. Parts for this carb are near impossible to find.
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Old 07-14-2018, 10:14 PM   #7
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Re: Bike won't stay running after warm up

I started the bike again, disconnected the other set of wires from the RR and the bike stayed on. So both sets of wires and have been pulled and the bike stayed on. If I understand "If the issue does not happen you have a shorted RR" correctly I need to replace my RR. I will see about taking it off the bike a little later to test it and all that with the volt meter.
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Old 07-14-2018, 10:53 PM   #8
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Re: Bike won't stay running after warm up

Sweet! Diagnosis is the hardest part!
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Old 07-14-2018, 11:02 PM   #9
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Re: Bike won't stay running after warm up

I have the service manual. I can't make heads or tails of part of one diagram. fun times. Can't tell if I'm testing it right or not at all. Ohm man.
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Old 07-15-2018, 12:54 PM   #10
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Re: Bike won't stay running after warm up

ok you said it takes 10 minutes for it to manifest as losing power.
once it has died, how long does it take till it can be restarted?

on a motorcycle where it will run for 10 minutes and you have to wait 15-20 minutes before it will restart and then dies again after around 10 minutes, points toward a clogged vent or coil heating up.

ride it till it starts to loose power and quickly try to remove the gas cap. if it is hard to remove and is accompanied the the sound of air rushing into the tank, you have a clogged
gas cap vent.

if not take a spare spark plug with you and ride till it quits and quickly pull the plug cap and plug in the spare plug and check for spark.
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Old 07-15-2018, 01:07 PM   #11
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Re: Bike won't stay running after warm up

Quote:
Originally Posted by notyou83 View Post
I have the service manual. I can't make heads or tails of part of one diagram. fun times. Can't tell if I'm testing it right or not at all. Ohm man.
a Regulator / rectifier on that bike is diode based, you check it by using the diode function on your meter.. you should get power flow one way only.

Also need to test the stator .. a stator shorting to ground can do all kinds of weird things besides just not charge the battery.
three yellow wires in the stator side of the connector..
Test Y to Y you should have very little resistance, almost none.
Test each Y to ground.. there must be NO connectivity ..the meter should show it as an open, or error.

Without the wiring diagram or service manual I cant confirm for sure how you need to test the stator the rest of the way if it has pick up coils as part of it..
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Last edited by E.Marquez; 07-15-2018 at 01:08 PM.
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Old 07-15-2018, 01:13 PM   #12
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Re: Bike won't stay running after warm up

Pay attention to Focus Frenzy and the gas cap. Yamahas in the early '80s are notorious for housing tiny insect nests in the gas cap vent.
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Old 07-15-2018, 01:44 PM   #13
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Re: Bike won't stay running after warm up

Maybe check your gas tank. Pull fuel shutoff valves if installed,flush and reseal tank, and install inline fuel filters.
May not be the issue, but it can't hurt.
Good luck.
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Old 07-15-2018, 10:52 PM   #14
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Re: Bike won't stay running after warm up

Quote:
Originally Posted by E.Marquez View Post
a Regulator / rectifier on that bike is diode based, you check it by using the diode function on your meter.. you should get power flow one way only.

Also need to test the stator .. a stator shorting to ground can do all kinds of weird things besides just not charge the battery.
three yellow wires in the stator side of the connector..
Test Y to Y you should have very little resistance, almost none.
Test each Y to ground.. there must be NO connectivity ..the meter should show it as an open, or error.

Without the wiring diagram or service manual I cant confirm for sure how you need to test the stator the rest of the way if it has pick up coils as part of it..
Thanks for the info. I'll take this and what Focus Frenzy said about the gas cap and see what I can come up with in the morning after work.
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Old 07-18-2018, 09:37 AM   #15
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Re: Bike won't stay running after warm up

Leon, I think you may have been right with the gas cap venting. That or I was simply flooding the engine. Spark plug was very black. The gas cap is part factory, part 20 dollar amazon replacement so the cover wasn't venting correctly I think. Not sure, but I managed to idle the bike for 2 minutes. Rode around the block twice, then back to idle for another 2 minutes to check the voltage was at 14.45-14.5.

It seems it lives. well for now anyway. I went ahead on got basic insurance on it so I can get it legal again.

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Old 07-18-2018, 09:52 PM   #16
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Re: Bike won't stay running after warm up

Thatís idling way to fast.
You need to ride it over to show and tell one of these Friday nights at the burger box.
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Old 07-18-2018, 11:59 PM   #17
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Re: Bike won't stay running after warm up

Quote:
Originally Posted by focus frenzy View Post
That’s idling way to fast.
You need to ride it over to show and tell one of these Friday nights at the burger box.
Burger box is way too far to ride that thing. Tops out at 55 and I live about 40 miles away. Idle is supposed to be 1400 per Yamaha, but it doesn't have a tach so I have to go by sound.
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Old 07-27-2018, 09:07 PM   #18
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Re: Bike won't stay running after warm up

I'm not sure I have this bike running quite right yet. It will fast idle for a while,(minute to minute and a half) then drop like its about to die. It always seems to bump back up to a fast idle again after a few moments of sluggish running (15-30 seconds estimate).

any suggestions? this is all during trying to warm it up, but not actually warmed up. I thought it might be the float, but it seems to be correct going by the drain tube as a measure compared to the factory service manual. That or I'm reading it wrong.
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Old 07-28-2018, 07:55 AM   #19
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Re: Bike won't stay running after warm up

Replace the dry rotted leaking intake manifold and stop cooking the motor.
Minute and a half on choke when its 105 out is cooking the engine.
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Old 07-28-2018, 02:56 PM   #20
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Re: Bike won't stay running after warm up

Its not on choke. The boot between the carb and intake is new and shouldn't be leaking, but it may very well be as I am bad at this kind of thing until I've done it 20 times.
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