will not run below 4000 rpms

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AZRD350LCGUY
Posts: 58
Joined: Sun Feb 21, 2016 6:53 pm
Location: Gilbert, az

will not run below 4000 rpms

#1 Post by AZRD350LCGUY » Wed Sep 05, 2018 2:35 pm

It starts and has good spark when kicked over and will start. but it will not idle. It will die when the rpm drop below 4K. If I open the throttle it will speed up again but as soon as it drops again I will have to increase the throttle.
I have checked the low speed coil and it checks out. I have also replaced the stator assy twice with the same result.
The carbs are clean and the petcock also. If it is not getting enough fuel at idle that it cannot get enought for higher rpms so the fuel system is not the problem.
Amy suggestions????
1982 RD350J aka RD350LC Canadian
1971 Kawasaki F5a Big Horn
2013 NC700X

Judge people by what they do and not what they say they will do.

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nokturnal
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Re: will not run below 4000 rpms

#2 Post by nokturnal » Wed Sep 05, 2018 2:40 pm

Compression?

Slides and floatbowls on the correct carbs/direction?
:smt017

AZRD350LCGUY
Posts: 58
Joined: Sun Feb 21, 2016 6:53 pm
Location: Gilbert, az

Re: will not run below 4000 rpms

#3 Post by AZRD350LCGUY » Wed Sep 05, 2018 3:11 pm

It ran fine the last 800 miles and then on a ride it started to not run below 4K.
It feels like it electrical. But I have traded out the CDI unit for one that I know is good and have traded out the stator assy twice for known good units. I am at a loss
1982 RD350J aka RD350LC Canadian
1971 Kawasaki F5a Big Horn
2013 NC700X

Judge people by what they do and not what they say they will do.

Hooligan
Posts: 1966
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Location: Calgary, Alberta

Re: will not run below 4000 rpms

#4 Post by Hooligan » Wed Sep 05, 2018 7:48 pm

Clean and reset the carbs.
'82 RD350LC in '81 colours, OEM pipes, UNI filters
'85 FZ750

hondaror
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Location: Alberta, Canada

Re: will not run below 4000 rpms

#5 Post by hondaror » Thu Sep 06, 2018 3:17 am

Plugged pilot jets. Even with clean carbs. Bad fuel or contamination from the tank is all it needs to plug up. Ask me if I've had to clean out pilot jets multiple times on the same bike.
Rory
2 1984 RZ350s
1985 RZ350
9 1986-1990 RZ350s
2000 ST2
2005 749
2005 749 with 999 engine

Hooligan
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Re: will not run below 4000 rpms

#6 Post by Hooligan » Thu Sep 06, 2018 12:29 pm

I run an in-line fuel filter in all my bikes. Helps prevent crap in the carbs.
'82 RD350LC in '81 colours, OEM pipes, UNI filters
'85 FZ750

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JonW
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Re: will not run below 4000 rpms

#7 Post by JonW » Thu Sep 06, 2018 9:12 pm

check the PVs are working. Easy to do, pull off the cover and check they move when you switch on the ign.

cold also be the air corrector jets, behind the balls.
80 XT500 Supermoto!
81 RD350LC Resto
82 RD421LC Hybrid
82 RD350LC decapitation project
82 RD250LC JDM '251LC' YPVS
83 RZ350 Resto
84 RZ500 Resto
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gpaddict
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Re: will not run below 4000 rpms

#8 Post by gpaddict » Fri Sep 07, 2018 7:23 pm

Have you by chance had any rust issues at all with your fuel tank?
tuned to Paris Hilton specs............rich and retarded!

hondaror
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Re: will not run below 4000 rpms

#9 Post by hondaror » Sun Sep 09, 2018 1:15 pm

Hooligan wrote:I run an in-line fuel filter in all my bikes. Helps prevent crap in the carbs.
That's a must do. I do as well. Good insurance.
Rory
2 1984 RZ350s
1985 RZ350
9 1986-1990 RZ350s
2000 ST2
2005 749
2005 749 with 999 engine

AZRD350LCGUY
Posts: 58
Joined: Sun Feb 21, 2016 6:53 pm
Location: Gilbert, az

Re: will not run below 4000 rpms

#10 Post by AZRD350LCGUY » Fri Nov 16, 2018 5:50 pm

Well I finality got around to sorting this out. Took off the carbs, they were very clean, put them back on and scoped out the low and high sped coils, both were good but there could be a broken wire somewhere. I replaced it with one I checked all the wires and and all the specks are good. I fired it up and all was good. Took it for about 8 mile low speed ride and entered to the garage. At about sundown I pulled part of the way out of the garage to time it. Less light better timing light. I fired it up and the same problem was there. While standing on the footpegs to start it I was looking at the tach and noticed that the lights went out when the engine cut out. That points to a short in the wiring harness somewhere.
The wiring harness was not very good to begin with - the water temp gauge would go to the hot end when the key was turned on, I disconnected that, the high beam wasn't getting power, and the front turn signals didn't work.
Now I need a wiring harness. Any suggestions???
1982 RD350J aka RD350LC Canadian
1971 Kawasaki F5a Big Horn
2013 NC700X

Judge people by what they do and not what they say they will do.

brrrappp
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Re: will not run below 4000 rpms

#11 Post by brrrappp » Fri Nov 16, 2018 10:12 pm

https://www.ebay.com/itm/1983-1984-Yama ... rk:26:pf:0" onclick="window.open(this.href);return false;

Ebay is your friend. The above is probably the most expensive way to go. You will probably find a used one for around $100.

silverstrom
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Re: will not run below 4000 rpms

#12 Post by silverstrom » Fri Nov 16, 2018 10:47 pm

1982 RD350LC

https://www.ebay.com/itm/Yamaha-RD350lc ... ctupt=true" onclick="window.open(this.href);return false;

AZRD350LCGUY
Posts: 58
Joined: Sun Feb 21, 2016 6:53 pm
Location: Gilbert, az

Re: will not run below 4000 rpms

#13 Post by AZRD350LCGUY » Wed Dec 26, 2018 9:00 pm

UP DATE: I replaced the main wiring harness and it now runs the way it should. idle well and all the problems have gone away
Thanks for all the input. It was all helpful!!
1982 RD350J aka RD350LC Canadian
1971 Kawasaki F5a Big Horn
2013 NC700X

Judge people by what they do and not what they say they will do.

RuZty
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Re: will not run below 4000 rpms

#14 Post by RuZty » Thu Dec 27, 2018 5:07 pm

Don't throw that old harness away, always handy to have one around to rob connectors from.

AZRD350LCGUY
Posts: 58
Joined: Sun Feb 21, 2016 6:53 pm
Location: Gilbert, az

Re: will not run below 4000 rpms

#15 Post by AZRD350LCGUY » Thu Dec 27, 2018 9:12 pm

Now I have two that I can take connectors from. I had to do that to get the current harness to work.
If you have a RD350LC, throw nothing away!!!
Thanks for all your help and encouragement!
1982 RD350J aka RD350LC Canadian
1971 Kawasaki F5a Big Horn
2013 NC700X

Judge people by what they do and not what they say they will do.

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