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Misfires and blown main fuse 1983 XV750

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Misfires and blown main fuse 1983 XV750

PostAuthor: Nygaard » Mon Aug 12, 2019 9:31 am

I have a 1983 Yamaha XV750 i have just finished building from the ground up.
The bike idles ok, but I'm having some issues with misfires at higher RPM, blown main fuses while riding (20A) and jumpring RPM readings on my digital Acewell RPM gauge (signal from TCI to front coil is jumping 0-1500 RPM at idling).

There is a complete new wire harness on the bike made according to below schematic and new Rick's voltage regulator, so I'm thinking my issues are related to the old unproven TCI.

The TCI did not come with the bike, but seller told me it would work with a 1983 XV750.
It has 20X-20 J4T0087 2X07 on it and the wires are connected as per below picture.

Could it be the TCI causing the problems?


Best regards,
Christian
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Re: Misfires and blown main fuse 1983 XV750

PostAuthor: bstig60 » Mon Aug 12, 2019 10:10 am

The reaction of the tach would indicate either a wire that is intermittently shorting out or a bad connection to the Orange wire on the tci.
The backfiring could be related to a bad connection in the wiring as described above. I doubt it is a bad TCI as the bike starts and idles OK. Blowing the main fuse would indicate a short to ground in the RED wire circuit somewhere. Do you use the Kill switch?
Bill
"It´s a friggen motorcycle, it´s not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you s**t your pants every now and then. "

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Re: Misfires and blown main fuse 1983 XV750

PostAuthor: Nygaard » Mon Aug 12, 2019 12:18 pm

The tach signal wire is solderet together with the orange wire at the plug on the CDI, my ohm meter shows no resistance between the coil and tach.
I cannot trig it to burn the fuse other than at sustained higher RPM (3-4.000 while riding). I'm not running the kill switch, only a very basic on/off switch for ignition.

bstig60 wrote:The reaction of the tach would indicate either a wire that is intermittently shorting out or a bad connection to the Orange wire on the tci.
The backfiring could be related to a bad connection in the wiring as described above. I doubt it is a bad TCI as the bike starts and idles OK. Blowing the main fuse would indicate a short to ground in the RED wire circuit somewhere. Do you use the Kill switch?

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Re: Misfires and blown main fuse 1983 XV750

PostAuthor: bstig60 » Mon Aug 12, 2019 3:13 pm

Blowing the main fuse while riding at speed still indicates a short somewhere in the wiring or a bad component. The only thing that goes directly to the fuse is the ignition switch, start relay and the R/R. Have you checked the output of the R/R at RPM? The R/R could be on its way out or putting out high voltage causing an overload.
Frankly, if it were me and putting the kind of time and money into your bike build that you obviously have, I would have replaced the TCI with an Ignitech device. http://www.ignitech.cz/en/
Bill
"It´s a friggen motorcycle, it´s not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you s**t your pants every now and then. "

Please take the time to edit your profile to show your location. City, State/Province, and Country.
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Re: Misfires and blown main fuse 1983 XV750

PostAuthor: Nygaard » Tue Aug 13, 2019 1:49 am

Ignition switch is only a simple on/off switch cutting out the + supply from the battery. I don't run a start relay, as i have a heavy duty starter switch that actuates the starter solenoid directly.
Tried disconnecting the R/R all together and were only running off the battery, the fuse is still blowing. Also measured the output at RPM and it's giving a steady 14V.

Did not know Ignitech, have been looking towards a Carmo replacement CDI but at $400 i wanted do make sure i needed it. :bg:
Will get in contact with Ignitech today, seems like their replacement is only $130, hopefully that will cure the problems!

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Re: Misfires and blown main fuse 1983 XV750

PostAuthor: bstig60 » Tue Aug 13, 2019 12:01 pm

Let us know what you find. I still suggest you have a hot wire shorting out somewhere. Because it happens while riding at speed indicates that it may be due to vibration. The ONLY thing that is going to blow the main fuse is a direct short to ground somewhere in the wiring on the RED or Red/White wires.
Bill
"It´s a friggen motorcycle, it´s not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you s**t your pants every now and then. "

Please take the time to edit your profile to show your location. City, State/Province, and Country.
It is easier to help you if we know where you are.


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Re: Misfires and blown main fuse 1983 XV750

PostAuthor: Cusstout 1100 » Tue Aug 13, 2019 4:16 pm

Just a flash-back thought here: I had a 1961 Volvo pv544 many years ago. One day on the highway home, the starter suddenly engaged. That resulted in an instantaneous burned out wiring harness (maybe that's why they use fusible links in new vehicles?). When that happens, the starter turns into a generator and feeds power back into the system. Not saying that's your problem, but maybe worth a thought? Maybe stick an inline fuse in there and see what happens?
My Ride, '97 XV1100, +14, 10" over forks, progressive rear, Jardine forward controls, cobra slip-ons, K&N Filter, Dyno Jet Stage 1, Kuryakin grips, heat demon heaters, custom fabricated seat, chrome side covers, bullet signals, risers, custom modified rear fender with modified FZ1 tail light, sectioned and reversed front fender, custom paint...

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Re: Misfires and blown main fuse 1983 XV750

PostAuthor: Arjay » Tue Aug 13, 2019 11:07 pm

You could unplug you rr and test run off battery only.
Beautiful work you done there...!

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Re: Misfires and blown main fuse 1983 XV750

PostAuthor: Jake » Wed Aug 14, 2019 9:10 am

bstig60 wrote:Blowing the main fuse while riding at speed still indicates a short somewhere in the wiring or a bad component. The only thing that goes directly to the fuse is the ignition switch, start relay and the R/R. Have you checked the output of the R/R at RPM? The R/R could be on its way out or putting out high voltage causing an overload.
Frankly, if it were me and putting the kind of time and money into your bike build that you obviously have, I would have replaced the TCI with an Ignitech device. http://www.ignitech.cz/en/

:yup:

Just because the R/R is new doesn’t mean it is good ! Test it per the service manual.

I also second the ignitech TCI, they have good reviews from members here.
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Re: Misfires and blown main fuse 1983 XV750

PostAuthor: Nygaard » Wed Aug 14, 2019 4:19 pm

Hi gents, thanks for all the feed back.

I'm confident the starter is not engaging, i would definitely notice the "box of rocks" action going on :bg:

I did try and unplug the regulator for a test run, same result as before.
While i had it disconnected i also measured the output at RMP to just above 14V.

A new TCI is already on its way from Ignitech, hopefully it will already have turned up once i get back from work in two weeks time!
Will keep you guys posted!

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