750 ignition - advice please

discussion about the 750 Sport and '89/'90 900SS, which share many mechanicals with the Paso series
Mc tool
paso grand pooh-bah
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Joined: Wed Dec 05, 2007 12:35 am
model: 906 Paso
year: 1990
Location: Newzealand

Re: 750 ignition - advice please

Post by Mc tool »

prince fritz first wrote:The saga continues.....

I installed the relay mod and it didn't increase the voltage at the coils at all (which is at 2V!) I guess it is possible the bike runs at this voltage. What happens is that when at idle it's somewhat hesitant and at a quick twist of the throttle it looses power and stalls. When riding though, it pulls very strong and I was able to take it to 120 quite easily. I know now, that the faulty plugs are most likely caused by the low voltage at the coils....

The wiring is absolutely intact and I checked over the connections. While looking things over I started to measure the voltage to see where the drop might occur... It isn't on the positive side of the current but actually on the negatives which go to the coils. I traced the wiring back to the Digiplex and it looks as something happens inside of it which causes the ground (negative) that enters the unit to drop the voltage down so significantly when it exits the digiplex - quite confusing (?). When I check voltage of the positive wire going to the coil against the negative, it is 2V and if I test it against a solid ground it is 12V. The ground entering the Digiplex gives me a reading of 12V.

Like I said in my earlier posts this bike is a time capsule and nothing has been modified on it so what exactly might be going on? Is the a simple fix for this or should I look into a new Digiplex unit?

When I got the bike, the plugs installed were the Champion RA8HC and I switched them over to the RA6HC. This is somewhat confusing as well... The sticker on the inside of the fairing states RA8HC while the workshop manual and the owners manual state RA6YC. I know this was replaced by the newer HC but why the two different heat ranges??
When you have the bike running the coils should get a constant battery voltage , the digiplex switches the negatives , timed to put the spark in the right place , so if you measure voltage from + to - at the coil you may well see 2v .
When you get faults as you describe with the side / main stand and inclines you gotta sit back and think what could be affected by the changes you introduce ........ and float level ( as Higgy says ) is gotta be one thing that would be affected . Id put money on your float level being out , most likely due to blocked filters or a sticking float , make sure the float ( specially if its the plastic coated foam block type ) is not full of fuel so it wont float :)
I wish I was young again............Id be heaps smarter than last time
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paso750
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model: 750 Paso
year: 1987
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Re: 750 ignition - advice please

Post by paso750 »

Hi,

Apologies if this question is a little obvious, I just want to be sure. Looking to improve voltage supply to the coils and I'm going to fit a 12v relay as per the suggestion by "G".

Should the inline fuse be 30a from the battery to relay pin 30?

Thanks
No, 30A is way to big. There`s no 30A fuse on the whole bike.
Check: https://app.box.com/s/6mqf34acdyjfs9yhrc0m (download the file then all pages will be shown correctly)

G.
deswoodau
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Joined: Fri May 02, 2014 10:08 pm
model: 750 Sport
year: 1988
Location: Australia

Re: 750 ignition - advice please

Post by deswoodau »

Thanks G, much appreciated.
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higgy
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Re: 750 ignition - advice please

Post by higgy »

Fuse size is dependent on the wire size you want to protect in general
A good place to start
http://matchlessclueless.com/electrical ... ng-a-fuse/
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deswoodau
Posts: 53
Joined: Fri May 02, 2014 10:08 pm
model: 750 Sport
year: 1988
Location: Australia

Re: 750 ignition - advice please

Post by deswoodau »

Hi Higgy, thanks for the article.

Now I understand why my older bike needed an upgraded glass inline fuse to handle the surge when activating the indicators. Well that was one of the reasons anyway :) Loose ignition switch pins didn't help either.

Cheers
D
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