Poor starting

discussions specific to the 906 Paso
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Kmamac
Posts: 93
Joined: Thu Jul 21, 2016 6:56 pm
model: 906 Paso
year: 1990
Location: UK

Poor starting

Post by Kmamac »

I think I know what your answers will be but maybe I just need pushing into doing it!! oK here goes. My 906 has never been a good starter especially when cold. So this is the list of what I have done previously and then this summer.
New cables and connectors from battery to relay to starter.
New earth cables.
Wires to coils checked for corrosion and cleaned.
Brand new starter ( noticeably quicker spinning)
Heads off so I could shim to perfection. Exhaust valves a little pitted so ground in. Checked they are not leaky as well.
Carbs (mikuni) running spot on in terms of mixture and sounding good and strong.
Choke cable working correctly and definitely richening the engine as it increases the rpm when started and adjusts as expected when slide up and down.
So it is still a bugger to start. When it does start it’s great.
It’s almost as if every thing is spot on but I have a sad little spark that is just not quite good enough!
Do I have to do the wiring mod in the FAQ? And if so can I get away with the simpler one or do I have to do the more involved one.???
Thanks in advance for you guidance
Best regards
Keith MM
Mc tool
paso grand pooh-bah
Posts: 1879
Joined: Wed Dec 05, 2007 12:35 am
model: 906 Paso
year: 1990
Location: New Zealand

Re: Poor starting

Post by Mc tool »

Hi Keith , assuming you have the technique correct :D with the weber carb its usually just a case of choking it , no touch throttle and hit starter .
The things you list above that you have done go a long way to getting things right . I would do the wiring mod , I think the simplest way is to fit a main relay
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I have a main relay and a relay for the digiplex and coils and another pair up front for the hi / low beams .....maybe a bit OTT but I aint had problems since .
By Mikunis I assume you mean a pair off an SS or monster ?......you'd think they would be bolt on and go . The fact that your idle increases when you operate the choke tells me the air bypass part is working but is it supplying ( enough of ) the extra fuel needed . See if giving a squirt of fuel down the carbs before starting helps things at all ( the weber has an accelerator pump so a twist of the throttle provides this squirt ).
purely for diagnostics ..... try hot wiring the ignition box and coils and see if this doesnt improve spark, and :) when did you last shout it a pair of spark plugs .
Hamish
I wish I was young again............Id be heaps smarter than last time
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paso750
paso grand pooh-bah
Posts: 5559
Joined: Sun Jul 18, 2004 12:00 am
model: 750 Paso
year: 1987
Location: southern Germany

Re: Poor starting

Post by paso750 »

Keith, what airfilter setup are you using and do you still have a fuel pump?
The wiring mod originally came from the P750. While the wiring design of the 906 with the main power running through the ignition switch is the same at least the coils seem to be of a better quality.
First thing to do is measure what voltage arrives at the coils. It should be at least 12V. 750s quite often have a voltage drop of 3V and more which causes hard starting and the engine running only on one cylinder unless the rpm is increased, the voltage increases and the other coil begins to create a spark. In this case the simple relay mod is the quickest fix.
If there are other electrical issues such as a dim headlight that lights up when the engine is revved or if it dims when the turn signals blink one may modify the main harness so the whole power drawn bypasses the ignition switch completely. However, cleaning up all electrical connectors as you did is the correct way to begin. (Incl. the ignition switch if that can be identified as the culprit).
Do measure what voltage there is on the middle fuse in the fuse holder when the ignition is switched on. Then you'll now how much volts the resistance of the ignition switch is consuming.
Another question I have is about the Mikunis. Meanwhile they are also rather old. In which condition are the rubber membranes. Are these still soft or are they stiff? If you check and remove the round covers beware not to lose the small o-ring that's positioned on the bottom if I remember well.

G
Kmamac
Posts: 93
Joined: Thu Jul 21, 2016 6:56 pm
model: 906 Paso
year: 1990
Location: UK

Re: Poor starting

Post by Kmamac »

Thank you for your suggestions. They are mikunis from a 900ss and running fine. I did the simplest mod as per the instructions FAQ ( basically providing 12 v directly to the coils via a relay). What a transformation! The old girl fires up within a revolution or two as opposed to the 4 or 5 seconds previously. I don’t quite believe what a massive difference this has made. The acid test will of course be on cold Monday morning. The wiring mod is actually even simpler than I assumed with no cutting or messing around with the old harness, just disconnecting the original coil leads and running a wire up to the switched side of the relay. Then the new leads (I used 2mm csa) I will post a couple of photos tomorrow. Many thanks again and for readers in the future this mod does make a difference.
Mc tool
paso grand pooh-bah
Posts: 1879
Joined: Wed Dec 05, 2007 12:35 am
model: 906 Paso
year: 1990
Location: New Zealand

Re: Poor starting

Post by Mc tool »

The ignition box will start doing weird things when the voltage gets a bit low , like 10 -10.5v too
I wish I was young again............Id be heaps smarter than last time
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