Darmah Front cylinder running rich

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Craig in France
Paso 750
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Joined: Tue Mar 23, 2004 3:58 pm
Location: Montpellier, France

Re: Darmah Front cylinder running rich

Post by Craig in France »

mdal8798 wrote: Wed Jul 22, 2020 1:19 am Pickups and wiring are are in good condition ... Resistance measurements are within specification <snip>
Well, I guess that's progress, Mark ... in a way :roll:

So, is it still banging and popping on the front? Back to basics, then:
- Have you checked the valve clearances?
- Don't forget the plug cap and lead (Unscrew the cap, cut the lead back a tad, wipe it clean, re-fit the cap. Use a new one, by preference - and of the right resistance)
- Check the quality of the connection at the coil too
- And of course fit a new plug
- You could also try swapping coils
- Exhaust sealing properly?
mdal8798 wrote: Wed Jul 22, 2020 1:19 amI have contacted Gowanlochs in Sydney ... he is of the belief that i just need to get bike on the road and basically blow the cobwebs out of it first then look at idle setup later.
I will freely admit that this kind of advice, especially when coming for a professional, always concerns me. Because if something is wrong, 'running it down the road for a few miles' it just as likely to make things worse as to magically resolve the problem. But each to their own ...

The advice from 900tlc about changing the ignition system is well-founded, however. All depends on how much time and money you have, and how frustrated you get chasing faults :evil:

@ 81mhr900ss: excellent advice as always. However, when Mark swapped the carbs over, the problem (banging and popping) stayed with the same cylinder (the front). Which suggests that the problem is not carb related.
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81mhr900ss
Parallel Twin
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Re: Darmah Front cylinder running rich

Post by 81mhr900ss »

Understood and agreed. After pulling out all the old stuff, I was able to determine that the likely culprit for my initial pre-Sachse lumpiness was the front coil. I'm very happy with the decision to go with a new ignition system.
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Craig in France
Paso 750
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Joined: Tue Mar 23, 2004 3:58 pm
Location: Montpellier, France

Re: Darmah Front cylinder running rich

Post by Craig in France »

81mhr900ss wrote: Thu Jul 23, 2020 8:40 pm Understood and agreed. After pulling out all the old stuff, I was able to determine that the likely culprit for my initial pre-Sachse lumpiness was the front coil. I'm very happy with the decision to go with a new ignition system.
Thanks for the info. Tell me, did you have Motoplat (red) or Nippon Denso (off white) coils ? Just being nosey ... :-D
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81mhr900ss
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Re: Darmah Front cylinder running rich

Post by 81mhr900ss »

Nippon Denso were the original coils on my 81 MHR
Last edited by 81mhr900ss on Sat Jul 25, 2020 4:06 pm, edited 1 time in total.
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Craig in France
Paso 750
Posts: 917
Joined: Tue Mar 23, 2004 3:58 pm
Location: Montpellier, France

Re: Darmah Front cylinder running rich

Post by Craig in France »

81mhr900ss wrote: Fri Jul 24, 2020 11:23 am Nippon Denso were the original coils
And sometimes Motoplat :). But I guess you had N-D, right?
mdal8798
Cucciolo - the Lil Pup
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Location: Mackay, Qld, Australia

Re: Darmah Front cylinder running rich

Post by mdal8798 »

Hi Gents,

Bit tardy with reply but i had to walk away for a while, this has been doing my head in.

Since my last post i have replaced pickup wiring with PTFE cable ensuring good crimp connections etc. (I am an industrial electrician)
What i did notice was, when testing resistance after crimp connections made, that resistance on front cylinder pickup was around 260 ohms (this was immediately after heating shrinkwrap tubing with heat gun) and rear cylinder around 250 ohms. These both dropped to around 230 ohms when cooled down. Manual states 220 +/- 5% which equates to 209-231 ohms. Manual doesn't specify an expected hot resistance although i would expect it to increase marginally. I had a bit of a hiccup with correct polarity initially, rectified this and checked with timing light and could see both cylinder's timing advance as revs picked up.

I thought i may have been on a winner because on inital start up from cold, engine sounded good and would run evenly between 2000-3000 rpm and would idle down to around 1200 rpm while i was adjusting screws for even vacuum. But alas, as soon as the engine warms up the front cylinder starts popping and farting again even at higher revs. This scenario has been repeated a number of times. Let bike cool overnight and start fresh next day for same result.

I suspect that the pickups are failing as engine heats up and as previously suggested I am looking at either the Sachse ignition (which i wouldn't see until the end of month due to supplier closed until 21/08/2020) or the Silent Hektik which is readily available in Australia. Price wise the Silent Hektik would be approx. $100 dearer, but it comes with coils. This is a bit annoying as just replaced coils with Dynatech units.

Thoughts?
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