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1996 900ss fouls rear sprk plug

4806 Views 3 Replies 3 Participants Last post by  Gunny Fitz
1996 900ss - 37,000kms genuine.
Recently started fouling the rear only spark plug.
Can get only 50 to 100kms before require cleaning, fuel consumption up 15%.
runs well until plug fouls, starts easily.
Actions carried out.
new ignition leads and coils
new plugs
Carb bowls removed and cleaned - all good.
Serviced by local experienced Ducati mechanic
carbs checked and tuned
valve clearances adjusted
mechanic could find nothing wrong - runs even smoother now
new plugs again but rear is blackening after 50ks front is perfectly clean.

Any Ideas?
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Usually this symptom will be caused by an exhaust valve needing its clearance adjusted or a weak coil.

But I see you have addressed both these.

The stock coils are worth replacing with better ones, as they only provide a weak spark. I have replaced many, and have an extensive collection of stock coils..

Bosch Transformers or Dynas provide much higher voltage to the plug, resulting in better starting, idling and performance.

Perhaps a compression check might be the next diagnostic step, to eliminate a problem related to the valves and seats.

The rear exhaust valve runs hotter than the front cylinder's.

A loss of compression would cause the plug to foul.
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Thanks for the advice.
I had not thought of weak spark as it runs so well with a clean plug. I changed the coils (Ducati stock part) around the time this all started only because of age not to attempt cure of the current issue. May have been too hasty.
I have a compression gauge so will try that too.
I will go through your suggestions - thanks again.

Compression test shows around 150 psi with rear slightly higher than front.
Blast From My Past - Love Your Bike Man!

Hey Don!

Just caught sight of this thread of yours before turning off my Macbook. That exact bike was my very first Ducati and holds a seriously special place in my heart. I had a 944 kit installed by the infamous Bruce Meyers and Kyle Thompson of the Original BCM Motorsports out of Laconia, NH. They were the true pioneers of Ducati's on the East Coast! Bruce is a legend and still has his hands deeply involved with DNA to this day!

Sorry I don't have a helpful answer to your matter here but know someone that would - the man who built my 900 / 944 personally. You can call Kyle Thompson himself and probably get and answer right over the phone, or maybe give you in depth details via email too. He is currently the Lead Master Tech at Seacoast in New Hampshire. Check out his confusing bio on the Service page. lol.
Also sorry for not contributing to your search for help on your 900ss, but it just triggered some very old memories this evening. Keep that gem as long as you can my friend! :)

Home - Seacoast Sport CycleSeacoast Sport Cycle

If you do call him, which you truly should if you want to solve this mystery, BE SURE to tell him up front that I referred you personally ok? Mention I told you about the 944 of mine he built too ok?

Few pics of the customized paint job and mods I did to it over the years. I seriously wish I kept that bike now- it pulled like a damn freight train and was a brutal wheelie machine for sure! Love those old 2 valve bikes! Best of luck getting it all fixed up and if you'd like any outstanding paint work done PM me for the connection that did 5 of my bikes and a ton for members here on this forum too! :)

Gunny out...............(BTW- Please post up some pics of YOURS too ok? )

PS. The one of it in the service bay next to the Limited Edition 1198s Corse was the day I said goodbye to it and traded it in on that numbered #244 Corse which was subsequently then traded in on the 1199s Tricolore which is the one I still have now, but don't ride at all.


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