Topic: High compression pistions

[Bodain]

I have a bike thats just about kicking my butt. Ok. It's not a SOHC Honda. Still an engine is an engine.

The bike has high compression pistions and fabulous compression. First question. I assume with high compression pistions you would need to go to a colder plug. At least that's what I've read... Comments???

Oh by the way. This is a very rare 1993 Ducati 900 SL Superlite.

The problem is..... I can put new plugs in the bike. Pulls like a freight train. Runs great. Within 10 minutes the plugs will foul. The bike is blowing some light smoke.. Light in color and stinks to high heaven. Anytime I ride it I smell like a gas station...

Pull the plugs... Looks to be consistantly running very rich. If this were true I would expect black smoke. Plugs are always very gasey wet or very dry dark black...  I couldn't rule out the basic potential that it is burning oil.... I pulled the horizontal head. Looking for evidence. I would look in 3 places....

The third oil scrapper ring... I would expect to possibly see excess oil on the cylinder wall.  There is none.

Two oil passage between head and cylinder with o- rings... Again no leaks.

Finally valve guides...  Again I find no evidence.

I've been beating this horse for 3 weeks now... Coils appear to be fine. I've been in and out of those carbs 30 times.  So I just gotta wonder at this point.. Does it require cooler plugs with the high compression pistons.

[Jay B]

We need a litle history here. Did you just buy this bike? Did you put the high comp pistons in? Did it start happening all of a sudden? You sound like you are running rich for sure. Get it sorted out, I miss my old duc a lot.

[warreng22]

You may already know this and/or have already tested it, but I thought I would mention it anyway.
Have you done a compression test?? Two Tired said it doesnt really matter what the compression it (to an extent) but there shouldn't be more then  a 10% +/- difference between each cyclender.
Just a thought.

Hope its an easy fix, and that you find it soon 
Good Luck!

[bryanj]

You say "high Compression Pistons" but unless these are replacement, even higher than standard, pistons, altering the recommended plug grade can get very expensive.
These bikes are HC to start with and, unless raced, dont need to go any higher

[crazypj]

 Does it have Dellorto's or Bing?
You need to check float levels and stock jetting.
 If the silencers have been changed to something quieter (it was real loud stock) it probably needs re-jetting whats on there, LaFranconi or some generic stuff?
Its not something to plod around town on needs more of a revving
PJ

[HondaMan]

My SOP in these situations:

1. Check float bowl heights by removing a full one to see if the fluid height looks reasonable.
2. Go hotter on the plug.
3. Go lower on the octane.
4. Put some carb cleaner in the gas: this will sort out the smaller passages that are hard to clean (I'm presuming this scoot has been sitting awhile).

An old question, but occasionally still valid: does this bike have "ticklers" instead of a choke? (If you don't know, it probably doesn't...). The o-rings or rods in these could get sticky and hold the rods down against the floats sometimes. The old desmo dukes had these (1965-ish).
So do old Brit bikes....and German...and Italian...and Jugoslavian.....

[mgmuellner]

My SOP in these situations:

1. Check float bowl heights by removing a full one to see if the fluid height looks reasonable.
2. Go hotter on the plug.
3. Go lower on the octane.
4. Put some carb cleaner in the gas: this will sort out the smaller passages that are hard to clean (I'm presuming this scoot has been sitting awhile).

An old question, but occasionally still valid: does this bike have "ticklers" instead of a choke? (If you don't know, it probably doesn't...). The o-rings or rods in these could get sticky and hold the rods down against the floats sometimes. The old desmo dukes had these (1965-ish).
So do old Brit bikes....and German...and Italian...and Jugoslavian.....

It'd have a choke.  I think they stopped with the ticklers in the early 80's.  I had an 81 SS bevel & a 95 900SS.  I loved those things!