Burnt Plugs

If you need technical information or help with your BOSCH ignition squarecase Ducati 900SS - Darmah engine - post your FAQs, comments & questions here.
rwhc80
750 GT
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Post by rwhc80 » Tue Dec 01, 2009 11:23 pm

Thanks Marty,

It appeared a bit odd the front cylinder flowed a little better than the rear, but both seemed slow compared to the darmah. Unless the taps have differing flow rates,( Paoli compared to brev orlandi ??) I will pull the tank off tonight and check both tank outlet and taps. Good thought on the igniter boxes I might experiment with a swap on those as well.

And Craig, failing the above, I will do carb swap and see what occures.

The painful thing is the bike needs 20-30 minutes of running before you can find out if the remedy has worked or not, be easier if the bike was running roughly ??
Cheers Rick
I have desmo disease, I just hope they never find a cure !!!

MartinMille BANNED
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Post by MartinMille BANNED » Wed Dec 02, 2009 12:28 pm

Hey Rick

Your last reply should have given you a clue !!!

"""bike needs 20-30 minutes of running"""

Swap the ign boxes over from your SD before you try anything else , it would take a little time for any electronic component over heat and fail once they have cooled down they will work as per normal

Cheers Marty

rwhc80
750 GT
Posts: 174
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Location: Melbourne Australia

Post by rwhc80 » Thu Dec 03, 2009 5:18 am

OK,
removed tank and petcocks and gave both a clean out. removed some rubbish but nothing severe. now have similar flow from both taps but also similar rates as before. I have now realised the ss taps have smaller feed holes than the Darmh Paoli taps so makes sense the flow was greater,
back to the drawing board. I will again look for vacuum leaks and swap Igniter boxes to see result.
Cheers
Rick
I have desmo disease, I just hope they never find a cure !!!

DaveDare
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Post by DaveDare » Sun Jul 25, 2010 7:14 pm

Hi Rick, how did you go, I am very interested as I have exactly the same problem on my S2. This is the first time I have found someone with the same issue. I have replaced inlet manifold gaskets, cleaned the carbs a million times, had the head removed and the valves reseated, have just put new rings in front and back. Took it for a run on the weekend ran like a dream for about 10 klms or so and then started to fail after I had it idling for a while trying to fine tune the carbs. Front cylinder seems to kill the spark plug and fires spasmodically. Pop a new plug in and all is good for another 10 or 20 klms.

Carb seems to blacken up a lot rather than look too hot or lean.

One thing I have noticed is that I have to screw the front idle stop in all the way to get the front to idle enough to tune it (1900 to 2000rpm).

This has been going on for about 18months. Please any ideas would be great.

A bit of history, I have replaced the pick wire and a new regulator has been put in along with new coils.

Thanks in advance.

Dave::

mizike77
860 GT / GTS
Posts: 272
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Post by mizike77 » Mon Jul 26, 2010 3:50 am

DaveDare wrote:Hi Rick, how did you go, I am very interested as I have exactly the same problem on my S2. This is the first time I have found someone with the same issue. I have replaced inlet manifold gaskets, cleaned the carbs a million times, had the head removed and the valves reseated, have just put new rings in front and back. Took it for a run on the weekend ran like a dream for about 10 klms or so and then started to fail after I had it idling for a while trying to fine tune the carbs. Front cylinder seems to kill the spark plug and fires spasmodically. Pop a new plug in and all is good for another 10 or 20 klms.

Carb seems to blacken up a lot rather than look too hot or lean.

One thing I have noticed is that I have to screw the front idle stop in all the way to get the front to idle enough to tune it (1900 to 2000rpm).

This has been going on for about 18months. Please any ideas would be great.

A bit of history, I have replaced the pick wire and a new regulator has been put in along with new coils.

Thanks in advance.

Dave::
How old / worn are your throttle slides? Try swapping your slides from carb to carb and see if the problem follows...
79 Darmah
78 900 GTS
86 F1B
80 SSD
02 Harley FXD
72 H2 750 triple
08 KTM 300XC
there has yet to be a motorcycle line made that is as satisfying to ride, hear and look at as the ducati bevels

DaveDare
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Post by DaveDare » Mon Jul 26, 2010 4:16 am

Hi Mizike, have done that already, no change. Slides were worn at the idle stop but have built them up with neadit, works fine.

Cheers Dave

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abmartin
SSD900 Darmah
Posts: 358
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Location: New Brunswick, Canada

Post by abmartin » Mon Jul 26, 2010 4:42 pm

This may be a long shot but my bike had a problem with one of the floats hanging up on the carb tickler. The plunger mechanism had created a small depression on one of the floats preventing it from returning to its proper level after starting the bike. Have you tried swithching the floats?

Bruce
1979 900SS
Fredericton, NB
Canada

DaveDare
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Post by DaveDare » Mon Jul 26, 2010 4:55 pm

Hmmmm. Haven't tried swapping the floats. Seems like an easy one to try so I will give that a whirl. Will let you know. any other suggestions please let me know, thanks.

I did have someone suggest a sticky shim when it gets hot. Not sure about that as I have had the head done by Pete Smith at epicycle, I would think that that would have solved that problem if it is that problem...thoughts?

Cheers Dave::

wdietz186
Cagiva Alazzura
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Post by wdietz186 » Mon Jul 26, 2010 7:49 pm

Had roughly the same problem on a friends Darmah last year,It was the ign. box.Ran ok cold but after a few minutes it would stutter,fart and backfire.Previously had never seen a bad Bosch unit but I guess they aren't as bulletproof as they seem.

DaveDare
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Post by DaveDare » Mon Jul 26, 2010 10:25 pm

Oh man I think you may have hit the nail on the head wdietz186.

That's about the only electrical component I hadn't replaced and would make sense when it gets hot. I can easily check by swapping over. Thanks for that gem. I will let you know how I go.

Dave::

DaveDare
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Post by DaveDare » Sun Aug 08, 2010 4:14 am

Here is an update. I swapped the ignition boxes over and the bike ran well for a while. Then after a few times out the front plug started to fail again.

So I have ruled out the ignition boxes. But here is the interesting discovery. I grabbed a previously failed plug and sprayed CRC on it and gave it a really good clean up all around the electrode and porcelain etc. Put the plug in to check spark visually and low and behold it was sparking strongly between the electrodes. Now the other plug that was failing when checked visually was sparking all over the porcelain and onto the side of the plug, then different spots on the earth electrode, basically erratically all over the place.

I put the plug in and the bike ran fine.

I took the recently failing plug and did the same thing, low and behold the spark was now concistently in the correct place and strong and consistent.

Popped the plug back in and went for an uninterrupted and consistent ride.

Now, before I cleaned the plug it was very black and sooty, really sooty.
So I think I can rule out electrical.

I am now pointing my finger at the carbs, anyone else think I am on the right track?

As I mentioned previously I have to wind the idle stop screw all the way in to get the front pot to idle (something in this maybe) as mentioned the slides have been built up to original height where they meet the idle stop screw so this is (probably) not the problem.

Any thoughts out there?????

Float level? Blocked idle circuit?

Thanks guys.

Dave::

DaveDare
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Post by DaveDare » Sun Aug 08, 2010 4:23 am

abmartin...I haven't changed the floats over yet. This would be my next try.

Dave::

machten
MHR / S2
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Post by machten » Mon Aug 09, 2010 12:27 am

Check that your enricher ciruit (choke) is sealing properly. The following are tell tales for it:

1. Sooty plugs
2. More exhaust smoke than you expect.
3. Wile the bike is running, you can wind the mixture screw all the way in, or close to it and the cylinder keeps firing - it should starve of fuel and stop.

Check that you have enough cable free play to the enricher plunger at the carb end. You should have 2-3 mm. You want enough to ensure the cable doesn't hold it up (open), and not so much that the cable end can slip up above the holder and sit on top of it and do the same.

If that looks OK, take the plunger out of the carb. The rubber at the bottom often hardens and doesn't seal properly. If it is worn, you will likely see a deep circular indentation in the rubber. Also look down the plunger void for any gunk that may be holding the plunger up off the brass pipe at the bottom of the hole,

You can try and take the rubber plug at the end of the piston out and turn it over (it is a bit fiddly, but it can be done) giving you a fresh flat rubber surface, but enricher pistons cost between $5-10 each, so it's a cheap fix if that is the problem.

Kev

wdietz186
Cagiva Alazzura
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Post by wdietz186 » Mon Aug 09, 2010 7:30 am

Dave, This may be a fart in the dark but are you running a lead subsistitute?The reason I ask is years ago I had a similar problem on my 900 racer.It would go fine for a few laps then start to miss at high revs then lower and lower until it went dead on one cyl.The plug would be sooty and a cleaning would make it spark again.The arcing to different parts of the plug was noticed by a friend with lots of 2stroke experience and he said he had the same problem once too.Turns out he got some old leaded race fuel and the lighter elements of the fuel had evaporated leaving a combustible but heavily leaded mix that coated the plug with a conductive glaze that shorted the plug out.Changing the fuel fixed the bike and made me wary of the freshness of the fuel I used.Pulling the heads later that week revealed blobs of something shiny and hard to remove splashed around the piston crowns and valves. Just a thought, Bill

DaveDare
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Post by DaveDare » Tue Aug 10, 2010 5:39 am

machten: Thanks for the reply this is all very helpfull. I will pull the plunger out and check it out this weekend. Although I can wind the mixture screw in and it will falter and stall.

wdietz186: Hmmm that's interesting. Yes I do use a lead substitute. I would be worried about not using though...??? thoughts?

I can't see how this would affect only one cylinder though, that seems odd. But I am open to all suggestions now.

I might run ome metho through the tank and see how it runs without the additive.

Thanks guys...of course anyone else that may have any ideas I am open to all.

Will report my findings.

Cheers.

Dave::

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