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Discussion Starter #1
Hi all,
I've got a 96 900SL which seems well down on power - thought I'd try here for any suggestions.

History: bought the bike about a year ago, running well. Over time it started running a bit rough and eventually wouldn't rev over 7000. I pulled down the carbs and cleaned them up (full of muck) and put in a factory pro jet kit. I've also changed to a BMC air filter, open air box, Remus slip ons and Dyna coils with new plug leads and changed the fuel filter. I used the example jetting suggested for this set up by factory pro. Normal services have been done, valves are getting close to time for a check again (store does this). The bike is much improved, no longer dies out above 7000 but still not pulling as strongly as it used to when I first got her.

I put it on the dyno on the weekend and we saw that HP is peaking at 62 (factory pro dyno, sea level, around 20 degrees C) at around 6500 rpm and then power drops off quite steeply (compared to data from a previous 900SS on the same dyno). We changed the needle from 2nd top to 2nd bottom clip position (plus removed the metal washer) and changed the main jet from 130 to 140. This improved the graphs in the mid range (was quite flat for torque) but made very little difference to the top.

Other symptoms: fouls plugs easily (suggests rich or weak electrics), I'm now careful to only keep the choke on for a short time and it is much better. Surges between 4000-5000rpm on the road with a barely open throttle (suggests lean). Also tending to pop and backfire through the exhausts when decelerating (suggests rich).

Sometimes when I switch her on a get quite a loud "pffft" back through the air box (this is not the tank/breathers - checked with tank propped up, lid open, breathers dis-connected, definitely coming from the carbs up through the air box). Checked for kinked fuel lines and breathers, all seem good. Checked all ignition electrical connectors, all well seated and not corroded, contact cleaner added. Fuel pump runs and seems to be flowing well does anyone have a figure for the flow rate?

I'm confused here as so many symptoms seem contraindicative. I'm now going to check ignition and valve timing. Any other ideas?

Thanks, Rob.
 

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Discussion Starter #4
Here is the dyno graphs to show the sad situation. I had to edit these a bit to get rid of an RPM offset between the two bikes - basically moved my curves to the right ~300rpm.
 

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