| by Anders Dinsen ... December 07, 2008, 11:26:23 pm |
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I have not been able to fix the running problems I started experiencing about a month ago  Removing and refitting the carbs didn't cure it, the air box didn't either (I didn't expect it to), and going back to the original jettings which actually ran when I first fitted the carbs, also did not work!
The persistent symptom is that once the engine has warmed up, it can only idle. It stalls when the throttle is opened and is very difficult or impossible to restart! 
I have checked the ignition, fitted a new rotor and distributor cap, I have checked the ignition leads, and replaced the plugs. I have also looked for air leaks, but there are none. I have wiped the coil clean of dirt, I have tried the old fuel pump (which ran with too high fuel pressure), and I have verified the float level - even straight after a stall.
I have also toyed with settings. An HTML copy of my current log sheet is available here:
http://tmp.dinsen.net/murena/jetting.html
Looking back on my notes, I think I have been focusing my attention on the wrong facts: My attempts to cure the running problems has focused on giving the engine more "juice", whereas I should have given it less! A look at this spark plug tip tells the tale: This particular plug has run less than 2 km on the engine at low speed, and the fouling indicates that it has been running a very rich mixture.
So it must be leaned off. Since idle is good, and so is first stage progression, the problem is with the main system. I actually saw a worsening going from 145 to 150 main jets, so I should back down to 140 to see how they work. The problem could also be that the main system comes on too early, and this can be adjusted by lowering the float levels. That's the obvious next try.
But why did this problem suddenly pop up? It used to run with the richer jets?
To rule out ignition completely, I'm going to replace the coil too.
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