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Jetting for the 673 conversion

  • Thread starter Thread starter Guest
  • Start date Start date
G

Guest

Guest
Hey folks, I'm slowly getting round to the 673 conversion of my 1980 GS550E. Now, I was going to change the main and pilot jets to the same spec as the GS650, but heard a lot lately about needing to go richer still when using modern fuels.

The bike will retain the standard airbox and exhaust.

Standard 550E main jet is 92.5, and pilot jet 40

Standard 650G main jet is 110, and pilot jet 42.5

Anyone got any input with this before I order jets?

Thanks in advance.
 
Engine is stripped at the moment. I've been running it for the last few years as a standard 550. The cam journals are worn though, and it finally burnt an exhaust valve out so I'm converting to a 650 because it seems impossible to find a 550 cylinder head in Australia.
 
You will have a 650. Jet it for 650 specs.

Not sure what your fuels are like, down under, but with the Ethanol here, it doesn't hurt to go one size larger on the main. No need to increase size on the pilots, just turn the screw out 1/4 turn or so farther than usual. You are going to tune the mixture anyway, just set the screws rich (I usuall start at 3 full turns out), then lean them for best running. When you find the best running, stop the engine, turn each pilot screw in, counting the turns. Record that number and turn the screw back out before continuing to the next screw. Note that they might not all be the same number of turns.

.
 
Cheers Steve, so maybe you guys get more ethanol in your fuel? I'm from the UK so not really sure what the quality is like here, but people do moan about it.

I guess I'll go with the 110's and see how it performs.
 
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