750SF valve timing/advance and compression numbers

I'm amazed that going from 138 to 140 mains would make that much diff. Pulling the enrichener would be adding a hell of a lot more fuel to the mix than one step in main jet. Main jets are cheap - worth trying larger again? Go too far so you find the turning point then take a step or two back to the sweet spot - a bit like tuning a dial on a radio.

But good news that you've got some power and revs happening.
 
Jetting was all over the place. I have 145 main and 45 pilots with the 265 atomisers and K2 needles. To test jetting you really need to put a registration (white tape or something) on the throttle grip and housing, for quarter, three quarters open. The mains do not com into play until 3/4 (the second handful on an SF with std throttle and 36mm carbs), before that they could be lying in the bottom of the float bowl. Half throttle is the middle of needle/atomiser.
 
Paul Marx said:
All my 750s, SFC included are running leaner and with hotter plugs. 5 to 10 points down on the idle jets.
I learnt that Gijs van Dijk who isn't a novice was doing the same.

I think that if basic tuning and twiddling doesn't get a freshly bought bike going correctly, the engine needs taking to bits .

Paul
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That’s not a general rule, also not for Van Dijk, so wouldn’t recommend doing that!

Marnix
 
MarnixSFC said:
That’s not a general rule, also not for Van Dijk, so wouldn’t recommend doing that!

Marnix
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Too late.
Has been so for a few thousand km now. 10 points down on the S, 5 on the SFC, 5 on the 500.
The 500 would cut out as if choke was constantly on. Cured.
Paul
 
In my post of June 12th, 2 weeks back now, I wrote that I'd gone down on the PILOT jets.
Mains are of course another matter though I doubt that the mains on many of our machines are appropriate.
And Craig, idle jets are not replaced, they are superseded. They are still passing fuel full throttle.
(Likely that many chokes are passing fuel as well on our bikes due to hardened rubbers)
Paul
 
Paul Marx said:
And Craig, idle jets are not replaced, they are superseded. They are still passing fuel full throttle.
Paul
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The more open the slides are the weaker the vacuum for the pilot system to operate. Sure, there might be something getting through but compare a main jet hole to a pilot jet hole AND then factor in the reduced pilot system vacuum.

All jetting needs to be done on a needs basis - i agree that default settings are a guide only and certainly not set in stone.
 
Paul Marx said:
And Craig, idle jets are not replaced, they are superseded. They are still passing fuel full throttle.
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Eh, what? Ce n'est pas moi qui l'écris, m'sieur ... ;).

Ah, the complexities of Italian - English translation circa .. What would it have been? Late 1960s, early 1970s?
 

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There are a LOT of ambiguities in the language in that manual. take about tortured English. The only way I could understand some sentences was to write them out like a maths equation, with Yesses on one side and nos on the other. There's not a lot of logic in its needle listings either. You might think starting at big and ending in small but not so much. I probably shouldn't complain, at least they tried and I was happy to at least have a hint.
 
There is a chart with all the needle profiles (is it in that manual?). They definitely do not just gradually get thicker or thinner. Lots of parameters for lots of compensating.
 
Vince said:
There are a LOT of ambiguities in the language in that manual <snip>
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Yeah, that's true for lots of (most?) technical publications.

Always best to try and find the original language version and then translate it yerself. Mind you, that only helps if the original is itself correct (and intelligible) ... ;)
 
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