R75/5 jetting for Siebenrock kit

[Foxy]

Siebenrock kit (1000cc) performing well in R75/5. Have just fitted Alpha Classic electronic ignition system as the standard points coil set up was doing the "ghost timing mark" thing. Not sure of reason for that, either bent cam nose or faulty advance unit. But Alpha system covers both and would recommend it highly. Put several tanks of fuel through old girl recently and has performed faultlessly.
Bike developed a leak from timing case post Siebenrock installation so replaced gasket, but also fitted deep sump spacer kit from Siebenrock. Running same amount of oil as before (approx. 2.3 litres). No more leaks. Have done 2 things here so hard to know if gasket solved leak or sump upgrade. Replaced duplex timing chain while in there.
As i said bike running very well with kit. No pinging. Heads, exhaust, carbs etc all standard.
Pulled plugs today after a fairly quick ride (70/80mph for last 30km or so) and they were a little on the white side, one slightly more than the other. Should i be worried about this? The bike idles perfectly, pulls well with no flat spots, starts well so i am a bit reluctant to start messing with jetting. Carbs were previously re kitted with all standard jets, needles etc.
Is it as simple as going up a size with main jet?

[sprints@pldi.net]

I found years ago that plugs have 2 readings - the center electrode indicates the heat range of the plug and the outside ring indicates the richness of the carbs. For example you can have a very sooth black outside with a white center (rich, hot plug) or you can have an almost white ring with a sooth center (lean, cold plug). So by saying your plugs are a little white - if it's the center use colder plugs, if it's the ring increase a jet size - Rod

[George Ryals]

70/80 mph is not nearly wide open throttle(on the main jet). I'd say raise the needles up one notch and try it. You might need to touch up the idle a little with the needles up a notch.

[Kurt in S.A.]

What plugs are you running? Weren't the plugs different for the 1000cc bikes versus the 800cc bikes of a given period? Seems like you would need an appropriate spark plug.

Kurt in S.A.

[Foxy]

Thanks chaps,
Good advice on reading plugs. I reckon it is mixture related so will try larger main jet sometime or perhaps raise needle, I reckon needle is currently on third notch. Can always go back. Ran bike at more moderate speed a few days ago and plugs are perfect tan colour, so its obviously just a little lean when pushed a bit.
Thanks again for tips.
As I said previously I am delighted with Alpha ignition set up. No pinging, no more ghost images with timing light, starting and running beautifully. I set it up with a green (3 OHM) Dyna Coil because I had one. Not that there was anything wrong with the 40 year old Bosch coils that I reckon would have come with bike from factory.
Thanks again.

[barryh]

There aren't huge jetting differences for the same size carbs on different capacity engines except for the main jet. That's pretty logical if you think about it as a 750 at certain throttle opening is pulling the same amount of air as a 1000 at slightly less throttle. The 1000 only pulls more air than a 750 when it gets to large throttle openings. So I suspect you will need bigger main jets. Bigger mains will impact lower down too. The idealist notion that main jets only have an effect above 3/4 throttle is simply not true. Part throttle may be controlled by the needle/needle jet but the fuel has to get through the main jet first and a bigger main jet will offer a little less resistance to fuel flow than a smaller one so I wouldn't touch anything else until you have the main jets sized correctly.

[Foxy]

Thanks Barry.
That seems logical. I am currently running the standard carb set up with #135 jets. Rebuilt carbs recently and replaced all jets etc as per Haynes manual. The only thing i didnt do was service the choke bodies. Both manuals recommend main jets sizes from #130 upto #160 for 32mm carbs. I will try a pair of #145 jets and maybe buy a pair of #150 to try.
As i said, i am reluctant to alter things too much as bike is running beautifully, just a bit worried re white outer part of plugs when ridden hard.
Is it OK to drop bowls off and simply screw in different jets?
Cheers

[barryh]

Is it OK to drop bowls off and simply screw in different jets?

Absolutely, it's a 2 min job.

You can use max. top speed as a main jet size check but that's hardly safe on public roads so short of a dyno the usual seat of the pants method (on a safe stretch of road) is to use full throttle in a high gear so the engine is pulling hard for a few seconds then quickly close the throttle to 7/8ths. If the engine seems to pull better at 7/8's then the main jet is too small. If the engine hesitates and then resumes smooth running, the main jet is too big. If there is little noticeable change in response, the main jet is close to correct.

[Duane Ausherman]

If you just pull the plugs when you get home, you know nothing about jetting. You must do a run and chop test to know anything at all. You may have done that, but I didn't see it mentioned.

[Ken in Oklahoma]

If you just pull the plugs when you get home, you know nothing about jetting. You must do a run and chop test to know anything at all. You may have done that, but I didn't see it mentioned.

Hmmm, didn't I read somewhere, probably here, that plug chops don't tell you much with 'modern' gasoline, i.e. ethanol laced?

Ken