Main jets, which size?

[Antti]

I have installed "Siebenrock 1000cc replacement kit" last winter. Kit replaces original cylinders and pistons, and compression ratio is a litle higher.

Main jets are now size 160, I think that bike works quite fine but plugs are pretty white. Should I try bigger jets? Should I get bike lambda measured if I want to be sure that mixture is OK?

 

[mikyh]

I have installed "Siebenrock 1000cc replacement kit" last winter. Kit replaces original cylinders and pistons, and compression ratio is a litle higher.

Main jets are now size 160, I think that bike works quite fine but plugs are pretty white. Should I try bigger jets? Should I get bike lambda measured if I want to be sure that mixture is OK?

I installed the same kit with a free flow exhaust and intake filter.
I have the original 135 mains and the bike runs great. I even lowered the needles one notch because the plugs were a bit blackish.
i had asked Siebenrock for guidence back then and they also said that usualy there's no need for bigger jets.
One more observation - bikes are usualy equipped with main jets on the rich side as precaution, and weak midrange fuel systems because that's where polution is checked.
If you want to check main jet performance, you should warm up engine good, put two virginaly new plugs in, and have a full throttle run against your brakes for as long as possible, than cutting the engine, coasting to a stop and that look at the plugs with a magnifying glass. the interpretation of what you see is not as easy as some people think.
Read this:
http://www.strappe.com/plugs.html

All the best, miky

 

[Antti]

Thanks mikyh for the link, I`ll study that. Has your bike originally been R80, and is it with 32mm carbs? My engine and carbs has been taken from some street model R100, so I have 40mm carbs.
I don`t know if there is any difference in Siebenrock kits, but they have "Power kit" for R80-engines and "Replacement kit" for R100.

I have change to use lambda measuring system as I get clamp for sensor fitted into exhaust. Everything is probably fine right now but after measurement I can be sure.

I`m just seeing nightmares about melt holes in my new pistons..

 

[mikyh]

yes, mine was an 800

the 800 to 1000 kit works with the original 32 carbs. I didnt understand that you had a 1000 engine with a kit so my experience is irelevant.
I would ask Siebenrock for their recomendation and play with midrange adjustment much more that main becaus there is where you use the bike 99% of the time (unless you are racing or a psyco).
You could also go for a Dyno test where usualy they have gas analizing option through the rpm and load range and you can see easily if there's a problem.

What is a Lambda system? is it a permanent CO sensor in the exhaust manifold?

Miky

 

[Antti]

With "lambda system" I mean air/fuel ratio measurement, i`m not sure if it measures CO and uses CO figure when calculating air/fuel ratio?? Something like that...

Here is brochyre of one manufacturer:
Motec

System wich I have opportunity to borrow is quite as above, but diplay has been made out of leds, it is kind of portable and can be assembled temporarily to the vehicle (if there is place for sensor in exhaust).

I think I try to play with needles and see what happens. It is just true what you say about midrange using time. Dyno run would also be interesting, not only for mixture but it would be interesting to see torque and power curves. Unfortunately I´m just about to graduate, because our polytechnic has dyno bench, it is ment for cars but with imanigation I think it could be used for bikes too...


Thanks for ideas!
Cheers!

 

[Howard Millichap]

Antii,
My R100GS has a twin plugged & gas flowed engine by Jim Cray. So the set-up could be similar to yours.
I run a K&N air filter, 2 long intake trumpets. The main jet in my 40mm carbs are 170's, the needles are 1 notch lower and I use NGK BP7ES & BP7HS spark plugs.
I've covered 40000 miles with this set-up with no running problems.
I hope you can find this usefull.

 

[Antti]

I have now tried 160`s, 165`s and 170`s jets. I´ve also tried different needle positons with 170`s, and now there is 170`s+needles in third position. I haven`t cheked size of the needle tubes, there is probably available differend sizes?

Anyway, bike feels to work well. I`ll leave it to these settings, and when I have time I`ll do sparkplug test with new plugs. And if it will be lambda measured then some more changes if needed.

Howard,
how big influent there was when twin plugging was done? How was gas flowing done, bigger valves?

 

[Howard Millichap]

Howard,
how big influent there was when twin plugging was done? How was gas flowing done, bigger valves?

Huge. Well I estimate power and torque went up 15%~20% and fuel consumption went down 15%~20%.
Jim Cray cleans everything up in the head and matches the combustion chamber size and reduces the squish so that it is to more modern combustion chamber theory. Don't forget these things were designed a long time ago.