main jet size for K&N's and a racing exhaust....

[Seana23]

Hi all, i hope everyone is well and groovy...
I'm building my GS850's carbs and am wondering if i need to up-jet the main jets from 115's to 125's...
I've not run the bike yet to do a plug chop, as i'm building it from scratch and the carbs are pretty much the last thing still to do before pressing the starter button... Exciting!!!!
anyway, i had a GS550 for some years and upjetted for an Alpha exhaust as it ran a bit lean, But this Harris racing exhaust is pretty much straight through and its also got K&N air-filters.

Thank you all in advance.
XXXSeanaXXX

[TheCafeKid]

Being a UK lass you probably have adjustable needles in the carbs, but you still may want to hunt up a DynoJet kit. Will make life much easier.

[hampshirehog]

Just to confirm. You're running BS32s, they are genuine K&N filters, not Emgos etc, and your Harris is a race pipe rather than a Harris road pipe (externally the same, internally different).

[Seana23]

gawd, now your askin...
they be CV carbs.... they be a bit smaller than the same 1000 CV carbs...
i'll google it and get back to you (im in bed and dont want to go downstairs as its cold!)....

.....BS32SS's i think according to an old GSF thread...

They are Genuine K&N's (from 20years ago) and the ehaust is 4 original downpipes running into a gentle 45 degree bend, then into a straight through, except for an end plate, Harris racing pipe.

XXX
oh, i looked in some GS1000 CV's and the jets in there were 145.5's (not sure what this means exactly but thought i'd say anyway.)
XXX

[Seana23]

just been lookin at Dynajet kit for gs850 and they offer 3 sets ov jets 155's, 160's and 165's...
so maybe the 145'5's from the 1000 carbs i have would be better than the 115's originally fitted...
Any thoughts???
XXXX

[TheCafeKid]

If they're at all like the carbies stateside, they'll be 32SS indeed. But the jets are not what you're going to be worried about so much as the needles. Even the adjustable "Canada spec" needles I've gotten a hold of over the years don't taper fast enough for vacuum carbs with pods. The DJ kits have special pointy pointy needles (like the rabbits teeth from the holy grail ) you NEED those. The jets are helpful but a simple maths formula can convert DJ sizes to Mikuni easy enough.

[hampshirehog]

A 155 Dynojet main is almost the same as a 145 Mikuni (they use a different way to calculate jet size). DJ160 is a Mikuni 150 and a DJ165 is 155 Mikuni. Worth a go with those 145s you already have (and new jets from Allens or your local boys are only £3 each).

The DK kit will set you back £110 -120. I would have go at using the parts supplied by Mr Mikuni.

You can try raising the needles - try the bottom notch first and see how it goes. The pilot circuit will probably tune in on the mxture screw though Allens will have bigger pilot jets if you need them.

If you don't know about plug chops do a search on here.