'78 GS1000 jetting for pods and header only

[slaveforthewave]

I had my bike running pretty well for a while. Fuel screw 7/8th from seated and the air screw 1 1/2 from seated. Seemed to really fall on it's face at higher rpm. I have no tach so it is hard to say at what rpm, but anyways. Currently I have the needle set to the 4th clip from the top with the big plastic spacer on top and the little plastic spacer on bottom of the clip, 15 pilots, and 135 mains. All jets and needles are Mikuni branded. I am running slightly restricted emgo pod filters and a 4-1 header only with no muffler or pipe back from the foot pegs.

I ran across a few posts by Keith Krause saying essentially run Mikuni 130 mains, with 15 (possibly 17.5) pilots, with an extra .022" spacer on top of the needle spacer to put it somewhere at 4.5 clips down.

Before I buy smaller mains and larger pilots to dial this thing in, does anyone have any real world tips to these VM26 carbs with similar set up?

[salty_monk]

Do you have a Dynojet needle in it? I think you'll struggle without the slimmer taper...

[slaveforthewave]

i do not. it is a stock needle. is there any way to acquire the dj needle without buying an absurdly expensive kid that includes a few jets, a screw, and a needle?

or possibly use this chart to buy a slimmer needle?

http://www.jetsrus.com/a_jets_by_carburetor_type/needle_mikuni.html

also my pilot fuel screws were snapped off and i had to sand them back into a point after i got the tips out of the carb bodies. could this be my issue? i cannot find new fuel screws ANYWHERE!

[MisterCinders]

Forget about RPM. What throttle position does the bike flatten out at?

[hampshirehog]

You're a bit all over the shop really and the best I can advise is you read all the threads that you can find on here on how to tune in carbs for pods and a pipe.

Basics is that ignore the engine revs as a guide to jetting - it's all about throttle position. Having the wrong pilot jets or the fuel screw in the wrong place won't change a thing when you're on full bore. Similarly, on tickover you don't even need main jets fitted. You have to tune each part of the circuit in, one at a time.

Having said that I would have thought you are pretty close and you don't need Dynojet needles with VMs - the existing needles tune in fine.

[slaveforthewave]

i have read many posts on this. even read through the mikuni tuning guide. i know this is kind of a subject that is beaten to death, and people probably get really sick of answering time and time again.

like i said i read that the dj 138 is made for pods and a pipe which is about a 130 mikuni jet size. at about 3/4 throttle that's when i get spitting and the bike just stops pulling hard. guessing i might be up a jet size. at idle bike has pretty well colored plugs so i'm thinking that the pilot system is doing okay.

i just didn't know is the header only with no pipe or baffle would cause me to need to go up on the mains or no. or if it would cause a back pressure issue.

this site is a wealth of information, so i thought i'd run it by everyone before going out and spending 75 dollars on jets, shims, needles, etc.

[hampshirehog]

At 3/4 throttle you are running on the needle (probably still take the mains out and it would run the same). You should really mark up your twistgrip with the opening fractions and do plug chops at 3/4 throttle but my guess is that you need to drop the needle clips in to the lowest slots.