main jet design

bigbore2 · July 31, 2012, 03:53:53 PM

84 1100 with 36 Mikuni carbs- I was suprised to see that Mikuni has no way to contact them to ask any questions. So I will ask you. The original main jets have a wide top/flange and my local dealer only has the, I assume its a newer design, where the top/flange is, say, 1/2 the size around of the original. I need to go up one size to a 117.5 from the 115 I have in there now as I am getting at WOT high rpm [ 7000-9.500 ] lean surging. I cannot see any difference in using the newer design as the threaded portion of either design is going to provide a seal in the jet tube and the flange is not a significant concern? I have not fitted them yet but was wondering what the brain trust here thought of this.

fj11.5 · July 31, 2012, 04:51:31 PM

just went through the same issue myself, 84 fj toooo

, , if the smaller jets have the inner taper/ cone shape into the hole you should be fine, they should be the same to look at just smaller than normal mikuni mains, , i asked the same questions, most on here said they will work, what i didnt notice till after using the small ones after issues they were flat inside the hole , causing lean surging at your same rpm ( 115 jets) , ,

fj11.5 · July 31, 2012, 04:55:55 PM

Quote from: fj11.5 on July 31, 2012, 04:51:31 PM
just went through the same issue myself, 84 fj toooo , , if the smaller jets have the inner taper/ cone shape into the hole you should be fine, they should be the same to look at just smaller than normal mikuni mains, , i asked the same questions, most on here said they will work, what i didnt notice till after using the small ones after issues they were flat inside the hole , causing lean surging at your same rpm ( 115 jets) , ,

ps i fitted 115 mikuni,s and effie is awesome ..... had originally been RICH po had drilled out the standard 112.5 to about a 140 size didnt know till comparing them to standard jets

bigbore2 · August 02, 2012, 11:24:53 AM

Don't really understand your comment of being "flat inside the hole." Do you mean that the hole does not come to the top of the head of the jet but is recessed down a millimeter or 2? That is the design of the original wide headed jets with the hole being recessed down inside the head.

fj11.5 · August 02, 2012, 04:50:40 PM

they should taper in like a funnel

bigbore2 · August 03, 2012, 06:47:51 PM

I understand . Thanx

fj11.5 · August 03, 2012, 08:38:09 PM

no worries, sorry if i confused you, confuse myself most days

bigbore2 · August 09, 2012, 03:08:43 PM

Talked with Sudco and they said they believe either jet size/design [ small head/ large head ] will work. Mikuni sends all their carb/carb related tech questions to Sudco. When I went to the 117.5 mains, I could not believe the difference in this motor[84-1100]. It just roars now. i can tell a difference from 2500-redline.

fj11.5 · August 09, 2012, 04:46:33 PM

im sure they will, just dont use the cheap small jets

fj11.5 · August 10, 2012, 02:31:26 AM

i ended up putting 115 mains in my 84 1100 she seems to like them, , put 117.5,s in the 89 1200 but havnt tried her out yet,she had 42.5 pilots fitted allready so all set for pods now once i raise the needles a notch

bigbore2 · August 11, 2012, 04:17:59 PM

What is ur elevation there? I'm at 5000 ft. 4 into one pipe with Yoshi can, K&N airbox filter 117.5 mains, airscrew 3 3/4 turns out, stock pilot jet, one washer on stock needle.

fj11.5 · August 11, 2012, 04:54:35 PM

I would say elevation is about 6'

bigbore2 · August 13, 2012, 05:58:13 PM

Guess you better get some pontoons and a paddlewheel for that bike.

fj11.5 · August 13, 2012, 06:04:26 PM

may just need them if the world keeps going the way it is, hmmmm water cooled Fj

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main jet design