Other carb changes...

[81xsproject]

I shimmed my slide needles the equivilant of what would be raising them 1 notch (.022"). This is the only change I have made and performance has suffered to incude stumbles and poor low end performance.

My question; Should I lean up the idles screws to compensate for the slide needle richening? Or better yet, what would you recommend? I may just remove the shims as it was running pretty damn good before I shimmed.

[DiverRay]

Leaning out the idle mixture may help. The 80, the screw adds AIR, not fuel. You may need to turn it OUT about 1/4 to 1/8 turn at a time, and try again.
Ray

[TopCatGr58]

Hey Diver,

Well, according to this fine diagram, and what I was told and thought, the pilot screw meters the air fuel mixture, not just the air, so turning it out richens the pilot circuit, turning it in leans it!

T.C.

[DiverRay]

OK, I may be a GURU, but I can still learn!!
I guess thats what happens when I only work on the '78 and '79 models. I try to remember most things, and get it wrong sometimes.
Thanks TC

[motoman]

Hey all.....easy way to remember on all these carbs, Mikuni, Kien, etc.........intake/filter side of butterfly=air screw, intake/cyl. side of butterfly=fuel screw.

[motoman]

HI there xs........have 'sometimers', are you running stock airbox? If so, at your almost sea level, 110mains are stock sea level jetting. I would put needles back to stock, as your allowing too much fuel by mains with the needle taper raised, and will be rich as the diaphrams raise needles with vacuum drop under accelleration. Your float levels can have a big effect with a lean/rich cond. also. With stock intake housing/stock exhaust, 23mmfloat setting, it should be real close at an almost sea level. Intake modified, pods, etc........exhaust modified, aftermarket 4into2 or 4into1, a guess would be on that year 115mains(2 steps from stock), needles stock single clip position as vacuum drop for diaphrams change no longer having stock airbox. Any intake or exhaust mods change everything as the CV carb diaphrams react differently, so all bets are off with jetting, and every bike responds differently. Just follow those procedures for CVCarb tuning.

[81xsproject]

This is a great post. I have decided to change my signature to contain all my mod data.

So
I have 120 mains
Stock 42.5 pilots
floats @ 23mm
Uni chrome end pods
4-1 exhaust
idle screw 3.5 turns out

[81xsproject]

I can't forget to mention the now

[motoman]

Just a suggestion..............remove spacer washers from needles, 115mains, 25mmfloat setting, re-sync with merc.stix(which you have to do after R&R carb bank cause they'll be off)don't ask how I know. and re-adjust idle mix...........bet it'll be close.

[Pat Kelly]

CV carb tuning website

I used the above site and proceedure with great sucess on my E (K&N in airbox, Jardine 'spagetti' pipes, Dyna coils). I went one size up on the mains and raised the needles one notch. Pilot jets are stock.
I noticed my LG sounds 'ragged' as I accellerate (K&N in airbox, 4 into one w/supertrapp) so after I install my bigbore kit and break it in I will follow the same proceedures.

My question is, with my LG, I think carbs 2-3 are one size richer (I have yet to take them off). When rejetting do I want to stay with the jet size differential or go the same all the way across (I'd prefer to have them all the same..... I think)?

[Brian_D]

Pat,

On my LH, all mains were the same size - 110's. According to the Service Data on Yamaha's web site, the ONLY model that came with different size jets from the factory was the G where 1&4 are 115's and 2&3 are 120's. The Servide Data for the LG (and all other 80-81 models) calls for 110's across the board.

Of course, the Service Data also indicates that the 80 G was the only bike to use a 51Z7 fixed jet needle. All other 80-81 models specify a 5GL16 fixed jet needle, and all 78-79 models specified the 5GZ6 adjustable jet needle.

So now the real question becomes, would the 80-81 model carbs perform better with an 80 G style jet needle and 115's across the board instead of 110's?

[John]

Could the difference in stock jetting be because the Special and Standard exhaust systems may flow differently?

[Brian_D]

Originally posted by John
Could the difference in stock jetting be because the Special and Standard exhaust systems may flow differently?

That, and the 80G was thier first attempt at meeting US emissions? I'm guessing the Standard was the first to be thru the production line in 80 (79).