main jets

[oldbiker648]

Yanked the carbs of the '81H and stripped them down. All 4 main jets are 110's instead of 1 & 4 being 115's and 2 & 3 being 120's. Someone had obviously been into the carbs before, could this have been a PO modification to improve fuel mileage? The original owner was an older gentleman who bought the bike new for touring, not street racing. I've got the stock air-box, should I re-jet to original factory specs?

[Pat Kelly]

Looks like someone put 78-79 carbs on it

[oldbiker648]

Pat,
Would there be any way to verify that the carbs were from a different year than the bike? Looks like I have 2 options, put the jets I have back in or order replacements and wait a week to try to fire this thing up. The other thing that looks different to me is that there is no jet pressed into the top rim of the float bowl near the tab, just a hole about 3/16" dia. When I posted that the bike wouldn't start last week, somone sent me a high-resolution picture of a jet pressed into the spot where I have the open hole. My idle screws were not capped and they were all screwed about 3 1/2 turns out from being closed. That sounds like a lot more than what I had seen posted (1 1/2 turns).
You have any suggestions?

[TopCatGr58]

Hey there Oldbiker,

My 81SH also had 110's straight across STOCK FROM FACTORY!! I think Yamaha changed their options even though the manuals state they should be staggered! With stock box and pipes, just put the 110's back in! That partial hole/depression is where the bowl vent opening used to be in the 78-79 models, they just changed the casting molds and had it sealed off, since it vents thru the inlet bell in the later models...so no jet required for just a vent! I was told by the racing shop to turn my pilot screws out that many turns, but I found it a touch rich when at higher mountain altitudes, so now run about 2-1/2 turns out!
T.C.

[skids]

Yep, my 81H too, TC. If I remember correctly, the 80SG was the same way.

Originally posted by TopCatGr58
Hey there Oldbiker,

My 81SH also had 110's straight across STOCK FROM FACTORY!! I think Yamaha changed their options even though the manuals state they should be staggered!
T.C.

[oldbiker648]

Thanks guys, I'll see if I can't get this thing buttoned back up tomorrow and try to start it.

[pggg]

That starting jet will be there, it's just way down the bottom rather than at the top.