79' SF 3H3 8XI Carbs

[TopCatGr58]

Hey Jeff,

I'm kinda late to this party, but here goes. As has been mentioned, the 78-79 carbs were essentially the same with brass floats/needle/seats. The plastic floats and viton tipped needles were 80+.

Someone several years ago found that the viton tipped needles wouldn't fit into the 78-79 seats. They found that the seats from the Yamaha XV-920 Virago would fit the screw size, and were designed to allow the larger viton tipped needles. So most likely the PO did that conversion to be able to put viton tipped needles and plastic floats in their 79Sf carbs. That's my theory as to why you found those NON-standard parts in the carbs.

Some folks think the viton tipped needles don't leak as easily as the solid brass types, YMMV.

T.C.

[bikerphil]

Jeff, I have heard of the very early late style carbs using brass floats but never the early type using plastic floats unless the PO changed them. I would go with all brass on the carbs you have there. I may have an extra good one lying around if you need one.

[JeffH]

Yeah, they used the emulsion tubes with 2 less air bleed holes in the 2 center cylinders for a time on the 79s in an attempt to keep those 2 cyls cooler by richening them a little. Didn't really work though so they abandoned that idea pretty quickly.

Yeah, my 78E has all four as 16 hole emulsion tubes. As does the 80SG set. So the 79 trial in SF and maybe F with 2X2 + 2X3 = 10 Hole for 2 & 3 must have been a flop. At least these SF carbs were 16-10-10-16


What is curious is when Mikuni switched to the Plastic Floats. E / F were of course brass floats. By 80' it was all Plastic. Anybody know if late in the 79' model production either the F or SF had plastic floats? Of course without a bushing for the pin. The 80' bushed Floats hit the needle and seat because the pin support in +1mm thicker than E/F brass. So it couldn't have been an early release of 80' bushed floats because then Needle & Seat would have needed to be lower so the float would align the Post holes for the Pin. Or, the Needle & Seat washer which is 1mm thick would have had to be thinner. All interesting TRIVIA


Jeff

[BA80]

Yeah, they used the emulsion tubes with 2 less air bleed holes in the 2 center cylinders for a time on the 79s in an attempt to keep those 2 cyls cooler by richening them a little. Didn't really work though so they abandoned that idea pretty quickly.

[JeffH]

OK gents ………………… THANKS

I was about 99% sure that was the case with these 3H3 carbs. Interesting to have 2H7 E / F with nearly the identical 3H3 (except for Nozzles in 2&3 and the new offset choke lever) and end up for the 1980 Model with a bunch of significant changes. EPA must have been giving all the bike importers the same problems.


So I'm going with E/F brass floats & E/F needle and seats just like my E. Perfecto hopefully zoom-zoom soon since in 10 days I head up to the VYR Rally in NC.


Thanks again guys. Helps to double check to make sure it wasn't wrong approach. The plastic floats and that shorty needle and seat that were in there got me all whacked. Mike said those may have been K&L. Plus the one bushed plastic float in there with the filed down pins. Now it will be proper.

Jeff

[motoman]

BA80 has got it right Jeff.

[BA80]

Anything in there without a square inside a square Mikuni marking get rid of.

[BA80]

That center float valve is probably an aftermarket replacement. All I've seen in 78 and 79s are like the first one.

All the 78s and 79s had brass floats. Looks like a mod artist has changed floats and put some non Mikuni stuff in there. I would get all Mikuni internals and straighten them out.

[BA80]

Looks like the needles are a little different also. But, as long as they are all the same it shouldn't matter.

[red bandit]

On the outside I don't think there is a difference between the 2H7 & 3H3. The main diff. was the emulsion tubes on 2&3 on the SF. I'm not sure if the slide needles were the same on the E/R vs SF. The seats, left one is E/F & SF but I think original plastic part with screen was brown. The middle is aftermarket or another carb that maybe fits. Viton tips are not E/F or SF. E/F & SF had brass floats. Plastic floats are 80/81.

[BA80]

The carbs are exactly the same Jeff. The Standard carbs had a little different size starter jet is all as I understand. Here's the charts.

http://hitechkc.dyndns.org:78/phpbb3/viewtopic.php?f=5&t=268

[JeffH]

I've got a set of 79' SF - 3H3 8XI carbs (marked clearly on the bell as 3H3)


I'm just trying to find out what were Original Parts for this tweener year of carbs. Specifically, did it come with same Needle & Seat and Floats as the E & F? The jet are of course the same as E / F in the SF. Also has shared pilot tunnel with screw on top same as E / F.


As we all grumbled a couple years ago, Yamaha Parts House and Partzilla removed the 1979 SF listing & diagrams. They show E, F then for 80' the G, LG, SG. Nothing about SF.


The only external difference between the 2H7 of the E & F with this 3H3 for SF is the choke handle lever was changed from straight up the offset.

A few Pics to show what I found in the Carbs upon tear down and what E/F look like


What I think I want to do is just put in E/F needle & seat and brass floats.

Maybe that was OEM for the SF. I don't know. Can't seem to find out definitively for sure. Just want to do it once ……..

For the guru's, what actually is different in this 3H3 79' F? Body appears to be identical to 2H7 of the E & F. Jets are all the same. Oh, only other thing is the Nozzles in the SF which are 16 hole 4 by 4's in Carb #1 & #4 with 10 hole Nozzle in #2 #3 for middle to be cooler. But what else is different 2H7 to 3H3?

Thanks,

Jeff