Topic: 064A carbs from what year(s)

[newday777]

I picked up a couple sets of carbs over the weekend at the Yankee chapter AMCA Swapmeet and Show.
One set is a 7A, the other is 064A roundtops.
I think the 7A are off of a K1?
Anyone know what year are the 064A set are off of?

The 7A are real clean inside, but the 064A unfortunately weren't put away well, look to have had damage from MTBE gas, white powder residue and have 1 busted float tower.

[newday777]

I don't see the 064A in the list of carbs

[HondaMan]

The 064a showed up in the late K4 and the K5, sometimes mixed in with 086a versions. The only difference I could see between them was the fancy plastic cap on the idle-mix screws and their extended screw heads (to hold those caps). It was supposed to keep the owner from adjusting the carbs more than 1.5 turns out or 0.75 turns out on the screw. The caps just broke and fell off by about 1980, though.

The 7A shows up in the F0/F1 sometimes, but there with just one of those tee-hose fittings for 1 petcock outlet. The 7A in the K1 bikes had 2 fuel input tees and plastic floats.

I can look thru my collection for an 064a #1 if you need it? I don't know for sure if I have one, though.

[newday777]

I looked through my bin and didn't have any 064A. I hadn't seen them before these. Yes do check and see if you do Mark.
I have a friend that has someone else who makes a new tower and uses a pin to set the new tower into the body. I'll have to talk with him to see his process and costs. I also have a set of 086A off the K6 with a busted tower that someone hacked a repair but the float doesn't set level with the repair.

[newday777]

The 7A set has brass floats. Did the 7A on the F0/F1 have brass floats or just the K1s?

[seanbarney41]

I think that chart has been discussed here before in some old posts...and consensus was its a misprint.  The 76f section called out 069a...I think that is supposed to say 064a.  I have never seen an 069a casting number on a cb750.  I have mostly seen 064a on 1976 built f bikes, but I have found them on k bikes as well, of course no proof that they were factory installed.  That chart also has other discrepancies from what I have seen, such as what was installed on F bikes built in '75...mostly 086a from what I have seen, but yeah, I have seen those other listed casting numbers too.  I have never seen a round top installed with anything but a 40 pilot ever.  Also this chart does not list jet needle and needle jet numbers, possibly the most complex part of the jetting equation.

In practice, I don't know that anyone has ever found any difference in the castings of any of the rack mounted round tops, just jetting differences...but are there slight differences?...perhaps in the air bleed passages? or the shape and contours of the venturi?  I dunno.
We do know that there were very many slight changes in engine specs from spark advance to cam timing to intake port cleanup, compression ratio, etc.  ...all possibly affecting jetting demands yet jetting varied little but different years and models ran very different.    I guess I just don't see the jetting changes coinciding with known engine changes.  It's all very mysterious.

[newday777]

Very true Sean.
These 064A have 98 Keihin mains in them. I don't remember seeing 98 main jets back in the 70s when I was parts manager.

[seanbarney41]

And ohh yeah!...thinking its just 064a and 086a that have the teeny tiny inlet screens on the float valve seats...

...and then those damn tiny screens turned up again in the damnedest place!...1987 cbr600 Hurricane!

[seanbarney41]

Very true Sean.
These 064A have 98 Keihin mains in them. I don't remember seeing 98 main jets back in the 70s when I was parts manager.

They got Keihin K stamp?  never have seen  main jet lower than 105 ever

[newday777]

Very true Sean.
These 064A have 98 Keihin mains in them. I don't remember seeing 98 main jets back in the 70s when I was parts manager.

They got Keihin K stamp?  never have seen  main jet lower than 105 ever

Yes. I was amazed. I don't have a good picture of it yet. Tomorrow.
I was thinking maybe the jets were out of a 550?

[newday777]

I enlarged and cropped the picture.
The pilots are 40.
I'll take a better picture tomorrow morning.

[seanbarney41]

Very true Sean.
These 064A have 98 Keihin mains in them. I don't remember seeing 98 main jets back in the 70s when I was parts manager.

They got Keihin K stamp?  never have seen  main jet lower than 105 ever

Yes. I was amazed. I don't have a good picture of it yet. Tomorrow.
I was thinking maybe the jets were out of a 550?

550 main jets press in with an o-ring and are held by the bowl pressing on those leaf spring thingies...no way they would fit a 750

[newday777]

OK scratch that idea. 550 weren't my bikes. Still aren't.

[newday777]

98 Keihin main jets. Just so you see it has them

[scottly]

I have a friend that has someone else who makes a new tower and uses a pin to set the new tower into the body. I'll have to talk with him to see his process and costs. I also have a set of 086A off the K6 with a busted tower that someone hacked a repair but the float doesn't set level with the repair.

Member Jim F can weld the broken tower back on:
http://forums.sohc4.net/index.php?action=profile;u=4044

[newday777]

I have a friend that has someone else who makes a new tower and uses a pin to set the new tower into the body. I'll have to talk with him to see his process and costs. I also have a set of 086A off the K6 with a busted tower that someone hacked a repair but the float doesn't set level with the repair.

Member Jim F can weld the broken tower back on:
http://forums.sohc4.net/index.php?action=profile;u=4044

Thanks Scott
I remember reading about someone who was micro welding towers.
Where is Jim located?

[scottly]

Jim is in Dacula, GA.

[newday777]

Jim is in Dacula, GA.

😊 thanks

[Don R]

   I think I stumbled on a set of 64A's and put them on the 76F bitsa bike that I re-built from parts that I had here, most of it came from my brother's parts stash and may have been assembled originally. They had the screens on the float valves also.
   I sold that bike last year.

[newday777]

I'll check to see if it has the screens. I haven't done a cleaning yet on it. Too many others ahead of it.

[HondaMan]

The 7A set has brass floats. Did the 7A on the F0/F1 have brass floats or just the K1s?

The 064a with the screens and brass floats were, IIRC, only on the F0 bikes, and not all of them, either. The floats went plastic in the F1.
Those screens were used on the bikes with the tank petcock without the bowl filter. They flow better (a little) than the petcocks with the screen.

There's a nice F0 around here (064a w/brass floats) that keeps reappearing in my garage every Spring to have the carbs cleaned [again]: the owner then takes it out for a short ride and forgets it until the next Spring. It hasn't had 300 miles put on it in 10 years!

[seanbarney41]

Just unloaded into my garage super early build F0, number 400 something, build date 1/75.  It's real dirty but ls mostly complete and under 20k on the odo.  Worst thing is someone swapped a 77/78k tank on and painted a really ugly shade of single stage red.  Got it from a junk hauler who was smart enough to get a title for $400  It will be fun to see what these carbs have.  I already saw the little plastic restrictor caps are gone from the pilot screws.  I think I got a set of the caps stashed.  Pretty sure this is gonna run fine with the carbs cleaned.  Almost hope not because a damn F tank is gonna cost more than the whole rest of the bike.

[scottly]

Worst thing is someone swapped a 77/78k tank on and painted a really ugly shade of single stage red.

Those were the ugliest tanks ever to foul the appearance of an SOHC, IMHO. Any tank would look better. Frank fit a 400F tank onto a 750, with only minor hammer work on the underside.

[seanbarney41]

Worst thing is someone swapped a 77/78k tank on and painted a really ugly shade of single stage red.

Those were the ugliest tanks ever to foul the appearance of an SOHC, IMHO. Any tank would look better. Frank fit a 400F tank onto a 750, with only minor hammer work on the underside.

yeah, I can't argue with that.  I got a couple cb200t tanks that somehow came into my possession...cant imagine they are gonna fit too easy, but who knows    was just looking at f tanks on eBay  How is total rusty garbage worth $600?!?  And then a clean or restored complete running riding cb750f tops out around $4500?!?!?

[scottly]

I always thought the F tanks, both 750 and 400, were the best looking. IIRC, the 200 tank didn't look bad? Give one a try!
Thread-jack over...