Topic: '75 CB750F0 064A NEEDLE POSITION-DIFFERING ANSWERS

[Buttmask]

So I'm getting differing views on the needle position on the 064A carbs from doing forum research. To my understanding the 064A and 657A are basically the same with the difference being the air screws.

Most people are saying the needle position is center on the 064A carbs, this chart that is always called upon is saying it's 4th position.

http://www.hondachopper.com/garage/carb_specs/carb_specs.html

Which one is it???

[lrutt]

Are you 100% stock or have you modified intake or exhaust in some way?

[Buttmask]

Running an airbox. But I have an open motogpwerks Yoshi-style pipe. Stock main and idle jets.

Getting lean conditions, even with the air screw only 3/4 a turn out. Mostly tons of popping on decel. My needle is in the middle position currently.

[Buttmask]

I've tried that, and it was nothing but too rich. Everyone kept telling me to bump up my jets, but it made me foul plugs like crazy. I went back to stock and it's the closest I've been getting it to run well. I'm gonna guess with my needle in the center, it's still too lean, considering that chart says it should be 4th. But I'm just getting differing views on where exactly it should be.

[Buttmask]

Yeah that's why I'm trying to figure out what exactly is the stock needle setting, and then go from there as far as upping jets and all of that. Because if the needle setting is actually 4th position, then center is lean, which would probably explain why I'm having lean issues. Just looking or input on stock settings for needle position of the 064A.

[Garage_guy_chris]

Im also dealing with a set of 064A carbs currrntly. I just checked how they were set up and I found the following
pilot #40
Main #105
Needle 3rd position "27201" needles

im not getting very far with research on these particular 064A carbs either I think the 657A's are close enough that anything but idle mix screw adjustments should be the same. Its interesting your running ok with 105 mains and the motogpwerks im gonna be setting my carbs up within the next week or two for my engine with a similar exhaust. Unfortunately I also have a 836cc port and headwork and a cam. But I was planning on starting my jetting at
Pilot #40
Main #120 or #125
Needle 4th

[Buttmask]

Yeah I really think the 105 jets are fine for mine, and the center-recommended clip position is just too lean. 4th position is stated on that chart I linked to. Which from my understanding is one below center, a richer position. I've been told my several old timers that even with an open pipe, you shouldn't have to up jetting if you're using an air box, and maybe just a little richer on the air screw. I'm gonna try the 4th position and get back since I continuously get back and forth info on the exact stock needle position of these carbs.

[Jerry Rxman Griffin aka MuthaF'er]

From a guy that bought his new - center is stock position.

[Buttmask]

Jerry, is that for the 064A carbs? Because I know the F0 came with more than one type of carb

[754]

4th position from where?
 Center I can understand..

[Buttmask]

Seems like no one understands why I'm referring to 4th position as a possible stock position. Here is an image where I circled exactly what I'm referring to on the hondachopper.com chart that everyone refers to for carb settings.



I've been told the 064A are basically the same carb as the 657A, as you can see JN is stated as 4.

here again, is the link to that chart. Am I to assume info on here may be incorrect?

http://www.hondachopper.com/garage/carb_specs/carb_specs.html

[greenjeans]

I'm running the same set-up on my 75 - also with 064s.  Stock airbox with a K&N filter.  I have my clip at the 4th position (1 from the top) and I'm running new Honda 40 slow jets and new Honda 112.5 mains.  Airscrews are 1 1/8 turn out.   Needles are original to the bike, at least I think they are.   I was going to try some 115s but got pretty darn close to a good tan, so I stopped.  My plugs are a pretty good shade of tan leaning toward rich - barely.

I was having more trouble with my low speed/rpms than WOT.  The new 40s and lowering the needle 1 notch cured that.

[Jerry Rxman Griffin aka MuthaF'er]

Jerry, is that for the 064A carbs? Because I know the F0 came with more than one type of carb

I'm curious where you got this info?? Mine are January 75 carbs but they are at home in my basement. I'll take a peek when I get back after work. Plus I'll open my Honda Service Manual and my Honda Parts Manuals. Not sure but my owners manual may have info too? Clymers, Chilton plus one more too 

The -392 carbs use different needle/needle jets. I happen to have 4 NOS -392 needle/needle jet kits too and I can look for needle ID numbers on those and my originals. Could be where the confusion comes in. Keep in mind that the 75 F0 was produced from January to the first week? of April so they couldn't swap too much around  .

Bottom line - factory settings may be irrelevant due to age, wear and tear, altitude, intake, exhaust, kits, etc but they provide the best baseline for YOUR bike to make necessary changes. 

[Jerry Rxman Griffin aka MuthaF'er]

...and lowering the needle 1 notch cured that.

And that means the clip physically went up one notch. Just so everyone is clear-

Wear on the needle and the needle jet probably opened it up more.

[Buttmask]

Jerry, again, look at the chart I posted. According to it the 75 F came with possibly B750A and 7A, 657A, 657B and 064A. I too have a January 75 F. Again, the chart states needle position for the 657A(and presumably the 064A) at 4.

Also, I too recently found a set of NOS needles and needle jet holders.

[Garage_guy_chris]

Lots of interesting information regarding these carbs. Its kinda moot point how they came from the factory. The jetting may have needed small adjustments depending where the bike was sold or mods done through its life. My 064A's supposedly came on my K4 engine number 2350454 I donno if they are original to that engine or not. Bottom line is there in very good condition so they are getting used.
There is no definative setupnon how your carbs needs to be set up. The only way your gonna get there is to swap brass test and repeat with a little help from us.

[754]

If a bike was sold in or near Denver, it may have had different jetting than a sealevel bike..
 I will probably. Follow Hondamans recommendation,  it's one of two positions.
 I am looking for relatively. Decent mileage..

[Jerry Rxman Griffin aka MuthaF'er]

Frank, the Japanese Honda guys didn't have a clue where a bike would go within the US. If it got adjusted it would be by the dealer IMO. I had 38 slows installed at my first dealer tune up in spring 76 at an elevation of under 500'.

I have researched 3 sources so far: a 1975 Honda Parts catalogue HC43212 P8175 1st edition, a 1993 Honda Parts catalogue Second Edition 133920M printed from my microfiche (both these first 2 reference 1975 and 1976), and a Honda Shop Manual with supplements up to 1978.

MY carbs are 064A.

All 3 list ONLY one carb part number for the complete unit 16100-392-004; only one part number for the needle sets 16012-392-004

The Honda Shop manual states on page 225 Needle Jet - 3rd notch and on page 247 'setting mark" - 064A

Don't know if you assume it is not correct but I do. I have seen other inconsistencies on that site also. I don't believe that they came with anything other than 064A's unless there is another original owner that can show otherwise.

Anyway, the correct settings are those that make a particular bike perform the best. New is one thing, 40 years later is another.

[754]

I am not disputing that is not correct.
 I do remember reading that they made changes for altitude, maybe not everywhere
 I just want to get to the top or bottom of things..like needle clips 4 from bottom or top.?
 I will just go by Marks book..

[lrutt]

First off: have you verified the float hieght?

Second: Are you using NEW jets that you know are good. Not old jets that might have been hogged out by some PO cleaning them with a drill bit.

Third: How many miles on this motor? and are these the stock carbs to this motor? IOW, you are sure the needles are relatively good and not all worn from a bike with 80k miles or so.

Ditto what everyone is saying regarding the mains. 1 up on those should not hurt you. When you say rich, you've verified this by pulling plugs and they are black?

So you say you have a stock airbox, do you have a stock paper filter? how old is it? are you flowing adequate air in? Are you sure your chokes are all the way off? Put the 110's in and run without a filter, what do you get? What about your timing? spot on at full advance? Old plugs or new plugs? what type and what heat range?

[jonda500]

Frank - 4th position is from the tip of the needle. One notch below th highest groove on the needle.

so to be clear... looking at the carbs right way up, the needle clip slots are numbered 1 to 5 with the bottom slot being #1 and the top slot #5? (I always thought they were numbered 1 to 5 starting at the top!??)

[Buttmask]

I thought it was the other way around. Have always gone by this which has been posted here many a time.

[754]

I think this is where half the the problem comes in.... You hold it by the big windows to re and re them, not sure why anyone would mention the tip.
 Then a chart gets posted without specifying from which end..
So to be clear please mention which end you count from..