77 stock needle clip position

[Gabby]

Hi gurus. I have a 77 police model - CB750P7. The carbs are PD41As and the stock main jet size was 115. Can anybody tell me where the needle clip should be set for stock please? Nothing in the manuals is conclusive. I'm certain the carbs had never been apart until I rebuilt them and the clips are in the top position (ie leanest). Is that correct?

Reason for asking is it has a Wiseco 836 kit now, but exhaust and intake are essentially standard and there are no other mods. The bike is just about running perfectly with 125 mains (I may yet go to 130) and the pilot screw just a bit further out than stock. It's just about fully run in and I'm very happy with the performance. The only issue of concern is that the plugs are showing it's way too lean at anywhere from 1/4 to half throttle. So my next step is to raise the needles.

The carbs were fully rebuilt and I left the clips where they were at the leanest. I have just now worked out how to get the needles out without taking the carbs off or disassembling them so it's not hard to fiddle about with them. But it would help to know where they should be as stock and I guess I'll raise them one notch at a time.

This particular model seems to be a hybrid of a K7 and F2 so anything is possible. Thanks

Added: Just noted the number on the needle: F2051E. Standard I hope.

 

[amc49]

Needle = F2D51E-1...................the -1 being the needle clip position IIRC.

 

[Gabby]

Thanks for your reply. My needles are F2051E, so perhaps different. Can you tell me where you found the -1? And does that mean one from the top?

 

[Gabby]

I might be able to answer my question now ... found an old set of identical carbs with the same as my original main jets too, in a bin and checked the clip - also in the top position (#1). I think these PD41As with 115 mains were used only in K7s (could be wrong though) so I'll assume that's stock for mine too.

Another question if anybody can help please: given my engine changes, am I wasting my time moving the clip one position richer to start? It doesn't seem a big change if it's already running very lean at half throttle.

 

[amc49]

Moving more than one slot at a time and you commonly get bad result unless you ALREADY KNOW you need that much, which is a whopper move. The classic move with no knowing ahead of time is always one at a time. Quite a bit just that. Yes, top clip groove is pretty much 1 on most carbs.

You pretty much don't jet for plug color except at wide open throttle ONLY as the plug color is for max effort and load. The plugs may take a week or longer to color up at lower loads, the DOHC for sure is like that, they can run pretty light at cruise speeds. Depends on how hot the plug is too. Be guided more about how the engine is running, if that lean you will know it by lag, or miss or just doesn't pull up right. If you needed a two clip move you should be able to tell that EASILY by the way it runs, it would be that far off.

You consider the plug of course but color alone at lower rpm does not rule. I look at plug color as pay more attention to it with the higher percentage of heavy throttle you use, when you are cruising you are off max engine temp and the plugs can mislead then. The lower temps don't bake the fuel on insulator so much, unless engine is lean enough to show it by the way it acts, of course, that alone will raise the plug temp again. You say you are happy with the way it runs though, I'd go one clip only to get it to too rich so you know and then back off if needed. Sometimes one only and it will run even better but you won't know if you jump two, which usually is too much. At least in my experience, and I' have done a lot of jetting both car and bike 2 stroke and 4.

Yours and do what you will.

The D or O needle thing could easily be the way it's read especially if reading off the needle itself. Could easily be a misprint in text too.

K7 is a '77 model and where I got my info, the K7 addendum to the official SOHC service manual.

 

[Gabby]

Appreciate your detailed reply. Perhaps I am being a little impatient; I will raise it one slot only and try again. I guess I am a little worried about being too lean and possibly causing damage, but I wasn't aware that the plug colour is less reliable at lower throttle openings. Thanks again.

 

[dirtdigger]

The PD carbs must be different over there because over here the needle clip isnt adjustable, needles have a single groove and you have to shim them to change the height.

 

[Gabby]

I guess it was emissions rules and they didn't want anybody messing with carbs (well, that worked!). As far as I can find out here, the K8 here had a different PD carb and needles were fixed, but the PD41s on K7s have five grooves.