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Need some troubleshooting tips

Started by kingston73, Oct 06, 2023, 07:57 PM

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Bob H

#30
Wow, that is crazy how 1 and 2 appear to have a vacuum hose connecting them, then a separate connection joining 3 and 4.

My uneducated guess is that the one with the extra hoses was a California bike, and rather than cap off the "nipples" someone did that odd joining.

If you look at my thread https://nighthawkforums.com/index.php?topic=214.msg1642#msg1642
California Emission Late Model 750 91-2003

I had similar placement of emission related vacuum stuff on a 1993 Honda NH 750 and it is unique to California. The 49 state carbs don't have it.
Partzilla has your carb diagram, and part 23 is similar to the "5 way" connector I had that joins the carbs then to vacuum canister. When Partzilla lists a model as "AC" it is California, at least that is how they designate the NH 750 California bikes.
https://www.partzilla.com/catalog/honda/motorcycle/1985/cb650sc-ac-nighthawk-650/carburetor-assy-carburetor-link



I would just cap them off. if you want to poor-boy it, you can put a bolt in a vacuum hose.

1993 Nighthawk 750

kingston73

#31
I noticed the 2 different listing's and didn't know what it was for.  Never considered the CA only versions.  Any idea what the reason is?  How do those connectors change anything emissions related?  I'll probably cap them, just curious.

My plan now is to use the new/old set while I rebuild the original set. 

Bob H

Quote from: kingston73 on Oct 26, 2023, 10:38 AMI noticed the 2 different listing's and didn't know what it was for.  Never considered the CA only versions.  Any idea what the reason is?
Partzilla sells parts. The parts are different for California carb and related parts. Wouldn't matter if you were replacing a handlebar, but for the junk in that diagram there are parts not found or different than the 49 state version of your 85 NH 650.

Quote from: kingston73 on Oct 26, 2023, 10:38 AMHow do those connectors change anything emissions related?
If you have a set of carburetors for a California model, they would have connected to a vacuum canister.

The partzilla diagram for a CA 1985 NH 650 shows (part 23 above) a similar 5 way vacuum connector that joins the 4 carbs with the 5th tube going to the charcoal canister, as shown on the diagram for MY 1993 CA model below



Those carb vacuum lines go to an "evaporation control valve" then to the canister.

It is a rat's nest of spaghetti, and the cars of that era weren't any better as they struggled to meet emission standards with carburation (before Fuel Injection took over)
1993 Nighthawk 750

mollusc

It could also be that whoever rebuilt those carbs didn't quite know what they were doing with those bits and so just joined them together.
Or maybe they were originally on a CA bike that someone who didn't know what they were doing converted, and everyone else has just followed that lead since then.
1984 Honda Nighthawk 700S
2012 Honda NC700X
2005 Vespa GT200
1982 Yamaha Maxim 550 (sold)
2006 BMW R850R (sold)
1981 Honda CX500B (sold)

Bob H

I am not an expert on the 650 Nighthawk (although Partzilla shows the California model having those vacuum lines from each carb joining -> for the charcoal canister).

I do know that for the 91-2003 NH 750 sold in California it will have ALL OF THESE vacuum nipples (like the OP has on the extra set of carburetors).

This is how you can tell if late model NH carbs are California - the 49 state will only have a vacuum nipple on carb #2 that goes to the petcock.

1993 Nighthawk 750

kingston73

Mine has the vacuum line attached to carb 2's rubber boot.  I capped all the extra tunes and I'm going to try getting things running g today

kingston73

Everything's back together and it is running smoothly.  Now it's just cosmetics I need to work on, plus probably new tires.  In my link are the front and back tires.  Is the front from 2001??  Is the rear 2010?  They have lots of tread depth but if they are really that old I'll be replacing them soon.

https://imgur.com/gallery/x8ZpRUn


Larry Fine

Yep. The 36th week of '01 and the 19th week of '10, respectively.
'72 CL450
'73 CB750
'82 CB750SC

'96 CB750ST
'01 ST1100
'96 ST1100

kingston73

Yikes, that's what I thought but I didn't want to believe they were that old.  I'm pretty sure this was kept in a garage for years so that makes sense.  I've got 2 Michelin commander 2 tires on order.

kingston73

 Next question, I'm trying to get my carbs properly adjusted.  I thought I had them right but after letting them sit overnight the next time I started it the idle is now getting stuck around 2k after it's warmed up.  If I apply a little choke it drops down to 1500.  Choke off it rises again.  What does this mean?  Too rich?  Dirty carbs?  Something entirely different?  I currently have the idle screws at about 3 1/2 turns out.

mollusc

Did you do a bench sync before you reinstalled the carbs?
Stock mixture (not idle) screw settings for the 1985 CB650 are 2 5/8 turns out from lightly seated.  3 1/2 is probably way too rich.
1984 Honda Nighthawk 700S
2012 Honda NC700X
2005 Vespa GT200
1982 Yamaha Maxim 550 (sold)
2006 BMW R850R (sold)
1981 Honda CX500B (sold)

Bob H

#41
Quote from: kingston73 on Nov 16, 2023, 04:17 PM...the next time I started it the idle is now getting stuck around 2k after it's warmed up.
Can't you simply adjust the idle speed? Pulling the carbs means detaching cables, so it is like starting over.

The odd part of what you are describing is that apparently you didn't have a fast idle when you put stuff back together and first start it. Now you have a fast idle. Double check cable routing OK, not binding around steering area - and that the throttle spring is fully placing the idle against the adjusting screw.

The idle MIXTURE (not the idle speed) controls such a tiny little orifice of fuel, I wouldn't really focus on that too much - but the way to adjust that is called the idle drop adjustment. You adjust the MIXTURE. The Bench sync (or manometer carb sync) is an adjustment of individual carb  SPEED settings (idle speed).

1993 Nighthawk 750