Topic: 1980 cb650c Head/carbs

[weltzing]

After measuring the intake on the head of my 1980 cb650c the intakes are spaced differently from the spacing on the carbs...why in the heck did they do that and still have straight carb boots?.....Now the middle two carb boots have to be angled and almost impossible to get a good seal on them, unless I have the wrong carb boots?? any help here?

Thanks

[onepieceatatime]

On my 1980 they are straight. The 1981 and 1982 are different carbs/ head spacing. If you have a '79 or '80 head and '81 or '82 carbs, or an '81 or '82 head and '79 or '80 carbs, they wont match up.

[cb650]

Yes when the carbs changed the head changed.   many threads on it.

[weltzing]

well I have a 1980 and have pd slide carbs. Does anyone have a picture of this because if I remember correctly If I measure outside to outside both are 10 inches. Then when I measure from #1 and #2 .and then between #3 and #4 its 4 1/2, But on my carbs its 4 1/4. Ok so not much of a difference but yet it is because the middle ones still do not go on all the way...

[kslrr]

Give us a picture of the top of the rocker covers.  That will indicate the year of the head.

[weltzing]

Well I am away from the bike atm, but here is one similar that is on ebay

http://www.ebay.com/itm/Honda-CB650-CB-650-CB650C-Valve-Cover-Rockers-Shafts-/400132684433?_trksid=p4340.m185&_trkparms=algo%3DSIC.NPJS%26its%3DI%26itu%3DUA%26otn%3D5%26pmod%3D110680330268%26ps%3D63%26clkid%3D7610322691661079579

[weltzing]

I am pretty sure it's the correct head, but why don't #2 and #3 carb boots go straight onto the head, mine are clearly offset about a 1/4 inch and the boots are do not compensate for that which leads to air leaks.
Please Help???

thanks

[cb650]

Give us a picture of the top of the rocker covers.  That will indicate the year of the head.

How is that?

[Hush]

The early model CB650 SOHC4 had mechanical carbs and straight carb isolators (what you are calling boots) if you line the carbs up with the head without the isolators do they line up?
If so I'd say you have the wrong isolators.

[trueblue]

I have a 79 and an 82 in my shed, on both the carb boots go straight into the head, the carb boots on the 82 are shorter than the 79, I'm not sure about the diameters of them, I currently have the carbs off of the 82, but I'm not pulling them off of the 79 to compare but it sounds like your bike has the later model head on it.

[davesee]

i have an '80 with '80 carbs and they line up pretty good. you have to wrestle a bit to get 'em on there.

as stated though, '81 and on have different head spacing and different carbs.

a picture is worth a thousand words here.

[weltzing]

Without the carb isolators on they do not line up. #2 and #3 are a little off so when I put the isolators on they have to be at an angle to go onto the head. The carb isolators that I have are pretty short, I would say (just estimating here) 2 1/2 inches long....They have and arrow and then the numbers 460 on them..It would make sense if they were too short because the air box would go on much easier if I had longer isolators....

[weltzing]

If I forgot to mention, they are the PD style slide carbs

[Mainerider]

Hi Grant,
It's Joe. Is it possible your original carb rack was disassembled at some point and misaligned during reassembly? If your carb Id number matches the number on the rack I sent you then you definitely have the right carbs. Also, this doesn't sound like your issue but just FYI fully seating the carbs into the isolators takes a good amount of force. First lube the inside lips of the isolators, then  grab each end of the rack and wiggle/PULL  towards the front of the bike (get in front of the engine , grab 1 and 4,and pull towards you-you get much better leverage this way). Even then, carbs 2 and 3 usually need some follow-up pulling forward to seat them fully. You know you're in fully when you feel the carbs "pop" into the step located in the isolators. It takes some true effort.

[weltzing]

Hey Joe,
I did take the plate that holds the carbs together off when I cleaned them, but it only goes on a certain way and is properly fit and tight to the carbs....I do know it takes alot to get those suckers on there, I also used a heat gun on the boots to soften them up more to push on there, but I think the next step is to get some new carb boot isolators. They are starting to get pretty hard and some of them are cracked on the edge so might as well invest in them now and do things right. Do your isolator boots have #460 on them? Also on the bottom there are numbers, I have 1, 3, 3, 6 or something like that...

[Mainerider]

Hi,

Yes, 460 is the correct part number.  Do you have the arrow on each isolator aligned with the rib at the top of each isolator intake port?

[weltzing]

Yes I do, they are just angled soo much that the carb isolators don't go on far enough. I'm going to call honda and order some new boots though

[kslrr]

Give us a picture of the top of the rocker covers.  That will indicate the year of the head.

How is that?

The outside valve adjustment covers are different between '79/'80 and '81 engines.  The '81(?) engine (CV carbs) says 650 on these covers.  I've been away from my bikes for 8 months, so I can't remember.

[trueblue]

Your engine is obviously not an 80 engine, it is meant to have cv carbs on it, the carb isolators on the pd's are about 2 to 2 1/2 " on the cv carbed engine they are only about 1 1/2 long.  The rocker covers may not be conclusive as they are interchangable, basically you can look at it one of two ways, you have the wrong carbs or the wrong engine.  The ports on the head and the carb throats should line up, give or take a millimetre, if they are off even 1/4" they won't go on.

[cb650]

Give us a picture of the top of the rocker covers.  That will indicate the year of the head.

How is that?

The outside valve adjustment covers are different between '79/'80 and '81 engines.  The '81(?) engine (CV carbs) says 650 on these covers.  I've been away from my bikes for 8 months, so I can't remember.

No the 79 is the only year they have SOHC 650 cast into them.  They do fit on all the other 650's.  I have them on all mine.

[kslrr]

Give us a picture of the top of the rocker covers.  That will indicate the year of the head.

How is that?

The outside valve adjustment covers are different between '79/'80 and '81 engines.  The '81(?) engine (CV carbs) says 650 on these covers.  I've been away from my bikes for 8 months, so I can't remember.

No the 79 is the only year they have SOHC 650 cast into them.  They do fit on all the other 650's.  I have them on all mine.

I stand corrected.  I have an '81 bike with the '79 engine installed and I have the '81 engine as well with a busted case due to a thrown chain.  Sorry for hijacking this thread a bit.

[weltzing]

So question is why are my carbs not lined up exactly as everyone else's?..everything is stock the carbs are the correct ones but yet the two middle carb boots have to be angled soo much that they are at an angle on the head so it doesn't seal correctly....Joe says I have the correct boots too

[trueblue]

So question is why are my carbs not lined up exactly as everyone else's?..everything is stock the carbs are the correct ones but yet the two middle carb boots have to be angled soo much that they are at an angle on the head so it doesn't seal correctly....Joe says I have the correct boots too

Ok I went and measured my carbs, the 79 with PD carbs are 9 1/4 inches (this one was a little hard to measure so may not be quite accurate) centre to centre of 1 and 4, 3inches centre to centre of 2 and 3.  The 82 with CV carbs are 9 inches centre to centre of 1 and 4 and 3 1/2 inches centre to centre of 2 and 3.  If your inner two boots aren't lining up YOU HAVE THE WRONG CARBS FOR YOUR ENGINE someone has more than likely fitted a later model engine to your bike.

[faux fiddy]

It would be nice to see someone  post what matches what for top ends in FAQ's, especially mixing years of 650 with 500 and 550 top ends.

It would take someone whose been around them all for sure.

[Hush]

And to think a few years ago we didn't have enough CB650 guys on here to make a thread up lol.