Topic: 1982 CB650SC Slides question

[Pappy]

Still trying to figure out why this engine will not accelerate past 4500 in 5th gear. That equates to a little over 60mph.
I have another post on the carburetors and what all I have gone through and checked to date.
Beginning to wonder if the slides are not opening properly.
I know they move freely by hand and the "seal" is installed properly as in properly oriented.
What would I need to look for that would keep these slides from opening properly?
Feels like the engine is running out of fuel.
I have checked and have good flow from the petcock and through each carburetor.
Engine runs like a watch otherwise.
Any help is appreciated.

[fizzlebottom]

Every time I've had carbs and taken apart to any degree, I do 2 things regarding the slides:

• Look for any rubbing marks both in the bore of each carb and the sides of the slide pistons.
• When I reassemble, I push the slide pistons up and down with my finger through the intake side. Listen for a 'woosh' sound, indicating that they're moving air instead of just pushing through it. Alternatively, with the carbs assembled and empty of fuel, you can just invert them a few times and listen.

[Pappy]

Hey Fizzle!
Thanks for the tip. Have sort of done this. Before installation I did check the ease of movement of all four slides. Also checked the bores and checked for drag marks on the assemblies. Clean and no drag. All felt equal.
Still scratching my head here as you can see!
No vacuum hoses, ports or anything you can think of that I may be missing?

[scottly]

Do you have the stock airbox and filter installed? CV carbs are sensitive to the built-in restrictions in the stock intake.

[fizzlebottom]

Hey Fizzle!
Thanks for the tip. Have sort of done this. Before installation I did check the ease of movement of all four slides. Also checked the bores and checked for drag marks on the assemblies. Clean and no drag. All felt equal.
Still scratching my head here as you can see!
No vacuum hoses, ports or anything you can think of that I may be missing?

Remind me if you still have that pesky stock vacuum petcock. Also if your two T-joint hoses are connected as they should be. Aside from those, no extra hoses or anything. I honestly think this isn't carb related at all. I think your valve springs are shot. Weak valve springs is one of the things called out in the high speed performance troubleshooting section of the FSM. Now I've never actually heard of anyone having that problem, but I suspect they put it in there for a reason.

[Flyin900]

Interesting issue. I did read your initial thread and it seems you have done everything in cleaning initially on the carb bank and have some good knowledge of the carb set.
Both long shots here, yet worth a look. The carb tops do have a vented port in the metal pipe that sticks down into the slide and those should be open and not plugged. You can see the opening partway down the pipe, so shooting some cleaner and compressed air will verify they are not plugged.
Did you have the little brass tube (1/2" long) out that sits under the long emulsion tube that the main jet screws into and the slide needle passes through it? This tube should be sticking up into the carb throat slightly, if installed correctly. I don't know if you can get it in backwards, yet if so the system won't work correctly and the main jet would sit lower in the float bowl, since you would not be able to screw the emulsion tube and jet holder back into the tower correctly.

[Pappy]

Interesting ideas.
The two vent tubes are not connected. I do have the Tees between 1-2 and 3-4 and a tee coming up between those carbs and vented to the atmosphere. Is that a problem?
Flyin 900. Looks like another trip into the carbs to check that. I do know that I am well into the main jet system at the 4500rpm mark. You are absolutely correct about needing those. I do not remember them when I cleaned the carbs. I remember the emulsion tube that the mains screwed into. These were properly cleaned and re-installed. If I remember correctly they were more like an inch or better in length?

[Flyin900]

So the part I am referring to is in front of the emulsion tube down inside the tower that the emulsion tube screws into and is shown as part #2 on the Honda parts fiche and it is part of the needle jet set kit. It doesn't always come out of the carb body when you remove the emulsion tube and main jet assy. It is about 1/2" long when removed with an open barrel top which faces into the carb throat about 1/8" when properly installed and the closed over bottom section with the small hole that faces the emulsion tube. The needle assy from the slide passes down through this and into the emulsion tube/main jet area.

Sometimes these fall out when the carbs are being cleaned with the emulsion tubes removed and guys don't know what they are or where they came from within the carbs. If these were removed, or lost, or put in backwards, if that is possible, then you will have issues for sure.

[Pappy]

World's cruddiest weather right now. Waiting for it to dry up a bit before I dive  back into them. Solid rain today and we have the tropical storm coming around the bend to his us around Tuesday of next week.
I can tell you there were no parts that fell out or were left out. What I cannot tell you is that they were there at all when I bought the bike for my wife. We (she) never got to ride it hard enough to discover the issue.....if it was there then.
Things that make ya' go...........hmmmmmmmm

[Flyin900]

You maybe able to pull the carbs tops with the carbs mounted on the bike still. Sometimes you get lucky with a little fenagling to get them off of there.

That would allow you to remove the slides and peer down to see if the small brass part is present and installed in the opening in the bottom of the carb throat correctly. You could then also check the caps to ensure the vent hole is open in the tube inside the carb top.

Here is the inside slide area of a CV carb throat assembly, just not your SOHC CB650 version. The picture shows the small brass insert installed correctly at the bottom of the slide passage area. It shows about 1/8" or less of that insert protruding into the carb throat base. Ignore the small brass cone on the right of the picture, as it is the slow speed emulsion tube jet from this model.

[kerryb]

I couldn't find your other post so here goes...  my 82 cb650sc  would run great for a 1/2 mile, and then quit like it ran out of gas.  After removing the pods and putting a stock aibox in, it ran great!