Topic: 1980 CB650 STANDARD - ISSUE

[Rider39]

CV CARBS.

HI ALL,

Just got a barn fined with 619 miles on it.  Cosmetically in horrid shape, it was kept in an 18 wheeler trailer, so it was susceptible to the  temp and humidity changes  here in New England.  All the chrome & aluminum have severe oxidation/rust.

Be that as I may, I've cleaned the tank out and coated it with Caswell, removed the vacuum operated gas shut off, overhauled the carbs, replaced the mouse house air filter, new spark plugs and gave it a compression test, which turned out just fine.

My issue is that while riding it doesn't want to (won't) go over 4,000 RPM while in gear.  It will rev up to red line in neutral.  It runs fine, in gear, under 4,000 RPM.  Knowing nothing about the CB650, I'm assuming it's a crab issue, but wanted to see if anybody might have run up against this issue and could lead me in the right/different direction.

Thanks -------------- Josh

[HondaMan]

"...rebuilt the carbs..."
Did you use all Honda parts, or something aftermarket? There is absolutely NOTHING aftermarket that fits those carbs properly, and the result can be exactly what you describe.

[scottly]

My issue is that while riding it doesn't want to (won't) go over 4,000 RPM while in gear.

Is it the same 4,000 RPM in all gears, or does it rev more in lower gears than higher gears? Are all four exhaust pipes spit sizzling hot? What do the spark plugs look like?

[seanbarney41]

Make sure the ignition advancer is not stuck

[Rider39]

Thanks ALL ! ! !

I verified the ignition advance was working properly, but I didn't verify with strobe, I'll do that.

The carbs were in good shape considering they sat for 45 years, luckily the gas was shut off and the vacuum valve also was working.    I just replaced all rubber parts, BUT I'm going back in and see if I might have screwed something up.  The tank was nothing but "varnish" and rust.

We'll see.

[MauiK3]

Fuel delivery, blocked jets, bad plugs?
Just thinking

[fizzlebottom]

If you have an '80 CB650, it should not have CV carbs unless someone replaced the original PD carbs with VB44 carbs. You could verify whether it is an '80 or '81 by looking at the tag on the frame.

The VB44 carbs are extraordinarily easy to troubleshoot, but can be finnicky to clean. Here's what you need to do:

• Measure the non-adjustable floats using a float gauge to see if they're in spec. If not in spec, replace with the expensive OE floats.
• Blast every single orifice, especially slow jets, with carb cleaner AND compressed air. Both look for and feel for the other side of whichever hole you're blowing out.
• Do. Not. Use. Aftermarket. Jets. #35 slow, #120 main (or #118 if '82 VB44C carbs).
• If you removed the pilot screws, you need to make sure you reinstalled them correctly along with the spring, washer, and o-rings
• Make sure you installed a fresh accelerator pump o-ring. They are tiny and notoriously easy to lose.

Unless you messed with the fast idle cam, that's pretty much it. The other big thing that goes down on these carbs is the 3-way joints between 1/2 and 3/4. They are not critical. Randakk's sells a set for the CBX which sure looks like they'll fit the VB44A/C carbs, but I haven't tried them yet. If yours are gone, you can either let it be or just kinda plug up those holes and I don't think you'd have any problems.

Oh, and make sure your air filter is new.