82 CB650 Carbs Run Rich

[arnoldy]

Hi guys,
Just bought a nice 82 cb650 (10,000 miles) for not much. Bike had been sitting and would not fire a lick. Gas tank and inline filter are clean and fuel flows strong at the carbs. Removed, disassembled, and cleaned carbs. Idle jets and some air passages plugged. Main jets and carb bowls were pretty clean. PO produced receipt for carb kits installed in 04. Floats and needles and needle seats looked good. Checked float levels per Clymer manual (non-adjustable). Upon re-assembly carbs noted to be missing the banana-shaped gasket that goes below the "air jet cover" (that's what Clymer calls it). This is the hard rubber part located below the vacuum cylinder and has a tang which extends into the main bore of the carb to keep the vacuum cylinder from turning. Since you can't buy this gasket without buying a carb kit from Honda ($42 x 4) I opted to assemble the carbs and give it a shot.
Bike fired up immediately but idled rich (some black smoke out the exhaust). No amount of idle screw adjustment makes much difference. It idles slightly better with the screws ALL THE WAY IN. I know that isn't right. Bike would not rev over 5,000 rpm on the road, seemed rich, and was bucking and snorting the whole time. I removed the airbox cover and air filter (new condition) and tried it again. The engine was MUCH happier but still rich at all rpms. This time I could get it to 8,500-9,000 rpm but it is still bucking with some backfiring through the carbs.
Conclusion that I come to is that I NEED these missing gaskets! Carb model # is VB44A. I am about to buy a used set of carbs off Ebay for $60 or so. The carbs I am bidding on are VB44C's off an 82 Nighthawk. I assume these carbs are jetted differently (mine are #120 main jets) but what I am really bidding on are the missing "air jet cover gaskets" which I am gambling would be serviceable and the same.
I know this has been long-winded but I wanted to give as much info as possible. No, I haven't pulled the plugs (need to buy a socket), checked timing, valves, or cam chain yet but I will. Thanks for all suggestions!

Dan A

[Volker_P]

Welcome here!
Sorry I do not know much about the CV carbs which you obviously have. But I think that everything that may impact the pressure conditions for the vacuum cylinders should be allright or at least present before you can expect a good running. So I would agree that you urgently need these gaskets. If you have an old gasket as a sample, maybe there is a chance to make the parts yourself from fuel-resistive rubber. As soon as you fixed it, check out that you are not too lean then. Maybe previous owner already did some things to overcome the problem somehow. Running rich is not that problematic like lean which may cause severe overheating damage. Keeping an eye on the plugs is important until you know you are safe. BTW, new plugs are a good investment for a bike that sat long and you know nothing about. You should also be sure that it runs on all four, just feel whether all pipes get hot.

[arnoldy]

Bought the used carbs off e-bay. Installed the missing gasket in each carb. To my surprise the bike doesn't run much different (still rich). Bought socket and 4 new plugs. Old plugs indicated extremely rich mixture. Bike almost runs decent with air filter removed but still rich. Verified choke is full open. The carbs I bought (VB44C's) have #118 jets. My carbs (VB44A's) have #120 jets. 118 jets are smaller than 120 jets right? I am thinking of putting the#118 jets in my carbs. That still wouldn't account for being rich at idle though. Any suggestions are appreciated!
Thanks,
Dan

[Volker_P]

Interesting, probably only the new plugs did the slight change. Maybe there is some some leaky vacuum hose to the vacuum cylinders?
Also check ignition timing before you proceed.
Other ideas:
Did your carbs and the ebay ones have the same size idle jets? I agree that 118 vs. 120 mains would not solve your problem unless the 120's you have were manipulated by a PO.
If you use resistor plug caps and/or cables together with resistor type spark plugs (I guess only plugs should be resistor type) you may weaken your ignition enough to make it behave and look like rich.
Good luck!

[Ibsen]

Welcome to the forum.

Have you checked the float heights? That is the first setting that has to be correct before you start playing around with jet sizes. And doesn't the CV carbs have plugs that are sealing off the pilot jets from the float bowl? If they do, check that these plugs are sealing properly. And there are a couple of non removeable air jets located under the vacuum pistons (if I remember correctly) that might needs to be cleaned. They are best cleaned by using a spray carb cleaner and compressed air.