Finalizing tuning. Some carb bits and questions.

[RJ CB650]

This relates to previous talks. My main bike is a Nighthawk, so my good mood bike is the CBX. Since getting it last year, I have been doing more and more services on it to get it running. With feedback, got most of the bugs worked out. Here is where I am at and looking for final advice.

1982 CBX usa model.

Done so far:
1. Full carburetor rebuild minus separating apart
2. New fuel lines and fuel system cleaning
3. Ignition inspection and mechanical timing

What needs to be done still
1. Would like to light time, but cannot find in the honda service manual if doable.
2. Replacement of wires and plugs

Why in carburetor section?

3. Replace accelerator pump and Air cut off diaphragms.
4. Rejet the low speed jets. (Or is it a needle issue?)

The first to will be done no matter what. The accelerator pump had rust on it when I cleaned, and the air cut had a slight crease which will eventually leak. Yeah, should have replaced when off, but could not locate replacement at the time.

The low speed jetting is something really think is needed after the others are done.

Symptoms:

Under more open throttle, even lightly applied, there is hesitation and roughness in the 3000-4500 range. On rebuild, it had 50s, set back to 35 for now. From the system when I got the bike it had a K&L air filter plus it has a more performance oriented exhaust it seems. Plugs do not show leaning, but it is richer at idle, and possibly not lean under lighter throttle so tough to call. In addition, altitude here is 580m (1900 ft) so that would mean I need it leaner.

It is so close to being nice and smooth. This one little issue though, just gotta track down the cause. Is it worth trying the 50's back in with near stall hesitation or is there some other common change jet on stock? Could it be a bigger issue could be at foot from your collective experience?

[EMS]

What needs to be done still
1. Would like to light time, but cannot find in the honda service manual if doable.

This is the regular procedure called "Dynamic Ignition Check" on page 3-5 in either the early model or 81/82 service manuals.

[spencer]

I am not the expert here, but from what you said, I think you are due for a more complete carburetor rebuild. Your accelerator pump is probably not working, causing the stumbling, and the low speed jets could be causing trouble too. While you're at it, separate them and replace all of the o-rings too. It's only a matter of time before they start to leak. Other more knowledgeable people will probably be along soon to give you a better idea of what needs to be done.

[RJ CB650]

I am not the expert here, but from what you said, I think you are due for a more complete carburetor rebuild. Your accelerator pump is probably not working, causing the stumbling, and the low speed jets could be causing trouble too. While you're at it, separate them and replace all of the o-rings too. It's only a matter of time before they start to leak. Other more knowledgeable people will probably be along soon to give you a better idea of what needs to be done.

Yeah, was considering that for the fuel connector o-rings. All internal components had been cleaned and done. I just really hate doing those flared screws holding the butterfly plates in.... I am thinking in the end might actually send them out for a 100% full rebuild considering the money that will be spent on the suspension.

This is the regular procedure called "Dynamic Ignition Check" on page 3-5 in either the early model or 81/82 service manuals.

Will re-check my book tonight, Thanks

[daves79x]

If you have all the stock ignition components, static timing is quite good enough. This assumes you've verified that your advancer is free and able to do it's job. It should really be taken out and cleaned and lubed. But your running issues are most certainly carb-related. Agree that you should separate them and replace the O-rings, or you'll be doing it when you least want to. Stay with the #35 low-speed jets and make sure all idle circuits are clean and flow freely. Guessing some are still plugged. You need to assure that your accelerator pump is working properly. Did you do that on the bench when testing them? You did wet test them? Are the float heights correct? The K&N drop-in isn't my favorite set-up. Much better is the Honda paper one. The K&N causes a lean spot in mid-range. Your bike will also benefit from shimming the needles .020 inch (where have I read this before?)

There are so many little things to get right with the carbs and they are what still needs attention.

I'm also assuming you thoroughly cleaned out the gas tank? If not, you just turned rusty gas right back into the carbs, filter or not. The tank HAS to be clean.

Dave

[RJ CB650]

If you have all the stock ignition components, static timing is quite good enough. This assumes you've verified that your advancer is free and able to do it's job. It should really be taken out and cleaned and lubed. But your running issues are most certainly carb-related. Agree that you should separate them and replace the O-rings, or you'll be doing it when you least want to. Stay with the #35 low-speed jets and make sure all idle circuits are clean and flow freely. Guessing some are still plugged. You need to assure that your accelerator pump is working properly. Did you do that on the bench when testing them? You did wet test them? Are the float heights correct? The K&N drop-in isn't my favorite set-up. Much better is the Honda paper one. The K&N causes a lean spot in mid-range. Your bike will also benefit from shimming the needles .020 inch (where have I read this before?)

There are so many little things to get right with the carbs and they are what still needs attention.

I'm also assuming you thoroughly cleaned out the gas tank? If not, you just turned rusty gas right back into the carbs, filter or not. The tank HAS to be clean.

Dave

Stock ignition components but the.... brain short here, cannot remember its name, but the equal to the points, the black induction disc on the right side with the advancer... Anyways, it was full on advance when I got it. I set it to align the markings, but still want to ensure it is workign correctly. The advancer is nice and clean and smooth operating.

All the passages were cleaned and check for flow last year on disassembly, but doesn't mean they still are. Tank was clean and all free flowing. On topic of tank, one thing I have done with my older bikes, but not this one is to have a rust neutralizing coating put in. But cannot be done on bikes that have certain internals. The CBX has a standard petcock, can these tanks get coated?

Checked accelerator pump for operation on bench, but doesn't mean I did it right. It could be off a little. Didn't do the wet test. Bad me.

Air filter, I dislike K&N just out of operational principles. I plan on getting a proper filter soon as well. The same power band issue does run slightly better with a little choke further leaning me over to the lean operation side.

Floats are exactly set to manual float heights.

Lastly, the needle shim. I am going to actually ask a second question on this part. By shimming the needle, I assume you mean the "washer mod" people like to talk about? On topic of needle height, that gets me thinking. The carbs had been gotten into and rebuilt before I got the bike. Anybody have exact measurements on the needle so if I have them apart again, I can compare?


Overall, that advice is a very good start. Will go back to basics, timing and the filter, my ignition wires since I am thinking number 3 wire is getting bad. Do a re-sync on the carbs. From there, I can look at the carbs and plan to have a professional rebuild. I rebuild my own carbs, but I was being pretty conservative on this bank of carbs. It is decided. With the left slide tube in front fork potentially bad (looks like a vertical groove) the aftermarket exhaust I dislike, and plan to replace the air rear before it goes, getting a full professional rebuild should just be matter of fact.

Thanks guys. Bike has more sentimental value above all else so if it means spending extra to ensure it is flawless, so be it.