Low RPM Stumble (Bog)

[budanddar]

This is Bud in Litchfield Park Arizona.
Starting my 1981 CBX after 2 years of sitting. Problem.....it starts fine but when the throttle is cranked it bogs down until about 4500 RPMs.
Have done nothing with the timing.
Rebuilt the carbs with Keyster parts and used Mike Nixon's fine manual for the needed help.
Valves were all set as per the manual. Compression range is 125-150 psi. Spark to the new plugs and wires.
The idle screws were turned out 2 1/2 times. The springs on the choke are very snappy and work well.
There was blue smoke for a short while initially but now it is fine.
Sorry if this has been posted before but I did search for more answers.


Thanks,

Bud

[NobleHops]

Did you pull the pilot jets Bud?

[heli_madken]

Rebuilt the carbs with Keyster parts

And did you use Keyster jets?

[budanddar]

I was very meticulous having never done the rebuild before.
The choke springs were very strong and worked well.
The springs on the throttle plates were the same....slam shut.
Replaced the Tee vents and the rubber sleeves between carbs.
Removed and cleaned the vacuum tops, installed new slide ring gaskets, and new needles.
None of the float bowl standpipes were cracked.
New float valves and needles.
New idle mixture screws.
New air cut valve.
Removed and replaced the idle jet with new.
New accelerator pump diaphragm.
New gaskets everywhere. Anything inside the carbs that were brass were replaced.
Bench synchronized.
I am a little afraid to run the motor more then a couple of minutes. Have a box fan on it between attempts.

Vote and then share your wisdom with me.

Thanks,

Bud

[budanddar]

I did use Keyster jets.

Bud

[bobcat]

Has it been sitting with fuel in the carbs for 2 years since the rebuild ?

[NobleHops]

Sorry if I am being tedious: You tapped and pulled the pressed-in idle jets? Further, did you empty the tank and clean it, and inspect the petcock screen? Are you using the 2 year-old gas, or the residue of it? Or are you using fresh gas? If old, can you swap in a bottle and try again? You might like to open the bowl drains and see the condition of the gas that flows out.

[daves79x]

In your searches here, you should also have found that you should never use aftermarket brass in these carbs. You should clean and reinstall all of your original jets, needles and float valves and seats. The aftermarket stuff is junk. Also, unless things have changed, Keyster kit rubber parts are not Viton. There are several sources for much better carb kits than Keyster.

It sounds as if you did not separate the carbs nor did you remove the pressed-in idle jets. The carbs need to come off again and be completely separated, cleaned, proper rubber parts installed, all circuits verified clean, bench synced, wet tested for leaks and accelerator pump function. Then and only then can they be re-installed.

The intake rubbers should also be replaced if they are hard, brittle or cracked.

Also, 2 1/2 turns out is to much for the mixture screws. Two turns is plenty.

There is no free lunch and there are no shortcuts rebuilding these carbs.

Dave

[bobcat]

Pressed in slow jets ? As I recall the 81-82 VB64A carbs had screw in slow jets, no?
The last 2 sets I did had screw in slows.

+1 Dave, never use aftermarket brass.

[JoeInTUS]

81 VB64A(A) carbs had pressed-in idle jets
82 VB64A(B) carbs had screw-in idle jets

[budanddar]

Dang you guys.........thanks for the help!
First to Bob, the gas is brand new.
Nils, the tank was pristine. took the petcock out and rebuilt it with a new filter and sealing plate. I did take out the pressed in jets. They were cleaned and inspected under a high powered glass to verify that was so. The gas is brand new and like I said..I was very particular on the assembly.
Dave, I did use Keyster. Followed two sources for the rebuild. First was Peter Rose's videos who uses Keyster and the other is Mike Nixon who may or may not use them. I separated the carbs and extracted the pressed in jets. New Keysters were put in. The parts, all, were removed and cleaned and or polished. The circuits were all verified to be free of blockage using a pressurized can of cleaner. Benched synced as per Mike Nixon's manual. Before the installation, I put gas to them. They leaked for 2 minutes and then stopped. I did not test the accelerator pump. Just put a new diaphragm assembly on. Hummmm? I will adjust the idle screws later today to 2 turns. Fellas, one other note, my unit has that vacuum system that stops the hydro lock condition. I have temporarily by-passed it by putting gas right into the 2 inlet tubes. The vacuum line to the #3 carb is been pinched off for this operation. Don't think this arrangement will harm what I am trying to do. The intake boots were in great shape and I carefully used some starting fluid around them to see if they were leaking. No engine rev so I am guessing I am good in that area.
JoeInTUS and bobcat, I used the method in Mike Nixon's manual by tapping the pressed in jet and extracting it.
I will give it a go again today with all of your advise. How long should I run it with this testing? I am concerned about overheating and have a box fan in the front of the engine blowing air by the fins. Thanks again for all of your time for addressing someone you don't even know. It is inspiring.
Bud in Litchfield Park Arizona.

[heli_madken]

Hi Bud,

Assuming everything electrical checks out, 2.5 turns I wouldn't think would cause a huge issue dependent on where you live of course. Chances are with a new diaphragm in the accelerator jets and assuming you cleaned all the carb passages this should be ok.

To me it will be the new Keyster brass. I haven't got any experience of using Keyster jets on a CBX so I dont know what the direct symptoms would be. I havent got any experience of using them because I learnt my lesson long ago. I spent weeks trying to fix a stumbling off idle GL1000 on which I had completely stripped and rebuilt the carbs, fitted all new Keyster jets and good quality Randakks rubber components. I was totally baffled and it was only when I went back to the original jets the the problem magically went away. Thankfully I had kept the original jets.

I know its a lot of work but if you have the original brassware I would go back to them

[bobcat]

Hi Bud, besides the aftermarket brass my guess is that the accelerator pump nozzles,
the short little tube that spray fuel into the carb throats are likely clogged
and they are hard to clean due to the tiny spray holes. That's why they must
be tested while the carbs are off the motor.

I would clean all the old brass and reinstall it like Dave and Heli suggested.
Something I found that works very well for jet and passage cleaning is Mercury
(brand) power tune or Sierra. Both are used for decarbonizing 2 stroke motors
and can be found at any boat or marine supply store. In a small jar or container
soak the brass, needles too for 6-10 hours in it and it will dissolve anything not
metal and the pieces come out looking like new. If you spray it into the accel.
pump sys. via the hole that feeds it, it will easily clear the spray nozzle holes.
Same for other small carb passages. It doesn't take much to work and it works
better than spray carb cleaner. I use either carb cleaner or PJ1 Super cleaner to
do the final rinse.

I'm sure Mike Nixon's book covers accel. pump adjustment but double check that.

We might not know you personally but I hope I can speak for the others here in saying
that you, as a dedicated CBX owner are family here and we look after family !
I learn something every time I can help or contribute to solving a problem.

PS; another possibility is if you haven't ridden it you might not have let it warm up
enough to accept much throttle.

This is assuming everything else with the carbs is correct.

[budanddar]

I am honored to be apart of such a giving group!
Thanks for all of the good stuff. It is vote day and in between results I will go out to the garage and give the old dog another try.

Bud

[daves79x]

Couple of other things - Did you verify that the slides are smooth in the tops and don't stick or hang up? I'm not at all clear just how the bike is actually running. Does it start and run on all six right away? Can you take the choke off or nearly off fairly quickly? You must not let it fast idle on choke in any case. These can be cold blooded, but the proof is in getting it out and riding it to really warm it up. It is impossible to do that just sitting in the garage. I've had guys complain about not taking throttle after 'warming it up'. Turns out it was just in the garage. You can't tell really anything until you ride it and warm it up vey well. 5-6 miles at least.

Do not try to further evaluate until you can ride it. Now if it won't hardly run at all after a cold start, then that's another matter. Are you positive you don't have any plug wires crossed?

Dave