Low RPM Stumble (Bog)

[budanddar]

Thanks for hanging with me on this Dave.
I posted before about the plug firing order. The shop manual has 3 different configurations that conflict each other. Had a great response on the correct locations. 1-6 on the first sparker 3-4 on the second and 2-5 on the third.

I did take the tops of the carbs off and all of them moved them up and down simply with gravity.

Today I turned the idle screws in 1/2 of a turn. Wow, the center 2 are hard to get at. Anyways, the bike starts up well and fires off immediately with the choke lever turned to the middle of the bike. The RPMs are about 4000. When the choke is turned to the outside of the bike, the unit dies. Just can't get it to stay at 900 RPMs even with the idle adjuster. The idle adjuster will increase the RPMs but if the choke is turned to the outside of the bikes (left) the bike dies even at 4000 RPMs. It seems happy other than that.
I could take it out for a spin.....a little afraid though but I am a big boy and if that is what it takes I will do it. Don't want to disassemble the carbs again.

Bud

[daves79x]

Something’s wrong with your choke. The choke lever should be all the way off (choke plates open) with the lever pointing straight back. Thumbing the lever to the left to it’s stop should fully close the choke plates for starting. After starting, the lever can be gradually moved back to the fully open position. It sounds like you have to do it backwards. Something wrong if your description is accurate.

Dave

[heli_madken]

Is the bike running way too rich for some reason?

[Jeff Bennetts]

You need to check the carb slide operation with the carb tops on and tight, push the slides up through the carb throats to check for a smooth stroke up and down.

[budanddar]

Dave,
I guess my last post didn't make it here.
I did adjust the idle screws to 1 and 1/2 turns out.
Yes, it does start up right away. The plugs and sparkers are correct. 1-6 3-4,2-5. I had noted in another post that the shop manual had 3 different configurations listed for the positions and firing order. The group here set me straight on that issue.
When the choke is all the way to the left the bike will die. To the right or toward the speedo, the bike will race to 4000 RPMs. When the choke is reduced the RPMs go down to zero and they it dies.
Just a little nervous doing this in the garage with out air flow across the motor. I have a box fan but that is now enough.

The other thing, I have by-passed the vacuum gizmo that is supposed to stop hydro lock. My gas is going straight into the 2 carb inlet tubes. I have the vacuum tube going from carb 3 to that gizmo pinched off so as not to loose that precious vacuum.

Thanks,

Bud

[budanddar]

OK,

I will now have to take the air box off and try some of the suggestions. Stay tuned brothers.

Bud

[daves79x]

I'm telling you, there is something wrong with the way the choke is operating. And it sounds like you may have the same problem another poster had - the idle is set way too high, allowing way too much air into the engine when trying to cold start. Back the idle screw off and try that first.

Dave

[bobcat]

I'm telling you, there is something wrong with the way the choke is operating. And it sounds like you may have the same problem another poster had - the idle is set way too high, allowing way too much air into the engine when trying to cold start. Back the idle screw off and try that first.

Dave

Or it could be the opposite and there's a description problem. When the choke lever is moved
to the left* (pulled back) the choke is operating normally and the fast idle kicks it up to 4k rpm.
When the lever is moved to the right^ (forward) the idle screw is set too low and the motor dies.
It might be as simple as turning the idle up. Sure wouldn't hurt to try it.
I just can't picture how the choke sys. could be connected to operate backwards.

*Away from the cable end, choke/fast idle full on.
^Toward the cable end, choke off/ idle screw adj.

[Larry Zimmer]

Let's try this: When the choke lever is turned counterclockwise to its 'stop', that is 'OFF'. Clockwise to its stop is 'ON'. If you have to turn yours clockwise for idle/running, something is wrong, as Dave said.

[bobcat]

Let's try this: When the choke lever is turned counterclockwise to its 'stop', that is 'OFF'. Clockwise to its stop is 'ON'. If you have to turn yours clockwise for idle/running, something is wrong, as Dave said.

+1 Larry, better description.

[daves79x]

I've seen the choke cable fold itself over at the handlebar lever, effectively freezing the choke plates where they are. I've seen choke cables installed with no slack at the carb end, resulting on some choke all the time. I've seen the cable installed backwards, with the rubber sleeve at the carb end instead of the bar end. I've seen the choke lever clocked quite a bit off it's normal position, maybe that's what's happened here. A few pics would be helpful.

Dave

[Larry Zimmer]

Basically, when you think your lever is 'off', be certain the chokes are OPEN!!! Ye gots to look at 'em. Good luck.

[budanddar]

Thanks to all of you again.......stepped away from it for about 3 weeks and will get back to it soon. Thanks for all of the good stuff for me to try.
Getting to think I need some counseling from Dr. Phil? This thing will not get the best of me!

Bud

[Duffey Lake rd.]

My Dynojet kit says to set air screws at 2.5 turns out.
I had mine at 1.5 turns and the idle was rough and cutting out a week after bringing them down from 2.0 turns.
It runs fine now at 2.5 turns with the Wiesco 1147 kit.
PDF Manual
https://www.dynojet.com/amfile/file/dow ... duct/2700/

Don't forget the pilot screws. I like the pilot screws at 2 1/2 turns on the CBX. This has to be done before syncing. This setting works very well, corresponding as it does to the correct 3 percent CO (carbon monoxide) this engine wants. Use that figure if you have access to an EGA. If you have 150 psi or more cylinder compression (lucky you!) *and* you removed the carbs' idle jets to clean them, then use 2 turns instead, a little less if at an altitude over 5,000 feet. If none of these things are true in your case, then 2 1/2 turns will be right. -Mike Nixon


I also JB welded a small washer into the #3 & #4 screw head slots so I don't need a 90 degree Carb Pilot Screw Adjusting Tool.
-Scott