CARB problem tube hit

[colin555]

Hello everyone!! I`m from Argentina and this is my first time, I have an Honda CB 650A 1980.
Sorry for my English, I speak a little so I hope I could explain my problem.

One of the four tubes that engages in the carburators doesn`t hit than the others three. Two days later I realized that the Jet screw was a little bit loose so I proceeded to adjust but didn´t work at all.
Could someone tell me how to adjust properly or it might be another problem? Just FYI the bike was carbureted 3 month ago.

Thanks and regards.

[Volker_P]

Welcome here!

I am not that sure what you are talking about. It sounds a bit like you have a loose carb slider.
These sliders move up and down when you twist the throttle. So your issue is that one of them does not move together with the others properly?

And what is the result of your problem? Does it not run on all four cylinders so one exhaust pipe stays cold?

Guess a picture would help a lot to figure it out.

[MEHall]

Yes a picture says more than 1000 word as a saying here in Sweden says!
I read this topic and i did not understand what it was about at all and i think i am enough proficient in english. But if a person who speaks Spanish using an online translator it will undoubtedly be errors in word order and even wrong words. And if that person dont know english so well he wont know if the online translator have translated correct.

[colin555]

Thanks you guys for making the extra effort to understand me.

I will try to explain again.

My bike start perfectly but one of the four pipes don`t hit as the others. For example (pipe1, pipe 2 and pipe 4 have equal temperature) (pipe 3 different temperature regarding others).

Why this happened?(I think )because the Jet screw of the pipe 3 was loose (please see attachments).

The question is: How to adjust this screw? What do you recommend me?

Thank you very much!

[Folsoml]

That screw is the fuel/air mixture screw. It determines how rich or lean your carburetor will run. The standard adjustment for the PD50A carburetor is 1 5/8 turns out, and the PD50B is 2 1/8 turns out. To make this adjustment, turn the screw until it is all the way in (be careful not to damage it by trying to screw it in too far). Then back it out the required number of turns. The number identifying which carbs you have should be printed on the side of one of the bodies.

It is worth noting that I do not think this screw being loose would cause that cylinder to not fire at all. Have you taken the carbs completely apart for a thorough cleaning?

[Volker_P]

Thanks for the clarification.
So your bike does not run properly on cylinder #3 (usually counted from left to right in riding direction).
As written, the idle mixture screw/needle needs a certain setting but this should not cause a cylinder not running at all.
In fact the full adjustment range of this screw does not make much more than one would swap to the next idle jet dimensions. Just to point out that this is something for the fine tuning.

So another question: Does the #3 exhaust pipe get a little warm or does it stay really cold?

At the bottom of the carb bowl is another screw. It serves to release the fuel out of the carb bowl and normally is closed of course.
You may open this screw for a test. If you have fuel in this carb bowl, fuel should come out (of the nipple at the bottom of the carb bowl or the hose if there is a hose on the nipple) as soon as you open this screw. Just to make sure you have fuel in this carb at all. Close the screw immediately again after this test.

My bike start perfectly ....

Are you really sure this is a CB 650?

[colin555]

Thank you very much Volker_P/ Folsoml!!!

The #3 pipe get a little warm ( is this usual or 4 pipes have to hit at the same temperature?). I think the 3# cylinder is running but not properly.

I going to chek this screw (the one at the bottom of the carb bowl ) and I will tell you what happened.

Just to be sure, the screw it´s the one that appears in the attachement?

Thank again!!

[Volker_P]

Yes, all four cylinders should work essentially the same. So also the exhaust pipes have to show about the same temperatures. If something is really different, something is probably wrong.

Your picture shows carb#4, it is a Keihin PD50B piston carb.

And yes, the screw at the bottom just above the small black hose is the release screw for the floater bowl. If you open it, fuel should come out. Interesting to know if fuel comes out there for your carb#3. As #3 gets warm a bit, one should assume it is not perfectly dry at least. Remove the black hose from the #3 floater bowl and try to collect the fuel in a glass. So you can have a look for possible dirt.

Another issue is the spark plug. Before you remove the carbs, turn out spark plug #3 and have a look. If it is dry, it should be a carb problem. If it is wet and black it is rather an ignition or compression problem. You may compare it to its neighbor from cylinder #4. Just swap the spark plugs (not the cables) between 3+4 when you turn them in again. If #3 still remains the colder cylinder, at least this is no spark plug problem.

Did you check the valve settings yet?

[CB650CPastor]

The most likely problem is that the #3 pressed-in pilot/idle jet is clogged. The hole in the jet is very very small. Time to clean the carbs, check the tank, and make sure you have a filter installed as well. If you've verified spark, and the valves are properly adjusted, I would definitely check the pilot jet.