Hitachi H34C carbs.

Hi I am new here and would like some technical help if possible. I have a 1980 yamaha sx 850 sg with hitachi h34c carbs. The bike has been sitting many years and I am trying to get it running. So far I have got it to idle but it is irregular and wants to rev after it warms up . I would like to take the carbs off and clean them up or rebuild if needed. My only resource is a clymer book that shows the carb parts but not exactly how they go in place. Does anyone on this forum have a diagram on how the interior carb parts go together so I can dismantle these, clean thoroughly and rebuild if need be. Thank you for any help or advise you can provide me. Chuck Saylor

 

The following links are for HSC 32 carbs, but the basics of the operation are the same.

IN THE CHURCH OF CLEAN

Replacing your Hitachi throttle shaft seals

Setting the fuel levels


Wanting to rev after warmup could be due to a vacuum leak, and not necessarily at the carbs.

 

I have checked for vacuum leaks and find none. It's more like surging to describe it correctly.

Thank you Abide. I will let you know how this works out. Any info on the carbs that show where each part goes in a rebuild would also help.

 

As I told you, sign on to www.yamaha-triples.org

 

I am not sure
I want to go to yamaha tripples as it is not a secure site?

 

Well, that is basically the world for your triple, as Xjbikes is the world for your XJ.

If you don't want to sign on, then just go there, and click on forums. scroll down to the 'maintenance and repair' section. Then click page by page til you find a forum with your carb breakdown on it.

Dave

 

Thank you sir. I will do that!

 

Abide do you know what the small brass (jets)? or air screws on the top of the main body of the carbs are called? These are brass and have a slot in them for removal. I am curious but see no mention of them anywhere in any diagram.

 

Those are the mixture screws. Pull them out to get the spring, washer, and o-ring. Technically;, you're not supposed to mess with them because they were set at the factory for EPA purposes . BUT in order to thoroughly clean the carbs, you need to pull them and service. When they go back in, we like to set the Xj ones slightly richer to allow the bike to run better, but you'll need to experiment and read about what is best for the triple.

Dfox

 

Hi Dfox I have drilled out the caps and removed the mixture screws already. The brass pieces I refer to are under the top half of the carbs after you remove them from the bottom halfs. There are two in each carb located in the top of the bottom half. They have slots to unscrew them for removal. Just curious as to what they are? Hope I have explained it better.

 

Then those are not on top of the body. They are underneath the body inside the bowl. Those are your fuel jets. Th one with the bigger number is your main jet, and it is screwed into the end of the emulsion tube. The tube then needs to careful byte driven out thr0ugh the top of the carb where the slide was. The needle on the slide goes into the top of the emulsion tube, the jet is on the bottom of the tube. The other jet with the lower number is your idle jet. That must b e removed to clean out the internal passages in the carb body. Both jets must be cleaned, as well.

 

I have removed the main and idle jets from underneath and inside the fuel bowl as you described. What I am talking about is on the main body underneath the top half and on top of the bottom half. Any ideas?

 

I would take a picture and send it if I could. These are not on any diagrams that i have seen.

 

Are you referring to the air jets that are underneath the diaphragm? You take the 4 screws out of the top cover, the spring comes out, then the rubber diaphragm, then underneath that there's 2 air jets. Are these what you are asking? If so make sure to denote their position as they are different sizes and placing them in the wrong locations will lead to performance problems. I'm not sure but I think I diagram in the manual has them backwards

 

I think you are correct, but actually have to separate the two halves to get to these. I will keep their places marked for re-installation so as not to mix these up. Thanks for your help here. I may be back for more advice as I work my way thru this.

 

If you pull the slide assembly out, and are looking straight down, there are two air screws down inside, as well. Bigger number towards the end inside of the carburetor smaller number toward the airbox side of the carburetor .

click on my avatar, and send pictures to my inbox… I can also give you my personal number so you can text them directly to me

 

I am very old school and don't have a cel phone. Maybe I can have my wife send pictures if she knows how? Will do as you suggest and see what is there. Thanks.

 

Hi Hogfiddles. Another question has come up for me. When I drilled out the welch plugs over the mixture screws and removed them I noticed something. The washer and O ring are on the top and the spring is on the bottom. Looks like that in the diagram also. Just checking to see if you think that is correct?

Thanks Chuck

 

To assemble the mixture screw correctly:
1. Slide the spring on to the mixture screw
2. Slide the washer onto the mixture screw
3. Slide the o-ring onto the mixture screw.

The top of the screw presses on the spring. The spring presses on the washer I like to orient the washer so that the very flat side is up for the spring to sit agains, and the ever so slightly curved surface is down. (because) the washer presses against the o-ring, and the o-ring seals the bore. I like to put the washer in that way so that the 'cut' edge of the washer is up against the spring, and the smoother side is against the o-ring.

Dfox

 

Why is it not installed that way under the welsh plugs or in the diagram? Maybe there are different ways to assemble these depending on the carb model?

Thanks Chuck