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

 

Show me the diagram.

 

In looking at different pics, I guess there are a couple different iterations of those. I believe I have a book on the triples...let me see what is in there.

 

I got the diagram from the yamaha tripples forum as a guest. Again I am not teck savy and don't know how to send you the diagram. These are hitachi H34C carbs.

 

I know they are...... I'll see if my book has them in it. I guess it is entirely possible that they are opposite for that model......we'll see.

 

Still unable to determine if my Hitachi H34C carbs have the mixture screws set up correctly. When the welch plugs were removed the mixture screws have the O ring on top followed by the washer and the spring is at the bottom. I am almost positive no one has ever replaced these carbs or replaced the welsh plugs as the bike has less then 6000 miles on it. Can anyone on this forum verify if these mixture screws are set up correctly for this carb model? Thanks in advance Chuck Saylor.

 

Ok, so I finally found the answer----- the screw for YOUR carbs appear to be slightly different than the rest of ours. YOUR mixture screw has a machined groove and integral ring that acts as a retaining washer for the o-ring and also as a seat for the spring. See the pic.

Part of the difficulty was that you gave a name that I believe is incorrect. It SHOULD be Hitachi HSC34. There is no such carb as the hitachi H34C that I could find.

 

Sorry about the misinformation on the carb model. Maybe I am a little dislexic. I really appreciate your time and effort. Great picture. Would there not be a washer used on these? ThanksChuck

 

I can't find a single pic that has one

 

I will go with your picture and no washers. Thanks again for all your valuable help!!!

 

Hi again Hogfiddles. New question sir. I am ready to install my very clean main nozzle, emulsion tube and needle jet into each HSC When I insert the34 carb. When I insert the main jet, jet and starter jet with O rings on top of each of these how much force do I use to seat them? Main nozzle and main jet how much force?, emulsion tube and jet how much force? and needle jet and starter jet how much force? Thanks Chuck

 

PERSONALLY, I simply go til they are 'snug', then give them a little extra tweak. I don't tighten the daylight out of them. I imagine in a b look somewhere there is a torque spec.

 

Since they are pushed in and not screwed in I will push them down snug. Ok?

 

They are screwed in. The emulsion tube slides into the hole. Then the washer sits on the end of the tower that the emulsion tube is in. The jet screws into the end of the emulsion tube. The jets snugs the emulsion tube in place.

 

Sorry again hogfiddles but they are not screwed in. Tere are no threads on them. They are pushed in and they have no washers.

 

Show me the tube and the jet that should be at the end of the tube

 

one end of the tubes should slide into the carb, that end has no threads, then the jet screws into the internal threads on the other end of the tube

 

Ok last winter I went to the church of clean and rebuilt my 1986 XJ700 Maxim Hitachi 34C carbs. I did not replace the shaft seals (bad decision). I have been riding it for almost a year now and it runs great. Carbs were synced and colortuned with little in the way of confusing results due to leaking seals. My issue is it is a bear to start when cold. I opened the jets slightly to allow more air in and that helped but at full choke it starts, runs a few seconds then dies. The other day I touched the shaft end of the outer carbs and noticed fuel on my finger tip. So I know they are leaking.

So I will replace them - but do I need to open the carbs up to do this. I know I have to break them apart, but otherwise that should be all I need to do to access the butterflies and the shaft - Correct?

 

You

will have to separate all four carbs from each other, and from the rails, in order to pull all four shafts out to get to all eight seals. You don't have to open the bodies themselves.

 

+1 on Hogfiddles reply.
Also, please start your own thread, or ask in an existing thread of yours. We don't want what's going on with your bike to get confused with the OP's problem.

 

No tubes in my carbs have any threads either internal or external. Must just be the way these carbs are made.

 

Then I guess you have o-rings that hold everything in place. They would need to be replaced. Those carbs are very different from the ones we use here. Here's an idea--

Sign on to www.yamaha-triples.org

That's the world for the triples.........

 

Thank you!

 

Hey boys,

Former XJ owner, and new XS850 owner here. Despite some miscommunication in this thread, there was some helpful info as well. I'd like to point out to modern readers that www.yamaha-triples.org is now defunct. & this site is a natural stopping point for XS850 owners as our bikes are very similar to the XJ.

The XS850 Carb is the HSC34, & it is quite a bit different from the XJ carbs. The main carb body breaks into 2 pieces pieces and there are 8 replacable jets in total. The lower stage has 3 jets with o-rings that are pushed in and held in with leaf spring by the bowl. The upper stage has 3 jets as well, which are thread fit. The air box side of the carb face also has 2 air jets that are thread-in as well.

Naturally this site is kind-of a go to since the XS850 is far more similar to the XJs' than it is to the 2cylinder XS650s. I've had my XS850 for about a month and have been to "church" and back with my carbs. Even replaced the U-seals at the butterfly shafts which I could ONLY find here... Thanks Len!

 

Here's the complete XS850 / HSC34 Carb parts list. Some of these parts have been superseded or discontinued, so double check with partzilla or another official Yamaha dealer.

 

Side note, not shown on the Yamaha diagram for these carbs is the V/U-seals that get installed on the butterfly shafts... These seals tend to dry out and crack and become a major source of air leaks.

2 per carb, 6 total on the XS850

HCP6838BSET6 OEM Hitachi throttle shaft SEALS, set of 6:
$ 43.95 (as of 12/2024)

HCP38BSET6 Aftermarket Hitachi throttle shaft SEALS, set of 6:
$ 39.95 (as of 12/2024)

To date, XJ4ever.com / Chacal (aka Len) is the only source I've been able to find for these V/U-seals, and as of 12/2024 he had them in stock.