Hitachi and Mikuni carb differences

I've previously only worked on the carbs on my 550, but last night I took apart the rack of Hitachis from the 1980 650 Maxim I recently bought. This bike was pumping fuel into the crank case and that appears to have been caused by the #4 float height being way off. It also appears that the "friend" of the PO who rebuilt these and charged $450 for parts opted for replacing all the jets and emulsion tubes in lieu of actual cleaning.

I'm noting some differences between these carbs and the Mikunis and thought it might be interesting to start a thread comparing them. I'm still somewhat of a novice, so maybe this will be helpful to someone else, too.

Butterly Valves
The Mikunis were brass, these are aluminum. They also do not appear to seal along the sides. I doubt that this is common with these carbs, but??? I'm planning to replace the throttle shaft seals, but I'm wondering if someone already has and didn't get the plates positioned properly. The plates themselves almost seem like they could be new but the screws look old.

Float Needle Valves
The needles and seats appear to be new, but there are no screens and no clips for connecting the needles to the float tang. I don't think that is how they originally were configured, but I'm also not sure if it's a big deal. Seems like it would be better to have both (which are part of the Mikunis).

The float pivot pins are all quite loose. In fact, I could easily slide them out without the use of a tool. That doesn't seem right, but again, I've never worked on these before. They were extremely tight on the Mikunis. (I even broke one mounting post trying to remove a pin.)

Idle Mixture Screws
My factory service manual says that these screws were set at the factory and they should not be adjusted. I assume that I should ignore this, but thought I'd check just in case.

Thanks!

 

Let's see if I can help...

Butterly Valves
All the carbs I've worked on these were tight against the sides. Don't know if I'd call it sealed.

Float Needle Valves
Screens may or may not have been replaced. Not needed with a precarb inline filter. The needle just rests on the tang. No clip.

The float pivot pins are all quite loose.
normal

Idle Mixture Screws
remove. Watch for the oring, washer and spring under each one. Replace oring and set at 2.5 turns out from bottom to get you started.

 

Thanks for your response, iwin.

This one makes me a little nervous. I'm inclined to take the one with the biggest gaps, get it cleaned up, then remove the screws and see if I can reposition the plate so it seals more tightly. If not, alternatives are unpleasant...

Good to know, and I am planning to add an inline filter.

10-4 on the rest. Thanks!

 

If I recall correctly the Hitachi float valves also have the wire hook that goes over the float tang.

Hitachi float pins are designed to be loose in the holes - the sides of the float bowl keep them from drifting out. Much easier to work on than those pressed in Mikuni pins.

 

True. but not an actual clip. They'll fall right off the float.

 

OK, I'm not sure what you're saying. There is no pin or clip of any kind on these needles.

 

From the sounds of it Bay, your carbs have had bits either left off or aftermarket replaced. Pictures?

 

Looke here: http://mok.fileave.com/FUEL%20LEVEL%20draft%208c.pdf

Page 3 on the left has a picture of needles. Yours look like that?

 

I'd like to post a picture but I've got an issue with my upload limit. Despite having removed photos the upload total won't go down. I've emailed admin about this and another issue but I can't seem to get anyone to reply.

Suggestions?

 

photobucket. Get yourself an account (free) upload your photos there and then copy paste the IMG code into your post. Plus they can then be bigger than 500x500. Do keep them reasonably sized though. Photbucket also resizes on upload free.

 

OK, I finally broke down and opened a PhotoBucket acct. Personally, I think it's far better to post the images directly to the XJBikes server. I know that this takes space, but it also ensures that people who actually search the archives for answers (which I think we would all encourage) or go back to look at old links will still be able to see the original images. Those other accounts will change, be opened and closed, etc. We already have LOTS of missing images in these threads. Anyway...

Here's one of my needles. It doesn't really even look like there's anywhere you could attach a clip.



I'd still like to know why I haven't heard from the site administrator.

 

Yeah I agree on the missing links in the forums, not just this one.

The "clip" could go around the base right before it becomes more square above the brass piece. I would just wonder some other needles. Those don't look like rubber on the top.

 

Yep, that's another difference. Hitachi uses rubber tipped float valves.

 

They're definitely not rubber-tipped. It would be nice to only have to buy new needles, but how confident can I be that they'll be a good fit for the seats I have? The seats also look brand new, by the way.

 

chinese japanese

 

You have a bit of work in front of you trying to figure out what parts are correct and what parts are acceptable "close replacements" and what are un-useable.
That needle looks completely wrong and I'd be very concerned about the other parts too.
Safest thing to do would be order the kit from Chacal which should come with new needles and seats. It will include the proper "beeny" screen on top and MOST IMPORTANT, the proper oring around the body to seal the outside of the seat to the carb.

Chacal will have the throttle shaft seals you seak also (and new butterfly screws)

The emulsion tubes and jets would be my next concern. Hopefully you can see some numbers on them.
I do NOT know if there are different sized emulsion tubes available to "accidentally" swap out, but you will want to confirm the jet sizes for sure.

It might make sense to nab a parts rack off Ebay to confirm your butterfly questions and it NEVER hurts to have some extra parts laying around.
http://cgi.ebay.com/ebaymotors/YAMAHA-S ... ccessories

Or just grab this nice rack (it's always fun to grab a rack)
http://cgi.ebay.com/ebaymotors/1982-Yam ... 45f6a174b9

I think the needle valves and seat kits will run you close to $80 by themselves.

 

Thanks for your reply, D_Mike. Don't worry, I am well acquainted with Chacal. I've already been through his catalog section for these carbs very carefully. There are several different versions of the float needle assemblies available in the pre-packaged kits that he sells, but I don't believe that any of them include an o-ring. I think think those are used on Mikunis. He has aftermarket needle valve assemblies are $39 for a set of four, $28 for needles only.

I had inspected and recorded all jet sizes when I disassembled and all are correct. Good advice, though, for anyone going through a set of carbs for the first time.

I had mentioned in another thread but I guess not in this one that I was able to ride this bike before purchasing. It started right up, ran amazingly well considering that one of the float valves wasn't closing, and it even idled. That makes me think that things are probably not too wildly out of whack.

Here are a couple of pictures of the needle seat.



I think the number stamped in the top of it is 2.0 or maybe 20, but it's really hard to get a decent photo of that without using a tripod and the right kind of lighting equipment. The hole at the bottom of the needle "sleeve" is slightly smaller than a 5/16" drill bit, about .70 or .75mm. The bottom of the sleeve (where the hole is) is flat not tapered.

 

The washer is used instead of the oring. I'd buy needles and seats together. That's the besy way to be sure they'll close when needed.

 

OK, I cleaned up a couple of these carbs, then did a little test. Here's the #3 carb with the butterfly plate temporarily reinstalled and positioned as good as I can get it.



Looking at it with the naked eye the gap doesn't seem quite as big as is indicated in the photo. The backlighting makes it "glow" a bit in the photo.

Does this seem like an extreme amount of leakage? As I said originally, the only other XJ carbs I've worked on previously were the Mikunis on my 550, and those butterflies all closed more tightly than any of these are going to.

 

Something is way not right with that butterfly. It should be light tight except for just a little bit at the shaft.

 

It looks wrong to me also.
The good thing is that the butterfly shouldn't get worn out...and any hitachi carb this size should give you a good butterfly.

OH....I BET someone did some carb mods. I bet they honed out the bore in attempts to improve performance thus making the butterflies not fit properly anymore (and screwing up performance)
Can you measure the bore accurately? ....and someone else will have to confirm an actual hitachi bore since I only have mikuni on the shelf.

 

I think you may want a different rack for this bike. Between the needles that belong to who knows what and these butterflies you may spend much more cash fixing up these than getting a different rack.

 

I went back down and tried to play with the positioning a little more, but it isn't going to get any better. When I took the butterfly and shaft out again and looked closely, I could see that there has been some rubbing where the light is leaking through. I'm not sure if it's the plate that's worn or the bore or both. When I run my finger over that portion of the bore I can't feel any groove, but it's slightly darker where it's been rubbing.

I don't have a tool that's really accurate enough to measure the bore. Maybe I can run down to the shop of a friend of mine in the morning.

 

I think I just figured out the mystery of the odd float needle. Here's a link to a product page on the Sirius Consolidated Inc site up in Canada. It includes all of the parts that appear to be new on these carbs - jets, emulsion tube, plus lots more - AND a float needle with no clip and no rubber tip.

 

Baytonemus,
Nice work on those carbs. Are you close to the cities? If you are and need a hand I could meet up with you.

MN

 

Thanks, MN. I'll send you a PM.

 

Greetings, everyone. It's been a LONG time since I've posted to the list. I spent much of the spring finishing a boat and motor restoration, so I'm finally getting back to this project.

Started disassembling the 2nd set of carbs I bought for the 650H. To recap, the set that came on the bike had some odd rebuild parts and a lot of leakage around the butterflies.

My question today has to do with the airjets. The factory manual shows both airjets on top as having a long nozzle on the end. Mine are all short like a set screw with a hole in the bottom. Also, the manual says the pilot airjet is supposed to be a 195 but mine are 205s. Is it worth replacing them for such a small difference on such a large hole?

Thanks!