XJ550 Slide Differences

Hey everyone. Opened up my carbs yesterday to look at the diaphragms and I noticed a difference in my #3 slide. Slides 1, 2, and 4 have 2 holes in the bottom besides the one the needle goes through, but number 3 has 4 holes. Anybody seen this before and know whats up?

 

You need to use a hosting site in order to post photos here.

 

I never do, he just needs to figure out the correct way to upload them.

 

Using my phone I click on the upload a file tab on the site and go to my camera on my phone and that works.

 

sorry bout that image issue. Here it is uploaded via my phone

 

No worries. Number three is the one with the four holes in the slide and number three carburettor is the one the vacuum petcock pipe connects too. Now l don't know if that is a coincidence or not? I assumed you are counting the slides from the left side of the machine, gear lever side. When the throttle plates open the engine vacuum lifts the slides. Question is do those extra holes on slide three have an effect on the vacuum in the pipe from the carburettor stub connection to the vacuum stub on the petcock and therefore fuel flow to the carburettors?

 

Looks like someone drilled extra holes.... but, I’m in the middle of some 550 carbs right now so I will look and compare

 

For me the petcock attaches to carb #2. I thought that was standard. Its possible that someone swapped the #2 slide into the #3 carb somewhere along the way, though

Thanks, let me know what you find

 

I am interested as to why there are extra holes in that slide, and if they would affect how high the slide will lift on engine vacuum. Might be as hogfiddles suggested. I think the vaccum line could connect to any carburettor stub and operate correctly. The line on my 900f goes to the third carburettor. I just assumed your bike was the same and therefore Yamaha for some reason had put four holes in it. Or is it from another machine?

 

Vacuum is vacuum..... it doesn’t really matter what port the petcock line is connected to. Standard fare was that the line was connected to #3 since that is the “guide” vacuum. When you’re balancing/syncing you basically adjust the vacuums to match the lowest vacuum anyway. The end result is that all the vacuums are essentially even. It doesn’t matter what port you hook your line up to since they’re now all the same.

 

Are the extra holes threaded? This is for the 550 Seca

 

Could it be that the Maxim got different slides for 1982, and that the one with the extra holes is from a Seca or a 1981 Maxim?

 

I doubt they would’ve had different slides. Seems like a lot more work on Yamaha/Mikuni’s part to have two different parts fit the same place. I’m wondering if it’s maybe a remanufactured slide made by somebody else. They could’ve changed the manufacturing process to fit their facility and had two more holes. I don’t know if they’re threaded. I’ll look when I get home this evening.

 

Number 4 looks like a JBM diaphragm, so that definitely indicates that someone was working in there. Note no tang on that one so you need to orient it like the others

 

I wonder if @chacal knows?

 

I did that one myself. I’ll make sure it’s oriented right.

 

Umm, well, cough-cough.......I would actually be more concerned with the ones that do NOT have the extra (threaded) holes.......the threaded holes should be there on all Mikuni vacuum pistons, since there is a small stepped "plate" that holds the needle in place (and also acts as the lower "seat" for the long slinky spring).......and this plate is held in place by two small screws, threaded into the vac piston......that is what those threaded holes are for. Here is what an XJ550 (and, basically, ALL Mikuni carbs) vac piston should look like:

www.ebay.com/itm/134035219273

just the same as the image faffi posted above.


Hitachi vac pistons had a threaded plastic "plug" fitted over the needle that threads into the vac piston internal bore, and thus no threaded thru-holes as on Mikuni carbs. Those other 3 pistons look a lot like Hitachi pistons........

 

So I disassembled slides #2 and #3 and took some pictures and some measurements. They appear to be exactly the same slide, the only difference being that #2's screws go into a blind hole, while #3's screws go into a through hole. The measurements I took using some calipers are below and are the same for both slides:
Slide Diameter: 24mm
Slide Length: 46mm
Needle Length: 44mm
Diaphragm Diameter: 63mm

@chacal Do you know of any Hitachi slides that have the same measurements as the Mikunis do on XJ550s?

 

Well okay, then they are Mikuni slides. If they fit the bore in the carb correctly, and they are the same height, etc., then I would assume that they are correct.

 

Alright. I'm throwing them back in the bike then. Thanks, y'all.