XS400 carb differences

[armyofda12mnkeys]

I have a pair of carbs from my 1978 XS400 (assume they are 1978) and one that came with a 80/81 XS400 engine (not sure they are from 80/81 but they do look very very similar to 1978 one minus some differences highlighted in the video below).

I am going to follow JBM's instructions to replace the OEM rubber diaphragms with their custom replacements.
But then i see in the instructions about making sure the slide 'pinholes' face the engine direction and get lost since my slide doesn't have an exposed hole like that (plus other notable differences highlighted in video between another pair of BS34 carbs that do and mine .... 80/81 carb has 1mm larger slide, and the idle screw is in the front-bottom as opposed to 1978 which is in the back-top area).

1. Just curious what I should do when I install the rubber diaphrams... does it not matter what direction that small unexposed hole on bottom of slide points?

2. Also what year is that other carb from with the pinhole possibly from?
Is it still considered a Mikuni BS34?
Is the one on the bike currently without a pinhole also still considered a Mikuni BS34?
They both have a 'Groove Diameter' of 73mm.

3. Would the JBM diaphragm fit both even though one slide is 1.2mm larger?

Thanks,
Ari

 

[xschris]

The hole on the bottom of the slide should face the engine. Sometimes the diaphragm will get loose and spin on the slide putting it out of alignment. The carbs with the air mix screws exposed (brass) are the 78 carbs. the others are 80-82 sohc xs400's. The large bolt/screw it the idle screw not pilot air mix screw.

 

[armyofda12mnkeys]

xschris.... but what i am saying in the video is my carb doesn't have an exposed hole and currently with the stock diaphragms/slide it doesn't face the engine anyway (on both '78 slides, so i know they didn't accidentally get displaced). its at an angle. Why doesn't mine have a hole and why are they at an angle? Do i have another version of the Mikuni BS34 carbs?

 

[xschris]

No, they both have a hole. The one on the 80-82 has a plate in it that holds the needle in place that may be out of alignment and not covering the hole.

 

[armyofda12mnkeys]

Interesting. the 80-82 carb is actually fine and shows the hole, maybe cause it has screws that I guess lock that part down (the 78 has a circlip instead).
Both holes on the 1978 are totally blocked off then. (oh my, I wonder what that would have done to performance of the bike hehe).

The 78 carb has a circlip that looks like I can remove to put it back in alignment...
Any tool I can use to get that circlip out, it looks really deep in the slide and Im not the kind to fashion my own tools by grinding down some long round needle nose pliers (which is what i saw someone else do for this). Gonna try to think of an alternative.

 

[xschris]

Actually they both won't have light show through them but air still will pass that's what is for. I don't have any 80-82's to look at at this time so I may be wrong on that one. Yes the 78's are a pain but will only go back together one way. Take your time doing it.

 

[armyofda12mnkeys]

Cool thanks for the pics Chris....

Tried my long needle nose pliers (still a bit too short and fat), my circlip pliers are too big...
Would any of these work for simply removal:

www.amazon.com/EXTRA-RETAINING-PLIER-INTERNAL-STRAIGHT/dp/B0031R7LKQ
www.amazon.com/Klein-Tools-73242-Retaining-Ring-Pliers/dp/B00085EQ6G
Below look too big, but look similar to what was used in the Suzuki Mikuni carb rebuild manual on page63.
www.amazon.com/Motion-Pro-08-0279-Master-Cylinder/dp/B000WJJ4U6
http://www.amazon.com/POSSE-INTERNAL-CIRCLIP-PLIERS-MOTORCYCLE/dp/B004MZ7EI0
http://www.motopartsoutlet.com/index.php?main_page=product_info&cPath=220_202&products_id=1409

Just let me know what is the best (price doesn't matter) and I'll buy one of them asap.

If the 1978s dont need to show 'light' through the hole, maybe mine are fine then ... But i might check out needle jetting at some point in future, so doesn't hurt to have a circlip tool on hand.

 

[xschris]

These pliers are what I use. I think I got them at walmart for a buck They work great

 

[armyofda12mnkeys]

Btw, I can vouch for these too: http://www.amazon.com/EXTRA-RETAINING-PLIER-INTERNAL-STRAIGHT/dp/B0031R7LKQ .... that one fit very well in that carb enclosure. Got it out easy. Putting it back, its a bit hard to keep a perfect angle with where you want it to snap back... So you use the pliers to get it 95% the best you can down there.
Then grab a long thin screwdriver... and while using the pliers to slightly hold it inwards a bit, apply light pressure with the screwdriver along the edges of the circlip to push it down farther down to 'snap' back where it was which is the complete bottom where you want it to be.