Mikuni BS33 float bowl drain screw

This is a re-post from the following "sticky" post in the XJ Chat Forum:

http://xjbikes.com/Forums/viewtopic/t=4 ... rt=15.html

Specifically, my question is in regards to the Mikuni BS33

and....

And no, I haven't actually fubar'd my drain screws.... yet :wink:

 

Wow, 50 views and not a.... :roll:

 

I've looked into that since I make screws for Hitachis but the screws in Mikuni carbs has a special fine thread that I can't duplicate. At the moment the only thing available for Mikuni carbs are the stock screws from the dealer.

 

Well, today I finally managed to extract the lone drain screw that had a damaged head from my #1 float bowl. I also picked up a few 5mm stainless allen head cap screws at the local hardware store.

Tomorrow I'm going to bust out the Dremel tool and cut off the top half of the heads on the OEM drain screws, and then cut off the heads of the stainless allen head screws that I just purchased. Then I'll use some JB Weld to attach the allen heads to the OEM screws. I'll post some pics if the transplant works.

 

I think you might also be able to tap the hole with standard size threads then you could use one of my screws.

 

Except even then the Hitachi screws do not have a provision for the o-ring that the Mikuni bowl drain screws use.......

 

An O-ring isn't necessary.

 

Why did the factory use it then?

 

Steve-

I've kicked around the idea of tapping the bowls and using Heli-coil inserts to accept the aftermarket Hitachi screws such as yours. I wasn't sure if the tips of the of the Mikunis and the Hitachis were of the same dimensions. Can anyone confirm?

I'm also a bit apprehensive about the possibility of trashing a bowl in the tap process. That's why I'm going to attempt the "franken-screw" option. Less risk of damage to the bowl, initially... and I already have one damaged OEM drain screw to test with.

Len-

There is no o-ring evident on my BS33 drain screws.

 

You are so right! I was thinking of all the other Mikuni's.......

 

The tips are nearly the same. It's not critical, they only have to be tapered and I don't think you would need helicoil inserts. If I can find an old bowl I might try just tapping it for 6X1mm to see how it works. Should only take a minute.

 

Not all Mikunis have O-rings but some of them do and so do the screws on Honda carbs. The O-ring is just there so fuel won't run out around the screw when you open it to drain the bowl or connect a clear hose to the outlet to check the float level. It's not used for normal operation because the tapered end is what seals the hole when the screw is in tight. Even without an O-ring you can still open the screw and it won't leak much and if it does you can always put some grease on the threads to help seal it if you need to open it for a while to check the float level.

 

Steve-

Anxious to hear how that turns out... better yet, pics?

 

I tried tapping the hole out for 6 X 1 and it works but doesn't feel really secure because there wasn't a lot of material for the threads so I'm going to try some other options.

 

The hole in the bowl is 7mm diameter and there's a lot of material around it so I can tap it for a larger size of 7 X 1 mm and make larger drain screws to fit. I can't make screw heads and 7mm screws don't come with allen heads, just hex heads, but they don't look too bad.
Posting a pic on here still doesn't work, it didn't even keep the text, just dumped the whole thing so I'll put it on my web site.
http://www.arizonasteve.netfirms.com/Ca ... Screws.htm

 

Steve-

So... correct me if I'm wrong, but when you state that "the hole in the bowl is 7mm in diameter", that dimension is after you tapped it?

Are you machining the taper on a standard 7M x 1mm Hex? I'll check tomorrow, but I may have a source for stainless, allen head 7M x 1mm screws.

Any thoughts about using Loctite Form-a-Thread in the standard (untapped) 6mm hole and then tapping for the 6M x 1mm thread pitch?

 

Just got in touch with a guy locally whose shop has lathes that can cut the thread so it should be doable.

Quantity is the question now.

Personally, I'd rather drop a few extra bucks on a screw that fits the bowl than start tapping, but that's just me...

 

Steve-

Checked on that 7M x 1mm allen head today and... I guess I picked the wrong week to stop sniffing glue :roll:


MaximumX-

Not sure if that quantity question was directed at me or the forum in general, but I'm interested. I guess the penultimate question is... what will they cost?

 

In case nobody has noticed it Mikes XS has Mikuni drain screws for $4.00 each, Part #48-0778, about half way down the page.
www.mikesxs.net/mikesxs-fuel_system.php?category_id=4.2