Topic: Carb drain screw sizes and replacements?

[buffaloejon]

Does anyone know where to get replacements? Replacements that *aren't* 18 bucks for 4?

I'd like to have new ones, but if anybody has some old ones (or the whole bowl!) laying around, could you PM me?

They're the from a set of 87a Keihins, I believe that they're common across most all of our bikes. Mine are stuck on pretty ridiculously, and I'm just gonna use a vice-grip to get them off cause I need to do some trouble shooting using fuel lines to spy on fuel level in the bowls. Speaking of that, what size fitting (nipple) would work? Or just find a smaller hose and jam it up in there?

Thanks!

[RickB]

Jon,

Funny, I was just going to create a thread on this very thing.

I too want to create a float level tester (like this) and would love to know the specs of the carb drain screws for a CB400F (I'm guessing they're all going to be the same?) so I can find a suitable nipple at the hardware store.

Any help would be much appreciated,
Rick.

[buffaloejon]

Well, I've used my google-fu a little bit and found that the thread seems to be a M6x.75 , which seems to be supported by the fact that our M6 x 1.0 thread gages at work go in about half a turn.

I haven't found any sort of suitable nipple, but I've read that 1/4" clear tubing fits in there pretty well without any sort of fitting, and doesn't leak "much". So I've read.

Anybody else have some input on this?

[HondanutRider]

Someone actually posted some time ago the technique of using clear plastic hose alone without any fittings.  I've done that and it works quite well without leaking for the duration of testing.  What you can do is gently heat a section in the middle of a piece of hose, using a candle or other flame, and then pull the ends apart to stretch the heated/melting section so that it shrinks down in size a bit.  Then you let it harden again and cut the stretched section so that you have two pieces with reduced diameters at that one end.  These ends should then be able to be jammed into your float drain hole and sort-of screwed into the threads to keep them in place and make a seal.

[RickB]

Jon,

The M6x0.75 spec is all I needed, thank you!

So it seems that that size is a common part or for some kind of maintenance of firearms. Being from Australia, I wouldn't really know, my exposure to firearms is limited. Anyway, do these look like they may work?

http://www.midsouthshooterssupply.com/item.asp?sku=00139A1401
http://www.midwayusa.com/product/119670/knight-red-hot-nipple-11-cap-m6-x-75-mm-thread-stainless-steel
http://www.rmcoxyoke.com/inc/sdetail/82
http://www.progunsports.com/traditions-revolver-nipples-6x.75-thread-3pk.html
http://www.kitterytradingpost.com/product.php/pid/2/sid/6/tid/32/prodid/10938

I think a steel one is a little over kill, I was thinking a plastic thing from a garden sprinkler or something may work.

I've heard you can jam in some tubing, but if a suitable nipple can be readily had cheap then I'd rather save myself any fuel leakage problems.

Thanks for the help guys,
Rick.

[lucky]

Jon,

Funny, I was just going to create a thread on this very thing.

I too want to create a float level tester (like this) and would love to know the specs of the carb drain screws for a CB400F (I'm guessing they're all going to be the same?) so I can find a suitable nipple at the hardware store.

Any help would be much appreciated,
Rick.

You do NOT need to do that!!!
Just measure the float height given in the book!
Just get a workshop manual and follow the instructions.
THIS IS ALL YOU NEED PEOPLE!!!
How SIMPLE CAN IT GET???

[RickB]

Lucky,

Haha, thanks for the advice but trust me, I've tried the simple stuff on these carbs.

Actually, I believe an external fuel level measurement is much simpler to do than taking my carbs off, unscrewing all the bowls and verifying the float height, again.

When you think about it, it's the only real way to verify that the fuel level is correct across all carbs. Sure it's not necessary for most people, but I'm trying to determine why I have such sluggish performance at low RPM's and with a warm engine, which I've been documenting in my project thread.

Thanks again Jon for the information.

Rick.

[Don R]

I've wondered about the density of a 40 year old float and the relationship to a proper float level. I took a set of old junky carbs, cut off the internal overflows and used clear tubing on the overflow tubes. It worked well. I did get my fuel levels closer than they were. Some carbs drain through these tubes when you loosen the drain screws. Mine do not.

[70CB750]

I once took all the floats off and checked their weight on reloading scale. They were within 10 grains or so - since I had to solder one of them.

But when i clean carbs and did the synchro the float weight did not make a difference. The fuel level is ok within 2 milimeters or so, it changes with turns and such too.

[buffaloejon]

Thanks a ton for all the help and input guys! Let me say, Rick, I didn't double check that thread size, and I have no way to verify what it actually is. Even at my work, where we love oddball threads, I can't find any examples of this thread. I'm gonna try the tube when I get a little time this weekend.

And lucky, as usual, you have no useful input. You haven't read the thread, yet know everything about our situation. Or rather, enough to know how simple our problems are to solve, if only we would do the simple things! We've obviously tried that. Float height won't mean squat if the carb is fuel starved, and setting float height is in no way easier than shoving a tube into a hole to verify a liquid level. Please stop replying to my threads with useless responses.