Topic: In Need Of Carb Help.

[Buga8tr]

Hi all.  When I rebuilt my carbs I broke/lost a little piece of plastic.  I could not find it on any of the parts list so I thought it might have been added by the PO.  Now that it is running the number 2 carb is dumping fuel and I believe it might be this part.  Below is a picture of where the part came from, it's a little hole next to the accelerator pump.  Is it possible just to tap this hole and put a plug in it?  Or does it require there be a little bit of fuel coming from there?  Any help will be great.  Thanks

It is a 1977 CB750K With 1977 Factory Carbs

[Spanner 1]

That hole in the picture is where the acc. pump squirts gas up to the fuel-rail to supply each carb. nozzle with it's spurt of gas....it's missing two parts, in the hole should be a little kinda brown colored piece which is a check-valve and second the 'o' ring that seals it to the upper carb. body..don't know if the valve is available, maybe someone else knows ?...unfortunately, the bike wont run without the acc. pump working as it comes into play just above idle....

[Buga8tr]

That is not good news.  I have the 'o' ring for it.  But that little plastic part is gone.  So I will try and hunt one down.

[eurban]

I would suggest you find a replacement bowl with the check valve in place; I doubt you will be able to find the part itself.  Perhaps someone here has a spare?  Also I think that you might benefit from doing some research on your bikes systems before you do much more work.  The factory manual for the K8 and F3 can be downloaded here:
http://www.mediafire.com/?5ttzdg9yyuz
Except for a few small things your bike is the same as K8.  There are also umpteen threads on working on the 77/78 carbs, particularly on cleaning the idle circuits, checking float levels and the acel pump.  I don't have links but the search engine works well, just make sure you search from the the Tech forum general page rather than from inside a thread.  Have fun.

[Buga8tr]

I am going to go to my local Cycle salvage place tomorrow, with any luck he might have one.  I already have the printed Honda Service Manual for the bike.  But thank you.  It was a air pressure mistake is how that part got out and broke.  I haven't seen much info on that darn check valve.  Oh well live and learn. 

[Buga8tr]

So I went to the local salvage yard and they didn't have the right year.  So I decided to go ahead a try to fix this problem.  The hole where the little plastic peice went I Tapped with a 8-32 tap.  Then I drilled a 1/16" hole in a 8-32 set screw.  Screwed it in place and gave it a try.  It runs a little rougher when cold then it used to, but once it warms up runs like a champ.

[Inkscars]

 
That's weird. I have a 1977 honda cb750k and my #2 carb does not have that.
Mine does have the accel pump in that carb, and the little boot that goes on it.
huh. craziness.

[eurban]

Stock 77/78 carbs have an accelerator pump on the #2 carb body so anything different from that would be non stock.  Also they all should have a plug of sorts in the hole that bug tapped on the #2 main bowl and at the bottom of the mini bowl for the accel pump.  I have seen mostly brass square plugs but also an occasional plastic one.  I am pretty certain that behind the one on the mini bowl resides a ball which acts as some sort of check valve.  I have never looked behind the square plug in the main bowl.  The carb body also has a round brass restrictor with a small round hole in it . . . Bug, while you may have fixed the leak, I would be suprised if you haven't disabled the accelerator pump which plays a significant role in the proper performance with these carbs.   Did you actually take a look and see if the nozzles were squirting after your "fix?"  I would suggest that you locate a replacement part and get the pump working correctly.  If the pump is not working properly, performance of your bike with its nice new exhaust will be limited until it does.

[Buga8tr]

That is why I drilled a hole in the set screw is so it can still squirt fuel.  It squirts a little more than I wanted but it will work for now.  I just went for a nice 1oo mile ride, no problems.  Seems to run pretty darn good.  No overheating, and no smoke, good power all the way up to beyond the speed limit.

[Spanner 1]

Wow !, the check-valve stops fuel from 'falling' back down from the fuel-rail so that pulses from the acc. pump tend to keep the lines to the carbs full and ready for the next squirt..not having this ?..I'm not sure how much ill effect that would be on performance.........

P.S.   I'm lost as to why you decided to go to the trouble with the hollow set-screw?, as there is no 'jet' required at that bowl/body juncture, just the o-ring so it seals , if leaving out the check valve .....

[Hush]

Hey if it works it works?
My 650 has the square brass one and it shoots gas quite high when plunged so maybe he will just have lousy gas mileage?
But if the bike goes and goes quite well by the sound of it we shall see if this is a repair that can be used across the board when we can no longer get such things as "check valves"

[Spanner 1]

Hush, will work fine until you need TWO quick throttle movements..i.e...when you accelerate with say medium ( or whatever ) throttle opening, the sequence would be; idle jet to acc. pump to main jet, shut-off and fuel that was pushed-up by the acc. pump now is free ( no check valve ) to get sucked back down by the retracting acc.pump diaphragm ..so on its next 'use' the acc. pump will create a 'stall' before fuel reaches the 4 carb nozzles..yaseewhatimean ?