Topic: Float needle question on '73 750

[Fabricator]

Howdy all,

  Bike in question is a '73 750K with 8400 original miles, and VERY clean carbs.

      Here's my question?  How much spring pressure is the little teat inside the float needle supposed to apply?  I know there is no spec for this, and it is a judgment call, but I noticed that a friends' bike (similar year 750 as well, with oem plastic floats) had enough strength that with the carbs upside-down, that the floats were not depressing the teat more than 5-10%. In other words, the needle spring was supporting nearly all of the weight of the float.  He also had aftermarket needles and seats from a Keyster kit. 
     The reason I bring this up is because my carbs have been leaking (ok... they pour) out the over-flow tubes intermittently.  Sometimes a good tap on the bowl helps, but more often there is no change.  After removing the bowls to verify that the overflow tubes are not cracked, I noticed that my #4 needle was stuck closed...  Additionally, #3 would not shut off fuel completly.  Off came the carbs for a careful check of the float levels.  all of the floats needed minor tweaking, but the worst were still within 1/16" of where they are supposed to be.  After completing the adjustment, I noticed that when the carbs are upside-down, the weight of the floats was completly depressing the needle spring.  I suspect that the needles are leaking due to insufficient seating pressure; resulting from these wimpy springs... At least that s my current theory.  Can anyone share their thoughts on this?  I really do not want to replace something unnecessarily.  Especially since the needles are OEM parts with so few miles, and the needle tips look perfect.

Fabricator

[HondaMan]

The springs should be soft, as you describe yours. The Keyster springs are too strong, and cause low float levels because they cut off the fuel too soon.

When you set your floats, lower the floats until they just begin to push the spring finger. Set the float for 26mm right there. Then, when the bowl fills to 24-22mm, it shuts off. This is the OEM spec.

Check your posts for tiny, tiny burrs: if the bike was sidestanded a lot, with the fuel turned on, on hot summer days, the sharp edges of the float bracket raises and lowers as the heat evaporates away the fuel and it then fills up the bowl again. This scrapes up a tiny burr that later prevents the float from being able to push the needle all the way closed. I see this on probably 75% of the carbs I get for cleaning and refurb. Remove the burr gently with a file: you can usually detect it by gently sliding a razor blade up along the post. Smooth off the sharp edges of the float brackets to prevent recurrence.

[Fabricator]

HM,

  Thanks!  I really hoped I could keep my low mileage needles.  I just did not have a "new" OEM needle to compare them to.  The burrs you are talking about:  Are they on the side of the spring finger ("teat"), or the side of the needle? 

On a related note: Would the folks with aftermarket needles need to use the clear plastic tubing trick to check fuel levels, as opposed to the "dry" test outlined in the manual?  Would this give a more accurate fuel level?

Fabricator

[tommye]

Interesting!
Can you recommend a different float level setting when using the Keyster needles ?
Tommy

[HondaMan]

The burrs you are talking about:  Are they on the side of the spring finger ("teat"), or the side of the needle? 

They are on the insides of the "posts", where the float's brass stamping rubs against the aluminum while the floats pivot on the pin.

On a related note: Would the folks with aftermarket needles need to use the clear plastic tubing trick to check fuel levels, as opposed to the "dry" test outlined in the manual?  Would this give a more accurate fuel level?

That would probably be more "visual", but I haven't done it myself in years. You can tell the  difference between 24mm and 26mm bowl depths pretty easily, though. I often just watch the fuel rise in the bowl as I slowly reinstall the full bowl, judging if it is deep enough to cover the pilot jet. That's the important measurement. 

[Fabricator]

HM,

   I mis-read your original post...  You are correct: There are "itsy-bitsy" burrs on the inside of the zinc/aluminum posts that the pivot pins ride in (it is most noticeable on my #3 carb).  I will burnish them carefully with a jewlers' file.  Thanks again. 

PS:  Should I do something to retain the pivot pins?  They pushed out easily with a small allen, and only fingertip pressure.  It seems as though the shape of the bowl would keep them from coming completely out.  On the other hand, I would think a tiny punch mark would be wise... Any recommendations?

Fabricator
   

[HondaMan]

HM,

   I mis-read your original post...  You are correct: There are "itsy-bitsy" burrs on the inside of the zinc/aluminum posts that the pivot pins ride in (it is most noticeable on my #3 carb).  I will burnish them carefully with a jewlers' file.  Thanks again. 

PS:  Should I do something to retain the pivot pins?  They pushed out easily with a small allen, and only fingertip pressure.  It seems as though the shape of the bowl would keep them from coming completely out.  On the other hand, I would think a tiny punch mark would be wise... Any recommendations?

Fabricator
   

Let them float, for sure. The looser they slide, the better the system works. The bowl will capture them, just like you imagine. 

[Fabricator]

Thanks.   I reassembled it all this afternoon, and it ran better, idled smoother, and had none of the blubbering issue from 4-5k.  No leaks unitl.... I tooled around our neighborhood after a nice afternoon ride, and #4 began pouring again.  I will look into it again tomorrow.  It is very intermittent, and only on #4.  I am going to verify that I got all the burrs.

Best regards,

Fabricator

[Fabricator]

Update on needle issue...

Took 2 hours to get to work this AM.... (16 miles).  #3 was pouring a torrent from the overflow, and #4 (after pulling bowl) had a teaspoon of fuel, and the needle was lodged in the bore of the valve.  I finally coaxed the needle out, but found no visible reason for the condition.  I re-assembled everything (roadside at 5:40am), and tried to get #4 to re-produce the issue with the bowl off, and could not get the needle to stick.  After putting the bowl back on and turning the fuel back on, #3 was OK, and #4 was pouring fuel...  I opened it up again, and found the #4 needle stuck in the bore.  I then swapped the #4 and #1 needles (I know it was not ideal) and re-assembled... I turned fuel on, and #1 (with the problem #4 needle) was pouring fuel.  I opened it up and surprise: the needle was stuck in the bore of the valve.  I used the 320 grit emery cloth I had in my tools to buff the lower corners of the valve (assuming the sharp corners were catching on the entrance to the valve bore) with no change.  I rode the remaining 3 miles in with one hand modulating the choke in relation to throttle position, just to keep enough fuel in things to make it go.  I am ready to replace the needles, and likely seats.   I cannot figure out how a bike with 8500 miles, that has run flawlessly for the past 250 miles, is giving me so much trouble!

Fabricator

[Spanner 1]

Fab, I think your problem is actually caused by slow fuel delivery !!..... If the fuel is not entering the float bowls fast enough, one carb will be 'favored' and the others unable to fill and it's random which carb will fill IMO. If the bowl fills too slowly the valve won't close, try it in your toilet tank ! 9 times out of 10 if you turn the water supply down low the float is 'fooled' by the slow water rise and wont shut-off !
Time to take the pet-cock off and clean it and the filter and check the gas cap vent........ my2c.

[Fabricator]

Spanner,

  Thanks for the tips.  Unfortunately my "problem needle" actually sticks in the needle bore.  The fuel comes through a high flow 3/8 npt "performance" petcock, and it is in a freshly cleaned tank.  When it overflows, it comes so fast that the overflows cannot handle the volume, and the airbox pours as well! 

Any suggestions on why the needles would stick in the bore of the float valves???

Fabricator

[Fabricator]

I am shamelessly bumping my own thread...

We called it quits an hour early in the shop (so the boss could work on his bike).  I hoped I could resolve my fuel issue....  Now another float needle is sticking!  The float needles are staying stuck UP inside the valve.  Sometimes this cuts off all fuel, but other times it leaks like crazy... Even when I hold the floats up with my finger!  My levels were lust set to 26mm last week, and it has run very smooth, and not puked a drop out the overflows; until this morning.   Any help would save me a lot of money on scotch tonight!

Fabricator