Sticking floats

[egsols]

I've been chasing my leaking carbs for a while now and thought I had it solved after changing over to viton tipped valves. I hadn't had a chance to ride for about a week now and went to go for a spin last night. I pulled the bike out of the garage, fired it up, took down to the end of the driveway and shut it off for a minute to go get my kid.

It starts to puke fuel from the air box again!!!!

Pulled seat, tank, loosened airbox and pulled the stacks to clear the back of the carbs. I could see that no. 2 and 3 carb were leaking. I fired it back up to see if I could drop the level of fuel in the carbs and make them leak again with it shut off. Nope. I guess the floats were sticking ever so slightly that by firing up the bike again it freed them.

Well I put it all back together and went for a spin. Stopped at a buddies and let it sit for while with the petcocks on. No leaks. Got home parked it. Came out this morning...no leaks.

Can the floats dry up setting for a while and then stick? I'm getting really tired of fuel soaked air filters.

Anyways here's a pic of how far I made it last night. You can see the puddle by the centre stand. (I didn't feel like leaking fuel on my driveway so I just wrenched on the road.)

[boyat68]

egsols:

I think your are a victim of physics. When you set the clearance of the floats, i.e. the drop of the float, the relative ambient temperature of the carbs was air temperature. When you go for a ride the temperature of the metal and fuel go up. expansion sets in. the air in the floats expand, and when you come back, the floats do not go back to there original shape as quickly as the metal as they are immersed in cooler fuel. the floats may stick if the clearance is not sufficient to take care of the differential. If you notice the plastic floats have ridges left over from the blow mold that add to the ability to grab the edges of the bowl. I sanded these ridges off of the new set that I put in just for that reason. Also note that if you bend the metal tangs on the back of the floats for drop control, they have edges that sometimes digs into the pot metal of the support post and hang ever so slightly especially if the post are not smooth.

[egsols]

Hi boyat68,

I'm still running brass floats in the '79. I've set the total drop to about 3 mm. Anymore than that and I think the valves get cocked.

I'll have to check into the tangs on the posts.

The only time they seem to stick is when the bike has been sitting for awhile.

The heating effect is why I think the manual says to check the fuel height, on the 81's, with the bike warmed up. But are you saying it would effect the brass floats as well as the plastics?

[boyat68]

egsols:

Yes, but probably not as much since the metal floats are brass, but expansion sets in even with metal floats, and two dissimilar metals contract and expand at different rates. If the clearance is not sufficient, then once the floats stick to the sides or whatever, then the buoyancy of the floats are not enough to free them from the rising fuel. Also double check the gasket edges as the gaskets from mikesSX extended over the lip of the bowl a few mm and had to be trimmed back. The other problem is the metal of the float supports being steel and if they are bent by insufficient force when adjusting, they have residual memory and will spring back towards their original shape. That is why you would use a spring bender on a flat spring relay as the spring bender deforms the metal at that point.

It is a lesson in futility to try and understand why Yamaha made the clearances of those carbs so critical.

[olebiker]

**** sorry to hear that Ernie I know you thought it was licked. I am now almost scared of the damn carbs. I do have to rebuild one petcock that leaks a small amount when off. I am scared that if I don't some time I will end up driving with diluted gas.

[egsols]

Thanks Carl,

My biggest worry is the gas getting into the oil. I know it had before and I think I rode it a short ways before realizing. Don't know now if any damage has been done, seems okay.

It's just a frustating exercise, everytime I think I've licked the problem, a couple of weeks go by and it resurfaces.

I check my oil before each ride and also stick my nose near the filler to smell for gas in the oil.

I'm wondering now if when it sits for a week or two enough gas evaporates out of the floats to drop them. I keep the bike on the side stand so if the floats are down a bit, leaning to the side, getting dry, could they stick just a little on the pins themselves?

[boyat68]

egsols:

If you only have a small leak, then the fuel only leaks out of the rear of the carbs as that point is slightly lower than the front. You can test this out the next time you take the carbs out and bench test them. Also you have a larger front tire than on the rear so the bike sits at a slight rearward angle. When you have a bigger leak and you are on prime, then the fuel may go forward, but I have not experienced this since my vacuum feed is intact. My leaks had been all rearward and out the airbox. The slant of the bike on its kick stand does put a small side pressure on the float since the hinge pivot is slop fit and the hinge rubs against the side support towers. I noticed that my old floats had brass inserts (sleeves) and the hinge pins fit closer where the inserts would hang on the pin. The new floats are very slopply fit around the pin. I suppose that the brass floats that you have may exhibit the same problem (tight fit), so that could add to the problem of free float action being hindered.

[egsols]

boyat68:

The brass floats are somewhat sloppy with some side to side play. That's why your comments trigured that thought. If they are horizontal they probably move up and down okay but if dry and leaning they could be binding on the post. I never thought of them binding on the posts because all the tests I did were with the carbs level.

If I get time I'll pull them and test them on an angle to see if that causes binding.

I checked for clearance around the gaskets and all looked good. I also checked if they were touching the sides of the bowls and couldn't see any evidence of that. I did make sure that the two pods, per float, were not bent outward thus making the float wider. I recall giving a couple a slight squeeze, before adjusting, just to make sure.

My octy is gone and I have to manually shut my fuel off when I park it. I don't generally forget to shut off the taps, but I have a bad habit of forgetting to turn them on when I ride off.

[randy]

Ernie;

A good float test, before installing the carbs is to blow into each fuel line while turning the carbs upside down. When the float valves close, you will feel the back pressure. This test ensures that the floats are not binding on the bowls and they are properly closing the valves.

[egsols]

Hi Randy,

Good idea, thanks.

I had tried boyat68's dental floss trick but, again I did it with the carbs level.

Will try your trick, don't think I can get them in for an MRI anytime soon.

[olebiker]

Originally posted by egsols
Hi Randy,

Good idea, thanks.

I had tried boyat68's dental floss trick but, again I did it with the carbs level.

Will try your trick, don't think I can get them in for an MRI anytime soon.

No crap. I think I am ahead of you in the lineup for an MRI. Been told it could be a while.