750ss Float Height??

Float height is a load of bollox on these carbs.............The float height affects the pilot circuit and lower rev range running.

Thus, there is no set dimension..........

However, it seems that a starting point is 14mm, measuring from the inverted carb gasket face to the top of the larger (square) float..............but.........

Firstly, when measuring, you have to angle the carb so that the weight of the float doesn't compress the float needle spring.

Secondly, when I pulled my carbs apart, one was 12mm and the other was 9mm (and I had also had fule peeing out of the overflows)..........so logically I set mine at 14mm..........no good; tried 13mm.......not right......; went to 12.5mm and it is better, but slightly weaker than it was, so the pilot screws are 4.25 - 4.5 turns out instead of 3.5.

Lumbux found a similar thing and I think his are at 12mm, so I reckon you should set yours at 12 - 12.5mm and hope for the best.........can't guarantee it will be correct though....

AL

 

The clear tube method obviously doesn't use the same way of measuring the fuel / float height though, therefore the dimension from the inverted carb gasket face to the top (bottom) of the float won't be the same.........

Somewhere I have details of the same carbs on a Tenere, and the tube method on that bike should set the fuel height (not the float height) at 5.2mm - 6.2mm.

 

I tested my float valves with the carbs held at the right angle in a vice..........filled them up with petrol via a short hose and made sure the hose was full............then fitted a footpump with a gauge to the hose...........

............gentle pressure on the pump meant the float valves were overcome at about 12 - 12.5 psi.

 

I thought mine were 12mm, but my mixture screws are not set the same, so I assume that they are different. not had an overflow problem before, and keep ajusting them to try to get the sparks plug colour correct, its taken 400 miles and I'm still fiddling.

 

My plugs are light grey with the tiniest bit of rust colour...........

Don't forget, as we are not using leaded petrol anymore and there is ethanol in fuels these days, the burn colours will not be like they used to be and the plugs will be cleaner.

 

I see you have checked the return hose, but did you check that fuel is actually running back into the tank?

When you check the float height (the dimension you give should be somewhere about right) did you:

1) Reverse the float bowl and screw it on to hold the float assembly in place while you check the dimension?

2) Check the float needle seats? Dried petrol residue can stick to them, so although the needle is fine, it won't seal properly.

See the attached.........These are of a new float assembly...........you can clearly see why mine keept overflowing.

I also suggest that you disconnect the fuel tank breather valve while you are working on the bike..........I had a faulty valve two years ago and bought a new one.......unbeknown to me, it was also faulty.

When the engine warmed up, the valve wouldn't release the tank pressure, so it pressurised the whole fuel system and fuel kept p*ssing out of the overflow pipes.

Fitted a new breather valve and this time it seems OK..........

However I have also noticed that if the tank is very full and the bike is on a paddock stand, the breather valve can get blocked by fuel (it will eventually start dribbling out of the breather hose).......the more upright the bike is, the more likely it can happen.

Also, on what seem like OK float assemblies, the needles wear the sides of the nylon needle recess which can either snag the needle itself, or allow the needle to slop about inside the recess......

 

Don't let the tank breather valve fool you into thinking its alright.......disconnect the breather hose from the tank and while you are at it shove a length of strimmer cable through the little stub pipe on the tank and make sure that is clear as well.......

.......the symptoms you are getting seem exactly like mine...........it took me two years to work out the breather valve was faulty...........if wasn't for the fact the little line around it had opened up to 2mm wide, I wouldn't have spotted it......the tank pressure was blowing the valve apart...........

 

Well, it seems as though you have no option other than to try new float assemblies............although bear in mind that if you left the tiniest bit of lint or fluff from a rag or cotton wool bud in the float needle seat it will cause problems like you have.......(and even more problems if the same fluff gets into the pilot circuit.....)

But I have also found that the float assemblies on these carbs can 'stick'.......tapping the float bowl will sometimes stop it.

I assume you have seen the attached image..........but it doesn't show how the reversed float bowl holds the float assembly still when you are measuring.......neither does it show the carbs tipped to stop the float needle spring from compressing..........

 

Mine quite often floods if I have left it for over a month or so without starting it. I am sure this is just down to sticking float assemblies as, if I tap the float chambers lightly whilst it is running it usually stops it. Then fresh fuel will normally keep things flowing properly and it doesn't happen if I am running the bike regularly.

 

BTW..........If you are in a hurry, I have at least four sets of float assemblies (used) you can try.........two were changed even though they were OK, because the faulty damn tank breather made me think they were up the creek.

 

I'm certain that the OEM pump produces about 3 to 3.5psi.............