FB Nikki Carb float level setting

[DaveCollins]

Eventually got round to rebuilding the carb on my FB.  Hopefully it was the cause of the rough running as lots of muck seemed to come out of it when I cleaned.

I have fitted new needle valves and seats and have now been spending hours trying to set the float levels correctly.  With the Mazda service manual setting of 16mm both sides of the carb flooded.  I am now at about 20mm to 22mm which seems a fair way out from standard.  So far not been able to get levels in both float chambers consistent and have found that when one is right then taking the air horn off and on to adjust the other end mucks up the level just achieved.

I have so far had the air horn on and off about 30 times and still no accurate level.  Does anyone have any tips on best way to achieve correct adjustment? 

Wish I had not changed the valve seats now and just left alone!

Thanks for any advice anyone has.

Dave

[clive]

Good to see your getting the car up and running again.

Cant remember properly as it as a long way back, but If the float has a metal bracket where the pin attaches the float to the carb body, I used to simply bend the bracket till the desired level was achieved.

 

[DaveCollins]

Yes it is the tabs on the float I am adjusting.  Just seems to be a pig of a job as you get one to the correct level and in removing air horn to adjust the other the first one then reads a different level when you connect fuel up again.

I am surprised that the current settings I have are so far away from the Mazda factory settings as the needle valves and seats appear the same length as the factory ones that came out.  I should have left well alone but as rebuild kit had new ones I changed them!

I will just have to start at a setting that I know gives too low a fuel level and then adjust each float 1mm at a time until approx. correct level is achieved.

Just need a few more hours patience!

Dave

[Casey]

It may no be much help with your present dilemma Dave, but I have a spare Nikki carb in pieces at the moment which I intend to clean and rebuild. I have a rebuild kit with lots of new parts to do the job, but have been awaiting a clear area where I can do this fiddly work. I now have space available but not sure I'll have the time to get it done for at least a month. I've been reading up and I can only state what has already been said, bending the tabs is the recommended procedure. I'll find out later whether this gives any issues, but at least I've got your "heads up" which means I'll check this item very carefully on assembly.

[DaveCollins]

Clean and rebuild were reasonably OK. 

I am actually using the old air horn gasket as neither of the two that came with the rebuild kit were totally correct.  I would certainly recommend not touching the needle valves and float adjustment unless you think there is a problem with them.  I just went ahead and fitted the new ones in the rebuild kit as I thought it would be the best thing to do!  Actually removing the old needle valve seats was a tricky job, as always the good old Haynes manual "remove the needle seat with a screwdriver" turned in to something a little more difficult.

When I set floats at the 16mm recommended in manual fuel was gushing out of all jets almost immediately pump was turned on.  One thing I have learned is do not put all the ancillaries back on carb before you try the fuel level.  Just connect it up as soon as air horn is back on.  That way it is much easier to keep taking it off to adjust tabs.

I will let you know how I get on after next weekend although can't decide whether to do this job or change the exhaust system on GT from Le Mans spec to Castle Combe trackday friendly spec for charity day later in the month!

[DaveCollins]

After another few hours of tab bending I have eventually got the levels within a couple of mm of the centre line of the window.  Decided to leave at that and see how it goes.  Last time I tried to get it more accurate than that a few more hours work gained no improvements.

All ancillaries now bolted back on the carb so next step it to bolt to engine and see if it fires up.  That will probably have to wait until next weekend.

Attached picture shows difference in gasket from rebuild kit to one that came off of carb.  Area of change is on right hand side above where needle valve comes through.  There is an extra area of gasket to cover the accelerator pump check valve.  I have not seen a gasket of this shape in any of the readily available rebuild kits so have used the old one.

Dave

[Casey]

Well spotted! I've just checked the my old gasket and the new one I have to replace it from my rebuild kit.

If I took a picture of both they would look exactly as yours does above