Why does it flood?

[alanp]

I'm stumped! My RGS  389 carb. floods for no apparent reason. By flood I mean it pours out of the tickler which is not jammed down. Here is a typical scenario - after a 30 mile 70mph run I stop at some traffic lights and the engine cuts out. I look down and petrol is pouring out of the carb. I turn off the petrol, restart the engine, turn on the petrol and all is well. When in the garage I inspect the float chamber and petrol feed parts, float/needle etc and there is a very small amount of fine red/brown dust in the chamber which I wipe out and can't find any other reason for the needle not to close off the fuel. There is no apparent problem with the needle tip (rubber), the float (correct part No. and no leaks) or the float needle seating. With everything clean and after a flush of the petrol pipes I reassemble it all, turn on the taps and woosh out it pours again staright away!  I pull it apart again and everything is as clean as a whistle. I pull it apart again, the needle closes off the fuel with a slight upward lift of the float and reassemble. Petrol taps on - no flooding!
Over the last few weeks this has happened maybe 4 times.
Any ideas chaps?
Alan

[MG]

Hmmmm, very strange indeed. Maybe the float gets trapped somewhere inside the float chamber or the cover? Do you have that little brass bush/distance piece fitted on the float shaft?

[bsa-bill]

Do you have that little brass bush/distance piece fitted on the float shaft?

and is it on the correct side of the float DAMHIK

[mike667]

i had a similar problem and found small burrs on seams on the float itself that where hanging it up on the bottom of the carb - i sanded the seam smooth and problem disappeared

i would bet, as Markus too mentioned,  the float in your carb is also catching on something too and not stopping fuel from pouring in

 

[alanp]

I think I've solved it !!!!!!
The float was jamming in it's lowest position due to the poor alignment of the 2 halves of the float when molded together causing it to have too big a radius from the pivot centre, which allowed it to lock on one of the cast screw bosses inside the float. I've dressed the float down until it clears the casting and it now doesn't jam and only rests on the square section casting inside the chamber that it's supposed to.
Check out the 2 photos attached.
You can see at the tip of the pencil the mark on the chamber casting where it touched/jammed the float. The other photo shows the dressing I've done on the float to reduce its radius from the pivot centre.
Here's hoping I'm right......
Thanks for your help chaps
Alan

[mike667]

I think I've solved it !!!!!!
The float was jamming in it's lowest position due to the poor alignment of the 2 halves of the float when molded together causing it to have too big a radius from the pivot centre, which allowed it to lock on one of the cast screw bosses inside the float. I've dressed the float down until it clears the casting and it now doesn't jam and only rests on the square section casting inside the chamber that it's supposed to.
Check out the 2 photos attached.
You can see at the tip of the pencil the mark on the chamber casting where it touched/jammed the float. The other photo shows the dressing I've done on the float to reduce its radius from the pivot centre.
Here's hoping I'm right......
Thanks for your help chaps
Alan

yup thats what mine was doing too...

[MG]

Instead of the float chamber cover, you could temporarily fit a piece of transparent clingwrap with a rubber band. This way you can see the float in action and check whether it works now.

Cheers, Markus


  my 400th post, party on!  

[bsa-bill]

Thanks for your help chaps

NO we thank you Alan, your problem solved may one day help all who read it

[alanp]

Markus et al, this makes me think about what you could use as a permanent window. Glass (can't drill the screw holes?), perspex, lexan etc? Something transparent which would resist staining etc from the petrol. Any ideas? Surely someone has done this on a carb. I've seen it done on a bevel cam drive Ducati single a few years back, it looked really trick.
On my Gold Star with its remote cylindrical float chamber, I had to fix up a transparent stand pipe to keep an eye on level and to set the chamber height. Very critical with a 1 1/2" GP carb.
An interesting point which I picked up locally is that original carbs don't have a sealing washer under the float needle threaded housing whereas modern manufactured 389s do. Apparently, I am told, this was due to the modern ones being more deeply spot face machined on the top surface of the float chamber for the threaded needle housing and the washer compensates for this to get the fuel level correct. The Amal reference book, with reference to the sealing washer says 'if fitted', acknowledging that there is a difference. Interestingly, this will affect fuel height if you get it wrong for your carb. body. Admittedly only a mm or so but......Any thoughts   
Alan
ps 400 posts Markus! Very well done! Enthusiasts willing to share their problems/help/solutions makes this forum great

[bsa-bill]

I think the washer is needed if using a Viton tipped float needle, otherwise no washer

[chaterlea25]

Hi Alan,
If you want to try drilling glass there are special drills available,
OR you can use a piece of coppertube and some grinding paste, with the drill mounted in a drillstand or use a pillar drill
I have even drilled the toughened glass on a cooker front to mount an extra switch (dont ask!!!!) this way!!

Bill, I believe the difference is in the carb body as Alan says not the needles ???? ????
HTH

John O R

[a10 gf]

Have followed this discussion, nice to see the problem solved ! And some very fine comments:

NO we thank you Alan, your problem solved may one day help all who read it

Enthusiasts willing to share their problems/help/solutions makes this forum great

(And congrats to Markus, for lots of help "beyond the call of duty")

[MG]

Thank you Erling, but looks like I was too hasty after you've deleted two posts, so one more to go.  

This forum is a great place for discussion, information and having some fun (plus it is a very welcome chance to brush up my English a bit, not using a foreign language is the best way to forget).

Cheers

[a10 gf]

Sorry for the offtopic. Some old threads were moved to the forum 'repository' (no post count there), but you're factual count is 400+ all the same.