Fixing the fuel tank

Hi Cobba
Have you checked the Butterfly Shaft for the Throttle for wear?
I play with old Fergy's a bit, and a common problem is exactly as you describe, with the fix being to replace the shaft and ream and bush the holes for the shaft in the body of the carby, as it simply wears and sucks a lot of air around the shaft, making the mixture and main jet adjustments almost useless.
Hope this helps
Cheers
Alistair

I find with petrol motors when what you are describing it is idling on the running jets and not the idle jets
The idle is set to high because someone couldn't get it to idle on the idle circuit


So I would let the butterfly fully shut and start from there
I believe and stand to be corrected that the butterfly should be fully shut at idle and the motor should idle thru another air supply and I fibd this is normally a hole in the butterfly

Paul

OK, when running the engine today I had a can of start ya bastard and sprayed it around the inlet maifold to the head, manifold to carby and the main throttle shaft all with no change in engine running or change of revs. The throttle shaft on this carby is so different, no bushes but rather it runs on 14 tiny needle rollers each side and originally the shaft was sealed with felt washers. Now they use nylon washers. I have installed an "O" ring on each side as they sit into a recess and then a nylon washer as well. There is no sideways or up and down movement on the shaft at all and opens and closes firm but not too firm and is smooth as well in movement.
Yes the butterfly does have a hole in it and the jet for the idle circuit is the one shown in the last pic I posted which when you look through it is perfectly clear. being a TVO (petrol / kero) engine these have specific jet sizes and all of them are absolutley labelled as being correct.
On the David Brown site one reply claimed I have the wrong mixture screw and in the link to the Solex carby and trouble shooting there is no picture of a mixture screw nor is it in the cut away view and they are therefore not identified as a part number or description but gets a mention in the tune up section.

Im not real good at explaining things so bare with me while I try to

The mixture screw on a carby is set, as in set with a screwdruver normally, the butterfly fully shuts and and that then threw the hole in the butterfly gives a fixed air volume and we (the human hanging onto the screw driver) adjusts the mixture to get the air fuel ratio right for it to idle smoothly

When the butterfly opens it also with the added volume of air rushing past the jets in the venturi part of the carby sucks the fuel at a metered volume in proportion to the air to suck fuel out of the bowl
The motor is now running on the tiny dribble of fuel from the idle screw and on its jets in the venturi
The bowl of course gets replenished by the needle and seat so as to keep a ready supply of fuel available for the motor at all times

You cant have the wrong size mixture screw as it is a very fine tapered screw going into a fixed size hole
The more you screw it out the bigger the gap and the more fuel that is allowed to be sucked into the engine

I believe your butterfly isnt fully shutting and that is allowing to much air to rush past the jets in the venturi and those are the jets that it is running on and not the little dribble out of the mixture screw

I am not trained in any of this and dont pretend to be a expert so I may well be leading you up the garden path lol


Good luck

Paul

Mrs,
You done 'splained it pretty good for a amateur like me! It took a lot of the mystery about carburettors away from the cobwebs where my brain used to be.

Well explained and thank you for your hints at setting this bugger up. I will post some pics of the carby that shows a big clear hole from one side to the other. This is where the blanking off plug goes on one side and the mixture screw from the opposite side, there is no tapered seat for the needle to fit into rather I am guessing that it is metering the air gap between the taper and the small hole in the body Taper is not fine, it's bloody thick as me! The butterfly shows a nice little Louvre like opening for the air to pass at idle and this is perfectly clear to allow that to happen.
So tomorrows episode will be a case of carefully looking at this mixture screw from when I totally remove it from the body when it runs best to how far in I put the mixture screw before it starts to play up. I will also once the engine is warm wind the mixture screw out 1 1/2 turns as nearly a standard thing to do, then reduce the idle back and keep adjusting the air mixture until I have no contact on the throttle with the idler set screw as you have suggested and see what happens from there. I never thought of setting it this way before and how you explained it does make sense to an unedificated bloke like me.
So now I cant wait to finish work in the morning and "have a go ya mug!"

Cobba
Guess you've already been here via the DB Club and similar.
Hope the link works.
Keep at it
www.oldengine.org/members/diesel/SolexCarbs/solex13.htm

Cheers

Yes thanks Tired Iron. That link can be opened to about 22 pages of hints and tips. Interestingly enough the air bleed or mixture screw is not shown in the cut away digram but gets a mention in the setting or tuning up section of the link. Tomorrow is another day of play time with it untilthe heat stuffs me and will be working for most of the morning so under the iron roof near the hottest part of the day or leave it until Sunday when the heat will be gone.

Episode 1,234, way too many.
Once again a night of ideas on what to do to resolve this mess. Fuel level in the bowl was measured by connecting a clear plastic tube to the drain cock on the bowl and holding the tube agaist the bowl. Level was about 3/4 full. I have an aluminium washer under the needle n seat and this raises the level too high, to the top of the bowl and floods so went back to having a fibre washer with the aluminium one and back to being 3/4 full. At the moment it does not starve on full throttle standing still but might when on the road, will find this out tomorrow on a quick run up to the forrest and back.
Next was to once again strip the czrby down to being completely apart and double checking cleanliness and re-assembly ensuring that the 3 parts of the main jet are assembled correctly and fitted firmly in place.
Then with yet another read of the Solex carby link something hit me hard in the face, bloody air cleaner. This runs an oil bath cleaner and when I dropped the bowl it was not only over full but the centre ring where the air breaths in was also full of oil. So I lowered the oil level and removed the oil from the middle. Hopefully this was the right thing to do.
Still with the oil bowl off I started the tractor and ran it for a while so it was warm. Then I dropped the idle screw right back so it was not touching the stop and all the time changing the mixture although it did not seem to do much. So I kept winding the mixture screw out until it was in my hand. You can hear the air rushing in through the hole and when you put your finger over the hole the engine revs drop and runs a bit rough. Threw the oil bowl back on and nothing changed there so that is done. There is a remote chance that there is still oil inside the air cleaner where the steel wool looking stuf is and may still be choking the engine. Maybe after the run tomorrow this too will improve.
With a couple of runs up and down the back driveway it certainly pulls well with no hesitation at all where in the past it did. SO if nothing else this has improved.
All I can do now is take it for a run up hill and down dale and along the road and give it a good gallop and re access it from there.

I wonder how it goes with no intake piping at all attached to the carby.

I was hit by a similar thing and had forgotten all about it. Driving my newly aquired Studebaker home from Proserpine to Ipswich some years back; every time I hit a hill it would die in the arse. Long story short, the air cleaner was blocking up every time I needed some power. (a flap of hessian had come loose).

Trying it with no air intake at all would certainly answer that question.

Jarrod.