solex - poor mpg

[MARK.WALSH]

actually - thinking about it I believe I have another better condition float kicking around in the garage so I will make a substitution and see if there is a difference.
The bistarter needs full choke on cold but soon goes back in - less then a minute. Still I will check it is not sticking and fully going home when pressed in.
Thanks for all the advice
Mark

[Pete.Silson]

Mark,

When I first ran my 4G after reassembly the fuel consumption was very poor and it was obviously running way too rich. It also had a tendency to dribble fuel if the machine was tipped to one side even slightly. Originally when I had stripped and cleaned the Solex carb it had multiple fibre washers on the float valve which I had assumed was incorrect so replaced them with a single washer. When I re-instated the extra fibre washers the mixture improved dramatically. These washers appear to be a way of adjusting the fuel level in the float bowl.

I have since done 700-800 miles, mostly at 40-60 around the local lanes, and am averaging a little over 50 mpg. The bike starts on full choke but can be dropped to half-choke almost immediately. I usually drive off on half-choke and flick it off as soon as I am on open road.

Pete

[simon.holyfield]

Mark,

When I first ran my 4G after reassembly the fuel consumption was very poor and it was obviously running way too rich. It also had a tendency to dribble fuel if the machine was tipped to one side even slightly. Originally when I had stripped and cleaned the Solex carb it had multiple fibre washers on the float valve which I had assumed was incorrect so replaced them with a single washer. When I re-instated the extra fibre washers the mixture improved dramatically. These washers appear to be a way of adjusting the fuel level in the float bowl.

I have since done 700-800 miles, mostly at 40-60 around the local lanes, and am averaging a little over 50 mpg. The bike starts on full choke but can be dropped to half-choke almost immediately. I usually drive off on half-choke and flick it off as soon as I am on open road.

Pete

That's really interesting. How many fibre washers were fitted?

[Pete.Silson]

Simon

I think that there were 2 originally which is what I have now.

Interestingly new float valves for VW Beetles, which are a similar carburettor, come with 3 different thickness washers.
See http://www.vw-resource.com/float_needle.html#washers

Pete

[simon.holyfield]

Interesting. An Amal monobloc has a mark on the float chamber showing the intended fuel level. I wonder if the Solex carries a similar mark?

There's no mention of fuel level in the Solex instruction book.

[chris.shearwood]

One thing I must pay attention to is the float height though, as the contact point on the float to the shut off valve is a bit concave from wear. I had thought of applying a bit of solder to ease the dimple in it - might be part of the problem?

Hi Mark,
I looked through my notes on Solex carbs and came across this from the AOMCC e-mail chat group written back in 2002 by Mark Carter:
"The float does have a largish dimple in the middle. That is normal"

and as for adjusting float height by adding washers under the needle/seat assembly:
"As far as spacing goes, they seem to need about 1/8" thickness of washers. Experiment a bit to see what yours requires".

And among quite a few other possible causes of poor mileage mentioned in a Solex manual which had been available on-line at http://oacdp.freeweb7.com/solex :
"If... fuel consumption is heavy check ........throttle spindle worn"

I don't know how a worn spindle could increase fuel consumption but it might be worth checking.
Regards, Chris

[MARK.WALSH]

Chris
thanks for the advice.
I think the dimple you mention refers to the section on the top of the float which has a sort of dimple but mine is a greater depression within that caused by wear.
I will certainly give the idea of changing washers a go as in the past I have noticed that the bike does idle better (for a few seconds only) if I shut the petrol off shortly before the engine stalls. That could also imply the float level is too high. Altering the valve height with washers therefore may help
Cheers
Mark

[nevhunter]

Don't add weight, use a fibre spacer. As the seat and needle end wear the fuel level rises any solder repairs add weight also. Sometimes the float only "just" floats. those carby's get hot. If the fuel gets bubbles in it the float sinks and then you really get through the fuel. Nev

[MARK.WALSH]

Well at long last I have pulled the carb off and inspected it. The air correction jet looked partially blocked so I blew some air down it which seemed to clear it. I then (for some reason not even known to me) blew air down the other end and then it looked restricted again - couldn't see daylight when when holding it up to the light. Again tried the other way and hey presto - clear. Thinking there must be a physical and partial obstruction I unscrewed the tube from the jet and there appeared to be a congealed bit of oil/muck which had accumulated between the two parts. I think blowing in different directions made the crud act like a valve. - anyway all removed so lets see if that's done the trick .
Out of interest, whilst looking at the carb I noticed I had a distinct ridge between the carb joint and the heat spacer. Looking closer it was obvious that solex carbs (because of the butterfly valve I assume) are not round on the induction joint but distinctly oval - narrower in width by a couple of millimetres than the height. So what I have done is filed down the heat insulator to remove what is a step on the induction at the top and bottom . Might be interesting to see if this makes any difference on tick over
Anyone else noticed this before - or would it make any difference?

By the way ,my latest project attached a 1938 Sunbeam lion - should have it running in no time!!!

sunbeam

[Eero.Korhonen]

Great Sunbeam, I like that look.
Br, Eero