Thread: Fuel usage S3 2.6 10MPG!!

Well I did the run into town yesterday. 145km (corrected for the swb speedo fitted) and used 29 litres. Thats 5km/l or 14.1 mpg.

Better than last time I did this test, which returned around 12 mpg. 12deg static advance instead of 3deg. Definitely livelier with that timing. Everything else is as per manual. Compressions being a bit low probably don't help, but I have driven totally clapped vehicles in the past which gave close to the factory fuel consumption, so I don't think that would be the cause of the problem.

I would have expected around 16-17mpg for this trip. Travelled at 80-90kmh where possible, a couple of hills needed full throttle.

Don't want to start modifying it with extractors, fuel injection and such, but I just think it should be better than it is.
Checked the oil bath air cleaner too, nice and clean and not clogged.

Wondering if the carb is an army bodge, having no mixture adjustment. Might see if I can get my hands on an adjustable needle holder and see what fitting that does.

Cheers,
Terry

Originally Posted by rover-56

Well I did the run into town yesterday. 145km (corrected for the swb speedo fitted) and used 29 litres. Thats 5km/l or 14.1 mpg.

Better than last time I did this test, which returned around 12 mpg. 12deg static advance instead of 3deg. Definitely livelier with that timing. Everything else is as per manual. Compressions being a bit low probably don't help, but I have driven totally clapped vehicles in the past which gave close to the factory fuel consumption, so I don't think that would be the cause of the problem.

I would have expected around 16-17mpg for this trip. Travelled at 80-90kmh where possible, a couple of hills needed full throttle.

Don't want to start modifying it with extractors, fuel injection and such, but I just think it should be better than it is.
Checked the oil bath air cleaner too, nice and clean and not clogged.

Wondering if the carb is an army bodge, having no mixture adjustment. Might see if I can get my hands on an adjustable needle holder and see what fitting that does.

Cheers,
Terry

a 1 3/4" SU in good order from an Austin 1800 or Tasman is a good swap. In my experience they don't need jet or needle changes just adjustment of the idle mixture and speed. Also good on Series 2.25 four cylinder engines. You need to get a 90 degree bend and make a copule of SAE flanges to weld on. Same thing. No need for jet or needle changes.

a 1 3/4" SU in good order from an Austin 1800 or Tasman is a good swap.

All of these carbies are now donkey's years old and will be worn and therefore of unknown quality unless he buys a fabulously expensive reco SU from Midel or someone..

IMHO the OP would get the same result by putting a kit including needle and seat and mixture needle and main jet through his Stromberg. The odds are that the main jet is worn especially if it does have a fixed needle.

Regards Philip A

Originally Posted by PhilipA

All of these carbies are now donkey's years old and will be worn and therefore of unknown quality unless he buys a fabulously expensive reco SU from Midel or someone..

IMHO the OP would get the same result by putting a kit including needle and seat and mixture needle and main jet through his Stromberg. The odds are that the main jet is worn especially if it does have a fixed needle.

Regards Philip A

SU's are good unless the throttle shaft or body is worn. Cheap and easy to get this rebushed. Pull apart, clean, new seals and any gaskets and bung it back together.

A big problem with SU's is that too many people are self-appointed experts and insist on fiddling with them. Get SU's set up properly and then put a big ball of barbed wire around them to keep the fiddlers away.

Originally Posted by PhilipA

All of these carbies are now donkey's years old and will be worn and therefore of unknown quality unless he buys a fabulously expensive reco SU from Midel or someone..

IMHO the OP would get the same result by putting a kit including needle and seat and mixture needle and main jet through his Stromberg. The odds are that the main jet is worn especially if it does have a fixed needle.

Regards Philip A

Hi Philip,

Yep thats the plan. I will try to get a piston with an adjustable needle mount while I am at it.
Probably out of an early RR.
Needle looks fine, Jet is a bit harder to see, I will replace them anyway.
I have always liked SU's, but the Stromberg should be fine, and no mods needed.

Cheers,
Terry

There is also two types of adjuster early ones a hex key and the later ones requires a slotted tool, the adjuster is next to useless but may help.
Take the carb off drop the float bowl and tap the jet up ,carefully around the outside of it, 1mm at a time reset the float as well
There seems to be varying specs on how high the jets should be