Low mpg

[Trafalgar blue]

Many years ago I had mini's, whilst tidying up the garage I came across a few parts. Since owning my Morris 1000 I wanted a more sportier sound to the exhaust. I was given a few exhaust parts so with the parts I had I set about making something up. I have I believe an su 1 1/2" carb on a torque master inlet manifold. A LCB exhaust manifold, front silencer, cherry bomb rear silencer. With 1 3/4" pipe between the silencers. It sounds great & go's well but it's drinking fuel quite heavily, I reckon about 30 miles to £10 So do I change it all back to standard? Or keep the exhaust I've made up & get a standard manifold and cut off the inlet manifold to fit the standard carb. Or again cut up a standard inlet, use std carb, use LCB and mate up to new std exhaust? Thanks

[cyclomethicone]

My car is totally standard appart from i have a cherry bomb rear can at home waiting to be fitted when i finish work. Just to give it that deeper sound. I was planning on a few other mods but ill be stopping at the cherry bomb if your only getting 30mpg. Be interesting to see what peoples thoughts are on this because iv no idea what sort of mpg im getting. Not to far off mot ready though.

[Trafalgar blue]

Where are you fitting cherry bomb? At the rear, is there a silencer at the front? Will it make any difference?

[cyclomethicone]

My silencer is at the front as standard and the cherry bomb was pretty cheap so thought it'd try it. Looks nearly hollow so dont think it will affect performance either. I have had the engine running and just put the cherry bomb over the end of the exhaust just to see what difference it would make. Gives it a much deeper pitch and sound really nice. Should sound even better once its secured on. Ill get a video of before and after and upload it to you tube because i can only find one half decent vis on it.

[chrisryder]

30 miles to £10 is a bit awful! £10 will buy you about 1.5 gal, so that's 20mpg!

I've got a 1 1/2" carb, LCB, large bore system and something akin to a cherry bomb on the back. I get 40mpg if I can resist the urge to use the extra power.

You're either running very rich, or the carb you've fitted is leaking fuel!

[Trafalgar blue]

I don't think I'm loosing any, I'm trying to drive economically due to mpg. I'll get the plugs out and see if they're black

[bmcecosse]

The whole point of larger carb etc is to get more power - so you can drive faster! Obviously - that uses more fuel....so yes if driving it hard, 20 mpg will be about right..... If you don't want to drive it hard/better acceleration etc - put it back to standard. An LCB is all wrong for a standard engine - they are for long overlap camshafts - 276 and above..... What needle is in the carb? And is the float bowl dead vertical?

[MarkyB]

Are you sure you didn't put a nice shiny pancake air filter on as well?
The temptation to give it some more throttle to get more of the nice sound is very strong, unless you resist it MPG will suffer

[Trafalgar blue]

Only had a pancake filter in the spares cupboard [frame][/frame]

[Trafalgar blue]

I made up an adaptor plate to fit the standard carb[frame][/frame]

[TFM150K]

I assume that before you started altering things, you were getting a lot more than 30miles to the tenner? In your first posting you say that going back to standard is one of the options and I guess that it is one that you are considering. If improved performance (always coming at a cost) is NOT an essential element in this episode, perhaps the idea of going back to what you had before, AND try just putting a Cherry Bomb right at the end of the exhaust system to give you a 'better' sound might just be a realistic compromise?
Dave

[MarkyB]

That pancake filter should be OK, it's the foam ones that are hopeless.
The way that carb has been fitted is little better than a lash up, from the look of it the choke is always on which would explain the poor MPG, how the throttle return works is a bit of a mystery too!
Sorry to be harsh.
Try keeping the exhaust as it it, put the standard carb back on with an adapter for that air filter and the MPG should improve while the noises stay the same.
Keep off the loud pedal for better MPG!

[Trafalgar blue]

I know it's a bit Heath Robinson but wanted to get it up and running first. I don't think the choke is on all the while ill have to check that. I've got a filter for the standard carb so I don't need an adaptor

[MarkyB]

When I say the air filter should be OK, that would be with K&N filter oil or some similar substance on it!

You will lose the inlet roar with the standard filter in place, but you may gain the trumpeting noise a standard Minor makes when you lift you foot off the accelerator.

The throttle return spring is normally much thinner and acts in line with the cable for maximum effect.
It's not all bad, the extension to the throttle cable and the carb adaptor look fine

[bmcecosse]

How on earth is an extra silencer (cherry bomb or anything else...) stuck on the end of a standard car exhaust going to make anything 'better' ???? Madness! That filter is not ideal - although not the worst I have seen... The flat face is too close to the carb inlet. It must be at least 1.5 X the diameter of the inlet hole, away from the carb. Still waiting to hear what needle is in there...... Making improvements to the engine by modifying the cylinder head/camshaft timing/optimising the ignition timing etc can all help improve mpg - but fitting a larger carb just effectively gives 'more throttle' - and so inevitably increases the possibilities to use more fuel! The lcb won't be helping either...... a 'three branch' as fitted to MG 1100/Mini Cooper etc is more efficient with the short overlap cam.

[Trafalgar blue]

It's strange how photos are sometimes deceiving, there is 2 springs, 1 for the throttle and 1 for the choke

[daveyl]

I've a 998 with similar set up + a mildly moded 12G202 head and can get a fraction over 40mpg and I still get to drive it quite enthusiastically.
Deffo think you need some carb adjustment, as stated.

[Trafalgar blue]

Needle is ABB or AB8. I also have a BDM needle spare if that's any better

[bmcecosse]

BDM is for the larger 1.75" carb......

[MarkyB]

A LCB exhaust manifold, front silencer, cherry bomb rear silencer

What sort of front silencer?
Too little back pressure lets a little bit of unburnt mixture escape through the exhaust every cycle, it soon mounts up!
Tuning the A-Series Engine: The Definitive Manual on Tuning for Performance or Economy is well worth a read.