14 replies to this topic

[mjpuds]

Ok quick question... Any body know what benefit it would have to fit two springs in a hif 44. Only I have just bought a new red spring for it ... Only to find there is already a red spring inside but the new spring has almost half the amount of coils... Odd I thought .., one fitting new spring there seems to be a lot more delay on the return after acceleration... I'm using 3 in 1 as my dash pot oil... Was using 20/50.... Any way back to the two spring idea would this give a better return...

[Punts]

Read somewhere that 3in1 oil isn't any good in the dashpot, and the bod recommened engine oil.
Dont know about fitting double springs, would probably need a lot more airflow to lift the pot, so you might never get passed tickover.
I'd be checking the throttle return spring or throttle cable. I had an MPI that had a return spring fitted to the throttle pedal, it had slipped up the pedal and didn't always return to tickover. Tensioned the spring and put a cable-tie round the pedal to stop it slipping.

[bmcecosse]

The lightest spring you can use without the engine 'gasping' is the way forward. Too strong a spring (or double!!) could prevent the piston from opening fully - ideally the spring should just allow the piston to be right up just before maximum revs are reached with throttle full open. Not open enough is a disaster - opening up too early is not so bad. 3 in 1 has always been fine for me........ I believe the BMC Works Cooper S cars used EP90 in the dashpots on rough road events - to try to stop the pistons bashing up and down on the Special Stages!!

[MRA]

Engine oil is generally a multigrade...... which means as the oil temperature changes so does the viscosity, for an SU carburattor that's a bad thing as it will alter the tuning of the carb

3 in 1 oil is a single grade oil and is fine, or the correct oil for SU's ....................

http://mra-minis.co....stems-butec.htm

[mjpuds]

Engine oil is generally a multigrade...... which means as the oil temperature changes so does the viscosity, for an SU carburattor that's a bad thing as it will alter the tuning of the carb

3 in 1 oil is a single grade oil and is fine, or the correct oil for SU's ....................

http://mra-minis.co....stems-butec.htm

still not sure about oil as in 3 in one ... i will check out the return spring....i have a spare off a old carb...and i might try the 2xspring just to see...air flow should be ok ..this is fitted on a longman gt7 headkicking out over 105 bhp..

[MRA]

I would say look at your ignition first..... as an engine that is NOT returning to tickover quick enough is normally too retarded

105hp will not affect the above statement nor will GT17 or similar heads the adverse is more likely with a race head.

[MRA]

The piston rising at the correct speed is exactly what is required, however, adding more springs to correct an obvious fault is not a good solution.

[Ethel]

The piston's weight would be a constant, its effect would be to increase the required pressure differential across the piston, to move it, at all engine loads. You could achieve the same with a longer spring of the same rate: without the added complication of increased piston inertia.

Multigrade oils are intended to have a more consistent viscosity over a temperature range - a synthetic multigrade would be the most consistent, but the added acceleration enrichment of an oil that's thicker when colder could be an advantage.

[Dan]

Are you sure you bought a new red HIF spring and not a red HS spring? They aren't the same.

[MRA]

Ethel, Please explain how it can be an advantage ?

[bmcecosse]

BUT - very little air getting into the engine! You want MAX air - and 'just enough' fuel. This is where the Weber scores - it doesn't have anything 'blocking' the air flow - and it does have a pump jet to squirt in the necessary fuel. So to replicate this with an SU you want lightest possible spring, highish fuel level - and rich mixture. It's obviously not going to give the best possible fuel economy - but we are chasing acceleration here!

[Ethel]

I merely mean it could act like the choke on a cold engine. All manner of effects are possible when you tinker about with carbs. You're probably best to stick close to the original factory specs, unless you have the time and resources to perfect any modifications.

Start with a carb set up for the nearest specification of production engine and make the minimum of alterations, such as needle profiling.

[MRA]

Ethel, Please explain how it can be an advantage ?

A slower rising piston means you have a richer mixture.......

Not that, I was asking about the multigrade oil ?

[mjpuds]

Are you sure you bought a new red HIF spring and not a red HS spring? They aren't the same.

would you know if the red hs spring is shorter...this would make sence..i did ask for a hif spring...

[Ethel]

Hif & HS springs are different diameters.

HS fit closer around the damper tube.

If the springs are the same diameter count the coils, it may just be one is stretched.