Runing SU carb without damper - how does it work?

Many people tell you, you always have to top up piston damper oil. And that the piston damper is essential for runing an SU carb. This however... Is quite to opposite. Acceleration improved a lot without the damper (nomen est omen?), throttle response is almost aggresive now.

Of course there's a bit more involved than just removing the damper ;-) - but the 'impossible' works; runing an SU without damper & oil!

Category:

Autos & Vehicles

Tags:

• SU
• carb
• carburetter
• carburettor
• damper
• function
• working
• principle
• MG
• metro
• mini
• cooper
• 1300
• 1275
• stage2

[BoogWar01]

Fuel eco should fall off a cliff. Sure it will work, but the mix probably isn't any where close to stoich. I would look into the size needle your using, and whether or not the carb / jet is sized right for the engine.

[DeiMuddaSeiMudda]

@BoogWar01 It'S not that bad. Surprisingly good, actually. I average at 35MPG (8l/100km). That's very acceptable for a 'hot'-ish 1300cc engine :-) And I'm not easy on the throttle.

A 1.75" carburetter is percfect for this engine and there's only one jet size available (0.100"). Needle is a modified BBW.

As for the mix being stoich etc. - Most engines will be on the rich resp. maximum performance side. And I bet you, even a 100% sound std. engine with a 100% sound carburetter isn't stoich ;-)

[BoogWar01]

@DeiMuddaSeiMudda Could be that you are running too much carb - the engine vacuum could be not strong enough to snap the piston off the jet when in anger. Experiment with weaker dashpot spring tensions until it starts to splutter, then go to the next firmer spring (at a drag strip). Seat-of-the-pants feel should indicate a better midrange pull. Just my two cents. As to the stoich, I was referring to part throttle operation. I think having such a light car is really confusing your situation.

[DeiMuddaSeiMudda]

@BoogWar01 A 1.75" carb is the right size for a 1300cc unit with ~70HP (though only a estimate from top-speed & 0-100km figures). It's all but too large.

The fiddling with spring tensions made this work - that's allready been done ;)

My english isn't very good - read Des Hammils book "The SU carburetter high-performance manual". The modifications are explained there. Hammil even goes as far as removing the spring!

All in all - it works as it was intended to work, it's not accidentaly working

[zrunner240Z]

I have been running my 240Z with Dual Su's like this for 14 years now. I picked up a tenth in the 1/8 mile after removal and never installed them again. I did have some sputtering on the road but cured that by dropping some long heavy screws in the oil resevoir. My 240Z's Best run to date was a 12.801 @ 107.26 mph in the 1/4 mile on cheap street tires. I also run a LD28 crank with L28 rods and pistons with 2 headgaskets which everyone said wouldn't work but is still running strong after 10 years

[abstractduk]

good for you man-thant was well interesting! so what else did you do other than remove the damper and oil?

[DeiMuddaSeiMudda]

Hello Mick! Exactelly what I'm thinking! ;-)

@All: Menawhile I found an educated author who did exactely the same thing; "The SU carburettor high-performance manual" by Des Hammil.

I found one problem, though: cold starting got a bit worse. But it's acceptable for the improvements this mod brings!

[DeiMuddaSeiMudda]

Oh, yeah, in the video I wrote MG Metro airbox... It's the same. Metro got a long hose to the grille, Rover Cooper got a 110° bend snorkel (much worse for airflow than temps can ever be!).

[DeiMuddaSeiMudda]

The Cooper, Cooper 'S' and Innocentis (all with 2xHS2) actually had the inlet directly above the centre exhaust branch. Warm air mixes better with fuel... '91 on engines even got a heated manifold which actually seems to have positive effects on MPG (1-2 more). Probably not the best thing to do if you'r after the last BHP - on a raod going car; I actuallydon't care... The carb modification was a experiment which is of course unneccesary too - but fun and turned out quite well. :-)