18 replies to this topic

[minivanman]

I won a set of twin HIF38s on ebay the other day (£25 - uber bargain). Having a quick gander at them today I noticed a brass circle soldered onto the butterfly. I opened them up and theres this on t'other side:

I was just wondering what it is? or am I being really thick?

[Big_Adam]

That would be an overdrive valve. also known as kack.

[Sprocket]

That would be an overdrive valve. also known as kack.

That would be OverRun

[minivanman]

so what does it do exactly? and why is it rubbish?

[Big_Adam]

That would be OverRun

Nuts, I was close tho.

"Rubber bumper MGs have carburettors fitted with overrun depression limiting valves fitted to the butterfly or throttle disc. The idea behind these valves was to clean up exhaust emissions by drawing in more air on the overrun. If the springs become weak and the valves fail to close properly an erratic tickover with a rising idle speed will result. This can be remedied by replacing the valves with new ones or by reverting the earlier specification butterflies without the overrun depression valves."

Thats what it does. It also feck the flow of the carb at full throttle something lovely.

[minivanman]

Ta Adam. Thats exactly what they're off - a rubber bumpered MG. I did think it wouldnt do much good for the flow having two great springs in the way! so thats something else on the shopping list then! I'm going to have a bash at reconditioning these myself.

[Big_Adam]

apart from the bushes in the carb it's easy (and relaxing) to do. If you want I can send you over the bit in Viards book on tweaking the carb for more flow.

Can get a hs4 to flow like a weber if you are so inclined. Their only little tweaks but they really work.

[Brutus]

just to help you out a bit, i have them on my twin HIF44's and they run smoothly. if that helps u out a lil more??

[icklemini]

on tweaking the carb for more flow.

be wary of some of these mods, as although yes on paper they give more flow, they do upset other charecteristics...

bin that throttle disc and get a solid one!

ttfn,
Dave

[minivanman]

twin 44s? what spec engine is that?

Cheers Adam, I've already got the big yellow bible. The bushes feel ok, I'll have a closer look tomorrow. I'l just have to build an engine for them to go on when I've reconned em!

[Big_Adam]

Ah, if there's a little play then a new spindle will probably remove that. Did on my Hs4.

[Brutus]

spec's endless but all i know is them 44's make it run sweet as a nut. engines worth 5k

[Jammy]

Still, twin 44s on a 1380 seems quite excessive!

[Turbo Nick]

depends on the cam to be honest dude. i know my mate could do with a pair on his 300deg cammed daily driver.

[jack54_turbo]

just by reading this i solved a problem on my 1275 metro engine, it was ment to have been sorted 3 days ago woops lol