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MG Midget and Sprite Technical - Blocking SU breather holes

Just out of curiousness, what would be the symptoms of blocking up these "breather" holes on the SUs with incorrectly fitting air filter gaskets?

Cheers,
Malc.
Malcolm

Oops. Picture


Malcolm

It won't rev up - limited RPM.
richard b

Thanks Rich' that would explain a lot :-)
Malcolm

Malc,
often you can find it's only one gasket fitted upside down which will on a twin carb set up give uneven idle and running and restrict revs (guess how I know).

I could 1st class post you four genuine SU hardly used gaskets if you need them, not all gaskets are cut well and alignment a bit iffy sometimes and some look like they might shed bits.
Nigel Atkins

Hi Nigel,

It's a car I am helping out with, twin HS2s on a 1275.

About 6 weeks ago I took it for a very short drive. It would barely do 30 mph! A bit scary really. It then did the decent thing and packed up all together! ;-)

Working through various issues, including leaking float valves, an intermittent fuel pump due to decrepit wiring, sparks that wouldn't fry the ar*e hairs off a gnat and carb jets set at wildly different heights.

Then I find one carb has the wrong gasket on - blocking up these holes. The other carb had no gasket.

The air filters have been refitted without gaskets for now (I only had bits for HS4s).

Now need to check the dizzy timing... but the crank pulley has no timing marks.

Phew! After that, I think I am out!

Malc.
Malcolm

Hi Malc,
I'd remembered you were looking at an A-series for someone, don't let it put you off the A-series engine.

You could make some (temporary for me) gaskets out of card using a small ball-peen hammer, to (or is that by) me they've never that good or neat even when using proper gasket paper.

Telling grandma how to suck eggs now but just to remind you in case the frustrations had caused distractions from the basics -

. also check carbs cable connections and linkages for correct set up and clearances (clean & lubed too)
. fresh oil in dashpots
. clean air filters (paper elements and inside of pans) are very important
. clean and correctly gapped (0.024-6") spark plugs in good condition

The timing marks are a pain to see if at the bottom only anyway.

Before checking the timing best to do the servicing chain from the start - set up tappets, points, plugs, timing and mixture in that order, if you adjust any item in the chain then you need to check/adjust all items that follow.

If the owner hasn't already got a copy then you should get him to buy a copy of the relevant Driver's Handbook, it'd help you too as there are differences to 1500s. You can both use the good book whilst you supervise him doing the work.

Obviously the carbs and engine are of very little real importance and you'll get him to check all the important items items to teach him correct priorities of brakes, tyres, steering, suspension, lighting, horns and windows - engine and carb fiddling last.

If you're just looking for an A-series to work on I can provide one with enough work to fully satisfy any interest you might have thought you had. :)

Nigel Atkins

Malcolm, you've got your answer but the principle is that the hole connects to the void below the piston. If it is blocked then the piston remains held down as when it begins to lift it creates a partial vacuum as air cannot get pulled in. So engine won't rev!
GuyW

Nigel, the hand book was the first thing I found for them. I advised them to sort brakes and go through all the servicing etc. Just as you always say :-)

Whether they listen to me or not... ;-) ha ha

Ignition is in the process of having a full do-over, new cap, red rotor, electronic module, leads and plugs (then it needs timing, hoping I can get a dial gauge down the spark plug hole).

Carbs reset as best as possible to "default" settings.

It should be much much better than it was.

If it were my car I would have it completly stripped by now for a full mechanical rebuild. But that's not what they want to do, so I am just assisting with the issues that present themselves.

The gaskets are up to them. It shouldn't be a big issue as it is upstream of the throttle and the gaps will be so small neglible crud should get sucked in.

Thanks Guy. That makes sense.
Malcolm

Malc,
you are truly learned, and the right person for them to know.

I'm trying out a 'red' rotor arm from Powersparks or Accusparks (I have one from each of them but mixed them up but both look from the same source) they might be good at the price but they're not the same quality as previous Beru and Bosch.

Dial guage! pencil not good enough for you now you're all electronic technical.

I'm with them about keeping the car on the road, you technical and engineering types sometimes don't give anywhere enough priority to actually driving the cars - for the sake of driving them rather than testing your latest workings. Again I offer, anyone, the opportunity to work on my car - and I won't even charge for the privilege.

Why not get your friend to join on here and learn, and teach, about their car and experiences with it - obviously they'll already know a lot if they read the good book but it wasn't designed to cover everything.
Nigel Atkins

Yippee! It works again, and loads better than before. It actually accelerates!

Timing and carbs only "roughly" set, so there is room for improvement. But for now, it is job done and another happy customer!

Malc.
Malcolm

This thread was discussed between 14/09/2020 and 15/09/2020

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