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MG Midget and Sprite Technical - Fuel Float jets

So I'm stripping down the carbs checking everything is what it should be and making a list of what I need. On checking the float level ( she's running to rich) it's not the 1/8 it should be but it's not the type with the metal bracket as you can see from the image. so how do you adjust them.

Moss replacement does have a bracket but SU show the type I have. Also I noticed Moss have a replacement jet called a Grose jet anyone tried it is it worth changing.

Rich




Rich65

Hi Rich
A lot of folk are not happy with the Grose jets these days. If the fuel level is too high then you can reduce it with small aluminium or brass washers between the jet and the body. 1 mm is usually very effective. However you may find fuel starvation up long hills. The best needle jet assemblies have the viton tipped needle I feel.

Peter
Peter Burgess Tuning

Rich,
The only adjustment is by using shims/ washers where the valve jet screws into the lid.

Grosse jets got a bad reputation, but I don't know why so that may just be a myth!

Sorry Peter, just using an echo keyboard!
GuyW

Thats ok ok ok ok Guy :)

I think I read the Grose jets are made elsewhere from where they were originally made and there is a problem with the valve fully sealing and tending to dribble. Like us blokes getting older probably, or is that gross spelling?

Peter
Peter Burgess Tuning

I have viton tip so I'll stick with them. Do you get a bit of tolerance with the float or does it need to be spot on, the front bowl was empty and the rear half full, I did try the air test the flow was reduced but not air tight
Rich
Rich65

I don't quite see how you can run rich with no fuel in one float bowl?
Peter
Peter Burgess Tuning

Also check out the wear in the fulcrum pin and eyes of the float hinge, a little here makes a lot of difference. I see quite a lot of worn pins, and some surprisingly enlarged float eyes. I find that with the correct SU valve (now viton tipped as noted above), new float, new fulcrum pin and no washers between valve body and float lid, the float height is always spot on.

If using shims they have to be very thin as there is a 5:1 lever ratio from valve to the easurement point on the float, and the target range 1/8 to 3/16 is quite small.
Paul Walbran

Peter, the rich running may have nothing to do with the floats it's just something people told me to check,
su's are new to me my lack of knowledge isn't helping, I have tried to tune them but even with the jets fully adjusted up without the 12 flats back it's still rich. the front carb is sticking, so I'm stripping them down to see what I need to replace. I know it's had a rebuild kit and New spindles

Rich
Rich65

Rich,
these John twist videos are excellent at giving information (in addition to the knowledgeable posters here). Some of the videos may not be exactly for the model of carbs in your car but the basic principles apply and all are full of useful information.

44 Secrets of the SU Carburettor Part 1 of 2 - http://www.youtube.com/watch?v=7GRAcqDySog

43 Secrets of the SU Part 2 of 2 - http://www.youtube.com/watch?v=60Bj_2cZQnc

(MGA) 29 SU H-Type Carburetters (MGA) - http://www.youtube.com/watch?v=GHNlT5yHDxk

41 Matching SU Air Pistons - http://www.youtube.com/watch?v=IfU47Oqq9wA

MG Carburetors & Doors (first part needles and seats, springs and carb oil) –
http://www.youtube.com/watch?v=v9QI3NlvwiY

Nigel Atkins

(part 2 of 2)

147 MG Carburetter Tuning - http://www.youtube.com/watch?v=4nvGLgO6pj0

35 Tuning HIF Carburetters - http://www.youtube.com/watch?v=ASeMfXfjNpw

222 MG SU Carburetters: Setting the Float Height (needle & seat comparison) - http://www.youtube.com/watch?v=82YNx-RkGNI

232 MG Carburetter Needles and Seats (odd sizes) - http://www.youtube.com/watch?v=pVX_JClyeDQ

245 MG MGB/MGC/midget SU HS Carburetor Jet Repair - http://www.youtube.com/watch?v=Elgfc1xZkt8

Nigel Atkins

Thanks Nigel they are helpful, i've also been using the tuning SU carbs pdf you sent me.

Has Paul said the float pin holes have enlarged so there is a lot of play but the pins have seized solid to the lids, so I think a bit of patience will be needed.

Rich
Rich65

Hi Rich,
I meant to put, video '222 MG SU Carburetters: Setting the Float Height (needle & seat comparison)' tells you about Grose and other jets - http://www.youtube.com/watch?v=82YNx-RkGNI

I'd forgotten I sent you a tuning pdf, if it wasn't the whole book just email me for it.

I'm surprised I didn't include the JT vids then (perhaps I did, I don't remember or keep record, or emails) anyway the links in the posts are updated shorter links from the ones I previously used.

When ordering parts don't make any assumptions double check and cross reference everything with at least two reliable information sources, there are many errors or omissions in almost all information.

Don't assume what components or parts you have fitted are correct or fully correct, check parts and components aren't mixed up, wrong to type etc. and are installed and fitted correctly.

Putting up photos of your components or parts, particularly fitted in situ, can sometimes highlight the issue or other issues.

Good luck.

Nigel Atkins

Gray I fitted new grose jets and they wouldn't shut off with resultant flooding
Grose jets went straight in the bin and new Viton ones went in end of problem
Cheers
R W Bowers

This thread was discussed between 08/11/2016 and 13/11/2016

MG Midget and Sprite Technical index

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