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MG Midget and Sprite Technical - Grose jets, not what I expected

I just retired on Wednesday. So I'm pretty happy.

Decided it was time to check the HS2 carburetors on my 1971 GAN5. I was surprised to see fuel coming out of the front overflow. I installed Grose jets back in 2002 and I've been lucky they've been trouble-free. Or I haven't noticed if there's been trouble.

I cleaned the front jet thoroughly, reinstalled, but after a minute fuel was overflowing again. Float is the non-adjustable all-plastic one, but there's nothing in it and it's set at just a hair over 1/8", so on the high side.

Spent some time in the archives here and decided to order the Viton tipped needle and seat for front and rear. But before ordering I figured I'd swap the Grose jets front to rear, expecting a leak at the rear. But it's not. Rear is dry, and the front started leaking after a minute or so. FWIW, the rear float is also empty, and is set a bit on the low side, nearer to 3/16", but still under.

I have an SU fuel pump bought in 2002, and always run a fuel filter after the pump. I don't have a second fuel filter.

I'm going to be off the road for a while, but still plan to bring in the Viton needle and seats. (That's what I do, replace parts.)

Am I missing something? I'm optimistic the needle and seat will solve the problem, even though my experiment tells me I haven't found the problem yet.

Thank you for any advice.



Mark 1275

Being a Grose jet fan, I'm shattered to think there could be a fault with the jet assy. ------
If you've swapped the jets over and the issue didn't swap with them --the fuel must be leaking between the float bowl cap and the jet body
Because the float level on that carb is under spec, maybe the little aluminium sealing washer between the jet body and the cap is missing on that one allowing fuel to bypass there
William Revit

Thank you for the quick reply, William.

I did check to verify the fuel is coming only from that right angle overflow tube. The gasket for the float cover isn't in great shape, so I'll replace those as well, but I did check and it's dry around the top, just spitting out that tube.

The Grose jet does have a fiber washer, and it's present. I'm hoping the Viton needle and seat changes the float level, but I'll also buy extra washers. (That's my strength, buying inexpensive parts.)

I've read a lot in the archives about Grose jets, but I don't remember if some were your posts. Would I be far off to take your opening line as sarcasm?? :-)

(By the way, you were right about my third gear problem. Car's been popping out of third for a few years and the used third gear I showed here solved the problem completely. You pointed out the condition of my existing third gear as not being optimal, and the used one was better.)
Mark 1275

Take off the cover with the suspect leaking gross jet in, and turn it/fix it, upside down so that gravity keeps the jet closed.

Switch on the ignition.

Is it still leaking? If it is, it can't be anything other than the jet or seat or the lack of a good seal between the jet seat and cover.

Viton jets were very hard/impossible to obtain last year. Are they back in stock now then?

Edit. Just looked. You can get them, but they've shot up in price.
anamnesis

Cheers Mark--Nice one with the 3rd gear, I'd forgotten about that, glad you got it sorted out.
With the Grose jets, no sarcasm, i honestly think they're good
Originally they were manufactured by a family business and were inspected/checked before being sent out, but the business changed hands a few years back and the family dedication part got lost--The jets are still the same/good but some don't seal properly, it's just that I think there can sometimes be an irregular finish on the edge of the hole where the ball seats--Usually a light tap on the end of the 'needle' into it's seat with a small hammer is enough to get the seat sorted and it's all go from then---just a mass production issue--still good jets in my opinion

willy

Just relooking at your pic, because the float level is right up there the float might be touching the side of the floatbowl preventing the needle and seat from shutting off completely----Maybe try a thicker fibre washer or double up thin ones to get it the same height as your other carb and see if that fixes it
William Revit

Mark

Congratulations on your retirement.

Minispares sell the Viton tipped valves:

http://www.minispares.com/product/Classic/Fuel/Carburetors/Spares/WZX1100A.aspx?130203&ReturnUrl=/search/classic/WZX1100A.aspxBack%20to%20search

http://www.minispares.com/product/Classic/Fuel/Carburetors/Fittings/VZX1100.aspx?130207&ReturnUrl=/product/Classic/Fuel/Carburetors/Spares/WZX1100A.aspxBack%20to

Cheers
Mike
M Wood

Appreciate the responses.

I turned the front float cover upside down, and it stayed perfectly closed. I was surprised the float would hold against the pump pressure, but it didn't leak a bit.

Just to try it, I swapped the floats so the high clearance/low bowl level float was in front. But before reassembling I found the original envelope from back in 2002, and it had two thin washers still in it. So I brought both float clearances to about 9/64". I really tightened the Grose jets against their fiber washers.

It ran for a good 5 minutes just fine, but then started leaking at the front again.

Usually I'm fairly confident new parts will solve my problems, but this time I'm not so sure. If the leak is between the float bowl cap and jet body, seems to me I would have seen it in the upside down test. And it was an unused (albeit 20 years old) washer at the front.

I'll order new parts tonight, but if there's any other tests I can try, please let me know. Moss does show the parts are in stock here in the U.S.

Thank you, Mike. My four days of retirement have been great so far. I'm still smiling just thinking about it.






Mark 1275

Mark
I'm glad 3rd gear is sorted. We had a useful discussion about dog teeth, I now remember, with Willy clarifying how things worked.
Bill Bretherton

Mark,
Is the leak rpm related? After 5 years I suddenly had a leak, but only at high rpm.It was solved with spring loaded Viton needles. One needle without spring leaked the other did not.....
Why leaking after 5 minutes . Is something distorting with heat?


Flip
Flip Brühl

Good point, Flip. I'm mystified by what's causing this. If I clean everything up with carb spray it will run without overflowing for about 3-5 minutes. I do rev the engine, and I can rev it quite a few times before the leak starts. It's such a finite system you'd think it would be easy to find the problem. I've ordered the spring loaded Viton needles from Moss. I'll be off the road for a while starting Wednesday, so probably won't install these until late June.

I don't think I'm running it long enough for it to be heat distortion. My suspect is that I might be getting grit that's interfering with the Grose jet, maybe in the fuel line after the fuel filter that's near the fuel pump. But it's never been a problem at the rear carb, only the front.

I also ordered floats so I can adjust them to optimal levels. I'm optimistic the new parts will solve the problem - even if I don't understand it - but if not I'll be back here in a month.

Bill, it's really satisfying that the 3rd gear problem is totally gone. I've challenged the gearbox in all the situations that used to cause it to pop out - up hills, accelerating, bumpy road - and it hasn't popped out once.
Mark 1275

This thread was discussed between 12/06/2022 and 14/06/2022

MG Midget and Sprite Technical index

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