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MG TD TF 1500 - 52 TD carb vent

cleaning up the carb and noticed that they do not have vents in the cap or the top vac tube. seems to me i read somewhere that SU carbs should be vented one place or the other. is my set up correct?
TLW Wright

If your carbs have what look like little angled gussets at the top of the dome they are vented, and should have no holes in the caps. If there are no angled gussets, then the caps need to have holes.

Tom Lange
MGT Repair
t lange

If you're talking about the float bowls it's my understanding that they are vented via the overflow tube by the gasket shown in the middle row, far right.

http://sucarb.co.uk/carburettor-kits/gasket-sets/h-type/h2-hv3-type-gasket-pack.html
Gene Gillam

I think he's talking about the piston tops Gene.



Paul161

Vented



Paul161

mine do not have the angled gussets and they are not vented. but neither are my caps. when i looked on one of the sellers parts page, they say non-vented caps for the TD. So was not sure.
i believe i saw that if you do not have a vent one place or the other, the car will run rich. My plugs seem to indicate that. so can i drill a small hole in the cap?

and while i am asking questions.... obviously the first time i have been in to the carbs...

on my front carb, i can push the piston all the way up so you can not see it and then it drops down. (slowly with no vent) on the rear carb i can push the piston about 3/4 the way up and it stops. took off the two pistons. compared front and rear. both look exactly the same. both of my piston rods are exactly the same. so i took a wire and ran down into the dashpot. they are both the same depth. but on the rear carb there seems to be a ring about 1/2" up that is hitting the piston rod when i push it up. Do i have the wrong piston assembly in there? or is that the way it works? guessing it was replaced with a wrong assembly at some point.

this started by wanting to extend the vent tubes. then i found the front carb float was taking on gas. then i figured while i was at it, i may as well clean out the suction chambers... car actually was running fine. it idles well at 800 rpm. it does not backfire. it does seem to be lacking a little power but then i have nothing to compare it with... so maybe it is running just normal.




TLW Wright

WHERE IS THIS RING?????

>>rear carb there seems to be a ring about 1/2" up that is hitting the piston rod when i push it up.<<

sTEVE
Steve Wincze

Both carbs should be exactly the same on movement. Also, do not switch the piston domes, the pistons and domes are matched, or are supposed to be. I forgot the size of the hole in the damper cap, but very small. As far as I know, all the pistons should be vented and as your aren't, it could cause a rich condition during acceleration as the pistons are moving too slowly. PJ
Paul161

well it isn't really a ring as such but it is more like the tube is a smaller diameter about 1/2" from the bottom of the dashpot. So it hits the piston rod as it raises. the piston rod is a bigger diameter than the hold at that point.
my guess is this was lifted off another car that used a shorter piston rod? not sure.
i am going to look into trying to drill it out. there is a machine shop just down the road.

yup, i made sure to keep all parts separate and put them back on the same carb in the same orientation.
TLW Wright

TLW - Sounds to me like someone put the wrong damper in your carburetors - both should have a small hole in the caps. Pictures wold be helpful. Cheers - Dave
DW DuBois

Dave, i believe you are right. i drilled a small hole in the caps. used a bit that would just about fit in the holes on my TR6 carbs. so that part should help.

then found there was a brass piece in the bottom of the rear dashpot. when i started to drill i noticed the shavings were brass. then the drill stopped drilling. i turned the piston over and tapped it on the bench to shake out more shavings and this brass piece fell out. i guess as i was drilling it started turning. See pic.

not sure why someone would put that in the carb???? it fit too well to just have fallen in there. but it is out now and the piston slides all the way up.

it will be interesting now to see if the carbs still run rich or lean. i tried the lift test. i did not get the initial increase in RPM. instead it stayed a steady RPM until it would eventually die out. both carbs the same.
still the idle is very good and steady. the engine seems to run fine. i went for a short ride... looked like rain again... and it felt like there was more of a pull at the 2200-3000 RPM range. could be my imagination but it felt like the engine was pulling a little more than before. before when i gave it gas, it just seemed to work up more speed. now you can a little more acceleration.

i thought about setting the adjuster nuts all the way up and back out two turns. then see how it feels. but i think for now i may just leave alone and check the plugs after i get some miles on it.

then i may play with the timing some at that point also. i read with the newer gas, maybe advancing 5* might be a better set up. right now i have it static timed to TDC.

All in a good week though. fixed the float, extended the vent lines, vented the caps, and got rid of that plug in the dashpot.

TLW Wright

here is a pic of my carbs on the car as i was finishing the vent lines.

TLW Wright

It looks like a damper sleeve has fallen of a previous damper and not been removed.
As to the advance, I have been running 5/16" advance for some years and it seems to suit my engine (TF 1250).
Ray TF 2884
Ray Lee raybar2(at) tiscalidotcodotuk

Seems like a large center hole to be a damper sleeve, Also the OS diameter on this sleeve was exactly the same size as the IS diameter of the tube.
But a damper sleeve makes more sense than anything else I can think of. Obviously my dampers had been replaced.
TLW Wright

Terry, What's the chrome pipe sticking up, which looks like it has a cap on it? PJ
Paul161

Ray... i believe you are right. after comparing, it is the same shape and size as the other sleeves.

Paul,
that is an overflow bottle for coolant.
TLW Wright

This thread was discussed between 12/05/2016 and 13/05/2016

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