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MG TD TF 1500 - SU Float depressing plunger

I think that now is the time to tap into the collective knowledge of this group.

My TD, an early one, has a hole for the plunger in the float lids but the plunger has been removed at some time in the past. I have been running the car with these holes in the float bowl lid but have never been 100% happy with the way these particular SU's take a tune. I have another set of float bowl lids that will fit and they do not have the holes.

My question......does it make a difference either way? Does the hole in the lid effect the operation of the SU?

Thanks All

Brian
Brian Smith

Brian,

The holes in the float bowl lid is an engineering flaw. Since they are lower than the vent (overflow) tubes, in the event of a stuck float or stuck inlet needle, fuel can escape from the hole instead of the vent tubes. A fire can result. Plug the holes with JB Weld, or use your new lids where the holes aren't drilled.

http://www.travelaire.photosite.com/MGTDRebuild/carburetors/front_lid_plugged_wth_JB_Weld.html

warmly,
dave
Dave Braun

I second Dave's assessment. I emailed Burlen/SU and using devcon or JB weld was their suggeestion, also.

I found out the hard way that you also need to make sure that you have the proper scalloped washer installed between the overflow pipe and the float lid. The vents are necessary to allow air to be displaced by gasoline.

On my car someone had installed solid washers top and bottom. As soon as I plugged the hole in the lid I had trouble running at high speed. Also, if you have rubber or plastic tubing attached to the overflow pipes as my car does, make sure that they are not plugged and that the ends didn't get melted (occluded) against the exhaust pipe.

Larry
Larry Ayres

"...make sure that you have the proper scalloped washer installed between the overflow pipe and the float lid."

Doesn't this short circuit the path for gasoline overflowing the fuel bowl? In other words, doesn't gasoline go out the venting scalloped washers in much the same location as if no overflow pipes were installed at all?

I would think the overflow pipe to fuel bowl lid needs to be air tight to accomplish its job. Obviously, the overflow pipe must be kept open to work and to equalize the pressure in the fuel bowl during normal operation.

Larry
Larry Shoer

No Larry, the scalloped washers allow the float bowls to vent to the vent pipes. With solid washers, there is no venting as the solid washers block the opening to the vent pipes. The scallop washers seal only the outer edge of the vent pipe banjos to the top of the bowl lid, preventing leakage onto the float bowl lid, and from there dripping onto something hot, while allowing the washer to maintain its centered position.

http://www.travelaire.photosite.com/MGTDRebuild/carburetors/special_washer_to_allow_fuel_bowl_venting.html

dave
Dave Braun

While keeping in mind my pins/holes are epoxyed shut and sealed, I don't think I consider the tickler pins and holes an engineering flaw at all. The pins were quite usefull to flush grit from a stuck open needle valve, check for fuel pump operation, and lastly when my choke was disconnected for some reason, you could run a little extra gas into the bowl to enrich for start on a rare cold morning. Years ago, with a rusty gas tank, no inline filter, and old-style needle valves, my rear carb needle would often stick open after sitting for a few days. A tap down on the pin would flush the grit. Lastly, back in the 70s, the replacement pin/springs came with a metal washer and a seal (leather or synthetic?), so the spring pressure pressed the seal against the hole in the float lid, and they didn't leak. George
George Butz

PS, Brian, to answer your question, holy or plain lids would have zero difference on tune. You have to have no air leaks manifold carb and head, freely moving pistons, correct dampers (with a vent hole in the top), the correct needle, good jet seals (with all parts assembled in the proper order), correct float level. Then follow the proceedure in the shop manual or the NEMGTR "T-series Handbook". That will do it. Also, of course the SU's are usually blamed for distributor/ignition/ and other problmes, when they are really fine. George
George Butz

I get it...

I was meticulous in sealing the tickler pins (actually, I cut off the top of the original tickler pins and bedded them in epoxy putty in the fuel bowl lid--it looks original, but the openings are sealed) and replaced my stubby overflow pipes with properly routed pipes. I don't recall whether the washers under the overflow pipe banjos are scalloped or not. Time for a little inspection.

Thanks for the clarifying this matter.

Larry
Larry Shoer

Thanks All, the collective wisdom of this group is second to none! I will switch to the solid lids as a safety measure.

I recently had a ride in another TD and was really impressed with the power and smooth running. The car had the rear end gears changed (I believe they were the 4.3) and it still had more power than mine with the standard rear end gears. It was apparently all original so I continue to look for ways to improve the power and smoothness of my car.

I actually thought it was running very well until I compared to another. All of my previous experience has been with MGA's and MGB's and so had nothing to compare it to.

Brian
Brian Smith

George, while I often agree with you, I think we are going to go the 'agree to disagree' route here.

As a recovering engineer, the 1970s fixes to the float bowl tickler pins were attempts to engineer a solution to an engineering flaw. The correct engineering solution initially would have been to add/improve the filter at the fuel pump and secondarily to improve the needle valves at the fuel inlet to the bowls and skip engineering in the leaky tickler pin holes.

Your use of the tickler pins, while common on our cars with dirty/rusted fuel tanks, was an expedient, but not as safe as your ulitimate restoration which will resolve all the difficulties and render the tickler pins unecessary.

How is the project going? I'm still waiting for my tub, with great disappointment that the person doing the tub missed his promised date of May 21.

warmly,
dave
Dave Braun

I'm going to have to side with George on the issue of "engineering flaw" regarding the tickler button on the H type carbs. I don't believe that this is so much an engineering flaw as just engineering of the era. The H type carbs were very early carbs and used on many different car, not all of which had the exhaust manifold under the carbs. This was also in the time of very dirty fuel. If you have ever read a history of the evolution of gas stations, even in this country, one of the things that becomes very apparent is that there was all sorts of junk in the gas. That combined with the fact that the filters of the day would only filter out rocks and small birds, makes the ability to flush out needle valves a real asset on the carburetors of the day. (Dave B, you are old enough to remember when all the gas pumps had the statement on them "filtered gas" - prior to pumps with filters built in, people used to pump gas into cans through their own filters in order to get relatively clean fuel to put in their tanks. While I know that the situation of overflowing float bowls can result in gas spilling onto hot exhaust manifolds in our cars (this includes the MGAs, Magnettes, Morrises and numerous other British cars), the incident of resulting fires is remarkably few considering how long the cars have been around with this arrangement and the number of miles that they have been driven. That said, I am a strong advocate of plugging the holes with JB weld and fully intend to do so on our TD (even though We have been driving it for over thirty years and close to 90,000 miles without incident). Engineering flaw? - Today yes, 80 years ago, more likely a stroke of genius. Cheers - Dave
David DuBois

Nope, don't recall 'filtered gas'...

But I was looking at some old TSOs and read an account in the Dec. 1976 issue of some crazy young guy from Washington State taking a TD and a PB from Seattle to Long Beach California... with about a half dozen kids on board. Sometime after the PB's block cracked in half, it then magically turned into a 1961 Aston Martin... and the trip continued.

Boy that unfiltered gasoline must have been really potent!

warmly,
dave
Dave Braun

While talking about engineering flaws, I was explaining to my son the other day that a carb should never have a U-shaped channel anywhere in the body. That way when you spray carb cleaner in one hole, it will never spray directly into you open eyes! This while attempting to repair his friend's dead Ford pickup (ran great spraying carb cleaner into the intake). After changing the fuel filter (lovely to do without a lift), etc., the furniture delivery guy said to press the pump cut-off impact switch- starts right up. Think I'll stick to British stuff next time- duh. Dave, I'm moving as fast as you. The body shop has the two Mustangs finished and gone at last, and have allegely started on my TD. The guy who is doing the real tough stuff (correcting the factory rear wheel arch to fender gaps, etc) is of course on vacation this week. They actually want me to come out on the 5th and go over the finer points again. This is driving me crazy, but I'm just nicely calling every week, and I think I'm close. It has given me time to finish restoring the jack, tools, grease gun, etc., and to have a life. George
George Butz

Dave B. - Actually it was only two kids, but is was the most memorable (not in a fond sense) trip we ever took. Cheers - Dave
David DuBois

It was still one heck of a story. Makes me want to try a long distance in the TD... when it is finished.

warmly,
dave
Dave Braun

Just don't leave on Friday the 13th in the pouring rain - it has a tendancy to go down hill from there. Cheers - Dave
David DuBois

Just don't leave on Friday the 13th in the pouring rain - it has a tendancy to go down hill from there. We have since taken several long distance trips in the TD (two of them in excess of 5000 miles) with absolutely no problems. Cheers - Dave
David DuBois

George, Fuel cut off switches, great safety improvement, if you can figure out where they are!

Sounds like progress on the tub. In my case, I have so much going on at work that I NEED the tub to take my mind off my day. I'm half considering buying an old 3.6 hp Firestone outboard just to have something to 'putz' with.

Dave, sometime I think I'll press West in the TD and see where I end up.

warm regards,
dave
Dave Braun

"...sometime I think I'll press West in the TD and see where I end up" - In the Pacific ocean if you go too far :) Take the northern route and stop by to see us when you do. Cheers - Dave
David DuBois

I would love to see your SU rebuild operation, and meet you and Liz... so I think I'll figure out how to make that trip some time. Perhaps we could even venture up to Whistler?

thanks!
dave
Dave Braun

Or when you get to British Columbia come on over to Vancouver Island and drive up the Island highway (Ocean Side Route) to Campbell River.

Brian
Brian Smith

Dave B. - In the words of the Present Occupant - Bring it on, We would love to host you and your wife and perhaps continue with you up to Whistler, or up Vancouver Island to Campbell River to visit Brian and Jan (he has been trying to get us up there for a couple of years, so this might be a good chance to do so). Cheers - Dave
David DuBois

Filtered gas? yup. I remember watching as the gas attendant inserted a large funnel into the tank inlet. Then carefully spread a chamois over it. The gas went right through the chamois but water and other bits and pieces remained on the chamois. I still do it when using stored gas.
C.W. Derby

This thread was discussed between 01/07/2007 and 06/07/2007

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