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MG TD TF 1500 - Float Bowl Needle Valve

(Oops, I forgot to mention that this will be a long post and your patience and help will be greatly appreciated) Back in June I started a thread "is this vapor lock" after experiencing bad stumbling on the Blue Ridge Parkway on a hot day after having stopped for about 15 minutes. That stumbling ultimately cleared up after about 5 miles of driving but ever since, I suffer what seems to be (and I am now pretty sure is) fuel starvation in the front carb in the heat of the afternoon. The car will start fine and take off like it's supposed to and then 1/2 a mile down the pike will stumble and lose all power. I know I need to remove the fuel filter in front of the pump and, after today's experience, that will happen in the morning.

I'd been planning on driving out most of the fuel in the tank to make removing the filter easier. Plan over executed - this afternoon I ran it completely out of gas (I'd been wondering and now I KNOW that my low fuel light doesn't work). Fortunately I was near a quickie-mart wher I bought a fuel can and 1-1/2 gallons of fuel. Very hard to restart but finally got it running and limped to the QM and filled it up. It restarted easily but ran horribly. I figured air in the line or such and that it would clear with a bit of driving around - Not to be.

I spent the next three hours going half a mile, pulling over, removing the front float bowl lid (the rear carb displayed no ill manners), jiggling it enough that, with the pump running, fuel would trickle through the needle valve and fill up the bowl. With that small supply of fuel to the front carb I could start, get up to 45-55 mph, feel the engine starve and try to die and coast on covering about 1/2-3/4 mile. I was about ten miles from home.

I finally made it and, after reading the WSM and the SU manual, started disassembling the carbs.

The first thing I noticed is that neither float bowl lids have the screen filter - I was really hoping to just clean the filters and be on my way. I'll order new screen filters since they are not included in the master rebuild kit from Moss.

The second thing is that neither carb has a spring above the damper piston. It seems that in a thread a long time ago it was mentioned that some SU carbs rely totally on the weight of the piston and do not have damper springs. Did that apply to the 1-1/4 SUs on TDs?

The biggest questions relate to the needle valves and forks. In the next two posts I'll attach pictures of the float bowl lids and you'll see that the fork on the rear carb hangs down to about a 45 degree angle allowing about .3 inches drop of the valve. The front float drops only to about 30 degrees allowing only about .2 inches of needle valve movement. Could this be restricting the amount of fuel getting to the front bowl and causing starvation in the front carb?

Pictures to follow. Thanks for your patience and help.

Jud
J K Chapin

Here's a pic of the rear float bowl lid. Lots of needle valve movement.
Jud

ps, in another thread there's been discussion of the tickler pins. Here's the PO's solution to no tickler pin spring.

J K Chapin

Here's the front float bowl lid. Very limited needle valve movement. The drop of the fork is limited by the ledge in the lid body where the hinge pin is. I see that the PO "fixed" the loose hinge pin by applying dabs for hard grey stuff at each end. Could it be that the hinge pin is too high (too close to the body of the lid) and that causing the restricted fork drop?
Jud
ps, here's the PO's solution to the tickler pin missing completely.

J K Chapin

Jud - I would be suspicious of the rear float lever drop being excessive - see the article, Float Lever Drop Adjustment in the Other Tech Articles section of my Homepage at: http://homepages.donobi.net/sufuelpumps/ If the lever drops too far, it will jam against the needle, preventing it from pushing the needle up to shut off fuel flow.

The other thing that I see is that the two needle valves are different. I think that I would opt for a new set of needle valves (not the Gross Jet style). There is a company who supplies valves that appear to be very good. They are at Daytonaparts.com and the P/N for the TD is 5251 (I have never used their product, but what they show makes sense to me).

The front float fork looks ok from what I can see in the picture (doesn't need a lot of needle drop to allow enough fuel to come through). The gray stuff around the pivot pin for the fork is probably JB Weld to cure a loose needle. Cheers - Dave
D W DuBois

Dave, thanks. This morning I'm going to remove the fuel filter before the pump, make sure that the fuel lines to the carbs are clear and that the pump is pumping adequately. I have the Moss master rebuild kit that includes new needle valves but for the life of me I haven't figured out how to get the old ones out. They appears to screw into the underside of the lid but the is not room to be a small wrench on them and turn them. I could use needle nose pliers but I doubt I could get adequate grip and I know I'd score up the brass. What tool do you use to remove and replace the needle valve bodies?

Thanks. Jud
J K Chapin

Jud, a spin-tite does the job very easily. If not, a 1/4" drive socket set is bound to have a socket that fits. Bud
Bud Krueger

KISS!!! I don't know about y'all but I tend to assume that every problem is the result of a failure of the most expensive, most complex and most difficlut to replace part. Today was no exception. (I just found out that there is limit on the length of a post - you simple lose everthing you've already typed and start a new line - so this will be in two parts).

Following Dave's advice I decided to empty the gas tank by pumping the fuel out through the SU pump and then replace the d@nged fuel filter ahead of the pump. I pulled the hose on the outlet side of the pump and replaced it with a longer hose going into a gas can, unhooked the wires to the coil and turned the switch. About two seconds of rapid ticking followed by maybe three very slow ticks and then nothing - no ticks, no fuel flow. Dang!! I need a new fuel pump!!

Well, I decided that since I was not going to get the gas out of the tank by pumping and since I had most of the fuel lines undone I'd just bite the bullet and pull the line going to the filter - spillage be hanged. I bundled up some towels to catch what I expected to be a torrent of fuel and pulled the hose off the steel (copper?) line from the tank. Stuck the long tube going to the catch can on and found that I had spilled very little fuel and that there was only a trickle going into the catch can.
(Part two follows)
J K Chapin

(Part two)
What I also found was that from the tube going to the filter enough dirt and crud to start a small farm had fallen out onto the towel. It seems that I had been looking at the "goes out" side of the filter which is pretty clean and not the "goes in" side which is totally blocked by dirt, crud and perhaps somebody's long lost pet.

I replaced the section that had had the filter with a straight piece of 5/16 " rubber fuel line and put the long hose to the catch can back on the pump outlet and turned the switch. A wonderful steady flow of gas into the catch can happened. It seems that with no back pressure and no inlet restriction the SU pump settles down to a rate of about two ticks per second with a nice steady flow of fuel.

I went ahead and cleaned the lids and needle valves with carb cleaner and made sure the fuel lines from pump to carbb and from carb to carb were clean and clear and put everything back together and reconnected the electricals and turned the switch and crossed my fingers - VARROOM!!! It started and ran better that I think it ever has.

I took it for a five mile test drive and it ran great - never missed a beat. Brought it home and parked it in the sun for about 15 minutes and took it back out. Purred like a kitten. Going out for about 90 miles tomorrow which will be the real test but right now I both cautiously optimistic and a happy camper.

Thanks to everybody for your help.

Jud
J K Chapin

Bud, what is a spin-tite?

Thanks.

Jud
J K Chapin

Silly me. If you pull the hinge pins and remove the forks I guess it's easy. Jud
J K Chapin

Sorry, Jud. It's a brand name for a set of nut drivers.


Bud Krueger

Jud - I don't see where you did any inspection of your fuel tank. Did you cleaned the tank clean the interior of the tank and have it sealed while you were restoring the car? If not, I would suggest that you at least inspect the tank now - that is the main (only?) source of debris in the fuel system. Cheers - Dave
D W DuBois

Dave, draining, inspecting, cleaning and sealing are on the to-do list. The car was restored by the PO in 1974-1975 and I have no reason to think he cleaned, sealed or coated the inside of the tank so that's probably very original rust and debris. All I've done since 2012 is try to keep it running. Thanks. Jud
J K Chapin

Dave or anyone else who knows, can you also respond to this question that was buried in my verbose post:
"The second thing is that neither carb has a spring above the damper piston. It seems that in a thread a long time ago it was mentioned that some SU carbs rely totally on the weight of the piston and do not have damper springs. Did that apply to the 1-1/4 SUs on TDs?"

Thanks.
Jud

J K Chapin

While not Dave I can answer that. The heavy brass pistons need no spring. The light aluminum ones do need the spring. I think. George
George Butz

George, thanks. Mine appear to be solid chunks of aluminum. Are the brass ones brassy colored and obviously brass?
Jud
J K Chapin

Jud,

There are 3 type of pistons
1/ Brass.
2/ Aluminum weighted with a steel ring.
3/ Aluminum non weighted.

Only 3/ requires a spring.

John

52 TD



J Scragg

I have an mgtf SU diagram with parts list that describes uses for dampers and piston springs ... including pistons with no springs and dampers with "no dampers". SU part numbers are included.

I'll post it when I get back in town in a few days.

Lonnie
TF7211
LM Cook

Jud - John states the three different pistons used in the carbs. I am sure that you don't have brass pistons unless you have a very early TD. The most common piston for the TDs is the aluminum with a steel insert in the dished area of the piston. Check with a magnet to see of there is a steel insert and if there is, then you don't need a spring. If there is no insert, you will have to get a spring to put in there, but I don't know which spring would be used in your car. Cheers -
Dave
D W DuBois

I'll do the magnet thing in the morning. The heft just holding them makes me thing thay have the steel insert and I just can imagine losing both springs so I'm hopeful. Thanks all. Jud
J K Chapin

I didn't know about the aluminum/steel ones. Thanks
George Butz

Fellas, Mine, TF8353, has the aluminum pistons with the steel incert, no springs. PJ
Paul S Jennings

Here is a picture showing the weighted (left)
and the non weighted aluminum pistons.

John


J Scragg

Both comparison to John's pic and the magnet test confirm AL with FE weighted inserts. Good, no springs and two less parts to worry about. Thanks. Jud
J K Chapin

I just finished reading Dave Braun's SU Caruretor Tuning article (publised on an other bbs but I don't know if it is polite to mention the other bbs by name) and note that he stresses the importance of ensuring that the piston domes are replaced in the same orientation as when taken off. During my roadside disassemblies, due to disparation, panic and fear of having to return home on a roll-back, I removed and wiped clean the domes. I know I put the domes back on the same carbs but I have no idea if I maintained the original orientation. Is there anyway to determine what the original orientation was? The domes appear perfectly round and rotatable 180 degrees when reinstalling. The car is running good and the pistons slide up and down smoothly. Does that indicate that I got lucky?

Thanks.

Jud
J K Chapin

I would say so, Jud. Bud
Bud Krueger

Dampers vs no dampers; strength of piston spring; and oil for the dashpot were discussed in this thread and in another recent thread.

I'm a newbee TF owner who is trying to vacuum every bit of reputable information and manuals that I can find to learn about my car. This TF info may apply to the TD topics.

DAMPERS
Although dampers were used on earlier SU carbs, the TF Workshop Manual states that no damper was used on early TF carbs. Clausager backs up the statment and says that piston dampers were added to TF carburetor dashpots starting with TF3495, Feb 1954.

DAMPER OIL
SU manuals recommend SAE20 oil. Some owners recommend automatic transmission fluid. Some recommend Marvel Mistery Oil. I use 3-in-One SAE 20 oil in the blue and white containter.
> Thicker oil = richer mixture on acceleration (piston rises more slowly).
> Thinner oil = leaner mixture on acceleration (piston rises faster)

SPRINGS, DAMPERS, OIL
RKF Wood included a diagram and parts list of a TF carb in "The XPAG Engine, Data Service Super-Tuning." The diagram shows the carb with no damper. Wood's notation at the bottom of the parts list states:
"For better accelleration, use red dashpot spring (AUC4287) and damper (AUC8102). For maximum power, use light blue spring (AUC4587), or no spring, and cap (AUC602) without damper, or cap with damper may be used, but do not put oil in the piston shaft.
http://www.dbraun99.com/technical%20index/WKF%20Wood%20XPAG%20Engine%20Book.pdf

NOTE: Damper AUC8102 is not on this parts list of an early TF carb. Cap and Damper AUC8102 is shown on MGA Service Parts List AKD1055, Plate KB, illustration #7.

Lonnie
TF7211

Early TF diagram, parts list, and comment by RKF Wood:

LM Cook

Great stuff Lonnie and it took me back for a pretty thorough re-read of D. Braun's site. Thanks. Jud
J K Chapin

This thread was discussed between 15/08/2014 and 20/08/2014

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.