MG TD TF 1500 Fuel level below the bridge?? BBS discussion at MG-Cars.net

MG TD TF 1500 - Fuel level below the bridge??

Check back in with Dave's site and see the many examples of SU restorations documented. SU Carburetor Restoration Projects https://www.dbraun99.com/SU_Carburetors/ This image can be found in the Austin Healey 3000 assembly. It depicts setting the jet 0.070" below the bridge. The fuel level is a bit trickier and must be done with carb installed after the fuel pump fills the float bowl. The main jet needs to be dropped temporarily to view the fuel, but if it is too far down, the hole in the side of the jet is blocked and fuel won't get in. I'd recommend a good flashlight with narrow beam and strong reading glasses to focus. You might try setting the jet at 0.160 and see if the fuel rises above or does not rise that high or just try measuring the fuel meniscus itself. The adjustment can be hit or miss bending the floats in very small increments to tweak the level. You'll likely be removing the floats and refilling the bowl a few times until you're satisfied the two carbs are even somewhere between 0.0120" and 0.020". It'd be wise to remove some gas between each test so the fuel pump gives a new level each time. You'll also want to install the gasket for the bowl lid with each attempt since it a factor in the level.

JIM N

Well, I attempted to set the floats and jet using in TF681 Dave Braun's method and Jim's suggestions. I kinda got in the ballpark. Not easy. The engine runs, so I'm not too far off. The H4 carbs in TF681 are a mystery. Body casting 4468. Some minor differences from 6020 in TFs. Don't know what vehicle(s) originally used them. Before setting the floats, I cleaned the carbs and parts, and did a minor rebuild with used parts. I used Teflon O-rings for glands and Viton O-ring for the jet washer. I temporarily plugged the vent holes in the dampers because the suction chambers are also vented. The jets and jet needles were damaged pretty badly. New ones plus other new parts are on order. I'll use the same method to set the floats after I rebuild. I found the easiest way to judge the fuel level at the bridge was to lower the jet to 0.160" below the bridge. Turn on the ignition to fill the float bowls. Then I touched a wooden toothpick to the top of the jet to see if fuel wicked up the wood and show that fuel covered the jet. If it was close, I used a Q-tip to remove the thin layer of fuel, and checked with the tooth pick again. Adjust the float forks and try again, and again, and again. When finished, the forks were substantially flatter than when set at 7/16". The float level was higher than @ 7/16. I removed some fuel from the float bowls before some of the tests. When I turned on the fuel pump, fuel shot up from the center of the jet and covered the jet and splashed into the carb. Had to dry them and measure again. At perfection, the top of the jet nearer the engine would be wet; the part away from the engine would be dry -- because the carb is tilted. Don't know if I ever reached perfection. Dave says that the fuel level should be between 0.200" and 0.120" below the bridge. Pretty sure that I am well within tolerance. After setting the fuel level, I adjusted the jet to 0.070" below the jet for the initial startup. It was rich. I balanced and leaned the mixture somewhat. Probably as good as it's gonna get before I install new jets and jet needles. Is this method better than the long proven 7/16" float setting. I dunno. I can always revert. Lonnie TF7211 TF681

LM Cook

This thread was discussed between 06/06/2022 and 09/06/2022

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