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Hello Everyone - TR3: All Choked Up

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gear_grinder

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Hello Everyone,

I am a newbie to this forum and my name is Abe. I have been a brit car lover (MGs and Triumphs) for decades and do all of my own work. I once was brave enough to have a '71 TR6 as my sole means of transportation. I was also foolish enough in my youth to own a TR7, but that's another story.

Now I have a '59 TR3 and it has SU carb problems. I replaced both entire jet assemblies a few years back because of mileage and mixture problems, and it never got any better. Regardless of how lean I set the jets, my gas mileage is terrible (about 10 miles a gallon), I still get black exhaust, and cannot get the things to behave according to the book. I have tried everything I know of to correct this, and still have the same problems. Any ideas out there?
 
:savewave: Hello Abe, and welcome to the Forum!!
 
First thing to check, are the jets returning fully home against the nut after you release the choke? New jets are sometimes not polished enough and the spring won't pull them through the seals.

Next make sure the pistons work _very_ smoothly, with no hint of even rubbing at any position from bottom to top. With the plungers out, they should lift smoothly and easily to the top, then when released fall quickly to the bottom and land with a distinct click. With the plungers installed, there should be definite but smooth resistance to lifting them, but they should still fall quickly and land with a click.

Next I would check the fuel pressure (must be less than 4 psi). Although there should be no way for a pump to fail by producing too much, there have been some replacement pumps sold that do produce too much pressure. Also check the float valves, to see if they leak. If someone has installed Grose Jets, my suggestion is to replace them with standard valves, as I have seen the Grose Jets actually cause the problem they are supposed to prevent. Check the floats too, any liquid inside is cause for replacement.

What happens when you try to set the mixture by the book? If you can't lean the idle out, you may have worn or mismatched jets and needles. There have been some defective ones on the market, so I would suggest buying new ones from TRF or Moss.

I gather this car is relatively new to you ... is there any chance a previous owner has installed a performance camshaft? Also double-check the valve clearances, as they can have an effect on mixture.

Oh, and just to state the obvious, are you sure the carbs are assembled properly? Both items 90 and 92 in this snippet from the Moss catalog can leak fuel into the carb throat.
 
The car is not new to me. I've had it for about 12 years, and it's always run acceptably, but never perfect. I have tinkered on and off with the carbs, but have never driven it more than a hundred miles in a season, so it's not bothered me too much: but I think I'd drive it a lot more if I could get the carbs the way I want them. Now I'm on a mission to figure this out.

I'm pretty sure on the assembly part, but I will double check all of the settings and centering on the jets, needles, & pistons. I have not checked the floats recently, and I've never checked the fuel pump pressure. What kind of gauge does one use to check the fuel pump pressure?
 
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