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TR4/4A adjust fuel level

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T

TR4eh

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Getting the 4A ready for some driving again. When I parked it last fall, I pulled the plugs and found 1 and 2 black and sooty, 3 and 4 not so much. The front carb had an non-adjustable float. Both floats are now new, the adjustable black viton type, with new seats and needles, and both floats are set at 1/8". However, the front fuel level is up to the bridge of the carb throat, but the rear fuel level is about 3/8" below the bridge. These levels should be equal but the difference seems too large for float adjustments to overcome.

I haven't set about tweaking the floats because, well, I don't really have a plan other than lower the front and raise the rear, and all you wise people might have a better plan. So I'm all ears :friendly_wink:
 
On some of the later carbs (SU HS6), the adjustment is by shimming the valve body. The pivot arm is cast plastic and can't be bent to change the level.

Fig 7.8 float all plastic.jpg

Sure sounds odd, though. Can you try swapping float chambers front/rear? I'm wondering if one of them is the wrong size or something.
 
I use HS6's on my two TR4's . The 1/8" on the carbs is to little. I have a guide that came with an older kit that says ( I recall) 5/16". When I have looked down the jet after removing the dome, needle and piston the fuel is normally 1/4" to 5/16" down from the top of the jet/ bridge. So your front carb is adjusted way to high. Most times the slope of the engine is the cause for differing float levels. Especially on the TR version as your float bowls are in front and then in back of the carb bodies. But you should still be able to get the levels close. There is a different float bowl that can be used to raise the fuel level. But you should not have to go to that extreme.
Charley
 
charleyf said:
I use HS6's on my two TR4's . The 1/8" on the carbs is to little. I have a guide that came with an older kit that says ( I recall) 5/16". When I have looked down the jet after removing the dome, needle and piston the fuel is normally 1/4" to 5/16" down from the top of the jet/ bridge. So your front carb is adjusted way to high. Most times the slope of the engine is the cause for differing float levels. Especially on the TR version as your float bowls are in front and then in back of the carb bodies. But you should still be able to get the levels close. There is a different float bowl that can be used to raise the fuel level. But you should not have to go to that extreme.
Charley
Click to expand...

Thanks much for this information, Charley. I removed a shim from the rear carb's seat, and using shims under the font seat and tweaking the arm on the float, I have both levels about equal but they are about 1/8" down from the bridge. I can't seem to get the front carb's level lower than that. I'll drive it tomorrow and see how it performs, and pull the plugs to check for color.
 
I looked up the reference I was trying to quote. And it was 3/16 not 5/16. It then went on to say that 1/8 to 3/16 was acceptable.
Have you ever used a Colortune? It gives you immediate results that you are looking at the spark plugs for. Unfortunately the cost is bit much for how often one uses it.
Charley
 
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