View Full Version : Running Lean after hard acceleration...

Tim Tucker
02-09-2008, 03:45 PM
HI all!

I have my TR6 idling smooth and steady as well as accelerating away from my driveway and then accelerating onto the next road very well. This would account for ~1000 yards of hard, 'barking' in 2nd acceleration. I am very pleased with that part of the car's performance...

then the wheels fall off...Smile

Once I hit the main road it soon starts to starve for fuel(IMHO). If I pull the choke out just a tad, I restore full power and she does OK. If I pull into a parking lot while out driving and let the car idle, I notice that the idle is rougher and then gets smooth again after ~2-3 minutes.

Here is what I have checked:
Fuel Line Pressure at carbs: 2 psig? (yes that is a two)
Fuel Flow at carbs: seemed fine at idle
Fuel Flow to pump inlet: definitely OK

Not checked:
Fuel Float Height setting:
If this was set such that the fuel level was being kept too low, wouldn't it show up fairly quickly when accelerating?

I am running the Pertronix electronic ignition and coil. I bought the car in May and have replaced wire, plugs, fuel lines, etc.

The fuel pump is rebuilt and seems to work well??? I checked that each stroke produces vacuum or pressure at the inlet or outlet. The two valves were put in as they were (also per the manual). The 2 psig at the carbs bothers me. I know my TR4 fuel pump produces far more than that. Also, when I return back from a run the clear fuel filter is virtually empty (normal?)

TIA! Any advice is appreciated.
Confused in TN,

02-09-2008, 05:01 PM
Two PSI of fuel pump pressure does sound rather low. IIRC, TR6 pumps put out more like five or six PSI. Is there anyway you can extend the hose for the fuel pressure gauge under the hood and tape it on the winsheild?? I do this all the time with Fuel injected cars that need certain pressures under differnet operating conditions. This way you can see what the pressure is when the car starts to break up.

But, since you haven't checked the float height, I would do that, especially if pulling out the choke seems to alleviate the problem. Also, check the position of the needles that go into the jets. Maybe one or both are too low.

That 2 PSI is still troubling me...even Webers like to see 3 PSI.

Geo Hahn
02-09-2008, 05:29 PM
4-cylinder TRs specify fuel pressure as 1.25 to 2.5 psi. It doesn't so much 'pump' as 'gurgle'. The TR6 may take more but I wouldn't think much more as it is still just a pair of ZSs.

An apparently empty inline fuel filter is normal (though counter-intuitive).

I would not rule out igniton as the culprit.

02-09-2008, 05:59 PM
The volume counts for more than the pressure here. But it does sound more like a supply problem than anything else. I'd still double check the float height, tho.

02-09-2008, 06:56 PM
Float height!

02-09-2008, 08:16 PM
Agree on checking the floats first (too low). Also make sure that the car is totally warmed up, they're pretty cold natured.

02-10-2008, 12:38 AM
Check fuel pressure when the problem happens. My guess is that fuel delivery is falling off for some reason. 2 psi is at the bottom of the normal range, but is acceptable if the pump can hold that while delivering full volume as well.

Easy way to check is to get a vacuum test gauge that also reads (carbureted) fuel pressure. Commonly found on ebay for $10-20. Put a long hose on it, tee it into the fuel line right at the carbs, then bring it out from under the hood/bonnet and stick it under a wiper. Take a test drive and see what happens when it starts acting starved.

Another possibility would be a blockage limiting flow inside the carbs, maybe in the bottom of the jet or in the float valve ... but I'd check pressure at the inlet under actual conditions first.

Tim Tucker
02-10-2008, 01:15 PM
Many thanks to all that responded each opinion and insight is greatly appreciated!

After reading the posts I decided to backtrack a bit and essentially start over setting the carbs. I set the shoulder of the needle flush with the air valve and went from there, setting the mix and re-synchronizing. When all was said and done the car ran well all day (dove 43 miles after tuning). The plugs looked good.

Basically the problem was: bad mechanic! (me) I hope I don't turn into a DPO!

btw, I re-check my TR4 fuel pressure 3-4#...