TR6 TR6 Fuel Delivery Issue

[mpatt]

Just switched over to SU HS6 carbs (Paltech) on my 76 TR6.

Problem #1: on open road car will not accelerate over 55 mph (running at ~ 3000 rpm). Seems like its being starved for fuel.

Problem #2: After driving for several miles in the Texas heat the car slowly starts to sputter until it eventually stalls. After sitting several minutes it will start back up and run for a short period before repeating the cycle. When this occurs, there is no visible sign of fuel in the fuel filter.

I'm thinking that the mechanical fuel pump just cant provide the fuel required by the Paltech Su carbs.

Thinking of switching to electric fuel pump. Any help greatly appreciated.

 

[TR3driver]

What did you do with the vent line to the fuel tank?

The stock pump should have absolutely no problem at all keeping up even at 100 mph, let alone 55. There is something else wrong.

 

[DNK]

, and you'll probably have hot carb issues too.

 

[simpson]

mpatt,

About the vent line - I think randall is getting at a problem some have experienced when the vent line is plugged for whatever reason - dirty, pinched etc. Can create a vacuum in the tank as gas is burned off and work against the fuel pump. Our mechanical pumps are supposed to only rate something like 2.5 lbs psi max and still supply plenty of fuel for dual carbs, and triples for that matter.

You might try a simple test of running with your fuel cap cracked open and see if it makes any difference. This would help to see whether fuel tank vacuum is coming into play.

 

[Gliderman8]

I just have to ask the obvious... have you changed the fuel filter. I mean if it has been in the car for years you might consider changing it to see if it helps.

 

[DNK]

Oh Elliot, quit being so obvious!

 

[toysrrus]

Hi There mpatt,

I had the same "Exact" symptons on a "Frogeye" I had. I went thru the whole routine, "Vapor Lock, Insulate Feul Lines, New Mech. Pump" etc etc. Nothing seemed to solve my problem?!?!?!? "Finally" after a whole bunch of time, (Myself and My Brit Mech), playing with the stupid thing; We added an "Elec. Pump" to the lines & "Problem Solved"!!

You just may want to save "Time & $$$" and do the same thing?!?!?!?

Russ

 

[hondo402000]

have you taken the fuel line loose and cranked the engine to see if you have fuel flowing at a decent rate? if you get an electric fuel pump get a carter low pressure unit.

Hondo

 

[mpatt]

Float bowl vents on Su carbs are tied together and vent to the charcoal canister. All of the emmissions components, except for the charcoal canister, have been removed from the car.

New fuel pump (VB purchased). New fuel filter.

I will replace all hoses, blow out hard lines, check the tank for crud, verify fuel tank vent line is open, and route hoses to carbs as far away from exhaust mainfold as possible. Anyone ever insolate the fuel lines in the engine compartment?

Have been contemplating a heat sheild for the carbs. Are these really effective?

Another issue I have noticed with the Paltech Su carb setup is that when the engine compartment gets hot, the throttle linkage starts to bind. When cold the linkage allows the throttle to return to normal idle. When hot, the linkage binds not allowing the throttle to return to idle. When this happens I can open the hood and pull the carb levers back to idle. I know it is in the linkage between the carb throttle shafts because I can also loosen the clamp bolts on the carb throttle shafts and they return to idle.

 

[poolboy]

Heat shields do an OK job of reducing percolation of fuel in the float chambers. Usually as long as you are underway and the engine is running, the combination of air flowing between the exhaust manifold and the float bowls and the constant flow of fresh fuel into the float bowls, percolation is not a problem.
It is when you stop moving and in particular stop and kill the engine that the conditions are ripe for percolation. No fresh fuel moving into the bowl, no air breezing across the manifold, the heat radiates up onto the bowls holding stagnant ethanol blended fuel, and once it reaches 170*F the ethanol component of the fuel starts to distill off.
Results in a hard to restart engine unless enough time has passed that the fuel has had a chance to cool and stop percolating.
I live at about the same latitude as you and just an off the shelf heat shield was ineffective at preventing percolation when my headers got really good and hot. I lined the heatshield floor wit a couple layers of heat shield insulation and now I.m not bothered wit percolatin fuel.

 

[DNK]

Where did you get the heat shield?

 

[poolboy]

That's one the Richard Good sells. I'm pretty sure it's Joe? Alexander's (ARE) design.
There's one for dual carbs, and SU's

 

[DNK]

Not the whole thing, the heat blanket.
And Ken ,do you have shots underneath at the exhaust .
I need to see if the headers end pointing down or pointing straight back?

 

[poolboy]

Don, got it from either Jegs or Summit.
The headers end going straight back, but those short sections have a dog leg bends so that they line up with the next section.
Don when I rebuilt that engine back in December I took the whole exhaust apart and it took me nearly 2 days to line every thing back up the way it was and those 2 short dog leg sections had to be rotated exactly right or from the flex sections on back were thrown off. I mean you couldn't be as little as 5 degrees off from their original position
Of course I did not realize what a problem that would be or A) I would not have removed anything other than the headers or B) I would have scribed a hash mark across both sections.
Live and learn.
Here's a link to the insulation: I got a 3ft X 3ft piece, but I don't see that size tonight.
https://www.jegs.com/i/JEGS+Performance+Products/555/32032/10002/-1

 

[DNK]

My header ends are pointing more toward the ground than straight back. That's what seems to be causing all the problem

 

[lbcs_r_fun]

Just switched over to SU HS6 carbs (Paltech) on my 76 TR6.

Problem #1: on open road car will not accelerate over 55 mph (running at ~ 3000 rpm). Seems like its being starved for fuel.

Problem #2: After driving for several miles in the Texas heat the car slowly starts to sputter until it eventually stalls. After sitting several minutes it will start back up and run for a short period before repeating the cycle. When this occurs, there is no visible sign of fuel in the fuel filter.

I'm thinking that the mechanical fuel pump just cant provide the fuel required by the Paltech Su carbs.

Thinking of switching to electric fuel pump. Any help greatly appreciated.

I'm curious, at least from a technical standpoint, why you wanted to change to a non-original carb. Also, considering the differences, wont the float bowls be at the wrong attitude? Could that be the problem?

T

 

[DNK]

Your thinking Volvo carbs. The TR6 ones fit correctly

 

[dougstr6]

I don't believe anyone has asked this question:

Were you having drivability problems with the Strombergs?

Since there is no performance improvment, the main reason for the switch is usually done if your prior experience / familiarity is with SU's.

Also assume there has been no ignition system changes with the new fuel system?

Cheers,

 

[poolboy]

Are your old ZS carbs for sale ? If so I'm interested.