Weird SUs part duex

[BlueStag]

For those who do not know my car: 1973 Triumph Stag with 260z engine, ZX distro, SUs built by Z Therapy about 12 years ago, just recently down off stands from 9 years storage, do not ever buy a house.

 

So in our previous episode, the SUs would suddenly not produce power (or the engine would not). One moment buzzing along at about 125 or so horses, next gimping like a lawnmower engine that has just sucked in a lot of water.

 

The first time this happened previously, I first tore the carbs down as far as you can without pulling them off the manifolds (which is pretty far) and when reassembled, hey presto, power again.

 

The second time I pulled the bell off the front carb and put it back, I took out the dampers and lifted the pistons to assure that there were no restrictions in their movement. A nice satisfying clunk as they dropped down.

 

And it ran again.

 

Today. Warm day, ran down the freeway about five miles to see some people. Parked for an hour. Ran back up the freeway, and just as I am two blocks from home, the dreaded power loss. I let it rest for about an hour, the engine had cooled enough that I choose to use the choke, it was a bit punk for a moment, then ran. Release the choke as the engine got hot? Power lost. Apply choke without pulling enrichment, power back. Park at grocery store, shop.

 

Start car, no choke, power as it should be.

 

What in the hell is the issue?

 

I wonder if I have some transient vacuum leak? But I cannot imagine a TRANSIENT vacuum leak.

[rayaapp2]

Be positive that you are not running out of fuel. Bring a Phillips Screw driver with you. Next time it bogs out, shut it off, pull out of gear, and get off the road.

 

Pull the tops of both float bowls off and ensure that your fuel level in both of them is good and not dry!

 

I would also be sure that your nozzle jet(the part that the needle slides into) does not have foreign debris/old fuel gunk lodged into the orifice.

 

Another thing I would check though unlikely is the slide piston for movement. It should have resistance with the dampener, but once you unscrew that actuate the slide up and down and check for a sticky point.

 

Sounds to me like your experiencing fuel starvation to one carb. Sounds like its running on only 3 cylinders? Most Z guys that have almost run out of gas know that lawn mower sound well... better be at the gas station corner or your S.O.L.

[BlueStag]

Be positive that you are not running out of fuel. Bring a Phillips Screw driver with you. Next time it bogs out, shut it off, pull out of gear, and get off the road.

 

Pull the tops of both float bowls off and ensure that your fuel level in both of them is good and not dry!

 

I would also be sure that your nozzle jet(the part that the needle slides into) does not have foreign debris/old fuel gunk lodged into the orifice.

 

Another thing I would check though unlikely is the slide piston for movement. It should have resistance with the dampener, but once you unscrew that actuate the slide up and down and check for a sticky point.

 

Sounds to me like your experiencing fuel starvation to one carb. Sounds like its running on only 3 cylinders? Most Z guys that have almost run out of gas know that lawn mower sound well... better be at the gas station corner or your S.O.L.

 

Ray, thanks.

 

Yes, I do need to have a Philips head in the car at all times. And yes, I like the idea of just slam it to the kerb and shut it down and check it out. Nice that I don't need to pull the air cleaner off........

 

As I wrote, I have done the test for the "slide piston", where one takes out the damper that the oil must push past, and check for flawless movement up and down, and have found no issues.

 

I do appreciate your insight that this might be ONE carb without fuel. That makes perfect sense, a straight six trying to move on three cylinders....

 

I would so like to see a float bowl made of Pyrex glass. I am sick of trying to set my floats. I find the whole business just mystifying.

 

I'm gonna go get a 280zx turbo and hang 300zx turbo gear on it.....

[BlueStag]

You know what I wonder? I wonder how quickly the SUs consume the oil in the dashpots?

[19762802+2]

Do you have an electric pump or mechanical? I have been having the same issue with my carbs lately as well, not exactly the same but the car would run like crap, I would check if its vapor locking, make sure your getting the right PSI to the carbs, also one of your float bowl needles could be sticking and causing it to go dry, also check your float level.

 

For a while I was having problems with having too much pressure from my electric pump (now I'm having problems with not enough pressure, so time for the mechanical pump. ) and it would cause one carb to starve out and the other to get too much fuel. I also was having problems with the fuel restrictor hole on the return line of the fuel rail so I'm now running a pressure regulator, but my electric pump doesn't flow enough fuel at higher rpms to keep the float bowls full so I lean out and lose power.

[19762802+2]

I would so like to see a float bowl made of Pyrex glass. I am sick of trying to set my floats. I find the whole business just mystifying.

 

I think I have seen somewhere about something were there were SU float bowls that had small glass windows so you could check the fuel level but I can't remember for sure.

[BlueStag]

Do you have an electric pump or mechanical? I have been having the same issue with my carbs lately as well, not exactly the same but the car would run like crap, I would check if its vapor locking, make sure your getting the right PSI to the carbs, also one of your float bowl needles could be sticking and causing it to go dry, also check your float level.

 

For a while I was having problems with having too much pressure from my electric pump (now I'm having problems with not enough pressure, so time for the mechanical pump. ) and it would cause one carb to starve out and the other to get too much fuel. I also was having problems with the fuel restrictor hole on the return line of the fuel rail so I'm now running a pressure regulator, but my electric pump doesn't flow enough fuel at higher rpms to keep the float bowls full so I lean out and lose power.

 

An electric pump, but I have a pressure regulator set to 3lbs. My floats operate gross jets, not conical needles, so I don't think they are sticking.

 

Damned float level. I am so sick of thinking about it. I am going to get a 280zx turbo, damnit.

 

I have no return lines on any fuel rail of any sort.

[Tony D]

"I would so like to see a float bowl made of Pyrex glass."

 

See that hex headed plug on the bottom of your float bowl?

Know what goes in there?

A proper banjo bolted fitting with a clear plastic tube that gets connected to the vent port on the top of your carb, and is "T'd" to the air cleaner so you have the same relative pressure in the float bowl as you do when running normally.

 

Lets you see the float level on a dyno under power without much ado. Very revealing about pump volume and what pressure you 'need' to run at what load...

[BlueStag]

"I would so like to see a float bowl made of Pyrex glass."

 

See that hex headed plug on the bottom of your float bowl?

Know what goes in there?

A proper banjo bolted fitting with a clear plastic tube that gets connected to the vent port on the top of your carb, and is "T'd" to the air cleaner so you have the same relative pressure in the float bowl as you do when running normally.

 

Lets you see the float level on a dyno under power without much ado. Very revealing about pump volume and what pressure you 'need' to run at what load...

 

Oh, I am aware of it. It certainly is not of much use when the air cleaner is on. But I take your point, get two fittings and two Ts, and see what there is to see. I certainly am not going to go buzzing around town with clear plastic tubing with pressurized fuel in it.....I'd be real interested in some good rugged glass in that role. Actually, I just installed a glass fuel filter that could serve, just do without the filter. But it is a bit large in diameter, I am not sure there is space.

 

Much as I'd like to put it on a dyno, I don't think my budget is open to that just now. How much do you think that time costs?

[Leon]

Oh, I am aware of it. It certainly is not of much use when the air cleaner is on. But I take your point, get two fittings and two Ts, and see what there is to see. I certainly am not going to go buzzing around town with clear plastic tubing with pressurized fuel in it.....I'd be real interested in some good rugged glass in that role. Actually, I just installed a glass fuel filter that could serve, just do without the filter. But it is a bit large in diameter, I am not sure there is space.

 

Much as I'd like to put it on a dyno, I don't think my budget is open to that just now. How much do you think that time costs?

 

Pressurized fuel? There is already a line venting the float bowl into the air cleaner. What Tony proposes doesn't change much of anything, just lets you see the float level.

[BlueStag]

Pressurized fuel? There is already a line venting the float bowl into the air cleaner. What Tony proposes doesn't change much of anything, just lets you see the float level.

 

That's a point. Still not crazy about the idea of a plastic tube not rated to fuel or pressure with an endless supply of fuel in the engine bay.

 

But I see how it could reveal the level long enough to understand if my floats are set correctly.

 

 

I'm lusting for a L28 turbo.....

[neotech84]

I think a clean tank might solve your issue......

 

If you drop a ping ping ball into a gas tank it will float around the inlet for a while till the suction is strong enough to pull it in and cut off the fuel supply. The pump stops and the ball returns to the top. Restart and problem returns. Great way to aggravate mechanics.

 

I'd say you have some sediment over a filter or a colapsing fuel line.

[BlueStag]

I think a clean tank might solve your issue......

 

If you drop a ping ping ball into a gas tank it will float around the inlet for a while till the suction is strong enough to pull it in and cut off the fuel supply. The pump stops and the ball returns to the top. Restart and problem returns. Great way to aggravate mechanics.

 

I'd say you have some sediment over a filter or a colapsing fuel line.

 

I am pretty sure it is not crud flaking off the fuel tank, as I had it boiled and sealed some time ago.

 

I could see replacing the fuel filter and lines in the trunk. Those in the engine bay are fresh.

[BlueStag]

I'll go make a thread about my over all project in due time, but here are some photos of the project:

Edited September 20, 2011 by BlueStag

[HowlerMonkey]

I had a mazda RX-2 that did this every once in a while.

 

One day, I pulled into a gas station and decided to fuel up while trying to figure out what was wrong.

 

When I remove the gas cap, it was difficult and a large sucking sound was heard as I got the cap off.

 

Apparently the tank was ending up with a vacuum in the evening after the sun went down in Washington DC and the temperature dropped 30 degrees.

[Tony D]

"Still not crazy about the idea of a plastic tube not rated to fuel or pressure with an endless supply of fuel in the engine bay.

 

Better pull that SU setup off, those fuel transfer tubes under the bowl to the jet bottom will pop at 7-10psi... They are vacuum rated tubes designed not to COLLAPSE, rather than not expand (which is what pressure-rated hoses are designed to do?)

 

The tank venting issue usually rears it's head after someone decides to redo all their tank hoses in a 240 and actually gets a good seal. Then it starts doing things it never did before!