General TR Fuel Pump Pressure

[KVH]

Is there a cheap tool to check this? What should the pressure be in a TR4?

 

[poolboy]

A vacuum gauge...The needle moves in one direction with vacuum and moves the other direction with pressure.
The ZS carbs can handle 1.5 to 2.5 or 3.0 psi.
If you have SU's I don't specifically know but it can't be that much different.

 

[TR3driver]

I believe the SU spec is also 2.5 psi. Check the gauge face before you buy. Certainly most of them will read fuel pressure, but I have seen units with a peg to keep the needle from moving backwards.

Here's one at HF
https://www.harborfreight.com/fuel-pump-and-vacuum-tester-62637.html
Should also be available at FLAPS, Sears, etc. (but Sears seems to be sliding downhill so YMMV).

 

[dklawson]

I had a Sears one for years. I loaned it to a friend who failed to return it. I replaced it with the Harbor Freight kit Randall posted the link for. I was pleased with its cost and quality. It is more than adequate for vacuum gauge tuning and checking fuel pressure.

 

[Geo Hahn]

Is there a cheap tool to check this? What should the pressure be in a TR4?

You're welcome to come over and borrow mine.

I had a Sears one for years. I loaned it to a friend who failed to return it...

Oh, I guess I'll need you to leave a deposit.

Really, I do not know which is closer - my house or Harbor Freight but you are welcome to borrow it.

 

[KVH]

Guys--gas everywhere from overflowing float bowls. I even bought new floats, needles and seats, and now I'm still rich and leaking again from both bowls. BUT, here are a few more new facts in case you have more thoughts or advice:

Both bowls appear to be leaking from the lids, right at the gasket. I've got new gaskets I can put in, but I've never seen those leak before. I pulled the lids, and the fuel is too high, even with the floats correctly set. In fact, the Moss Video says it's not all that precise. So, I tried one more adjustment to the float level, and it made no difference.

I then pulled the hose off the rear carb and there was so much pressure built up that gas shot onto the valve cover like a water pistol. Is that normal? It was a good squirt of three ounces or so.

I guess what puzzles me is that if the pressure is too great, wouldn't the gas just run out the overflow hole and not cause a leak at the lid? The problem can't be just my gaskets. Would it be a correct assumption that excessive fuel pressure is allowing enough gas into the bowl to cause both a rich mixture and a level just high enough to escape those gaskets?

I put a new fuel pump on four months ago. I've had this rich problem the whole time. The pump was the last of a run that had "defective" threading at both input and output. Nothing in the spec sheet mentioned any other defect.

So, my question: Is all this now sounding more like a fuel pressure issue?

PS Hey, Geo, thanks for the offer as always. You're too good to me. I may call you if I decide I don't need to own one.

 

[Brinkerhoff]

Too much fuel pressure pushes past the needle and seat in the lid and raises the fuel level in the bowl and the jet causing you to not be able to lean your mixture out ! Its very critical to the proper running of your engine.

 

[Vila]

I agree with the previous comments. To much fuel can be as much of a problem as to little.

For the younger readers of the forum, don't lend tools to friends or family if you want to keep the tools or keep them as friends. Around 40 years ago I lent a friend a power ceramic tile wet saw along with the attachment that was needed for it to function properly. When he bought it back the attachment was missing and that model was no longer made so I could not even buy a replacement part. That was the last tool I ever loaned out.

 

[dklawson]

As others have said, excess fuel pressure will overpower the float valves leading to high fuel levels in the bowls. That can indeed get the bowl gaskets wet and/or cause them to leak. Aim for pressure no higher than 3 PSI max. If you need to add a pressure regulator, the Holley low pressure unit has a much better reputation for accuracy and reliability than the round, pancake shaped ones.

If you are using Grose Jets, remove them and clean them thoroughly with spray carb cleaner. For storage, their steel balls are supposedly covered with a protective coating which can interfere with proper operation. I have seen them stick open... and I have seen them stick closed. Better yet, buy new float valves from Joe Curto.

If your car does not have a fuel filter before the carbs you should consider adding one. You should also make sure that all the rubber lines from the fuel pump to the carbs are new. Old lines can deteriorate and shed crumbs of rubber which interfere with the float valves.

 

[TR3driver]

I'll agree, it seems odd that your fuel level is just a little too high, but not high enough to overflow out the bowl vents.

But, it's still too high.

IIRC you mentioned before setting the float level to 1/8". This document https://drive.google.com/open?id=0B2H2NJt34OffYmIyM2Q5ZGQtY2YyMi00ZmVkLThiYWEtZTE3MTUyZDEyMDM0
says it should be 3/16", with just the weight of the float resting on the valve.

BTW, the fuel pressure spec in the TR4 workshop manual is 1.25 to 2.5 psi. It appears the same pump was used on all TR4-4A, so the late 4A spec should be the same. But the above document suggests it should be in the 1.5 to 2.0 range. Perhaps they just tightened up the spec (and lowered the float level by increasing the float measurement) to help meet the early smog requirements.

 

[Geo Hahn]

Sounds like the pump or the valves. I cannot readily picture how that pump can deliver too high a pressure but anything's possible.

Buy or borrow the gauge (I'm home all day) and rule the pump in or out.

If not the pump - move on to the valves (I possibly have extras of those if you don't).

 

[KVH]

I drove home past HF, and just had to buy that gauge. My floats are set correctly, but the carbs are flooded and the level at the jets is way too high. So, doesn't that mean the floats are set wrong. But they're not wrong. I even called Moss and they seem convinced the problem is elsewhere if the floats are reasonably close. So, the pressure from my fuel pump is 1.5 pounds. Meaning I still have no answers. I'm going to disassemble everything, clean all the parts, reassemble and see what happens. Oh, but I've got another question: would I get an incorrect fuel pump pressure reading if I took it on the far side (toward carbs) of the fuel filter. I know that sounds crazy, but it wouldn't seem the filter should alter the fuel pressure; otherwise it would also alter engine performance, right?

 

[Brinkerhoff]

You are sure your overflow tubes are not blocked ?

 

[Brinkerhoff]

You are sure that you don't have the inlet and overflow ports on the lids mixed up?

 

[TR3driver]

With fuel flowing, there could be some pressure drop across the filter, particularly a filter that has been in use for some time. But it certainly can't increase the pressure; and besides, at the carbs is where the pressure is important.

I've lost track : have you checked that the float valves work by blowing into the inlet with the lid held upside down? It should take no more than very light finger pressure on the float to totally shut off the flow of air.

And you're not using Grose Jets, right?

Only other thing I can think of is floats that are wrong for the application; or simply too heavy. They can sometimes absorb fuel until they don't float high enough to shut off the fuel; especially if they are the old non-ethanol resistant floats. When I had that problem with my motorhome, the first pair of replacements I got developed the same problem within just a few days. Fortunately we were home from our camping trip by then, and I was able to search out some brass floats that fit the same carb.
If that is the problem, this might be the solution
https://sucarb.co.uk/float-chambers-spares/floats/hs-floats/su-hs-type-stayup-float.html

 

[KVH]

I've lost track : have you checked that the float valves work by blowing into the inlet with the lid held upside down? It should take no more than very light finger pressure on the float to totally shut off the flow of air.

And you're not using Grose Jets, right?

Only other thing I can think of is floats that are wrong for the application; or simply too heavy. They can sometimes absorb fuel until they don't float high enough to shut off the fuel; especially if they are the old non-ethanol resistant floats. When I had that problem with my motorhome, the first pair of replacements I got developed the same problem within just a few days. Fortunately we were home from our camping trip by then, and I was able to search out some brass floats that fit the same carb.
If that is the problem, this might be the solution
https://sucarb.co.uk/float-chambers-spares/floats/hs-floats/su-hs-type-stayup-float.html

Yes, I did try blowing into the tube to check the valve. Seemed OK. And, correct, viton tipped standard Moss needle. Another hint here: both bowls show evidence even with new gaskets that gas is trying to seep out at the lid. I'll check the overflows again, too. When I remove the bowls the gas is about 5/8 to 3/4 inch from the top of the bowl. Maybe I better swap out the pump just for better assurance here. I'll read that article, too. About the lids, I've got them on correctly. I'll solve the mystery one day.

 

[poolboy]

There's no indication that you have a problem fuel pump, quite the contrary...why replace it ?