Waxstat Jets

[bushnell1954]

Hi everyone,

 

My wife and I have had a 1980 TR7 since 1992. It was off the road for about 5 years whilst I replaced/repaired most of the panels on the car. It is now MOT'd taxed etc and I'm using it to 'shakedown' any problems before she gets to use it! I've had a few minor problems which I've solved, but I'm left with a hesitation/flat spot. I changed the HT system, plugs, points, condenser during the rebuild. Also checked the distributor bob weights, vacuum advance and bearings, all OK.

 

The car starts and ticks over fine, it will rev whilst stationary and seems fine in 1st gear. When you change into 2nd or any other higher gear it is hesitant until you back off the throttle to about 1/4 or so, when it picks up. If you open the throttle the problem starts again.

 

One of the problems I fixed was a seized float arm on the fuel guage sensor so I know the tank & pickup is clear, also checked the fuel pump and cleaned the guaze.

 

So I'm at the carbs now! The float chambers and needle valves are clear, the dashpots lifting freely, clean and full of oil. I'm only really left with a massive air leak or, ( my favourite) the jets or feed pipes. These are of the waxstat type and I confess that I don't know their purpose or how they work. Anyone had any trouble with these or can explain how they work?

 

I've checked for the air leak but I'm happy there isn't one big enough for this, so I'm thinking its' fuel starvation. Any idea?

Edited June 10, 2007 by bushnell1954

[Hasbeen]

Could be a fuel pressure, or flow problem.

 

I suggest you check the fuel pump valves are working properly. They may be sticking, & not allowing full flow, or the inlet valve may be allowing the fuel to flow back to the tank.

 

Could also be a split diaphragm, but that should give you a little leak from the top of the pump.

 

Either way, you would get reduced fuel supply, & the starvation you describe. A pressure gauge in the line should show any problem.

 

I got this problem when I had a lot of muck in the tank, & a partially blocked inline fuel filter.

I have also heard of an inline filter being almost full of water causing these symptoms.

[bushnell1954]

[

Edited June 10, 2007 by bushnell1954

[bushnell1954]

Thanks 'Hasbeen', stripped the carbs today and found some debris in the main jets. Cleaned it out and the car ran a bit better but I've added an inline filter just before the pump. This is clear plastic and it's quite obviously nearly empty most of the time! I'm sure these should fill up completely so I reckon the pump is weak. Unfortunately they don't come apart other than the top for the filter guaze, so I can't see the valves. I think I'll order a pump as they are only around £25 delivered.

 

Any ideas what the fuel delivery pressure should be? I imagine it's quite low as it only feeds the float chambers. I think the pump on my other car (Pontiac Fiero) is around 80lbs per Sq. Inch. I have a guage for that, but it won't read below 10 lbs per Sq. Inch.

[Hasbeen]

Bushnell, before you do anything else, remove the air filter, & try the car. It

may be lack of air. If the filter is OK, your problem should be worse.

 

Then find someone to test your fuel pump for presure, & if possable flow.

You don't need that much of the latter for a 7, & you want no more than

2 PSI more for SUs. More than that WILL make them flood, at least sometimes,

if not continually.

However, much less than 1.75 PSI will generally cause starvation at sustained

high revs.

I have tried a presure regulator, & had more trouble with it than it was worth.

 

One other problem is that many TR7 fuel tanks are now at the age where they

are suffering from internal rust, & causing many fuel blockages. Is your line

clear? Can you blow through it?

 

Yes, that is how those disposable fuel filters work, at least on a 7. They always

look as if the fuel is not flowing.Don't forget that the pump is gravity fed, on the 7,

once the fuel flow is started.

 

There is no mechanical pump available, that I know of, which is a direct replacement

for the TR7 pump. There are a couple which are claimed to be so, but are not.

There is a short leaver, [although I've not found one in Oz], & a long leaver, which

has a few problems.

The short leaver may work OK, if you can find one, I have no experience with them.

The long leaver will pump at far to high pressure, flooding your SUs, until the leaver

brakes, as the cam moves it beyond its designed travel. In Oz they come with 2

spacers about 5/32" & 1/4 thick.

 

I found the 1/4" spacer gave me 1.6 PSI fuel presure, & starvation at revs.

The 5/32" spacer gave me 2.25 PSI, & flooding. A few extra thick gaskets reduced the

pressure, & cured the flooding.

That was 3 1/2 years ago, & its given no problem, [in the fuel dept] since.

 

Try something like SAE 40 oil in your dampers, it may help.

 

I have found that 7s only run well, with the valve clearances very close to correct

[8, & 18 thou], & Iridium spark plugs. We get some lousy petrol in Oz, sometimes,

which is, I think, why the need for Iridium plugs.

[bushnell1954]

[

Edited June 16, 2007 by bushnell1954

[bushnell1954]

Thanks for the help Hasbeen.

 

Sorry for the delay in reply, problems with my ISP, so no internet.

 

Right the progress so far ---- I got a replacement pump from Robsport in Hertfordshire. It was a Quinton Hazell pattern part with the lever too long. They supplied a 12mm cork spacer which gave the same throw on the lever as original. However before I got to fit it the car started running even worse and wouldn't run without the choke part open. Also the car stopped ticking over and went onto two cylinders before dying.

 

So I changed the fuel pump and the driving improved, but the tickover still died. The pump was obviously working better as the filter was full and the hesitation was nearly gone.

 

I stripped the carbs, cleaned and blew them out, then reassembled them, still the same tickover. I took the dampers & pistons out and the fuel level inside the jet on the back carb was much lower than the front!! So I took off the float chamber covers and the fuel levels were the same!! Weird or what??

 

The floats are fine, as are the needle valves but I swapped them for some spare tops, still the same.

 

I started to run out of time, so in desperation I swapped the pair of carbs for an old set ------ problem solved, except a sticky throttle spindle which I fixed with WD40. The car runs perfectly again, ticks over and drives beautifully.

 

So what are we left with? Float levels correct but low fuel in the rear jet tube. All there is in between is a flexible tube, the mysterious 'waxstat' unit and a jet tube. I took off the jet tube and flexi, tried blowing through it and it seems restricted. High pressure air wouldn't shift it so I'm at a loss to explain it.

 

I think this goes back to my original question, what is the 'waxstat' unit for, how does it work and what can go wrong with it? I realise that the repair is a straight swap but I am just interested as to what could cause such an obscure fault

 

Anyone out there got any ideas?

[Rhodri]

Throw away the waxstats- they are so unreliable, normally causing difficult starting when hot. They are meant to adjust the mixture slightly according to temperature but are so tempremental. There was an article on the net showing how to render them inoperative with a 1p piece. At great expense you can buy a proper conversion kit to convert them . The other thing, that is often used with them is a spring loaded poppet valve on the throttle disc- most people solder them shut or replace with a plain disc.

[peterh]

Hi

There a small filter on the pick up in the tank this can block up and cut the fuel feed try blowing back dowen the fuel pipe hard

Peter

[bushnell1954]

Thanx Rhodri for the advice on the jets etc.

 

I think it would be difficult to change the waxstats for older style ones without radically altering the choke linkage, as I recall the older lever had simple screws fixing it on the jets, not the ball ends and clips on the newer ones.

 

PeterH,

 

I am going to put an airline through the fuelpipe after disconnecting it at the tank end, but I really think it was a carburettor fault as the improvement with the spare set was so dramatic. I took the filter out of the tank when I freed off the sender unt, checked the inside of the tank as well and it was clean.

Edited June 18, 2007 by bushnell1954

[Rhodri]

Peter- Type in "waxstat conversion" to google and open the www.nireland...... site. It will show you how to do the conversion and, I think, retain your linkages.

[bushnell1954]

Thanx for all the help, the swapped carbs solved the problem, saw the 4p conversion and may well do that when I refurb the other carbs.

 

Looking at the diagram on the NIreland website I think one of the Waxstat jets had failed/jammed on the old carbs. So it was impossible to balance the mixture starting from the jets fully wound up then winding down 2 1/2 turns. Hence the huge flat spot!

 

Any way it's running fine now so thanx again for the advice.

Edited June 23, 2007 by bushnell1954