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stillp

Loss of power

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Since I retired I've been hoping to spend more time in the TR rather than under it, but not having much luck. Took the diff out last year to get the seals replaced. In the process I pulled the flexible coupler off the fuel pipe, so the tank drained - mostly onto my shirt, but I managed to save a couple of gallons. While the system was dry I changed the needle valves and floats in the Strombergs as they'd been flooding occasionally. And of course I'd had to take the exhaust off to drop the diff, and found some cracks in the silencers, so changed that too.

 

Put some petrol in, charged the battery, started up and ticked over fine. Went for a drive round the block, and after a couple of hundred yards lost a lot of power. Felt like it needed choke, but pulling the choke made no difference. Tweaked the carbs using two Colourtunes - good blue flame in all cylinders. Same symptoms - fine for a short distance, no power thereafter.

 

Since then I've rechecked the tappets and ignition timing, changed the plugs, distributor cap and plug leads, coil, condensor, LT leads. Checked the fuel tank for obstructions and removed a 6" length of the chrome finisher for the rear screen seal. Tank has some slight rusting inside, but there wasn't much in the fuel that drained out, and not much in the fuel pump filter. Blown through the fuel pipe from the tank.

Last thing I thought it could be was the fuel pump, so sent it to Dave Davies for refurb, and refitted it today. Feels to be pumping better, but still losing the power on the uphill stretch of the 'round the block'. Uphill as in used to need the O/D switching out to drive up at 30-ish in 4th, so not that steep, now needs second gear.

Compression is around 160 on all cylinders.

 

I'm stumped now, can't think what could be causing this. Does anyone out there have any ideas?

 

Pete

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Thanks Stef. Tried giving it a whack, made no difference. Diaphragms look OK, and when I've had them fail in the past pulling the choke would help matters. Both pistons seem free, jets centred, pistons seem to go up and down together, hiss at carb inlets are similar.

No backfiring.

 

The chrome finisher looks a bit the worse for wear after a few decades immersed in petrol!

 

Pete

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Try the following, when going uphill as it looses power, cut the ignition and stop. Check a couple of plugs, are they weak ( too white) if so or not sure it could be float level too low so running out of fuel under load. Does it also do it if at high revs in 3rd? Does it loose revs when stationary if revved to over 3000 for a minute. Lastly but not likely is exhaust system free you can get this problem if someone has pushed something up the pipe like a potatoe. If it is lack of fuel under load then this would not show on colour tune at lower revs when stationary. New floats need to be checked for height from face of carb casting and new ones my need the tangs bending to get the fuel level right.

Chris

Edited by potts4a

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Hi Pete,

I've no idea about Stromberg carbs but a friend of mine with SU's had similar fault and found that one of the needles had come out of the piston and was sitting loose in the jet.

Ticked over but wouldn't drive

 

Roger

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Hi Chris,

 

Plugs look OK - maybe a bit dark. Doesn't seem to matter which gear, loss of power is still there, need high revs to get up that slight incline. Float level might be a possibility - I have reset them, but the valves and floats are one of the things that I changed since the car was last running well. How precise do float levels need to be? That is, precise with a rule, or precise with a vernier?

Off load, it'll sustain high (3000+) revs. Exhaust is new, no spuds that I can see.

 

Pete

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Hi Chris,

 

Plugs look OK - maybe a bit dark. Doesn't seem to matter which gear, loss of power is still there, need high revs to get up that slight incline. Float level might be a possibility - I have reset them, but the valves and floats are one of the things that I changed since the car was last running well. How precise do float levels need to be? That is, precise with a rule, or precise with a vernier?

Off load, it'll sustain high (3000+) revs. Exhaust is new, no spuds that I can see.

 

Pete

Pete, Fuel level in jet is not critical, a few mm below the surface will do. 5mm lift needs a depression of only 0.01psi while the 'constant depression' is likely to be ca 0.2psi - about 20-times higher, although I dont know that number for Strombergs.

 

 

It could be fuel starvation due to pump pressure or float valve restricition. You've done the pump so why not swap back to the old float valves.

 

But.......the diaphragms are a known weakness, I'd fit new. I'm not convinced that have been tested. Any check with car stationary is not going to be useful when its fails going uphill under load, whatever the rpm. Standing still and revved it might make 2-3hp, going uphill it will need maybe 50plus, so the air and fuel flows are much greater. As Chris says Colortune tell you nothing about loaded operation. Equal hisses at tickover does not necsssarily mean good lifts under load, the diaphragm is not extended.

 

Edit: also make sure atmospheric pressure can get under the diaphragm. The passage connects I think to the two drilllings above the air-filter mounting bolt holes. Often there's a thin rubber seal between filter and carb and the two upper holes may not have been punched out.

Peter

Edited by Peter Cobbold

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Yes, I'm beginning to suspect the diaphragms, if only because they're the only thing I can think of that hasn't been changed. Last time I had one split though I couldn't get a good tickover, and the choke made a difference. If not those then swapping back to the old needle valves is a good idea.

 

I understand the difference between off-load and on-load running, but it's harder to see the Colourtune at 30 mph! I do have a USB camera though...

 

Pete

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Yes, I'm beginning to suspect the diaphragms, if only because they're the only thing I can think of that hasn't been changed. Last time I had one split though I couldn't get a good tickover, and the choke made a difference. If not those then swapping back to the old needle valves is a good idea.

 

I understand the difference between off-load and on-load running, but it's harder to see the Colourtune at 30 mph! I do have a USB camera though...

 

Pete

Pete, I'd not risk a Colortune on a loaded engine it think it could explode through the bonnet. But the USB camera would tell you if the carb pistons were lifting equally going up that hill - a good diaphragm test. Peter.

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Thanks for the warning about the atmospheric pressure holes Peter. I'll check that on the NOS diaphragms I have.

 

Pete

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Hi Chris,

 

Plugs look OK - maybe a bit dark. Doesn't seem to matter which gear, loss of power is still there, need high revs to get up that slight incline. Float level might be a possibility - I have reset them, but the valves and floats are one of the things that I changed since the car was last running well. How precise do float levels need to be? That is, precise with a rule, or precise with a vernier?

Off load, it'll sustain high (3000+) revs. Exhaust is new, no spuds that I can see.

 

Pete

No text bl**** phone Edited by potts4a

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Hi Pete, float level is fine measured with a rule, has to be very low to cause starvation.

Re the air inlets to the diaphragms , it is possible to fit the gaskets between the carbs and air filters upside down closing off the holes, also poss with some air filters to fit them upside down.

One more thought, as the car has not been use for a while worth jacking up the rear wheels and checking the wheels move freely, the brake hoses can collapse and hold the brakes half on, after a short test drive check none of the hubs are hot.

I know it's a new fuel pump but try removing the pipe feeding the carbs and put end in a jamjar , crank the engine with ignition off and each pulse of the pump should deliver about an egg cup full of fuel and 10 seconds should half fill a jamjar.

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I have written this before

 

Just a quickie - check the polarity feed to the coil - had this issue with an E Type that ran like a bag of poo when under load.

Simply start by looking at the battery for which terminal is connected to the bodywork - Your car is probably negative earth.

 

If the car is negative earth ... the low tension Lucar - ve terminal of the coil should be connected to the distributor and the 12 volt feed from the ignition switch/loom should be to the + ve.

 

Simple check - correct if wrong.

 

If you have a coil with CB (contact breakers) and SW marked on the low tension connectors you might find the wording positive earh or negative earth stamped on the base of the coil - or even a sticker announcing the coils intended use.

Cheers

Peter W

Edited by BlueTR3A-5EKT

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Peter W,

Yes, that's the way both the old coil and the new (which made no difference) were wired.

 

Chris,

Yes, A good spurt from the pump at each stroke, took less than 10 seconds to fill my jamjar, and the filter gaskets are the right way up. All wheels rotate freely.

 

All,

Just trying to fit the new diaphragms I had in stock, and not sure if I have the correct type. The one I took off has a locating tab that protrudes outside the circumference of the diaphragm, whereas all 3 of the new ones I have (from 2 suppliers, but I can't remember who) have the tab on the circumference, but protruding below the outer ring of the diaphragm, i.e. not visible from the top, but visible from the side. Are these correct?

 

Pete

 

ps Sorry if I seem to be rejecting everybody's suggestions - I've already tried everything I can think of, at least once. I'm now meeting Einsteins definition of insanity - repeating the same actions while hoping for a different outcome!

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Pete,

If the diaphragms don't do the trick I'd be inclined to double swap the condenser. Your symptoms fit with a failed one.

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Looking at the usual suspects' web sites, it does indeed seem I have the wrong diaphragms in stock. Looking at this picture the ones I have look like the centre image, the ones on the carbs are like the LH image.

 

Pete

post-12352-0-49173300-1458059407_thumb.jpg

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Looking at the usual suspects' web sites, it does indeed seem I have the wrong diaphragms in stock. Looking at this picture the ones I have look like the centre image, the ones on the carbs are like the LH image.

 

Pete

Pete, Are you sure the ones on the carbs are correct for the carb? peter

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Peter, the notch in the piston fits the diaphragm that's been there since 1989, but not the new one, so they're probably right for the carbs.

 

Pete

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Pete, the tabs align the Pistons, you can probably still use them but you will have to align the Pistons by eye after taking the air filters off.

Does your engine have the P S V valve fitted. If so disconnect it and block the pipe to the inlet manifold with a suitable bolt. It could be drawing air under load and weakening the mixture. I threw mine away 15 years ago just vent the rocker with a piece of rubber pipe down past the chassis onto road!

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Chris, the diameter seems slightly different, so the piston was binding. The diaphragm I took of looks OK when stretching it with a light behind. Might just put it back and try the one on the other carb.

I don't have the crankcase valve, like you I have a piece of hose from the rocker cover. Should really plumb it into the chassis as a rust preventer.

 

Pete

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I suffered exactly the same problems after fitting a new electronic distributor, my old system was from Accuspark with Accuspark plugs and everything worked very well for years until I fitted the new system. I spent weeks trying to track down the problem until one day I found my old plugs in a box bunged them in and bingo problem solved

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Once had loss of power with a Series One L/Rover. Checked everything - mixture, timing, compressions, all fine, but she could hardly drag herself along.

 

Then one day in the rain noticed the rear drums steaming ! Turned out it was just old brake hoses, they'd let the fluid out to the whell cylinders but not back again, so the brakes were just sticking on.

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Sounds like a fuel supply problem, after you've used up what's in the carby bowls.

Could be a bit of crud in the tank intermittently covering the pipe in the tank, but some of the experts here have also mentioned internal breakdown of the rubber hose that is in various parts of the fuel line, that can restrict flow in demand situations.

Edited by littlejim

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