Revs limited

[dra890]

I wonder if anyone can help me.

I have a series 3 2.25 petrol with an SU hif44 carburettor that was left undriven for a year. Upon starting to drive it again I found that the revs seem to be limited. At first I couldn't get above about 30mph in third gear and low forties in fourth - about 2500rpm on my landrover (32 inch tyres).

After seeing fuel coming out of the overflow I thought 'Aha, sticking float' so I emptied the carburettor's float bowl and sprayed carb cleaner in through the fuel inlet pipe until it came out of the overflow, then again with my finger blocking the over flow so it came out of the jet. I then ran the engine and found it much better.

The engine will now run to around 40mph in third , but this is still only around 3500rpm. There should be around another thousand rpm available. It pulls strongly up to 40mph but then refuses to pull any higher, almost like it has a rev limiter. What could this be?

It is not the ignition. I've tried individually changing the coil and distributor for correctly set known good ones, and different spark plugs have been tried. Pulling the king lead/individual plug leads I can get strong sparks to the block.

I've since stripped and cleaned the top of the carburettor. I removed the dash pot and cleaned inside with a soft cloth and petrol, the same for the piston, and carefully wiped and inspected the needle without damaging it. None of these were dirty or in bad condition. I also sprayed carb cleaner down the jet with a straw attachment, and spraying into the float bowl through the fuel inlet with the overflow blocked it came out of the jet strong enough to miss the engine and wing and nearly hit the next car over. I then correctly reassembled the carburettor and refilled the damper, but this has made no difference. The piston opens fully when revved.

I've also tried looking for vaccuum leaks but found none. All the hoses are attached correctly and the engine has good vaccuum - over 22 inches at idle.

It never used to do this. Does anyone have any ideas?

[tacr2man]

is the advance working correctly ?

[dra890]

Yes, I've checked the advance works correctly, both vacuum and centrifugal. Plus, as I say I tried changing the whole distributor for a known good one, with no change for better or worse.

Dan

[JBorges]

There Is a electronic ignition inside the distributor?

[tugboat]

Sticky valve?

Stale petrol?

[timppl]

Check there is fresh oil of the correct type in the dashpot on your SU. If the oil is not right it can limit the revs available.

HTH

[tugboat]

Any joy yet, DRA890?

Let's suppose the carb overflowing and the "separate" running problem are connected somehow. Otherwise, to have totally unrelated issues at the same time would be quite literally a coincidence and the probability of that is a bit less.

That would point me towards looking for crud coming through from the tank. That is possibly what caused your needle valve to stick. It could also have partially blocked the small flex pipe between the bottom of the float chamber and the jet, and the jet itself. You've blasted these through so in the first instance, you could maybe assume the source of the problem is elsewhere.

Crud could also have blocked the strainer and/or either of the valves in the fuel pump. Is it the type with a sediment bowl? If so, how does it look? Is there sediment or water in it?

The way the engine is running has all the hallmarks of fuel starvation (but possibly other things besides). You've tried some obvious quick fix solutions including ignition (I'd have done much the same) but I think you may now have to tackle it methodically. [Only a couple of other thing on the quick check front first - how is the compression? If you don't have a compression gauge, either turn it over by hand and feel each cylinder, or spin it on the starter with the coil disconnected. Do the cylinder read/feel/sound reasonably even; if so, we can probably assume there's no stuck valve. And are you absolutely certain the plug leads, plug caps, distributor cap, rotor arm and points are all ok? Old points build up a non-conductive crust if left unused for a long spell. If in doubt with any of these, chuck.]

Back to methodical. Given that there was, FOR SURE, a fuel problem I'd now be ensuring that the whole fuel system is running clear from tank to jet. The problem may be the tank itself. If you don't feel like draining it first, then do the checks on the pump; clean the pump strainer and bowl (best to have a new washer handy for the bowl first), flush through with the hand primer and then pump some fuel into a jar and have a good look. If it's carrying noticeable sediment, or if the bowl quickly shows more sediment coming through, you need to go to the tank. It may have a lot of internal rust. If there has been a lot of previous contamination and you suspect the fuel pump valves or diaphragm are damaged or dirty, you could have a go at rebuilding but I've heard bad reports about some repair kits; I'd try to source a new Delphi replacement pump (should be under £20 if you can find a supplier - ssldieselparts.co.uk are excellent for Delphi diesel pumps and might be worth contacting) but failing that fit a £15 ebay copy.

Once you are sure you have a good supply of clean fresh petrol, you might still have to go back to the carb and strip and clean it.

On the plus side, at the end of all of this, the engine should be sweet!

[dra890]

Update.

Okay, so after ruling out ignition (no really it is definitely NOT the ignition - different coils, points, plugs and distributors have had no effect and I've checked the ignition system out several times) I decided to look more closely at fuelling.

Incidentally, I checked compression shortly before leaving it for a year and the readings were, from cylinders 1-4, 147, 144, 144, 151, and that was dry with the spark plugs still in the non-tested cylinders, so with less than a 5% spread and decent figures I don't think there'll be anything wrong there.

I also thought of a sticky valve, but unless it's only sticking at higher revs it would've shown up on the vacuum guage. So I'll not persue this just yet.

I'd already checked out the glass bowl on the fuel pump and there was no water or sediment. Fuel pressure and volume at idle seemed fine, but admittedly this doesn't tell me if it can keep up when demand is high. I decided that since blasting carb cleaner through the carb had helped maybe I just hadn't gotten all of the dirt, so I removed the carb and opened up the bottom half (HIF44). It looked clean inside but since I was already in there I gave it a good spray around with carb cleaner, and sprayed up the jet from that end for good measure. I then re-fit the carb and gave it a run (mostly to make sure I hadn't stuffed anything up).

The landrover pulled up to 47-48mph in third - just over 4000rpm in my landrover, before showing the same symptoms, so it is an improvement but it's not quite there yet. This was last night.

My next port of call is my inline filter. While it seems clean it isn't impossible that it might swell or partially collapse under high flow conditions, and it's an easy, free test to run with a spare, or without for a day or so. I also intend to check the filter gauze in the fuel pump itself just above the glass bowl. A small issue in each area could combine to make a bigger problem.

Wish me luck.

Dan

[tugboat]

Pointing more and more towards fuel. Everything else sounds good.

If the volume at the float chamber pipe is fine at idle, or with hand priming, that would take me back to the carb again and the original fault - the float valve. Have you taken it out and had a look? Back in my BMC SU days, I would change valves and seats every two or three years. The Viton tipped valves were more forgiving than the older metal ones which used to wear a shoulder into the taper and then without warning jam fully open (been there, completely stuck - hence my 2-3 year rule) but they DO still wear and tend to seep or stick rather than let you down completely. I see they're about £11 from sucarb.co.uk for the HIF44.

Best to clean the pump gauze and replace the filter as you say - they should really be annual service items anyway, especially if your tank's not so new.

[Briarston]

Just a thought. Is the needle in the carb. piston set correctly?

I think it's shoulder should be flush with the base of the piston,

but its a long time since I worked on an SU. so time may have affected memory!

[tacr2man]

It will also have a compensator for temp on the jet adjuster , (which is the enrichment adjustment ) , which afeter needle position will affect power .