Engine Problems

[Manxman]

Hello,

My partner and I have a 1947 P2 16hp, although it is fitted with a 1938 engine and SU carb.

Recently the performance has gone down and now when you press the accelerator there's no power at all, but yet it ticks over at idle okay.

I have the workshop manual and have read a few bits on here, including the service bulletin so have checked the following so far;

1. Ignition timing - which looked fine and I can't see why this or the valve timing would have changed recently
2. Distributer - I've reset the point gap and all looks okay in there
3. Ignition Coil - looks okay on a multimeter although I don't have a spark tester yet
4. Spark plugs and leads - I cleaned the spark plugs up and again tested them with a multimeter, no shorts and look okay. The only strange thing, I think anyway, was that 4 of the 4 were all sooted up, the other two being clean.
5. Tappets - I managed to get the car to run long enough on idle to warm everything up so these are set right
6. Electric Fuel Pump - I took the pipe off the float pull and there's plenty of fuel coming through, admittedly I haven't checked the pressure yet
7. Compression - Wasn't exactly high but all the cylinders were the same at 100 psi

All of the above is leading me to think it's the carb, the fuel pump changes note when it's at pressure and no longer does this so I', thinking over fueling/flooding. I've already looked at the float bowl and the valve in there works fine, but it looks like it's been leaking from the connecting to the body and only had a washer on one side. The butterfly spindle is also loose and when I looked at the needle it had R6 stamped in the bottom. According to the manual that is for a 14, not a 16. Presumably that would affect performance as well, but obviously not this much?

Thank you for taking the time to read this and any advice you can give.

Best wishes,
Mark

[TonyG]

Hi Mark,

A couple of questions spring to mind from what you have said; firstly, was the car running ok until recently and secondly, was any work undertaken just prior to the problem starting?

My assumption is yes to the first and no to the second. On that basis it does sound like a problem with the carb. SUs are simple and effective devices. The float chamber works like a small water tank, allowing in petrol via a float valve and shutting off when up to the allotted depth. Providing there is fuel in there the carb should work. Don’t get too hung up on float levels at this stage. As the butterfly is opened by the accelerator pedal, more air is allowed through and the suction causes the piston and needle to move, allowing more fuel through the jet, which the needle sits in. The engine revs should increase. So the first check is to see whether the piston is moving when you open the butterfly. If not, is it stuck, perhaps due to lack of oil? Check it moves easily with a screwdriver down the opening. It should move easily and return back again. Alternatively, you could have a blockage between the float chamber and carb body. East enough to remove the piston cover and withdraw the piston. Take care not to bend the needle. Once removed you can try squirting carb cleaner into the jet where the needle goes. With the float chamber cover off and float removed you should get the cleaning fluid back into the chamber. Obviously clean everything out. Take care not to get carb cleaner on any paintwork as it will damage it. Unleaded fuel with ethanol can attack some rubber pipes and seals etc, which could result in bits in the carb. However, you should have a filter in the fuel pump and at the input to the float chamber and these are worth checking.
If this helps but not totally successful it may be that the carb needs a full rebuild. A kit of seals, jet etc can be bought to do this.

Hope that helps a bit.

Tony.

[Manxman]

Hi Tony,

Thank you very much for the response and the answers are yes and no.

Before I took the carb off the car I tried the piston, which was stiff but works wonderfully now I've oiled it! Whilst the carb was off I took the opportunity to blow through the hole and there's no blockage and the float valve works fine.

I decided tonight to look at the low voltage side of the distributer, something I missed/overlooked before. Even when there's a gap in the distributer I had a connection between the distributer and ignition coil.

After some checking I traced this back to the ignition wire that has a connection to ground, presumably it has rubbed through somewhere and this will be giving a very weak spark?

I've put the distributer and carb back together for now as I intend to replace the ignition wire and try again, do you know the best way to get access behind the dash? Is it from underneath?

It looks like my two winter jobs are rebuilding the carb and re-wiring the car.

All the best,
Mark

[GOY189]

There are 2 screwed panels on top of the bulkhead. Removing those should give you access behind the dash from the top.

I wonder is there are several small problems ganging up so to speak!
- When were the plugs last changed? NGK B5ES or Champion N8 are the ones to look for.
- If the carb spindle is loose, it will be admitting air, weakening the mixture.
- Does the coil get hot when the car is running? If so that would indicate a failed or failing condenser.
- Is the rotor arm new? Some modern rotor arms are prone to failure, although its usually a sudden mysterious "failure to proceed" rather than a gradual one

If you set up a spare condenser with its body attached to a large crocodile clip with a length of wire and its lead attached to a small croc clip again with a length of wire, you can connect the large clip to a good earth and the small clip to the contact on the distributor or even at the coil end. If the car then runs as it should, the condenser in the distributor is the culprit.

Hope that helps

Mike

[TonyG]

Mark,

Mike is absolutely right. It is frequently the case that the most puzzling of faults turn out to be a combination of things. Checking through the basics is an excellent idea before getting too involved in pulling the wiring apart. On that point, if you suspect a fault in the low tension circuit, I’d suggest removing the existing wires and, effectively, hot wiring the ignition. All you need is a battery feed to the sw or - ve side of the coil (assuming pos earth) and another from the CB or+ve side to the distributor. Make sure all the wires you remove are insulated as you will need to turn the ignition on to operate the fuel pump and starter button. Pulling old wires about behind the dashboard could create more faults than you remove and this avoids touching that unnecessarily.

A couple of other thoughts; is the engine earth strap in good shape? Also, you mentioned that the carb needle was for a 14 and that the engine had been swapped for an earlier one. Are you sure it isn’t a 14 engine? Just a thought. Engine numbers are detailed in workshop manual I believe so easy enough to check.

Tony.

[Manxman]

Thanks for your responses Mike and Tony.

I suspect it is a number of things but will try a new feed to the ignition coil and go from there.

That's an interesting idea about the engine Tony, I'll have to check as I thought maybe the carb had been changed and not the whole engine.

Thanks again,
Mark

[Phil - Nottingham]

Are you sure the points gap is set correctly - its not the usual 15 thou, its 12 thou, If it is too wide the spark will be too weak when revs try to build up. I made this mistake and reducing the gap cured the non-reving problem instantly. It also affects the dwell so check the timing is correct when the points have been set

You really must try hot wiring the coil and if no joy try a substitute - almost any standard 12v will do

[Manxman]

Hi Phil,

I've tried running a separate feed to the coil form the better and it ran much better. I currently have all of the wire off the regulator and am checking for any earth faults. Once I've done that and fixed anything wrong I'll see how the car runs, probably swapping the plugs for new ones as well.

Unless I was a little cack handed when I set it the point gap should be 12 thou although I will double check.

Unfortunately with the relaxing of the lock down rules over here the roofers want to start next week so the car will have to wait for now!

Thanks for your help,
Mark

[Manxman]

Hello All,

I know it has been some months since I posted but I've started working on the car again, well technically last year but only just!

The car is back together and I'm just waiting on some new plugs before I try it; NGK B5ES's.

Whilst I had the sides off I looked at the engine number. The number 951822 which was a 1939 16HP Saloon according to the book.

So the car is a 1947 16HP Saloon, with a 1939 engine and carb from a 1938 14HP judging by the needle.

It ran before so although it has the wrong needle that isn't the main problem, but will need changing when rebuilt.

All the best,
Mark

[Phil - Nottingham]

A bit of a mongrel then! Is it the later 14 engine ie narrower bore 16 with the manifolds on the O/s?