Help please with virtually non running C

[Havana Henry]

So, I'll try to remember the correct order all this happened in, and all the many things I've tried, hopefully won't leave any vital bits out.

Bottom line is the car will start, idle but won't properly rev, or drive. Any load at all, it coughs and gives up, then takes a while before it will start again.

I've tried lots already, but am now stuck. Recent history is it started running rough under load, and acceleration. Did a few miles to friends houses over the course of a couple of days to chat and check the obvious things, and coming home after the last one it got to where it is now, and basically stopped running, and was pushed into the garage

So, proper diagnosis began. Trying things one part at a time. First issue, found cracked connections on HT leads at dizzy, so new leads and plugs installed. Nope.

Then onto points, new ones fitted and gapped, new condenser, coil swapped for known decent other one. Spark at all times looked good at plugs but went through this stuff anyway. Static timing reset. Tried checking advanced timing with a strobe, and when it did rev up and hold steady for a few seconds it looked OK.

Fuel arriving at pump when tank pipe pulled off, plenty coming out of the pump when turning over, and looks to be arriving nicely at carbs. So next was to take apart carbs, all bits out and blown through. No crap or broken stuff found apart from a dodgy accelerator pump, this was changed and carbs reassembled, but no change.

As it starts and runs for a bit then dies, it seems like there's not enough fuel getting through, like it's using what's in the float chambers, then running out. So although the pump output looks fine, the last thing I've done was to take apart the fuel pump to see if the diaphragm was split etc, but it looks fine. Annoyingly it now leaks from the top cap as that gasket fell to bits, so new one needed there, but I digress.

Bit of background : car was a barn find acquired 6-7 years ago, myself and friend (@pauldvern) rebuilt the engine, didn't split the case, but thoroughly rebuilt upward from there with new pistons and anything else that was needed. Stock apart from 1720 and Dansk sports exhaust. Has run like an absolute champ ever since over many thousands of miles, I've never hesitated to hop in and drive it all over the UK and Europe, and it's never let me down until now!

Looking for suggestions as to what to try next if anyone has any thoughts please.

Cheers, James.

[Nine One One]

Personally would try running a low pressure in line electric fuel pump to see if that solves the problem.

Have you checked to see if the needle valves that act on the float are free to move in their guides to allow fuel through, once the float chamber starts to get low of fuel.

Also when fitting new points, clean both surface contact points, as often they have a coating on them - run a piece of card or something between them.

Have you fully checked the fuel line from the tank. If it was stood for some time, you could have some crud trapped in the line from the tank itself, Its basically gravity fed to the pump so any restriction is going to effect the fuel feed.

Hope that helps as a starting point?

[Havana Henry]

Needle valves at the top? they seemed OK.

I'll clean those points surfaces.

Tank, yes have run compressed air through the line, all fine. Tank not the original, was brand new 6 years ago.

Electric pump was something I was thinking about anyway as those carbs certainly do need a bit of turning over to fill up when you're not using them daily. But as a fitting too to see if it's fuel pressure related anyway is not a bad idea I guess.

Thanks for those.

[Kneeslider]

Hi there James.

I think that I would give the fuel tank breather a looking at. It could be that initially fuel gets through, but after that the headspace above the tank is airlocked. The simple way to check is to run it with the fuel cap off and see what happens.

When the engine does die, can you quickly try a voltmeter on the + side of the coil just to make sure that the electrical supply side is OK?

Mechanics at a distance are always tricky!

[mycar]

Hello, sounds like it could be a fuel thing, have you gone through all the filters ? What carbs do you have ?

http://sparkingplugs.com/resources/Bruc ... l+43-1.pdf

[roy mawbey]

James,

All good replies actually. With the ignition fully checked and the carbs also, it would seem the problem is fuel orientated. Yes the vent on the tank should be clear, the fuel pump delivering the volume required and the carbs needle valves operational.

!). Are you positive the idle jets are all clear even one clogged up can make it rough. I once had an insect block one of mine and that jet hole is so small in diameter you need a good light to see its clear even after using a compressed air blow through.

2).Have you taken off the air cleaners then looked over the top of the venturi's and then depressed down the two levers to see if the accelerator pumps are in fact squirting fuel into the venturi's? This should be clear to see happening and is it happening on both carbs?
3). I once had the petcock handle turned just past the 'on' towards the 'reserve' position so not in the perfect position. The car sputtered and I slowed to stop pushing on the accelerator to try to keep it going. Lucky I moved the petcock handle to a positive 'on' and the engine came back to life. Daft but you never know! Likewise presume the petcock itself and its filter is fine? You might try putting it into the reserve position and trying that. When I rebuilt my petcock the cork gasket then 40 years old or more then was like wood to remove. It all broke up in little pieces.

4). Be careful with the fuel pump top cover. The 10mm bolt if tightened too much distorts the aluminium top cover. I had to modify mine. And after fitting a new rubber gasket be careful to be aware after a short time you will need to retension the top nut.

Finally, a stupid maybe question but the battery connection including the earth ones are all tight and perfect?

As someone said above difficult to advise from a distance? Hey on other point you replaced the plugs and leads but is the dizzy cap's carbon brush perfect ? Worn out it could lose contact with the rotor. Is the rotor arm brass contact clean and not pitted?

Roy

[slipslide]

Hi
I had a similar sounding problem on my 912. I struggled to get my head around it as I was getting fuel but we changed the fuel pump and problem solved. I would definitely try an electric pump.
Good luck

[Havana Henry]

Loads to try - thanks everyone! Heading into the garage now.

I have a loaner electric pump now too.

[simon james]

Sounds to me like an obstructed jet.
We had this on a vintage car a couple of years ago. Turns out there was a tiny piece of rubber in a jet.
Or to quote Dougal Cawley “Pubes in the carb”

[mycar]

The handbook recommends you clear the idle jets with a horse hair.

Which part the horse the hair be plucked.... there be no indication.

[Havana Henry]

Well it's not fuel delivery, tried the electric pump, plenty of flow!

One last try at ignition before I take the carbs apart again, and search for a horse to pull some hair off - going to borrow a dizzy from a mate to eliminate in one hit any niggles (points, arm, cap, advance) that may be lurking there.

Thanks for all the help.

[BD55]

I take it you put some fresh fuel in? Did you check fuel was squirting down the carbs when using the throttle? One thing I had once, the points were not insulated from the dist body....You can get jet cleaners if you can't find a horse

[Havana Henry]

Forgot to mention, yes, all four accelerator jets were squirting nicely on last run up. Car was run fairly regularly during the summer, so fuel not old. Dizzy lend will eliminate any points issue if Paul will lend me his for an evening.

So it's main or idles I guess. When carbs were in bits I could feel compressed air on my fingers on the inside of the idle jet holes when blowing down those so I don't think it's them, but I'll check again, and take out the mains again.

I'll see if any local friends have jet cleaners, if not purchase the proper thing, as don't fancy horse plucking

[roy mawbey]

I can advise something that has worked for me but might raise the eyebrows of some on here!

If you have a wire brush and a pair of side cutters snip off a wire about an inch long. The wire should be somewhat smaller than the inlet jet bore. I measured mine with a micrometer. Insert without pushing in any way the wire in the jet and it should easily pass through. You will not change the size of the bore by doing this, just lightly pass it through, then hold it up to a light to see there is no obstruction.

Done this for years and years. You have to remove the jet from the jet holder of course.
Roy

[Peter Roberts]

Had a similar problem when i restored my SC and i struggled for weeks. I had stripped the carbs and put in a full new overhaul kit. Car would start but not run properly after a short while. Ran all the tests, jet cleaning, pump testing etc which you seem to have done including checking fuel levels in the carbs. All seemed correct. After about the tenth time of taking the tops off the carb and checking that the fuel level was correct in desperation i took out the shut off valves which i had successfully blown through a few times to make sure they were clear. Inside i found two tiny bits of rubber. Not enough to stop you blowing though the valve but sufficient to restrict the flow. When you started the engine the engine would run for a while until the fuel level in the float chamber dropped. By the time i had taken off the top of the carb the residual pressure in the feed line had filled up the float bowl so all looked in order. How it got in past the filters i do not know but it was one real headache.