Help! Suspected carburettor problem.

[MJacobson]

Morning all,

I am a club member and have, for several months now, been using this forum as an invaluable resource but this is my first post.

I have a 1968 2-door with, to the best of my knowledge, a mostly standard set-up (1098cc engine, four speed transmission, HS2 carb) though it does have one or two modifications, such as an Accu-Spark coil and distributor.

Yesterday evening, I finally got around to taking out my spark plugs for inspection; all four were caked in dry, powdery, pitch-black, soot. I have a heap of spare plugs that were given to me by the car's previous owner so decided to put these in, at least until I clean the used set. Both the used and new plugs are NGK BPR6ES. Using a feeler gauge I gapped all the new plugs to 0.64mm and fitted them, taking the distributor leads out one by one so as to not confuse them.

I then fired up the car and it started very well, better than it had been prior to the change. Once the engine was up to running temperature I did a little fine tuning of the idle mixture/speed as the car sounded like it was hunting slightly. The outcome of all this was that the car sounded much healthier.

After a little reading overnight I decided that the apparently carbon fouled plugs indicated a rich running mixture and so, this morning, I took off my air filter, the lid of my float chamber, and dismantled the suction chamber.

The float chamber lid seemed fine and, as far as I could see, was adjusted correctly and wasn't overfilling. I replaced the lid as I had found it.

I cleaned the needle (which looked ever so very slightly bent), the piston and the suction chamber with a petrol soaked rag, replaced them exactly as I had found them (I think), refilled the dash pot with SU carburettor oil and screwed the plunger back on.

The air filter I did nothing with and replaced it as I had found it.

After all this I nervously started the engine and found that it needed the choke out to stay alive, even when the engine warmed up. Without the choke the engine struggled and the oil pressure warning light flickered rhythmically with the engine, until the engine died. With the choke out the engine stayed alive but sounded awful, sputtering and vibrating fiercely and reacting spongily and inconsistently to the accelerator being pressed.

I am planning on ordering a carburettor service/repair kit from ESM (I know there are mixed feelings about them on this forum but I've only ever found them professional and helpful). In the meantime, does anyone have any suggestions about how to get back on the road?

All the best,

Mike

[bmcecosse]

Don't start overhauling the carb - you are only going to get deeper into the mire....... Check that the piston is sliding up and down easily - if not - try rotating the bell 180 degrees. Obviously the needle should not be 'bent'..... Did you remove it from the piston and refit it? I note you say 'mixture adjusting screw' - but the mixture is not set with a screw - it is the hollow nut below the jet assembly that sets mixture.. And -check that the 'choke' is going off completely when you push the knob in.

[The vast minority]

Is the air filter clean?

Run it without and see if it still runs sooty

[MJacobson]

Oops, my mistake, I have been adjusting the mixture with the nut beneath the jet and the idling speed with a screw above, I believe this is correct?

I have tried taking the bell off and turning it 180 degrees but this doesn't seem to have changed anything unfortunately.

As far as I can tell, the piston slides up and down without any problems. Various technical manuals and the like for the HS2 talk about lifting the piston, allowing to drop and listening for a metallic click. I cannot hear a click when I drop the piston, could this indicate a poorly centralised jet?

After trying to adjust the idling mixture/speed again, and after what seemed like an improvement, the engine now refuses to switch on.

I am at a loss. Any other ideas?

The help is enormously appreciated!

Mike

[mogbob]

Mike
You should be hearing the clunk / click of the piston hitting the bridge as it falls.
Try removing the needle from the piston, you'll need a thin flat screwdriver to remove the tiny grub screw. Don't loose it !
To check your theory that it is " ever so slightly bent " roll the needle on a perfectly flat surface e.g sheet of glass , kitchen
work surface. A straight needle will roll in a straight line. If it doesn't even roll or wobbles you have got a bent one. It will need replacing. The size is in very , very small punched letters/ numbers on the end.A standard needle on a 1098 cc is an " AN ",rich is "H6 and weak " EB ".

Try the piston back in the carb without the needle....does it clunk now ? If yes, then replace the old needle if was OK or the new needle making sure the "shoulder " is level with the flat surface of the piston .Try again. I am assuming that the metalwork , after your clean up, removed all the old deposits of petrol and that there were no rough surfaces that would impede the piston's fall ?
Once the correct fall is obtained and you can hear the clunk then you can resort to adjusting the carb. Refer to your books
and once warmed up blip the accelerator every now and again ( 1/2 mins ) to see what effect your adjustment has made.
Note down on paper what effect , adjusting the jet up or down makes e.g. two flats of the main nut clockwise , makes.

If the air filter is black and clogged up , then replace. You should be able to see some of the paper element colour not just black.
If you add your location to your profile ( nearest town , not your full address ) a local member might take pity on you and
give it a tweak for you. You never know , worth a try.
Good luck.
Bob

[bmcecosse]

Yes the nut is correct for mixture - I just wondered when you wrote screw. The piston must clunk down nicely - take the damper out when doing this test. Engine 'won't switch on' - so do you now have an electrical problem too? Maybe the battery is flat? And is the pump definitely delivering fuel? Test it by pumping a pint into a jar.

[MJacobson]

First of all, many thanks for the quick replies and all the helpful advice.

I ordered a new needle as the original was, possibly, bent and I didn't want to chance it.

When the new needle arrived I put it into the piston and realised my mistake - when I had replaced the original after cleaning I hadn't secured it's shoulders flush with the piston, it was all the way into the needle recess. I suspect this is what caused the problem I was having after cleaning the carb - giving a vastly over-rich mixture?

I installed the new needle correctly but when I tried to centralise the jet assembly I found that the jet bearing was completely corroded together, I suspect that I've been moving the entire bearing, lock nut and all, each time I attempted to make adjustments for some time now.

So I ordered a bearing kit from Burlen, and decided that it would be foolish not to also replace the jet assembly as I have no clue how old the original was. I also have been given to understand that a worn jet assembly could account for the carbon fouled plugs so it seemed a good idea, all round, to renew.

The new jet assembly and bearing arrived the following day and I excitedly got to work replacing old for new but quickly discovered that I couldn't unscrew the old union that connected the nylon tube (from the jet) to the bottom of the float bowl. I took the float bowl off the carb and cleaned it thoroughly before boiling it, soaking it in penetrating oil, boiling it again, and eventually just hitting it, all the while trying to unscrew the old union - no luck! All I succeeded in doing was completely rounding the hexagon on the union.

So I gave up on the old float bowl, it was also much filthier inside than I had ever realised. I spoke to the guys at Burlen and they explained that while the part number was the same, they float bowl shape had been changed over the years and I would need a different one to replace the old one. I ordered the advised float bowl, along with a rubber adaptor for securing and a new gasket for the lid.

The new float bowl arrived today and I discovered, much to my frustration, that the old bolt which secured the float bowl to the carb is too big for the new float bowl. So back on the phone to Burlen I went and they sent me out a new bolt, which should arrive tomorrow.

In the meantime I had decided this was probably a good time to get rid of the cigar shaped gizmo in the fuel line which apparently acted as a lead replacement (I've been skeptical since day one and have always used Castrol Valvemaster Plus when fuelling) so I ordered a new metal braid fuel hose. In my eagerness to be proactive I removed the old pump-to-carb fuel pipe, along with the 'lead replacement' gizmo beforehand and thought nothing of it, intending to instal the new pipe when I could finally attach the new float bowl. A few hours later I went to the car to grab a book I had left inside and was met with an overpowering smell of petrol. I opened the bonnet to investigate and discovered that petrol was slowly dripping up and out of the fuel pump and had wrecked some of the cheap paint under the bonnet. I'm not too fussed about the paint but am now terrified that if I start the car the whole engine compartment will ignite!

I won't be able to start the car until tomorrow at the earliest anyway and I'm hoping that the petrol will have evaporated by then, any advice regarding this? In the meantime I've attached the new pipe to the fuel pump and propped the other end facing upright, with a tapered wad of tin foil plugging the end.

Once again, any advice, or input would be much appreciated.

[MJacobson]

Oh, and bmcecosse...

Don't start overhauling the carb - you are only going to get deeper into the mire.

... feel free to say "I told you so!"

[bmcecosse]

A sad tale of woe - but I doubt you needed to 'centre the jet' - and all along the stupid/useless 'lead replacement' was possibly the cause of all the trouble... Of course not setting the needle correctly was also a big mistake - yes - extremely rich mixture. Can't see why petrol should have dripped - the pump is much higher than the tank so should not have been able to siphon. Oh and no point wasting money on 'lead additive' either - one of the biggest con-tricks ever...

[mogbob]

Mike
Experience is a great teacher. If you find an experienced mechanic , who claims never to have made a mistake.. don't believe
him or her.
You don't say if the car was garaged or not. Check the actual leak has stopped and that there is not a smell of fresh petrol still.
If outside , not a problem , the fumes will have dissipated. In a well ventilated garage you should be OK.
Either throw open the garage door and side door / windows ( ? ) to get fresh air circulating or belt and braces , slip the hand brake and roll it out into the fresh air before working on it.
When you're ready to fire up just turn the ignition on for a few seconds to allow the fuel pump to activate and then switch off.
Look for any leaks and wipe joints with dry kitchen paper. If no sign of leaks , fire her up.
You've learnt a few new tricks over the last few days. Slow and methodical usually wins the day.

It's never problems just obstacles to overcome. There are loads of guys and gals on the Forum , who have learnt the hard way , the best way of doing things and are happy to share their knowledge. I'm still learning things so thanks from me folks.
Bob

[The Issigonis Kid]

So what happen, was it the carb needle that was bent, was it a dirty float chamber or was it the stupid unleaded additive in the pipe. Was the poor running problem fixed or did the car just burst into flames when he tried to start it, explaining why the fix wasn't posted !!

[bmcecosse]

I agree Richard -these 'endless' threads are very annoying. Surely only polite to come back and leave news of what the problem was - or still is !

[The Issigonis Kid]

When I fix my car, I'll update this thread as I have abit more information.

[The Issigonis Kid]

One of the concerns this owner had was the clamp around the exhaust had cracked blowing hot fumes onto the carb area. After a successful run to the nationals and back, I can confirm my issue was down to a very light layer of dust around the inside of the distributor cap and I also lightly rubbed the contacts with some fine sand paper. My petrol pipe was also hanging under the carb so moved it above (although I don't think this was the problem). So if your cars stuttering under higher revs, wipe the dust our your distributor cap.