Engine running rough

[Tea]

Hi all,

My 1971 Morris Traveller has recently developed a rough running issue — it's spluttery, lumpy, and juddering, especially under acceleration.

So far, I've replaced the fuel pump (the old one had worn points and was not delivering enough fuel), fitted a new braided metal pump-to-carb pipe, and installed new spark plugs. It ran great for 3–4 drives (around 100–150 miles total) and for the m.o.t, but yesterday it started running rough when cold — though it smoothed out once warm. Today I’ve put in fresh petrol and although it seems somewhat smoother, is definitely still idling a little rough and lumpy with accelerating - downhill is much better.

What I’ve done so far:

Checked the fuel pump is working
Confirmed there’s spark at the plugs
Emptied float chamber and blown through the jets to clear potential blockages
Reset the points in the distributor and checked distributor cap which looks fine

What should be the logical next part to check? I’m assuming fuel or ignition related.

Thanks in advance!

[dudload]

check the dashpot to make sure there's oil in there - lumpy under accelleration can be caused by the carb dashpot being dry

[Tea]

I had filled the dashpot, but your comment got me thinking whether I’d used the correct oil as I have one can with a generic oil and one with engine oil.

I believe I’ve topped it up with the generic oil by accident. I’ve taken out what I can with a pipette and refilled with engine oil and it definitely has a smoother idle.

I take it I’ll need to dismantle the dashpot, properly clean and renew with fresh engine oil?

[Jim McCrae]

I would start by eliminating potential ignition problems:

• Replace the condensor in the distributor
  Check the braided earth wire beteen the distributor body and the points mounting plate
  Check the plug leads
  Check coil connections
  Do you have the correct coil fitted?
  Is the coil in good condition?

I had a similar problem which was caused by a coil designed for a ballast resistor ignition system that had been fitted to my Morris by a PO. The coil started to fail after prolonged use at with a 12v ignition system.

Remember most carburettor issues are electrical!
Good luck

[svenedin]

I would check the spark plugs. If the fuel mixture is too rich the plugs will get sooty. Perhaps this is why you had some good drives for a while after replacing the plugs. On the other hand, if the fuel mixture is too lean the engine can run hot and damage the plugs.

Stephen

[simmitc]

Check the compression. Using a gauge would be good, but you can do a basic check without: With the ignition OFF, handbrake ON, gear in NEUTRAL, use the starting handle to turn the engine over. You should feel four equal points of high resistance. More advanced test:@ remove all spark plugs and press thumb firmly over each hole in turn. Again, turn over using the handle and confirm that you feel the pressure building equally on all four cylinders.

Once you are happy with compression, then move on to other tests.

[myoldjalopy]

Tea - to answer your question about the dashpot oil, mark a line across the suction chamber and carb body so the suction chamber goes back the same way, unscrew and remove the damper, unscrew and remove the suction chamber, remove the long spring, then lift out the piston carefully so you can tip out the remaining oil. At this point, you might as well clean the piston and suction chamber with some carb cleaner and a cloth. Don't use anything abrasive. Be careful not to bend or disturb the needle. Then put it all back together, replacing the oil before screwing back the damper.
Of course, I don't know what this 'generic oil' you mention is, its thickness, nor whether it has actually caused a problem....

[Tea]

Thanks for all the suggestions.

Spark plugs are a biscuit colour and dry.
Compression seems fine

I’ll start with cleaning the dashpot and putting engine oil in before altering parts that had been working prior to my tinkering. The “generic oil” is a multipurpose oil (cannot say more than that as the can doesn’t specify further) that is a noticeably thicker than engine oil.

[svenedin]

Ok it sounds promising. I don't suppose you might have put the HT leads back on in the wrong order? I don't wish to offend by suggesting something so basic but it is easily done. You mentioning it runs better downhill makes me think of the float fuel level. It is worth checking but do have a new gasket to hand before you do as they often leak after being disturbed. Things to look out for is dirt in the float needle valve, incorrect fuel level setting, and a pinhole in the float causing it to partially fill with fuel. Another thing you might check is the manifold isn't loose.

Lastly. It's a 1971 car. Does this have a Smiths PCV? These are classic split in the diaphragm symptoms.

Stephen

[oliver90owner]

I don't suppose you might have put the HT leads back on in the wrong order? I don't wish to offend by suggesting something so basic but it is easily done.

You really think it will run on two cylinders ‘normally’ when warmed up? I doubt if it would start easily on two cylinders.

Another thing you might check is the manifold isn't loose.

Plugs are reported as ‘biscuit’ colour. Both sides loose - I doubt it would even start. One side loose - two plugs correct colour, other two not.

[Tea]

Dashpot dismantled, cleaned, reassembled and fresh oil put in. Sadly no luck with improving how the engine is running.

Will put in a new condenser next.

Worth changing points and rotor arm if condenser does not make a difference?

[svenedin]

It's worth taking the rotor off and having a good look at it but if it looks OK and there is no sign of arcing or burning I can't see the point in replacing it. With the rotor off you can put a few drops of oil on the spindle lubricating pad. As for the points it depends on their condition. Definitely check the points gap is correct and if the points are pitted or damaged in any way, replace them. Remember to clean the contacts of new points with petrol, contact cleaner or similar as they usually have an anti-corrosion coating that must be removed. Whilst in that area examine the distributor cap for cracks and check the central carbon contact is not worn out. Check also that all of the HT leads are making a good connection.

Stephen

[myoldjalopy]

Worth checking the rotor is not shorting to earth. A faulty one is not always apparent just from looking at it. Remove dizzy cap and hold the king lead from the coil about half an inch from the top of the rotor arm and crank the engine. If a spark jumps to the rotor arm then it is shorting out and needs to be replaced.
Worth replacing the condensor if the rotor arm proves to be OK and you have undertaken the other checks suggested earlier in this thread. Faulty/failing ones can cause the sort of symptoms you have been experiencing.

[Tea]

Compression is between 165 and 175 on all four cylinders.

New condenser, rotor arm and points fitted and no change in the running.

I’ll order new plug leads as I’m not happy with the fit on a couple of them. I’ll also get a new air filter and distributor cap too.

[svenedin]

Is it only rough running when cold? Is it running normally once warmed up?

Stephen

[Tea]

Seems to improve once warmed up. However the route I’ve taken on the two trips has been circular with uphill on the way out and downhill on the way back.
Still lumpy on idle at the end, but not as lumpy…

[svenedin]

Hmm. Your first post says it is especially bad on acceleration. Have you checked the vacuum hose from the carb to the distributor? Early ones are metal pipes and later ones are plastic with rubber connectors that perish. Also the vacuum unit on the distributor has a rubber diaphragm in it. That perishes eventually. If it was my car I would first satisfy myself that the spark was good to all cylinders. You can buy a set of 4 spark test things that go on the spark plugs and then just watch as you let the engine idle and then speed it up. Then I would check the fuel mixture (but I note you say the plugs are a nice biscuit colour). Then I would check the ignition timing (but this should never really change once set unless there is a problem with either the centrifugal weights in the distributor or the vacuum advance. Do you have or can you borrow a strobe? If you do you can check the that both the centrifugal and vacuum advance are working. It's really difficult to diagnose these things remotely!

Stephen

[Tea]

Success!

Replaced the distributor cap and new leads. Also checked vacuum hose, which although was in fine condition, wasn’t in the rubber connector as far as it could be pushed. Likely from pulling the plug leads in and out so many times.

I also changed the air filter.

The car is now back to running perfectly. Would almost go as far as to say that it’s running smoother than ever before.

Thank you again for the help!

[svenedin]

Great to hear. Maybe you had a hairline crack. Not easy to see on black plastic.

Stephen

[myoldjalopy]

Happy motoring!