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Post by kelsham on Dec 30, 2010 16:58:10 GMT
My car is a 1968 Morris, I have owned it since the late 1980s. A few years back I fitted an ex MOD engine.
After driving it for some time I decided to strip the engine and convert it to unleaded head.
While doing this I went slightly mad and removed the engine and box to allow me to replace the pistons with high compression replacements. I also changed the distributor to the correct one for the higher compression engine.
When I stripped the engine I found out that one big end was wearing away the side of the shells. I suspect the engine had a rod refitted by the MOD rebuilders that had suffered a big end failure.
I replaced the rods and pistons, unleaded head, plus a new clutch, and ran the engine for a year or so.
This year I began to suffer from misfiring. All the usual suspects were replaced , coil, condenser, HT leads, rotor arm and cap. still misfiring.
The effect was a slight pulling back on steady throttle. Cleaned the carburretor thoroughly. Still misfiring, I have lost track of all I have tried.
The MOD engine came with a MK3 manifold and carb.
I have decided to fit the MK1 manifold and carb, complete with the air cleaner. I am doing this in an attempt to prove it is the old carb.
I contacted Tony Wood who I have always found very helpful and a new Jet and Needle are on order with new air filter.
I will keep you all up to date as to progress.
Regards Kels.
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Post by Keef on Dec 30, 2010 20:08:12 GMT
I will keep you all up to date as to progress. Thanks Kels. Have you carried out a compression check lately? I'm wondering if you have a weak valve spring? |
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Post by dave1800 on Dec 31, 2010 1:53:40 GMT
Before you change the manifold and introduce other variables, I would suggest you check the compression to ensure you haven't got an exhaust valve problem, and as the effect is most pronounced under steady throttle, check very carefully for an air leak on the inlet side - check the manifold nuts are tight, the vacuum advance /retard diaphragm in the distributor, all pipes and the diaphragm in the closed crankcase ventilation valve - and ensure the filler cap vent isn't blocked. Finally check the ignition timing hasn't slipped. Good luck regards David My car is a 1968 Morris, I have owned it since the late 1980s. A few years back I fitted an ex MOD engine. After driving it for some time I decided to strip the engine and convert it to unleaded head. While doing this I went slightly mad and removed the engine and box to allow me to replace the pistons with high compression replacements. I also changed the distributor to the correct one for the higher compression engine. When I stripped the engine I found out that one big end was wearing away the side of the shells. I suspect the engine had a rod refitted by the MOD rebuilders that had suffered a big end failure. I replaced the rods and pistons, unleaded head, plus a new clutch, and ran the engine for a year or so. This year I began to suffer from misfiring. All the usual suspects were replaced , coil, condenser, HT leads, rotor arm and cap. still misfiring. The effect was a slight pulling back on steady throttle. Cleaned the carburretor thoroughly. Still misfiring, I have lost track of all I have tried. The MOD engine came with a MK3 manifold and carb. I have decided to fit the MK1 manifold and carb, complete with the air cleaner. I am doing this in an attempt to prove it is the old carb. I contacted Tony Wood who I have always found very helpful and a new Jet and Needle are on order with new air filter. I will keep you all up to date as to progress. Regards Kels. |
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Post by dave1800 on Dec 31, 2010 2:44:09 GMT
One further thought, has the car been stored if so maybe the fuel is old and lost some of its volatility?
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Post by kelsham on Dec 31, 2010 14:05:13 GMT
Good suggestions, However the car has had several tankfuls of petrol on a run from Beaulieu Autojumble to Newcastle and then back to Wales.
I carried out a compression check before the journey and all was well, It might be worth a recheck though. The car has presumably been running weak. Performance is good though.
Regards Kels.
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Post by ahctog1 on Dec 31, 2010 18:05:21 GMT
Had a similar problem years ago on a 1300, in that case it was an air leak on the manifold, made worse by a dirty air filter. Just a thought......
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Post by tommydp on Dec 31, 2010 19:17:54 GMT
Here are some further suggestions:
valves adjusted to tight?
low tension leads in ignition circuit: loose connections, bad earthing inside distributor?, tighten screws holding the plate inside distributor. Especially check LT connection on 25 D distributor. On 45 D type (later) especially check if baseplate inside is loose.
Check advance springs inside distributor, broken? (One is supposed to have a loose fit..)
loose connection on ignition switch?
Overcharging/ undercharging generator?
Engine earth strap OK?
Battery earth connection OK?
Check for blue cracking spark at plugs
Fuel pump? Clean filter if you have SU mechanical type.
Clean carburetter, check that piston moves freely, check needle and damper spring.
Correct coil? Car not fitted with a ballast resistor in the ignition circuit?
Weak mixture?
Check spark plugs. Oil on one or more plugs?
Best of luck from Norway! Keep us informed, and I'm sure we will solve this:-) Misfires are the most annoying things..
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Post by dave1800 on Jan 3, 2011 10:51:15 GMT
You've had lots of good ideas here, but I have just remembered an odd one I had once where the flexible wire connected to the contact breaker in the distributor tested OK but when the vacuum advance operated fully it went open circuit for a fraction of a second.
A quick test which would show this and possibly any weird timing issues is to unplug the plastic pipe from the distributor, plug the end that goes to the carb temporarily and see if the symptom is still there. You can do this without getting your hands dirty and it could point you in the right direction.
I know it sounds crazy - but ...
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Post by kelsham on Jan 3, 2011 14:30:13 GMT
Hi, Thanks for the suggestions, I am afraid I was guilty of leaving out much of the remedial work I have tried.
The situation was complicated by reason of changing the pistons and distributor on the MOD engine to increase performance.
I had tried swopping the manifold earlier but used the later carb on it. When I decided to revert to the later manifold I found that I had disposed of the later air cleaner and the Mk1 cleaner did not have enough clearance.
Perhaps a recap of the fault may be of interest. I had not used the car for a few months, seemed ok on a short run.
I called at a friends house and we spent some time discussing how reliable she had been.
One mile down the road she died, investigation showed the rotor arm had failed.
Towed home by friend who had trouble giving the matter the serious concern it deserved.
New rotor arm. She ran but had a tendency to sort of hold back on steady throttle.
New plugs, points, condensor, Ht leads. still the same sometimes felt better.
Retime engine after removing distributor for a check on the bench. Dismantled carb and cleaned blew jet through with airline several times. Seemed much better and I thought it was cured drove down to Beaulieu Autojumble.
The fault now became that when cruising round about sixty the engine would cough back through the carb and loose power for a second then recover and travel on as if nothing was wrong.
Bought a new petrol pump at the Autojumble and fitted it by the the roadside, can you feel the desperation?
No better, Drove to Newcastle and then back to Wales, occasional cough, cleaned the dashpot and piston with various available cleaning fluids. Seemed slightly better.
One difficulty is that the later engine is not fitted with the oil separator on the valve cover, I am trying to swop and match parts.
Thanks for the input I am awaiting the spare jet from Tony and will replace the manifold with the early one, and refit the Mk 1 aircleaner. Tony suggested blocking of the two drain pipes on the early manifold as I cannot source a replacement easily. Any onyone else done this?
Regards Kels.
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Post by tommydp on Jan 3, 2011 15:11:21 GMT
Tony suggested blocking of the two drain pipes on the early manifold as I cannot source a replacement easily. Any onyone else done this? Block them with suitable screws, no problem. Done it on all mk 1 crabs I've owned. |
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Post by tommydp on Jan 3, 2011 15:55:38 GMT
Regarding the oil separator, this is on the tappet cover nearest to the radiator, below the manifold. It's either a can type, or a type where just a pipe comes up from the cover, the separator being inside the cover on this one. These are interchangeable, but keep them clean using diesel for instance. From the oil separator a rubber hose runs to either the carb or a valve on top of the inlet manifold, is this hose ok? Have you got the breather valve on the manifold? Clean it, check diaphragm. Check hoses, tighten clips.
I suspect you've got an air leak somewhere, either in the breather valve hoses or at the carb, if the hose from the oil separator is mounted her. Also, there could be a leak in carb gaskets and manifold gasket. How about the hose to the brake booster from the manifold or even the one way valve at the booster? Try listening with a length of tube to your ear around these places at idle, listening for hissing, meaning air leak.
When it comes to manifold, I would try listening for air leaks first, as well as other tips mentioned. Note that mk1 and 2 carbs and manifolds should not be mixed, has something to do with different semi downdraught angles.
Is the carb needle centralized? when you lift the piston assembly inside the carb and let it fall, is there a metallic "clonk"? It should be. The sound should be the same with mixture screw fully up (weak) and fully down (rich). If not, the needle is not centralized in the jet.
Speaking of idle, how does it idle? any spitting etc?
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Post by Penguin45 on Jan 4, 2011 1:16:29 GMT
I've read through this a couple of time now and the randomness of the problem is worrying. With due respect to the above posters, I think I'd be looking seriously at the ignition. There are well documented problems with current Lucas components all over the internet, relating specifically to distributor caps and rotor arms. The DISTRIBUTOR DOCTOR has components which work and are not particularly expensive. My own car got through several black rotor arms in short order before fitting one of his red ones. No problems since - probably because there's a spare one in the door pocket.  You could try the "In the dark" test - easy at this time of year. Get the car properly warmed up, then lift the bonnet in the dark. If the ignition circuit is breaking down in any way, you will see random sparks or even rather pretty electrical tracks along the leads. You will need to rev the engine quite hard to see any effects. Chris. |
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Post by dave1800 on Jan 4, 2011 3:49:26 GMT
I know you said in your first post that you had changed the coil already, but I agree with Chris that this looks very much like an ignition problem and with the intermittent nature and symptoms I would be on it being the coil if the timing is OK and you have tried disconnecting the vacuum advance temporarily as a no cost check.
Keep us informed, regards David
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Post by Keef on Jan 4, 2011 8:49:23 GMT
I would be on it being the coil What about the wiring (and connectors) to the above? Dry joint makes and then breaks. |
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Post by dave1800 on Jan 4, 2011 11:24:45 GMT
Yes, I agree it is important to check all leads to the coil in case there is a bad contact or even fractured wire. If a multimeter is available then check the voltage to the coil + terminal is close to the battery voltage with the ignition on but not started. There should be only about 0.6v drop across the wiring and ignition switch. Similarly check the voltage drop across the contact breaker with the ignition on and contacts closed is less than 0.5 volt. The current measured in series with the coil should be around 3.5-4 amps engine not running - contacts closed. It is very difficult to test coil breakdown, especially intermittent even with a scope (unless there are clearly shorted turns) so the easiest way is substitution. I would be on it being the coil What about the wiring (and connectors) to the above? Dry joint makes and then breaks. |
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