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Exasperated by stuttering SP250... all suggestions welcome!

Big Col
Posts: 407
Joined: Tue Feb 16, 2016 12:45 pm
Location: Leeds

Re: Exasperated by stuttering SP250... all suggestions welcome!

Post by Big Col » Thu May 30, 2019 9:51 pm

Yes there is a filter soldered on to the bottom of the pick up pipe in the tank. Well on the reserve set up anyway.
After saying it all points to fuel, on a personal note, I don’t like the idea of electronic ignition on older cars. In my mind they are too fragile to cope with old electrical wiring and components. I hasten to add it is only my opinion and I know people are very happy with electronic but I have my doubts.
Colin,
I may be slow but I’m rough as well !

Petelang
Posts: 216
Joined: Sat Feb 13, 2016 10:23 am
Location: Nottingham
Contact:

Re: Exasperated by stuttering SP250... all suggestions welcome!

Post by Petelang » Fri May 31, 2019 12:10 pm

One possibility occurred to me. Check engine to chassis earth is good, clean tight connection.
Peter
Peter Langridge
Cloud Nine Classic Weddings, Nottingham.

Agnello11
Posts: 12
Joined: Tue May 21, 2019 4:07 pm
Location: Thames Valley

Re: Exasperated by stuttering SP250... all suggestions welcome!

Post by Agnello11 » Fri May 31, 2019 12:54 pm

Thank you Peter, a good suggestion, but alas that one has been ticked off the list already as new earths have already been completed - unfortunately symptoms remained.

Last nights round of testing produced further interesting observations and revelations... I feel like I am edging closer to the problem, simply by eliminating things, but what the problem could be has me still totally in the dark! :lol:

As suggested, I have verified fuel delivery when symptoms present. I took the car out and ran it from cold until the issues presented. Again, it ran like a champ when it was cold and pulled like a train - those few miles of it running well are such a joy! ..... Then it began to stutter.
I travelled exactly the same route as the previous night and the symptoms presented in pretty much the same place as last time (within half a mile or so) so at least they are consistent and repeatable. There doesn't appear to be any correlation between symptoms presenting and Kenlowe kicking in.

When the symptoms presented I stopped, measured the resistance on the coil (3.6 ohms across the LT circuit, so a little higher than when cold but still within spec range) and then began to check the fuel. There was still fuel pressure in the line to the carb float bowls. I plugged my temporary fuel tank supply onto the float bowl connection and dropped the cars fuel supply pipe into the filler neck of my temporary tank. Now essentially I had a gravity feed to the carbs, plus a receptacle to collect any fuel that might be pumped through by the car's electric fuel pump. Juggling all that with three hands :ugeek: I hit the starter and it fired right up and ran like .... a pig. Just the same as before :cry: There was masses of flow coming out of the car's fuel supply pipe, so it definitely ISN'T being starved of fuel supply. From this I'm concluding that the tank pick up is fine, the pump is working properly, the filter isn't blocked and the engine is receiving sufficient fuel. It's good to have this verified though, so thanks for the thoughts and suggestions to undertake this task.

Whether there is crud in the float bowls that is slowly clogging the jets as I drive is yet to be determined.... I didn't fancy taking the float bowls off with the engine hot, so will check those when it's cold. I don't get the impression this is the case as this issue is affecting both banks simultaneously and the chances of that occurring as a result of crud in the carbs are slim, but...... I need to rule it out....

SO... having established that it very likely isn't fuel related, focus has switched back to ignition.... I haven't changed the base plate back to points as it's quite an involved job, but I can see I may be heading that way.

I think the issues still present like some sort of spark failure.... I changed the king lead (from copper to silicone) - made no difference. There is no obvious tracking or arcing on the rotor arm or distributor cap and no evidence of HT current leakage when viewed at night... yet the intensity of the light emitted by my little spark tester does diminish when problems present. It flashes away brightly when ticking over and running properly, but dims when attempting to rev and the symptoms present. Again, the symptoms ONLY appear once the car has got warm - it runs perfectly from cold, so it suggests something is breaking down as it heats up.

One interesting observation I made last night was checking the ignition timing with a strobe. It is absolutely bang on the timing mark at idle. If you very gently open the throttle and allow engine revs to gradually rise, the timing advances as one would expect - the mark on the pulley when viewed by strobe heads off anti clockwise away from the engine pointer out of sight. If you open the throttle more aggressively, the mark on the pulley only advances a few degrees - I would estimate a maximum of 5 degrees - and sits there. This coincides with the rough running symptoms and seems to suggest that the timing isn't advancing anywhere near enough, which is what the running symptoms sound and feel like - the engine sounds like it is horribly retarded. The pulley mark also occasionally hops around wildly when viewed under strobe, suggesting the spark is being fired way off time every now and again. I immediately assumed this was related to the advance / retard mechanism, so disconnected the vacuum hose to eliminate it... but the symptoms were exactly the same. For whatever reason it isn't seeing anywhere near enough advance when it is presenting with poor running symptoms.

To me this is now potentially pointing to an issue with the electronic ignition.

I'd be very grateful for any thoughts. It MUST be something simple, something I've overlooked as it runs so well otherwise and so many things have been replaced already (not that replacement can rule them out definitively!)....

User avatar
Kbeal
Posts: 75
Joined: Mon Feb 15, 2016 9:01 pm

Re: Exasperated by stuttering SP250... all suggestions welcome!

Post by Kbeal » Fri May 31, 2019 5:38 pm

Have you checked the bob weights in the distributor? That’s what governs the advance
Kevin

Sydsmith
Posts: 795
Joined: Sun Feb 14, 2016 11:15 pm
Location: Aberystwyth Wales

Re: Exasperated by stuttering SP250... all suggestions welcome!

Post by Sydsmith » Fri May 31, 2019 6:07 pm

Heck Larry, top marks for persistence and effort. Looks like it may well pay off, I have had a similar problem which as Kevin suggests was down to the auto advance and retard mechanism sticking. I have also heard that a slightly bent distributor shaft can cause a similar problem. Syd

bakergh
Posts: 68
Joined: Wed Feb 24, 2016 1:57 pm
Location: New Forest, Hampshire

Re: Exasperated by stuttering SP250... all suggestions welcome!

Post by bakergh » Sat Jun 01, 2019 9:51 am

"so disconnected the vacuum hose to eliminate it... but the symptoms were exactly the same. For whatever reason it isn't seeing anywhere near enough advance when it is presenting with poor running symptoms."

Maybe you have found the problem that the vacuum advance gives up when hot. Could it be a rubber pipe collapsing or the diaphragm.

Graham

Ian Hastings
Posts: 100
Joined: Tue Mar 15, 2016 3:00 pm

Re: Exasperated by stuttering SP250... all suggestions welcome!

Post by Ian Hastings » Sat Jun 01, 2019 8:46 pm

Bit of a long shot and probably not your problem but worth checking anyway.
On the condenser in the distributor there is an insulated cover that protects the tabs on the flexible and solid wires from touching the base plate when they are bolted to the condenser terminal. If that insulating washer is missing or fitted incorrectly then a short can occur causing all sorts of problems.

Please don't ask me how I know................ :shock: :roll:

harty
Posts: 1
Joined: Sun Jun 02, 2019 3:18 pm
Location: london

Re: Exasperated by stuttering SP250... all suggestions welcome!

Post by harty » Sun Jun 02, 2019 3:33 pm

had the same problem on my saloon ,did everything the same as you have ,found that when changed from dynamo to alternator some wires left connected in regulator box which seem to be switching on and off when hot sending the amp gauge mad ,disconnected all wires in reg box and fitted new amp gauge hasn't missed a beat since then ,worth a look as least.

daimlersteve
Posts: 339
Joined: Wed Mar 09, 2016 11:20 am

Re: Exasperated by stuttering SP250... all suggestions welcome!

Post by daimlersteve » Mon Jun 03, 2019 3:14 am

Hi all, may sound silly , but have you tried going back to the points setup to eliminate the electronics . The initial problem may have been an accumulation of defects . The mech. advance has been looked at and corrected as necessary i'm assuming .Drive dogs and springs corrected ? All advance checks should be done with the vac. disengaged.
My car (or two) has a Fast ign. optical setup . Runs perfectly on my two cars . when put an a car with the org. generator it malfunctions, swap to my car and runs perfectly . Re-install points to problem car and it runs perfectly.This car had had the Fast setup previously to overcome low compression issues and tuning , then played up with the Fast . As said, swap into my car and no problems .Same unit -- different car .
If its still a no-goer , call me to run through it.
Now , back to assembling my 2.8 engine . Heads should be on soon.

Regards Steve

Phillmore
Posts: 847
Joined: Sat Feb 13, 2016 1:25 pm
Location: Worcestershire Herefordshire border

Re: Exasperated by stuttering SP250... all suggestions welcome!

Post by Phillmore » Mon Jun 03, 2019 7:35 am

bakergh wrote:
Sat Jun 01, 2019 9:51 am
"so disconnected the vacuum hose to eliminate it... but the symptoms were exactly the same. For whatever reason it isn't seeing anywhere near enough advance when it is presenting with poor running symptoms."

Maybe you have found the problem that the vacuum advance gives up when hot. Could it be a rubber pipe collapsing or the diaphragm.

Graham
Have you investigated this further? Isolating a system under fault conditions and getting no change usually means that's where the problem is.
Andy

1954 Conquest Mk1, 1956 Conquest Mk2, 1957 Conquest Century Mk2, 1955 Austin A90 Westminster

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