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Bikergonebald
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Post by Bikergonebald » Tue Feb 13, 2018 1:46 pm

I just bought my car, when i viewed it it started from cold ticked over perfectly and sounded good but i couldn't test drive it. On receiving it the garage that MOT'd it and fitted new radiator hoses said it ran great but within in few days it was seriously misfiring. I eventually tracked this down to a loose LT lead on the coil but in the process i had removed all of the plugs. Even after fixing what was obviously the cause it was still miss firing, but i tracked this down to the HT leads (which are new silicone type, new distributor cap and electronic pick up instead of points) not connecting properly to the tops of the plugs so i corrected that. Now it starts from cold with a bit of cranking and needs some help to keep it idling during which time it throws loads of black from the exhaust that quickly leaves a thick black patches on the drive.
If i take it for a run after 15 minutes or so it starts to run great with only a slight miss under hard acceleration.
The engine has been gas flowed and has piper cams with tubular manifolds but this was done by a specialist 30 years ago.

What could the problem be?
Auto choke? Would air in the cooling system restrict water flow to the auto choke affecting the operation when cold?

Any advice?

Thanks
Kevin


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Post by Bikergonebald » Wed Feb 14, 2018 10:23 am

I have more info.
I went for a drive last night and it didn't get better when warm, it was barely driveable, any more than the slightest use of throttle and it was miss firing badly on multiple cylinders, maybe all of them. I'll check the colour of the plugs later, I'm now thinking its ignition related.

I might buy a new coil to test, should I buy for ballast or not? Currently it has a ballast resistor but I don't know the pros and cons of each type.


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Post by scimjim » Wed Feb 14, 2018 10:50 am

I think I'd start with ignition - what models of electronic pickup and coil do you have?


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Post by rebel alliance » Wed Feb 14, 2018 12:07 pm

Any chance you have put the plug leads back on in the wrong order ?



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Post by Bikergonebald » Thu Feb 15, 2018 1:43 pm

Answers
I assume the pickup is from accuspark the same as the ht leads, not sure about the coil. I will check at the weekend when I can check in daylight.

I was really careful about the order of the leads but things can happen. I will check the colour of all plugs at the weekend which wI'll highlight if it's just two cylinders but in between taking all the plugs out I had one good run in it (once warm) before the problem came back.


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Post by Bikergonebald » Mon Feb 19, 2018 1:46 pm

Hi.
The pickup is Accuspark and it looks like a new Lucas coil, probably from Accuspark as well as they sell them.
I checked all of the plugs and 4 of them were dry and really black and sooty, two of them were a little wet (not oil). The last time the car was run it was fully up to temperature but running badly so the soot won't be from multiple cold starts. I didn't think about checking the plug gaps until i'd put most of them back in but the two i measured were 0.7mm which is close to the stated book setting of 0.6mm, the plugs all look quite new and are Bosch WR7DC+ which are correct for the engine.
I remade the connections to the LV side of the coil with soldered terminals instead of the crimped connections and i removed the condensor as it's not needed for Accuspark systems.

From internet searching the black soot on the plugs is probably due to being very rich but could also be due to weak spark. I'm investigating options talking to Accuspark and will probably fit a new coil just in case.

What about the mixture? It's done less than 200 miles since passing an MOT so the carb should be OK but could it be the autochoke? The coolant was all replaced before the MOT so what are the chances that there's air in the system stopping the auto choke from heating up and working? Is there a way to temporarily disable the autochoke to test it?

Any special tips on how to bleed air from the cooling system?

Thanks.


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Post by scimjim » Mon Feb 19, 2018 1:53 pm

If you had air in the system it would probably chuck coolant out of the expansion bottle when you shut down. The autochoke is fairly agricultural and will work on air temp as well as coolant temp. Easy to check by running up to temp with the air filter removed.


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Post by AJL Electronics » Mon Feb 19, 2018 1:55 pm

As Jim says, look down the spout, you will soon see if the choke has disengaged.


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Post by Bikergonebald » Sun Apr 01, 2018 7:38 pm

After replacing the coil, lots of soldering of connectors and checking resistance of all the HT leads I was getting worried so i did a compression test. They were all 115psi or more so i put new plugs in. Ran fine, hurray, then it dumped power steering fluid on the drive. That will be a separate post. I've still got to check the choke and mixture but it drives well.


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Post by Jimscim » Sun Apr 15, 2018 10:56 am

Hi , Don’t be fooled by car running better after fitting new plugs . If you have a car that is running very rich the eventual effect will be the plugs will soot up and then the plug can’t work properly . If you replace the plug you have removed the effect but not the cause . Best of luck :lol:


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Post by siw1800 » Sun Apr 15, 2018 12:01 pm

I had an SP250 with similar sorts of problems a few years back. We tried everything. In the end my mechanic took the distributor to bits and found the weights all over the place. He set it up properly and then started it, ran worse than ever. We put a new distributor in it (not cheap) but fixed it. If you don't know the history of the car, a previous owner may have done what was needed to sell it with the faults known but masked!


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