1800 wont start when warm

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1800 wont start when warm

Postby reb78 » Wed May 15, 2019 10:20 am

As above - I have been having a fiddle with out Magnum before starting the resto work on the body. Started for the first time in about five years on Saturday. From cold she starts with the choke out first turn of the key. Once warm she is really troublesome to start - currently I am having to put a small amount of petrol (15-30ml) into the carb and then she will start eventually - with some backfiring. When warm, she runs very rough and cuts out if you try to accelerate too hard. Any thoughts on where to start with diagnosis? I would kind of like her running well before i pull the engine out to start welding but it isn't essential.

My first thoughts were to strip and clean the carb, but I am worried about gaskets availability etc for the engine if I need to replace any as i go.
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Re: 1800 wont start when warm

Postby 1972nail » Wed May 15, 2019 10:36 am

Is it a Zenith downdrauht or Stromberg carb? Fred will have all the necessary engine gaskets and the carb gaskets, parts, rebuild kits etc are all available from various suppliers. The jets in the downdraught carb do get gummed up a bit. Soaking in carb cleaner may help. The Stromberg suffers from a split diaphragm and the oil in the dashpot may well be like glue by now.

I would first check things like the servo vacuum pipe and the vacuum advance pipe for leaks and security of all the carb and manifold bolts before stripping anything further.
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Re: 1800 wont start when warm

Postby reb78 » Wed May 15, 2019 12:06 pm

Thanks for that. Its the Zenith on this one.

I will check the pipes as you suggest first. I nipped all of the manifold bolts up last night after reading other threads on here (didnt get as far as starting though) - they were all tight with only a marginal amount to nip them up further.

I will need to compile a list of parts - Fred, if you take a look at this, I would like to put a set of gaskets together for this engine if you are able to help.
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Re: 1800 wont start when warm

Postby reb78 » Thu May 16, 2019 9:10 am

The vacuum pipework all looks in good condition on inspection. I was hoping to find a big issue there to simply explain the problem!
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Re: 1800 wont start when warm

Postby 1972nail » Thu May 16, 2019 9:19 am

Just reading the original post again. Seems like we were assuming fuel problems due to the adding fuel temporary solution, but we shouldn't ignore electrics. A dodgy coil may produce the same problems. The spark gets weaker as it heats up and the internal insulation breaks down.

Try swapping the coil for a known good one, but beware, there is a resistance wire circuit in the ignition feed which necessitates the use of a 'ballast' type coil. Or you could bypass the resistance circuit and fit a normal 12V coil, see the link attached for instructions.

viewtopic.php?f=12&t=22328&hilit=bypass
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Re: 1800 wont start when warm

Postby reb78 » Thu May 16, 2019 9:40 am

Thanks for that. I have a new coil in the spares box so will give that a go.

How do i know if it is a ballast type coil? Is there something obvious that will tell me? (Sorry if some of my questions are basic - i somehow fell into running oil burners from about 2000 onwards so havent done much with petrol systems for quite a while!!)
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Re: 1800 wont start when warm

Postby reb78 » Thu May 16, 2019 10:05 am

Had a google - found the answer - measure the resistance...http://www.accuspark.co.uk/faqs.html#q1
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Re: 1800 wont start when warm

Postby reb78 » Thu May 16, 2019 5:25 pm

I have three coils. One is a brand new Lucas. Two read 1.6 ohms across the positive and negative terminals and the older Delco Remy original 1.8 ohms so they are all in the ballast resistor range. I will give the new one a try and see what happens.
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Re: 1800 wont start when warm

Postby 1972nail » Thu May 16, 2019 7:09 pm

I've been on oil burners since 1986 so know how you feel. Modern petrol engines can take a bit of getting your head around and you do get out of touch with diagnosis of older engines too, but you probably know a lot more about them than the modern 'technicians' in your local dealership.

It's probably a Lucas DLB110? If it's a Lucas DLB198 then be prepared for a fried loom! It will draw too much current due to the extra windings. It has a low resistance like a ballast coil but was designed for amplified electronic ignitions that can supply high currents and have a dwell time limiter or a V8 engine where dwell time is restricted due to having to supply 8 sparks instead of 4.

If the coil already on the car is an AC Delco coil it probably is the original and is the correct ballast coil.
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Re: 1800 wont start when warm

Postby reb78 » Fri May 17, 2019 3:37 pm

My new one is a dlb102. Is this ok to use?
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