Today's stupid question: Correct Spark Plugs and Carb behaviour

Doug

Doug

Member
Hi folks

What are the correct spark plugs for the 1725cc engine, with cast iron head ? (ie .. completely standard)

Our van had NGK BP7ES ( think that's right - definitely a 7) but just as a test I've replaced them with new BP5ES (think that's right) from my Triumph 2500. He runs just fine but it's a hotter plug.. not sure what the significance of that is, but I'd like to replace with the right ones, so am just checking.

And furthermore ..
I'm used to SU carbs so the Zenith is a bit of a mystery at the moment. When starting, if I happen to flood the engine, a way of clearing it (with SU) is to run the engine on the starter for a bit with the accelerator right down. Flushes out excess fuel, eventually the mixture is right, and the car starts.

Would that work with the Zenith as well?

I've become a bit paranoid about starting the van as he misbehaved quite resoundingly over the last week; lying about having a good spark, flooding easily, using up loads oc Cold Start, giving the impression the battery is on the way out, etc. Naughty.

It turned out to be muck in the points gap giving an intermittent spark, now cleaned, so he's behaving now (I think) but I wanted to understand the carb more in case such naughtiness returns.

thanks all

Doug
 
Aha - according to this site:

http://sparkplugcrossreference.co.uk/1231-ngk/1245-champion/n9y-n9y-n9y.html

N9Y = NGK BP6ES so the BP7ES he had were too 'cold'. Hm.

The NGK site suggests symptoms would be:
"Carbon fouling occurs when the spark plug firing end does not reach the self-cleaning temperature of approximately 450°C (842°F). ... When the heat range is too cold for the engine speed, the firing end temperature will stay below 450°C and carbon deposits will accumulate on the insulator nose."

- the plugs I took out were a nice colour (tan) but with fairly heavy deposits. Not bad, just a bit. Figures :)

thanks all !

Re the Zenith carb: According to some diagrams I've seen, prodding the accelerator actually pumps a bit of fuel into the mixture, so possibly putting the accelerator down when starting would flood the engine further.
Sound right ?

HIF44 is a very desirable conversion but we've only had the van a month or so, so lots to 'get used to' first.

D
 
I'm no expert on carbs and I am not familiar with the Zenith, but I am familiar with Solex and Weber fixed jet carburettors. You are correct that pushing the throttle pumps fuel to prime the carburettor, which can lead to flooding. The technique I have always used with these when flooded is to push the choke fully in, lift off the throttle and crank it on the starter. When it fires (hopefully), add some throttle and pull the choke out halfway until it warms up. Hope this helps.
 
Yes the Zenith accelerator pump does just that, squirts a couple of mils down the throat when you push the pedal. Not very scientific but it works. I have heard suggested that, because of modern fuels burning hotter, it's an idea to go to a hotter plug - but I've always got by with the 9's
The carbon deposits you describe sound like it's been used on shorts runs for a while the engine needs a good long run to get a decent idea. If possible coast to a stop withe the engine off then check the plugs.
The sooty plugs could also be a clogged up air filter.
 
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Ace info! Thanks all :)

Best avoid flapping the accelerator about then.
At some point we'll do the HIF44 conversion but first things first .. gotta get him running well and get used to driving him, which is currently going very well :-D
 
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somebody say carb? Here's mine for the van... Twin float chambers, twin acceleration jets and 4 barrels
 

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