Hot start problem!

[jpyke]

Parked in Halfords this afternoon, came out after 20 mins absolutely nothing I could do would provoke the engine to start. Spark = good, fuel = good, checked plugs (= dry) tried a little choke (nothing).

I had this problem before and thought it was because the little vent valves werent opening. A few weeks ago I stripped and totally rebuilt the carbs, checked float levels, all new seals etc. Was running nicely (and still is).

In desperation I whipped off the air filter elbows and lifted one of the dampers and tried it. After a second or so of cranking it sprang to life and ran smoothly. Air filter back on, off we go.

Its just done it again now, although wise to it I just removed a dashpot and lifted the damper with the sleeve of the adjustment tool (which I had in the car). Again, started immediately.

I've got the fuel hoses routed nicely away from the hot engine but still can't work out what to do to solve it. I havent properly set them up yet (i.e. balanced them) but I have set the mixture with the method in the ROM (0.8mm damper lift = slight die away in revs then comes back to normal).

This weekend is supposed to be my "drive it a lot and decide it I dare risk going to France in July" weekend. Not doing so well so far!

Any suggestions please folks?

Thanks!

[Guest]

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The old girls sometimes do odd things in hot weather, if that's as bad as it gets I wouldn't worry ! If it does it again, pull the overflow hose off each carb in turn and see if any petrol's coming out, sadly new needle valves can be as bad as old ones, frustrating. Martin.

[Ian Durrant]

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I can only think that the piston isn't falling back properly and is maybe getting stuck without dropping the needle fully into the piston. If you remove the elbows and (with the dampers in) lift the piston with your finger an let it go, it should hit the bridge with a clack. then try with dampers in, it should still fall all the way til it touches the bridge, if not its a bent damper rod.

I have also noticed that any oil on the piston damper tube seems to make mine stick. a wipe with a dry cloth usually sorts it.

[V Mad]

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Two things spring to mind with hot startung problems: fuel vapour lock and rich mixture.

The currrent weather is causing problems with vapour lock; modern fuels vapourise easily. But as your car started after lifting the air valve (piston) this suggests it allowed some extra air in to release excess vapourpossible due to flooding or rich mixture(a common Stromberg problem). Are your plugs the correct colour?

[jpyke]

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Hi Vmad,

I've checked the plugs - they seem ok, dark grey coloured - perhaps a little too dark but I've not adjusted the carbs with the use of a gas analyser so I suspect it may be a little rich. I balanced them properly yesterday and got around to fitting the fuel overflow pipes (big risky leaving them disconnected!). Since then it has seemed ok when hot - at least, it has started easily enough but it does seem to act up a little for about a minute or probably less when you drive away - runs lumpy and will stall if you take your foot off the throttle. It wears off quickly enough though and settles down nicely. I'm guessing this is when it is using up the hot fuel in the fuel bowls and it runs nicely when it has been replaced with fresh cooler fuel?

I'm getting used to its foibles gradually. Went to bristol and back this morning and I have to say it was a very pleasurable drive. Its pulling really strongly so I think the mixture and timing must be pretty close to optimum.

Thanks everyone for your input, this forum is a Godsend!

James

[stustag]

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Hi James

Dark Grey colour plugs - they should be a nice light chocolate colour.

Have you tried adjusting the choke and throttle cables correctly as these have a huge effect on how well the carbs perform hot or cold?

Stuart

[jpyke]

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Hi Stuart,

Yes, choke and throttle cables are nicely adjusted - but you got me thinking, I hadn't checked the plugs since I balanced the carbs and adjusted the mixture and set the timing yesterday. I went to bristol and back this morning so thought I'd whip out the plugs:

Even bank:



Odd bank:





I think the even bank looks ok but the odd bank! No. 3 cylinder (2nd from left) was wet when I took it out so I must admit I panicked a bit. And set off this train of thought: Why is it wet? Doesn't smell of fuel and doesnt evaporate very quickly. Not oily feeling so horror of horrors - is it coolant? I can't see how it can be since I've just had the heads skimmed and pressure tested and theres new payen extra thick gaskets on there. So, I just popped them all back in, started the engine and let it idle whilst watching the exhaust. After about 30 seconds a few small droplets of waterspat out of thethe RH pipe exit. After a little longer the LH one started to moisten up. This could be condensation I suppose as the pipes would be cold... And I can think of 2 reasons why it may not be coolant (a) the cooling system isnt being pressurised and (b) it cant be the cause of the hot start problem as the engine would start if only one cylinder was wet. Perhaps its just that the inlet valve was open when the engine was stopped on that cylinder.

Oh dear! Am I worrying about nothing?

[jpyke]

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I've had another thought. I have a slight leak from the inlet manifold (wasn't skimmed with the heads) I'd left it until now as it was minor (get a little water in the V after standing for an hour or more after a journey which has got the engine up to operating temperature). I do have the payen inlet gaskets but I guess there's a possibility that it may be leaking into the inlet a little as well as getting out to the block. However, plug no. 3 is on an inlet tract which only has the small water hole in it, and that's adjacent to plug 1, not plug 3 so I think my theory is a little tenuous at best.

[V Mad]

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Plugs do not look good to me. There are some black deposits on some insulators which may cause shorting. Also gaps look way too large: what are they set to?

I would try a new set or at least clean all plugs thoroughly and start again.

[jpyke]

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V Mad wrote:

Plugs do not look good to me. There are some black deposits on some insulators which may cause shorting. Also gaps look way too large: what are they set to?

I would try a new set or at least clean all plugs thoroughly and start again.

Hi Chris, thanks for the answer. Plugs are set at 30 thou (as seemed to be the concensus for electronic ignition users looking back through previous posts). They're the NGK iridium ones though so the tip is much thinner than a usual plug. I agree, they don't look amazingly good. I would expect better since this is a completely rebuilt engine with every gasket and seal renewed, heads skimmed, carbs rebuilt, new timing equipment etc.