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Mk3 spitfire engine splutters and cuts out


Andy Moss
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Reaching the end of my tether.

I like to go for a evening drive in the spitfire. Trouble is that after a few miles the car starts to run badly then it stalls and I coast to a lay by. Restored a few years ago. So far:

Ignition system has sparks, Carbs have fuel, changed HT leads, changed from accuspark back to points and condenser. I don't understand, if there are Sparks and fuel why does it not run ok ?

It usually happens after a little while at constant speed (e.g. 40mph).

Each time I have got home having restarted the car and using lots of choke. The car never has and difficulty turning over. Idle can also be erratic, runs fine at 7-800 rpm then suddenly drops to 200. I tried switching the coil over at the side of the road, but the fault never went away.

Could I have vapour lock due to heat. How would I know. Checked valve clearances (a little while ago), ingition 6deg btdc, dwell ~40deg.

Baffled - please help!

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Hello Andy.

 

From what you have described, this sounds like fuel starvation rather than an electrical fault.

 

Additionally, fuel vaporisation (vapour lock) normally occurs when the engine has been running at full temp, then switched off and left - with difficulty on restarting. For the moment I think we need to get your engine actually running properly !! 

 

My first suggestion would be to see if the fuel tank is breathing properly and a vacuum not being caused as the petrol is being used by the carbs. I presume on the Spitfire there is a breather either in the tank or more likely the fuel cap ??

 

Secondly, is it possible that the tank has been disturbed at any stage and sediment has become free to be sucked in to the fuel line ?? If you do not have an inline filter at the moment, I would suggest you get one as this may determine if any sediment is being sucked through by being trapped by the filter.

 

if you have changed over the electrics and are happy with that, then fine. However not all replacement parts can perform properly and in question I would flag the rotor arm.

 

Put the electronic ignition back on, you will find that this aids better idle and accelerator / carb response.  

 

This will be a step-by-step investigation but I would most definitely look at the fuel side of the car as your first step as I think this is where your problem is.

 

Hopefully other Spitfire owners will be able to give some clues.

 

I hope that helps ??

 

Regards & good luck.

 

Richard.

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This has the old nutshell of floating debris which jams in the back of the float needle valve

 

often bits of rubber from fitting the hoses to the metal tubes

remove the top cover and clean the back of the valve, give the pipe a flush by cranking over

 

make sure the jets return to the adjusting nut when the choke is pushed home, any sticking here wil give poor very rich running and stalls.

Check the air filter is not blocking any of the front face ports on the carbs.

check the coil 12v (or the balasted feed) is on the correct polarity dizzy to the coil neg.

 

stick to an97+ ron fuel and advance tillmpinks and then retard a little

 

dont use plugs with an R in the suffix

 

 

get a red rotor if you have lucas dizzy

 

 

just some ideas but fuel is first choice

pete

 

Check the timing as points and electronic will not remain the same when you swap

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Just sucked the filler cap lid (quite an unpleasant experience) but there seems to be air coming through. Probably not causing much of a vacuum, but I will give it a try next time it conks out. I removed the in-line filter tonight to see it that was the culprit. Not talent it for a run yet. I will probably put the accuspark back first.

Please keep your suggestions coming.

Thanks guys.

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You need to check behind the float valve, and with pipes off, pump a few good squirts into a jar see what comes out

if its slivers of rubber they float back and forth in the supply tube to the carbs

 

other places are jellied fuel in the small flexi pipe from chamber to the jet assy

Where abouts are you ?

pete

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I had a similar problem.  There was so much debris in the petrol tank that it partially blocked the in-line filter that I had installed.  I tried cleaning the tank by removing the sender unit but too many ridges to flush it out properly.  Then the tank developed a pin hole leak so was replaced with a second hand unit and have had no problems since.

 

Graham

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Fit a red rotor arm.  Costs a few pounds and takes 30 seconds to fit. Exact same symptons in my 2500 spitfire a few years ago. Tried everything to cure what I thought was fuel vaporisation. But nothing worked. Since the Red rotor arm the car hasn't missed a beat.

 

Good luck

 

DJN

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Put electronic ignition back and reset timing. Checked carb floats/valves - no debris. Already had red rotor that is a couple of hundred miles old. Sorted fuel leak after messing with the connection to fuel pump lots of fuel leaking so doubt a blocked pipe. Did have an after market fuel pump a while ago, but swapped back to an overhauld original, checked it functioned last night, causing the oil leak. Off for a spin. Let you know, but I don't think I've found the culprit yet.

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All fine but it was a cooler evening. I reckon it must be vapour lock. I have wound somes string round the copper fuel pipe near the manifold to insulate it. I think I'll replace it with something more substantial soon. Hope that solves it.

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If you have an engine driven fan vapourisation is a myth used to cover other basic problems

 

whilst modern fuels are inclined to gas more easily , my rorty vitesse 6 with open un wrapped 631

would idle in traffic for hours and never missed a beat

 

keep under bonnet air flow with a engine fan and a cold air supply to the air box

 

Like wot triumph designed and it works

pete

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Andy.

 

Just out of interest, do you have a carb heat shield fitted ?? 

 

If not, it will be worth getting one - either in standard form or even better, a stainless steel unit; they do not cost much.

 

I have a Vitesse Mk2 and prior to fitting a heat shield I suffered from various heat / fuel problems.

 

After fitting, never had a problem to date.

 

Worth considering.

 

Regards.

 

Richard.

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  • 1 month later...

I seem to me getting a bit fed up with the breaking down problems. Usually 5 minutes in. I tried heating the carbs and fuel lines with a heat gun when the engine was hot. It didn't replicate the problem.

I have a Lucas sports coil fitted with the accuspark ignition. Could that be the problem?

I am tempted to get an accuspark coil and try that.

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Andy.

 

I have an Accuspark dizzy & coil on my Alpine and never had a problem to date ( that has done it !!)

 

On the Vitesse I have a Lucas sports coil & Simonbbc electronic ignition - again never had a problem. 

 

Not sure where you live but perhaps a rolling road session may assist. If the car breaks down at least you are at the right place; but more importantly their systems will be able to detect the start of component failure earlier then you will driving the car.

 

I think you have got to the stage where swapping stuff around may prove to be an expensive hit & miss affair.

 

Regards.

 

Richard.

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if the idle drops off again pull the ht leads off 1 2 or then 3 4   this will show if its carbs it wont run well on 2 or 3 pots but its gives aquick indication if the front half is running better than the rear half,  then you know its fuel related 

 

this still sounds like one carb is dropping out due to low fueling

 

Pete

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Andy.

 

May be worth flagging the RR company on this thread or a new one to see if any other member(s) has used it. 

 

Additionally, you need to be happy that the company is conversant with your carb / engine set-up.

 

I know this sounds odd but for instance, some RR units are great with Webbers & SU's etc, but for some reason not all are happy dealing with Stromberg's. Not a great difference in operation between SU's and Strom's but tuning and setting them is a different kettle of fish.

 

I'm sure you will be fine as I assume you are running SU's - worth asking the company before booking and parting with hard earned cash !!

 

Regards.

 

Richard.

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  • 1 month later...

Ok. Convinced that the problem was vapour lock I have bought and fitted a heat shield. Driving along fine at 30, but when I accelerate to 40mph it did the same just now. I was expecting it and this seems to be the way the fault is exposed. Instead of cranking the engine over, I pumped the manual fuel primer on the fuel pump. Normally, when the fuel pump has primed the system this lever has no real effect. But as I pumped the lever I could hear the float chambers refilling. I now suspect that the fuel pump is man enough to maintain 30mph, but as more fuel is used at higher speeds the float chambers become depleted and the car dies.

 

What do you think to the above idea?

 

I replaced the pump seals the other year because I wanted to keep the original unit. Does anybody know where I can get a good original unit?

Thanks for the help and advice. Andy

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Thats sound like theres a pump lever and cam positioning problem

 

Remember the hand prime only works if the cam is on its back, if the cam has the pump pulled down the hand primer wont do much.

 

If its always easy to hand prime you could bebon the right track in that the cam is not fully operating the pump lever and diaphragm pull down.

 

Pete

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I fitted the new pump tonight a nasty looking aftermarket one, but if it works then great. I made sure that the leaver was on top of the cam, so it was angled forwards and then tilted back onto the studs as it was fitted. Connected it all up and it was fine. Then I developed what I thought was a misfire again. I removed the ht leads to front and rear plugs and found that the 2 rear ones had no rear effect. Because it was affecting both of them I thought it's probably not ignition, but the read carb. I switched off and removed the rear carb float chamber lid and found there was vertually no fuel in it. The front one didn't have much in it either.

I am either developing a fuel blockage, vacuum, or the pump is not operating after a short drive. Any clues?

I am sure it's not the pump. Could the mechanical fuel pump leaver be falling off the cam shaft.

Help me - anybody?!!!!!!!

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you can have hoses on tanks and places that go hard , dont leak fuel but do suck in air despite much clip tightening, thes give problems when demanding more flow , fine at idle but more air than fuel when running, canyou fit a clear hose to the pump outlet then you can see whats arriving,  fuel or bubbles !!

 

also the flare or olive fitting in the pump pipes can give troubles

 

but dont go chasing too many obscure things at once , the heart of the problem does not seem to have departed ...just yet.

 

Pete

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