Spitfire Will not restart after warm up, Spitfire mk1

[tomgt6]

I have a 63 spitfire mk1 with SU carbs. I have checked all the timing, points and spark. If the car is cold it will start right up. I don't even have to choke it. I let it run for 5-10 minutes or even longer and when I turn it off and try and restart, it will not fire off.

I have check the spark, it is good, vacuum is good, timing seems to be ok, compression is about 125lb per cylinder.

I pull the plugs and 2 and 3 are wet. 1 and 4 seem to be a bit wet but not like 2 and 3.

I wait for 24 hours and come back and the car will start again. If I try even 12 hours later it will not start.

I am thinking that maybe I am flooding the 2 and 3 cylinders. Or I may have some issues with the rings or head gasket that shows up after the car warms up.

The oil is clear, antifreeze is good. The car is burning on the rich side at the moment but until I can get the car starting and running reliably the fine tuning on the carbs will have to wait.

In the head do 2 and 3 intake ports sit lower so gas could pure down into these cylinders?

Any ideas or help would be great. Thanks. Tom

 

[Andrew Mace]

Tom, if the engine is original, there are only two intake ports total: one is shared by 1&2, and the other by 3&4. Meanwhile, you say the car seems to run rich; could it be something as relatively simple as the choke cable not releasing completely and/or the jets not returning "fully home"? Or, since you say you don't need choke to start it cold, could the carbs just be set way too rich?

 

[tomgt6]

Good questions, I am pretty sure the choke is all the way off. But I will check that again.

I assume to lean the mixture I would need to move the bottom tube up further. The needle is getting all the way down but it sounds like your saying the bottom tube may be set to low in the first place.

 

[Andrew Mace]

...I assume to lean the mixture I would need to move the bottom tube up further. The needle is getting all the way down but it sounds like your saying the bottom tube may be set to low in the first place.

Right! Again, it's one of several possibilities, but it's easily checked (and rectified). The jets do bind occasionally.

 

[Bob Claffie]

I'm with Andy on this one- just too rich. Have you tried starting it as if it was flooded? Hold the gas to the floor and crank it long enough to clear out. Also stuck floats will pour raw gas into the engine which will soon cause a running engine to stall and stay stalled for some time. Bob

 

[billspit]

My Mk I runs pretty well and no way it will cold start with no choke. I'm guessing you are way rich or the choke is really on and you don't know it. Time to take off the air filters so you can look. You might want to screw the jets all the way home and back them off the correct number flats (don't recall the number right now) and star over. Also check that the needle is not binding on the jet.

 

[Andrew Mace]

...You might want to screw the jets all the way home and back them off the correct number flats (don't recall the number right now) and star over....

Twelve flats is usually a good starting point!

 

[tomgt6]

I have been looking at this more and agree with you. If I start the car and after I kill it I get drops of gas coming out the front air intakes of the carbs. I get about a teaspoon full of gas before it stops. So your right the float is set to high and the jet is to low giving it to much choke. I guess I need to go back to the carbs and work on them again.

As for the question about clearing the engine after flood I have tried foot to floor and long cranks. No luck.

If you have any other suggestions that will help let me know. Thanks. Tom

 

[Andrew Mace]

Before messing too much with float levels, just be sure that everything in the float bowls is clean and free to move, especially the needle valves. It wouldn't hurt to undo the needle valve, blast it with carb cleaner and maybe some compressed air, and reassemble. If, at any point, the car sat for a lengthy period of time, it's easy for old gas, tiny bits of rust particles from the tank and whatever else might have been floating around in the old gas made its way to the carbs and began to clog them up, and the float bowl is the first place you'll see evidence of this.

 

[tomgt6]

Thanks, I will look at that again.

I have another question for you guys. I have an extra set of stombergs from my GT6. Would they be easier to work with and tune for the spitfire?

 

[Andrew Mace]

In a word: no. Nothing wrong with Strombergs (originally developed by Standard-Triumph in part to skirt SU patents and avoid buying expensive SU carbs from then-rival BMC); in fact, later Spitfires used a single Stromberg 150 very similar to those of the GT6. But they're bigger (at 1.5" than the 1.25" SUs you have now, so they won't fit your manifold. And most folks feel that SUs are simpler and perhaps more reliable.

 

[tomgt6]

The other idea is to put a couple 38 -40mm Mikuni's on. Has this been done by anyone?

 

[Andrew Mace]

That's also a bit of a band-aid solution, especially if the engine remains relatively stock otherwise. The SUs really are about as good as it gets, and they're really not that difficult to maintain or even rebuild if needed!

 

[TR3driver]

FWIW, I agree with Andy. Nothing wrong with ZS carbs as such, but there is a much smaller assortment of tuning parts to chose from than with the SUs.

If the float level seems to be right, you might also look at fuel pressure. I've heard stories of replacement fuel pumps putting out a bit too much pressure, which can force the valve open against all the force the float can exert. And it's at least possible the problem only happens at "hot soak", since hot fuel is less dense and hence the floats don't float quite as well in it. The fuel pressure might also be rising, as the fuel in the lines gets hot and expands.

Also, if your carbs have 'Grose Jet' float valves installed, I would remove them and try stock type valves. The Grose Jets seem to also have problems sometimes with not holding back the fuel.

 

[Tomster]

Could this be something as simple as vapour lock occurring in the fuel lines near the the engine?
Vehicle in motion-more cooling-good gas flow
Vehicle stopped-heat rises and boils off the gas in the line creating the lock ?
Jus' guessin"

 

[tomgt6]

I thought that as well about vapor lock but I can run the cold engine for 1 minute and turn it off and never get it started again. Really not enough heat to do anything at that point.