engine not starting

[yesfan54]

My moggy wont start. If I turn it over the engine the spark plugs remains dry. The fuel line is ok, there is petrol in the bowl and the jet has petrol coming through( if I insert a screwdriver handle into the bowl, petrol flows out of the jet) There is no blockage etc. But there is no suction when I hold my hand across the carb air intake( air filter and housing removed). Compression test show good psi. Its not electrical, I have good spark. It was running perfectly and well tuned ,then out of nowhere it began misbehaving. If I blow butane gas into the butterfly it wants to start. I have inspected the inlet manifold for cracks and blown butane gas around it as I crank the engine and there is no signs of life. Any ideas ?

[svenedin]

Can you see that the throttle disc is actually opening properly? Is the choke operating correctly (the car is very unlikely to start with no choke)? If it was all working fine and you have spark and fuel I am thinking something simple like a linkage has become detached. Check that when you pull out the choke that the jet moves down.

Stephen

[yesfan54]

Thanks for your comment. Yes the butterfly opens and the choke adjusts the jet ok. If I don't get any suction across the jet then no fuel is going to make it to the cylinder.

[svenedin]

Thanks for your comment. Yes the butterfly opens and the choke adjusts the jet ok. If I don't get any suction across the jet then no fuel is going to make it to the cylinder.

Yes exactly which is why I thought the throttle disc might have become jammed shut. The throttle disc has to be open a little bit at startup or as you say, there is no air flow past the jet.

Check that the throttle disc is open slightly when the car is about to be started with the choke out as you would normally do a cold start. If you find the throttle disc is completely closed then: assuming you have the standard SU HS2 carburettor, check the screw (fast idle screw) that adjusts how much the choke alters the throttle. It is possible that this has worked loose and pulling out the choke is not also opening the throttle. There is another screw that is used to adjust the normal slow running on top of the carburettor. I have seen the HS2 incorrectly set up so that the slow running screw is doing nothing and the only thing adjusting the throttle opening at idle is the choke idle screw (fast idle screw). If that works loose you will have a closed throttle and the car will not start. Sorry if I have explained this poorly.

BTW, you are close by to me. I am the other side of the flyover. If you cannot fix it PM me.

Stephen

[oliver90owner]

Spray (thick) oil around the manifold/carb gaskets while cranking - it may well be a leaking gasket.

What were the compression test readings?

[svenedin]

Also worth checking whether the nuts have worked loose on the studs securing the manifold. Do not over tighten. Torque setting is 15 Lb/ft.

[StillGotMy1stCar]

If it has a brake servo fitted, that can be another air leak source.

Regards John

[yesfan54]

Thanks for all your comments. They did lead me to consider the float level in the bowl. And then it hit me! there was no gasket installed. This would lower the petrol level in the jet by the gasket thickness, maybe enough to cause the issue. When I reassembled loosely and held the float above by gasket height (petrol leaking of course) it burst into life. So gasket ordered. If it works I will post the good news or plough on with the investigation.

[svenedin]

Thanks for all your comments. They did lead me to consider the float level in the bowl. And then it hit me! there was no gasket installed. This would lower the petrol level in the jet by the gasket thickness, maybe enough to cause the issue. When I reassembled loosely and held the float above by gasket height (petrol leaking of course) it burst into life. So gasket ordered. If it works I will post the good news or plough on with the investigation.

The level of fuel in the float chamber is important and is set by adjusting the float. See this video: https://www.youtube.com/watch?v=Z6Le_HkrkKQ

To get the required gap you can use a metric drill bit as your measuring rod. 1/8" is 3.18mm and 3/16th is 4.76mm so a 4mm drill bit is ideal.

The above assuming you have an SU HS2 with a nylon float and not the later non-adjustable type.

Stephen

[myoldjalopy]

I would be surprised if a missing gasket made that much difference, apart from leaking fuel (especially as the OP said it was running perfectly before it went faulty "out of nowhere") but we shall see.......

[yesfan54]

great video. Mine is the all plastic bowl, So intrigued how to adjust the cut off needle with washers. I will await the gasket and observe any adjustments that may be necessary. Fingers crossed.

[yesfan54]

Re: myoldjalopy. Its been two years since this fault appeared and I have not had much time to look at it. I would be surprised, like you say, if this is the fix . The gasket may have been lost in my previous attempts to fix it and may therefore be a red herring. However the fact that it can fire up when I mess about with the float is promising. All I know is the spark plugs were bone dry on cranking and petrol could make its way to the jet.

[svenedin]

Good luck and if you need a hand my offer still stands. I’m only in Croydon

Stephen

[yesfan54]

Thank You Stephen. I will await this gasket and take it from there. However it will be nice to meet up. Let me see if this gasket and float has any impact, but its always nice to have a like mind around.