Won't start

[Nickol]

'It seems to have been successful having done two cold starts since then where it start on the button!

My Traveller hibernates in winter. We are 600m high with often a lot of snow and salt on the roads so it stays in the garage all covered up. In any case I do not have any winter tyres for it so it would not be legal when conditions are bad. I have a routine of removing the battery and storing it in a frost free dry place but temporary replacing it ca. end January just to start and run the engine for a couple of minutes.

[myoldjalopy]

Well.............let's hope it starts OK in January then!

[Nickol]

Sorry to bring this topic up again.

Although the car is presently hibernating for the winter, before it had been difficult to cold start again. As it runs perfectly well and has a good even idle once the engine has fired up, even before it has warmed up.

The choke mechanism works as it should but my question is - should I remove the Carb and perhaps give it a service of some kind?. Certainly while it is off the road and I do have a warm workshop to do it in - just as well , it was minus 11°C last night.

[svenedin]

Sorry to bring this topic up again.

Although the car is presently hibernating for the winter, before it had been difficult to cold start again. As it runs perfectly well and has a good even idle once the engine has fired up, even before it has warmed up.

The choke mechanism works as it should but my question is - should I remove the Carb and perhaps give it a service of some kind?. Certainly while it is off the road and I do have a warm workshop to do it in - just as well , it was minus 11°C last night.

You could if you wanted but unless you know that there is a problem with the carburettor I am not sure what it would achieve. I remember this thread but without reading through it all over again I can't remember what was wrong.

Here are some tips for starting in cold weather that may help. Ensure the battery is fully charged. Turn the ignition key to the first position (assuming key start) and listen for the fuel pump filling the carburettor float bowl. If the car was very recently started the float bowl may be full already. WITHOUT pulling out the choke, spin the engine over on the key and as the engine is spinning pull out the choke fully. The engine should start. This method is supposed to help reduce the wear from starting a cold engine especially an engine that has been sitting hibernating.

Stephen

[mike1864]

After any long lay-up, a few turns on the starting handle (ignition OFF) would probably be beneficial in terms of engine wear, ie getting some oil going round at a very slow cranking speed, and gently overcoming any stiction/corrosion.

[myoldjalopy]

Nicol - as you previously said the car started up OK after re-setting the points gap, I would leave things alone until you start to use the car again.

[Nickol]

Thank you all for the feedback - it will be a little while before springtime comes around and I can try again.

[Nickol]

I was browsing you tube yesterday and came across a video where someone's Minor would not cold start. He diagnosed that the carb piston was stuck and having freed it, the engine started.

Is this phenomena believable?

[svenedin]

I was browsing you tube yesterday and came across a video where someone's Minor would not cold start. He diagnosed that the carb piston was stuck and having freed it, the engine started.

Is this phenomena believable?

We have to understand how the SU carburettor operates in order to answer that question.

When the choke control is set for cold starting, the jet moves downwards. This has the effect of moving the needle out from the jet which allows more fuel to flow. The throttle position, which is a throttle disc or "butterfly" is also altered by the choke control. Pulling out the choke also opens the throttle a little so that the revs when engine starts are at "fast idle". As soon as the engine fires, more air is drawn in through the carburettor and the piston should rise to reach a steady state at fast idle.

So the answer is yes, a stuck piston will cause difficulty starting and the engine cannot accelerate if the piston is stuck.

It is very simple to free a stuck piston. First unscrew the dashpot damper and remove the plunger. Then undo 2x screws holding on the dashpot. Remove the dashpot carefully, there is a large spring above the piston and oil in the dashpot (or there should be). Lift the piston upwards; do not bend the needle!!! Clean the inside of the dashpot with carburettor cleaner (or alcohol or clean petrol) and kitchen paper or similar. Also clean the piston, especially the area that contacts the dashpot. NEVER use anything abrasive. The piston is a metal to metal fit in the dashpot (with a film of oil). Any abrasive could cause the piston to leak air. Reassemble taking care to very carefully reintroduce the needle into the jet without any bending. Do not forget to top the dashpot back up with light oil (special carburettor oil is available). Job done.

Stephen

[Nickol]

Thank you for your detailed reply. Very good of you to make the time to do so.

It will not do any harm to do as you say and give the carb piston a good clean and see if that makes any difference. I have actually done this before , many many km/miles ago when I first got the car in 2011 and had to refurbish it with new parts. Until last year it was always a good cold starter. Re- setting the distributor points and spark plug gaps seemed to work initially but not any more. Might have been coincidental.

As previously mentioned, once it does start and gets warm the engine runs perfectly with a smooth idle. - Last year anyway before the current winter hibernation.

[svenedin]

Thank you for your detailed reply. Very good of you to make the time to do so.

It will not do any harm to do as you say and give the carb piston a good clean and see if that makes any difference. I have actually done this before , many many km/miles ago when I first got the car in 2011 and had to refurbish it with new parts. Until last year it was always a good cold starter. Re- setting the distributor points and spark plug gaps seemed to work initially but not any more. Might have been coincidental.

As previously mentioned, once it does start and gets warm the engine runs perfectly with a smooth idle. - Last year anyway before the current winter hibernation.

You're welcome. When your car emerges from hibernation, Ich drücke dir die Daumen! (I'm crossing my fingers for you; literally I'm pressing your thumbs for you).

Stephen

[Nickol]

Danke vielmals - ich sage dir Bescheid.

Thanks a lot, I will let you know

[Nickol]

So, I have removed the carb and have been checking it over, cleaning etc. First thing I noticed is the wobbly throttle spindle which is visably worn. Have ordered a new one as part of the rebuild kit as well as a AN standard needle and Spring. I have my doubts that the loose spindle has anything to do with the difficult cold start but it needs doing anyway..

One of the screws which hold the float bowl in place is a replacement bodge so someone has had the carb dismantled before. Does anyone know what the correct size/thread is for these screws? I should have ordered a set from SU but it is too late now but it should be possible to get a replacment proper one locally. It may need rethreading.

Will see how it all goes in due course.

[svenedin]

Float bowl screw is 3/16" Whitworth. You should be able to find a screw from a scrap carburettor.

https://www.minispares.com/jzx1394-su-c ... -top-screw

A worn throttle spindle allows air to leak past the throttle butterfly which can cause rough idle, a weak mixture and generally erratic performance. It could well be contributing to difficult starting by partially offsetting the effect of the choke when starting a cold engine.

Stephen

[Nickol]

Float bowl screw is 3/16" Whitworth. You should be able to find a screw from a scrap carburettor.

Stephen

Great, thanks for that - I see that I can get the screws locally as a set - will do that.

[Nickol]

The service kit arrived from Burlen today.

Interesting that the new red coil spring is much longar than what was installed. How important is that I wonder?

IMG_1528.JPG (471.59 KiB) Viewed 38556 times

Also it seems that there is anew arrangement for thefuel bowl inlet valve in that the float has less free movement than before. whether this is correct or not?


I may need to fiddle with the holding nut for centring the needle again as hte piston does not quite seat itself in the lower position. I have not yet put any oil into the piston cap , which could be the reason why. will check tomorrow.

[les]

Regarding the spring, maybe the old one has been compressed over time. The distance between the coils are smaller, which would suggest this ?

[svenedin]

I think the spring has just become compressed over time as Les suggests.

The float needs to be set correctly or the level of fuel in the float bowl will be incorrect. A new needle will require the float to be set again.

"HS carbs with the early nylon float and steel needle. The gap between the lever and the face of the lid should be between 0.125" and 0.187"

3.175mm to 4.74mm. So you can use a drill bit of 3.5 or 4mm to set the float correctly. Unless your rebuild kit instructions give a different figure?

Centring the jet is tedious but it must be correct. The test is that the piston falls with a "soft metallic clunk"

This is a good book that covers all of the common SU carburettors and fuel pumps with clear instructions and diagrams. https://sucarb.co.uk/catalogues-manuals ... anual.html

Stephen

[Nickol]

Strangely the kit instructions, which are generic anyway, do not mention anything about the float setting.

However, I have already been made aware of the gap setting and it seems the adjustment is done by just bending the metal strip attached to the float. Certainly, as removed from the car, there was no gap at all! The float went hard up against the top of the chamber lid. Now whether this had anything to do with the difficult cold starting, I have my doubts but it obviously has been a good exercise to renew, check and reset everything.

I will have a further fiddle with the jet needle centringtomorrow to ensure smooth and unhindered movement of the piston. I have noticed that the lower mixture adjustment nut has to be loosened off to allow any movement.

[Nickol]

In light of suggestions made I had a good rummel with the setting of the needle jet.

I found that that freeing the choke mechanism connection to the fuel line made for smooth piston movement. When connected, the fuel line was apparantly slightly twisted which then led to a small but noticable reluctance of the piston to freely fall. Easily solved by undoing the connection to the fuel chamber to loosen and untwist the fuel line and then retighten.

But, and this is a bit strange.

When I put the dashpot cover in position, with the new spring installed everything works ok, (i.e. the piston falls freely) until I finally tighten the two holding screws. Then the piston jams. Finger tight is fine, the dashpot cover is fully home and the difference between a tight screw and a finger tight one is very minor. What can it be?