Is anyone able to suggest why my buggy struggles to start when it is warm?
When I start it from cold it fires pretty much immediately on a press of the button but when it is warm (i.e. has been running and driven for more than about 10 minutes) it turns over but does not fire.
In the current climate it gets warm very quickly and I am getting to the point where I am afraid to switch off unless I know I am gong to be a good while so that the engine will get chance to cool down.
It does also worry me that it may completely overheat and cause some serious damage.

Get it spinning then gently push accelerator, very easy to flood otherwise. If you have electric fuel pump switch it off when standing or it could slowly flood.

Single or twin carb

Could be fuel evaporation if a pipe is close to a hot spot and on twin carbs the heat from the manifolds can boil the fuel in the carbs.

Could be a hot coil breaking down but more likely fuel if it starts first touch cold with the chokes on if fitted.

I have heard that the float chambers of some twin carb setups can evaporate and empty when hot, and you can buy some heat deflectors to go between the inlet manifold and the carb to slow this down a bit. Never had the problem myself as I have an electric fuel pump that fills the carbs the minute you press the button.

As long as you have good oil in the engine, I would not panic about overheating 

Yes Dave my 1600 engine with mechanical pump is exactly the same viz starts easily when cold but at a petrol station it takes a few seconds turning over to catch but - as the other Dave said - if you very slightly squeeze the throttle that helps.

I've never liked switching engines on for short periods or on/off in short shift, so try to plan my buggy activities such that if I stop to look at a map I leave the engine ticking over for 20 seconds. And if I stop then I aim to 'treat' the engine to at least 10 minutes of cooling before starting again.

However, Snoopy is right about fuel evaporating since after running for an hour or so when I stop I inevitably can hear at least one carb boiling petrol for a few minutes. But after 10 or more minutes the engine inevitably immediately re starts without needing much turning over so the good old VW engine fuel system is darn clever. 

Thanks for all the replies guys.
It sounds like you have hit the nail on the head with the fuel evaporation in the carbs. Hugh's comment about hearing the petrol boiling rings a bell as I definitely heard something similar earlier today.
The oil is checked regularly so you've put my mind at rest about overheating.
Thanks all.

For all us guys old enough to have driven carburettor fed vehicles way back in the mists of time.....   fuel evaporation was common during the long hot summers.... Generally speaking..... waiting for about 5 mins with the vehicle on the level sorted things.   It`s hard to be sure you have this problem at times. It usually is at it`s worst when coming to a halt on an incline when you would need acceleration to start away again. Single carbs seem to be more troublesome than twins.

One thing to check.... thoroughly... as it can be devious to pinpoint..... Do you have fuel in the line drawing back-over, even only a little..... is the float valve closing fully.... and so on.  I suspect this thing will become more noticable  the hotter our summers become.

So that's the issue. Assuming you have a mechanical pump it has to turn over a while to get fuel back into the float chambers

Thicker or 2 normal gaskets between carb and manifold will help, sorted.mine. I then added an electric pump and have the opposite problem if I leave power to the pump and forget to switch it off it floods, although I've never checked the float height, that's on the list

I had this on both a single carb and twin ICT34s.   In my case it was definitely fuel boiling.  It only happened to me on warmer days.  I did add thicker gaskets that helped a little but did not resolve the issue completely. I put and electric fuel pump on to my ICTs and the issue was resolved for me.

Noticed a couple of comments about electric pumps and flooding.  IMHO that is dangerous.  A safety shut-off relay for electric fuel pumps should be fitted and then there is no chance of this and in the event of an accident you dont have a pump doing its best to push as much fuel out as possible. This is what I have fitted to my buggy https://www.csp-shop.com/en/brand-shops/safety-shut-off-relay-for-electric-fuel-pumps-127-025-000r-18015c.html

Quote from: Krug on July 12, 2022, 08:15:46 PM
Noticed a couple of comments about electric pumps and flooding.  IMHO that is dangerous.  A safety shut-off relay for electric fuel pumps should be fitted and then there is no chance of this and in the event of an accident you dont have a pump doing its best to push as much fuel out as possible. This is what I have fitted to my buggy https://www.csp-shop.com/en/brand-shops/safety-shut-off-relay-for-electric-fuel-pumps-127-025-000r-18015c.html

Agree Tony, at the moment I have manual switches, will have a look at the cutoff.
The thing I mentioned is leaving a pump with power too long with the engine off can flood a little.

I have also found any throttle movement before spinning the engine pumps too much fuel in and inevitably backfires

The CSP unit is currently not available and there is the £200 minimum order statement to contend with. Don`t know if any of the UK outlets have a stock.

Not looked into the additional feature the CSP unit has responding to rpm. You should find that the standard coil primary is 3 ohm.s if you go down that route.

Things are complicated beyond the past norm now with ethanol content of petrol. E5. for example, has 5% volume of what generically could be described as "alcohol". On a 34 PICT 3 carb for example, but principle applies to all, the standard idle jet was determined for leaded fuel and it`s subsequent "octane". The more ethanol the lower the petrol octane you have. Theory states that a larger idle and main jet should be present to dump more fuel in.. . Problem is no two set ups will be the same..  If you look on the web and search for standard 34 pict idle jet you will find more than one size bandied about. This is in a way correct as the various carb years had differing jet size. (No surprise there).

There is something you can try on a 34 carb....... The idle jet, located on the choke element side, does respond often to being very very slightly unscrewed anticlockwise. (Some jets have o rings some don`t).    The passage way has also got to be spotlessly clear.  The float level is critical as the idle/mixture screw only affects idling mixture. Above idling the float level is the item that determines the mixture.

I have just noticed something for the first time since 1970 and that is the other day with the buggy sat in the midday sun as I worked on it and by chance with the air filter off I could see that the choke flap was fully 100% open. Touched the carb body and it was almost too hot to touch. Simply from direct sunshine with the outside temp at 31 degrees. A different environment entirely from that of a beetle.

All in all a lot of things that can affect a hot start/smooth hot idle .



Just a few thoughts in an effort to help getting

Wow! Thanks Paul. Sadly a lot of that is over my head but I will save your post for when the buggy goes over for its annual check up in the winter (although I won't have the problem then unless the weather is extremely unseasonal!)
The fuel thing did cross my mind too because whilst I have stuck with E5 it has meant that I have had to move to super unleaded as all the standard unleaded is now E10. I don't know if that has had an effect.

I have had the CSP one fitted for years.  The actual one I had does not seem to be available anywhere now.  It also had a roll over cut out just in case the buggy ever rolled.

EuroCarb still sell the one on the CSP site https://www.dellorto.co.uk/shop/vw-carburettor-kits-parts/vw-aircooled-manifolds-linkages-parts/other-parts-vw-aircooled-manifolds-linkages-parts/csp11-electric-fuel-pump-safety-cut-relay/

And Heritage (though out of stock) https://www.heritagepartscentre.com/uk/ac127219-electric-fuel-pump-safety-relay.html

To be honest I always thought these were expensive (I think my one was around £30 when I bought it years ago).  I am sure someone who is more electrically skilled could identify the correct relay for significantly less.  My main reason for buying it was it came with wiring instructions so it was a really easy job for me.

Just noticed - on the EuroCarb web site you can download the wiring instructions.   So if someone can tell others what the relay is that would be needed, this could save people lots of cash.

Hope this works - just cut out the diagram ... I remember it was quite an easy job.

I can understand many people looking at a 34 PICT 3 and earlier wondering what on earth everything is in principle and how it works. Remember that all a carb is doing is mix air with petrol to form a mist of droplets that gets sucked into the cylinder and bang.....

The 34 Pict 3 is more complex in so much as you don`t use the screwed bit on the throttle lever to adjust the idle. often it is stated it has 3 separate fuel routes. separate is not the best word I think. It`s all inter-related. The problem as I see it is that despite differing opinion the mixture screw was blanked off from factory with the statement that the factory setting was not to be disturbed. Fine back then when the carbs were new but all these years on I cannot remember seeing a 34 with the plug still in place and even if it was there are decades of wear.

I very recently came across, by chance, the original VW training video for all carburettor types. in English. I remember this from my youth.
It`s quite long but it shows all the fuel / air routes and so on with exact instruction on how to adjust. Now then... I am sure anyone watching the videa will be initially overwhelmed as I was. I simply watched it all those years ago at Mill garages and drew and wrote down  as quickly as I could.

There is one thing I can guarantee..... If you watch this video and make a point of working through the details you will have far more knowledge of carb build / tuning than anyone in a garage nowadays....

Here is the link....

https://www.youtube.com/watch?v=CzG_Uedu8Kk