2.25 petrol hot start issue. Can anyone offer advice?

Hi folks,

I have a 1984 S3 with a 2.25 petrol engine. Over the past few years, he has been absolutely, 100% reliable.

However, today, I was sitting in traffic for about 30 minutes with the engine idling and then turned the engine off for 5 - 10 minutes. Come restarting it, it just wouldn't fire up. The starter motor was turning fine. Also, prior to sitting in the jam, I had had a couple of instances where the engine kind of died and picked up again as I was driving along (almost like it didn't get any fuel for a second or so). I got it bump started, drove it home and tried hot starting on the drive a few times, with no issues whatsoever.

I believe it may be a fuel issue, as a couple of weeks ago, the tank ran very empty and I limped it into the local petrol station literally on fumes (the engine was dying occasionally in the last mile or so). I tanked it right to the top and all was fine. Early this morning, I filled it up with fuel again, so I know there is plenty of petrol in it.

So, a couple of questions:

1: by running the tank super low, could I have picked up some crap in the fuel?

And

2: is it relatively easy to clean the fuel pump filter (it is a mechanical fuel pump).

Any advice would be most welcome

Someone else on here had this, think the fuel line running from carb to pump was heating up and vapourising fuel? Unless you have a diesel sorry!
Sure they will be along to advise but try rerouting it or wrapping in some heat shield type material?
That or crud in carb, use an inline filter always. Fuel pump easy to clean but more likely carb jet or inline filter if its a blockage anywhere.

Mine's a petrol. I've checked the routing of the fuel lines this evening and they are not too close to the engine block (they are all zip tied away from the top of the block). Looking at the inline filter in front of the carb, it is only ever less than 1/4 full of fuel (although, I've never had this issue before and the fuel filter has always had the same <1/4 full appearance).

Is the fuel line away from the top of the rad? Basically anywhere hot is potentially a problem. Inline filters are pence so change that first, then try cleaning the carb and checking for the zenith warp ( lap the mating surfaces) then try cleaning the fuel pump. All low cost to do. Dont rule out ignition mind, dodgy ht leads etc....

The fuel line is well away from the top of the rad. I have double checked that. My strong suspicion is a clogged filter somewhere. I'll change the in line filter before the carb tomorrow, but can anyone point to how I access and clean the filter in the fuel pump on the bottom RHS of the engine?

Just remove the oil bath air filter, disconnect fuel line each end then unbolt lift pump. Be aware oil may flow out of the hole too! Its easier to go underneath for the lower nut, just two to undo.
There is a sediment bowl and gauze, check the diaphragm too.
Good luck

Failing coil maybe?.Had these hot starting symptoms with a mini 1275GT many moons ago and a new coil and condensor fixed it.Wish I'd kept instead of scrapping it in 1987

Hot start could be the condenser as above. i cant see it being fuel related if its starting from cold. Saying that it could always be a co incidence that it started before and something may have blocked the jet etc.


I would check for spark first as its free and simple, but the condenser would be my guess if its when its hot and still starts from cold.

how well does it start from cold?

It was me that had all these problems. I spent ages on this replacing everything (carb, coil, dissy etc) multiple times until I nailed it. My symptoms sounded very much like yours.

Either being stuck in a jam or stopping for petrol I'd have problems with restarting, first the normal problem of over-rich. This is normal for carbs and is just the fuel in the float bowl expanding and overspilling into the manifold. Foot on throttle and turn over to clear.

Then there would be all sorts of problems it would either not fire up at all (no fuel getting to carb) or would fire up but the fuel would be delivered so slowly that it would run out of fueld when accelerating, changing into 3rd and limping slowly would all the float to slowly fill up but then trying to accelerate again would cause it to cut out.

It WAS the fuel heating up, in the mechanical pump mainly. Most new petrol (all now I think) is 5% ethanol which boils at a low temperature. The mechanical fuel pump has its valves at the top and gets air locked quite easily.

Rerouting the fuel pipe round the fan cowl helped as it stopped additional air locks in the fuel filter.

A complete cure was effected by fitting a facet electronic fuel pump and pressure reducer. I've run this for best part of a year now with only one problem. My first fuel pump was a cheapo chinese copy from ebay and failed after a couple of months. If you're going to do it pay the extra few quid and get a proper facet pump.

I've confirmed my theory by having everything the same but swapping between mech pump and facet pump (both fitted and plumbed in at same time) and the mech pump consistently plays silly buggers.

I've wired mine up with a safety cut out....there's a relay which cuts power to the pump when the oil pressure light is on. This means that if I roll the car it will cut the power as the oil pickup will not get any oil and so oil light comes on and cuts fuel. Many people just wire pump straight to ignition though.

I've put a push button on the dash to prime the carb for starting but this only needs to be used occasionally. Most modern cars have a similar set up but they have a timer relay to prime the pumps for a few seconds when the ignition is first turned on - I could do that but the push button is good cos it will confuse anyone trying to rob it!