Warm start problems - 88 1.6 carb

[Jack&Bec88]

Quick question - I'm new to both petrol engines and carbed engines, I'm usually messing around with PD or VE diesels.

My partner and I picked up an '88 GT 1.6 carb about a month ago. After playing endless silly buggers with the Pierberg I dropped a Weber 32/34 on there and it now cold starts, revs up, and idles perfectly. Also fixed a massive vacuum leak on the big brake booster hose, and replaced all other vacuum lines just to be sure. Threw a cam belt on it.

The only problem I have now is a hot start issue. It's the same with the Weber as it was with the Pierberg so I'm assuming it's not related to the carb in any way. On cold start it'll bump into life with zero issues. On hot start it needs to turn over for 10-15 seconds on the starter before it'll juuuuust catch and fire up, and then need coaxing with the throttle for a few more seconds to settle down into a decent idle. Then it'll drive absolutely fine. If you hot start it within a minute or so if shutting it off it'll start fine, leave it any longer than that and you have issues until it's fully cold again.

Is this a fuel non return valve issue? Some kind of fuel pump or lift pump issue? I'm still learning my way around these engines so a direction to head in would be much appreciated. Hoping it's not the accumulator..

Thanks!

[C 20 CCO]

I’ve been drumming through my head what might be causing this but struggling. Only because you’ve changed carbs and still have an issue.
Some members have also changed from a Pierberg to a Webber, and hopefully they can clarify that all is hooked up well.
I was going to say float chamber in the carb,
Fuel lines all clear, but if it gives the beans under normal conditions you obviously don’t have a fuel starvation problem.....
Starter solenoid ???? I have a lazy start when my 1.8 carg gt2 is warmed up. Kind of winds itself up starting slow then wham...

[GT_II]

Is the engine turning over fine on the starter when the engine's hot? If so, have you tried pressing the accelerator pedal while starting? Unlike on fuel injected engines, for which you should always keep the foot off the gas while starting, carb engines require a different technique when the engine is hot. According to the manual:

Carburettor engines: Starting a warm or hot engine

Slowly depress the accelerator pedal while starting and hold it in the full throttle position - do not pump the pedal!

Release the accelerator pedal immediately the engine starts.

[Jack&Bec88]

Thanks for your reply. After I put the Weber on it felt really flat so I checked the distributor timing (camshaft pulley timing mark lined up to the top of the cylinder head) and had to adjust the dizzy body 5-6mm clockwise to get the rotor arm to line up with the timing mark on the body. That really woke the car up, but I'm assuming the dizzy and the carb could do with a little more fine tuning to get them just right. It's a little lacking under 3000rpm but once you hit 3k it pulls hard right up to redline.

I do wonder if the advance on the distributor could "stick" and not fully retard the whole way, possibly causing the meh performance in the lower half of the rev range and the hot start issue? Like I said, very new to petrol/carbs/dizzies so still learning my way around them. That said idle is rock solid so I don't really know.

In terms of how I hooked it all up, I kept the vac reservoir and plugged that into the first T in the vac line from the manifold to the booster (rather than blanking off the first T and deleting the reservoir). Second T goes to the dizzy vacuum advance. Vacuum line from the back of the carb comes up and around and goes into the rearmost fitting on the left of the plastic airbox. Frontmost fitting goes to the hot/cold air valve in the intake. I assume that's all correct?

[Jack&Bec88]

Is the engine turning over as fine on the starter when the engine's hot? If so, have you tried pressing the accelerator pedal while starting? Unlike on fuel injected engines, for which you should always keep the foot off the gas while starting, carb engines require a different technique. According to the manual:

Carburettor engines: Starting a warm or hot engine

Slowly depress the accelerator pedal while starting and hold it in the full throttle position - do not pump the pedal!

Release the accelerator pedal immediately the engine starts.

Throttle to the floor is the only way it'll start when hot. With no throttle it'll just not start. It takes 10-15 seconds of throttle to the floor to get it to catch. Starter motor is turning it over fine.

[GT_II]

Have a look at this Wikipedia article which may well be relevant:

https://en.m.wikipedia.org/wiki/Vapor_lock

The symptoms are consistent with fuel in the carburettor and/or fuel pump vaporising when the fuel flow stops due to residual heat from the engine. This vapour lock then requires purging and/or replenishing when you start up again with the engine still hot. If you allow the engine to cool down, the fuel vapour returns to a liquid state, avoiding any starting issues. Unfortunately, if that is the cause, although interesting, the article doesn't help to solve the problem. I guess as an initial step, check the fuel hoses are not routed too close to the engine.

[RussGLAuto]

This might sound odd, but check fuel system from the filler cap to the carb for rust.
The give away is black particles captured in the engine bay fuel filter, the filter won't catch them all and will play merry hell with the carb as you describe.

My own 1.6 Pierburg was replaced with the Webber back in 2018 because of 'rough running'.
I put the Webber on a rolling road and measured only 55 hp at the wheels. Had to change the jets as they weren't correct, brought it up to 72 hp but still a pig to start some days. The FR engine should have 85 hp.
Got fed up and had the Pierburg refurbished and refitted. Only to have that cough and splutter again also.
Found rust in the filter so had the tank & fuel lines all replaced, full of rust when inspected, now she's good as gold. The Pierburg is a gem when running with clean fuel.

Just my own expieriance and it may not be the same as your issues, but something to check to help with keeping your sanity!

[Eagle1]

Also use a barbed fuel filter. I've had a replacement filter spin the inner filter so that fuel was essentially going straight through. One of the other things I have done is to route the fuel line around by the offside headlight so as it's not above the warm air pipe/manifold.

[bruntonpasty]

It sounds like a vapourisation problem to me, as mentioned earlier in the thread. I would also suggest double checking all other general settings you can, Ignition timing, plugs, mixture/CO, etc

[GT_II]

Is there a possibility the fuel is stale, perhaps having absorbed water vapour? If you're not needed to fill up since you bought the car, that might be a factor.

[Jack&Bec88]

To answer all of your questions - the car has had a brand new fuel tank and filler neck recently (not looked through the paperwork I got with the car properly yet but they look immaculate and the MOT tester commented on them) - it also had new fuel and brake lines fitted a few years ago so I'm pretty confident with the condition of the fuel system.

It has a clear inline filter in the engine bay and the fuel line swings right around over the driver chassis leg before going back in to the fuel pump.

The car didn't have much fuel in it when I bought it and so far I've put about 30 quid of cheap supermarket fuel through it (live out in the sticks so "super" branded fuel is harder to come by) so that should have any old fuel out of the system/heavily diluted by now.

When I initially put the carb on it ran but was really flat throughout the rev-range. I retimed the distributor back to the timing marks in the body with the engine on TDC cylinder 1. This woke up the engine above 3krpm but it still hesitated and didn't pull well under 3k. I assumed the Weber would come with a reasonable base mixture but turns out it was mega rich so I set it up by turning the mixture screw all the way in, backing it out two turns, and turning it in until just before the engine started running a little rough - so I'm running at about 1.5 turns out now. I then went back and advanced the distributor a little which the engine really appreciated and it's now pulling hard all through the rev range with no hesitation lower down. A buddy at work has a timing strobe so I'll get the distributor dialled in properly with that when I can.

Still doesn't like hot starting though.. Next step will be to shoot some brake cleaner down the carb while my partner turns it over to see if that makes it fire. If it does then it's lack of fuel/vaporised fuel, if it doesn't then it's too much fuel or maybe some weird ignition/coil problem?

Thanks for all the input so far! To be honest at this point I'm just glad it's driving well. It's only a weekend/project car and we both have slightly more modern cars for commuting (I have an '05 Audi C5 A6 PD130, and she has an '00 VW mk4 GTTDI) and up until this point the Pierberg was making driving it miserable. Would idle at 3000+rpm when cold and then would just die rather than idle once warmed up. Wouldn't hold any settings, munched through fuel, couldn't decide if it would over-rev or just die. Mega lumpy idle as well. It's now running like a top and the only engine related issue is the hot-start problem.

[mark1gls]

You need to decide on what fuel you are going to use before finally setting the timing as it needs to be retarded by 6 degrees if using normal unleaded and advanced if using super unleaded.
I’m not sure if you need to use super unleaded in your car, in my 1978 Mk1 1.6 Scirocco I can use normal unleaded as it was designed to run on old school 2 star (if you are old enough to remember it) 91RON petrol so 95RON normal unleaded it fine. My 1988 Mk1 GTI golf cabriolet need and runs better on super unleaded as it want 98 RON super unleaded.

It maybe worth taking it to a local friendly MOT garage and see if they can hook it up to there exhaust emissions tester to see what the mixture is like. I can’t remember the exact figure but I think about 1.5% CO is where you need to be?

[Jack&Bec88]

You need to decide on what fuel you are going to use before finally setting the timing as it needs to be retarded by 6 degrees if using normal unleaded and advanced if using super unleaded.
I’m not sure if you need to use super unleaded in your car, in my 1978 Mk1 1.6 Scirocco I can use normal unleaded as it was designed to run on old school 2 star (if you are old enough to remember it) 91RON petrol so 95RON normal unleaded it fine. My 1988 Mk1 GTI golf cabriolet need and runs better on super unleaded as it want 98 RON super unleaded.

It maybe worth taking it to a local friendly MOT garage and see if they can hook it up to there exhaust emissions tester to see what the mixture is like. I can’t remember the exact figure but I think about 1.5% CO is where you need to be?

I have a good relationship with the local MOT place so I may well go and speak to them about that. What's the correct order - set mixture then set dizzy? Or does it not matter too much?

I see you're in Somerset, I'm in Shepton Mallet!

[mark1gls]

You need to set the timing 1st then the mixture. Make sure the ignition side of things are all good and the air filter is either new or nice and clean then it’s the mixture.

Your not far from me then, I’m about 10 miles down the the A37 towards Yeovil in a little village of the A37.


I don’t use any lights etc to set my timing... I advance the timing till the engine “pinks” underload then back it off a little till the “pinking” stops.
You do need a quite road and preferably with a slight incline to drive up and down then stop and twist the dissy to set it.

I would mark where your dissy is now so you can see any adjustment being made.

[mark1gls]

Just another thought after reading through your post... Is the new cambelt put on right? It’s really easy to be a tooth out when refitting it as when you tension the belt things move... I’ve done it before and ran for a few months with the belt a tooth out, my car was lacking a bit of power and not as smooth so it was before...