cant find the source of my Vacum leak

[mrsoundcraft]

Im getting a lot of hesitation under acceleration!

Not sure of the source of the problem and hoped I might be able to get a few pointers and tips.

While trying to fix it I have replaced the plugs and leads, had the carb off sevel times (now replaced carb base gasket and used loads of gasket sealer) and used colour tune to check the mixture.

But its still not right!

The car now runs perfect when everything is hot (fan goes on and off) but after a few minutes of driving It starts to spluter a bit when I put the foot down. So today when this started happening I stopped and had a look at the carb, didnt do anyting but after a few minutes I starded driving again and it ran very well, but after a few minutes began to hesitate and splutter under acceleration.

The only theory that I have now is that when hot the mainfold, carb and all gaskets seal up (expansion), but with the rush of cold air passes over the car while driving the cooling effect causes contraction and opens up loads of gaps causing leaks.

What do you think? How cheaply can I fix it?

[volvosneverdie]

I experienced identical probs with my old B14.
Never managed to find the prob either.

Sorry mate, I know thats not much help, but I feel your pain.

[macplaxton]

Tis a bit chilly at the moment. When you had the carb off did you clean it all out and blow through all the jets?

I was having issues with a couple of carburettor cars before Christmas and I was leaning towards the petrol (and the <5% Ethanol that gets sneaked into it unlabelled)

But I could be talking out of my hat.

[Ride_on]

which engine?

Air leaks normally affect tick-over mostly as the volume of leak is proportionately lower under power.

1.4+1.7 Carb icing? usually takes a bit longer than a few minutes though, check your pre-heater pipes + air thermostat position.

1.7 -weak spark- oil in the distributor?

[volvodspec]

if you take the airfiltercover off and look into the barrel with the choke valve, do you see a direct jet of petrol (accellerationjet) going only in that barrel if you apply the throttle?
if that jet goes loose, it leaks petrol in both barrels so when you drive gently it starts filling the second barrel up; untill you give more throttle when it all plunges down into the engine.

[mrsoundcraft]

Thanks for the replies its nice not to be suffering alone!

I was thinking about changing the manifold to head gasket this morning but, so far nothing Ive replaced has changed anyting so I thought I'd save myself from disapointment. Anyway I know it will be coming off again soon so I'll try and give it a proper clean out this time. Im hoping the petrol is up to scratch, Ive used quite a veriety of petrol from different stations and the car has driven consistantly.

Im doubtfull that its a carb icing issue because these parts are all hot to touch, I was just thinking it was the temperature difference between hot and very hot. and I hate to admit that I have a K&N. Its also a 1.4 and every time Ive checked under the dizzy cap its been bone dry in there.

Anjo, I will have a look at this, as its interesting to note that with the colourtune under some sustained throttle the engine was running really rich, and never "leveled out" which is the opposite of what I was thinking was happening. Do you think then that Im dumping fuel in to the cylinders and soaking the plugs?

Also I do find that the issue is at lower revs or if I jap the throttle. The other thing that Is a bit odd is how long it takes for the revs to drop back down to idle if you rev it in neutral, not sure if this is normal, its not run right in so long.

[volvodspec]

if the carb is iced the engine will stall if you apply the clutch, a K&N filter unit does make the risk of getting an iced carb much higher though..

[pettaw]

If the engine is showing rich on the colourtune when under throttle, then I would suggest maybe your carb is flooding. Check the needle valve is in good condition and check the float height is correct.

Am I right in thinking you've got realy cold weather at the moment? It could be carb icing but I would check the carb properly first.

[mrsoundcraft]

Its got really cold overnight and started snowing again, so I havent even been out the house! I had planned today to look at the carb and do some bodywork up at my shed, but its freezing up there.

Im considering the possibility of carb icing, but the car has been displaying the same behavour since early September (It was still quite sunny back then).
It was strange becuase it was maybe a friday when I drove it to work, then spent the next three days in vans then on the sunday night went to drive home and it wasnt running right, so it went from perfect to faulty after sitting for 3 days.

However if you put the choke on a bit the car runs smoothly.

Hopefully have a full day of looking at it tomorow.

[Bjorn Belter]

Interesting.

My 340 Variomatic is playing up in a similar way. It starts OK, even after a few days, engine sounds sweet on tickover in neutral and even when revving it up - again in neutral, not park!

But, once in drive and trying to drive anywhere, it stutters and coughs and has little pulling power.

That's one of the reasons that I have decided reluctantly to let it go.

I'm sure there is a simplish explanation though.

[pettaw]

RIght, if you can drive it with choke on and it runs fine, but then drives like crap once you take it off, there's your problem. You've got an air leak.

Do a forum search for air leaks and there's loads of threads on them. Really common on 1.7s due to bad design leading to warpage of the carb base and/or manifold. Volvo half solved the problem by making a modified base gasket that was much thicker stopping the hot spots but that only slowed the warping down. Do a forum search and it'll tell you how to locate the leak and how to fix it.

[mrsoundcraft]

Finaly after busy month at work Ive got some time to hopefully sort this out.

Here's what Ive discovered in the last few days







The old carb-manifold gasket is falling apart.

But the carbon build up on the faces suggest to me that the manifolds weren't making a good seal with the head?

Out of interest does anyone know the torque settings for the bolts that hold these on?

[volvosneverdie]

Stupid suggestion of the day:
Is it not in the Haynes or the Green Books?

Sure ive seen it somewhere.

[CBA]

maybe not making good a good seal...

[mrsoundcraft]

Just for the record the car's all bolted back together now, after some cleaning and light re facing. Also the addition of some gasket paste.
So far its running nicely!