I thought I'd start a little thread on this in the tech department.

I'm really struggling to get my 343 to behave and idle properly. I feel like this is a fairly basic thing, so I've hesitated in asking for help, but no matter what I do it just doesn't quite behave right. I will set out a description of the behaviour, and see if someone more qualified than me has any ideas.

The first thing to say is that the car generally is run with the vacuum pipe to the clutch disengage servo disconnected. This is how it was when I got it. The following description is for when the clutch disengage servo is therefore not connected to vacuum.

No matter how I set the carb (mixture screw and idle speed screw), the car runs at idle with an uneven put-putting from the exhaust. It feels rich, all the time. It needs full choke just to start, and very quickly copes with a lot less. The old spark plugs I took from the car were very sooty. From the inside of the car, the idle is acceptable. It drives fine and overdrives beautifully. However, if I hold the car at standstill on the brake, the idle immediately becomes shaky, and the car vibrates. It's not a huge problem, I just put the handbrake straight on, but it doesn't feel right, and consequently I don't feel like I can fully trust it.

I shall add to this mix a different issue, which I have mentioned before, which is the engine speed when letting go of the throttle. Now '77 cars don't have a tachometric relay; instead they have a switch on the carb which is triggered by the throttle, as soon as the throttle is engaged, the switch operates to energize the overdrive solenoid. It works fine, apart from when I relax the throttle. So for example, when cruising at 30mph, and I approach a speed camera, I might want to slow to say 27-28 just to be on the safe side, so I slightly relax the throttle. The revs immediately shoot up and the engine is extremely noisy, even though the car is slowing down slightly. It takes a long time after that for overdrive to take hold again at the new lower speed, and for the engine speed to reduce to a normal cruise. Now I understand that this is how it is supposed to operate, but the revving seems excessive to me. Any thoughts?

Now, a third issue. The pesky vacuum pipe for the clutch disengage servo. When I reconnect this properly, the car seriously vibrates at idle, to the extent that my legs resting on the floor when siting in the car are moving independently. I have been out for a good while playing with the carb settings to see if I can cure the vibration, but the best I can do is increase engine speed beyond what feels normal, and that reduces it slightly. It's still unacceptable. Pressing the brake pedal makes no difference in this situation, as it's already very vibrat-y. I'm a little scared to take it for a drive when it's like this in case it shakes itself to a stall. The exhaust pipe is still very put-putty. I have checked, and all the vacuum pipes are properly connected, as far as I can tell.

Interestingly, the gears don't crunch at fast idle whether the clutch disengage servo is connected or not!

I would be grateful for some thoughts and ideas!

S10NPH wrote:I'm really struggling to get my 343 to behave and idle properly.

Welcome to the world of the early "complicated" 343's. If you mean that they behave different compared with the post 1978 cars you are absolutely correct.

S10NPH wrote:The first thing to say is that the car generally is run with the vacuum pipe to the clutch disengage servo disconnected. This is how it was when I got it. The following description is for when the clutch disengage servo is therefore not connected to vacuum.
No matter how I set the carb (mixture screw and idle speed screw), the car runs at idle with an uneven put-putting from the exhaust. It feels rich, all the time. It needs full choke just to start, and very quickly copes with a lot less. The old spark plugs I took from the car were very sooty. From the inside of the car, the idle is acceptable. It drives fine and overdrives beautifully. However, if I hold the car at standstill on the brake, the idle immediately becomes shaky, and the car vibrates. It's not a huge problem, I just put the handbrake straight on, but it doesn't feel right, and consequently I don't feel like I can fully trust it.

The fact that your car is running rich, may be a good thing as the unburnt petrol will actually help to cool the pistons in the engine. Have you checked the vacuum circuits? I have a feeling that you may have a leak somewhere. The clutch disengage servo (white box on the inner wing) is identical to the ones on the later 300's so you can swap that one out with a "younger" sample. Is the electrical circuit that controls the clutch servo and the EMV still working? Mind you, the high pressure switch on the brake booster is different to those on the post 78 cars.

S10NPH wrote:I shall add to this mix a different issue, which I have mentioned before, which is the engine speed when letting go of the throttle. Now '77 cars don't have a tachometric relay; instead they have a switch on the carb which is triggered by the throttle, as soon as the throttle is engaged, the switch operates to energize the overdrive solenoid. It works fine, apart from when I relax the throttle. So for example, when cruising at 30mph, and I approach a speed camera, I might want to slow to say 27-28 just to be on the safe side, so I slightly relax the throttle. The revs immediately shoot up and the engine is extremely noisy, even though the car is slowing down slightly. It takes a long time after that for overdrive to take hold again at the new lower speed, and for the engine speed to reduce to a normal cruise. Now I understand that this is how it is supposed to operate, but the revving seems excessive to me. Any thoughts?

This is normal and the exact reason why Volvo introduced the tacho relais. The only thing that I can suggest is that you make sure that all of the vacuum related parts work correctly and that all of the electrical contacts are clean. Reading the fact that the engine revs shoot up leads me to believe that the switch on the carb still works. I believe that Volvo described a way to set up the switch on the carb properly to keep it from overrevving but I'll have to look that up.

S10NPH wrote:Now, a third issue. The pesky vacuum pipe for the clutch disengage servo. When I reconnect this properly, the car seriously vibrates at idle, to the extent that my legs resting on the floor when siting in the car are moving independently. I have been out for a good while playing with the carb settings to see if I can cure the vibration, but the best I can do is increase engine speed beyond what feels normal, and that reduces it slightly. It's still unacceptable. Pressing the brake pedal makes no difference in this situation, as it's already very vibrat-y. I'm a little scared to take it for a drive when it's like this in case it shakes itself to a stall. The exhaust pipe is still very put-putty. I have checked, and all the vacuum pipes are properly connected, as far as I can tell.

Interestingly, the gears don't crunch at fast idle whether the clutch disengage servo is connected or not!

Is the vacuum pipe to the clutch servo capped when it is not connected to the servo? If so I have a feeling that the servo is buggered and gives you a vacuum leak.

S10NPH wrote:Interestingly, the gears don't crunch at fast idle whether the clutch disengage servo is connected or not!
I would be grateful for some thoughts and ideas!

Is the clutch gapped correctly? Assuming the clutch disengage servo is NOT connected, I can imagine that the clutch doesn't care whether it's the idle speed that's high or if it's you pushing the accelerator. If the clutch is only connecting at very high revs it might be worth while checking the shims.

I can't imagine the gears not crunching, on a correctly gapped clutch without a functioning disengage servo.

Cheers

Tom

trabitom99 wrote:Is the clutch gapped correctly? Assuming the clutch disengage servo is NOT connected, I can imagine that the clutch doesn't care whether it's the idle speed that's high or if it's you pushing the accelerator. If the clutch is only connecting at very high revs it might be worth while checking the shims.

I can't imagine the gears not crunching, on a correctly gapped clutch without a functioning disengage servo.

Cheers

Tom

Tom, You're right, I overlooked that possibillity.
Can hit myself with a hamer for that.
And knowing that most owners don't know that that needs to be checked as well...

Thanks guys - I have to confess that I have realised that I have misled you slightly. I had forgotten that when I first got the car, the gears were crunching all the time. I lowered the engine speed and so the crunching stopped. Perhaps I ought to invest in a timing light so I can adjust the engine speed accurately, rather than just using guesswork.

volvomania wrote:Is the vacuum pipe to the clutch servo capped when it is not connected to the servo?

It's like this:

A posh timing light could be used to set the RPM or a Maplins automotive multimeter (has an inductive pick-up) 25 quid http://www.maplin.co.uk/module.aspx?moduleno=222059

I know you don't do accessories, otherwise I'd suggest a clutch of worry gauges and you can worry about what's going on all the time you're driving

Thanks Rich, that's a really good idea, I will get one. I think I also ought to get a vacuum gauge, so I can carry out the diagnostics and adjustments needed - does anyone have any guidance on what I need? Will something like this do what I need: http://www.ebay.co.uk/itm/Vacuum-Gauge- ... 1e79a0eaf9