Engine Cough

[Mr Pharmacist]

Hello,

When idling my engine occasionally 'coughs' - i've attempted to show it in the short video below - about half way through there's a high pitched squeak type nosie - thats the cough. it seems to come from the right hand carb?

it seem to happen more when the engine has been running for a while and is hot.

it s fine when the revs are up - no sign of it at all there, and the car goes very well. th eonly other engine issue i have is backfiring on decelaration - occasionally it makes similar slight cough, but more often than not its much louder.

can anyone offer suggestions as to what i can look at to try and solve this problem?



Many thanks
Stuart

[912uk]

hmm it's almost like a little miss fire. I would have said

valve adjustment ( mine does this alittle when cold once warm it stops and I can only think it's valve related )

The timing and the disy it's self what are the points like are they propperly set up..

carb wise how old are they to their last rebuild? as this could be more of the main problem

[Mr Pharmacist]

I did the valve adjustment a few weeks ago, but have done 2000 miles since - it seems to have got a bit worse (i.e. its does it a bit more often) the more miles i've done - i should check the adjustments again i guess.

Its got a petronix iginition system, so it shouldnt be the points etc?

and carb wise - i dont know when they were last rebuild to be honest - perhaps they've never been touched since they were first installed.

Whats involved in a carb rebuild? is it something i can do or do they have to be sent to the professionals?

[tjbates]

Thank you for the replies.

I spent a good few hours after work playing with the car tonight and I found that even thou I had tightened the distributor clamp fully, when the engine was warm it was really easy to turn. I check the timing and it was not where I had set it previously (which was 33 degrees advanced at 3000+ RPM which meant I was getting approx 1-2 degrees advance at 900RPM).

I removed the distributor and clamp, detached the clam from the distributor and then armed myself with a hammer. I then 'tapped' the clamp until it offered a tighter fit.

I have now re-installed said clamp and distributor (with a slightly tightened fit, re-set the timing to what i said above and so far so good...

I have ordered a new clamp to try and stop this happening in the future.

[neilbardsley]

Thank you for the replies.

I spent a good few hours after work playing with the car tonight and I found that even thou I had tightened the distributor clamp fully, when the engine was warm it was really easy to turn. I check the timing and it was not where I had set it previously (which was 33 degrees advanced at 3000+ RPM which meant I was getting approx 1-2 degrees advance at 900RPM).

I removed the distributor and clamp, detached the clam from the distributor and then armed myself with a hammer. I then 'tapped' the clamp until it offered a tighter fit.

I have now re-installed said clamp and distributor (with a slightly tightened fit, re-set the timing to what i said above and so far so good...

I have ordered a new clamp to try and stop this happening in the future.

Is the distributor seating correctly? Are you sure it's the clamp? Are the two end of the clamp touching when you tighten it? Have you tried put a spacer inbetween the clamp and distributor? Perhaps like a strip of rubber. Like the type that I get with a new bike light to clamp it onto the handbars? Do you have a cast iron distributor? If not perhaps you need to be careful not to over tighten?

Sorry if you have already checked all the above.

[neilbardsley]

Hello,

When idling my engine occasionally 'coughs' - i've attempted to show it in the short video below - about half way through there's a high pitched squeak type nosie - thats the cough. it seems to come from the right hand carb?

it seem to happen more when the engine has been running for a while and is hot.

it s fine when the revs are up - no sign of it at all there, and the car goes very well. th eonly other engine issue i have is backfiring on decelaration - occasionally it makes similar slight cough, but more often than not its much louder.

can anyone offer suggestions as to what i can look at to try and solve this problem?



Many thanks
Stuart

I had something similar in my 912 and I advanced the timing a little which helped. I'm wondering if you should check the points gap as maybe they have narrowed and your timing is a little retarded?

I've also swapped out my 009 distributor for a 123 with a 022 curve which gives me more torgue lower down the rev limit and it has pretty much stopped coughing. However, it still takes a couple of minutes for the engine to warm up before all is running well.

[mycar]

Afternoon Stuart, did you get to the bottom of this ?

Sounds like a bit of a carburetor sniff to me, take the air filters off and have a listen.

If it is a bit of a sniff or a cough from the top of the carb, the engine's running a bit lean on one or more cylinders, maybe there's the smallest bit of rubbish in a idle jet or the carbs need a bit of a tweak to bring them back into tune.

Are they Webers or Solex ? Here's some info on both from over at the Registry...

https://porsche356registry.org/article/47

https://porsche356registry.org/article/48

And if I can reduce a pair of carbs to their component parts and put them back together so they're better than were before.... Then so can you my friend, so can you. But I'm sure that's not necessary just yet, maybe just a clean and tune will suffice

Regards, Mike..

[Mr Pharmacist]

Blimey you lot know how to rub it in - almost a year to the day that i sold my 912 and you start advising me how to fix it!!

[mycar]

2008 ! How did that happen ?

Time travel, brought to you exclusively by DDk.

What would you tell your 2008 self ? Never mind carburetors... buy more RS's

Mike.