Compression figure

[Dave ThornleyParticipant]

Toaday seen a possible buy but have a ciuple of questions.

11 Compression reads about 90 psi on all 4 cylinders. Have read a couple of articles where yhey mention a figure of 77.7kg/cm2 this equates to 110psi. Am I worrying unjustly, all 4 cylinders were well within the 10% tolerance often mentioned.

22 On removing the spark plugs to do the test I noted all 4 were, in my opinion, somewhat sooted up. Now I ssw the car hsd a K&N air filter fitted and quite a small one. Additionally I believe the manual ignition advance/retstf switvh is never touched. Could either of these be the cause of the soot?
<p style=”text-align: center;”>Thanks</p>

[Dave ThornleyParticipant]

Sorry about the typo mistakes I am on a train.It should be 7.7kg/cms and advance/retard I was trying to say.

[BernieParticipant]

David,

The sooner you get a good car, the sooner you can ditch the train …. but don’t try to type and drive.

I would normally expect compression figures of at least 100 – but was the engine warm/hot?  If not, figures are likely to be lower.

Sooty plugs … not likely to be a function  of advance/retard but more probably mixtureof not just the result of using the choke to start but not following up with a decent run.

B….

[BernieParticipant]

I have no excuse for my typo but the last bit should have said …..

“but more probably mixture, if not just the result of using the choke to start but not following up with a decent run”

B….

[Dave ThornleyParticipant]

Thanks for the reply.  The engine was warm as had not long finished about a 40 minute trip. You are most probably correct in the soot on the plugs as I do not think it gets many decent runs and lots of little 5 minute warm ups are a recipe for such sooting. Not having ever had a vehicle with an advance/retard

I was unsure as to if possibly contributing to it.

 

Thanks

• This reply was modified 4 years, 6 months ago by Dave Thornley.

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