Experience Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.
Organizations Associate member SAE
EAA member
Publications Import Car magazine
Education/Credentials ASE Master Auto with L-1 certification up to 2000
I've checked the following:
Dwell 35
Timing 4 ATDC
Vacuum 14 hg and steady (brake booster disconnected & plugged gauge connected to anti-run valve port)
Compression: 90# all cylinders w/ throttle plates closed.
Plugs gapped at .025
Idle set at 800rpm
Carb mixture setting 1 turn down from full rich.
Carb's are in sync.
Car missing at all speeds, but not a steady miss. Seems fine under load. Any Ideas? Thanks Craig Jones
ANSWER: HI Craig,
You are giving me confusing info, "90 PSI compression test with the throttles closed is useless info. (not much air in= not much compression)
and I don't understand "Carb mixture setting 1 turn down from full rich".
You need to hold the throttle open to do a compression test since almost no piston gas engine will run below 100 PSI.
The method to set the mixture is to lift the spring loaded pin just under the side of the each carb and note the response, then adjust the mixture as per the response. If the engine speeds up and stays fast the OTHER carb is too rich, if the engine dies you either didn't get them in sync or the OTHER carb is too lean. When the OTHER carb is correct the engine will drop off and run slow and sound like a two cylinder engine running slow. It is advisable to rev the engine a little between each test and adjustment. (most books don't tell you that you are checking the other carb.)
Howard
---------- FOLLOW-UP ----------
QUESTION: Thanks for the quick response.
I re-did the compression test with the throttles open and the results are as follows #1-120#, #2-120#, #3-110#, #4-120#, #5-90#, #6-120#... Looks like rings are in order. Know any recommended mechanics in Washington?
Thanks Craig
Answer Craig, you should either have a leak-down test done to get a better idea as to weather the low cylinder (#5) is low because of a ring problem or a valve problem.
An additional "Wet" test is in order. You can do this by just squirt about 4 or 5 squirts of engine oil in a plug hole and do another compression test on each cylinder. If you see a lot more than 10% to 15% higher readings then there is a good chance it is a ring problem. If the Wet test are not more than the 15% then it is a valve problem and you can just do a head repair.
Sorry, I'm in Tenn. and I don't know anyone in Wash.
Howard
