Recently purchased boat in poorly running condition (would start and briefly rev up, but would not idle). Engine is 454 magnum w/ Bravo drive, 1989 model yr. Transom exhaust.
Have removed and thoroughly cleaned carb (and checked that it has all correct jets)...its a q-jet by the way; adjusted idle and rich/lean mixture screws...now idles great at 650-750 rpms.
It seems to have a major intake leak:
- very loud "hissing noise" at all engine speeds
- vacuum gauge is steady but low (10-11)
- hesitates or backfires under load/acceleration at around 1800-2500 rpms
Anyways, my first step was to replace carb to intake gasket (I had re-used old one, assumed it was bad from re-using multiple times so replaced)....that did NOT fix hissing noise / vacuum readings. Next step was to spray carb cleaner around intake....did NOT change engine rpm at all despite spraying generously around carb and intake to head spots. Cannot feel intake leak anywhere.
QUESTION - should I just assume it is an intake leak, replace gasket for intake to cylinder head, and re-diagnose? Or are there other "tests" I should do before doing this. Looking for input here......
It also has an exhaust leak on the starboard side exhaust manifold (I can visibly see this). Planning to replace head to exhuast manifold gasket and see if problem persists.
Comments and answers please...thanks...
Have removed and thoroughly cleaned carb (and checked that it has all correct jets)...its a q-jet by the way; adjusted idle and rich/lean mixture screws...now idles great at 650-750 rpms.
It seems to have a major intake leak:
- very loud "hissing noise" at all engine speeds
- vacuum gauge is steady but low (10-11)
- hesitates or backfires under load/acceleration at around 1800-2500 rpms
Anyways, my first step was to replace carb to intake gasket (I had re-used old one, assumed it was bad from re-using multiple times so replaced)....that did NOT fix hissing noise / vacuum readings. Next step was to spray carb cleaner around intake....did NOT change engine rpm at all despite spraying generously around carb and intake to head spots. Cannot feel intake leak anywhere.
QUESTION - should I just assume it is an intake leak, replace gasket for intake to cylinder head, and re-diagnose? Or are there other "tests" I should do before doing this. Looking for input here......
It also has an exhaust leak on the starboard side exhaust manifold (I can visibly see this). Planning to replace head to exhuast manifold gasket and see if problem persists.
Comments and answers please...thanks...