Crusader 96’ 454 TBI low compression

How long has it had low compression? And, how long was it sitting before it had low compression? If it's been sitting a while, it may be worth it to take it out, run it for a while at cruise, run it moderately hard for a couple minutes, then test it again after it cools.

Personal opinion, I don't think you're going to be able to get lapping compound past the valve guide, and if you did, it would likely get caught in between the valve and the guide, and cause premature wear of the guide and valve.

I'd recommend waiting until you have the proper time to pull the head for a day and do a valve job. Any good shop, with notice, should be able to have the head back to you in a day. That would rule out the head gasket, valve, etc., and get a proper grind/seat/lap job on the valve.

you should have rotators on the valves so I'd say you have other issues the 'bandaid' won't help with.

using GM's updated compression test parameters, you are still in the serviceable range (but not by much).

Before tearing the top ends down, I'd suggest a leakdown test to isolate the source of the 'leak'...no point in tearing down an engine and then rebuilding it only to find you haven't made an improvement....

I bought it this way a year ago at 802 hours, pretty sure the boat sat on sideline for some time period, pretty much like new, I have added a few hours and still use it. I’m up to 978 today and hope to add more. One issue is port RPM tops out at 36-3700, and Stbd 3900. I still cruise at 30-3200. Other than compression what would keep me from obtaining normal max 4400? I’ve done all tune up things after purchase. Sounds good, starts good, bottom is clean. The leak down test sounds good. I have not checked timing at high speed added to port 12 from 10 DBTDC. No real difference noticed. During this process I found a post on the run/time plug corroded off. Next trip is when that motor backfired as it lost power restarted okay, but repeated twice more on the way home. I have been laid up for a while, back at it next week. As a youngster I remember turning the key off while running to make a backfire. That’s what it seemed like happened. I may have. Disturbed a connection while doing this last job. I plan on checking out. Distributors next not sure of the manufacturer.

my third set of these 454’s had a84 Silverton C37 for 18 years, -2000 hours when sold, 98 392 Silverton with 454TBI engines, never had to open up any of these motors, now this Tiara 31 has me on the run.

Thanks for any and all suggestions, Capfish

Tuneup, cap, rotor, plugs, wires, bad injectors, bad gas, bad fuel pump, clogged fuel lines, bad fuel filter, and most importantly, props can all effect your max engine RPM.

Some people choose to over-prop their boat, thus lowering it's max capable RPM, because they prefer how it rides and consumes gas at their optimal cruise speed with the new props... and some people goof and buy the wrong props, and after making a $1k mistake, they don't do anything about it... Are you certain that the props on your boat are factory?

With the 'new to you' aspect, unless you know that the boat was setup correctly and actually achieved 4400 RPM you may never find the cause.....many are setup from the factory when empty so normal gear and additions over the years keep adding to the load....without any adjustments.

Normally, on a well used boat, unable to get to WOT rated RPM, I'd suggest checking the timing for full advance....most of the TBI setups I've seen have the spark timing controlled by the ECU - so unless the knock sensor i driving the timing retard it usually isn't an issue...

On the backfire - the procedure you described will send it into the exhaust on a vehicle in motion.....and those are from the 'rich' mixture induced.....a pop' thru the carb (TB Unit) is typically caused by a lean condition....one 'deccriptor' for two totally different events...