Communication always better in person than phone than text than email than psychic. :wink Arctic friends mentioned what is more likely.

I’m looking for/finding more issues for you and poss things that are adding to it.

Again, most people with engine issues have rigging issues. Been here for almost 20 yrs and been around boats/cars/most motorsports for 42yrs ?

as far as the grey linrs, again.’some new aftermarket one’s inner liner melt away almost instantly. Lot of junk china **** surrounding us.

I believe the current standard black fuel hose fir enclosed compartments is A1 ? Soneone pleas correct this. Use this from table to inlet of the oe placed filter /water separator.

Just a thought, but how bad was the backfire? Is there any binding with the throttle linkage? If there is it is possible the throttle blades are bent.

Again, dont dismiss the old gas and fact you have over 10-1 compression with iron heads, small cam or your next post will be detonation related, very important! I tell all my customers I tune boats for, you need to take o2 readings unless your real good at reading plugs and most people are not. Theres no reason NOT to take 02 readings running under various conditions, it tells you everything. work your way up on total timing, with your compression I will guarantee you will have spark knock with anything more than 32 or 33 on 87, Smitty

The thing is, it was running good for 20 minutes then something seemed to have something happen to it.


Next time we go to trial it, I'll too off tank with fresh 93

No way that cam is causing low vacuum. It should idle at 700rpms easily.

Merc used Weber carbs on the 7.4 and 454mag for several years in the 1992-1994 range.
The Weber carbs used on both of them are EXACTLY THE SAME.
454mag https://www.mercruiserparts.com/bam/...31802/1621/140
7.4 https://www.mercruiserparts.com/bam/...31914/1621/140

I somehow missed/forgot his compression info. Thanks for bringing it up.

10:1 or more in a cruiser no less. Anazing how many times people do this. People are forgetting (or not learning) about old school engines faster then ever it seems.

try finding someone to work on carbs!!! Old timer here at work (he's 80) has a 1969 mustang that wouldn't run right...took it to two different shops where he said there was an "older guy" that knew how to dial in a carb.....never had it run right. He was told to replace the carb at the first place so he bought an edelbrock.....second place told him edelbrocks are junk he needs a holley and a new intake manifold....so that went on next....still didnt run right. told him to bring it to work and lets have a look at it. First thing i see is the manual choke plate is not hooked to anything! and half closed.....zip tied it back....then hooked a vac gauge to the manifold and started playing with the mixture screws. They were each out like 5-6 turns! ran them all the way in then out 1-1/2 turns and started playing...mistake i made on that one was not checking the float levels first! They were way too high and as soon as i took the screw out of the float bowl it was pouring like a faucet. Anyway straightened it all out and now he actually drives the car! He's had the thing for almost 40yrs and has driven it maybe a handful of times in the last 10yrs cause it never ran right and was always frustrating him

^^lol. ^^^

Since i seem to miss stuff on this thread, did we compression test after the overheat ? Wouldn’t be first time head gasket blew between cyl’s from doing so.

My understanding IF im reading the information posted correctly: motor was overheated then repaired again
18 cc domed 4.280 bore pistons
113 cc peanut ports, IF motor was overheated they had to have been milled/surfaced at least once
block, again, if bored, rebuilt and overheated at one time deck clearance went closer to zero from its original .022-.028 in hole
I ran thru compression calculator, over 10-1 with iron heads, with a small cam thats design is to build torque by spiking cylinder pressure
we run over 10-1 on aluminum headed motors with 20, 30 dgrees more cam duration , strictly on premium
no knock sensor so no way to hear /tell if its knocking
only way it will live is jetted fat to mask the detonation with good premium
buy a 02 bung, put it in a riser, see what you cruisng afrs are and wot, id jet the hard cruising into mid 12's and the wot in mid to maybe upper 11s with that compression with iron heads

I also want to say from memory when I dynoed a motor 5 years ago here with really similar intake that #3 was one of the burn down lean cylinder on my afrs, we blamed it on the sharp turn in dual plane, fwiw