ok last time, i might give up

M

mh11

Petty Officer 2nd Class
Joined
Oct 19, 2008
Messages
126
Hello there, thank you to all of you that have helped me. This hopefully is my final post.

1978 galaxie 22xl with merc 260 chevy 350 crate motor with 110 hours on it now.

Was pulling around 4000 rpm with the 17p prop on boat with a stuck exhaust valve, and actually one of the plug wires off. Don't know how I got there with 6 out of 8 cylinders, but that is the fact. Boat backfired at wot.

Took comp test after fixing stuck valve, all cylinders within 10% of one another. Things seem good.

A friend of a friend who was an auto shop teacher for 35 plus years, helped me get everything back together, set the timing at 6 degrees btdc, check all wires, points, etc, and got it running smooth at idle, everything seems perfect.

My problem is I can go 95% throttle at around 3200 rpm with 17p prop on boat. Soon as I mash the throttle down all the way, maybe hit 3300-3400 boat backfires. Back off the throttle to around 3200 rpm, and ran perfect for an hour no problems......supposed to be around 4200-4600 at wot correct?

Now I thought lean condition causing backfiring, checked fuel pressure has 5-6 pounds of pressure, that should be good according to what everyone has told me.

I went two steps richer on secondary metering rods. Still backfiring....WTH??

My friend gave me vaccum gauge to test. This should tell me whether I have another valve problem correct? The backfire is coming out the carb which should indicate sticking intake valve, or possible lifter problem, or weak or broken spring correct?

This is my last ditch attempt to get this boat running smooth, I got this for a steal, I don't want to dump anymore hideous amounts of money in to it, or I will just sell it.

Please help!!!!

Thanks!!
 
B

BF

Lieutenant
Joined
Apr 8, 2003
Messages
1,489
Re: ok last time, i might give up

dunno how much help this will be... but here's a story...

My dad had a 4 cyl mercruiser that he fought with for about a whole season. It seemed to idle fine, but lacked power and would occasionally backfire. I was out visiting him when he was going through carb adjustments (again) and switching to his old distributor cap/rotor etc etc. Still the same. As he's doing this I'm flipping through the manual and notice the diagram that shows the firing order of the cylinders. I check, and sure enough he switched 2 wires around by mistake at some point in the past (probably when he put a new cap on the season before). He was sure he hadn't made the mistake, but I asked him to humor me... Once it was correct, we had to re-set the idle mixture etc, (which he had monkeyed with and got it to idle pretty good), biggest change was improved power and lack of backfiring. We were both surprised that a 4 cyl motor ran as well as it did with 2 wires swapped.

So... I'd double/triple check the wires and that the firing order is correct.

Good luck!
 
Apollo75

Apollo75

Petty Officer 1st Class
Joined
Sep 2, 2009
Messages
272
Re: ok last time, i might give up

Give us a little more information on when this first started. Also, crate engine --- marine or car --- did you change the cam to marine --- etc.

Why was the valve stuck ?

Boat sitting in water ---- rusted valve stem --- weak valve springs --- rebuilt engine ?

OFM
 
M

Maclin

Admiral
Joined
May 27, 2007
Messages
6,761
Re: ok last time, i might give up

The spark plugs can show a lean condition. You would have to run it a while at the top rpm then shut it down as soon as you can with as little idle time as possible and take them out and look at them.

It could still be a valve train issue. You might have even flatted the cam, chances of that depend on how it was broken in and then used at first.
 
J

jtybt

Senior Chief Petty Officer
Joined
Aug 5, 2009
Messages
730
Re: ok last time, i might give up

maclin has a lot of good points.

Carb? Q-jet?

Sounds like secondary spring too loose and opening too fast and too much. Next time you're running(have someone else driving) open flame arrestor and close secondary trap doors a little to see if it runs better. Be careful, with full throttle, if this is the problem, the boat will lurch forward with full power.
 
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