Backfiring carb issue

Chris Ellis

New Member
Sep 12, 2021
16
Boat Info
1999 Sea Ray 215 Express
Engines
Mercruiser 5.0 W/ A1
I just had the intake manifold gasket replaced and now it’s backfiring out of the carb. It’s making a “popping” noise that increases with the throttle and slows when idling down. Did something happen when the mechanic changed the gasket? The noise was not there before the gasket change and is there the first time starting it after the repair.
 
Recheck the torque on all of the intake manifold bolts that you can or straight take it back to them and have him fix it
 
It is a 2 hour trip each way to drop it off to who did the intake (it’s the guy I got the engine from). I am trying to figure out anything obvious before making that trip again
 
I know that does suck it's a long ride but he owns it and if it didn't do it before I would take it back to him see if you can set it up to where he can either redo it or fix it while you're there in the meantime recheck the torque on the manifold balls I have read in post lately that the insides were just finger tight the ones on both sides closest to the carburetor
 
So we figured out the cause of the popping issue, it was a broken push rod. Now on to the next issue. After the motor swap, I lost about 8 mph and now have trouble getting up on plane if there are more than 2 people in the boat. What would cause less power when everything is the same that went beck in. 5.0 for 5.0.
 
Is it the same year or a rebuild long block
 
The motor is 3 years older. The carb is off my old motor and most everything else is brand new
 
So we figured out the cause of the popping issue, it was a broken push rod. Now on to the next issue. After the motor swap, I lost about 8 mph and now have trouble getting up on plane if there are more than 2 people in the boat. What would cause less power when everything is the same that went beck in. 5.0 for 5.0.
Push rods don’t just break without something else going on.

Broken pushrod + loss of top end speed + won’t get on plane = you need a compression test.

Your “new” motor may be a dud.
 
I’m thinking to same thing. We did do a compression test and all were right around 150
 
Push rods don't just bend because they want too. Definitely a reason
 
Now on to the next issue. After the motor swap, I lost about 8 mph and now have trouble getting up on plane if there are more than 2 people in the boat. What would cause less power when everything is the same that went beck in. 5.0 for 5.0.

wrong cam. Slip neighbor got a deal on crate engine. Was a car engine. Could barely get on plane. Had to re-pull the engine and put in a boat cam. A 5.0 is not always the same 5.0. Sounds like his situation. Check the spec on your new one.
 
Don't know the cam spec for a marine application but would like to know. 260 horse out of a 305 Chevy is pretty good considering the small bore size compared to a 350
 
Horsepower is useless measurement on a boat engine. Its all about torque. Horsepower is a mesure of power at high rpm, torque at low rpm. High cam lift generates HP. For boat you need low long cam lift.
First thing you want to do is contact where you got the engine. Ask them straight up what application is it for? Boat or car? If they don’t know, ask for the specs on the cam. Write down, then call Comp Cams and talk to tech support. They will tell explain and advise.
I no engineer but i done enough drag racing and engine building that i telling you, my OPINION you got the wrong cam.
Allow me… why do race cars run 3.90 to 4.11 rear gears? Because the cam doesn’t make any power until high rpm and those gears allow the engine to very quickly spin up to the high power band. High HP. Useless on a boat. In a car a V8 is redline at about 6500rpm, same V8 in boat maxes at 4400 rpm, (350), lower torque, lower cam, lower power band.
 
Yeah I knew it was something like that horsepower is torque multiplied by RPM or RPM multiplied by torque something like that I'm not an engineer either but thanks anyway I appreciate it
 

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