New 350 Merc Long Block problems

asgrinne

Petty Officer 2nd Class
Joined
Jul 16, 2002
Messages
105
Ok here is the scoop... Timing is as 8 degrees btd center 32 degress at 3000 rpm.<br />We have checked double checked the timing. Carb changed props.  <br />Boat runs starts idles runs low rpm great. <br />Tested again with 600CFm top rpm. Had the carb cleaned checked etc to make sure its good. <br />Put a Edelbrock 5000 intake manifold on. <br /> <br />3600RPM with 21 Mirage<br />4000 RPM with 19 pitch <br />Clean Bottom, bottom painted. <br />Exhaust seems fine with no restrictoons. <br />The old motor ran a 21 Mirage at 4700 RPM approx 50mph<br /><br />Fuel pressure 5.5 6lbs<br />All fuel lines are good and clean <br />Fuel filters are all good<br />The anti siphon seems to be working fine. <br />checked the linkage it is fully extending. <br /> <br />We put a 750 Holly on just to test the possibility of the the cab being to small. <br />Zero change <br /><br />Can anybody think of anything else we can check. <br />It just never gets going. I really think we should be able to get the rpms higher? With more power behind it. <br />The guy we got the motor from says its at least 310 horse. We are simply baffeled at any other things that could be hosing it up. <br />Thanks very much in advance.
 

jmccall001

Petty Officer 2nd Class
Joined
Feb 23, 2005
Messages
103
Re: New 350 Merc Long Block problems

if you are playing with the prop try a 17 pitch, that should bring your rpms up to abt 4400. close to specs for the 5.7L
 

rbezdon

Senior Chief Petty Officer
Joined
Jun 20, 2004
Messages
689
Re: New 350 Merc Long Block problems

Sure you dont have a dirty bottom or an exhaust restriction. See many of the posts and solutions for FreebyTony, especially the suggestions from Don S on the exhaust restrictions. (Check the flappers!!)
 

asgrinne

Petty Officer 2nd Class
Joined
Jul 16, 2002
Messages
105
Re: New 350 Merc Long Block problems

If you are one tooth off on distributor would the timing appear correct and read "right" would that cause the no top end problem
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,074
Re: New 350 Merc Long Block problems

anita, If you are off a tooth, the timing would be off as well, and you would turn the distributor body to adjust it.<br /><br />Are all the plugs firing? I hate to say it, but do you have good compression in all cylinders? It just sounds like a tired engine, rather than a new one.
 

whywhyzed

Banned
Joined
Feb 1, 2005
Messages
1,871
Re: New 350 Merc Long Block problems

a thousand pounds of water under the floor boards?<br /><br />what cam went in the engine? cam out a tooth?<br /><br />compression test it just for laffs..
 

asgrinne

Petty Officer 2nd Class
Joined
Jul 16, 2002
Messages
105
Re: New 350 Merc Long Block problems

engine has a Marine melling performance cam and lifters your cam spec is 220@50 with a 110 lobe separation <br /><br />Not real sure what this means. But does that help? <br />We are going to check the resistor angle now.<br />Boat is dry
 

Borre16610

Recruit
Joined
Aug 23, 2005
Messages
1
Re: New 350 Merc Long Block problems

Ive had the same problem. The valves was too tight..I friends new long block had the same. Both GM 350s<br /><br />Borre
 

rbezdon

Senior Chief Petty Officer
Joined
Jun 20, 2004
Messages
689
Re: New 350 Merc Long Block problems

that means .220 inches of lift at 50 thousndths clearance. 110 degrees of cam rotation between the intake and exhaust lobes. Sounds like a very stock cam. Search for a posting by me on cam specs, ralph posted the marine, car and truck specs for roller and flat lifters. You can compare. Cam lift is then multiplied by the rocker arm ratio to get valve lift. Stock rockers are 1.5 to 1 so your getting .34 lift. Low for marine I think but check the posting to make sure.
 

Fishermark

Vice Admiral
Joined
Oct 19, 2003
Messages
5,617
Re: New 350 Merc Long Block problems

I would definately do a compression check before doing much else. <br /><br />
The guy we got the motor from says its at least 310 horse.
I don't know if you have posted something else in another post, but if this is a used engine you have installed, or even a "rebuilt" engine, it could simply be low compression. Either from being old and worn out, (like me with every passing day :D ), or from improper break in.
 
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