1970 merc 800 starts easy, runs weak...

[ozarkjeep]

compression is 120 in each cylinder, plugs are good, plug wires are good, has good hot spark, new fuel pumps, carbs cleaned out.<br /><br />timing at idle is 5 degrees, carbs almost closed, adjusted max timing to 20-21 degrees, throttles opengin all the way up.<br /><br />engine starts easy, and idles good, after appling throttle it just doesnt rev up.<br /><br />fresh gas, 50:1, bulb stays hard.<br /><br />any ideas? IM ready to sink it and start over.

 

[papasage]

Re: 1970 merc 800 starts easy, runs weak...

sounds like a gass probablem . rebuild carbs .

 

[Clams Canino]

Re: 1970 merc 800 starts easy, runs weak...

Assumong all else is right:<br /><br />How are the idle needles set? Too lean and it'll fall on it's face accellerating.<br /><br />Also is it overpropped for the boat? Try dropping a couple pitches.<br /><br />-W

 

[Clams Canino]

Re: 1970 merc 800 starts easy, runs weak...

Also try borrowing another gas tank and line. I've seen that before.

 

[ozarkjeep]

Re: 1970 merc 800 starts easy, runs weak...

Its got whatever prop came on it, the engine came from a 19ft fiberglass ski boat, its now on a 16 foot aluminum boat, I dont think its any over propping issue. It has ran slightly better than this before, but that was with the max timing around 30 degrees max ( the way the engine came to me)<br /><br />are you thinkg starved for fuel with the tank fuel line swap?<br /><br />I have bypassed the fuel fitting, and ran a line straight into the top fuel pump... it is a brand new tank, bulb and line.? I guess it could be insuffecient for the engine..<br /><br />the idle/air mixture screws are about 1 5/8 each, if they were lean would it not eventually catch up and rev a little?<br /><br />ideas and suggestions are welcomed and appreciated!

 

[Clams Canino]

Re: 1970 merc 800 starts easy, runs weak...

I always try another can to eliminate the external fuel system is all.<br /><br />Try them at 2 1/4 - sometimes they won't catch up.