305 trouble

[JLAfarms]

Hi guys,<br />I have a 20.5 foot monterey with a 305 17 pitch prop. This spring I replaced the carb, intake, plug wires, cap and rotor. I have been to the lake 3 times the first two the temp outside 75 to 80 degrees water temp 50, boat ran great. the last time the temp was 102 and water temp was 75 the boat ran fine till the heat of the day then seem to back fire some with a slight miss but not all the time. Anytime it did this it seemed like I could increase throttle and problem fixed for a while. The boat also seems to be running cool at 130 or so never hotter than 135. The boat had simular issues last summer in the heat of the day but I thought i had fixed it with the intake and carb after two flawless trips to the lake this year. So do I replace the coil and ignition or what do I do next?

 

[Don S]

Re: 305 trouble

For one thing, you need to verify the temperature gauge and replace (or install) the thermostat. 130° is too cold for the engine to run, and it should be up around 160 to 170° to run properly.<br />Did you replace the sparkplugs when you changed the other other stuff? New spark plugs can also give you problems, what type did you use and what engine and drive do you have and what year?

 

[JLAfarms]

Re: 305 trouble

boat is a 1991 with a 5.0 murcruiser and alpha one or two i am not sure which. Yes the plugs were replaced with ngk ur4

 

[Richard Petersen]

Re: 305 trouble

Don. Can it be a lean carb adjustment in hot weather? A touch richer and it is gone?-------------------Air temps of 102 and more are tough on a smooth engine.

 

[Don S]

Re: 305 trouble

It could be carb adjustment.<br />But it also has the wrong sparkplugs in it.<br />Should be an NGK BR6FS plug, not sure what a ur4 goes to. Put the right plug in and it will probably work. Make sure the timing is correct and you are getting the proper advance timing.<br />You still need to address the cooling system. While the temp may show low, you probably have hot spots in the engine that aren't getting the proper flow.

 

[JLAfarms]

Re: 305 trouble

guys, what should the timing be set at and what thermostat,I think maybe a 145 ?

 

[Don S]

Re: 305 trouble

The timing should be 8° BTDC @ 650-700 rpm.<br />The thermostat you should have is 140°.<br />The Merc PN is 807252T 1

 

[JLAfarms]

Re: 305 trouble

I took the six hose housing off that bolts to the intake and the thermostat was not shuting propperly and it is also a 160 deg thermostat!<br />It appears that the thermostat is held in with a brass collar, do I just drive this collar out and get a new one? Or can I put the thermostat under this housing directly on the intake?<br />Thanks,<br />Jerry

 

[Don S]

Re: 305 trouble

The thermostat needs to be in the right location or you will really have a cooling problem.<br />There are several different raw water systems on your year engine, so you really need to get a service manual if your going to be doing your own work. Makes things a lot easier and faster, and correctly instead of just guessing.<br />Here is a link to a site for part numbers and parts breakdown drawings that may help.<br /><br /> http://dougrussell.com/partscatalog/collections/index.cfm?fuseaction=collectdetails&colid=04