1979 70HP fuel delivery problems continued

[Mike7970]

I have a 1979 70 HP Merc. Long story short...it sat for a couple of years. I took it to a mechanic<br />he cleaned and rebuilt carbs and a few other no fuel related things. When I got it back it would<br />not idle too well and it would bog down on acceleration then correct itself and run great until I <br />dropped down to idle speed. Sometimes it would cut off on take off but would crank again easily.<br />I was told to replace the fuel line and bulb. Done but no change. I was told to rebuild the fuel<br />pump. When I did that I discovered that I was sucking air at the point where the fuel line screws<br />into the external tank. I corrected that and tightened the rest of the fuel line connectors and put<br />it into the water. Now it will not idle at all and stalls severly on acceleration. Does this sound<br />like I am still sucking air somewhere or something else? Thanks

 

[The Marine Doctor]

Re: 1979 70HP fuel delivery problems continued

The 70's were bad for dropping the exhaust baffle underneath the power head.<br /><br />Also check the restrictors under the intake ports.<br /><br />TMD

 

[Mike7970]

Re: 1979 70HP fuel delivery problems continued

Thanks. I am going back to the mechanic today and hopefully he can straighten me out. I think that I may have trash in the carbs again. We'll see what the pro says.

 

[The Marine Doctor]

Re: 1979 70HP fuel delivery problems continued

Ppppsssstttt.<br /><br />I am a Pro.<br /><br />TMD

 

[Mike7970]

Re: 1979 70HP fuel delivery problems continued

Sorry, I meant my local pro. Based on all the useful info I have found on this site it seems that there are many pros on it and some **** good amateurs. And thanks to this website and my well worn Clymer's manual I am on my way to being a better marine mechanic.

 

[SeaHorse]

Re: 1979 70HP fuel delivery problems continued

What's an "exhaust baffle underneath the power head" and how do you "drop it". How do you check for this?<br /><br />How do you "check the restrictors under the intake ports?". What the heck are restrictors?<br /><br />Thanks.

 

[The Marine Doctor]

Re: 1979 70HP fuel delivery problems continued

To check the exhaust baffle you must remove the powerhead.<br /><br />The restrictors are underneath the intake port on the starboard side of the engine. <----The cover runs the length of the powerhead and is usually held on with 1/2in bolts on 65-70hp engines. The fuel pump is mounted on it aswell.<br /><br />3cyl engines 1 cover 1/2 bolts<br />4cyl engines 2 covers 7/16 bolts<br />6cyl engines 3 covers 7/16 bolts<br /><br />TMD

 

[petryshyn]

Re: 1979 70HP fuel delivery problems continued

Mike<br />I'm not a pro, but another thing to check is for sagging motor mounts. Remove the engine cover and see if idle improves. If it does, you may have sagging motor mounts which can allow exhaust gases to enter under the engine cover....this will cause rough idle and stalling.....

 

[Mike7970]

Re: 1979 70HP fuel delivery problems continued

I got the boat back yesterday (nearly 3 weeks in the shop which is why it has been so long since I posted this subject) dropped it in the water at lunch time and it ran the best it ever has. Basically, my local mechanic found that one of the nipples that a bleeder hose slides onto was broken. I hope this update helps others with similar hard to diagnose fuel troubles. Thanks to all that offered suggestions.

 

[SeaHorse]

Re: 1979 70HP fuel delivery problems continued

Thanks for the update. I was about to tear my powerhead off to check my restricted baffling plates.