1975 70hp Evinrude has no vacume in cylinder

[timayres]

Motor has spark and 120lbs compression in top cylinder but when I put my hand over the top carb it makes almost no difference in the way it runs. the other two carbs are very sensitive. I tried spraying gas in that carb but it doesn't change. I don't think it is a fuel supply problem. Any suggestions would be appreciated.<br />Thanks

 

[foxjohnc03]

Re: 1975 70hp Evinrude has no vacume in cylinder

I'd check the gasket between the engine and carb and on the actual intake side. Could also be a reed problem.

 

[harley909]

Re: 1975 70hp Evinrude has no vacume in cylinder

How does the motor run otherwise? Is it running OK or has no power, or ........?

 

[timayres]

Re: 1975 70hp Evinrude has no vacume in cylinder

The engine runs as good as could be expected on two cylinders

 

[marinegrh]

Re: 1975 70hp Evinrude has no vacume in cylinder

what is the compression on the #2&3 cylinders, you say 120 on #1, ??????????

 

[timayres]

Re: 1975 70hp Evinrude has no vacume in cylinder

#2 is 120lbs and # 3 is 115lbs. I was told by someone today that it is possible that the skirt of the piston is wore out or groved. Is this likely?

 

[marinegrh]

Re: 1975 70hp Evinrude has no vacume in cylinder

having a borescope laying round is slim to none, might want to try an look into this a little futher, id pull the carbs and check the reeds, your compression, good as it is, leads me to think we should look at the easier steps first, 2 bolts and the carb is off, look carefully with a flashlight at the reeds, make sure they are all there and against the stops, you can poke them with a finger or lightly with a screw stick, id would also consider pulling the head, unfortunately there is no bypass covers on that engine, if you have a spun sleve the compression will still be there, but nothing else, how is the engine reacting to full power, ????

 

[timayres]

Re: 1975 70hp Evinrude has no vacume in cylinder

Additional info: I have only had this boat in water one time. At that time the carb housing around the air mix screw on the lower carb was broke and I spent my time messing with the lower carb and finally got the motor to move past idol. It ran good on mid and upper end. I took it home and fixed lower carb and then realized the problem with top carb. I have it hooked up to a hose and it runs at idol like you would expect on two cylinders. I do think it starts to pick that cylinder up a little as the idol increases and I assume it will work at high speed.

 

[The Marine Doctor]

Re: 1975 70hp Evinrude has no vacume in cylinder

When you remove the #1 spark plug...what does it look like? <br /><br />All Wet???? I am thinking you do not have adequate spark on #1 cyl.<br /><br />TMD

 

[marinegrh]

Re: 1975 70hp Evinrude has no vacume in cylinder

MD has a good point, run the engine, and with a good pair insulated pliers remove th ign wire to the # 1 cyl, does the enginge drop rpm, if so, your getting fuel and fire, i think you need to be more descriptive with your problem, it sounds like so many things could be happening

 

[timayres]

Re: 1975 70hp Evinrude has no vacume in cylinder

I had just put new plugs in it. after running for a while the top plug still looks new but if I hang the plug and start the motor it has a good spark. My thought was the plug was firing but it wasn't burning anything. Even if I didn't have spark I have a hard time understanding why I wouldn't have any suction on the carb?

 

[The Marine Doctor]

Re: 1975 70hp Evinrude has no vacume in cylinder

Alright..concrete evidence.<br /><br />IF the spark is not wet at all..there is NO gas getting to it. Remove the top carb and take a peek at the reeds.<br /><br />If they are ok...Remove the front bolt in the carb and see if fuel comes out.<br /><br />IF the reeds are fine. You will have to recheck the compression on that cyl.<br /><br />As you stated before...you sprayed that cyl an nothing happend...provided there was spark.<br /><br />Also...when you put your hand on the carb...does it suck at all?<br /><br />TMD

 

[ob]

Re: 1975 70hp Evinrude has no vacume in cylinder

Tim,This may sound like a dumb question but since I can't see the engine and you made no mention ,have you insured that the carb flap is opening on that cylinder?Also a very clean plug in relation to the others may be indicative of water ingestion on that cylinder.I realize that your compression reading was 120 on the one in question.

 

[timayres]

Re: 1975 70hp Evinrude has no vacume in cylinder

I took this boat to the lake this weekend. I adjusted the carbs several times. The bottom two adjusted great but the top one barely changed. I had to set the idol a little high to keep it from dying when I put it in gear. Mid and high speed are great. The plugs look good and the same on all cylindars so evidently the top is working fine above idol. The compression was 120lbs on the top two and 100 on the bottom. The motor did make a noise at the lower end of acceleration that sounded like piston slap to me, but once it wound up it sounded great. My guess is the motor is worn out. Is there anything else I should try? If it is a worn piston in the top cylindar can it be changed without tearing down the whole motor? I realize this wouldn't be a very good way to do it but could it let me use up the rest of the motor?

 

[Solittle]

Re: 1975 70hp Evinrude has no vacume in cylinder

http://www.outboardrepairs.com/carburetors/

 

[The Marine Doctor]

Re: 1975 70hp Evinrude has no vacume in cylinder

When you say you adjusted the carbs...Are you turning that screw in the front..that houses the fixed yet????<br /><br />If you have the carbs I think you do...you do not have adjustable low speed jets. All 3 screws are to be tightend.<br /><br />TMD

 

[timayres]

Re: 1975 70hp Evinrude has no vacume in cylinder

Each of the carbs have an adjustment screw in the front top of carb. They all seem to run best when turned approx 3/4 turns out. On the top carb this screw makes almost no difference but the other two are very responsive. If I turn either of them in the engine will die.

 

[The Marine Doctor]

Re: 1975 70hp Evinrude has no vacume in cylinder

Are you sure its a 1975?<br /><br />TMD

 

[The Marine Doctor]

Re: 1975 70hp Evinrude has no vacume in cylinder

If you do have the adjustable jet carbs...you will have to remove the top one and take it apart and clean it up. There seems to be no fuel getting to the cyl for low speed.<br /><br />TMD

 

[The Marine Doctor]

Re: 1975 70hp Evinrude has no vacume in cylinder

It would also appear that you have poor compression on #3 cyl.<br /><br />TMD