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Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 11052
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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Starts idles bogs down n dies under load, in water...with

Customer Question

Starts idles bogs down n dies under load, in water...with baffle runs fine.
JA: Sometimes things that you think will be really complicated end up being easy to fix. The Marine Mechanic I'm going to connect you with knows all the tricks and shortcuts. Tell me a bit more about what's going on so the Marine Mechanic can help you best.
Customer: I accidentally mixed gas 40/1 not 50/1 but it's been the same. When it dies under load, I have to crank a lot and finally it'll start then idle for a few then bog again
JA: Is there anything else the Marine Mechanic should be aware of?
Customer: Rebuilt carbs last season. Replaced fuel feed line this year
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Marine Mechanic about your situation and then connect you two.
Submitted: 1 year ago.
Category: Boat
Expert:  Tan replied 1 year ago.

Hello. My name is Tan.

Could I get the make, model and serial number of the engine you are working on please?

Customer: replied 1 year ago.
1976 evinrude 70hp 706730
Expert:  Tan replied 1 year ago.

Ok we need to start out with a spark and compression test. The spark must jump a 7/16" gap on a spark gap tester. The compression must be 90+ psi with no more than 10% difference between cylinders.

If these check good then we know we have a fuel related issue. Now there are a couple of tests you can do with engine running. When you throttle up the engine push the choke does engine pick up and run? If no change squeeze the primer bulb when engine starts to bog.

Post back with findings and questions.

Customer: replied 1 year ago.
I throttle up try n choke it and it dies. Primer bulb stays solid. Tried the bulb squeeze and it died. Also when idling for a while idle slows to almost a stall under load
Expert:  Tan replied 1 year ago.

Ok we need to do the other tests. Spark and compression.

Customer: replied 1 year ago.
Would the fact that I mixed gas ratio have anything to do with it?
Expert:  Tan replied 1 year ago.

All that would do is foul the spark plugs.

Customer: replied 1 year ago.
I'll check them tomorrow after work. And check for soot to see if it's getting too much fuel or not enough. ...I possibly gauged the carb floats off a hair.....but I'll keep you posted about 22 hrs from now....and try n find a compression tester as well
Expert:  Tan replied 1 year ago.
Customer: replied 1 year ago.
Dumb question but which of the plugs is #1...top middle or bottom. ..advance timing could be off too
Expert:  Tan replied 1 year ago.

Top is # ***** The timing should not change unless someone has been messing with the linkage. There is no reason ever to mess with the linkage.

Customer: replied 1 year ago.
I never met previous owner. My dad bought boat so Im just asking....I've been wrenching on auto's for years but 2 yc is totally new to me
Expert:  Tan replied 1 year ago.

Has the engine ever run right for you or your dad?

Customer: replied 1 year ago.
It ran but never planed out....tilt n trim was unhooked n it was a "fishing" boat. I had it plane last year, as is....but cables never let it go to wot ...new control unit does now....but the bogging started
Expert:  Tan replied 1 year ago.

Ok we have either no or weak spark or low or no compression on one cylinder.

Customer: replied 1 year ago.
Ok I'll check tomorrow and get back with you....thanks a lot! #!
Expert:  Tan replied 1 year ago.

Ok have a great evening.

Customer: replied 1 year ago.
Thank you you as well
Expert:  Tan replied 1 year ago.

Thanks.

Customer: replied 1 year ago.
Checked plugs... oily but what is the proper gapping?
Customer: replied 1 year ago.
Just wanna make sure I didn't get something wrong
Expert:  Tan replied 1 year ago.

.030-.035

Customer: replied 1 year ago.
Ok thanks. ..but what's that spark jump thing vs . gapping?
Expert:  Tan replied 1 year ago.

Open this link this is a spark gap tester. http://www.nationaltoolwarehouse.com/Ignition-Spark-Tester-with-Adjustable-Gap-P41027.aspx?zmam=31282435&zmas=50&zmac=750&zmap=THX404&gclid=Cj0KEQjwvZq6BRC9kfq2zKfQ_94BEiQAOeUVC2XyPq2yMOs1LeCKA7Y_JOMqpcrcK-IBo_e0Uwj0g_kaAslz8P8HAQ

Set the gap at 7/16" crank engine spark should jump the 7/16" gap on the tester.

The spark plug has nothing to do with checking spark.

Customer: replied 1 year ago.
Oh ok....had a brain fart lol
Expert:  Tan replied 1 year ago.

The spark plug has a small gap to fire under compression. So to accurately test the spark it has to jump a 7/16" gap on a tester. If it won't jump 7/16' you have no or weak spark.