Mercruiser 170 in the 2019 season - Now Bogging
 

So, this past summer saw the v20 in various states of repair work. First firing up of the season uncovered a leaky timing cover from the cam seals. Redi-sleeved and replaced the seals with little problem.

PRO-TIP - Go rent a crank pully puller from the auto store prior to starting. You'll need it when you reinstall the crank pully too...
Also got the fuel tank sucked out and flushed and cleaned up.
Discovered that the block off plug on the exhaust runner (casting hole/access? was rusted out. Repaired that.

Finally got on the water this past Sunday. Floats, Idles, shifts into gear

all OK. Get out into the channel and bring up the RPMs - Bogs and Falls flat.

WTF!!!!!??? Anyway - idled back to the launch, tried some things, went back out, came back in and put it back on the trailer, all in 30 minutes.

Went home, pulled the dizzy, checked that the weights were free, rechecked the timing, etc etc.
Went out today and picked up another carb, (Mercarb for a 120/140 though...) threw that on, idles great, but still same bog. Annulars are dropping fuel in - I thought it would be more of a mist, but it's more like sloppy drops. Didn't rebuld this 2nd hand carb yet - literally sprayed some dust off it, sprayed some silicone in it, worked the accelerator pump, slapped it on, plumbed it up and started up.



Did not pull the spark plugs, did not check compression. yet.


So that's where it stands on Sep 3rd. Any advice? Anyone want to come drink beer and speculate on repairs here in Norfolk?



Pretty discouraged, but still hopeful :D

Sounds like a fuel issue to me, but I'd still check the plugs and make sure they're clean and properly gapped. That's easy and quick.

Did you replace the fuel filter/separator when you flushed? I presume yes. Filter, pump and fuel supply lines would be my first stops. Also check the tank vent line to make sure it's free and clear.

After all that I'd measure the resistance on the plug wires and make sure you're not getting a cold spark.

I have that engine - have you checked the screen in the carb where the fuel line attaches?

Thanks for the replies
 

Fuel Good - Filters Good - Pump Good, no junk in carb screen, vent good. I am now suspecting coil / dizzy and will be checking that today. I don't believe I am running a 3ohm coil. It is a flamethrower, but it was one I had kicking around from my 6-cyl mustang.


Of course it's impossible to run down to a store and find a pertronix 3ohm coil...

I was wrong above. FUEL PUMP BAD. Ran on a electric carter pump I had laying around. Perhaps this weak pump is why I was not seeing fuel transfer from idle to the venturis. MUCH better.
Sheesh. ALSO - Cleaned and lubed dizzy counter weights - that was an issue as well. Still need to get a 3ohm coil.

Glad you pinpointed it! :clap:

Took old fuel pump apart - top diaphragm cracked, bottom diaphragm not much better looking.
Sierra 18-35437 Fuel Pump is not the right replacement for this engine. Not sure if it purports to be, but the cross reference I found listed it as one... not. Wrong cam lever for one... Wrong port orientation for 2.
My engine is A678730 - Listing Fuel Pump: 8M0073435 which is proper.


This looks correct:

https://boats.net/product/mercury/8M0073435

I got the same motor, was thinking fuel pump too. Glad you figured it out. Check Ebasicpower, I've bought a lot of parts from them. They will get them to you quick!

Getting back to my fuel pump... AMK Products makes a complete carter rebuild kit that looks like the correct dimensions, but with an extra check valve for the mercruiser application. I've ordered a new OEM one, but I'm going to get one of these kits and try it on my old one.


https://www.deadnutson.com/carter-hi...p-rebuild-kit/ << the comments here talk about mercruisers...



Great instructions -> https://www.428cobrajet.org/how-to-fuel-pump

https://www.cjponyparts.com/67-and-u...-1967/p/AFP67/

The AMK Kit Works - AFP-67 - Rebuilding the OEM part is a possibility. Everything fits, proper dimensions. :sun: