1978 Mercury - Reed Valve Check

[kb67]

Hello, I have a 1978 Mercury that I bought from the original owner after sitting for a few years. Had it for a few years and it never has run quite right. Rebuilt carbs, fuel pump, some wires, replaced stator, rectifier,trigger, coils, and check switch box with know good one. Tried gas tank and primer bulb from my other good running boat (1982 50H Merc) I've had various problems, but now it seem to not want to idle in neutral, and the RPM's aren't steady when I give it gas. When I spray some gas in the upper carb it revs up (bad, right?) but the lower carb doesn't do anything when I spray gas in it. I checked out the upper carb again and it looks clean and the float is set correctly. Out of process of elimination, I would like to check the reeds. Can I at least inspect the reads by taking the crank cover off? Do I need to pull the crank out to replace them, or can I sneak the read blocks out once the cover is off? The Seloc manual says complete overhaul is needed, but I really don't want to do that if I don't need to.
Thanks for the help.

 

[racerone]

In order to work on the reeds you need to remove the powerhead from the exhaust housing.----It is not a simple job.-----Reeds rarely fail for both cylinders.----Do more trouble shooting.

 

[enginepower]

Carbs "looking" clean doesn't mean anything. The jets are tiny holes that feed fuel through passages to the engine. Any single circuit in that is restricted or partially restricted, it will not allow proper fuel deliver. If you are sure everything is good in the carb, adding fuel and making it rev up can be caused by an air leak. Possibly top crank seal leaking? That usually produces heavy oily film all over top of engine. Of course, reeds could still be a problem not pulling fuel due to lack of suction across carb. Not really a way to check reeds without pulling them unless you see a bunch of spit back coming from that carb. A compression test doesn't tell you anything about reed condition either.

 

[racerone]

If sprayning fuel into the bottom carburetor does nothing you may have a spark issue.---A broken reed valve would only affect one cylinder and the reed block feeds both #3 and #4 seperately.----Plug wires on correctly and is there spark that will jump a gap of 3/8" on all 4 cylinders ?

 

[kb67]

Thanks for the comments. I forgot to add compression is 120 on all cylinders. Also, when I do run the engine it does seem to go through a lot of gas which pushed me towards the reeds a bit, but that may just be because I was running at high rpms.
I've checked the spark gap before with a checker and it was good (7/16, blue spark). My plug wires are a little suspect, I'm pretty sure they are original. I will check the spark again and retest since I've gone through the top carb.
Going on vacation and going to be using my dad's boat next week...will tackle when I get back.

 

[kb67]

Back from vacation and back at it...after a couple of hours of messing with the carbs with a friend (which helped things a bit) finally decide to do the spark check. All cylinders good except for #1. #1 does fire when checked with a timing light, but would not jump a 1/4" gap or less on the spark checker. I swapped plug wires, coils, and jumpered the wired from the trigger without any help. Got dark so I turned in for the night. I'm guessing the next thing I should do is swap trigger outputs, right? It seems odd to me that only one cylinder would have a week spark if swapping coils did not do anything.

Thanks.

 

[kb67]

Sorry, meant to say jumpered the wires from the switch box with no improvement.