1991 force 150 flooding bad

jspana

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Sep 2, 2015
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8
Hello, New to the posting but long time lurker. First off thanx for all the write ups they have helped me in the past greatly. I purchased a new boat and it has a force 150 on it, While out on her maiden voyage we had lots of "carb issues" hesitation, bogging, stalling, etc. Really only wants to be just off idle or wide open. The main issue is that it is dumping raw fuel from the prop exhaust. I noticed this when i was washing it down and saw it pouring out! then calculated and found we went through 40 gallons of gas in 4hrs of trolling! yikes. I have since checked spark and compression, all really good, cleaned the carbs which were nice and clean. I now have the top two carbs off and the reeds out, only on one reed pedal you can see minor daylight through would that be much of a problem or is it somewhere else? Thanx in advance for any help out there.
 

pnwboat

Rear Admiral
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Oct 8, 2007
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4,251
Sounds like you may have excessive amount of fuel going into the engine.

Could be a carburetor needle valve that isn't closing off the flow of fuel. Either because the float level is not adjusted correctly, or the needle valve itself is bad, or maybe a piece of crud is stuck on the tip of the needle valve preventing it from closing. You should have an in-line fuel filter between the fuel pumps and carburetors.

Also a fuel pump diaphragm could be torn or have a hole in it dumping fuel into the motor.

Maximum gap for the reed petals I believe is something like .010 inch. You're probably OK.
 

Frank Acampora

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Jan 19, 2007
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Reeds are usually allowed to stand open about .010 at rest. So a little crack of daylight on a couple of reed petals would be considered normal. The bigger problem is why is it dumping that much fuel?

Remove the fuel pumps and examine the diaphragms for holes or cracks. In fact, they are cheap. replace them as normal maintenance. Check all fuel lines after the fuel pump for cracks and leaks. Check the enrichment valve to see if the red lever is in "Manual" position. This is a small cylinder with very small fuel lines running from it to the carb bowls. It may have a manual button on top. Crimp the hoses shut and see if that helps the problem If it does, the enrichment valve is stuck open and must be replaced.

Of course, remove the carb bowls and check that the floats are moving properly. Hold them up and see if they block fuel when the primer bulb is squeezed. If the do not the carbs must be cleaned and the needles possibly replaced.
 
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jspana

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Sep 2, 2015
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Thanx guys, It turns out its the fuel pump diaphragm, didn't think to check it because it was running good at WOT, figured that if the pump was bad it would starve for fuel. Pulled the vacuum line off the block and hit the primer bulb and fuel PORED out of the upper pump vacuum line!! guess the lower pump was good and was feeding the motor and the crankcase through the upper pump. Ordered the parts today and Ill post back on how it turns out next time I hit the water. THANX AGAIN!
 

jspana

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Sep 2, 2015
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Ok, got that sorted out, bypassed the second pump and ran it on just one. What a difference it made! runs pretty good now.. had a really high idle but it was not touching the timing tower cam so i found that the carb linkage was off and two of the three carbs were more open than the middle one. I fixed that and its idling better, still slightly high but better. The exhaust burns your eyes so I know its fat, im guessing it has something to do with the idle too. What should the carbs mixture screws be set at as as starting point to tune this thing? Ill take it out on the lake after it get the fuel pump parts in for a timing and final tune but Im sure someone has been in there twisting screws :( just need a base line to get it all back in order . Thanx
 

Frank Acampora

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Jan 19, 2007
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The pumps are in series and if one is not working there may be a loss of performance. You are feeding three carbs and a lot of cubic inches (about 125). That is why the factory put on two pumps. They did not add in extra money just because it looked nice.

Do NOT run the engine at full throttle with only one pump. There is a danger of running lean and doing damage. If you absolutely must run before ordered parts come in, do yourself a favor: Go down to your local Mercury dealer and get another diaphragm and gasket--probably 5 bucks for the two and they should be in stock.

The idle mixture screws should be started at about 1 1/4 to 1 1/2 turns out from lightly seated. Then, slight adjustment either way for best idle. Do not go less than about 7/8 turns out from lightly seated.

AS far as carbs not closing all the way in neutral, there should be a spring-loaded quick connect on the throttle cable. This should be adjusted so there is about 3/16 to 1/4 inch of the center slug pulled out at idle. This will apply pressure to retract the timing tower.

Watch my video called Tutorial at the top of the forum. It shows how to synchronize carbs and timing. If you can not access it from there, youtube Frank Acampora videos
 
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jspana

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Sep 2, 2015
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Thanx Frank, Yes I know the second FP is needed, I have the parts on the way. I just plan on getting the carbs in order at the house at low speeds before getting the boat wet. The bar that connects the carbs is what was holding them open at different amounts, the middle carb was closed, the top was barely open and the bottom was like 1/32 throttle.. I loosened the screws on the bar and let all of them close with the tower cam out of the way then set the bar screws. This helped greatly. I then spun the eccentric screw back till it just barely made contact with the tower cam. This is where i am at now, it is much better. I know i still have to do the timing like you have in your video but i need to get the rich issue under control first. You are a great help and im very appreciative to have some of your time here. thank you.

Oh and what should the cylinder compression be @ ? mine was averaging about 145psi in all 5.
 

Frank Acampora

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Jan 19, 2007
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12,004
145 PSI on a 91 150 would be excellent. Accepted common knowledge says 10% difference between cylinders is acceptable. Nothing to worry about there.
 

jspana

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Sep 2, 2015
Messages
8
Hey thanx for all the help guys! Have had a few great trips out on the water with friends and family! I'm learning lots about this boat and motor the more I get to use it. Last time I was out the motor just cut out completely, no warning or anything. It fired right back up too, it did this twice then I noticed my voltage was low. I made it back to harbor fine. Upon inspection I found that one of my battery cables was loose, I have duel batteries so I'm not sure if it mattered. . The motor runs great but dies when the battery is unplugged and it's not charging. Any ideas?
 

pnwboat

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Oct 8, 2007
Messages
4,251
Depending on what ignition system you have, the battery connection may be the culprit.

If you have the Prestolite ignition system with the 5 light blue colored coils and 3 light blue colored CD modules, then the stator supplies the ignition voltage. This ignition system will run without the battery connected. The battery's only functions to operate the starter, gauges and accessories

If you have the Mercury ignition system with the 5 dark blue almost black colored coils with a switch box and battery converter box, then the battery supplies the ignition voltage. If you don't have a good battery connection with the Mercury ignition system, the motor will die. You can purchase an aftermarket stator that does away with the battery converter box so that the stator supplies the ignition voltage so you don't have to rely on the battery. Note: the battery converter boxes are getting hard to find these days. They are no longer made and the only ones out there are mostly used ones and some folks are asking prices that would make you think that they're made out of pure gold.

So if you have the Prestolite ignition system, it's probably just a coincidence that the motor dies with the battery disconnected.

If you have the Mercury ignition system, you must have a good fully charge battery and fully functional charging system.
 

jspana

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Sep 2, 2015
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ugh.. looks like Mercury Ignition system for sure. So the battery has to be hooked up and charged to run the boat?! Ok well at least I have two big deep cells. is the converter the same as the rectifier/regulator? would that be a good place to start throwing money at or do you think the stator might be a better starting point?
 

pnwboat

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Oct 8, 2007
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The battery converter box and the Rectifier/Regulator are two separate components. Below is a picture of the battery converter box. I would be hesitant to throw any money at it right now. Double check and make sure your battery connections are all good and clean. Don't just do a visual check. Take the connections off and look at the underside and clean with a wire brush. Don't forget the ground lug that attaches to the block. If it does it again after checking all the battery cables, then you can start trouble-shooting.

battery converter box.JPG
 

jspana

Cadet
Joined
Sep 2, 2015
Messages
8
Yeah I have that same box on it. We took off the regulator and cleaned it real good and sanded the mounting points to help get a good ground. Didn't seem to make a change after being out on Sunday. Ill do the converter box when I get home and see how it goes. Thanx again for all the help.
 
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