cant figure this out. any help is appreciated

[avanti16]

so after tons of reading and researching for about 2 months. Im throwing in the towel and asking for help fomr the gurus on this site..

engine: 1987 mercruiser 120. Clean, previous owner always had is professionally serviced ( i have ALL the receipts) .
Boat sat for a couple years with a little bit of gas in the tank with fuel stabalizer.

The problem: it was a b*tch to get her started when i got her. Changed the coil, condenser, points, and cap and she fired right up. Wires are new, plugs are in good shape and are getting great spark.

while on muffs the engine runs good, great at times, but mostly good. on the water, different story. It would bog and hesitate the first day i brought her on the water to test her out. so im thinking ok carb rebuild time. BUT for about 10 min or so half way through the trip she woke up and took off like a bat outta hell!! after that, hard starts and more hesitation.

What Ive done: Rebuilt carb, all new filters, seafoam added to a full fresh tank of gas, checked the plugs over and over, the gap was set at about .050 so i regapped to .035 but it didnt really change anything. checked for air leaks, checked to see if choke is operating properly, checked timing and its at 6 degrees. all fuel lines were replaced when boat was winterized, this guy was a fanatic with this boat. ive adjusted the idle mixture screw to spec.

Question- when the engine is not running, i hit the gas and i get a steady stream into the carb, but when its running the stream seams broken or like a mist and not constant. could it be a possible faulty accelerator pump in my kit?? and would that explain why shes sputtering and hesitating?

Thanks in advance guys!

 

[fat fanny]

Re: cant figure this out. any help is appreciated

The key to a good carb re-build is to make sure it is extremly clean! so that being said did you use a good carb dip? did you wash all parts in soapy water before and after each dip followed by blowing all orifices out with compressed air? Making sure wash,blow out and repeat will improve your chances of success. Just using spray carb cleaner isn't gonna cut it and a carb re-build is a 50/50 shot at success. If all this has been done then before firing up check all fuel lines,pump pressure, pick-up tube and it's screen,anti siphon valve and vent for blockage,leaks and functionality.

 

[mpdive]

Re: cant figure this out. any help is appreciated

Two things.......You never mentioned water seperator. Fresh tank of fuel does not eliminate water and contaminants. Have you taken a fuel sample, say a mason jar full, to get an accurate read on the fuel? Secondly, the stream will not appear as strong from the accel. pump with the engine running since there is partial atomization going on. If your seeing a strong steady stream key off, you have the same stream key on. In a case like yours, after verifying good fuel, you can run the boat off an auxillary tank. This serves the purpose of eliminating all fuel system components from the pump back. (anti-siphon valve, fuel pickup, etc. Sounds like your on the right track here but it's best to make sure all tune up settings are to spec before condemning a sub system. Were the points set with a dwell meter? Was timing procedure correct for that engine?

 

[ktbarrentine]

Re: cant figure this out. any help is appreciated

Have you ruled out a leaking fuel pump diaphram? They get old, they get brittle, and they dont like to sit for a long, long time in a gas-bath. Just another easy diagnostic thing to rule out early.

 

[avanti16]

Re: cant figure this out. any help is appreciated

my day of diagnosing was cut very short by rain, gotta love nj lol.. im going to bypass the fuel system and see what happens. i checked out the fuel pump when i replaced the filter in it and it looked ok. according to my reciepts it was replaced in 2009. A fuel/water seperator is on my list of next things to buy lol.. when i rebuilt the carb i soaked it in carb dip overnight, pulled it out, cleaned out the passages with compressed air and carb cleaner, then let it soak for another day and a half and blasted every crevice with compressed air. you could eat off the inside of the bowl. i have an outboard tank im gunna hook up when the rain stops here. hopefully its that easy. the gas i lose when i disconect the fuel feed line ill catch it a mason jar and see what i got... if theres water in the fuel it should seprate correct? water on top of gas?

 

[ktbarrentine]

Re: cant figure this out. any help is appreciated

Gas on top of water (gas weighs less)..... Just for info, I recently replaced my fuel pump and it lasted a whopping 7.5 engine hours before the diaphram failed on it... It can "look" fine, but could be sending gas to the carb through the sight-tube (easy to check, but engine needs to be running). Just sayin, and you may have already ruled that out... Good luck on the separation test...keep us posted!

 

[mpdive]

Re: cant figure this out. any help is appreciated

my day of diagnosing was cut very short by rain, gotta love nj lol.. im going to bypass the fuel system and see what happens. i checked out the fuel pump when i replaced the filter in it and it looked ok. according to my reciepts it was replaced in 2009. A fuel/water seperator is on my list of next things to buy lol.. when i rebuilt the carb i soaked it in carb dip overnight, pulled it out, cleaned out the passages with compressed air and carb cleaner, then let it soak for another day and a half and blasted every crevice with compressed air. you could eat off the inside of the bowl. i have an outboard tank im gunna hook up when the rain stops here. hopefully its that easy. the gas i lose when i disconect the fuel feed line ill catch it a mason jar and see what i got... if theres water in the fuel it should seprate correct? water on top of gas?

Sounds like you were very thorough with the carb rebuild. Auxillary can is a good diagnosis tool. As Kt mentioned, look at the clear tube from the pump to ensure there is no fuel in it. I'm curious on the fuel sample. Keep posting your progress.

 

[achris]

Re: cant figure this out. any help is appreciated

....Boat sat for a couple years ...

Have you checked the advance mechanism in the distributor? It consists of a couple of weights on springs. Time sitting may have frozen them up... Pull the cap off the dissy and give the rotor a twist. It should be easy to move, then check that you have the full advance curve.

 

[avanti16]

Re: cant figure this out. any help is appreciated

sorry i forgot to mention checking the clear tube, it is empty.. i got some time to do the fuel test and it checked out ok, no seperating or anything. so i did the aux. tank test just to confirm. Little bit of fresh gas added to the tank, maybe 1/4 gallon. started the engine with the hose in the aux tank, ran like crap, reved it a little bit to get the gas flowing faster and she started clearing up, then she was running pretty good, great throttle response reved easy and idled good. aux tank started getting low so to confirm sh*tty gas i added the jar of test gas to the aux tank contents, ran fine for a few, i repeated the reving and then it ran like total sh*t. RPMs dropped to about 500, lost the throttle response and the whole engine was shaking. it resembled a cold start.

I havent checked the weights in the dist. but thanks for that info ill check that asap.

I checked the accelerator pump stream again while the engine was off, and its strong and steady. Im going to replace the plugs with NGK's.

Also, there were about 5 gallons of fuel in the tank when i bought it. the previous owner "said" he put stabalizer in there, but this guy was so not mechanically inclined im suprised he can open the cap on the bottle. so if that gas sat for 2 years or longer it could have broken down even with stabalizer in there right? Im gunna fill the aux tank and perform this test again, it just wasnt long enough for me to feel comfortable taking her on the lake again, thank god for trolling motors on calm days lol.

I also wanted to add that when i did the aux tank test, i was shutting the engine off for a min or two and starting it back up because i was having problems on the lake with starting after shutting down. And while doing this the motor almost always caught when i would let off the key, or stop turning it and kind of catch hard, if that makes sense. Maybe im just useto car engines lol

Thanks for all the help so far guys, im gunna try and keep this thread going so anyone in the future who finds themselves in my shoes might get some info from it.

 

[achris]

Re: cant figure this out. any help is appreciated

If the fuel is that old it will have lost some of the lighter elements, and the octane value will have dropped, significantly... Not surprised you were having run quality problems... Good catch...

I guess now the hard part comes, cleaning out all the rubbish from the tank. Is it removable?

Chris...........

 

[avanti16]

Re: cant figure this out. any help is appreciated

update: syphoned alot of the gas out today, the gas in the bottom of the tank was BLACK!! so just guessing this is where my problem was, we shall see when i clean the tank out and run some fresh gas through it with a can of seafoam. I dont think the PO had put in stabalizer. It makes sense now thought, when running at any rpm it would hesitate and then pick back up and then hesitate again, so what was happening was the pick up tube was gettin good and bad gas, right?

 

[achris]

Re: cant figure this out. any help is appreciated

You are going to need to replace all your filters now... I'd also be looking at removing all the fuel lines, fuel pump and carbie and giving them a clean out too....

 

[avanti16]

Re: cant figure this out. any help is appreciated

will do.. thanks for the advice, ill keep you posted with any more findings/problems!

 

[avanti16]

Re: cant figure this out. any help is appreciated

sorry for the delay, lot of things going on so couldnt get the boat out..so i cleaned everything, new filters, cleaned out the fuel tank and put fresh gas in. took her out on the lake and she ran great! hit 4500 rpms at full throttle which i think is the operating range. had a couple hard starts but she seems to be running alot better. thanks for the help guys!

 

[Don S]

Re: cant figure this out. any help is appreciated

Here are the starting procedures from an owners manual. See if this might help in your starting procedures.



4 Place control handle in NEUTRAL.

5 Push THROTTLE ONLY button and position throttle setting as follows:
COLD ENGINE - Move control/throttle lever to full throttle, then return to about 1/4 throttle. In extreme cold
it may be necessary to pump lever more than once.
WARM ENGINE - Move control/throttle lever to 1/4 throttle position.
FLOODED ENGINE - Move control/throttle lever to full throttle. Be prepared to decrease engine speed to
1000-1500 rpm as soon as engine starts.

6 Turn ignition key to START. Release key when engine starts and allow switch to return to RUN position.

7 Carbureted Engines - Move control/throttle lever back to decrease engine rpm to 1000-1500 rpm if necessary.

8 Check oil pressure gauge immediately after engine starts. If oil pressure is not within specified range (see
SPECIFICATIONS), stop engine immediately and determine cause.

9 If engine is cold, run engine for 1 or 2 minutes at fast idle (1000-1500 rpm).

 

[wrestling coach]

Re: cant figure this out. any help is appreciated

If you are using today's Ethanol fuel could any of your 1987 fuel system components be affected by the long time it spent without being run. I'm thinking fuel pump and rubber fuel lines if any. Just thinking out loud.

Dennis

 

[avanti16]

Re: cant figure this out. any help is appreciated

thanks for the info Don!