Strange activity on 50hp Merc. 2001 outboard 4 stroke

[ttreewalkerr]

Engine runs good till last 1/8 throttle.... I can get her up to 4800 RPM, sometimes on certain weathered days 5000 RPM,, but then to give the last 1/8 throttle I can give it a quick push of the throttle it will take that extra gas from the "plungers" squirt, and run up the RPM for about 2 seconds then bogg down in RPM... I can pull back and it runs fine again...
I suspect that it is leaning out last 1/8th throttle..

i have cleaned the carbs good, soaked them and dissassmbled... carbs are good still had same problem....

Can the fuel pump go bad like this ?? I mean can the fuel pump function good most of rPM range and have problems at WOT ???? This is my last option i can think of.... Max fuel flow seems to be the thing im trying to diagnose....

I'm looking for input on this issue,, is the fuel pump a good next option ? Reason i ask is it's a 70.00 try at it.....

Awaiting replies !!!

Cheers, Todd

[redtech]

has this always bin like this or has it just started?
to put my two cents in sounds as if a cylinder isn't firing because of fuel or spark

[RMSOSF]

What altitude are you at?

Try two things. First try pumping the primer ball at full throttle and see if the engine spools up. If it does, then you have either a fuel restriction (clogged fuel line or fuel filter, water in fuel etc...), clogged fuel tank vent or bad fuel pump.

If that does not work, then there is a possibility that the carb has the wrong high speed jets in it, the throttle linkage between the carbs is not adjusted so the carbs open exactly synchronus or there is still some crap blocking the high speed jets.

[ttreewalkerr]

I bought the boat used, 2002,, it sat for 2 years, carbs were gummed... I took it upnorth and it would only go 5mph,, it did this same problem at 1/2 throttle.... I had comapny at the cottage so i did a quick fix and took off carbs used a bent fish hook and chipped the had mold off the jet hole, it was D shaped on 2 of the 4 carbs.... It then ran great other than this 1/8 from WOT.... i enjoyed the rest of the week and it runs great,, no missing on cyliders cause i did the plug pull theory to see if 1 bad plug.. All cyinders firing.... So weeks later i took off the carbs (4)....
Took them all apart soaked each one in special gallon of soak w/ basket from auto parts store,,Wow looked good,,, carb sprayed all little ports in the carb,, spayed my eyes more than twice... Was so cleaned i said if it does it again it's not the carbs.
Same thing,, runs great till 4800-4999 RPM then does sound like it leans out and chokes to about 3000 and will stay there and sound like crap,, i usually quickly just pull back to 4800 and runs smooth and great...
Fuel starvation is the onlt thing i can think of...... Vacum to the tank i don't think so just cause when im at 4800 and just to test plung it WOT it will run to 5200 for 2 seconds then pull back,,, i think the plungers squirt that raw gas in and pasify it for the 2 seconds then leans out...
What do you think ???

[ttreewalkerr]

I did have my wife bring it to 4800 RPM,, i hung off the back and started squeezing the bulb, (it was a mid squeez strike and it was hard to the point i could not do a full squeez), so i just massaged it was all it could do cause it was non squeezable at 4800RPM,,,,, anyhow i did do this then yelled WOT to her,, same thing 2 seconds or 1 second statred to run and pull back to nothin...

This non squeezable bulb at 4800 RPM,, it this a clue ? Just mushy to mid squeez,, not fully squeezable.

[Frosty]

Youve got a tank pickup filter blocked,--or half blocked.

definately fuel starvation.

Can you borrow another tank and pipe to try?

[redtech]

if it was the pick up the primer bulb would go flat and not be hard
? ttreewalkerr said that if held at wot the engine chokes back to 3000 rpm and stays there if this happens every time then its not fuel this sounds as if the warning system might be engaging but why? if it chokes back to 3000 rpm and comes back then it's fuel
not sold on fuel i'll get back to it at lunch

[Frosty]

[QUOTE=ttreewalkerr;

This non squeezable bulb at 4800 RPM,, it this a clue ? Just mushy to mid squeez,, not fully squeezable.[/QUOTE]

I take this to mean that it was part flat!!

[ttreewalkerr]

the bulb is definetly not flat, it seemed like it was,, if you were plug both ends and you were to sqeeze a bulb,, that how it felt... Squeez and it just seems to expand or deform to give me the illusion im sqeezing it 1/2 way.. thats a better description.

At 4800 RPM,, then plunge throttle to WOT, it will run up to 5200 then lean out in a way like out of gas (1-2 seconds),, run like complete crap and it just wont be neccesarrily 3000 then humm,, no maybe 3500 struggle then drop right to a stall or a different low RPM then definetly wants to stall... I can just tell it's not good at all on the engine. im thinking lean cause the buterfly is open suckin in the air and no fuel to mix and it compounds the problem as RPM lowers.
So for fast driving i usually will run it up to 4500,, then bump till i start to feel it do it's pull back,, then just bum the lever just a little back and it runs awsome, at roughly 4800, plenty fast. now on certain weathered days it will do this at a slightly higherRPM, just a typical Carborated issue w/ atmospheric pressure.... Just for tubing situations it would be nice for that extra throttle im missing....

[ttreewalkerr]

Maybe the bulb valve is trashed... Even just sitting in storage you can't pump the bulb....
Do these go bad ?

[redtech]

jack frost i thought that at first myself but couldn't copy thy problem
ttreewalkerr yes the bulb can go bad eather by the rubber hardening or the valves inside not working
if possible try using a portable tank to feed the engine and seperate boat from engine do not use boats fuel line this will tell you boat or engine is the place to look ? what is the fuel pressure at the carbs at wot before and after the engine starves out

[RMSOSF]

still sounds like carbs to me. Possibly the passages leading from the high speed jets to the inmmulsion tube. I could also be an improperly set float level in the carbs.

[ttreewalkerr]

I think i will check the easy thing first,, bulb... Easter I will be going upnorth Michigan to get away,, i will remove bulb and inspect. Also good look at the gray hose from tank to fuel pump,, i heard these hoses can fray apart on the inside causing restrictions.

[Frosty]

Cant you borrow another pipe bulb and tank to try?

Tell your local friendly workshop your problem and put a suitable deposit on one for an hour or two.

I dont like the cleaning carb story with a fish hook at all. If a another bulb and tank doesnt fix it then you need a full carb job.

[redtech]

i agree with jack frost, other tank to test. something isn't right find out boat or engine then take nother look at the one that has the problem. if it run good on other tank then look at the boats fuel system if if doesn't run on the other tank check the engines fuel system (carbs, pumps, and hoses)

[Frosty]

When the engine is running both the bulb and the valves with in are just letting fuel pass through.

The bulb and its internal one way valves work only when you pump it up for starting.

It is possible that an internal valve in the bulb is partialy blocked, stuck.

It may also be that someone has fitted an inline filter under the cowling and this is partialy blocked.

[ttreewalkerr]

This is a upnorth cabin it's at,, right now it's on blocks and begining in May i can get it in water... There is no one really around to borrow a tank from...

But one fact, the bulb should pump,, it does'nt,, it's like a mushy stress ball that just deforms no colapsing.

When the floats are full and floats are up,will that stop the bulb from pumping ?

Or does this no pumping bulb raise a flag ?

[ttreewalkerr]

Remeber in my previous post that i did the bulb squeeze at hi RPM, same stress ball feel,, no real pumping.

Thats gotta be it.

[Frosty]

You can buy replacement bulbs, and if the pipe is old and hard replace that too.

While its up on chocks take the tank apart and clean it. Try blowing into the tank, it should be quite free.

[ttreewalkerr]

still sounds like carbs to me. Possibly the passages leading from the high speed jets to the inmmulsion tube. I could also be an improperly set float level in the carbs.

I went up to check out boat, still on blocks, bulb seems fine, squeezed it and it worked properly. Heard gas shootign in the carbs as i squeezed... Hose is still new looking.. 2002...

Like i said i cleaned the carbs real good last year still had the problem.. Could it be float improperly set ? All other RPM ranges runs fine,, just high RPM is the problem..

[ttreewalkerr]

Could float adjustment cause this problem ? Not enough fuel ?

Bowl runs out and leans the engine ?