poor performance... WHY

[Secondwind218]

Hey all. I am new to this site and am looking for professional advice.

heres my issue. I have a 92 bayliner with a 3liter mercruiser. Runs great idles normal at 6-700 rpms and is smooth. oil pressure is good. BUT right when get on it gives me a backfire through the carb and forces me to smoothly accelerate to avoid this backfire. i cant get this boat to go past 3900 rpms or 29mph if theres more than 3 people on my boat it wont even plane out. Theres something restricting its full performance and it is beyond me! Also My temp gauge will not go past 120 degrees. Is the fact that the motor cant properly warm the reason why its performing poorly?? does it need a tstat? is the automatic choke stuck? Not to mechanically inclined but know the basics. Has anyone had this problem before?

thanks for any nsight in advance.. Nick

 

[achris]

Re: poor performance... WHY

Sounds like you have a few issues..

1. Not accelerating sounds like the accelerator pump in the carbie not working. Strip and clean, put a kit through the carbie...
2. No more than 3900 rpm... If the boat has never done more than that, then I would suspect the prop is too big.. Post up some figures (current prop pitch, maximum revs and speed and I'll do some calculations on the prop for you)..
3. No more than 120?, sounds like the thermostat either been removed or failed in the open position... Easy to check, open up the thermostat housing and have a look...

Manual for your engine -> https://docs.google.com/viewer?a=v&...YjU0Mi00N2MyLWE1YmQtNDc5ZTllODNiNzRl&hl=en_GB

Download and SAVE... It will be you best friend...

Chris...

 

[Secondwind218]

Re: poor performance... WHY

Sounds like you have a few issues..

1. Not accelerating sounds like the accelerator pump in the carbie not working. Strip and clean, put a kit through the carbie...
2. No more than 3900 rpm... If the boat has never done more than that, then I would suspect the prop is too big.. Post up some figures (current prop pitch, maximum revs and speed and I'll do some calculations on the prop for you)..
3. No more than 120?, sounds like the thermostat either been removed or failed in the open position... Easy to check, open up the thermostat housing and have a look...

Manual for your engine -> https://docs.google.com/viewer?a=v&...YjU0Mi00N2MyLWE1YmQtNDc5ZTllODNiNzRl&hl=en_GB

Download and SAVE... It will be you best friend...

Chris...

Thank you for the quick response. Boat has done 35 before with 4 people. current prop pitch s 19. max r's ive gotten her to 4500 but never pushed it farther. max max recommended is 4800. Thank you for the Manuel.. And i plan on rebuilding the carb. including acc pump. will post results.

 

[Scott Danforth]

Re: poor performance... WHY

the backfire thru the carb is probably ignition. make sure you have new cap, rotor, wires and plugs as well as make sure the timing is correct.

the poor acceleration is either bad fuel, or gunk in the carb.

 

[achris]

Re: poor performance... WHY

the backfire thru the carb is probably ignition. make sure you have new cap, rotor, wires and plugs as well as make sure the timing is correct.

the poor acceleration is either bad fuel, or gunk in the carb.

Good advise here... Just that the backfire will be a 'lean pop', caused by the accelerator pump not working...

I'd go through and do a full tune, compression test, plugs, cap/rotor/leads if it needs it.... You know the drill....

Chris.....

 

[jopes]

Re: poor performance... WHY

a lean pop on accel is usually the carb, do a rebuild kit like said before and start there.

 

[Secondwind218]

Re: poor performance... WHY

Last night i removed the air cleaner. And immediately noticed that the choke was in the up and down position. turned the key to on and it did not move. if i understand these electronic chokes correctly shouldn't the choke be almost closed when cold then open up as the motor warms? perhaps my choke is not working.. Could this be the problem all along? besides needing a tstat.

Nick

 

[nola mike]

Re: poor performance... WHY

No, that's not your problem. The choke sets when you pump the throttle. And it should be all the way open in short order anyway once the engine starts. Only problem would be if it isnt closing and you're not able to start the engine.

 

[Secondwind218]

Re: poor performance... WHY

Well the engine starts fine, so i guess thats not it. thanks..

 

[stonyloam]

Re: poor performance... WHY

A compression check might be a good idea. In the meantime, at idle pull the plug wires one at a time and note the response, you might have a weak cylinder or two.

 

[Secondwind218]

Re: poor performance... WHY

Went to go and set timing on her today.. come to find that my crankshaft (harmonic balancer pulley) is soo banged up i cant find the notch. does ANYONE know where i can find a replacement one of these. new or used??

 

[Secondwind218]

Re: poor performance... WHY

just did a compression test. cyl 1, 130. cyl 2, 123. cyl 3 125. cyl 4, 129. so that checks out. Next is too time it. Then if that fails onto the carb. btw new wires and coil on the way.

 

[Don S]

Re: poor performance... WHY

Went to go and set timing on her today.. come to find that my crankshaft (harmonic balancer pulley) is soo banged up i cant find the notch. does ANYONE know where i can find a replacement one of these. new or used??

Any Mercruiser dealer, or site online that sells OEM Mercruiser parts can get you a new one. Without that mark, you are not going to be able to time it..