mercruiser 3.7 180 hp surges at idle

[spanishmackeral]

I just bought a 87 dixie 21' walkaround cuddy w/mercruiser 3.7 180hp inboard i gave it a complete tune up (plugs,wires,points,cap,rotor,oil change,coolant change,out drive oil change) i then fired her up, it ran ok idle was a little rough and surged would idle around 750 rpms and drop to 400 and climb up to 1100 rpms so i attacked the fuel system with both hands i removed the 65 gal fuel tank drained and cleaned it then went to the fuel pump i did not have a good fuel preasure guage so i removed disassembled cleaned and inspected diaphragm a little dry rotted so i reassembled and reinstalled and yes i have ordered a new one should be in tomorrow but the old one does pump alot of fuel i replaced all the fuel filters. the carb rochester 4 barrel i noticed the accelerator was not pumping so i completely rebuilt it (soaked it,blew out all passages,clean as a whistle) reassembled completely adjusted and reinstalled set idle mixture screws, set idle. started it up runs a little smoother but still stumbles and surges at idle. ((i am baffled)) anyone have any suggestions? last night i ordered a new carb should be here fri i did not what to do next i can send it back if i don't use it. Thanks for any suggestions

 

[spanishmackeral]

Re: mercruiser 3.7 180 hp surges at idle

Here is what i came up with so far. The new fuel pump came in and i installed it pumped to much fuel 10+ psi flooded motor a second pump same thing went back to the old one i will probaly have to add a fuel preasure regulator.
I replaced coil it was leaking oil, motor ran better getting closer. i went and check voltage at the starter 13+ volts then went to the ignition switch 8 volts mmm could it be? then checked voltage at the coil 9.6 volts I replaced the ignition switch surging is gone runs pretty smooth. but when you shut it down and go back a while later and restart it will idle real low around 500 rpm's if you hit the throttle a couple times it will idle perfect at 750 what do you think this could be i have rechecked the float set right at 7/32 it does not heasitate and accelerates great. i will take her out this morning and run her. let me know what you think. Thanks

 

[dry dock]

Re: mercruiser 3.7 180 hp surges at idle

your fuel should be 3 to 5 psi well i have a older 470 not sure if is the same as yours check the adult only section and find your motor and year and it will tell you what you need. on mine i also put a eletric because it would vapor lock that solved it. welcome to iboats and good luck.

 

[spanishmackeral]

Re: mercruiser 3.7 180 hp surges at idle

when it vapor locked on yours did it quite running or did it stumble, hesitate and or idle rough? i took her for a ride this morning it ran well if you shut her down it was a little hard to restart any thoughts? thanks

 

[Bondo]

Re: mercruiser 3.7 180 hp surges at idle

Ayuh,... Those old Rochesters tend to Leak air around the Throttle Shafts when worn,...
That could possibly be an Issue...

 

[spanishmackeral]

Re: mercruiser 3.7 180 hp surges at idle

I just performed a compression test 125-128 all cylinders also checked vacuum fluctuated between 19 1/2 to 20 is that a sign of sticking valves? thanks

 

[spanishmackeral]

Re: mercruiser 3.7 180 hp surges at idle

i have a new carb in ups transit will be here tues, that should take care of any carb issues. thanks

 

[spanishmackeral]

Re: mercruiser 3.7 180 hp

Re: mercruiser 3.7 180 hp

OK i officialy agree the 470 mercruiser 180 3.7l is a piece of s**t. I have always been very mechanicly inclined but this motor what a peice of crap. Today i have dropped it off at a local merc dealer, let them deal with it i am totaly baffled the new carb came in today so i installed it expecting things to atleast be a little better, Wrong it started with a hole bunch of new issues what a finicky piece of crap. I will get it fixed so i can run it this season but this winter i am installing a 4.3 v6 and i am going to use the 470 as my bow anchor i would hope this will keep me from drifting. Ok now that i have vented if i get a donor boat will the 4.3 work with the out drive thats on the boat now or will i have to change it all out??





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[Bondo]

Re: mercruiser 3.7 180 hp

Re: mercruiser 3.7 180 hp

if i get a donor boat will the 4.3 work with the out drive thats on the boat now or will i have to change it all out??

Ayuh,... The Outdrive itself, the upper,+ lower will work with a 4.3....
Everything Forward of the outdrive itself, is maybe Parts, or saleable to recover the expence...

 

[spanishmackeral]

Re: mercruiser 3.7 180 hp surges at idle

i posted a add on craigslist i just got email from a guy who has 89 thundercraft with a 4.3 mercruiser and outdrive but i will have to take the boat also i suppose i can find something to do with the hull. thanks for the info..

 

[stonyloam]

Re: mercruiser 3.7 180 hp surges at idle

Mac: If you yank out the 3.7, don't just toss it, sell the parts, they are worth more than you might think, especially the 4V manifold and heat exchanger (if 4").

 

[spanishmackeral]

Re: mercruiser 3.7 180 hp surges at idle

Yesterday i found a 89 thundercraft with a good running 4.3 complete with outdrive. everything there and runs good all for $500 i think this is a good deal i will still go through the motor and do the swawp this fall.

 

[spanishmackeral]

Re: mercruiser 3.7 180 hp surges at idle

Well here is a update on the old 470. I had sent it to the mercruiser dealer they had it for 6 weeks and could not figure it out. I spent my vacation going over this boat with fine tooth comb. I FOUND the problem the wire going from the points to the coil had a crack and was shorting on the distibutor housing, i made a new one and runs absolutly perfect. I also went to a alternator kit and resealed the front of the motor. All is good. I will run this motor for the summer and this winter i will remove and install the 4.3 i have in my garage. Its amazing the smallest things can cause such big problems. Thanks all!