MerCruiser 120 issues

[Mschramm10]

Just bought an '85 Larson Citation from and older gentleman that has obviously taken care of this boat. I went through and inspected everything I could think of, he started it and it ran fine. Just as a precaution I started it again the following day and it again started and ran fine; no strange noises. Took it out on the river yesterday and it ran great for about 30-40 minutes then the engine started to bog down and was making a "thumping" noise every so often. I'm new to boats, and have an aptitude for mechanics, I just don't have that much experience dealing with issues...any help with this issue would be greatly appreciated!

 

[Bondo]

Just bought an '85 Larson Citation from and older gentleman that has obviously taken care of this boat. I went through and inspected everything I could think of, he started it and it ran fine. Just as a precaution I started it again the following day and it again started and ran fine; no strange noises. Took it out on the river yesterday and it ran great for about 30-40 minutes then the engine started to bog down and was making a "thumping" noise every so often. I'm new to boats, and have an aptitude for mechanics, I just don't have that much experience dealing with issues...any help with this issue would be greatly appreciated!

Ayuh,.... Start with checkin' the fuel filters, 'n spark plugs,......

Restricted fuel would cause a bog, 'n loss of power,.....
Plug color might confirm, or deny it,...

 

[thumpar]

You may want to replace the points and check timing also. Since it is new to you I would suggest impeller if you don't know the history.

 

[achris]

Whenever I buy anything second hand, I ALWAYS start with a FULL service, top to bottom... That way you have a baseline and you know to the best of your ability that everything is the way it should be... So, out with the tools, and start servicing...

 

[Mschramm10]

Thanks folks! My research had me headed toward spark plugs, but I'm definitely going to give a a thorough look over. Busy with work this week so won't be getting back to the boat for a few more days...