1996 8 hp, head gasket replaced and now it runs slow

I had a mechanic check out my motor and he said that because the motor wasn't pumping much water that i has accidently overheated the motor and i needed to replace the head gasket. He replaced it and the impeller and when i picked it up it sounded great in the tanks. I bring it home and the next day i take it out to test it in the water, it started and idled great but once under way it was acting funny. At half throttle it would be very slow to raise in rpm( i would turn throttle but it would take at least 5 sec to get to the proper rpm). Max speed i got was 12 mph, before he fixed anything it would max out at 19 mph. Know at full throttle it will run for a while but then all of the sudden it will make a noise almost like it's hitting a rev limiter. It runs but not at all how i think it should. What could be wrong? Is it related to the head gasket, am running on one cyl., is it something unrelated? What do you guys think? I swear i have the worst luck with outboards.
thanks

Re: 1996 8 hp, head gasket replaced and now it runs slow

Could it be something simple like a bad gas line or bulb? I have no idea what it is and i spent all my money on this motor.

Re: 1996 8 hp, head gasket replaced and now it runs slow

Is it 'revving up' but going no where?

You could have a spun prop, although I only say that because of your one comment, and is completely unrelated to the mechanics actions.

Re: 1996 8 hp, head gasket replaced and now it runs slow

Sounds to me like a sych problem, but it could be lost compression due to a warped head.

Re: 1996 8 hp, head gasket replaced and now it runs slow

Could be a few things, but lets get to the first step, you mentioned it over heated, replaced head gasket.

Need a compression check, this will eliminate the compression factor. If compression is good then need to look at fuel or ignition. Get the compression check done, call your tech and see if he can do it for you if you do not have a compression gauge, if he is not loaded down with work this time of year he wil most likely be able to check it for you. Once you know the compression numbers it will just be a matter of eliminating possible problems.

dirty carbs, weak spark, etc. etc.

Re: 1996 8 hp, head gasket replaced and now it runs slow

The motor revs very slowly no matter how quickly you turn the grip, the acceleration seems to match the rpm increase. If you twist the grip slowly the motor will match the increase and seems fine, but if you twist it any more than slowly the rpm and speed is very slow to increase. Why would my motor have lost top end speed? it sounds like it's close to WOT but not quite all the way there.

Re: 1996 8 hp, head gasket replaced and now it runs slow

Take the hood off and twist the throttle wide open and check to make sure the carb opens fully too. Look at what moves and make sure all linkage is connected properly.

Re: 1996 8 hp, head gasket replaced and now it runs slow

after going through some old posts, i'm thinking that it may need a link and sync. The mechanic told me he removed the carb to check it out but said it was perfectly clean. I assume that he replaced and didn't do a link and sync, would this cause the conditions i'm getting? I have a manual for this motor but have some question before i attempt to do this. I will try to tackle this tomorrow and get my questions ready for you guys.
thanks

Re: 1996 8 hp, head gasket replaced and now it runs slow

YES, if it is not link n sinc correectly it will caus ethis problem. really hope it is as simple as a adjustment on link n sinc