Slower speed and less rpms. Timing?

[adamfsunrunner]

I have a sunrunner 22foot boat with a merc 5.7litre V8. 260hp. I have lost about 500 rpm and about 8 or 9 mph on gps. I'm wondering if it could be the result of timing being off. I had a manifold and riser put in last season and the boat slowed down after that. Fuel has been checked..carb is good...prop is good. Is it time to put a timing light on the engine??

Thanks.

 

[Don S]

Re: Slower speed and less rpms. Timing?

I had a manifold and riser put in last season and the boat slowed down after that.

You don't just replace one side when doing manifolds and risers, you do both.
You need to do a compression test and see if the engine has any problems before you do anything else.
Then some info as to what year and model engine and drive you have would be very helpful.

 

[adamf24601]

Re: Slower speed and less rpms. Timing?

both were done. I just didn't say it right.

 

[freddyray21]

Re: Slower speed and less rpms. Timing?

if you had the manifolds and riser both changed and it dropped rpm's after that then look to the manifolds and the riser. Possibly smaller ports on the new manifold?

 

[newport dave]

Re: Slower speed and less rpms. Timing?

It's possible they did not install one of the exhaust shutters correctly and it is not able to open fully or fell down in the Y pipe. No easy way to check for this, you would have to pull the risers and do a visual inspection.

Dave

 

[adamf24601]

Re: Slower speed and less rpms. Timing?

well...from what I'm reading no one seems to think this is a timing issue?

 

[Don S]

Re: Slower speed and less rpms. Timing?

You've never mentioned what year it is either.

 

[freddyray21]

Re: Slower speed and less rpms. Timing?

first rule of thumb if you do something to your boat and it runs worse after you did it look to what you just did.

 

[freddyray21]

Re: Slower speed and less rpms. Timing?

one way to tell stick a timing light on it and check it