My Top Speed Dropped from 45MPH to 35 MPH

[Reel Poor]

Re: My Top Speed Dropped from 45MPH to 35 MPH

Do you have a set of ear muffs?

If not it would be in your intrest to purchase a set. Put them on and run you engine in the driveway, set timming and check the timming advance. Like tommays said, it can affect engine performance alot if the advance is not working.

 

[milkyway]

Re: My Top Speed Dropped from 45MPH to 35 MPH

I have the muffs and I use this after each boating. But I am hesitating to rev the rpm to 3500rpm because the muffs might collapse, at least I read somewhere. If it collapses, I lose water supply and then I have another fixing to do. Have you done this before on muffs?

 

[Reel Poor]

Re: My Top Speed Dropped from 45MPH to 35 MPH

Bungie cord them on so they don't fall off, turn the water on full blast. It's not like your going to run it long to check timming. Get everything ready to read the timming, have a helper bring the RPM's to around 2800, take you reading then have them bring the RPM's back to idle, make any neccessary adjustments then repeat process to check again. This may take all of 15 to 20 seconds to take your reading, . Shouldn't be any problem, common practice.

 

[milkyway]

Re: My Top Speed Dropped from 45MPH to 35 MPH

What necessary adjustments am I supposed to make if the advanced timing is not to specs? Rotate the distributor?

 

[Reel Poor]

Re: My Top Speed Dropped from 45MPH to 35 MPH

Not neccesserarily, There may be a problem with the distributer. If the base timmimg is correct the advance curve should come to specs also. If it doesn't check the Knock sensor and ignition module.
Do you have the specs for your engines timming and advance curve? Unfortunately it's not on the internet, and I don't have them.

 

[milkyway]

Re: My Top Speed Dropped from 45MPH to 35 MPH

It says total spark advance 20 deg minimum to 23 degs maximum at 3400 rpm minus initial timing which is 10btdc. Also 15-19 degs at 2500 rpm.

Using an advanced time lite, with it set at 10degs, the marks are aligned to set the initial timing. If I turn the dial between 30 and 33 degs. (10bdtc plus 20to23) and rev the rpm to 3400rpm, the marks should align again, right?


I don't klnow how these numbers add up to get the advanced timing but I will report what I see.

 

[Reel Poor]

Re: My Top Speed Dropped from 45MPH to 35 MPH

If I turn the dial between 30 and 33 degs. (10bdtc plus 20to23) and rev the rpm to 3400rpm, the marks should align again, right?

Or, with engine reving turn the dial till the mark on the balancer lines up on the TDC mark on the tab, then read the light. This will tell you what it's totaling at, even if it's off.

 

[John_S]

Re: My Top Speed Dropped from 45MPH to 35 MPH

The T5 is an electronic advance system. If you are not seeing advance at high rpm, look into the knock detection system. If engine is knocking or the system "thinks" its knocking, it will retard the advance timing. There is a diagnostic flow chart in the Merc manual to troubleshoot this. My manual is with the boat (3 hours away) so can't post a flow chart.

 

[milkyway]

Re: My Top Speed Dropped from 45MPH to 35 MPH

Will check further advanced timing and will take it from there.

 

[Purduebarry]

Re: My Top Speed Dropped from 45MPH to 35 MPH

All that malarky about the props (several posts back) had me puzzled. You switched props twice and don't know the pitches? You could be seriously lugging the engine. This is not good and will cause problems including lower speed. After all is said and done go check out the props fourm and see what the guys over there have to say.

 

[milkyway]

Re: My Top Speed Dropped from 45MPH to 35 MPH

I must had 17 when I bought the boat, then I think I tried 21 but then I hit a rock , then I went down to 19 realizing the rpm was way too low. And 19 is what I have now for the last 2 seasons. I am considering going back to 17. It may be only a prop issue, but I will still check the advanced timing to cover all bases. I can use a spare for emergency anyway.