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87MCProstar
04-27-2009, 08:33 AM
Got the boat out and running yesterday. Pretty much doubled the time in the boat since last summer, due to issues I had. Noticed that the top speed isn't there since the motor rebuild. I am chalking this up to either no tuned right or the prop isn't right, I'm running a standard 13x 13. What do you think?

TMCNo1
04-27-2009, 09:39 AM
Got the boat out and running yesterday. Pretty much doubled the time in the boat since last summer, due to issues I had. Noticed that the top speed isn't there since the motor rebuild. I am chalking this up to either no tuned right or the prop isn't right, I'm running a standard 13x 13. What do you think?

Usually 44 to 45 MPH, give or take a couple MPH with calibrated speedometers. Recheck the timing on the water now that it's been run some.

87MCProstar
04-27-2009, 02:26 PM
How would i go about checking the timing on the water? never done that before.

87MCProstar
04-27-2009, 02:27 PM
the wholeshot doesn't seem to be there or the top end. it isn't popping or missing, wierd.

TMCNo1
04-27-2009, 08:06 PM
How would i go about checking the timing on the water? never done that before.
Take the timing light with you to the lake, find some shade, have someone lower the motor cover down till you can see the light flashing on the harmonic balancer/block timing tab and go from there, Marking the timing line in the harmonic balance and the timing tab on the block@ 10 degrees BTDC with a Whiteout pen will help make it show up much better.

Also, you may want to check to see if the centrifugal advance weights and springs are free, lubed and moving in the distributor.

EJ OJPROP
04-29-2009, 11:21 AM
the wholeshot doesn't seem to be there or the top end. it isn't popping or missing, wierd.

What is the max RPM of motor? Has the 13 X 13 been repaired?

87MCProstar
04-29-2009, 03:56 PM
the max rpm is about 4000, and the prop has been repaired EJ

Hoosier Bob
04-29-2009, 04:31 PM
Not enough RPM. Are your secondaries kicking in? Listen for them. Timing, Linkage to carb and secondaries are a good start. 40 mph and slow go may be you are running without your secondaries. You should get 40 mph at 4000 rpm +- but you should definately turn more RPM and mph.

mrprostar
04-29-2009, 05:40 PM
Is this true of EFI too? I'm running no more than 3800 and about 38 mph and always attributing it to 6000+ elevation. Same prop (13x13).

etduc
04-29-2009, 07:08 PM
Got the boat out and running yesterday. Pretty much doubled the time in the boat since last summer, due to issues I had. Noticed that the top speed isn't there since the motor rebuild. I am chalking this up to either no tuned right or the prop isn't right, I'm running a standard 13x 13. What do you think?

A bad tune, would go to drivability, hard starting, not running at all. I would have carb looked at, and distributor, as mention above.
My Tristar would rev 4500 rpm, 45 mph. 13x13 (1400 hrs+)

1. Check the simple things first, and don't guess or assume it was done right. Confirm.

2. Other things that can contribute to your lack of performance. Bad drive train alignment
and quality of engine build (engine built tight)

3. Hire a good mechanic

EJ OJPROP
04-30-2009, 09:18 AM
Is this true of EFI too? I'm running no more than 3800 and about 38 mph and always attributing it to 6000+ elevation. Same prop (13x13).

You might look at a 13 X 11 to increase the RPM.

EJ OJPROP
04-30-2009, 09:19 AM
the max rpm is about 4000, and the prop has been repaired EJ

You should see 4400 to 4800 with that prop.

Jesus_Freak
04-30-2009, 01:06 PM
Is this true of EFI too? I'm running no more than 3800 and about 38 mph and always attributing it to 6000+ elevation. Same prop (13x13).

I am not certain about your particular speed limitations, but, in general, the engine can only "pump" so much mass in a given rev. Higher altitude = lower pressure = lower density = less mass pumped per rev. EFI will respond with less fuel, whether it relies on mass air flow or speed-density.

Bellinghamster
05-01-2009, 12:26 AM
I suspect my '78 S&S is a bit lighter, and adding 150lbs of wife and kids drops the top speed to 46~47 or so, so weight makes a big difference. I can peg the speedos at 50mph if I'm by myself in the boat with less than a full tank of fuel. 351W, 13x13 cupped prop and 1:1 transmission. I don't recall what RPM at WOT... I need to remember to look next time I get crazy.