Help Please....

[67Bertram]

So I just restored a 1967 Bertram B20 with a 190 HP Merc 470. The prop that was suggested to me by a "pro" was a 15.25 X 15P The boat jumps up on plane and runs great, but the WOT RPM is only 3800 RPM. Manual says max RPM should be 4600. I suppose I should be closer to this range.. Right? IF so what prop should I try next?

 

[Sea Rider]

If the theoretical Rule of Thumb applies need to drop pitch to a 11 pitch prop. How loaded was combo to achieve 3800 wot rpm ?

Other alternative, send that 15 pitch prop to a prop shop and have it repitched to a 13 one, will perform much better than a 15.

Happy Boating

 

[alldodge]

At 15 pitch now you don't have any room to go less. If you are trimming correctly the only way I see to go is change your transmission ratio (assuming inboard and not outdrive).

 

[alldodge]

Cancel what I just posted right now, you have engine troubles, so they need to be fixed first before you get to the prop issue

http://forums.iboats.com/forum/engi...-engines-outdrives/10464468-no-start-when-hot

 

[jimmbo]

Before you go ripping the engine apart... or spending a bunch of money on props.
Is the tach correct?
Is the carb opening fully? I don't recall if yours is a 2bbl carb or the 4 Bbl Q-jet? If a Q-jet, is the air free to open or sticky?
Is the timing set correctly and is the mechanical advance working?
Have you done a compression test on the engine?

 

[67Bertram]

Before you go ripping the engine apart... or spending a bunch of money on props.
Is the tach correct?
Is the carb opening fully? I don't recall if yours is a 2bbl carb or the 4 Bbl Q-jet? If a Q-jet, is the air free to open or sticky?
Is the timing set correctly and is the mechanical advance working?
Have you done a compression test on the engine?

The carb is a 2barrel newly rebuilt. The ignition has been converted to electronic so no mechanical advance...Right? I have not done a compression check, but I am also not sure what that would have to do with a hot start problem like this. It very much felt like a timing issue, but I put a light on it when right after it happened and found 10 BTDC

 

[Maclin]

Typical electronic ignition conversions such as Pertronix replace the triggering method (points) only. In a typical conversion the mechanical advance remains intact.

 

[67Bertram]

Typical electronic ignition conversions such as Pertronix replace the triggering method (points) only. In a typical conversion the mechanical advance remains intact.

So please excuse my ignorance, but would not the mechanical advance be under the distributer cap? There is nothing there, hence why I believed it was a true electronic ignition. Although the coil looks like a OEM part.

 

[jimmbo]

Often the mechanical advance is below the breaker plate, out of sight. GM did put their weights under the cap, but I can't think of anyone else who did. Grab the the rotor and gently twist it back and forth, if it has mechanical advance it will rotate and spring back. If it doesn't move, it either doesn't have it or is seized

 

[67Bertram]

Often the mechanical advance is below the breaker plate, out of sight. GM did put their weights under the cap, but I can't think of anyone else who did. Grab the the rotor and gently twist it back and forth, if it has mechanical advance it will rotate and spring back. If it doesn't move, it either doesn't have it or is seized

I will do that. Thank you, however I don't think that is the problem because once it does fire, I have put a timing light on it and found the timing to be correct.

 

[jimmbo]

Does the timing advance when you speed up the engine?

 

[Maclin]

For a typical marine engine to be able to achieve the rated power level, a smooth timing advance curve needs to happen beyond that initial 10 degrees as the RPM's rise and load is applied. At 2400-3000 rpm the advance should be close to 30 degrees total. As jimmbo alludes to, watch the timing mark and momentarily rev to 2000-2200 rpm's.