1993 mercury 175hp carb

[Shill51]

I’ve been messing with this boat for a while replaced both switch boxes due to rpm’s would not go over 2000 rebuilt carbs due to trash fuel cleaned tanks replaced fuel lines fuel filter and housing primer bulb checked fuel pressure with muffs hooked up with in spec removed flywheel checked for any broken magnets no issues found stator checks fine checked height from pad and tried different props boat will not get over 4600 to 4800 rpm’s and runs a little warm if any ones thinks it’s the sink and link or timing would appreciate the feed back before I take it to a shop and throw money way if they have seen it before

 

[Shill51]

It also has a trim safety switch to not allow the motor to trim to high I have it trimmed as far as it will go when this is happening

 

[racerone]

Post the compression test values.

 

[QBhoy]

Compression test to rule out the nasty result. Otherwise, check carbs, tiger floats, pump and reed valves.
Make sure you’re definitely getting a sustained voltage from the stator and rectifier/regulator.
Is your tachometer good ? Sorry to ask. You’ll know by ear what she’s doing perhaps anyway. What speed and what’s the boat doing when you hit this wall ? Checked the plugs are ok visually?

 

[brodmann]

If it's running good and just not reaching the RPM's you think it should, then you might be over propped. What size/pitch prop are you running?

 

[Shill51]

If it's running good and just not reaching the RPM's you think it should, then you might be over propped. What size/pitch prop are you running?

Tried smaller diameter props and lowest pitch was a 21 still no change in rpm’s

 

[Shill51]

Post the compression test values.

Average 125psi lowest being 123 best being 128

 

[Dukedog]

kind and size rig???.. sounds like its droppin' a cyl... what kinda sw. boxes?.. how was link n sync/timin' done?

 

[Chris1956]

Firstly, I doubt that motor has a mercury switch that kills the ign, if she trims too far. The design of the PTT units does not allow over trim.

If she runs warm, it is time to fix that. When was last time waterpump was rebuilt? Thermostats changed? Poppit valve inspected?

If I understand the thread correctly, at this point she spins 4600 - 4800 RPM. If so, you are past troubleshooting and are into tuning the boat/motor combo.

A 21P prop would be suitable for up to an 18 foot runabout or thereabouts, but a heavier, larger boat would need a lower pitch. The motor should be mounted with the Anti ventilation plate even with the bottom of the hull, for most boats.

 

[Dukedog]

that TnT system is two parts.. it reaches tha trim limit (short rods) will keep runnin' at all rpm.. if not under to much power it will go to tha large tilt cylinder.. tha single cyl. will only hold a little amount of pressure then release and drop back to tha trim rods... there is a "mercury" switch mounted above tha switch boxes that will kill tha motor if its over trimmed/tilted.... think its there for tha newbs ta keep from startin tha thing with it tillted way to high (outta tha water), boat beached..............

 

[Shill51]

1993 18ft pro craft dual 180 pro I bought cdi switch boxes from a mercury dealer

 

[Dukedog]

plenty motor for that boat... rare but have seen bad "new" boxes... if ya don't have an oem manual i can send ya one in pdf if ya send me an email addy..... you can check ya L/n/S plus tha timin'.........

when ya say "warm" is sounding tha over heat buzzer?