300X tune up

[mlb75]

Just got a 32 Skater with trip 300x's and now that I've got it I want to go through it, clean things up and replace the normal "tune up" items.

Where's the best place to get fuel filters, and what plugs should I go with? Two of the motors have Champion QL77CC plugs the other has QL77PP plugs which should it be? What other parts should I look at replacing?

What should compressions be and should they be taken cold or after warming up? I assume for leak down anything under 10% is OK? If the motors are a little short or high on compression does that just mean they are a little low on power or a ticking time bomb? If it's ticking at what numbers do I quit running and rebuild immediately?

When I rebuild what is all involved? I assume pistons, rings, crank and rod bearings, new gaskets, reeds, what else?

The lowers supposedly have the MadEFI seal kits in them, if I rebuild the lowers do I have to get new seal kits or are they reusable?

The motors supposedly have exhaust tuners on them, should the ECU's be done as well, if so how would I tell if they have been?

It appears that there are thermostat's at the top of both heads, should they be in there or should I take them out? I'd think they are just a potential restriction and as long as I don't start up and take off on the limiters but let them warm up a bit first it would be best to remove them???

Last question for now, on one of the motors I've got good water pressure according to smartcraft and the temps are perfect but it's not pee'ing like I'd expect (almost no flow) it looks like it's all coming out of the poppet relief, any idea's? I'd immediately think water pump but smartcraft is happy with the pressure so???

Thanks
Mike

[R.grover]

Drop the lowers and check water pumps regardless if you think you have an issue or not. check gear oil and that it is not overfull. if you strip the boxes you do need to reseal it. Replace poppet diaphragms gaskets and springs, check the seats etc. thermostats are at the top test them and make sure they are all the same temp marked on them to.ql77pp should be the spark plugs. compression should be around the 140psi mark.
Do the diaphragm fuel pump kits to. get the injectors tested to.
300x are hard on reed blocks so check the rubber on them.

[mlb75]

Thanks for the input I'll get on it.

[chardt]

You should also add Lakeland marine expansion tanks to the lower units, if not you'll be replacing lowers. (especially the center) Change the oil in the lowers every 10 hours or so.

I second what R.grover said:
Champion Ql77pp plugs
Keep the Thermostats
Check rubber on reed blocks and reeds for burnt corners

How Many hours on them?
If you don't have a ddt you probably want to buy one if you plan to do your own work.

[mlb75]

Thanks for the replys. New plugs will be here tomorrow, did the fuel filters and water seperstors they looked good but did them anyway. Changed oil in all the lowers they looked good as well. Did compressions and two of the motors are a little low between 125-135 on all but one cylinder which is at 120 but the center motor was between 135-140 on all 6, done cold. A rebuild is coming very soon but I assume it's ok to run it a little longer.

I figured out the water issue, there was some kind of blockage in the line before it went into the small port that comes through the cowl lower and was preventing proper flow. I took the hose apart ran it for a sec it cleared then I put it back together and it's flowing perfectly.

I'll use a bore scope to check the reeds tomorrow when I do the plugs and will look into the poppets. The motors have poppet diverters on them now, what are the pros / cons of the diverters. My understanding is that they divert water out the back of the motor rather than send it down the exhaust but I'd think that would limit the water flow back to the gear case which I'd think would not allow them to cool as well. What's the point of the diverters?

Will also look into diaphragm fuel pump kits.

thanks

[R.grover]

I have tried the poppet divider and had issues. top seals in gear box and water pipe grommet melted

[chardt]

I have ran the simon poppet diverter and haven't had any problems, didn't think it mad much of a difference in performance.

As far as compression I thought I would mention on all my motors the port piston is 0.004" shorter then the starboard (factory mercury pistons); this results in the port side running around 4psi less in compression on average. The machining of the dome on the mercury factory heads are terrible, they can vary by a couple cc's in volume. With that being said 125 to 135 is on the low side and I would rebuild them this fall. Make sure to run good fuel, mix a little 110 octane in if you can't get good 93octane.

When you use a bore scope to look at the reeds look for burnt reeds in the corners of the reeds; this normally indicates the rubber cage material has deteriorated and you will need to replace the whole cage.

[mlb75]

Thanks for the input. I've got pretty reliable fuel and it never seems to sit in the tank for more than a week at most lol. I'm definitely going to rebuild all three this fall so I know what I've got I'm just trying to get through the next few weekends the way they are.

Funny you mention the port vs strbd because the lower comp numbers are all on the port sides.

Unless someone has a reason to run the diverters they're coming out and going back to factory next week.