switchbox ?'s

[geb]

I'm still not reaching the potential for this motor, merc 140 ser/5744... I notice that I have 1 newer switchbox on the side. It appears I also have 1 original switchbox on the side. I'm going to changed out all the wires running from each to each coil because they are really flimsy feeling. I can pull the wiring cover off by hand. So that would be a good idea to fix. My question is this, how does the switchbox work? Is it possible for 1 to be going bad, slowly? The boat is an 81 glastron fiberglass 15'5 fishing boat. I can only get to about 4500 rpms with gear and passenger. Alone I can just touch 5000 rpms. That is still far short of the 5500-5800 that the motor should handle. I'm just curious if the switchbox would be a cause for this lacking in power or if it would just go out at once. Like I said it appears 1 has been replaced at some point but the other is what I believe to be original. I would sure appreciate any input on how the switchboxes affect over all power. And if they can be intermitent power problems. And the switchboxes are the last thing left on this motor to actually replace...I'm still running the 21p prop, because at this point even if I drop to a 19p I will only gain about 400 rpms. This 15'5 footer should be screaming across the lake with that 140 on the back the way it's set up now Thanks

geb

 

[geb]

Re: switchbox ?'s

additional question...what gauge wire should I use when I replace all wiring to all the little terminals???

geb

 

[Barnacle_Bill]

Re: switchbox ?'s

If the wires are not cracked or corroded they probably don't need changed. Marine grade wiring is flimsier than other types as there are more strands in a given gauge. I've always changed switch boxes in pairs because the newer ones are usually a later revision level. Hopefully someone can clarify that.

 

[geb]

Re: switchbox ?'s

well from looking at 1 wire the coating can be peeled off by hand and looking at the wire it appears to be somewhat corroded, in the wire, not at the connectors.

geb

 

[Barnacle_Bill]

Re: switchbox ?'s

well from looking at 1 wire the coating can be peeled off by hand and looking at the wire it appears to be somewhat corroded, in the wire, not at the connectors.

geb

That don't sound good. Most of them (the smaller) are probably 16 gauge.

 

[geb]

Re: switchbox ?'s

Well, I guess I'm definitely looking at changing all the wiring. But will that affect how the switchbox is working?

geb

 

[Barnacle_Bill]

Re: switchbox ?'s

It could if one or more of the wires going to it is bad enough.

 

[geb]

Re: switchbox ?'s

Well, I got all the wires changed and the worst one was the one that connects both switchboxes together. (white wire badly corroded) I will be testing it on Wednesday when I get my new troller put on. Thanks

geb

 

[CharlieB]

Re: switchbox ?'s

Before you condem the ignition, a couple of questions.

Did this boat/motor combination every turn those RPM's? When?

When is the last time you checked compression and what are the #'s?

How clean are the carb's?

How old is the fuel pump, what's it's output?

How deep is the motor set , the gearcase/hull relationship?

Many, many factors can effect WOT, start with the basics and rule them out in a logical sequence before assuming anything, especially that expensive ignition parts are bad, they could be fine, test, test and test agaiin to be sure before you buy.

 

[geb]

Re: switchbox ?'s

as stated in previous posts:

compression 120-125 across all 6 cylinders
3 blade prop 12 3/4 x 21P
stator -------check
trigger -------check new
fuel pump ----check new
coils --------check 1 new
switchbox ----can't confirm unless all firing means all good even at WOT
carbs --------recleaning tonight 3x
battery ------it's a deep cycle starting battery
fuel tank -----check
water sep ----check and new to boat
water pump --check new
prop ---------check no wear and tear at all and wasn't a problem before (reached at least 5500 rpms in past)
lower unit ----check new lube
control box ---check
tachometer ---check
speedometer --check
motor height --mounted correctly
wiring ---------new btwn switchboxes and coils

This set up turned 60mph 6yrs ago, before complete rebuild. !5'5 glastron fiberglass bass boat. I've already troubleshot and rebuilt/replaced what has been needed to this point. I just recently got the timing corrected on it to even run at WOT. Now I'm just trying to maximize the motor's 140 hp potential (45mph isn't it on this boat). My questions now concern the switchbox ability to perform with corroded wires and would that make a difference to the overall output of the motor itself. And would they just loose power all at once or just kind of fade out if it was going bad? Thanks

geb

 

[Chris1956]

Re: switchbox ?'s

Geb, Check the plugs for water intrusion after running. Check the spark plug leads for arcing to ground, expecially on the lower cylinders. That motor should make full RPM, especially with the 19P prop.

 

[geb]

Re: switchbox ?'s

No water intrusion and I haven't gotten to changing to 19p prop...have 21p at this time and dropping to 19p would give me about 400 more rpms...that might put me pretty close to 5500 rpms, which would be acceptable if that's just all it will do. My reasoning for not changing props just yet is b/c this prop took it to 60mph in past. Hopefully changed wires will make a difference, if not then most definitely will be changing props...

 

[ricksrster]

Re: switchbox ?'s

Try moving the trim.

 

[Motor Boater Bill]

Re: switchbox ?'s

Have you checked the weight of the boat to see if you're hauling a couple hundred pounds of water in there? Floatation can get saturated.

 

[geb]

Re: switchbox ?'s

moved the trim up and down to maximize...as yet I haven't checked the weight of the boat...I don't even know which model glastron it is and classicglastron.com seems to be down. so short of calling the company themselves I don't know where I could find any info on my model #. I've attached a pic of the boat if anyone can help with what weight should be...or any other info on the boat itself

 

[CharlieB]

Re: switchbox ?'s

Can you do a cyl leakdown test.......from the intake side?

What I am beginning to suspect is that the crank seals were not replaced during the rebuild.

If the crank seals are leaking pressure between cyls the motor will start and idle fine, but only run up so far as crankcase pressure allows.

The only way I can think of to prove it is to pressure test the intake side, I don't know the numbers but they should hold both pressure and vacuum, howo much, I don't remember, it's been way to long, another of the old timers may remember better.

 

[geb]

Re: switchbox ?'s

I'm guessing I could put together a leakdown tester and check each cylinder but not from the intake side. I wouldn't know where to begin to do that test on intake side. I'm not familiar with what the #'s should be either.

The crank seals you're talking about...GASKET, CRANKCASE TO CYLINDER BLOCK...is that it? If so, then I'm pretty sure it was replaced, I'm not quite sure if there is another seal you are talking about, sorry I'm not familiar.

 

[CharlieB]

Re: switchbox ?'s

Cyl rings are OK with comp in the range 120 -125 from your earlier posting.

Between each cyl on the crank there is a seal to contain the intake carge as the piston moves down stroke, pressurizing the crankcase and forcing the fresh charge up thru the transfer ports into the cyl above the piston.

If these seals are leaking a % of the charge into the adjoining cyl then top speed/power is reduced.

Removing the carb, fabricate some sort of plate with a port for an airline, rotate the crank so the piston at the cyl is EXACTLY at bottom dead center, charge the intake/crankcase and listen carefully to the adjoining intakes for the sounds of air leaking.

Repeat on all intakes.

if this is a stacked 6 I believe the crankseals are a labirynth contained/part of the main bearing housing/reed blocks. Once these get sloppy the only cure is to replace the blocks, NLA from merc, there must be another source, by test first to prove or disprove any need.

 

[geb]

Re: switchbox ?'s

Just so I'm understanding what you're saying...when I charge the 1st intake, that will cover pistons 1 and 2. Then listen for airflow/loss. Then charge the 2nd intake, that will cover pistons 3 and 4. airflow. Then charge the 3rd intake, that will cover pistons 5 and 6. airflow. That's each intake behind each carb. And any sounds of airflow from either of the 2 intakes is bad news. I will see what I can come up with, the tester would indicate the % (and not sure what that would be) correct? Assuming there is a significant airflow then I would be looking at replacing with new bearings and races and some decent used reed blocks and main bearing blocks? OUCH! Let's just hope there's no air leak! And if it passes the test then I'll just drop a pitch or 2 in props and just run it with what it's giving me and be happy to even be moving across the water!! Thanks for the help, I really appreciate it!

geb

 

[CharlieB]

Re: switchbox ?'s

Intake pressure is directly related to load, rpm, altitude, throttle position, it's a function of the combination of all these things.

Leaky intake seals, if that's what it turns out to be, are not necessarily cause for an immediate rebuild.

You can concievably lighten the load by reducing prop pitch and continue running it until compression begins to fall, the old tower of power, stacked 6 design is tried and true tough old bird, and will continue running and performing acceptably well for a long long time.

They can be finicky, hard to start, sure likes a LOT of choke sometimes, but once warmed up, running decent fuel, mid-grade, name brand gas, QUALITY oil, she'll run longer than you will.