Mercury 175 v6 floods out as boat reaches plane - losing spark?

I have a 1979 mercury 175. The engine runs beautifully up until the boat goes on plane, then the engine completely floods out and dies. It can be hard to start following this, and after I get it started, I have to rev it at high rpms to burn up the excess fuel. Removing the plugs following this scenario revealed that they were pretty wet. Otherwise, I can run all day just tooling around, but I am unable to put the boat on plane.

I have the factory service manual, and performed the checks listed for the stator and trigger, as well as the coils. all were within acceptable limits. The book recommends having the ignition checked using the ignition diagnostic machine (obviously don't have, and if i could afford to have the shop check - i would'nt be posting here).

I should mention that i completely disassembled the fuel system, changed the fuel filter, went through the carbs, and all of that is in really good shape. Also have great even compression on all cylinders. The fuel pump is in good shape.

One of the 2 mercury power packs has been replaced, I still have 1 of the originals I think on there. I have ordered a replacement for $135 that will be here on Tuesday, that is returnable if it is not the problem. I do not know how old the one that was replaced is, but it does not look too bad.

Supposedly the stator was replaced just before I bought the boat, but I can not verify that for sure.

I am wondering if it might be over-propped -the existing prop was a bit furry, so i had the local propeller guy rework it. i have not picked it up yet. if i am over propped would it flood out, or just reach a maximum lower rpm than expected. the issue ONLY materializes just as the boat get to plane. otherwise, i can run all day at the lower rpms (pontoon boat speed).

Is there anything else I could be missing?

Re: Mercury 175 v6 floods out as boat reaches plane - losing spark?

I noticed somewhere else in the forum here - someone had an issue on a 1979 50hp that turned out to be the magnets in the flywheel. Any thoughts on that?

Re: Mercury 175 v6 floods out as boat reaches plane - losing spark?

anyone had an issue like this?

Re: Mercury 175 v6 floods out as boat reaches plane - losing spark?

If your flooding it might be an idea to rebuild carbs.Replace all gaskets,needle/seats and check floats still float.Floats need to be reset to correct height as per spec.Try and find mercury manual for your model.It will make this and all future jobs a lot easier.

Re: Mercury 175 v6 floods out as boat reaches plane - losing spark?

carbs are in great shape. the issue is no spark at the point of plane. got the mercury switch today - will post results of swap out.

Re: Mercury 175 v6 floods out as boat reaches plane - losing spark?

Too much prop can bog your engine down too hard as it tries to plane and make it actually lose rpm as throttle increases. Mine did when I had a big prop on there and tried to pull 2 knee boarders out of the water. Had to go full throttle to get it to plane, anything else and it would bogging.

Did you do a link and sync on the carbs/timing and replace the spark plugs? I had some plugs one time that were either defective or crapped out quickly.

Re: Mercury 175 v6 floods out as boat reaches plane - losing spark?

You need to verify stator output with a DVA meter.

A weak high speed winding can kill high speed performance, yet still allow you to rev the motor in neutral high enough to throw the rods right out the side.

Since there is NO RETURN on electrical parts, do NOT buy anything other than a DVA meter or a DVA adaptor to use with any volt/ohm meter.

Re: Mercury 175 v6 floods out as boat reaches plane - losing spark?

444 said:

Too much prop can bog your engine down too hard as it tries to plane and make it actually lose rpm as throttle increases. Mine did when I had a big prop on there and tried to pull 2 knee boarders out of the water. Had to go full throttle to get it to plane, anything else and it would bogging.

Did you do a link and sync on the carbs/timing and replace the spark plugs? I had some plugs one time that were either defective or crapped out quickly.

Click to expand...

ok - i should have mentioned i do have new plugs in.

more clues. i got the switch box from amazon yesterday. it is teleflex and it is returnable. $119. i first swapped the box that looked older, and it ran worse. i then replaced the innerbox, which looked newer, and it ran much better. it was still bogging down under load, but not flooding out.

i unloaded my family on the dock, and went out by myself and suddenly it ran great. i was able to plane out and run fast and everything. turning resulted in a little cavitation and i would have to let it come down before it would 'catch'.

loaded my wife and 2 teenage children, and it would bog down, and not reach plane at all.

i will try to pick up my prop from the prop shop tomorrow and post results.

Re: Mercury 175 v6 floods out as boat reaches plane - losing spark?

CharlieB said:

You need to verify stator output with a DVA meter.

A weak high speed winding can kill high speed performance, yet still allow you to rev the motor in neutral high enough to throw the rods right out the side.

Since there is NO RETURN on electrical parts, do NOT buy anything other than a DVA meter or a DVA adaptor to use with any volt/ohm meter.

Click to expand...

so i need to check the output while running it on the water under load - right? supposedly the stator was replaced recently. what about missing magnets on the flywheel? any way to check other than pulling it off?

Re: Mercury 175 v6 floods out as boat reaches plane - losing spark?

With a DVA meter and the FREE Ignition Troubleshooting Guide (did I say available for FREE) from the Support page of CDIElectronics

You can test your ignition system yourself!!!!!!!

Once you verify that you have a good ignition, then you can start checking into the fuel system. Carbs MUST BE clean, floats adjusted correctly, if they have adjustable idle mixture screws, they MUST BE adjusted correctly, or the motor will not perform correctly. Often a motor that bogs, speeds up some then floods, is in dire need of proper carb cleaning and adjustment.

Before you start tearing things apart, first check these links and see if you can download a copy of the factory service manual

http://1manual.com/Mercury manuals/Service_Manual_Index.html

http://forums.iboats.com/showthread.php?t=309079&p=2072211#post2072211

Build your own spark tester, it is helpful in solving starting problems

http://forums.iboats.com/showthread.php?t=526087&highlight=Joe+Reeves+Spark+Tester

Re: Mercury 175 v6 floods out as boat reaches plane - losing spark?

CharlieB said:

With a DVA meter and the FREE Ignition Troubleshooting Guide (did I say available for FREE) from the Support page of CDIElectronics

You can test your ignition system yourself!!!!!!!

Once you verify that you have a good ignition, then you can start checking into the fuel system. Carbs MUST BE clean, floats adjusted correctly, if they have adjustable idle mixture screws, they MUST BE adjusted correctly, or the motor will not perform correctly. Often a motor that bogs, speeds up some then floods, is in dire need of proper carb cleaning and adjustment.

Before you start tearing things apart, first check these links and see if you can download a copy of the factory service manual

http://1manual.com/Mercury manuals/Service_Manual_Index.html

http://forums.iboats.com/showthread.php?t=309079&p=2072211#post2072211

Build your own spark tester, it is helpful in solving starting problems

http://forums.iboats.com/showthread.php?t=526087&highlight=Joe+Reeves+Spark+Tester

Click to expand...

thanks - i did download the correct manuals. i had the old mercury shop manual, but it was not nearly as helpful as some of what i found there.

for now, next step it trying to figure out the correct prop pitch. the loaner i got was a 24, i think i had a 21 on there. which still may be overkill.

is not flooding out now after the mercury switch box installation, but still running a woeful rpms underload. just me in the boat - it runs great.

Re: Mercury 175 v6 floods out as boat reaches plane - losing spark?

If you tried a 24, you're going in the wrong direction. Try dropping down to a 21 or even a 19, depending on weight and shape of your boat.

Re: Mercury 175 v6 floods out as boat reaches plane - losing spark?

DVA test triggers cranking, plugs out, wires grounded (saves battery and starter).

DISCONNECT the throttle cable and while testing each trigger, slowly move the throttle arm/timing lever from idle to WOT and back, if a trigger wire is broken yet abutted, two cyls can fire at some positions and fail elsewhere as the wires flex.

Re: Mercury 175 v6 floods out as boat reaches plane - losing spark?

was the mercury switch and the prop. now running great!