Mercruiser 170 Shifting & Stalling/Idle problems after hot

Wellcraft170 · Jan 20, 2015

hows it goin guys? been thinking about it over the course of the winter so far but originally my first problem was basically when i first get out on the water everything is perfectly normal. then if i stop for a few minutes and try to go again the engine will stall when i put it in gear (forward or reverse). the engine will start back up but have a really bad idle and eventually stall as well. right before it stalls i would try to put it in gear but it'll still stall. the even weirder part is that after this happens, you can wait again till it cools off and everything goes back to normal until it gets hot again.

Wellcraft170 · Jan 20, 2015

when i originally brought this up, a few guys all came to the conclusion that the shifting problem was a bad shift cable or that it needed to be adjusted?? and im thinking the stalling is because i had it upgraded to the electronic conversion kit but used the original standard coil and i should get the flamethrower to help support it better

johnzonh · Jan 21, 2015

had similar issue on my 165. originally thought it was the cutout but that would have given me problems coming out of gear. found out my idle was low about 100 rpm. bumped it up and haven't had a problem since, either hot or cold. I had to pay closer attention to how the idle was set (both in and out of gear, in the water under load) helped a lot

stonyloam · Jan 21, 2015

Sounds like you have the Petronix conversion. If so there are a couple of things: if you are using the original coil and you attached the red wire to the + terminal of the coil, ( with the original resistance wire in place) you are not supplying the full 12 volt battery voltage to the module. If you have not done so, you should remove the red wire from the coil and splice it into the choke wire (near where the purple resistance is attached). If you have the original Petronix module the stock coil should be fine, if you have the Petronix II then you should upgrade to the Flamethrower II and get rid of the resistance with and run a stranded copper wire from the choke wire directly to the coil +, and attach the Petronix red wire there. That should take care of your ignition questions.

stonyloam · Jan 21, 2015

I had a similar hot idle problem that turned out to be that the fast idle stop screw had backed out and the stop was loose, so when the engine was warn the idle screw did not contact the stop properly and the engine would stall out. Something to check.

Wellcraft170 · Jan 21, 2015

stonyloam said:
Sounds like you have the Petronix conversion. If so there are a couple of things: if you are using the original coil and you attached the red wire to the + terminal of the coil, ( with the original resistance wire in place) you are not supplying the full 12 volt battery voltage to the module. If you have not done so, you should remove the red wire from the coil and splice it into the choke wire (near where the purple resistance is attached). If you have the original Petronix module the stock coil should be fine, if you have the Petronix II then you should upgrade to the Flamethrower II and get rid of the resistance with and run a stranded copper wire from the choke wire directly to the coil +, and attach the Petronix red wire there. That should take care of your ignition questions.

yeah i gotcha on all of that. i got the original module and my mechanic friend set it up for me last year. now i know thats not the problem. thanks

Wellcraft170 · Jan 21, 2015

stonyloam said:
I had a similar hot idle problem that turned out to be that the fast idle stop screw had backed out and the stop was loose, so when the engine was warn the idle screw did not contact the stop properly and the engine would stall out. Something to check.

i played around with that screw a ton last year and it wouldnt make a difference. i actually set it quite high so the boat wouldnt stall out but it still would even with a high idle

stonyloam · Jan 21, 2015

Have you tried adjusting the idle mixture screw?

Wellcraft170 · Jan 21, 2015

stonyloam said:
Have you tried adjusting the idle mixture screw?

is that different from the screw that lowers or highers the idle?

stonyloam · Jan 22, 2015

Yes. It is a needle valve in the lower carb body (#26 here https://www.mercruiserparts.com/Sho...r=50&bdesc=CARBURETOR(MERCARB)+(165-170-3.7L) ) that adjusts the fuel air mixture to make it run richer or leaner at idle ( 700-800 RPM range). With the engine ideling as you turn that screw in (lean) or out (rich) the RPM should change, to the point where it might stall at the extremes (too lean or too rich).

Wellcraft170 · Jan 22, 2015

stonyloam said:
Yes. It is a needle valve in the lower carb body (#26 here https://www.mercruiserparts.com/Sho...r=50&bdesc=CARBURETOR(MERCARB)+(165-170-3.7L) ) that adjusts the fuel air mixture to make it run richer or leaner at idle ( 700-800 RPM range). With the engine ideling as you turn that screw in (lean) or out (rich) the RPM should change, to the point where it might stall at the extremes (too lean or too rich).

so it should be somewhere in the middle so its not to lean or too rich

stonyloam · Jan 22, 2015

Correct. For an initial setting, turn all the way in ( do not force) then back out 1 1/4 turns should get you in the ball park. From there adjust for a nice smooth idle (give it a little time to settle in after each adjustment). If you turn it in or out too much the engine will start to stumble. If you get no response then something is probably plugged and you should probably clean and rebuild the carb.

stonyloam · Jan 22, 2015

BTW here is the manual for your engine http://boatinfo.no/lib/mercruiser/manuals/mercruiser8.html#/0

achris · Jan 24, 2015

You do need to confirm that you don't have a shift cable problem as well. Have someone else shift while you watch the cutout switch... It MUST return to the centre position immediately after coming out of gear, and it shouldn't move AT ALL when going into gear (either forward or reverse)...

Chris.

Wellcraft170 · Jan 24, 2015

stonyloam said:
BTW here is the manual for your engine http://boatinfo.no/lib/mercruiser/manuals/mercruiser8.html#/0

thank you. too bad i gotta wait a few more months to get back to playing with it! lol

Wellcraft170 · Jan 24, 2015

achris said:
You do need to confirm that you don't have a shift cable problem as well. Have someone else shift while you watch the cutout switch... It MUST return to the centre position immediately after coming out of gear, and it shouldn't move AT ALL when going into gear (either forward or reverse)...

Chris.

thanks for the tip. gotta test it out in the spring

Mercruiser 170 Shifting & Stalling/Idle problems after hot

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