Starts on muffs, not in lake

[gurugod1]

New development...1989 30 hp Mariner motor runs fine, tell tale seems to work well, and does well on muffs in the driveway. Had it starting on one or two pulls after a carburetor rebuild. Like a champ on the muffs, so I took it down to the water this morning, couldn't get it started. Tried taking off silencer cover, engine started after several pulls, then put the silencer cover back on and engine died. Brought it back home, hooked up to muffs, ran like a top again, no problems, didn't have to take anything off. Took it back down to water, same no starting issue.

Seems that the back pressure from intake being submerged in the water is causing an issue here. I checked compression on both cylinders after 2nd attempt in the lake, both read 110ish, right where the manual says they should be.

I have a timing light, but no battery, as my motor is a pull start, so I'm hesitant to hook that up not knowing if I'd really need to. Any ideas as to what the issue may be? Here's a quick list of what I've replaced and checked recently (last 3 months):
- compression is good
- water pump is new (impeller, gaskets, housing, etc...)
- spark plugs are new, not fouled
- gas tank is new and properly vented
- primer bulb and fuel line are new, in correct position, and correct type
- carburetor cleaned and rebuilt, new gaskets, float, needle, etc...
- new pull rope on starter housing (not that this has anything to do with my issues)

I want to think it has something to do with timing, but I'm not sure why that wouldn't affect starting on the muffs. I also think that I could get into adjusting the float height in the carburetor bowl. A second thought would be the fuel pump diaphragm and gaskets, but I would think that this issue would affect performance on the muffs as well. My last thought is exhaust choking out the engine, but not sure how I would diagnose that.

 

[oldman570]

Re: Starts on muffs, not in lake

Getting a plastic 55 gallon barrel and cutting the top off and using it at home will save trips to the water for testing and setting the carb as it needs to be done. The use of a battery to check the timing of the motor is simple and you do not have to hook it to the motor. Set it nearby and just hook the battery leads of the timing light to it and hook the light pickup lead to the top cylinder plug wire. The timing has to be checked with the motor running and in FWD. gear for the idle timing and the WOT timing can only be done in a test tank or on the water while running WOT in FWD. and is not a safe way to do it. As long as no one has changed the timing rod length since the motor was new the timing should be fine. JMO
Oldman570

 

[gurugod1]

Re: Starts on muffs, not in lake

Thanks for the info. I was thinking the same thing about the timing, shouldn't be off unless something was rebuilt. Any idea if the fuel pump would be a culprit? I think not because I should have the same issues at home on the muffs if it is the pump, as it's just a vacuum type setup.

I think I'm going to take the carburetor back off and look at the float height first, maybe adjust that and try it in a tank. Any tips for height of the float inside the carburetor? My clymer manual is pretty vague and tricky to understand as it pertains to the float height, so that's why I'm asking. Once I get that adjusted I can play with the mixture and idle screws as necessary.

 

[buddhapi]

Re: Starts on muffs, not in lake

[QUOTE:Seems that the back pressure from intake being submerged in the water is causing an issue here.]
IMO the water pump from the house would have more pressure than the lake water. my first question would be if you have a transom saver rod, and at what angle of degree do you haul the motor around on your boat?

 

[oldman570]

Re: Starts on muffs, not in lake

It's not the water intake that needs the backpressure, its the exhaust thru the prop that needs it. That water pressure is what causes the motor to run different than on muffs. You might have a bad crankcase ventilation check valve that will cause trouble if it is not operating properly. It will cause loss of vacuum between the cylinders, thus less fuel to the piston. The manual http://boatinfo.no/lib/mercury/manuals/30-40_2cyl.html#/144 calls for the float to be set at 9/16" for your motor. JMO
Oldman570

 

[gurugod1]

Re: Starts on muffs, not in lake

Yeah, exhaust through the prop being affected by backpressure makes more sense. Upon further review, the engine decided to decline to start with the silencer cover on and the muffs on, so I took off the silencer cover, opened up the carb flapper about halfway, and started the motor in a trash can filled with h20. Motor started and ran, telltale was working properly. After about 15 minutes of running, I shut it off and dropped the lower unit to check and just make sure water pump was working properly, as I recently installed a new one and was a bit skeptical of the parts involved. The first thing that became apparent upon dropping the lower unit was that there was a white, greasy substance all over the drive shaft and the water pump housing. Exhaust?

If so, that starts to paint a clearer picture about the engine not being able to start with silencer cover on - being robbed of fresh air due to exhaust being diverted into the wrong places, like towards the carburetor, under the cowling, and into the intermediate housing. Exhaust was coming out of the appropriate port on the back of the intermediate unit, so I don't know if I'm dealing with some destroyed gaskets or something more serious. Compression is fine, so I want to rule out cylinder issues, but I'm just not sure. I hope to take it to a mechanic soon for an appropriate diagnosis, but I won't be able to pay a couple hundred bucks for the presumed problem (gaskets, or worse). Where would you start?

Thanks for all the input - I'm glad I finally started posting after a few months of research and reading. You guys have definitely been very helpful.

 

[oldman570]

Re: Starts on muffs, not in lake

The white milky exhaust is a normal happening when water/hot exhaust gases mix in the driveshaft housing. As the motor warms up it will dissipate some and not be as noticeable. As you have noticed, when running a motor in a nonvented area the exhaust fumes will collect more and be sucked into the carbs and this will be less oxygen for the combustion of the gas in the cylinders. I would not be worried about anything just yet and run it with a fan blowing the exhaust away from the motor before even taking the motor to a shop. JMO
Oldman570

 

[gurugod1]

Re: Starts on muffs, not in lake

So there's supposed to be water and exhaust gas mixing in the driveshaft housing? I was under the impression that h20 shouldn't really be in there except to flow through the water pipe for the cooling system.

By the way, also checked the lower unit oil - looks good, no water or burned oil.

 

[gurugod1]

Re: Starts on muffs, not in lake

[QUOTE:Seems that the back pressure from intake being submerged in the water is causing an issue here.]
IMO the water pump from the house would have more pressure than the lake water. my first question would be if you have a transom saver rod, and at what angle of degree do you haul the motor around on your boat?

I do have a transom saver rod, and I haul the motor around at a less than 45 degree angle, meaning the lower unit is only about 6 or 7 inches away from the transom, approximately. I haul less than a mile to the water, but I store the engine on the transom saver in the driveway. Carb float is where I see this idea heading...

 

[oldman570]

Re: Starts on muffs, not in lake

When you store the boat it is best to remove the transom saver, and put the motor clear down so all the water will drain from the motor. Otherwise some could be trapped in it, and if the weather gets cold and the water freezes, it can crack the motor and cause more expense. JMO
Oldman570

 

[turtles11756]

Re: Starts on muffs, not in lake

go over EVERY fuel line , from the tank to the carbs ! adjust carb

 

[MH Hawker]

Re: Starts on muffs, not in lake

It often needs to be a bit more rich on the mixture in the lake vs muffs, I have found mine has starting problems if its to lean.

 

[gurugod1]

Re: Starts on muffs, not in lake

Okay, I'll try to enrichen the mixture and see what happens. My motor has two screws that are adjustable (according to my knowledge and from what I've read in the manual), so should I be tweaking the pilot screw on the upper left side of the carburetor or the idle screw on the front of the carburetor? Both?

 

[oldman570]

Re: Starts on muffs, not in lake

The idle jet screw that needs to be opened up is on the side of the carb. You need to open it up about 1/4 turn or less to get the motor to run right. The first setting of that screw should be 1 &1/2 turns out from lightly seated, and then adjusted from there as the manual states. JMO
Oldman570

 

[gurugod1]

Re: Starts on muffs, not in lake

The idle jet screw that needs to be opened up is on the side of the carb. You need to open it up about 1/4 turn or less to get the motor to run right. The first setting of that screw should be 1 &1/2 turns out from lightly seated, and then adjusted from there as the manual states. JMO
Oldman570

I was out tweaking and tinkering today and managed to break the pull cord and rewind spring....woohoo. Was adjusting the carb screw and couldn't get the engine to do more than start and sputter out. Another thing to replace now. Aggravating.

 

[oldman570]

Re: Starts on muffs, not in lake

If the pull cord is what broke, chances are that the coiled spring has just unwound and is not broke. If you have never replaced the rope before, it might be best to just pull the whole recoil unit and take it to a shop and have them replace the rope and the spring if it is broken.
If the motor would only start and not run, then there is still a problem with the fuel lines, fuel pump, or carb. The tank is not venting, the fuel hose and fittings are sucking air, the carb passages are still plugged, the carb float is not set correct, the inlet needle is sticking, any or more than one of these can be the problem as long as you are getting good spark at the plugs. JMO
Oldman570

 

[gurugod1]

Re: Starts on muffs, not in lake

If the pull cord is what broke, chances are that the coiled spring has just unwound and is not broke. If you have never replaced the rope before, it might be best to just pull the whole recoil unit and take it to a shop and have them replace the rope and the spring if it is broken.
If the motor would only start and not run, then there is still a problem with the fuel lines, fuel pump, or carb. The tank is not venting, the fuel hose and fittings are sucking air, the carb passages are still plugged, the carb float is not set correct, the inlet needle is sticking, any or more than one of these can be the problem as long as you are getting good spark at the plugs. JMO
Oldman570

Replaced the starter spring in April, so I know I can replace that. Sucks that its already broken....not sure what the deal is with that, but I guess I have that magic touch. Fuel line to motor is new, carb rebuilt and passages clear, new gas, spark is good, float adjusted, needle seems to move freely, and tank is vented. I guess I could have a fuel pump issue. At least I'm narrowing it down....maybe....