70hp Force Runs Good Then Bogs Down

[scout-j-m]

I have 94' 70 hp Force. I recently bought it and I haven't done much to it except clean the plugs spray in a little carb cleaner. I have taken it out 3 times so far and have had this problem: I get it in the water and start it up ok, idle out, and take off. It seems to run pretty good but after awhile it begins to cut out, stall, and jerk. I can bring it down to idle or stop and fish for a while and it may or may not be back to normal. My dad thinks it is the top cylinder coil and that it is either bad or has some electrical problem. I can believe this as it seems like its only running on 2 cylinders when its messing up and the jerking/surging is almost like that cylinder is only firing every once and a while. Also, this coil is black and has electrical tape on it while the other 2 coils are a blue/purple color. I plan on doing all the other stuff like cleaning the carb, fuel filter, etc soon. Does anybody know what's going on and why does it run fine when I first go out? Does the engine heating up having anything to do with it?

 

[john from md]

Re: 70hp Force Runs Good Then Bogs Down

You can do a resistance check on t he coils if you have a manual and meter.

Check the primer bulb when it does this and see if it is soft. Your problem can be fuel related as well. You will need to troubleshoot and note your findings.

If you want to see if your problem is related to one cylinder, pull a plug wire off and see how it affects the engine. Let it run for a minute after putting it back on before pulling the next one. See if the engine acts differently.

Let us know your findings,

John

 

[bman1bpm]

Re: 70hp Force Runs Good Then Bogs Down

Does pumping the primer bulb when it bogs down help any? if so its probably the fuel pump.
I had a similar problem wiht my motor, ended up being electrical, the wire for my CD box was rubbing the flywheel and its jacket was stripped.

 

[scout-j-m]

Re: 70hp Force Runs Good Then Bogs Down

I tried pumping the bulb when it started acting up last time I was out and it didn't really help. I ordered a manual the other day so I will try and do checks on the motor once I've gotten it in.

If the motor runs good for a while and from then on sometimes runs fine and sometimes runs rough, what could that mean electrically? Is there a separate ground for each component or do they all lead together and ground in one spot?

 

[john from md]

Re: 70hp Force Runs Good Then Bogs Down

The coils are grounded to the rack that they are attached to. I made a my own ground cable and grounded each coil to it and one end I attached to the engine block.

John

 

[scout-j-m]

Re: 70hp Force Runs Good Then Bogs Down

I've heard time and again on this forum about cleaning/rebuilding the fuel pump and replacing its filter and even the lines. Where can I order the parts for this and what all needs to be done?

 

[tmet01]

Re: 70hp Force Runs Good Then Bogs Down

May sound simple but did you open the vent on the gas tank? It will bog down if the tank isn't vented.

 

[john from md]

Re: 70hp Force Runs Good Then Bogs Down

1. Buy a Clymer manual.

2. Parts can be found at Iboats, mercruiser.com, crowleymarine.com and Westmarine.

John

 

[scout-j-m]

Re: 70hp Force Runs Good Then Bogs Down

Yes, the tank is properly vented. Also the bulb remains firm.

I just thought of a possible solution. Could it be a bad thermostat? I don't know what the engines do when they start to run hot nor do I know exactly how the thermostat works on them. From the parts schematic it looks like most kinds where the thermostat spring coils as it gets hotter allowing more water to flow through or across. If this was the issue and the engine wasn't getting cooled as it should, what would it cause the motor to do?

 

[john from md]

Re: 70hp Force Runs Good Then Bogs Down

Bogging is not related to the thermostat at all. Try cleaning out the recirculation system orifices. This is the system with the thin hoses running on the side and front of the engine.

You might also adjust the mixture screws in the carbs. The manual tells you how to do it.

John

 

[roscoe]

Re: 70hp Force Runs Good Then Bogs Down

""My dad thinks it is the top cylinder coil and that it is either bad or has some electrical problem. I can believe this as it seems like its only running on 2 cylinders when its messing up and the jerking/surging is almost like that cylinder is only firing every once and a while. Also, this coil is black and has electrical tape on it while the other 2 coils are a blue/purple color.""

You have a single carb motor, so cutting out is not a fuel problem, so that eliminates the carb, primer bulb, pickup tube, and fuel pump.

Electrical - coil failing after it gets hot.

Replace bad coil. They should all be the same. Seems someone put mismatched coils on there.

On a 1994 model, they should all be MERCURY coils, and black in color. Not to be mistaken with the old USMarine coils from the 80's.

 

[foodfisher]

Re: 70hp Force Runs Good Then Bogs Down

It's also been said time and again "did you check and clean the spark plugs?"

 

[scout-j-m]

Re: 70hp Force Runs Good Then Bogs Down

I cleaned the plugs and check individual sparks by turning the flywheel. All was good.

I don't know how to check though after the engine warms up. It idles pretty good when warm and only misses or experiences power loss when I go beyond forward idle speed.

 

[scout-j-m]

Re: 70hp Force Runs Good Then Bogs Down

I finally got my clymer manual in the mail. First thing though, I'm taking the boat out tonight for a run before I get to work on anything else.

I plan on warming it up and running around until it starts acting up. I think I should try to isolate the problem to the ignition but I don't know a good way. Is it beneficial to kill the motor, take off the cover, remove the wire to the plug I think is not firing like it should, and try running it like that? I would think that if the motor didn't surge when i was above forward idle that that would tell me the surging is due to that cylinder not firing all the time, probably due to the crappy looking coil.

Anyways, I'd like an opinion on what I might try. Be honest though if what I want to do is totally pointless.

Also, I might try to put some pictures of the coil set up on here tomorrow in case that helps in any way.

 

[roscoe]

Re: 70hp Force Runs Good Then Bogs Down

Yes, that would be beneficial.

Or hook up a timing light to that plug and see if it is getting spark while it is surging.

 

[john from md]

Re: 70hp Force Runs Good Then Bogs Down

Use a rag or rubber glove and pull the wire off when the engine is running. The plug that doesn't affect engine operation is the problem.

John

 

[bowman33]

Re: 70hp Force Runs Good Then Bogs Down

Ave A Question. I Own A 1995 Or 1996 40 Force Outboard Motor Which I Have On My 16" Spectrum Boat . When I Go Over 2000 Rpm The Motor Seems To Miss.. Sometimes When I Am Running It It Will Sort Of Bog Down So I Throttle Down And Slowly Throttle Up And It Runs But Still Has The Miss.. We Checked Spark,, Compression, The Gas,, Replaced Fuel Lines,,, Put A Water /fuel Seperator On It. Replaced Fuel Pump Diaphrams.... Got New Spark Plugs,,, Checked The Reeds Out ( No Cracks ) Look Very Clean.. I Am Not Sure How To Check And See If The Fuel Pump Is Working Correctly....... Any Suggestions ? Any Help Would Be Great...it Misses Worse At Higher Rpm's .. Oh I Am Not Sure The Year Since The Manual Says 1995 But The Pull Starter On Top The Engine Has 1996 Stamped On It... This Is A Electric Start Engine With Power Trim..

 

[john from md]

Re: 70hp Force Runs Good Then Bogs Down

Bowman 33,

Please start another thread and give us more detail as to the nature of the problem. A miss can mean different things to different people.

John

 

[scout-j-m]

Re: 70hp Force Runs Good Then Bogs Down

I wasn't able to make it out and do my planned test but I took a couple of pictures to show my coil set up. It may take a couple of posts to make it work.

 

[john from md]

Re: 70hp Force Runs Good Then Bogs Down

If you think your coil is leaking, get a rubber handled screwdriver, attach a wire to the shaft and to a ground and then touch around the coil. If it is leaking, the engine will let you know.

John