Motor requires throttled up before each start

[Nitro2014]

115 hp 1985 Johnson outboard motor
The motor pushes the boat great! The boat idles good. Motor will occasionally die at idle but not often. Here is the problem: Each time I start the motor I have to throttle up before each start. It doesn't matter if it just went on a 10 min run or if it's been setting for five minutes. Always the same. Push throttle up, then start, then put throttle back in normal position to allow for normal idle. Put in gear and run just fine. Background info. The motor will start on muffs without having to throttle up and will idle all day long if I let it. But once in the water, the back pressure gets the best of it. I have changed the plugs and wires. Replaced the fuel filter as well. I run fresh ethanol free gas with quick silver full synthetic 50:1. Can anyone perhaps tell me how I can resolve the issue of having to throttle up before each start while on the water? Thank you!

 

[GA_Boater]

Just a guess - Since it starts on muffs OK with no back pressure as you say, probably time to look at the carbs or carb adjustments.

 

[Bosunsmate]

I do that every time on my 1982. Sometimes only a bit of throttle but it always requires a bit to get it to start

 

[Bosunsmate]

If the motors dying at idle when its warm then you could try adjusting the minimum timing a fraction more advanced by adjusting the stopper out a little bit more

 

[emdsapmgr]

When you move up the idle lever for slightly more starting throttle, it does advance the timing slightly-which may in help in starting. You may want to check the "sync and link" on the engine- possible the relationship between the carb opening and the spark advance needs tweaking. It's also possible the idle may be too low. You noted that it will ocassionally stall at idle. Low idle is probably caused by too little spark advance, as Bosun notes. Set the idle when the boat is floating in the water and is in forward gear. Set it to 650-750 rpm's. Can't set it on the trailer.

 

[Nitro2014]

Thank you all for taking the time to reply. In the past I have brought up the idle but it doesn't seem to do a whole lot except send me off to a fast speed when engaging in gear. I am definitely not an expert with carb adjustments/sync and link/ checking relationship between carb opening and spark advance? How much would a mechanic charge to fix the issue?

.

 

[Bosunsmate]

Thank you all for taking the time to reply. In the past I have brought up the idle but it doesn't seem to do a whole lot except send me off to a fast speed when engaging in gear. I am definitely not an expert with carb adjustments/sync and link/ checking relationship between carb opening and spark advance? How much would a mechanic charge to fix the issue?

.

Probably a couple of hundred dollars. You definitely dont want it at a fast speed when engaging gear as you say, as that ruins parts in the leg.
Its not hard to do a sync and link especially since its only idle you are needing to check.
Just check that your carb butterflys are closed at idle and then set the idle so its not low enough to stall out or too fast that it is clunking as it goes into gear.

To be honest i think that you just need to get use to using the warm up lever at start, its what most motors require of that age as they dont have the quick start function which means you dont need to do it.
Id imagine that having the mechanic look at it will cost you a lot and nothing will change. Post a video of what you have to do if you would like and then people here can see if what you have to do looks too excessive.
Since it idles ok as you said at the beginning i doubt theres anything wrong with it at all, if it was backfiring then id suggest carbs but they cost any more to do, so since it isnt indicated id suggest just be glad its not like my old tractor which needs about four things done too start it.

 

[Bosunsmate]

The only other thing i can think of is that its down on compression, which can happen even if it pushes your boat great, too check that you need a compression tester which are like ten dollars and theres a write up on this site how to do it.
Since it idles constantly ok on muffs, no backfiring and its only the backpressure that changes that then to me its most likely a slightly low idle timing ,or as a from leftfield option low compression. But if it only dies very seldom at idle then id say thats just outboards for you, i was out in my mates 2004 Merc 90p the other day and it needed throttle to start and died at idle once or twice.
I didnt really think twice about it

 

[emdsapmgr]

Also, in addition to the carb butterflys being closed at idle, you want the roller on the carb arm to not quite touch the cam lobe at idle. You want to be able so slip a pc of paper between them. Also, make sure that both the carb throttle plates are closed. (there should be an adjustment between the carbs to make sure they are both absolutely closed at idle.

 

[Bosunsmate]

Heres the compression guide
http://forums.iboats.com/forum/engi...ion-test-by-jb?t=313963&highlight=compression

 

[Nitro2014]

Wow, I am amazed and grateful for the amount of knowledge and time you guys took in replying! Is there anything else I may need to check? Could a bad primer bulb or a small leak in a fuel line cause the problem?

 

[Bosunsmate]

Wow, I am amazed and grateful for the amount of knowledge and time you guys took in replying! Is there anything else I may need to check? Could a bad primer bulb or a small leak in a fuel line cause the problem?

Not really, if you can prime the line and the bulb holds firm with engine "off" then those parts would appear ok

 

[emdsapmgr]

Any engine will seem to run just fine on the trailer-even with only 2 or 3 cyls firing. That's not much of a test of expected performance on the water. When the exhaust has to come out 20" underwater, you need the engine to fire on all 4 cyls and be properly tuned/adjused. Do the suggested checks/adjustments when the boat is floating normally in the lake and see what you find. One more easy check when in the water and in forward gear. Remove the cowling and put an inductive timing light on each plugwire. The flashes from the gun will show the quality of the spark. Intermittents, weak firing, no fires. Expect to see, regular, rhythmic, strong flashes on each plugwire-that's normal. Do it on each plugwire. You should do a compression check. It becomes a benchmark for the engine during your ownership. Future compression checks then can be compared to the benchmark figures. Problems become more apparent when those numbers begin to vary significantly with age/run hours.

 

[Nitro2014]

I probably am due for a compression test. If anything it gives me something to compare to in the future as stated. I guess I just don't understand how my throttle starts could be related to a weak cylinder though. The boat gets on plane within 3 seconds. It is a 1985 17 foot fiberglass fish and ski nitro boat by the way. With just me on board, the motor tops out at 56 mph confirmed by gps and it is strong sounding. I can still get 53 mph with two people on board. (Added 260 lbs) Planes out in roughly 4 seconds. After it warms up a little I will run through all the tests. Makes a guy a little nervous when someone suggests he has a compression issue. Haha