Engine misfire when starting kills engine?

[dorelse]

For lack of a better way to describe it...so I took a video of it this weekend when on the lake.

When starting it will give either, what I can only describe as an exhaust 'cough'. Only to restart it and all is well.

Or...like is in the video, it starts right up, and then seems to misfire and kill itself...it seems to predetonate? on a cylinder which causes it to die.

I will preface this by saying that it definitely runs better off of good old 87 octane, vs. the 91 octane which is all that is available at the resort we were at.

Is this something that needs attention?

http://www.youtube.com/watch?v=ACvNOZ7QksI

Otherwise, it runs all day long like this:

http://www.youtube.com/watch?v=13CXh16eDjs

Btw...I do have the telltale added, I can hold my hand under the telltale water all day, its warm, but nothing too hot to touch. Same goes for the head & motor block.

 

[ammermanfam]

Re: Engine misfire when starting kills engine?

Same thing happens with mine. It happened once in the driveway it was actually a backfire. Not sure what the cause is. If you figure it out please let me Know. Thanx John

 

[john from md]

Re: Engine misfire when starting kills engine?

The engine is backfiring probably because it is too lean. This can happen for a number of reasons.
Have you checked your choke rigging ever?
Have your carbs every been rebuilt?
Do you know what your timing is?
If you are mechanically inclined, tell me what maintenance or preventive maintenance you have performed on the engine.

John

 

[Frank Acampora]

Re: Engine misfire when starting kills engine?

Does it only happen on a cold start? if so, are you pushing in the key and holding it in while cranking, to choke?

Otherwise if it happens on every start, cold or hot as stated above, the engine is too lean.

 

[dorelse]

Re: Engine misfire when starting kills engine?

The engine is backfiring probably because it is too lean. This can happen for a number of reasons.
Have you checked your choke rigging ever?
Have your carbs every been rebuilt?
Do you know what your timing is?
If you are mechanically inclined, tell me what maintenance or preventive maintenance you have performed on the engine.

John

I am mechanically inclined, however, depending on the complexity, this may be beyond my abilities.

Maintenance, I'm not 100% sure what's all involved with a carb rebuild, but last summer (13 mos ago to be exact), the carbs were taken apart, cleaned with new reeds installed in all 3 carbs. Compression was at 135 lbs on all 3 cylinders, as I asked for this before I purchased boat & motor.

I'm in Des Moines, and there is pretty much 1 shop in town (maybe 2) that will work on these that actually know what they're doing.

I asked for an received a full tune up on the motor, I believe they did it as the motor ran much much better after they were done with it.

For winter storage, I fogged the carbs with Deep Creep and tucked it away in my garage.

I will say this though, the problem is much less prevalent on 87 octane vs. 91...I'm mixing the oil 45:1 because I'm completely paranoid about under lubricating the cylinders...

BTW...I know I'm sounding like a noob, but I'm trying to learn. I've spent tons of time redo'ing this boat this spring, and love it, so I want to keep it running in tip top condition.

 

[dorelse]

Re: Engine misfire when starting kills engine?

Does it only happen on a cold start? if so, are you pushing in the key and holding it in while cranking, to choke?

Otherwise if it happens on every start, cold or hot as stated above, the engine is too lean.

It is not just on cold starts, and not on every start for that matter, warm or cold.

Yes, I'm (I think it was you Frank) that posted instructions on how best to start these engines, I'm starting with Choke engaged & then holding it for 2-3 secs after its fired. Which has really helped when starting when cold, it starts up immediately...if it does this 'clearing cough', then the next time I turn it over, its starts up and stays running.

This video isn't as good as it was taken on our one windy day at the lake, but if you listen carefully, you can hear it kind of 'fighting itself' (if that makes sense) to stay at a smooth idle, and not kill itself, which it does...

I wish I could be more specific...but that's why I tried to shoot the videos...

http://www.youtube.com/watch?v=Jmk_ySy5O1U

When it is up and running, it can really move my boat:

http://www.youtube.com/watch?v=-XPCssBQRYg


You guys are both the experts, so if you think its lean I'll take your advice gratefully. The thing drinks gas like its going out of style. I'm lucky to get an hour (maybe 2) of tubing/kneeboarding off of a 6 Gal gas tank...which would be in line with the 10% gal per hour fuel consumption guideline I've read on this forum (8.5 Gal/hr at WOT).

I suppose specifics would help huh? Sorry, its a 1986 85 HP, no tilt/trim, running a Piranha Prop 17P. Compression is 135 across all 3 cyls.

I guess I was thinking the 91 octane was causing a predetonation condition, but...again, that was just my thinking.

This is my 3rd Force engine, first was a 1990 90HP, that blew a piston ring. Second was a 1992 90HP that ran beautifully, when I decided I *must* have an I/O. Honestly, I found it difficult to work on, always bending every which way to try to winterize it and maintain. I *MUCH* prefer an outboard, and I've rebuilt my boat to have a sundeck on my 1986 Bayliner Capri 1600.

TIA for both of your help!

 

[john from md]

Re: Engine misfire when starting kills engine?

Don't get too worried, overall, your engine is running great, it just needs some tweaking.

If you have a manual, checking the choke plate settings is easy.

If you have a inductive tachometer ($25 from ebay), you can adjust the carbs and idle.

If you have a manual, I can talk you through the process.

BTW, 91 octane will not cause the engine to experience preignition or detonation, lean burning will. 91 octane has more knock resistance than 87.

For a miriad of reasons, an 85hp Force engine operating at WOT most of the time will not be economical at all. I get my best economy at 21mph and depending on the sea state, that is 3 to 4 miles per gallon.

At WOT, you can watch the needle on the fuel tank move real fast.

John

 

[dorelse]

Re: Engine misfire when starting kills engine?

Don't get too worried, overall, your engine is running great, it just needs some tweaking.

If you have a manual, checking the choke plate settings is easy.

If you have a inductive tachometer ($25 from ebay), you can adjust the carbs and idle.

If you have a manual, I can talk you through the process.

BTW, 91 octane will not cause the engine to experience preignition or detonation, lean burning will. 91 octane has more knock resistance than 87.

For a miriad of reasons, an 85hp Force engine operating at WOT most of the time will not be economical at all. I get my best economy at 21mph and depending on the sea state, that is 3 to 4 miles per gallon.

At WOT, you can watch the needle on the fuel tank move real fast.

John

I have a CD of the OEM manuals on order, I'll get the tach you suggested, and get to work on checking the choke plate settings.

I'm glad to hear I'm not killing the motor, b/c it does run great! Thanks John, I'll check back in a week or so when it has all arrived.

 

[dorelse]

Re: Engine misfire when starting kills engine?

So, is the exhaust 'cough' really because the motor has too much air in the system (ie lean), and once it clears it, it runs fine?

 

[roscoe]

Re: Engine misfire when starting kills engine?

Its a very strong indicator that the air/fuel mixture is a little lean.

Can tweak and fix this easily, and it won't effect the overall fuel economy very much.

What will save you fuel is running at 3500 - 4000 rpm. Any more than that and the fuel to speed ratio is out the window.

 

[dorelse]

Re: Engine misfire when starting kills engine?

Its a very strong indicator that the air/fuel mixture is a little lean.

Can tweak and fix this easily, and it won't effect the overall fuel economy very much.

What will save you fuel is running at 3500 - 4000 rpm. Any more than that and the fuel to speed ratio is out the window.

Yeah, I'm not looking for fuel economy, although you are right in that there is a sweet spot it seems for cruising. I just want to make sure its running as best as possible for many more years of reliable service.

 

[eight tracker]

Re: Engine misfire when starting kills engine?

50:1 mixture is correct for this motor,45:1 my be a little lean but will not cause the problem you are having.Minre does the same thing and i have not touched the carbs since i had this motor { 10 years } 1985 85hp force it only happens on cold start- up but runs fine after,bogs down sometimes so i'm thinking stator wire or coil,anyway if you find out what it is,a lot of us would like to know.
Tom

 

[john from md]

Re: Engine misfire when starting kills engine?

FYI, the extra oil will not affect anything but the economy of operation and it will increase your carbon build up to a degree. With today's TCW3 oils, you don't have to add extra as it is just wasted.

Whenever an engine backfires through the intake, it is either too lean or the timing is too advanced. Most of the time with outboards, the condition is that the mixture is too lean.

The thing to remember is that these engines use the idle circuit thoughout the entire power band. That means that if you are lean at idle, you will be lean at WOT. Lean burning at WOT results in bad things like holes burned in pistons.

John

 

[dorelse]

Re: Engine misfire when starting kills engine?

50:1 mixture is correct for this motor,45:1 my be a little lean but will not cause the problem you are having.Minre does the same thing and i have not touched the carbs since i had this motor { 10 years } 1985 85hp force it only happens on cold start- up but runs fine after,bogs down sometimes so i'm thinking stator wire or coil,anyway if you find out what it is,a lot of us would like to know.
Tom

Yep, I know the 50:1, I just don't want to under lubricate, so I've gone a little higher on the oil ratio, as besides smoking just a little bit more, my thinking was to provide as much lubrication on the cylinders as possible without overdoing it.

I guess I didn't see the harm in it if I kept it very close to the 50:1, and a little extra lubrication couldn't hurt...

 

[dorelse]

Re: Engine misfire when starting kills engine?

FYI, the extra oil will not affect anything but the economy of operation and it will increase your carbon build up to a degree. With today's TCW3 oils, you don't have to add extra as it is just wasted.

Whenever an engine backfires through the intake, it is either too lean or the timing is too advanced. Most of the time with outboards, the condition is that the mixture is too lean.

The thing to remember is that these engines use the idle circuit thoughout the entire power band. That means that if you are lean at idle, you will be lean at WOT. Lean burning at WOT results in bad things like holes burned in pistons.

John

Ok, I have a lot to learn...I will get on this as soon as my manual arrives.

Asking a dumb question time: I can easily get back to a 50:1 mixture in the tank, its a 6 Gal tank with 3 Gals left, so 50:1 won't be an issue. My question when you speak of too lean, we're talking now about the fuel to air ratio in the actual cylinder when it fires, rather than the mixture of oil to gas. Correct? Too lean meaning the balance of air to fuel in the cylinder is too much on the air side, with too rich meaning too much fuel, not enough air...I need need to get the proper balance, yes?

 

[john from md]

Re: Engine misfire when starting kills engine?

Now you have it. The ideal mixture at sea level on a perfect day ( memory fails but it is something like 59 deg F and I forget the humidity) is between 14 to 16 parts of air to one part of fuel. By being too lean, we are saying that the engine is getting less of a fuel mixture than optimum.

On many reciprocatiing engines, the carbs have a separate idle circuit which essentially stops operating when the throttle moves to mid range and WOT. The Force carbs utilize the idle circuit to provide fuel along with the main metering jet throughout throttle travel. They were cheaper to make this way and in reality, the Force engines are pretty basic, no frills types. (Which is a good thing for self maintainers as they are very simple machines)

John

 

[dorelse]

Re: Engine misfire when starting kills engine?

Thanks so much for the detailed explanation. I'm the first and so far only boat owner in the family, so I'm kinda on my own...except for the iboats folks!

 

[john from md]

Re: Engine misfire when starting kills engine?

Welcome to your new, extended family. There is a wealth of knowledge on these boards. Some can express themselves better than others but nontheless the information comes across.

Happy boating,

John

 

[gregmsr]

Re: Engine misfire when starting kills engine?

Hey, I have the same "cough and die" problem sometimes while cranking. So, im hearing this is a sign of running too lean. Should a person slightly turn the mixture screws out say, 1/8 turn to help this? Or, start from the beginning, lightly seat, then back out one full turn +/- and risk screwing it up?

 

[john from md]

Re: Engine misfire when starting kills engine?

No, you should 1st check the linkage to make sure it is adjusted properly then adjust the mixture per the manual procedures. If you just start turning mixture screws without making sure the throttle plates are set right, you could be masking a problem and it will never run right.

John