Idles fine, than surges than pops and back to fine idle?

[exp2000]

I finally got my 90 hp, 1997 Force to start, starts very easy, don't have to do much, just push the key in, and after 3 turns is starts right away. Than every 3-4 sec is pop a little, rpms drop down then go up slowly and than pops again and so on, every 3-4 sec. It never dies. I observed the filter, I could see that every time it pops (it does not back fire I think) it looks like a surge of air happens in filter. I'll take a video later and post it but for now, does this sound familiar, and what would be the reason? Carbs were rebuilt as well as pump, and hoses were changed.

 

[steveclv]

Re: Idles fine, than surges than pops and back to fine idle?

Generally pops and backfires are a sign of a weak mixture - in a 2 stroke that is not a good state of affairs as the fuel carries the lubricating oil. Richen the carburetor idle mixture screws by a 1/4 turn and see how that affects it. Better too rich than too lean.

 

[exp2000]

Re: Idles fine, than surges than pops and back to fine idle?

Ok, will do, since I did not really adjusted them yet, just kinda put them back how they were. What I don't understand in descriptions is the term "lightly seated". What does that actually mean?

 

[steveclv]

Re: Idles fine, than surges than pops and back to fine idle?

It means just screw them in until they stop - just stop - if you overtighten them you will ruin them so lightly seated means just until it stops using finger pressure only.

 

[exp2000]

Re: Idles fine, than surges than pops and back to fine idle?

Thanks for explanation, one more question, when you say enrichen by 1/4 turn, you mean to screw it in 1/4 turn?

 

[SwampThing]

Re: Idles fine, than surges than pops and back to fine idle?

Thanks for explanation, one more question, when you say enrichen by 1/4 turn, you mean to screw it in 1/4 turn?

NO! Back it out 1/4 turn to allow more fuel mixture to flow through. The screw on the carb that you are turning is a long needle shaped screw. The needle shaped tip of that screw fits into a tiny (brass?) orifice inside of the carb. This is the "seat".

When properly set, that needle screw and the seat (aka, "jet") work in conjunction to insure just the right volume of fuel mixture is allowed. When you over tighten the needle screw you run the risk of damaging the screw tip or the damaging the seat. It doesn't take much as the screw and the seat are a precision fit to each other.

When you "back the screw out" you are increasing the distance between the tip of the screw and the seat, thus increasing the volume of fuel that is allowed through, known as "enriching". "Turning the screw in" reduces the distance between the needle and the seat, reducing the volume of fuel that is allowed through.

In a two stroke engine the oil that lubricates the engine is contained in the fuel mixture. The reason everyone is adamant about NOT running the engine with the screw backed out less than 3/4 turns from fully seated is that it will not allow for a large enough fuel mixture to properly lubricate the engine and damage can result.

Indeed, in just about all carburated engines (boat, car, motorcycle, lawnmower) you'll find the optimum adjustment somewhere between 3/4 and 1 & 1/2 turns out from fully seated. You'll know it when you find it because your idle will for the most part smooth out and the engine will be at it's most responsive performance-wise. If you can't find the optimum adjustment somewhere in this range you most likely have a problem somewhere else. ie, restricted fuel flow issues, incorrect ignition timing, etc.

The other benefit of having a "properly" tuned engine, besides a great peace of mind out on the water, is that when properly tuned your engine will also have the best "fuel economy" that it was ever designed to have under all conditions.

Hope this helps to explain things a bit better.

 

[jerryjerry05]

Re: Idles fine, than surges than pops and back to fine idle?

Turn in air screws(gently) to the bottom.Turn out 1 and 1/8th turn.
Start motor,warm it up.In gear at an idle,motor running,warm, turn in top air screw till the motor just bucks,kicks cough.Then out 1/2 turn.Then #2 and #3
Then set the idle 750-800rpm. in gear motor warm.J

 

[crazyinkc]

Re: Idles fine, than surges than pops and back to fine idle?

My 10hp "Sailor" did the same thing when I first got it. I tuned it and what a difference it made. I run it on a 20ft pontoon and before the throttle response was a bit slow but now I can blip the throttle around the trees to get to where the crappie are. My screw was very sensitive but I am running one very small carb so I expected that. I think I ended up wit a 1/8th turn out from where it was when I got it and anymore it flodded out and any less it stalled. So in total I had less than 1/2 turn window to work with.

 

[exp2000]

Re: Idles fine, than surges than pops and back to fine idle?

I'll try it this weekend on the lake, cannot really work in the neighborhood. Hopefully we'll have some nice weather.

 

[exp2000]

Re: Idles fine, than surges than pops and back to fine idle?

Took it to the lake this weekend for the first time and had a somewhat good time.
It cranked immediatelly, it run beautifully, did not have to do any adjustment. I could get WOT and I run it for 5-10 min. Than I would let it run on idle.
Seems like my tachometer is not right. It is showing 4K rpm on idle, and on WOT it is over 6K, cannot go anymore. Several times when I would open the throttle, it would die, at about 2/3. It if would pull it back to idle it would not die. When it would die, it would start right back. So some work needs to be done to tune it...

Now for "funny" stuff. I forgot to engage the pin on the winch, so the strap got loose. Lucky for me, had to stop at gas station. One of the straps on the transom fell of too.
Battery on my truck died too, so had to have somebody jump me. Water was kinda choppy, and I did not check when I was pulling the boat out, it did not sit right on the trailer; it is little bit to far back, and a little bit to the side. Lake is just 5 miles away, so will have to get this in order too. And my dog decided to jump of the boat into the water, and he jump in front of the boat, while boat was moving, so had to rescue him. By the time I turned around, he was swimming on his back, 10 sec more he would have drowned. What a day... Thought boating was supposed to be fun....

 

[jerryjerry05]

Re: Idles fine, than surges than pops and back to fine idle?

D%^& YOU need to PRAY before you go boating.Bet the dog don't jump again.
On the back of the tach is a tiny slot,try turning it while the motor is running.
Check for water in the gas,do a compression test,change the filters.Make sure the idle is 750-800. A TINY TACH is a good thing to have in your tool box.J

 

[exp2000]

Re: Idles fine, than surges than pops and back to fine idle?

He would not come out of the boat by himself, had to carry him out. LOL

 

[exp2000]

Re: Idles fine, than surges than pops and back to fine idle?

Ordered one from Amazon, did not know they existed before, thanks for the tip. I think that compression is great (have not tested it), but it goes like a rocket on WOT (when it works ). Will hop to Autozone and get one to test it out. All filters are brand new, the fuel pump has been rebuilt, and carburetors have been rebuilt, and gasoline was brand new too, all hoses are new, the primer bulb is new, and does not go flat after running for a while. Also tank vent is not clogged. Cold starts after immediatelly, just like a car, couple of cranks and it is running, and really smooth.

This is what I noticed when adjusting the carbs, the bottom one idle screw seems to have no impact at all, I can screw it in all the way in (lightly and slowly) and no change noticable. I can take it out 2-3 turns nothing.