Boat wont run without choke?

I have a Mercury 2 stroke on a boston whaler. The motor has been converted from oil inj. to mixed with gas. The motor will start when the throttle is pulled up and the choke on the key is rpessed, it dies unless you continue to push the button over and over. the carbs were rebuilt 4 months ago, and im really not sure where to begin looking for a problem. it runs smoothly and sounds fine as long as i continue to press the choke button in. any ideas would be appreciated.Boat wont run without choke?
You need a new fuel pump diagphram. Been there many times and thats what it turns out to be. The choke richens up the mixture and it runs ok when you are not getting enough fuel from the pump.
that symptom really only has one cause.



your hi-speed jet(s) are clogged.



The choke floods the engine with gasoline. It's necessary for a cold start, but any other situation in which the engine doesn't shut off when choked, means the fuel mixture is too lean to catch fire (not enough fuel vapor mixed with the air in the combustion chamber).



If the fuel pump were inoperative, the carb bowls would run dry; the choke would not be able to supply enough gasoline to make the engine run when choked.



Sometime in the last four months, the engine has either picked up some kind of debris that passed through the filter but caught in the carb, or else it sat unused and the evaporating gasoline gummed it up.



solution:

Remove carb(s), disassemble, soak overnight in carb cleaner, blow out all passages with compressed air (or aerosol carb cleaner), reassemble with new carb kit(s), reinstall, link %26amp; sync, adjust mixture screw(s) (if equipped).



And STOP running it like that -- your engine gets it's lubricating oil from the gasoline, so which ever cylinder(s)' starved for fuel is also not getting any lubrication. It's being dragged through a dry hole -- not good.Boat wont run without choke?
Here is a big "if"-- if it ran fine after you converted to mix, and this is a "new", not an "ongoing" problem. Then all the deep thinking about jets and oil injection are mote. In short, something went wrong in the carb, or reeds or seals.



First do a compression test to be sure you have something to work with.



The first thing to try might be the "hail Mary" vacuum clean of the jets and passages. To do this you will need access to the intake.



Run the motor up to 2000 rpm and slap your hand over the intake while it is running. Hold it there till the motor dies. The restart might take some time ,and you may want to do the procedure more than once. If there is some stuff in there this will probably move it around. If you do notice a difference, then you need to do the carb again and find out why stuff is getting past the filters.



If that had no effect, you will need to find out if the problem is common to one cyl or all.



Using your fingers as a choke to keep the motor running- slowly spread your fingers to lean the mixture. One or both (how many?) cylinders will drop out. If one drops but the other wants to keep running, you may have seals on the crank shaft failing. If it pops back thru the carb and scares the heck out of you, then you have shattered reed tips.



Either problem will require some one who is familiar with mercs.
There could be several things actually. With the oil inj. gone, the mix ratio that was variable with engine RPM is now gone. Play around a bit with your ratio to get it right or adjust your carb jets to choke the air down enough to run. Having a motors' system taken away plays havoc for a while. But keep in mind that you do not go too lean with the mix and that the underlying problem may be the motor itself may be going south on you. Do a full check on compression and your ignition systems, like checking for the burn pattern of your plugs, may give you a hint of where the problem may be. Good Luck.Boat wont run without choke?
I would say you have a carb problem, if it is leaning it out when you shut off the air it runs, check for the throttle plates opening, and that it is getting fuel at low idle
you could try bumping up the idle speed a little bit, or raising the octane of the fuel before you mix it with oil
obvious fuel blockage ..check feeds and inlet too carbs....
I have come across something like this with an old suzuki. The issue is that at idle the oil injection is at a ratio of at least 200:1, possibly even much less as the engine only needs the extra oil at high revs/load. With dykes type rings and full roller bearing systems a modern two stroke needs very little oil at low load to avoid wear. Were the carbies tuned for pre mix fuel at rebuild? I would expect the primary jets are too small to give enough petrol at low revs. You do not say if the engine can be coaxed up to high revs and then how it runs. The additional oil in the mix means that there is less petrol in a given drop of pre-mix - and this oil content is now four times what the engine had with the original system, so creates a lean burn situation, the additional oil also slows the flame front so the original timing may now be out enough to create an issue. When converted did the oil injection system get fully examined and all potential air leaks get blocked off correctly? Sorry to go on but the symptoms are of a very lean condition, The manifold seals between the carbies and the engine must be checked to ensure there are no leaks of any sort.



Good luck.:)



Doh! Thanx Mark. The fuel pump diaphragm is an excellent suggestion. I have just got a little 6 Evinrude going that had a pump fault - fixed by swapping out the pump for one off an old dead engine. All fuel lines and the tank pick up required attention It had the same symptoms.......... It was late when I typed the first part.