1998 40hp 4 stoke "weak hole shot"

Thank you in advance to anyone that can help with this issue!<br /><br />1998 40hp 4 stroke Merc (manual start, tiller)<br /><br />This motor runs great all the time, except on full throttle hole shot. It performs fine from half speed to full speed. The motor seems to be staving for fuel on the hole shot, but I dont know how to give it any more.<br /><br />To date I have cleaned and inspected the carbs (twice to be sure), checked the "auto enricher" to factory specs, checked and cleaned the entire fuel system from tank to carbs, replaced the spark plugs. The last time I tore down the carbs I set the floats to allow a little more fuel in the bowls, within factory specs, and that helped some but it did not solve the problem. When I run the motor with the intake removed, where I can see in the carbs, and I give it throttle I can see fuel spraying in the bottom and middle carb, but not the top. There are really no adjustments on this motor (timing or carbs) any 4 stroke experts out there???

Re: 1998 40hp 4 stoke "weak hole shot"

Don't know what to say about your upper carb not misting fuel. If the engine runs out ok after the hole it must be getting fuel. No reason for it to not get it on the hole then magically get it once you are up and running. Maybe the mist is too fine to be seen.<br /><br />Assume you haven't dinked with your timing so the throttle advance timing is working correctly.....<br /><br />Prop is the only thing I can think of. Don't know what kind of boat you are running, but you are apparently overloading the engine on the hole. 3 suggestions.<br /><br />1. Deliberately move a lot of gear forward just for the purpose of seeing if your hole improves. If so, it supports the overload theory.<br /><br />2. Take everything out of the boat that is not absolutely essential and try again to see if the hole improves.<br /><br />3. If 1-2 fail, you may have low compression or something in the engine.....but "runs great otherwise" doesn't support that. Could be carboned up and need a Sea Foam decarb job....which I know (BTDT) will improve the hole, idle, and starting.<br /><br />Then there are a couple of options....reduce pitch of prop, or you might try something the big boys do. Higher HP props, especially for bass boats, have porting holes drilled in them to force cavitation in the hole. <br /><br />This allows the engine to come up to rpm's immediately allowing the engine to deliver it's hp (instead of bogging down) and then as the boat picks up speed, water pressure (running by the side of the prop) seals the holes off and you don't know you have them. I had a 115 with ports and they work, period.<br /><br />Haven't heard of any porting on a 40 hp, but why not. Ask your local prop shop (they can do it).<br /><br />HTH,<br /><br />Mark

Re: 1998 40hp 4 stoke "weak hole shot"

Thank you Mark. I hope that the compression is not an issues, but i have not though about that. I know it is not a prop issue, because when i run it on the muffs and aggressively give it throttle from idle it boggs a little before it revs up. I will have to dig out the compression tester and see what i have.

Re: 1998 40hp 4 stoke "weak hole shot"

I was brousing through my service manual yesterday and in the trouble shooting chart it talked about opening your low speed jets if problems such as yours were experienced.<br /><br />I have a similar hesitation problem and I have just opened my jets 1/4 turn. Will go to the lake, when the storms pass over, and see if this is the answer.<br /><br />Before I adjusted them, I checked their setting and all three are at 1 1/4 turns where the book says to start. (Then if that's too lean, open up till it levels out......if that is the problem.)<br />To meet EPA rulings, in the manual, they talk about the 14.7 preferred fuel/air ratio and what happens above and below that....but they still tell you that if she is strangled give her some more fuel.<br /><br />Have no idea why compression would be a problem for you in that late a model engine. Sea Foam will surely improve it however.<br />HTH.<br /><br />Mark

Re: 1998 40hp 4 stoke "weak hole shot"

I do not think my jets are adjustable on my 4 stroke, am i wrong? The only adjustment screws i have are the idle and synchronization screw. Please advise if i am mistaken...

Re: 1998 40hp 4 stoke "weak hole shot"

Did adjusting your jets fix your problem?

Re: 1998 40hp 4 stoke "weak hole shot"

my jon 30 hp 4 stroke did the same thing, starved for fuel after 3 years. talked to merc mechanic, said to drill out brass plugs (carefully) and enrichen slightly, fixed mine, now i run a 10.25x14 pitch yamaha prop on it. runs bout 34. brass plugs are bout 3/8 in, and drill bout 1/16 deep, CAREFULLY, dont go to deep, will strip out screws under caps. good luck ron

Re: 1998 40hp 4 stoke "weak hole shot"

Ron, I am not sure which brass plugs you are referring to... Please advise. How did you enrichen your carbs, because i do not believe mine have any adjustments.

Re: 1998 40hp 4 stoke "weak hole shot"

hi jr, look on your carb bodies, it is a smooth , brass cap that is flush with carb body,the enrichening screw is behind this cap. you have to drill through the cap to adjust the screw under it. the cap is bout 3/8 inch width, it is located on the outside of carb right above linkage. unscrew bout 1/4 turn and try it. should help a lot. my 2000 30 hp 4cycle merc has 3 carbs, one for each cylindar. have to do this to all three to balance out. good luck ron email address is rdavis003@charter.net.

Re: 1998 40hp 4 stoke "weak hole shot"

just got my 02 404 stroke back, i had a "stumble<br />and rough running problem, turned out synching<br />the carbs fixed the rough running, but the stumble was fixed by a new fuel pump diaprham and new crankcase gasket,....

Re: 1998 40hp 4 stoke "weak hole shot"

I am going to run the motor Saturday, I will let you know the results. Ron, i am going to email you pics of my carbs. I have a cavity where you are describing the enrichening screw. They could just be hard to see, is it an allen head by chance?

Re: 1998 40hp 4 stoke "weak hole shot"

I took the boat to the lake, after adjusting the floats, and it is no better. I am thinking my original post should have said no hole shot. The motor still will try to die at full throttle from idle. I pumped the bulb while accelerating, but it made no difference. Can i rule anything out with that? Is this hassle common with 4 strokes? What a pain!

Re: 1998 40hp 4 stoke "weak hole shot"

I have a 1999 40 4 stroke that has the same hole shot problem, sometimes my engine will even stall as I throttle up. I've had it to the dealer, they synched the carbs for me but it's still difficult to get on plane. My carbs don't have any brass plugs as mentioned by others. Does your engine ever stall when pulled back from WOT to idle?<br />I feel your pain !

Re: 1998 40hp 4 stoke "weak hole shot"

hi guys. i promise you that all the motors need is enriching, i wouldnt take nothin for mine. i used my gps to see how fast it runs this weekend, it is rated 30 hp, i enlarged the holes in the restrictor plate,(black isolator plate). and now have a 40 hp. With 1500pd boat , it runs 33.2 mph. i had the same problem with mine that you guys have, after removal and cleaning and inspecting the carbs a 4th time, i called a mechanic from The Fishin Hole in St Lious mo. told me how to fix it , said the motors take time to breakin, and the epa settings are to lean. My manual says to seat screws then out 1 5/8 turns + or - 1/2 turn. I'm swinging a 10.25x14 pitch yamaha prop. gas mileage is great and plenty of power. its a 2000 model 30 hp. Checked blackbox, fuel enrichener,timing, fuel pump, all ok, just had to turn 3 little screws out 1/4 turn , fixed all my problems. hope this helps, ron

Re: 1998 40hp 4 stoke "weak hole shot"

Fishin Nut, my motor will stall on the throttle up, but it has never done so on wot to idle... I am searching for these brass plugs. Ron sent me a page out of his service manual that appears to be my carbs. I will let you know what happens. <br /><br />Ron i emailed you back, thanks for the info. I hope you are right, cause you might save me a buck or two.

Re: 1998 40hp 4 stoke "weak hole shot"

fishin nut, stay with this post, when i get it resolved i will let you know, and you do the same. It is very frustrating.

Re: 1998 40hp 4 stoke "weak hole shot"

check your valves, a tight intake valve can couse<br />fuel misting out the carb and decrease in low end.

Re: 1998 40hp 4 stoke "weak hole shot"

jr your right , your carbs have the hole but i dont know if it is adjustable, suggest you email mercurymarine.com with your question, to see if it is adjustable, I must be lucky, i use my motor extensively in the ohio river, run miles a day almost every weekend, no problems other than a roached o-ring in my gas asist power trim. best motor i've had, realy economical and quiet. starts easily in cold or hot weather. i change oil and filter every january, i never "store" the boat, i use it all winter, only use my 374 commanchee ranger when i want to bass fish, or get in a hurry, hahahhahha good luck, ron

Re: 1998 40hp 4 stoke "weak hole shot"

Ronnieboy, I also found holes where the plugs and screws should be, but nothing is there. They must have changed the design for the 40 hp. I'm purchasing trim tabs to try and help get on plane.<br />Don

Re: 1998 40hp 4 stoke "weak hole shot"

Re: 1998 40hp 4 stoke "weak hole shot"

Don, our carbs are not adjustable. Merc has come out with a part to fix our problem. The part number is 803914, and it is a replacment Nozzle in the carb that allows more fuel. Mine are on order, and i will let you know how it works