Yamaha 250hp 2 Cycle - Bogging Down?
 

Looking for some help on solving a problem I am having with my 1993 Yamaha 250hp 2 cycle engine, thought someone on here may have had the same problem or knows what can cause it. I tried searching other sites and the answers ranged from trash the motor and start over to bad fuel.....

Here's what happing, it starts fine, idles find but when you give it fuel is starts out as normal then about 10 second later it start slowing down (bogging) sometimes to a idle sometimes just drops a few RPM. After a few minutes it clears up and runs fine. This is what I have tried, new gas/water separator filter (no water found in gas). New gas lines, removed an after market auto filter that was in line before the carburetors, new plugs. OEM bulb primer pump (old one had smaller entry & exit ports & was sucking flat). Seafoam, Deep Creep and another fuel product that they advertise on Sea Shape TV(can't remember the name).

When I pull the plugs they all look the same in color and wetness. I really think it's a fuel problem. If all else fail the next step is to rebuild the six carburetors. But if it is the carburetors wouldn't one or two plugs look different and the problem consistent?

Thank you for your suggestions.

Re: Yamaha 250hp 2 Cycle - Bogging Down?
 

Jeff, if you think you have suspect fuel try running off a seperate 6 or 12 gallon tank. I just had similar problems with my engine and when I ran on six gallon tank the engine ran great. Also I have had luck with a quicksilver product called power tune in an carburated engine a couple years ago. Hope this helps and good lick.

Re: Yamaha 250hp 2 Cycle - Bogging Down?
 

i had a simmilar problem with my two engines started fine then when they warmed up the would basically die down to about 1200 rpm found out the gas i bought with the boat was bad when the engine warmed up there wasn't enough kick in the gas get a 6 gallon tank put fresh gas in it and see what happens if the same thing you will know it's not the gas that's what i did and it ran fine pumped out the gas put in startron and filled up and it hasn't done anything except purr

Re: Yamaha 250hp 2 Cycle - Bogging Down?
 

The bulb sucking flat could indicate a blocked (or partially blocked) vent. If the vent hose isn't alcohol resistant it may be the problem.

Re: Yamaha 250hp 2 Cycle - Bogging Down?
 

I had a similiar pfoblem with an I/O years ago. It would idle fine and then either shut down or refuse to accelerate like it should. It kept getting worse as the days went by. Finally talked to a mechanic and he said to check the float chambers of the carb for water. Sure enough. There was enough water in the chambers to preclude anything more than a trickle of fuel across the water's surface and into the engine. I suspected that when it shut down it actually sucked enough waster to simply kill any combustion.

Good luck.

Re: Yamaha 250hp 2 Cycle - Bogging Down?
 

Thanks guys, I am going to try the 5 gallon fuel tank idea if I can get off work early enough one day this week. Also going to drain the bowls again and put in another set of plugs.

Just got back from running it the bay, it bogged down a couple times when we 1st got there. Coming back in it ran like a new engine until we had to slow down for a "NO WAKE" zone, that was it for the day it would never even get enougn speed to get back up plane again... if I had extra $20k setting around I would re-power it tomorrow.... would save enough in fuel to pay for in a couple of years... :rolleyes:

Thanks again for your help! I will let you know what I find.

Re: Yamaha 250hp 2 Cycle - Bogging Down?
 

all I can say is isolate and eliminate - it works - try the different tank that isolates and eliminates the tank and fuel lines as well as the vent - save your money on another set of plugs that ain't it. Does sound like a fuel issue though but if you have drained the carb bowls and found no water anywhere I wouldn/t bother doing that again either - you eliminated that unless you found trash in them.

rebuilding carbs is nothing more than cleaning the bowls out - you did that - and new gaskets and a new needle and seat, I would pull the air box and make sure the carbs are not overflowing fuel which is eliminating the needles and seat. Do not run WOT without the air box on it - it will lean it out too much, just look for flooding carbs

Re: Yamaha 250hp 2 Cycle - Bogging Down?
 

Pull the carbs down completely and blow/clean every nook and crany out with carb cleaner and compressed air.

Re: Yamaha 250hp 2 Cycle - Bogging Down?
 

Check your pickup in tank ethanol is breaking loose a lot of old sludge in gas tanks. Screen in tank could be sucking up trash intermittently. Also gas hoses have been separating inside and collapsing another ethanol dilemma. Especially the gray hose. After that have carbs rebuilt by a competent mechanic.

Re: Yamaha 250hp 2 Cycle - Bogging Down?
 

I am back... work has kept me tied up. :(

Ok made some progress; after trying the "fuel can" idea was able to rule out a fuel delivery issue.

Pulled the carburetors, cleaned and set the pilot screws to 5/8 as the manual stated (they were set @ 1/4 to 1 turn). Cleaning the carburetors made a world of difference no more bogging down. But after idling back through the no wake zone developed a miss and lots of smoke and gas smell. Pulled the plugs, 3 of them were soaking wet. Changed them and adjusted the two pilot screws I could reach to a 1/4 turn from a soft seat. Ran much better. Got home and adjusted the other carburetor to a 1/4 turn and took her out again. Almost back to normal but still not 100%, pulled the plugs and they look pretty consistent in color and wettness... scared to tweak the plot screws to much.

Also checked the plug wires getting 7.2 - 8.4 ohms resistance on them....

Now running around 4800 RPM tops (41mph)... was around 5200 RPM (45 mph) before the bogging down issue started. But not complaining.

Re: Yamaha 250hp 2 Cycle - Bogging Down?
 

I just worked thru a problem on my 98 carbed yamaha 200. It needed constant bumps on the choke to idle and it would bog down while running and again using the choke I could get it to preform for a short distance then id need to pump it again. I pulled the carbs cleaned them no help. ran a seperate tank nothing, I also took apart one of the fuel pumps it looked fine. finialy I decided to de-carb(I have not ever done this to this motor.) using sea foam. It did the trick. although the seafoam may have cleaned somthing I missed besides the carbon, Its running great now.

Here is the seafoam de-carb procedure I used.

Also Yamaha wanted 53.00 each for new bowl gaskets! :eek:

http://www.switchbait.com/forums/showthread.php?t=159

Re: Yamaha 250hp 2 Cycle - Bogging Down?
 

Thanks bbh57, I will give it a try.

I have read about using Seafoam to decarb but was never really sold on the idea. I read were they talk about it smoking while doing the decarb and thought it was just the Seafoam burring off... but after reading this procedure where it stops smoking after 2 or 3 times I am more convinced.

Thanks again for the link, I will let you know how it goes.

Re: Yamaha 250hp 2 Cycle - Bogging Down?
 

Ive read something about 02 sensors on a yamaha clogging up with carbon and causing surging, loss of power and excessive smoke, might check into that

Re: Yamaha 250hp 2 Cycle - Bogging Down?
 

Tried the Seafoam decarb mixture...

Mixed 3/4 gal gas, 1 can of Seafoam and 3oz of two cycle oil.

Removed the line going to the primer bulb and gave it a few pumps started the motor and let idle for 15 minutes. About 5 Min's in it started to smoke like it was on fire. Cut motor off after 15 Min's and let set for 15 Min's... discovered that in 15 Min's of idling the motor used almost the whole gallon of fuel... only about 6 oz left.

Restarted the motor after 15 mins and it smoked like crazy!!! Ran better, but still not back to normal.

By doing this test I may have discovered the problem. 1 gallon of fuel in 15 Min's while idling seems really high so I think it's a choke or fuel pump issue...

PS: on the way home today broke an axle, had to rig up a brace to get back to the boat ramp to launch the boat so I could take the trailer about 20 miles to get it welded :( So new axles will be required ASAP...

Re: Yamaha 250hp 2 Cycle - Bogging Down?
 

My old carbed 115 V-4 burned 2 gal/hr at idle, and a V-6 would burn even more, so the fuel you used sounds about right!

Re: Yamaha 250hp 2 Cycle - Bogging Down?
 

I think mine burns more at idle than at wot!! :( Use that seafoam a couple more times. Let it sit a while longer also. The seafoam acts as a solvent to "dissolve" the carbon in the cylinders and the crud in the carbs.

Re: Yamaha 250hp 2 Cycle - Bogging Down?
 

Thanks Guys! I feel better now about the fuel usage. Me and the boy love to go WOT, but the women wants to idle everywhere we go, now I have an excuse to go faster... I am saving fuel!!!

I will try the seafoam treatment again. The primer pump bulb is sucking shut again, so got to do some more investgating.... I may name the boat "Something Else" cause here lately it's always something esle... but still love here.

Re: Yamaha 250hp 2 Cycle - Bogging Down?
 

That means there is a flow restriction UPSTREAM of the primer bulb, like a plugged filter, plugged screen on fuel pickup in the tank, plugged elbow, etc. Sounds like maybe the "ethanol-fuel-cleaning-out-tank disease! :D

Re: Yamaha 250hp 2 Cycle - Bogging Down?
 

Check the anti siphon valve on the tank. You can remove it and change it or just leave it off.

Re: Yamaha 250hp 2 Cycle - Bogging Down?
 

Replaced the primer bulb and solved the collapsing problem. The old one was very soft and had no resistant.

Ran another can of Seafoam throught it. Pulled carbs and cleaned and put in another new set of plugs.

But still not running right, when I go to WOT it will only run about 2000RPM for about 3-10 minutes before taking off. But still not getting the old top speed of 47mph, top speed now is 42 in ideal conditions.

Anyone know a good trustworthy Yamaha or outboard tech in the Mobile, Al. area?

Re: Yamaha 250hp 2 Cycle - Bogging Down?
 

Did you check this?

Re: Yamaha 250hp 2 Cycle - Bogging Down?
 

I don't think I can remove it from my tank. From what I can tell the fuel gauge sending unit is the only thing I can remove from the tank, but I could be wrong, wouldn't be the 1st time. I will take a picture of my fuel tank when I get back in town later this week.

Re: Yamaha 250hp 2 Cycle - Bogging Down?
 

Yes do that. The Anti siphon check valve should be right in front of the sender. It may be hard to do, but most are just a barbed fitting. It is attached right to the street elbow.

Re: Yamaha 250hp 2 Cycle - Bogging Down?
 

Haven't had a chance to remove the cover and take a picture of the tank... BUT think I got it fixed. Saturday pulled the hood. Found one problem right away a pinch fuel line and then noticed that one of the linkage arms were loose. After fixing these two items it ran much better. Then adjusted the jets additional 1/2 turn out on each carburetor. Tried it again, it ran better than ever!! Hit 48mph quickly with no bogging down out of the hole!!!!

Wow was I excited!

But then the *@$#ing foot locked up!!! Motor wouldn't even turn over. Kept working with it moving from forward to reverse it finally clicked and was able to start the motor but it was hung in reverse!! SO we backed almost 2 miles back to the dock... kind of embarrassing!! :o

When I got the boat in OCT 09 I changed the foot oil and noticed shavings on the magnet on the drain plug and then changed the oil again a few weeks ago and noticed a few more shavings so I knew there was an issue but I guess I thought it would fix itself :D

Been pricing lower units found new OEM for around $5,000, rebuilt for $1000 and "used" for $695.... did see one company called SEI that offers "NEW" lower units (not OEM) for $795 with a 3 year warranty. Anyone every heard of them? May need to start a new thread to discuss the lower unit issue.