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Author Topic:   Yamaha 150 2-Stroke Hesitates

Joe Hick posted 10-03-2013 08:18 PM ET (US)
Hi all, newbie here. I have a 1998 18 Dauntless with a 1998 Yamaha 150. Just yesterday for the first time, the engine hesitated for a couple of seconds during initial acceleration. After the first two seconds, all is normal.
This behavior repeated all day yesterday. Any idea what can cause this two second hesitation that had not previously occurred?
tjxtreme posted 10-04-2013 09:20 AM ET (US)
Could be lots of things, but have the spark plugs been replaced recently?
jimh posted 10-04-2013 10:00 AM ET (US)
Check the spark plug electrode for proper gap. It is common for the spark plug electrode to erode and the gap to increase beyond the recommended setting. This seems to manifest as hesitation on acceleration, in my experience with classic two-stroke-power-cycle outboard engines.
Jeff posted 10-04-2013 12:21 PM ET (US)
I have had the same problem with my very low hour and only freshwater used 1999 Yamaha Saltwater Series (SWS) II carbureted engine. I checked and replaced all of my plugs and re-gapped them all. Still had the problem.
I then ran it on a remote auxiliary tank and the problem basically went away except when I went from a cruise to WOT with an instant hard acceleration. I am planning to run all new fuel lines supply and vent lines this winter to see if that completely remedies the problem.
Out side of that, I and at a loss. The carb's seem to be set fine and clean and I decarboned the motor and run a lot of sea foam through the motor.
Joe Hick posted 10-04-2013 07:08 PM ET (US)
Thanks guys. I went ahead and replaced the plugs today but the symptom remains. One other thing I noticed was a hiccup of a backfire today, just once.
I too will make this a winter project and start going thru the fuel system. I'm just a bit surprised as I used the boat quite a bit this summer and the symptom just appeared. I filled the gas tank three times this season. I take it out at least twice a week for 2-3 hour runs. I run it for an hour to the clamming grounds, putz arounda a bit, and run it back home.
Anyway thanks again and I'll keep you updated on any remedies.
GRAND NUSSIE posted 10-04-2013 07:28 PM ET (US)
The hiccup and hesitation COULD mean that your engine is running a little on the lean side. Possibly dirt or gum in one or more carbs. In the really old days, the low speed mixture was adjusted by a knob on the outside of the cowling and we thought nothing of changing the mix as needed. My 8hp. Merc is very sensitive to temperature changes so I keep a screwdriver handy to change the mixture if needed. With multiple carbs changing the low speed mixture could be very tricky and I would suggest you not do so unless you know what you are doing.--Dick
Joe Hick posted 10-04-2013 08:09 PM ET (US)
Thanks GN. I definitely do not know what I'm doing so I'll start basic by adding some Quickleen or Seafoam to the gas. I bet I go thru another tank of gas before the end of the season. Before I pull it out, I'll try a remote tank, then take it from there. If I do need some carb adjustments/work, I'll have my local mechanic take care of it. Thanks again.
mcole posted 10-06-2013 11:36 AM ET (US)
Joe, I agree with Grand Nussie. You are explaining the signs and symptoms of a possible lean idle condition. One or more of your carbs low speed pilot jets may be partially or completely clogged. This manifests into a flat spot or hesitation when coming off idle. I would yank all carbs and have them gone thru. Don't just throw carb kits at them, sometimes they can be pulled off and cleaned without buying any parts at all. Good luck--Mike
BQUICK posted 10-11-2013 10:05 AM ET (US)
I had one doing the same thing and just turned the six idle mixture screws out a quarter turn and fine ever since. Worth a shot, as you can always turn them back.
Joe Hick posted 10-12-2013 09:55 AM ET (US)
Thanks BQUICK. When you say turn them out, I'll be turning them to the left, correct?
Swellmonster posted 10-13-2013 12:44 AM ET (US)
Counterclockwise
Like taking the lid off a bottle of root beer :)
Swellmonster posted 10-13-2013 12:45 AM ET (US)
Counterclockwise
Like taking the lid off a bottle of root beer :)
Joe Hick posted 10-20-2013 12:46 PM ET (US)
I pulled off the air silencer last night and turned out the idle mixture screws 1/4 turn. It was getting dark so I put the cover back to finish this morning.
This morning I noticed two hoses that were unconnected. One runs from the oil tank and the other runs from the bottom of the carb.
It looks like these two hoses potentially connect to the air silencer cover. Is this the case?
Joe Hick posted 10-20-2013 12:48 PM ET (US)
ps - I checked the service manual but it makes no mention of these two hoses.
Joe Hick posted 10-20-2013 01:11 PM ET (US)
The small hose that's disconnected runs to the top of the engine's oil tank. Per the service manual, this is the "oil hose". Could this be a misprint? Could this hose be the breather hose? If so, should it be connected to the air silencer cover?
PeteB88 posted 10-20-2013 06:45 PM ET (US)
My 40 Yamaha has similar symptoms intermittently. Besides decarb procedure, what has worked for me is pull off cover, motor running on muffs, warmed up and shoot Deep Creep (Seafoam) into carbs and/or Evinrude Tune-up stuff direct into carbs repeating many times. I also spray heavy into the carbs until motor starts to run hard and shut down and let solvent dwell for a couple hours. Seems to work but I still suspect goo in carbs.
Bottom line - I need to have a certified Yamaha mechanic do a link and synch w/ possible carb rebuild to solve this once and for all. Local Evinrude, Mercury, Yamaha dealer has done good by me in the past, fair and quoted super fair price for work described above. This is the time of year to do that.
Keep us posted.
Joe Hick posted 10-20-2013 07:01 PM ET (US)
I think I need a "service manual for dummies". My oem Yamaha service manual, I think, assumes the user has some intimacy with the motor, i.e. id the two tubes (mentioned above) should be connected and if so, to what.
I started putting the pieces together (after two hours) and I connected what I believe to be an oil overflow hose to the air silencer cover. I also connected the loose fuel hose to the silencer cover. I think these are overflow type of connections, the thought being that the gas and oil overflow will pour into the silencer cover as opposed to the floor of the engine. The silencer cover has two male ends that "look" like some type of hose should be connected to them. Hopefully I won't blow up anything.
The sympton remains, a two second pause upon acceleration. I'd like to add some carb cleaner to the gas and run it for a month or so. I know that I'll probably need to get the carbs cleaned, a winter project. But in the interim, what is the best carb cleaning fuel additive?

jimh posted 10-20-2013 07:46 PM ET (US)
Most two-cycle-power-stroke engines have oil re-circulation hoses. These hoses take oil from areas where it tends to accumulate and re-circulate the oil to other areas. Typically in the air silencer cover there is a possibility for some oil to collect from the fuel-air mixture. This oil drips to the bottom of the air silencer cover. A hose typically takes that oil and routes it into the engine block to provide lubrication. I don't know specifically how the oil re-circulation hoses are configured on your specific engine. The service manual ought to clearly show the hose routes.

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Author	Topic: Yamaha 150 2-Stroke Hesitates
Joe Hick	posted 10-03-2013 08:18 PM ET (US) Hi all, newbie here. I have a 1998 18 Dauntless with a 1998 Yamaha 150. Just yesterday for the first time, the engine hesitated for a couple of seconds during initial acceleration. After the first two seconds, all is normal. This behavior repeated all day yesterday. Any idea what can cause this two second hesitation that had not previously occurred?
tjxtreme	posted 10-04-2013 09:20 AM ET (US) Could be lots of things, but have the spark plugs been replaced recently?
jimh	posted 10-04-2013 10:00 AM ET (US) Check the spark plug electrode for proper gap. It is common for the spark plug electrode to erode and the gap to increase beyond the recommended setting. This seems to manifest as hesitation on acceleration, in my experience with classic two-stroke-power-cycle outboard engines.
Jeff	posted 10-04-2013 12:21 PM ET (US) I have had the same problem with my very low hour and only freshwater used 1999 Yamaha Saltwater Series (SWS) II carbureted engine. I checked and replaced all of my plugs and re-gapped them all. Still had the problem. I then ran it on a remote auxiliary tank and the problem basically went away except when I went from a cruise to WOT with an instant hard acceleration. I am planning to run all new fuel lines supply and vent lines this winter to see if that completely remedies the problem. Out side of that, I and at a loss. The carb's seem to be set fine and clean and I decarboned the motor and run a lot of sea foam through the motor.
Joe Hick	posted 10-04-2013 07:08 PM ET (US) Thanks guys. I went ahead and replaced the plugs today but the symptom remains. One other thing I noticed was a hiccup of a backfire today, just once. I too will make this a winter project and start going thru the fuel system. I'm just a bit surprised as I used the boat quite a bit this summer and the symptom just appeared. I filled the gas tank three times this season. I take it out at least twice a week for 2-3 hour runs. I run it for an hour to the clamming grounds, putz arounda a bit, and run it back home. Anyway thanks again and I'll keep you updated on any remedies.
GRAND NUSSIE	posted 10-04-2013 07:28 PM ET (US) The hiccup and hesitation COULD mean that your engine is running a little on the lean side. Possibly dirt or gum in one or more carbs. In the really old days, the low speed mixture was adjusted by a knob on the outside of the cowling and we thought nothing of changing the mix as needed. My 8hp. Merc is very sensitive to temperature changes so I keep a screwdriver handy to change the mixture if needed. With multiple carbs changing the low speed mixture could be very tricky and I would suggest you not do so unless you know what you are doing.--Dick
Joe Hick	posted 10-04-2013 08:09 PM ET (US) Thanks GN. I definitely do not know what I'm doing so I'll start basic by adding some Quickleen or Seafoam to the gas. I bet I go thru another tank of gas before the end of the season. Before I pull it out, I'll try a remote tank, then take it from there. If I do need some carb adjustments/work, I'll have my local mechanic take care of it. Thanks again.
mcole	posted 10-06-2013 11:36 AM ET (US) Joe, I agree with Grand Nussie. You are explaining the signs and symptoms of a possible lean idle condition. One or more of your carbs low speed pilot jets may be partially or completely clogged. This manifests into a flat spot or hesitation when coming off idle. I would yank all carbs and have them gone thru. Don't just throw carb kits at them, sometimes they can be pulled off and cleaned without buying any parts at all. Good luck--Mike
BQUICK	posted 10-11-2013 10:05 AM ET (US) I had one doing the same thing and just turned the six idle mixture screws out a quarter turn and fine ever since. Worth a shot, as you can always turn them back.
Joe Hick	posted 10-12-2013 09:55 AM ET (US) Thanks BQUICK. When you say turn them out, I'll be turning them to the left, correct?
Swellmonster	posted 10-13-2013 12:44 AM ET (US) Counterclockwise Like taking the lid off a bottle of root beer :)
Swellmonster	posted 10-13-2013 12:45 AM ET (US) Counterclockwise Like taking the lid off a bottle of root beer :)
Joe Hick	posted 10-20-2013 12:46 PM ET (US) I pulled off the air silencer last night and turned out the idle mixture screws 1/4 turn. It was getting dark so I put the cover back to finish this morning. This morning I noticed two hoses that were unconnected. One runs from the oil tank and the other runs from the bottom of the carb. It looks like these two hoses potentially connect to the air silencer cover. Is this the case?
Joe Hick	posted 10-20-2013 12:48 PM ET (US) ps - I checked the service manual but it makes no mention of these two hoses.
Joe Hick	posted 10-20-2013 01:11 PM ET (US) The small hose that's disconnected runs to the top of the engine's oil tank. Per the service manual, this is the "oil hose". Could this be a misprint? Could this hose be the breather hose? If so, should it be connected to the air silencer cover?
PeteB88	posted 10-20-2013 06:45 PM ET (US) My 40 Yamaha has similar symptoms intermittently. Besides decarb procedure, what has worked for me is pull off cover, motor running on muffs, warmed up and shoot Deep Creep (Seafoam) into carbs and/or Evinrude Tune-up stuff direct into carbs repeating many times. I also spray heavy into the carbs until motor starts to run hard and shut down and let solvent dwell for a couple hours. Seems to work but I still suspect goo in carbs. Bottom line - I need to have a certified Yamaha mechanic do a link and synch w/ possible carb rebuild to solve this once and for all. Local Evinrude, Mercury, Yamaha dealer has done good by me in the past, fair and quoted super fair price for work described above. This is the time of year to do that. Keep us posted.
Joe Hick	posted 10-20-2013 07:01 PM ET (US) I think I need a "service manual for dummies". My oem Yamaha service manual, I think, assumes the user has some intimacy with the motor, i.e. id the two tubes (mentioned above) should be connected and if so, to what. I started putting the pieces together (after two hours) and I connected what I believe to be an oil overflow hose to the air silencer cover. I also connected the loose fuel hose to the silencer cover. I think these are overflow type of connections, the thought being that the gas and oil overflow will pour into the silencer cover as opposed to the floor of the engine. The silencer cover has two male ends that "look" like some type of hose should be connected to them. Hopefully I won't blow up anything. The sympton remains, a two second pause upon acceleration. I'd like to add some carb cleaner to the gas and run it for a month or so. I know that I'll probably need to get the carbs cleaned, a winter project. But in the interim, what is the best carb cleaning fuel additive?
jimh	posted 10-20-2013 07:46 PM ET (US) Most two-cycle-power-stroke engines have oil re-circulation hoses. These hoses take oil from areas where it tends to accumulate and re-circulate the oil to other areas. Typically in the air silencer cover there is a possibility for some oil to collect from the fuel-air mixture. This oil drips to the bottom of the air silencer cover. A hose typically takes that oil and routes it into the engine block to provide lubrication. I don't know specifically how the oil re-circulation hoses are configured on your specific engine. The service manual ought to clearly show the hose routes.