99 yam 150 carburated rough idle

[jerry walters]

last year i failed to replace the fuel/water seperator and sucked in some water.i replaced the filter. it still ran good when i was going fast so i did'nt do anything till last week. heres what i did.
pulled it out of the water and replaced impeller and lower unit oil, pulled all 3 carbs and had them cleaned. replaced them and ran the motor. discovered that one fuel filter diaphram was torn and replaced it. I thought it was good so I put the boat back in the water and on the way from the boat ramp back to my dock 1.5 miles. it ran real rough at lower speeds but as i pushed the throttle foward it would take off and run perfect.it starts right up but it shakes at an idle as if it is missing. i then checked all the plugs and even ran it and pulled one plug at a time and it has good spark on all 6 and the motor seemed to run rougher as each plug was removed. i cheked the fuel seperator several times to see if i had more water,there is no more water in the fuel. i have good gas and good spark as far as i can tell.:mad-new
i'm thinking that an idle jet must still be dirty or i've damaged a cylinder wall and have lost some compression. i havent done a compression test yet. i havent replaced the spark plugs yet. i beleive that the linkage on the carbs is fine. what should i try now? what do you think?

 

[99yam40]

Re: 99 yam 150 carburated rough idle

Filters do not have diaphragms, maybe you are thinking of fuel pumps.

Did you follow the link and sync in service manual after reinstalling carbs? Needs to be done each and every time they are reinstalled.

Could be you have water in tank still and will hit lines when boat is moved in the right position while under way.

Probably need to replace both pumps if one went.

Trash or what ever hiding in lines. primer bulb, and pumps will end up in carbs if they are not drained and flushed out before putting clean carbs on

 

[jerry walters]

Re: 99 yam 150 carburated rough idle

Filters do not have diaphragms, maybe you are thinking of fuel pumps.

Did you follow the link and sync in service manual after reinstalling carbs? Needs to be done each and every time they are reinstalled.

Could be you have water in tank still and will hit lines when boat is moved in the right position while under way.

Probably need to replace both pumps if one went.

Trash or what ever hiding in lines. primer bulb, and pumps will end up in carbs if they are not drained and flushed out before putting clean carbs on

yes fuel pump. thank you! i am trying to find directions for sync and link . its not in my manuel unless it means the settings on the individual carb spring screws. witch are light seat then 1 turn out plus minus 1/4 turn. the linkage seemed to be fixed so i thought it would be fine. i replaced 1 fuel pump diaphram but was told that they are really diffacult to get right so i guess i'll buy 2 new ones.

 

[99yam40]

Re: 99 yam 150 carburated rough idle

link and sync makes sure all carbs are opening and closing exactly the same and addresses timing linkage also
Get the Yamaha service manual not a aftermarket, and make sure it is for your motor

 

[jerry walters]

Re: 99 yam 150 carburated rough idle

i've done it all and it is still skipping a little

 

[jerry walters]

Re: 99 yam 150 carburated rough idle

what could be causing this missing between idle and 2800 rpms. i recleaned the carbs and rebuilt the pumps! I've checked all of the fuel lines. i set the carbs 1. main needle out 1 turn from a light seat. 2. removed ilde screw and linked carbs by loosening upper and lower screws, made sure all carbs were closed, then tightened upper and lower screws. 3. start motor and set idle at 700 rpms. i've replaced spark plugs, put 65 gallons of new fuel in the tank(and the tank is clean) and that is all it has in it is new fuel. I've checked spark by pulling the plugs while idling and moved them back up to the plug and heard them all sparking. also with a timing light a saw them spark. a strong spark. the motor starts right up. I checked compression-- 1-124 2-120 3-118 4-118 5-112 6-112. could that be why it wont idle smooth? where do i go from here? i really want to fix it my self . when i asked the marina how much coils were, his reply was, "its not the coils, they never go bad" so , is it my stater? the original one was replaced 8 years ago and the symptons were similar . and how do i test the stater if so. any input gives me something to go after. thank you

 

[99yam40]

Re: 99 yam 150 carburated rough idle

If you want to rule out stater.
follow the test procedures in service manual using the proper test equipment