Carbed Yamaha 150 - RPM tops out at 2500

[Pure Country]

I have a carbed 2003 Yamaha 150 that the RPM tops out at 2500. It ran fine the last time out, but now won't tach up under a load. It will tach up fine in neutral or even in gear on a flusher hose, but when you put it in the water the RPM won't go past 2500 unless you shift it into neutral. I have no alarms or fault indications on the mult-function tach. I have decarbed it, changed spark plugs and even ran it on a seperate tank of gas. I have ran it with the intake cover off and the best I can tell, it's putting fuel through all 3 carbs. I'm outta options without a dealer visit. <br /><br />I think I've looked at the obvious. <br /><br />Does this engine have an RPM limiting feature that won't be accompanied by a fault alarm/indication?<br /><br />Could it be a limp home feature on a bad ignition unit?<br /><br />Any ideas anyone?

 

[rodbolt]

Re: Carbed Yamaha 150 - RPM tops out at 2500

sounds like you have a fuel delivery roblem, drain the engine filter and look for water, if ya find any pull the drains and main jets and flush the fuel system, if the alarm is working it will limit RPM to about 2500 but you will get a visual and and audible. also test the spark. if all 6 spark test the high speed charge coil for opens and shorts to ground. dont rev it that high with no load. its rather hard on roller bearings as they tend to chatter when trying to slow down.

 

[Pure Country]

Re: Carbed Yamaha 150 - RPM tops out at 2500

Rod Bolt: I should have mentioned this in the first post. I didn't have any water in the filter when I pulled it and I pulled the side plugs out of each carb and sprayed them full of Sea Foam from a spray can and let them set a hour or so. Do you think with that and running a decarb mix of 1 1/2 to 2 gal can of gas mixed with a can of Sea Foam could have still left me with a carb/fuel problem?<br /><br />I'll check the spark on the cylinders one at a time, but what do you mean when you say "if all 6 spark test the high speed charge coil for opens and shorts to ground"? <br /><br />Are you referencing the individual coils for each cylinder?<br /><br />PS<br />I'd like to figure this out with a dealer visit, but I have a few months of warranty left and don't want to tear into anything that'll cause me warranty issues.

 

[rodbolt]

Re: Carbed Yamaha 150 - RPM tops out at 2500

the high and low speed charge coils supply operating voltage to the CDI. the break is about 18-2500. if the high speed coil is bad it may not run correctly above that speed. and have you tested the fuel pumps for internal leakage? usually a bad diaphram will cause a poor idle as well.

 

[Pure Country]

Re: Carbed Yamaha 150 - RPM tops out at 2500

Checked the spark & compression, it was good. Couldn't do much more without upsetting the warranty. Took it to the shop and they found fouled up carbs. The boat has never set more than 1-2 months and I've stored it with a generous treatment of Stabil. I've heard that you should store a boat with the carbs ran dry.<br /><br />Any thoughts on how to prevent this again or if the dry carbs is the answer? <br /><br />The bill is $430.00, so I'm quite interested in preventing this again!!!

 

[rodbolt]

Re: Carbed Yamaha 150 - RPM tops out at 2500

depends on what fouled the carbs, if you just run them"dry" it will leave enough fuel to do it again. I reccomend if ya gonna let her sit over 30 days crack the drain plugs and drain them.<br /> see what I say about snake oils in the fuel, just dont work. once the carbs are fouled they are fouled and the only safe way to unfoul them is dissasembly. but fouled carbs are not warrenty <br />430 for a carb job in my area is a tad high but not to bad. 2 hours labor plus kits and maybe a seatrail.

 

[Pure Country]

Re: Carbed Yamaha 150 - RPM tops out at 2500

Your right about the warranty and do I know it...<br /><br />The dealer suggested the same as you on not "running" the carbs dry, as they will still be half full. When you say "crack the drain plugs and drain them". Do you mean the drain plug screws on the side of the bowls or on the bottom? Because the bottom ones will be a son of a gun to get to each time...<br /><br />The dealer did suggest using only Amoco 93 octane gas, which he referred to as a "white fuel"???<br /><br />Any comments?

 

[rodbolt]

Re: Carbed Yamaha 150 - RPM tops out at 2500

white gas is a brand of unleaded, its not nessasary.<br /> if your carbs do not have the little 10mm brass hex on the lower leading edge of the carb then its difficult to impossible. I dont reccomend loosening the main jets as the oring on the jet may get damaged. I reccomend keeping fresh fuel and stabil. if the gas in the tank is old no amount of additive will help it.