Re: 1999 Yamaha 150 SS OX66 EFI Bogs down
some things to look at: #1 compretion and /or leak down test. (probbubly not the issue but easy to do) #2 i normaly would start here with the steps needed to trouble-shoot the fuel system-but- the fact the motor acts up at 2500rpm, is the same as the rpm limit of an over heat or no oil warning. this could happen if you do not have a yam. gauge with warning lights and a bad or disconected warrnig horn. will the r.p.ms go to 3000 in nutral?(do not "free wheel the motor more than a cuple seconds). if r.p.ms do not exeed 2500, try unplugging the temp senders and try aigin. a temp sender can trigger r.p.m reduction, but not trigger the warning horn. if motor rev's freely take a look at the fuel system. #3 "o.k", fuel system basics:
chk. the rail pressure at the time the motor is bogging/missing. it should be about 35 p.s.i. next, chk. for exessive fuel vacum between the motor mounted filter and fuel pumps. (dont forget to "t" off after the in line chk. valve) you should not have more than 4 in hg. use a 3/8 clear hose in line with the fuel line and chk. for exssesive "air bubbles" in gas line. you said the fuel pulse pumps are new. a quick way to truble shoot them is to prime the fuel system with the primer ball, then use a presure tester pumped up to 5 to 6 psi. it should hold, if it drops a dighram is leaking.#4now the harder stuff! your motor has an oxygen sensor. this usually can affect the runnng of the motor above 4000 rpm's, not usually at 2500. next:t.p.s= there are specs. that are easy to test for in a good repair manual. sorry so wordy! good luck!