84 Yamaha 70ETLN Hesitates on WOT hole shot

CEB1557 · #1 June 20th, 2005, 11:45 AM

My Yamaha 70hp outboard hesitate when I try and go to WOT from idle about 50% of the time. If I back off the throttle and bring it up slowly or wait about 5-7 seconds it will then run fine. It actually runs very good at WOT after the hesitation but if I stop the boat and immediately try to go again it will repeat the same hesitation. The other 50% of the time it takes off with no hesitation. I read a number of posts and I think it is either a fuel pump or timming problem. I rebuilt the carbs last year and this problem didn't start until the third or fourth time I had it out this year. I was planning on rebuilding the fuel pump but wanted to get some feedback first. The compression is about the same on all three Cyl. It is a little low but I expect that with an older motor. Any help would be appreciated.

CEB1557 · #2 June 28th, 2005, 11:58 AM

Anyone have any input on this. I would greatly appreciate it.

bernieb · #3 June 28th, 2005, 12:19 PM

Is your gas tank clean?how new are fuel lines and bulb ?Any fuel filters that need changing? How about the right plugs? How about decarbonizing the engine and replacing the plug wires.By all means replace the fuel pump or at least try a rebuild kit.There's something wrong so be careful or you'll lose it.Don't mean to be throwing parts at the engine but it's got some age and need replacing anyway. (Fuel pump first)

CEB1557 · #4 June 30th, 2005, 10:55 AM

Thanks for your input bernieb. I installed a new Tempo gas tank last year, new fuel lines on the motor. I did not replace the fuel bulb or line. Installed all vent lines as required. New spark plugs and fuel filter. I did not replace the plug wires but I was thinking of doing that and decarboning when I rebuilt the fuel pump. I also replaced the oil injection pump. The thing is this motor runs great most of the time it only hesitates once in a while, a problem when trying to pull up a skier. I have a repair manual and I was going to check the timming advance after reading some of the other posts. I am not sure what you mean by be careful or I may lose it. The motor just hesitates just like a car when you press the accelerator fast and it hesitates before accelerating. You can hear that the butterflies are opening it just seems like it is not getting fuel. I am ordering the fuel pump kit and seafoam deep greep and I will see if that helps.

Again thanks for your input.