Yamaha 130 rpm problem

[Yukahey]

My 1987 yamaha 130 sat for two years. When fired up, engine would bog down at 4000 rpm. Cleaned the fuel tank, added fresh premium, changed the fuel pump, removed internal G/W separator, replaced all gas lines, rebuilt carbs, changed plugs, checked electrical connections...no change in the RPM.<br />It now will throttle up and stay at 4200. When throttling passed 4200, will bog down. Throttle it more and it will run clean at 4500 rpm but no more. However, every so often, just for a split second at full throttle, will jump to 5500 rpm but just for a split second.<br /><br />I'm thinking electrical now. Here's another clue...when throttling down from full throttle, it sounds like it's missing a cylinder. I'll turn it off, fire it back up all cylinders seem running and it purrs at idle and up until I reach 4000 rpm. Help!

 

[jim dozier]

Re: Yamaha 130 rpm problem

I think you're right, you are loosing a cylinder over ~4000 rpm. Its gotta be electrical. Get a manual and go through the ignition system with a multitester according to the manual specs, somewhere your electrons are asleep at the wheel.

 

[rodbolt]

Re: Yamaha 130 rpm problem

sounds like a fuel pump andor carb is still nasty. do it again. the 87 ign system is basic and will work or die. good luck and keep posting

 

[rowbards]

Re: Yamaha 130 rpm problem

have you tried choking it when it acts up?

 

[Ray Neudecker]

Re: Yamaha 130 rpm problem

It certainly sounds like a fuel restriction. There have been problems with the engine mounted fuel filter after motors of that vintage have sat for a while. The passage can become clogged and cause this problem. Bypass the assembly and see if this helps. If so then replace the assembly.

 

[Yukahey]

Re: Yamaha 130 rpm problem

I thank you all for the postings.<br />Took the boat out and tried the choke advice while the wife drove, which stalled the engine. Then I tried squeezing the ball and voila' the engine took off - ran beautiful until I stopped squeezing. Actually, it ran during the pressureizing and bogged down as the ball tried to pull gas which seemed like it was straining to get gas but I should compare this on another boat first. Took apart, for the second time, everything from the fuel ball to the gas tank including G/W separator (replaced) and the gas pickup tube in the tank. Nothing found like before. Gas flows well. Sealed all connections. Still boggs down. I've replaced the fuel pump once with no change. Could the compression in the cylinder which pumps the diaphram on the fuel pump be the problem? It was 125. Is their a different design in the fuel pump? This one is too simple for my liking! Could I put an electric fuel pump on this type of setup. Thanks for your help.

 

[rodbolt]

Re: Yamaha 130 rpm problem

try a fuel system vacum test. it should be below 4"hg at wot. its definately a fuel issue you have. you may have to do it all again but so far its not mechanical or electrical. good luck and keep posting

 

[Ray Neudecker]

Re: Yamaha 130 rpm problem

You can use a inline fuel pump as long as the pressure stays below 6 lbs. We use a blue Holley with the regulator many times. You still need to find the restriction first though. Try bypassing the engine mounted fuel filter first though. It has driven me up the wall several times in the past, usually where the engine had sat up for a while. Good Luck. The life of the engine depends on your finding the problem.

 

[Yukahey]

Re: Yamaha 130 rpm problem

Well,<br />I purchased a pressure/vacuum gauge and found thier was little pressure and no vacuum so we're back at the fuel pump region again. It makes no sense that the fuel pump is the problem because I've changed it with no difference. My theory has always been that the oscillating pressure behind the cylinder that drives the fuel pump is the issue. My question is what could possibly be wrong? I see small hoses coming out the back on the other cylinders but do not see anything leaking. What kind of pressure should be coming from that small opening? The gasket has been changed twice...no difference. Thanks for all the replies.

 

[jim dozier]

Re: Yamaha 130 rpm problem

Perhaps you have a restriction between the fuel pump and the the gas in the tank. Does the fuel bulb fill nicely when you squeeze it? Are your fuel lines in good shape with no air leaks at the connections? Does your tank have an anti-siphon valve that might be sticking. Is your gas vent open? Did you replace the diaphragms in the fuel pump? Despite the fact that you seem to have addressed all of these perhaps you missed something. If the engine improves when you squeeze the fuel bulb you have a problem with either the fuel pump (most likely) or the fuel lines back to the tank or both.

 

[rodbolt]

Re: Yamaha 130 rpm problem

try looking at the quick connect fitting or just bypass it. I have had 2 fail so far this year. the fitting on the engine side has a small *** that must be depressed by the line fitting and sometimes its just not depressed enough and will restrict fuel. but you say it now only bogs at the upper mid range. I still think your carbs are dirty.<br /> good luck and keep posting.<br />ps where and how did you do a vacum test? how did you attach the gauge ?

 

[Yukahey]

Re: Yamaha 130 rpm problem

The vacuum test was completed by teeing the fuel line before the fuel pump. Pressure was done after the fuel pump. If there was any restriction before the fuel pump, vacuum would be high (suction) which it wasn't. That tells me that my complete overhaul of all the gas lines, G/W separator and clamps as well as sealed all screwed brass fittings did nothing more than take up a Sunday. I checked everything including the quick connect, internal fuel filter(removed) and check valve(did not exist). I even removed the pickup tube and checked the screen. Fuel flows freely when I pump. A restriction does not exist and never did.<br />I was reading the manual on where the orafice for the fuel pump goes... into the crankcase where, on a 2 cycle, contains fuel mixture before getting sucked into the pistons. I'm going to remove the fuel manifold and check if that orifice is gummed. T<br />hanks for traveling along with my issue. <br /><br />Sign me...Bypassing the biting bass in boston to f--- with a fuel flowing flaw.