1986 GT150 Fuel Issues ???

[mperkins122]

Ok, this is my first post and its a doozie. I have an 86 GT150 thats giving me a headache.. To bring you up to date this is what has been done. Cleaned fuel tank, replaced all fuel lines from tank to motor, replaced the bulb 3 times, new plugs and coil packs. OK. Last week i took out from the dock and it ran fine for about 5 minutes and died. Bulb was flat. I had a new spare with me and replaced it. It took about 10 minutes for the motor to start again and it sputtered for a minute then ran fine. I should have went back to the dock but I thought everything was ok. The next time i went to crank the motor, it sounded ok but when i went to accelerate, it bogged badly. It wouldnt exceed 4-5 mph although the bulb was not flat. I went home and replaced bulb again and the plugs to see if that was my problem. After replacing the parts It started fine and idles great. On the muffs you can accelerate no problem but I dont run long cause i know its not good for them. I took it out the next day and in the water however, it idles fine but when u go to accelerate, it bogs down so badly i can only do 4-5mph pr GPS at full throttle. When you choke, it tries to die or does die. Also depending on its mood, it might flatten the primer bulb, other times it does not. After it dies and I reprime the bulb if needed, wait a few minutes and it starts fine and idles but under load it still goes nowhere. I replaced the bulb so many times because that is all anyone on the lake would tell me. If in gear idleing, it runs fine as well. All plugs are wet and plug wires are secure. Compression was ran at the shop when I had the coil pack replaced and they said the motor was fine. I read another post and saw something called a "check valve"? I looked in my tank at the fitting and saw nothing inside. I looked all the way from motor to tank and no "check valve was found, must have already been removed. Next I was told it was an exhaust problem. Im so confused. Can anyone point me in a helpful direction?? Any input would be great. I get tired of taking this thing to the shop and either they tell me it seemed fine running using the muffs. Thanks -Mike

 

[mperkins122]

Re: 1986 GT150 Fuel Issues ???

Oh yeah, I also checked the breather hose and vent. It was clear. It runs the same with the fuel cap tight or loose.

 

[R.Johnson]

Re: 1986 GT150 Fuel Issues ???

If the engine is sucking the bulb flat, you have a severe restriction. The screw in connector on your built in fuel tank is an anti-siphon valve, it is probably your problem.

 

[mperkins122]

Re: 1986 GT150 Fuel Issues ???

Ok, I will change that 90 degree elbow tomm and post results. Also, there is a screen in the pick-up tube. Should that be there or should I remove it. Thanks for your info. -mike

 

[emdsapmgr]

Re: 1986 GT150 Fuel Issues ???

As RJ mentioned, the aluminum hose barb on the top of the tank is probably an antisiphon valve. Over time, they can get grit or debris in them, causing the ball bearing to stick and impede fuel flow. You can clean it with carb cleaner and an air hose, or just replace it with a regular hose barb. While you are there, you might pull the fuel pickup out of the tank. Check it to be sure it is not clogged.

 

[mperkins122]

Re: 1986 GT150 Fuel Issues ???

Thanks guys. Today I replaced the aluminum hose barb on the top of the tank. The old one did not have a ball bearing in it and was completely clear of obstruction but still replaced it anyway, as was the pickup tube. I removed the fuel gauge sending unit to look in the tank for "trash" and found none. Took it out on the water and the same symtoms remain. Could a defective fuel pump diaphram cause this? If not, maybe a defective coil pack? I have 2, one per side feeding 3 plugs each. Any info is greatly appreciated and thanks so far. I am just glad to see that there are still people out there willing to help. Thanks again guys. -mike

 

[R.Johnson]

Re: 1986 GT150 Fuel Issues ???

Ignition has nothing to do with the fuel bulb being sucked flat. That fuel pump has to be pulling a vacuam on the fuel line. Have you tried a different hose, and a remote 6 gal. tank?

 

[Dhadley]

Re: 1986 GT150 Fuel Issues ???

This may be a silly question so forgive me -- is the line from the tank all the way to the motor 3/8" ID?

What else is between the tank and the motor besides the bulb? Filter? Shut off valve? Bulkhead fitting? More 90* fittings? Any tie-wraps holding (pinching) the line along the way (between the tank & bulb)?

RJ's suggestion of a completely different system for testing is an excellent place to start.

 

[emdsapmgr]

Re: 1986 GT150 Fuel Issues ???

The hose bulb should be hard only when first priming at the start of the day. After running, it should get soft, but not collapse. If the bulb collapses flat, it can be a restriction or a stuck ball valve in the bulb. Have you tried pumping the ball when out on the water, when it is not running right? This will force fuel around the pump into the carbs. If constant priming gets the engine to run ok, then you probably have a weak fuel pump.

 

[mperkins122]

Re: 1986 GT150 Fuel Issues ???

Great idea! I will try to run it this evening if i get off in time with a portable tank. To answer your question ,from the pickup tube the fuel line connects and runs to the bulb, from there it goes directly to the motor. All line is Marine 3/8 as well. While not running, it runs normally. The symtoms only occur in the water, not on the muffs. On land, it cranks and will idle great. I can accelerate and it never misses a beat. If this turns out to be a weak fuel pump, can I replace the diaphrams or should I buy a new non VRO fuel pump. The VRO was removed before I got it so I have always used a premix.

 

[Dhadley]

Re: 1986 GT150 Fuel Issues ???

If the pump is strong enough to suck the bulb flat, the problem is from the bulb to the tank. A weak pump will not suck the bulb flat. It may not pull enough fuel to keep the motor running but it won't suck the bulb flat.

 

[mperkins122]

Re: 1986 GT150 Fuel Issues ???

Ok guys, I ran the boat today with a portable tank. I let it warm about 5 min and took off. It ran great but for only ten minues or so. All the sudden, RPM's dropped until it died. The last few seconds of it running it had a severe vibration and it sounded really rough. I checked the bulb and it was not flat but it was soft. It took about 5 minutes to start again and when it did, It would only do about 5mph. When u choked it, it sputtered and tried to die. I docked it and let it sit about 5 hrs, when i tried again it did the exact same thing (ran good for about 10 min then die). Im thinking now either a coil pack or maybe the carbs. What do you think? If it is the coil pack how can i test it? Thanks again guys, we are gettin closer to a solution. -mike

 

[R.Johnson]

Re: 1986 GT150 Fuel Issues ???

If you have, or can get your on hands on a peak-reading volt meter, you can do a running test on each ignition component, sensors, charge coil, and pack output to each ignition coil. The service manual explains how to do this, and is an excellent way to isolate, and pin down a problem. You could also do a vacuam, pressure test on the fuel system, this is also in the manual. Get the needed information, and tools, look over the procedures, and I think you will find your problem.

 

[emdsapmgr]

Re: 1986 GT150 Fuel Issues ???

Agree with RJohnson. You may have an electrical issue. You could be dropping one or more cyl. These issues tend to show up when the engine gets fully warmed up. Electronic parts tend to fail when heated up and tend to go away when it cools down. Take a timing light with you. When the engine starts to stumble, put the timing light on each plug wire. You are looking for sharp, strong, constant flashes from each plug wire.

 

[mperkins122]

Re: 1986 GT150 Fuel Issues ???

Ordered my manual today. I checked plug wires again too. I removed 1 plug wire while running and it didnt change the way it ran at all. Plugged it back in and it still had no change. I did the spark test though and it has spark, I just wonder if it is enough.

 

[emdsapmgr]

Re: 1986 GT150 Fuel Issues ???

The ignition system works harder when the engine is under load. It could idle fine, but still break down under load.

 

[mperkins122]

Re: 1986 GT150 Fuel Issues ???

AS it turns out, I had 2 problems. 1, the primer bulb wasnt strong enough, I spent the extra 6 bucks and bought OMC and it cured the flattened bulb prob. Now the second prob sounds like a carb issue. While running in water, it will run great for a few minutes but then bog severely. If i push in and out on the choke repeatedly (bout 10x) it will eventually pick up and go, almost like it has burned something out of the motor. If i let off the gas and then reaccelerate I have to do the same thing to get her to run. I feel it is my high speed jets. what do you think. Is there a possibility that trying to decarbon the thing will help. Ive never rebuilt a carb and the ETA at the shop is 4 weeks. What should I do?? Thanks again