F50TLHD motor problem

[starcraft59]

Hello,

This is my first post and it will be a long one. I have a 2005 yamaha F50TLHD motor that is having fuel/engine problems. I live in Ca and use only Chevron 92 octane along with 2oz of Marine grade Stabil in my fuel along with a can of Seafoam everytime I fill up. My gas tank is poly and it is 18 gallons. Here is my problem About 2 years ago I replaced all injectors, spark plugs, new VST filter, and low pressure fuel pump and added a Yamaha water fuel separator.

The engine works great when on trailer and water muffs connected. I put the the boat in the water and put the engine idle warmup on for approx 5 minutes to get the engine up to temp. I leave the dock enroute to fish and the motor works fine. The problem occurs after a period of low speed *****ing ( 1.5-2.5 mph) and when I get ready to motor out the motor sputters/surges and wants to die; as if it is starving for fuel. I was told by my mechanic to put the engine in idle and rev the engine idle warm-up to purge the engine before I go WOT.

I have checked to make sure there is no water in the fuel and have checked sparkplugs and all hoses. This motor is an international Yamaha I bought over the internet and it came from Canada. My mechanic has tried everything he can think of. We were goning to test the fuel pressure on the fuel rail but there is no connection port on the rail The only shrader valve that can be seen is located above the VST. I am think that the high pressure pump inside the VST is going out. If anybody has ANY idea what could be occcuring please feel free to PM me. Thanks

[marinermikes]

First, I'm not faniliar with your model but I would be checking the CDI. Does your motor have the CDI with the timing arm on it. If so that may be where your problem lies.

[starcraft59]

Hi,

Thx for the reply.. I will check on the CDI on timing arm. The motor is from Canada and is an international model.

[starcraft59]

I checked the pressure regulator that is located ontop of the VST tank and there is a small vacuum hose that is note connected. i connected it to a small air detent located on the air baffle (sp) and the engine surge alittle and rpms dropped. I unplugged the hose again and the engine rpms increased. Should this hose be plugged in. Also it sounds as if there is a vacuum leak somewhere up by the water/fuel cooler area. Any ideals?

[MJohnston7]

Another 50HP with the dreaded surging issue. Starcraft59, welcome to the club. MarinerMikes, did you order your a new CDI yet? This now makes four of us with what sounds like the same problem (see "Bogging on Acceleration" and "50TLR 2005 No WOT after warm up"). Maybe we can get a group discount. I haven't had a chance to order mine yet. Got to save up the money since they are not cheap. Really wish there was a easy way to test those things. Whoever puts a new one on first, please let the others know if this fixes the issue.

[marinermikes]

Order it last week. It should be here any day. I'll keep you posted.

[99yam40]

You can test the input and output voltages of the CDI along with the timing to see if there is a problem with the CDI. All you need is the Yamaha service manual and the proper test equipment to see if it has a problem while the problem is occuring

[marinermikes]

You can test the input and output voltages of the CDI along with the timing to see if there is a problem with the CDI. All you need is the Yamaha service manual and the proper test equipment to see if it has a problem while the problem is occuring

Easier said than done. First I ran the motor for an hour with the hood off. No problems. Start , stop, full throttle never missed a beat. I put the hood back on ran for about two miles stopped the boat waited five minutes restarted gave it the throttle, it went on plane hesitated a couple of times and quit.

Took the hood back off and started checking everything. The engine would start and idle. Carbs full of gas, good spark to the plugs, timing mark was ok but as soon as my friend would put it in gear and try to give it ever such a little throttle it would die. I would die so fast that I could not get a good timing reading to see if that was the problem. All this hanging on the back of the boat in boat chop and 95 degree weather.

I finally disconnected the timing arm and moved it advanced manually. When I did this the rpm's rose slightly. I moved it a little more and had my friend give it some throttle from the helm. The rpm's rose a little more. I had him slowly give it more throttle while I slowly advanced the timing until we were back at full throttle. I reattached the timing arm and we rode around for another twenty minutes with the hood off and never had another problem.

I could not get this motor to do this in my test tank. probably because I don't have a test prop.

My final conclusion is that something is getting warm in the cdi and disrupting the timing.

[99yam40]

If that is true then you should see a problem with the timing light

[marinermikes]

99yam40. First of all, thank you for your replies. I just hate intermittent problems. If the thing would just fail it would be so much easier.

A good way for a Yamaha dealer or just a Yamaha outboard mechanic to make himself a couple of bucks would be to come up with a system of testing these CDI's. One simple way would be to have a motor around for just this purpose. Of course you can't have a test motor for every different CDI but these ones that have the timing incorporated into them are particuarly troubling. The other types either spark or they don't. Thanks again. Mike

[99yam40]

I have never seen Just the timing not advancing properly causing a motor to die, just not pick up RPMs as it should maybe.
Loss of spark or weak spark can cause motor to die which can be measured with the proper meter.
Lack of fuel is harder to find out, but monitoring fuel pressures and vacuum may help at least to eliminate that as a problem. But you can still have carb passages plugging

[starcraft59]

Hi,

Thx to all who have chimed in with ideas. I was able to test the high pressure pump by splicing in a tee connector to a pressure guage. The guage read 42lbs as soon as I turned the key. After the motor started it dropped to 40lbs. I checked with the mehanic and he said that is in range.

I also did some other research and I hear that the ISC vavle could be bad. It attaches to the back of the intake manifold and its held on by two screws. I sprayed starting fuild behind the intake to see if I could hear the engine change rpms and listen for a vacuum leak. As soon as I did the motor stalled and quit. I fired back up after I started it again.

My question is does anybody know if the ISC could be the problem that I am experiencing with the surging? At this point it looks like I'll be throwing parts at this motor to something fixes it

[99yam40]

I seem to remember Rodbolt17 posting some on the F150 stalling problems and how to cure it, but I do not know of any on the F50. Hopefully some one will chime in and give you some help

[CHIEF AT STAR MARINE]

Same trouble ,, if you sprayed the isc and the engine died ,you have a vac leak ! The isc controls engine speed with a con*****ed vac leak . Above idle it help control air to fuel mixture ,and if it leaks you have a lean condition it can not compensate for and it will surge and die ! Try to remove the isc and check the rubber gaskets , if they look ok ,for a test reseal it with silcon .and recheck with carb spray with the red tube for a more direct test ,this makes your spray point more easy to pin point the leak . Note i do not recamend the use of starting fluid , it can damnage the engine ..

[robert graham]

Wish Rodbolt would hurry and get back from wherever he's at, he could probably shed some light on this puzzler!...