Yamaha F150 Starting Problem

[WClery]

1991 200hp outbd compression

I tested my compression and got mostly 116 - 125. one cyl was 105 psi. I probably did not do it fully accurate since I left the plugs in except for the test cyl. The book comp ratio is 5.9. multiplying 5.9 x 14.7 psi (atmosphere) = 86.7 psi. What should I be reading in psi. It appears I am way over their ratio. Is 105 - 125 good?

[sachin2021]

Oh well. The euphoria was short lived. I went to start the motor today it started and ran for a while. I turned it off and upon trying to restart got the same hard start and when it started it cut out at the faintest hint of giving it some throttle. Truth be told I also tries to tighten the plug leads at the coil end as this seemed to be the problem over the weekend and after I tightened one it ran flawlessly.
I may have further damaged it. Will borrow a pair of coils from a friend this weekend and see what I can come up with.
If anyone has any ideas/experience with this sort of problem I sure would appreciate feedback.

[TownsendsFJR1300]

f150

Just for the heck of it, run the engine in the dark and look for any any shorting/arcing with the hood off. Also, try moving any wiring harnesses a little while trying the throttle.

If you haven't already, disconnect the battery, then unplug/inspect/clean every electrical connector you can get to.

I'm also wondering if the safety switch in the throttle control itself (prevents starting in gear) is acting up turning off the engine IMPROPERLY as if you were starting in gear, just a thought,.....

I believe a couple of previous posts ago, there was either a F115 or a F150 with corrosion problems similar to yours (here on this forum). The poster found the problem and was able to repair it, do a search...

[sachin2021]

Ok, Townsends.
I really thought I had it sorted after tightening the plug leads and it ran like a champ. Mind you it did that once before when I changed the primer bulb only for the problem to return.
I will check for arcing and also try a new set of coils from a friends motor as well as another main relay.
Does anyone know how many grounding points are on the motor and where?

[TownsendsFJR1300]

F150

I have the F150 Yamaha shop manual as a PDF file if you want it. It should show it. PM me or send me your full regular e-mail address and I'll send it..

Mention F150 in the header so I don't delete it as spam...

Scott

[sachin2021]

Well, I decided to check all connections from various harnesses. Started the motor and it idled but would not run once in gear or at any hint of throttle in neutral.
Unplugged a connector and the motor immediately smoothed out.
Have it some gas and it throttled right up.
Put the connector back on and it started running rough. Pulled it out and it throttled right back up.
Repeated this around 30 times with the same result.
It is in the same harness with some wires running down to the coils so I guess this is why I thought it had to do with coils and plug leads.
Pulled out the sensor and it is a water sensor. I am guessing water pressure. Correct me if it is a temp sensor. No alarms went off when I disconnected this sensor.
Alarm sounds if I try to start without lanyard in key switch to the horn is good.
My question is if that sensor is a water pressure or temp sensor and where can I find one. (fast)
Also what are the dangers of running without it. I see a few older F150 motors do not have this sensor or at least not where it is mounted on mine.
Appreciate the help.
Sachin

[TownsendsFJR1300]

f150

Looking at page 8-14 on the manual I sent you, the thermoswitch works off water temperature, not water pressure.

On that page, it shows how to test the switch. I suspect it thinks the engine is overheating and turning off some modes allowing the engine to idle (and pump water) and limp home.

[sachin2021]

Thanks.
I looked it up and a thermoswitch it is.
I am a little puzzled as to why the overheat alarm is not coming on but will test the switch to ensure that it is faulty and not the wires running to it.
Thanks again

[TownsendsFJR1300]

F150

Seems that switch is for OVERCOOLING.

"An over-cool prevention cooling system with a 60-degree Celsius thermostat maintains proper engine temperature for more fuel-efficient operation and additional durability".

See the below link:
Yamaha F150 — The World’s First 150HP Four-Stroke Outboard

[sachin2021]

Hi Townsend.
Thanks so much for the help.
I managed to borrow one from another motor and the motor runs like a champ. Ordered the part off boats.net so in a week or so it should be good to go.
Also a big note of appreciation to all other forum members that helped me sort this out.
Big props all the way from the little Fiji Islands!!

[TownsendsFJR1300]

F150

Excellent and congrates!!!

[sachin2021]

Update on the situation.
Motor has been running well since the thermoswitch sensor was changed. Did a 130 mile trip over the weekend and all was good.