1998 Yamaha F50TLRW Knocking after Warmup?

[larrye44]

I have a 1998 Yamaha F50TLRW that starts knocking after it warms up? It sounds like a lifter knocking. It only has about 150 hours on it. I use Yamaha Ring Free in it on a regular basis. I use 1 oz. per 10 gals. I bought it used and the owner said it only had about 10 hours on it. I did a shock with the Ring Free and then started the regular use. I don't remember the knocking when I first bought it and don't really remember when it started. But, now it is a knock that is very obvious. Is it normal for an outboard to knock a little when running. It runs real smooth and just sips gas. I can run it all day and maybe use only 4 gallons of gas. I change the oil regularly (when I winterize it). Thanks for the help everyone. Larry

 

[rodbolt]

Re: 1998 Yamaha F50TLRW Knocking after Warmup?

does it sound like a lifter tapping in a wore out old chevy?

 

[larrye44]

Re: 1998 Yamaha F50TLRW Knocking after Warmup?

Yes sir, that's what it sounds like.

 

[rodbolt]

Re: 1998 Yamaha F50TLRW Knocking after Warmup?

next time it does that.
pump the primer bulb.
if the noise goes away.
fix the air leak/restriction in your fuel system.
the fuel pump needs fuel to balance the diaphram.
if you have an air leak, or a restriction. the pump will chatter exactly like an old chebby with a bad lifter.
sounds the same.

 

[larrye44]

Re: 1998 Yamaha F50TLRW Knocking after Warmup?

Thanks, rodbolt, will do. I'll bet you are exactly right. My fishing buddy said he could smell gasoline last time we were fishing. I will let you know what I find and thanks again for the help. Larry

 

[rodbolt]

Re: 1998 Yamaha F50TLRW Knocking after Warmup?

also, check your oil. a bad fuel pump diaphram will make the same noise AND load your crankcase with gas.

one would almost think I deal with this


occasionally.

 

[larrye44]

Re: 1998 Yamaha F50TLRW Knocking after Warmup?

Let me just say this rodbolt...YOU DA MAN!

 

[larrye44]

Re: 1998 Yamaha F50TLRW Knocking after Warmup?

rodbolt, I replaced the diaphragms in the fuel pump because it was putting oil in the crankcase. They looked okay, but I replaced them anyway. I was unsure if anything else could put fuel in the crankcase. I know if the carbs are way out of whack that can do it also. I just had the carbs rebuilt and sync'd by a certified fuel tech at the Yamaha place here where I live. I know the carbs are okay. Before I put the fuel pump back on, I just wanted to check and make sure there is not something else I should look at. Thanks for the help. Larry

 

[larrye44]

Re: 1998 Yamaha F50TLRW Knocking after Warmup?

Well, I put her all back together and no more knocking. I changed the oil and won't have to worry about gas getting into the crankcase. The diaphragm looked okay. No cracks or creases or holes, but it was stretched way out of shape.

It runs smooth and quite as can be. It only starts knocking after I unplug the fuel line to run all the fuel out of the carbs. Just like you said, rodbolt, air leaks will cause it to knock. This engine has low hours, but the guy I bought it from took some bad advice. He told me he was told that 4 stroke engines don't need the fuel run out of the carbs. That's why I had to have them rebuilt. I sure appreciate the help. Larry

 

[99yam40]

Re: 1998 Yamaha F50TLRW Knocking after Warmup?

4 strokes do make oil when not propped correctly or run lightly, you need to run them hard. So check the oil often.
Running the fuel out of the carbs is something that has been discussed quite often, so do some searching and read what all was said.
If it causes the pump to knock it probably is not good for the pump is my thought.
Did you notice the word under Rodbolts name? Apparently he stepped over the line one to many times

 

[larrye44]

Re: 1998 Yamaha F50TLRW Knocking after Warmup?

No I did not notice that. As you can see, I'm new to the forum.

Thanks 99yam40 for the tips. I usually run mine at about 5K rpms. I wasn't aware of the prop problem. I fish the flats on the Florida coast and sometimes hit the bottom. I use an aluminum prop and after a while it gets a little nicked up. What should I look for to know it is time to renew the prop?

I'll do a search on running the gas out of the carbs and try to determine what to do. Now that I have changed the diaphragms it does not knock at all unless I unplug the fuel line. I didn't like hearing the knock when I ran the gas out, but thought that was the correct thing to do. Would you mind giving me your opinion? Thanks again for the help. Larry

 

[99yam40]

Re: 1998 Yamaha F50TLRW Knocking after Warmup?

keep Stabilized the fresh fuel in it and run it often, If you can not run it every week or so then drain the carbs by using the drains on the float bowls

 

[larrye44]

Re: 1998 Yamaha F50TLRW Knocking after Warmup?

Thanks, 99yam40, I use Stabil Marine and 1 oz of Yamaha Ring Free per 10 gallons of gas. I use this all the time and never fill up without adding these two items. I can't go to the coast that often, so from now on the carbs will be drained by removing the plugs. Thanks again for the help. Larry

 

[eldercaddy]

Re: 1998 Yamaha F50TLRW Knocking after Warmup?

Hi larrye44. why don't you bring it to a mechanic? I'm sure they know a lot of them. I suggest that because I don't know how to fix it. Sorry.

 

[99yam40]

Re: 1998 Yamaha F50TLRW Knocking after Warmup?

Thanks, 99yam40, I use Stabil Marine and 1 oz of Yamaha Ring Free per 10 gallons of gas. I use this all the time and never fill up without adding these two items. I can't go to the coast that often, so from now on the carbs will be drained by removing the plugs. Thanks again for the help. Larry

How often is the motor run and how much?

 

[larrye44]

Re: 1998 Yamaha F50TLRW Knocking after Warmup?

About once a month and run it 4-5 miles at about 5,000 rpms. Then it is drift fishing. Don't do much quarter throttle running. Thanks.

 

[larrye44]

Re: 1998 Yamaha F50TLRW Knocking after Warmup?

Thanks, eldercaddy, that is good advise. One thing for sure, I don't want to try doing things I'm not qualified to do. Larry

 

[99yam40]

Re: 1998 Yamaha F50TLRW Knocking after Warmup?

Sounds like you do not turn over your fuel very often, only using about 1-2 gal every trip.
The rest of the fuel sits in the tank for a long time. Not sure how big of a tank you have but it will get old too even if you add a gallon or two once a month if it is a large tank.
Not too bad if it is a small 6 gal one.
You need to readjust your priorities and go more often

 

[larrye44]

Re: 1998 Yamaha F50TLRW Knocking after Warmup?

My priorities are right. Number one priority is fishing. The problem with that priority is having the funds to keep it in the number one position. It's a sad situation, retired so I have all the time I want to fish, but retired and now fixed income doesn't always cooperate.

My tank is a 15 gallon and you are right, each trip is just a couple of gallons. What would be the best solution for this situation. Should I just keep 5 gallons in the tank and not fill it up? That way each time I go out, I'd put in 2 or 3 gallons. I can't think of any other solution, but if you have any ideas I sure would be interested.

Thanks again for all the help. I really feel like I'm getting a handle on this problem now. At least now I will stop two things that is apparent to me now was bad. One was running the carbs dry instead of draining the bowls and two was filling the tank and letting it go stale. The mechanic at the Yamaha place that rebuilt and sync'd my carbs said the gas did smell funny and he drained it and cleaned the tank.

 

[greengrass]

Re: 1998 Yamaha F50TLRW Knocking after Warmup?

I agree with Rodbolt dealt with him a few times certainly knows his stuff like me, I`m a qualified Marine Engineer Outboards & Inboards good luck.