Valve rework and startup of 2004 Yamaha F90

Fragamag

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Have changed all 8 intake valves, and lapped all exhaust valves. Cleaned all four carbs without adjusting floats. Assembled, aligned marks on cam gears as shown in manual, set #1 at TDC, and flywheel at mark on block. Started up and idles nice. But above 1200 Rs, it either chokes out and dies or starves to death. Changed to new plugs, a little help. What other variables could be causing my problem. I know there are some smart guys on this forum, how bout it.
Thanks
 

Silvertip

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Re: Valve rework and startup of 2004 Yamaha F90

You changed all 8 intake valves and lapped all exhaust valves. How about lapping the 8 new intakes? Did you run a compression test after this work? Not lapping the intakes means they are not lapped to the existing seats so you may be losing compression. If this is an EFI engine rather than carbed, you may have missed an electrical connector or damaged a sensor in the process of this work.
 

Fragamag

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Re: Valve rework and startup of 2004 Yamaha F90

I made an assumption that it was known that I lapped the new intake valves at installation. To be clear, I lapped all 16 valves. I put new oil seals on all 16 valves. Compression is not verified, bad guage. I will update when good data is available. It has 4 carbs, and I was very careful to pay attention to all connections at assembly. I took video and pics prior to the work, and have checked to compare before and after. It doesn't mean I did not overlook something. Timing light does show it to be 13 deg retarded, unless I am taking readings at the wrong RPM, if that makes any difference. Is there an external manual adjustment that can be made to the carbs? Should I have adjusted the floats?
Could it be the TPS? Throttle position sensor.
 

Silvertip

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Re: Valve rework and startup of 2004 Yamaha F90

If you had the carbs apart adjusting the float level is essential. I don't know off hand what the timing spec is for that engine but 13 degrees AFTER TDC (retarded) sounds way wrong and would account for the lack of performance. Timing is normally some number BEFORE TDC (advanced).
 

robert graham

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Re: Valve rework and startup of 2004 Yamaha F90

Just curious...why all the valve work on a 2004 motor?:confused:
 

99yam40

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Re: Valve rework and startup of 2004 Yamaha F90

My thoughts are they let it get out of time and bent valves.

At what RPM is it 13 ATDC ?
Do you have a Yamaha service manual for this motor?
 

robert graham

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Re: Valve rework and startup of 2004 Yamaha F90

My thoughts are they let it get out of time and bent valves.

At what RPM is it 13 ATDC ?
Do you have a Yamaha service manual for this motor?
Out of time and interference bent valve, pistons might also be damaged?
 

Fragamag

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Re: Valve rework and startup of 2004 Yamaha F90

Thanks so much for the feed back guys, I will try to answer all your concerns.
First to Silvertip. I tried to comprehend the manual instructions on the carburetor floats, but was not sure the floats were off from specs. My thought was, if the float had not been banged around, why would they need adjusting from factory settings. But that may have been a major error on my part. I am still researching the timing specs to understand how much, how far, and when. I wonder if the 13 deg is at idle and as acceleration is increased that number changes as the rpms increase, relative to computer input. Which brings me to the TPS, Which I will check once I understand the specifications. But I am finding out that the TPS is critical to a smooth engine. OK Robert Graham, To condense the story, the boat had been in storage at the Lake for app 1 1/2 years. Brought it home to get some use out of it. Cleaned as well as I though practical. At first crank it backfired once and then nothing. At closer inspection, I removed the flywheel cover and found that Dirt Dobbers had nested on the intake cam gear which threw the cam out of time, resulting in the bent intake valves. There was only slight damage to the pistons as you could see where the valves hit the piston, but I could not find any piston damage other than that. 99yam40, I do have a manual I purchased online. My RPM instrument is not working, but it idles very smooth and I am guessing at 800 Rs. Robert, I am reluctant to report suspect data, but to let you know what I know, using substandard equipment, I was able to record 120 psi on compression, so if there is piston damage other than what the eye could see, what would it be? All of the pistons come all the way up nearly flush or at flush with the block face.
 

Silvertip

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Re: Valve rework and startup of 2004 Yamaha F90

You are checking timing using the right cylinder (typically #1)??? You are certain the cam timing is correct? You still need to determine what the timing spec is. I can be reasonably certain 13 degrees ATDC is not correct. The service manual should be very clear on that. That number is typically listed in the table of specifications and will be xx degrees BTDC @ xxx RPM. Timing light goes on #1 plug wire.
 

Fragamag

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Re: Valve rework and startup of 2004 Yamaha F90

I have taken a lot of pains to insure that the cam timing is correct. They are lined up on the money. Yes, I am checking timing using #1 cylinder, and the specs are ATDC = 5, and BTDC = 20. The specs continue to list voltage at xxxx rpm, but I am not sure what it is telling me, if anything about degrees @ xxx rpm. The motor idles very smooth. I did play with the TPS a little and it did improve acceleration. But I am still doing a lot of reading and researching before I extend my full confidence to this engine.
Thanks Silvertip, for making me do my homework. It is guys like you who really make this forum a valuable tool to all who use it.
 

99yam40

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Re: Valve rework and startup of 2004 Yamaha F90

Not sure about your F90 problem, but myC40 had a idle timing of 14 ATDC when it should have been 7 ATDC, finally had to replace CDI to get it back into proper timing. the TPS wiper on mine was part of CDI
 

Fragamag

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Re: Valve rework and startup of 2004 Yamaha F90

Thanks 99yam40
Yea, I am sorta looking at all that also, well not looking, just suspecting. When I was able to make a difference adjusting the TPS, I was anticipating other electronic issues. I have still yet to take readings on the TPS, but hope to get to it early next week. I need to get my RPM instrument working to give me some help on troubleshooting.
None of this stuff is cheap. I did find my parts at a discount house, and looked for the TPS, to be app. 117 dollars, then shipping, too scared to see what a CDI is.
Tanks for the input.
 

Fragamag

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Re: Valve rework and startup of 2004 Yamaha F90

Well, decided to take the boat out in the lake and see if there was a different response to throttle increase. Not much. With kid gloves I was able to get up to full throttle and it seems to run well. But there is still a question of rather or not it is at its peak, I believe not.
I still have to get past that dead spot without chocking down.
Now its back to the TPS, and or CDI.
Can't test the TPS properly without a test harness. So, stuck again. If I thought just changing the TPS would fix the problem, I would do it in a minute, but just changing out parts without understanding whats going on doesn't seam like the way to go.
I am not afraid of good advice.
 

Capt Ken

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Re: Valve rework and startup of 2004 Yamaha F90

When you re-installed the carbs, how did you sinc them? You cannot just bolt them back on without sinc'ing the intake vacuum
 

99yam40

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Re: Valve rework and startup of 2004 Yamaha F90

you can back probe the connecters without damaging the wire insulation to take readings if you are careful
 

Fragamag

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Re: Valve rework and startup of 2004 Yamaha F90

Hey Capt Ken,
You are just on time with that info. I understand the electronics on these Yams are fairly reliable. But please be more specific on the sinc issue. Di I really need that vacuum equipment to do all that? What is the most accurate but cheap way to sinc the carbs, I also understand that is critical.

Hey 99yam40, What do you mean by back probing the connecters. I have tried to take readings on my TPS, but without the wiring harness I will not be able to check it while it is running.
Thanks guys, I am learning a lot here.
 

Fragamag

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Re: Valve rework and startup of 2004 Yamaha F90

After talking with a few locals, I need to get a Manometer to sync my carbs. I found a lot of them on the internet. I also watched several U-Tubes showing them using their home made Manometer. If I build my own, I still need to get the vac port adapters. Any way, I have been told that the electronics on the Yamaha's are very reliable, and shouldn't need to fool with that just yet.
 

Fragamag

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Re: Valve rework and startup of 2004 Yamaha F90

I, decided to change the timing belt to eliminate any doubts as to integrity of the old belt. I thought I would never get the flywheel to pop loose. Started up and idled fine. Check compression and showing, #1=150, #2=90-130, #3=148, #4=148. So, whats going on with #2? Tried to pressure test #2 at 115 psi. (max on my compressor), but could not detect any leaks at (intake port), (water jacket), (crank case) or (exhaust). The methods I used are not reliable, but had to start somewhere to see if there was an obvious point of escape. Tried using Marvel Mystery in #2 but no help on compression. I'll try oil next to see if compression comes up. Thought I would try to sync carbs, but no sense in that until I get #2 fixed. As I have stated before, I could not detect any cracks on #2 piston when I had the head off. I did not do a die test, but I could not detect anything with the necked eye. Can I get into the crank case and remove #2 without taking the whole engine apart?> Any suggestions?
 

Capt Ken

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Re: Valve rework and startup of 2004 Yamaha F90

Yes you do need the vacuum equipment to set those carbs up and you can't do it with just one guage. Even with several guages, you have to sinc them with a constant vacuum to be sure they all read the same. I use a vacu-mate and I can tell you that just the weight of a screwdriver on the screw will affect the setting. You would be ahead of the game and cheaper to take to someone with the equiptment.
 

Fragamag

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Re: Valve rework and startup of 2004 Yamaha F90

Put oil in #2 and ran a compression test. Results = 100 psi. OK, like a PC, garbage in garbage out. If I can't get nothing in, I can't get anything out. I took the access port plug out of #2 intake manifold and ran another test. Results = 205 psi. I put the plug back in and locked open the valve on the carb, and ran another test. Results = 205 psi. Released the lock on the carbs, and ran another test. Results = 100 psi. So what gives guys? I am convinced there is nothing wrong with the compression chamber, piston or rings. So, should I go ahead and perform a sync on the carbs using a manometer? These carbs are shiny clean, so on and so on.
 
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