Yamaha 1200 Carb Catastrophe - Page 3 - PWC Forum: The best hang-out for Personal WaterCraft enthusiasts
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post #21 of 29 (permalink) Old 09-20-2019, 09:48 AM Thread Starter
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They were running it high because of epa standards. I have seen where folks are running pop off on the 1200's in the range you have with no issues. If it's starting easy hot or cold, idles good, off idle acceleration is good, not running rich up to 1/4 throttle, I would leave it.
I see what you are saying, I just really want it to be perfect at this point. Plan to check it one more time and then leave it, I'll probably still take it out this weekend and get busy later over the week (like always) when my gauge comes in. I mean i gotta enjoy it a bit before winter eh!?

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post #22 of 29 (permalink) Old 09-22-2019, 12:17 AM Thread Starter
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Heres me, and something I skipped over thinking it wasn't an important part. Now that I'm really into this stuff I've been researching two strokes all day which coincidentally led me to this issue that I almost skipped over.

All criticism is welcome, feel like an idiot right now.

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post #23 of 29 (permalink) Old 09-22-2019, 08:23 AM
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Good to catch it now. Not only that, it will cause a lean condition from sucking in raw air. That's the big issue with bad crank seals.
My concern is, why did the seal come out in the first place ? There are 2 seals on the pto end of the crank. Did you split the cases ? I always apply a coat of three bond to the od of the seals and the corners of the cases at the seal bores.
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post #24 of 29 (permalink) Old 09-22-2019, 12:21 PM
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Unfortunately, to fix your issue correctly you'll have to pull the motor, remove the PTO coupling, split the case, install new Yamaha seals, and reseal.

Reinstalling the existing seal will not hold. Plus it's ID is probably damaged from being run at odd angle on shaft. They need to be held with a light coat of Yamaha bond/three bond. With a small amount of marine grease between them for shaft/seal lube. Any oil or grease on the OD of seal or case half can cause it to come out again.

It may have back fired once upon a Time and blew seal out. It doesn't look to have any sealant on it.

Last edited by Dave in DE; 09-22-2019 at 12:29 PM.
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post #25 of 29 (permalink) Old 09-22-2019, 03:55 PM Thread Starter
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Never split the case, I managed to do a decent inspection of crank without having to actually having to split case. I have already ordered the new seals and should get them thursday. If if the combination of bad sitting gas and water can cause a backfire or the related I bet my ass thats what caused it. And I can almost guarantee that was the culprit for the meltdown. I learned a lot yesterday about 2 strokes doing research and I guess this damn seal can cost you a whole top end on a 2 stroke. I will order three bond now and get ready to remove engine once again.

THAT WAS A CLOSE ONE
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post #26 of 29 (permalink) Old 10-14-2019, 08:25 PM Thread Starter
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To anyone who is still getting notifications on this thread. Finally done with the whole rebuild, two months later and it's purring like a Cadillac. Replaced crank collar, and crank seals and all around which caused mag and pto compression to raise 2 psi cylinders reading 118, 116, 119 m-p. Removed RTV on main cylinder and replaced gasket, was already disintegrating, officially done using that stuff unless service manual says so. Finally, rebuilt the carbs once again with genuine kit which are no longer leaking. And the results!? Well, not in the water quite yet but running it off of the hose it's noticeably much much better already. Took about 5 seconds to start right off the bat after priming by blowing through return lines. With a +1/2 turn on H and L screws to compensate for bore it idles perfectly and starts without a problem. Even revved it a bit without hesitation, buying an actual pop off pressure tester really helped get it perfect. Forgot the PSi but I believe it was a user on this forum who posted his results and I copied them verbatim. Can't wait to put it on the water, I'm pretty positive it'll be near perfect. I'll update once I know, it snowed last weekend but supposedly supposed to be 63F this weekend which is good enough for me.

Thanks to everyone for their help, I owe you guys so much!!!!!

As a quick edit, seals installed by dealer from prior owner never had yama/threebond or grease on ID. Also by looking at the sides of them they are the SBT ones, known for popping out and overall being crappy. New ones are yamaha.

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post #27 of 29 (permalink) Old 10-14-2019, 10:05 PM
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Glad to here it running better. Hopefully you'll have more good news after a ride or two. Enjoy.
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post #28 of 29 (permalink) Old 10-15-2019, 08:53 PM Thread Starter
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Glad to here it running better. Hopefully you'll have more good news after a ride or two. Enjoy.
Thanks! Can't wait!

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post #29 of 29 (permalink) Old 10-21-2019, 03:59 PM Thread Starter
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Hello,

Out of water on trailer it can rev all the way to limiter and go back down to idle no problem. Finally putting it on the water yesterday and I was not impressed. Cold starting requires choke like normal and when warmed up it starts almost instantly. When setting out I feel no hesitation until I reach 6K RPMS. At that point it will either completely die or more commonly bog down and rev up once again until 6K. Now I would like to believe this issue is carburetor related and am pretty positive it is or it could be fuel lines but havenít been convinced enough to replace that yet. I started by richening the high speed carb screw and it got a bit better, after I noticed low speed screw was a little too rich so I leaned it out a tad. Lastly, I did a run across lake still had same issue however pulling choke half way immediately before bogging and it will go wide open no problem until you let go of throttle having to start acceleration process over again. So I richened high speed screws again just a quarter turn ran it without air box and once again reached full rpm, putting air box back on and the issue came back just not as bad. Sometimes it will reach full rpm hold it for a few seconds and bog and stay like that for 30 seconds and then once again fine to go full throttle all over again repeating this process. At this point I was done for the day. Putting it back on trailer and starting it to drain water it revs all the wav to rev limiter once again as if nothing ever happened. Does this mean maybe going a little richer on high speed screws or replacing fuel lines will solve it? Canít tell because I ran out of time today.

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