Yamaha 1999 T 9.9 over reving

[mangomike2]

Hi …. I'm having a problem getting my Yamaha 1999 T 9.9 XEXR to idle . I just finished rebuilding the carb. The carburetor itself seems to be working fine. So I think it's part of the electronic choke or start set. I checked the starter set for continuity and applied 12 volts to see if the piston moved. Both seem fine, but I'm not sure. Here's what happens, when I start the motor . it seems to over rev. If I tap on the linkage it will slow down to an idle. But, then it will start to rev back up again. The same thing happens when I take the boat out of gear. It does not seem to matter whether the engine is warmed up or not. The linkage seems to have the right amount of free play in the idle position. So it seems like it must be either a spring or some type of the electronic message that tells the motor to rev up. Thanks for any help.

 

[bigbrownbuku]

Re: Yamaha 1999 T 9.9 over reving

Originally posted by michael-mainecat:<br /> .... and applied 12 volts to see if the piston moved. Both seem fine, but I'm not sure. Here's what happens, when I start.....

im not sure what you mean here? are you referring to the choke piston mounted atop the carb?<br />try adjusting the idle mix screw out 1/4 turn at a time. also try partially choking the intake to see if this makes a difference.

 

[mangomike2]

Re: Yamaha 1999 T 9.9 over reving

Hi BenC... yes, in the service manual . they referred to it as electrodethermal valve. It is inside the black cylinder that sits on top of the carburetor . the instructions say , to check for continuity, resistance and the second thing . they advise is to connect the 12v battery and to wait for several minutes to see that the valve moves. I think ,it moved about a 16th of an inch. Adjusting the carburetor idle screw does not seem to have any effect. The only thing that changes the overreving is tapping on the linkage. Or if you just let it run . It will slow down after a while, and then rev back up. As it had a mind of its own. I'm completely stumped.

 

[mangomike2]

Re: Yamaha 1999 T 9.9 over reving

OK, so here's an update. On BemC's advice . I partially covered the air intake . this makes it idle out immediately. I had to almost completely cover the intake. I hope this helps.

 

[garyN]

Re: Yamaha 1999 T 9.9 over reving

I have a similar problem with a year 2000 9.9 power thrust. My problem started like yours - then got worse and the dealer replaced the carb (cleaned it once, then replaced it) Now, 10 months later and only about 40 hours of use - it is doing it again. really disapointed in this Yamaha.<br /><br />I need to know if you found out a cause. I believe it has something to do with that electric choke or accelerator pump.<br /><br />I cannot use the engine now as, when it is in gear is hunts up and down about 500 rpms and sometimes stalls.<br /><br />GaryN

 

[garyN]

Re: Yamaha 1999 T 9.9 over reving

Update<br /><br />I took the motor to the dealer and he insists that the oil was overfilled - and that was the reason it did not run properly. He charged me $180 to remove, clean and adjust the carb, change the plugs and drain and replace the oil.<br /><br />It is very easy to put more oil in than required - I think the thing only holds a quart and they sell it in Liters. <br /><br />I will try it today and be more careful about the oil.<br /><br />Gary N

 

[bigbrownbuku]

Re: Yamaha 1999 T 9.9 over reving

interesting. based on what you said about the intake you needed your carb cleaned properly. these motors will make oil when used for long periods trolling also. yamaha recommends not filling the engine to the full level on the dipstick, anywhere between 1/2 and 3/4 is fine.

 

[garyN]

Re: Yamaha 1999 T 9.9 over reving

Update<br /><br />Got engine back - fully clearned, linkage adjusted etc. and it runs even worse than before. Now it will simply stop and stalls - then is hard to start and smokes. Now it also backfires out of the carb and then stops.<br /><br />This engine could kill me and put my boat on the rocks - really poor initial quality and customer service has been, to date, very poor. We will see. I plan on posting once it is back at the dealer who says he is going to inform Yamaha he simply cannot fix it (can you say lemon?) <br /><br />This engine has been a complete disapointment and I am not likley to purchase any Yamaha products ever again.

 

[mangomike2]

Re: Yamaha 1999 T 9.9 over reving

Well I finally got running, here is everything I did. On the advice from a person on another board . I took my carburetor back apart , and was very careful to clean the choke valve. On my motor , this is tucked into a hole, sort of on the outside of the bowl. Is a brass cylinder with a spring-loaded BB inside it. And while I had the carburetor off . I recheck and clean everything else. But no luck . the engines still did the same thing it would over rev and hunt up-and-down trying to idle out. So I tried covering the intake horn again, and it idled out. This seemed to indicate to me that the engine was getting air from somewhere other than the horn intake. So I took some carburetor cleaner and spray it directly down onto the carburetor(not into the horn) and sure enough , it stalled out. So I took the carburetor back off , and put in new manifold gaskets, and the little plastic plate that fits in between the gaskets, and sealed the fuel intake line. I also put gaskets sealer round the black plastic cylinder on the top of the carburetor . my book calls this a starter set. I dressed all of these things with gasket dressing. And that did it. It idles out, and starts just as it should. So I had an air leak in one of those places. Hope this helps , GaryN and anyone else with a similar problem .

 

[garyN]

Re: Yamaha 1999 T 9.9 over reving

Update #2<br /><br />Motors actually runs much worse since the service. After only one day it has oil coming out of the carb again and now it will not stay running if in gear. Stalls when slowed down.<br /><br />I am meeting a Yamaha rep this week to talk about a buy back of my lemon. Really disappointing since Yamaha four strokes with carbs should be avoided completely.

 

[garyN]

Re: Yamaha 1999 T 9.9 over reving

Here is the work of Yamaha on my problem. <br /><br />The final word, according to the dealer: they thought I was just being fussy and didn't understand how a four stroke runs, but finally they thought it was fixed and I insisted they run it hard in the tank and then they noticed excessive smoke. They shut it down<br /><br />Turns out the engine had a bad fuel pump diaphram and, because of that, it was pumping gas into the crankcase and when it had no place else to go, it went into the carb.<br /><br />Yamaha has agreed to supply the part for free (4 monts out of the original warranty) - I pay labor, kind of chicken **** as I already paid for service that was not necessary ($180.00 to remove, clean and adjust the carb twice for a total of $360.00). I will try to get Yamaha to pay all of it.<br /><br />Anyhow, the thing that is important is that the engine did run, with the bad pump so you cannot immediatly assume the pump is good just because it runs. According to the mechanic, this is a mechanical pump that runs off the crank. <br /><br />I do hope they actually solved the problem, I am waiting for the part to arrive and will get the motor back next week. If it is still running badly I will file a lemon law action againt Yamaha and get there attention. <br /><br />Thanks for all the help from everyone here.<br /><br />Gary N.