Yamaha not idling and loosing rpm

[rnellie4]

I have a 40hp 1997 yamaha percision blend moded 40tlrv. This motor was bought 4 months ago and has been sitting at the shop off and on for 4 months. I brought it in when I first bought it for him to go through. Said he tested it on the river and it ran good after he fixed some things. Then I brought it right back after the first time I put it on the water because it would get to plane then drop rpms. Now it still does the same but also will not idle. He said he has checked every possible fuel issue it could be, changed fuel line, changed connections, changed gaskets, cleaned carbs 8 times, rebuilt carbs, new fuel filter and pump, new diaphragm. Compression is 100,100,100. He said he can not fix it. Please let me know if you have any other ideas what could be wrong with it as I am at a complete loss of words, thoughts and extremely frustrated as you could imagine. I have $800 in mechanic hours into it and over $500 in parts. Or do you think I should:

1. sell it not running and loose a lot of money
2. have him keep trying to fix it
3. take it to another mechanic and start over which will be very expensive

Thanks!

 

[99yam40]

Re: Yamaha not idling and loosing rpm

Check some of my posts. I have been fighting the same type of problems on a 99 C40 and have not found all the answers yet. but I am still looking. My latest find is that it runs fine with the silincer and cowling off but not with them on, making me think it is running rich. I also know that the idle timing is way too far retarded, caused by the CDI unit as far as I can tell. Mine still idles but rough mainly drops RPM at high RPMs

 

[jbjunior66]

Re: Yamaha not idling and loosing rpm

Have you tried to sync the carbs. I rebuilt my carbs and i could get it to idle at specs. 800 +/- 50 rpms. After reading another post that had the same issue and had tried everything under the sun so they thought. just something to look at.

 

[rnellie4]

Re: Yamaha not idling and loosing rpm

thanks for the help fellas. I will give these ideas a try and keep you posted

 

[rnellie4]

Re: Yamaha not idling and loosing rpm

Update - the local mechanic working on the motor thinks the problem is internal and to fix the problem I will need to split my crankcase and go internal. Seems to be bypassing oil. Another theory but not 100% thats the issue

 

[99yam40]

Re: Yamaha not idling and loosing rpm

what does he mean bypassing oil? Not getting oil to some parts.
What does he think is wrong with it and what is needed to fix it? gaskets, seals, plugged passages?

 

[rodbolt]

Re: Yamaha not idling and loosing rpm

use the Yamaha Marine Dealer locator function on google and find a shop in your area that employs a master tech.
I dont deal much with tiny mite engines but enough to know what to look for and I have the test wheels and harness adapters as well as the service manuals.

 

[Eshaw150]

Re: Yamaha not idling and loosing rpm

use the Yamaha Marine Dealer locator function on google and find a shop in your area that employs a master tech.
I dont deal much with tiny mite engines but enough to know what to look for and I have the test wheels and harness adapters as well as the service manuals.

Agreed stop wasting ur time and money with this so called machinic and i dont see what he means bypassing oil. If oil was not getting to all the parts u would have a lot of noise and low compression reading and have bearings locking up. I think he is shafting u Do as rod bolt states.

 

[rnellie4]

Re: Yamaha not idling and loosing rpm

Fellas - Thanks for the advice. I have the boat back, but gonna be a little while before I take it somewhere else (job situation has definately been better). I will let you know when it gets fixed or I find the problem.

 

[robert graham]

Re: Yamaha not idling and loosing rpm

have you checked/replaced primer bulb, fuel pick-up in tank, fuel quick disconnect on motor in-leaking air?, how do your spark plugs look...run motor and turn off quickly and check plugs for condition...plugs can tell you something of problems. maybe a simple/obvious problem that's been overlooked. Good Luck!