70 yamaha 1990

[droptheline]

I have a 1990 70hp yamaha that had been sitting around for a few years, its the precision blend deal, i emptied the oil tank and put in new, and eventually got it started, revved up good. i hadnt noticed at the time that i was just controlling the fuel to the carbs and not advancing the timing but it did rev up well to high rpm. Today started it, idles fine but its missfiring and studdering when i try to give it gas, i was doing it the correct way this time advancing the timing with it, tried it like i did yesterday without advancing the timing same thing. Took the 3 carbs off and scrubbed and blew them out clean. there were some clogged jets so i thought i had it but started it and same thing. So i check the timing ( i have a manual) i dont have a tach which i know is important for timing, but after warmed up at a low idle it was reading almost 20 deg. btdc which seemed way off to me, i advanced the timing to 7 btdc it seemed like it was running better but the rpms were way to high for idle and when given gas it gave me the same result. I am running a small outboard tank with fresh fuel and clean filters so i dont think thats a problem. The plugs keep fouling 2. Anyone know what direction i should be heading in from here cuz i dont.
Thank you

 

[jiggin joe]

Re: 70 yamaha 1990

Assuming carbs and filters are ok how abouut fuel pump?

 

[99yam40]

Re: 70 yamaha 1990

What does the manual say about idle and wot timing for that motor?
20 BTDC or even 7 BTDC does not sound right at idle as you said it was and is running, but I do not know for sure.

If there was crud plugging jets and passages and you filled them up again with crud from inside the pump and lines , you will need to clean the carbs again

 

[droptheline]

Re: 70 yamaha 1990

Sorry its 7 degrees above top dead center not below. the book says it should be 7degrees atdc at 750-850rpm idle, but when i set it there it idles really high and still bogs and runs like $%^& when revving up. I cant get to wot settings because it wont revv that high but it should be 22 btdc @ 5k-6k rpm.

 

[99yam40]

Re: 70 yamaha 1990

BTDC stands for before top dead center and is considered advanced
ATDC stands for after top dead center and is considered retarded
The more advanced the timing is the faster it will idle or run.
Did you do the link and sync like the manual says after putting the carbs back on?
If not get a manual and follow the steps and make sure the timing, adjustments, and all linkage is according to the manual.
If it is then you may need to go through the carbs again.
Making sure the compression is good on all cylinders and the spark is good at problem RPM is a must also ,along with the timing.
Once all that is good the it is only the fuel/air mix that needs to be focused on

 

[droptheline]

Re: 70 yamaha 1990

After adjusting the timing to 7 adtc and the carbs & linkage as directed in the manual the motor is giving off heavy exhaust fumes and still bucks as it did before past 1/4 throttle. I cleaned the carbs again and they looked as clean as when i did it the first time. im def. getting spark on all 3 @ idle but when it bucks my timing light stops blinking on all 3 so im going to try to get an inline spark tester at the auto store and see where this leads me. Any help on why it might be doing this is appreciated, thanks!

 

[99yam40]

Re: 70 yamaha 1990

Best thing to do is get the proper peak reading meter or a DVA adapter and check the input and outputs of the CDI as the manual says to see where the loss of spark/voltage is happening if you are loosing spark.

Did you check the fuel pump like was mentioned for a bad diaphragm?

 

[droptheline]

Re: 70 yamaha 1990

no i didnt check the fuel pump but i will and will get back with the result. does the heavy smoke suggest that my timing is still off?

 

[99yam40]

Re: 70 yamaha 1990

no, but too much fuel will cause smoke and fouling a plug but not all of them

 

[droptheline]

Re: 70 yamaha 1990

ok i just checked the pump, i was easily able to blow from the inlet thru the outlet, and was also able to blow a slight amount of air from the outlet and thru the inlet which the book says you shouldnt be able to do, so i will replace it and report back with if it was the fix or not. Thanks

 

[droptheline]

Re: 70 yamaha 1990

SUCCESS. well sort of, the fuel pump was bad and starving the engine causing the bucking and lack of revving. but it still smokes more then normal and i have gas rising up out of the small pipe behind the choke valve and pouring out of the carb into the motor. More help please. Thanks!

 

[droptheline]

Re: 70 yamaha 1990

Back to failure. Got the carb sorted out by readjusting the needle. put it all back togather & my oil pump linkage was jammed, finally had to remove the oil pump and found that the crown on the shaft that powers the pump off the motor was broken and the pump was siezed. $200 worth of parts this is getting old, maybe ill trade the boat for a nice riding lawnmower or snowblower????