Yamaha F100AET intermittent loss of revs

[wirlybird]

Hi Guys,
I have an issue with my engine loosing revs every now and then. The engine will loose revs at full throttle both by hearing and the tachometer dropping to 0 not all the time just when it feels like it. Also this issue occurs at 3000RPM but much more prominent.

I have cleaned the carburetors the fuel tank and the fuel pumps replaced the spark plugs and filters.

Does any one have any ideas what else need to be replaced or what it could be????

The engine is a Yamaha F100AET

Cheers

 

[wirlybird]

Re: Yamaha F100AET intermittent loss of revs

Hi Guys

i have done some more testing when i remove spark plug leads for cylinders 2 and 3 when running the engine still runs when i remove 1 or 4 the engine dies is this normal?

i have evened the spark issue out by adjusting the throttle angle sensor

 

[wirlybird]

Re: Yamaha F100AET intermittent loss of revs

Ok i have cleaned the carbs for the third time and noticed one of the the prime starter assy was less free flowing than the other could this be the cause of my problems and how do you clean it out with a drill or something??????

 

[wirlybird]

Re: Yamaha F100AET intermittent loss of revs

....

 

[turn2]

Re: Yamaha F100AET intermittent loss of revs

If your surge is rapid ,like turning off the key and back on , it is electrical. If it boggs slowly and slowly returns it is in the fuel. Did this happen from one trip to the next? Or did it progrees to this stage?

 

[wirlybird]

Re: Yamaha F100AET intermittent loss of revs

Voltage regulator blew (I mean caught on fire) ever since i changed it out the rapid loss of revs has occurred.

I am starting to get some patterns the drop out of revs happens only when warm so i replaced the temp sensor i also replaced the throttle angle sensor as every time i reset the timing the performance would improve. I also am getting a dropped cylinder for a minute or so at warm up. Does this sound like a stator problem or a pulsar problem?

 

[wirlybird]

Re: Yamaha F100AET intermittent loss of revs

i have taken the stator off due to the intermittent flashing of the timing light during the start up. i noticed some burnt looking bits on the bottom and some of the protective stuff on some of the fingers looks different is this normal????

 

[wirlybird]

Re: Yamaha F100AET intermittent loss of revs

anyone

 

[wirlybird]

Re: Yamaha F100AET intermittent loss of revs

i pulled of the prime start assy again to see if it was clogged again and it was!! its got me baffled as to where the gritty stuff is coming from since i have striped the carbys twice now and put a new fuel filter on it would explain the lean sneeze.

so what i am getting is i hit some rough water and the grit and dirt gets mixed up in the fuel and makes it to a point in the system where it clogs up but where is it hiding??

And when the engine is warmed up where should the timing be set? -10 or +10

 

[wirlybird]

Re: Yamaha F100AET intermittent loss of revs

bump

 

[rodbolt]

Re: Yamaha F100AET intermittent loss of revs

no ign timing setting on the US market F100,engine must be running and you set the TPS to .7V plus or minus .02V.
stator on that engine has nothing to do with ign, that engine uses a TCI ign and a set of pulser coils.
one pulser controls 2&3 the other 1&4.
do you have the correct manual or are you trying to use 2 stroke methods that simply dont apply much.
check that the battery isolator lead isnt pinched,check all 12V charging leads for chafing.
as the ign system is 12V any loss of 12V will shut you down.

 

[191Seanymphstriper]

Re: Yamaha F100AET intermittent loss of revs

anyone

Normal! It is 1 or 3 things or 4 but the 4th is expensive. Its not the fuel! Its a coil pack a wire from coil to spark plug a plug if its the 4th its the power pack and that sucks bc its the most expensive thing. Try hooking up a sep little tank of fuel with sea foam in it and run it a little. make sure you have full ball presure as well with the little tank. Burn up half a tank. If the prob is still there its not the fuel at all. But to be safe before you run the little tank drain all the carbs to be sure there no water in them. Then buy all new coils and all new plugs and just change them. There cheap enough and may need to be changed anyway if they havent been. GL!!! Also really check those wires goiing from the coils to the plugs. If you se green build up that can be grounding out a plug!

 

[rodbolt]

Re: Yamaha F100AET intermittent loss of revs

be aware
if its fuel and running lean its very possible to wipe a valve or detonate a piston LONG before the snake oil works.
see it at least once a month.
its just to simple to test the coil primary voltage,if it stays steady fix the fuel issue,if it does not find the electrical issue.
that motor uses a TC/CDI ign system,its a 12V system that the CDI turns on and off primary ign current.its an odd setup but works well.
the two pulser or pick up coils feed information to the CDI for RPM and crank position,the TPS give throttle angle information the CPS gives coolent temp information.
the CDI,based on these signals will adjust the ign timing between 5*ATDC and about 25*BTDC.
NO TIMING ADJUSMENTS.
its a funky set up that worked well but we only had it on the F80,90 and 100 from 99-04.
engine MUST be running on the US models to set the TPS voltage.
but remember your engine is an international model and may not be exactly like the US model.
some clean pics of the coils and coil wire colors will help.
remember, this engine is a waste spark, that means any time 1 fires 4 fires anytime 4 fires one fires.
same with cylinders 2 and 3.
odds off losing a coil that would affect 3 and 4 and not shut off 1 and 2 as well are slim for ign controling parts.
loss of 12V or low voltage to the CDI will result is loss of spark on all 4.
inside the CDI assy is a DC to AC cnverter that feeds the CDI portion and the computer fires the coils in pairs 1&4 then 2&3 based on inputs from the two pick up coils and the TPS.
lose a pick up coil or the TPS and the engine defaults to a fixed 10* BTDC.
engine will idle high and top speed cannot be reached.
unless japan did something very very different for the F100 international market engines.

 

[wirlybird]

Re: Yamaha F100AET intermittent loss of revs

i will get some pictures of the coils and post them up tonight

i am having a hard time getting some sea foam in Australia would slick50 do the same thing?

Thanks for your replys

 

[wirlybird]

Re: Yamaha F100AET intermittent loss of revs

There is some pics as requested

I ran some BRP engine tune through the engine as i could not get some sea foam it hasn't seemed to make any difference. I did notice a lean 1 sneeze on warm up then once warm it was like a miss or a slight exhaust cough once warm weird.

Rodbolt i think it may be one of the two pulser or pick up coils but would this be intermittent?

i will also strip the sheathing and check all the wires just to be sure.

The pic on the left is the 3 pulser coil wires and you should know the other one with their connecting wires on top

 

[wirlybird]

Re: Yamaha F100AET intermittent loss of revs

the two pulser or pick up coils feed information to the CDI for RPM and crank position,the TPS give throttle angle information the CPS gives coolent temp information.

engine MUST be running on the US models to set the TPS voltage.

Rodbolt if the pulser coil is gone would this explain the erratic tachometer????

and how do you set by the TPS voltage the only way i can see is by using a timing light and moving the TPS until you achieve TDC when the engine is warm or am i way off the mark ?????

 

[rodbolt]

Re: Yamaha F100AET intermittent loss of revs

your so out in left field your not even in the ball park.
you CANNOT set the TPS voltage with a timing light.
you MUST use a digital voltmeter or an incredbly expensive analog type.
you MUST also follow the procedure in the service manual.
even if you lost a pickup coil the symptoms would be low top end and high idle as the ECU would revert to fixed timing.
you can use the winky blinky or your digital voltmeter to check for code 13 bieng set or loss of output voltage from the pickup coils bu you have to have it set up when its failing.

 

[191Seanymphstriper]

Re: Yamaha F100AET intermittent loss of revs

Heres an idea. If you have a mechanical pump and the diafram is bad you will still be getting fuel to all cylenders but you will be dying out at idle and you will be flooding the main cyl that pumps the pump making the motor sound like its elec or timing etc. try changing the diafram or replacing the fuel pump and crank her over. A $3 part could be causing this mess believe it or not...

 

[191Seanymphstriper]

Re: Yamaha F100AET intermittent loss of revs

Please send me a P.M if this fixed it. I am 99 perc sure this is the prob. I just went threw a similar situation!

 

[rodbolt]

Re: Yamaha F100AET intermittent loss of revs

diaphram retails for about 128 USD.
I would test my old one at that price before chunking one on it.
however I would have tested the entire system as per the service manual first anyways.
with the tach resetting to 0 I would chase electrical issues.
remember if the ECU loses its 12V it shuts down and the tach resets.
tach signal comes from the CDI assy. but its not a CDI unit like ANY two stroke ran.
it takes the pulser coil inputs and the TPS inputs to generate tach out and when to spark it and where in the heck is the crankshaft at.
lose one pulser and the engine will run, idle timing will be fixed at 10* BTDC so it idles fast, top speed cannot be reached. lose both and your calling for a tow.
but start with correctly setting the TPS voltage.