Yamaha F100AET intermittent loss of revs

[191Seanymphstriper]

Re: Yamaha F100AET intermittent loss of revs

Ok listen. Put the boat in the water on your trailer with all trailer tie downs still locked down at the transom and bow of the trailer locked. Back her into the water so the motor when tilted down is fully submerged and able to pump water. Or if you keep it docked just tie up real good. Make sure your parking break on the truck is on good! But in reverse the thrust is less so you wont have a issue!


Start the boat. Rev it up and get her in reverse at 1700 rpm. With your air breather off of all the carbs close each butterfly one by one with your hand by sticking your finger in the carb and close each one and see if it bogs down on each cyl while the boat is under load at 1700 rpm in reverse.


They each should bog down the motor!


If you close one butterfly and dont here a bog or takes longer then others to get boged thenn that cyl is either getting to much fuel so the cyl is flooded or barly sparking and working less causing your ruff idle.


Now this can mean a couple of things. If the fuel pump is conected to the cyl that takes longer to bog its the fuel pump. because whats happening is the diafram in the fuel pump is warn punctered etc.

And what will happen is that cyl will draw alot of fuel flooding it causing the ruff idle and low spark bc of the flooded plugs.

Just because the fuel pump is shot does not mean that the other cyl arent getting fuel and wont get fuel.


It just means 1 cyl is getting to much fuel....


Or that cyl that takes longer to bog or dosent bog at all may have a bad plug or failed plug, or a bad coil, or a bad wire that goes from the coil to the plug.


Now these are the quickest easyiest ways to fix and try to solve the issue. Do these techmecs before you start ripping the carbs off...


""""(Also when the fuel pump is removed from the engine, start the engine with all hoses disconnected etc just as you disconnected it. And give some throttle and let it come down in idle and put in nuetral. Now if it is the pump she should idle in nuetral because now the 1 cyl is not getting extra fuel and the fuel left in the carbs will even out and should idle for about 2 min to 5 min,,,,,)""""""

"""""(Now if she dosent idle without the pump in then its not the pump!)""""


Now if you change the difram in the fuel pump and you change the coil, plug, wire and you still have a issue with that cyl then take all the wires off the plugs and do a complete comp test and be sure you have good even comp. Anything within 15 psi of each other is still considered good.

So if its 115 120 110 105 its still good but will give you a little uneven ness but not enough to sound like a uneven idle or be an unevian idle.


So if you check compression and its all good..... Then take that carb yjay bogged slowly or not at all off and rebuild it and put it back on.... Then it should be fixed..... You may find debri etc or signs that moisture may have bean in it etc.

Let the carb soak excluding the float in (SEA FOAM) (a product to clean fuel systems) for about 3 hours as long as all plastic pieces are off yje carb. Then rebuild the carb!


Those are the only things that can cause the un even idle....

You now at this point after doing this have checked and repaired spark,fuel,air, carb all the things you need to make her run... If you don't know how it works you wont be able to fix it!


Unless your stater is no good which if it is that would be most unlikly and it wouldnt even start at all. Or a elec short which is all uncommon


Follow these steps and trust me youll find the issue...


Dont start drilling your carb etc etc ...... Just not a good idea with debri shavings etc..could cause more problems.. ( No offence to Daviet at all) (I Just wouldnt do it at all personally!)


Get a very small hook pick and a small strait pick and get it out... And again No offence to daviets advice at all but I just wouldnt do that personally! Daviet may be a very experienced mechanic for all we know and he may have a very steady hand!

You can do whatever or however you would like to get it out! But just be carfull if your drilling


And tell me what happens...


Also your phone number was edited out and you cant post your number directly on the thread. You can click on my screen name and send me a P.M (personal Message) with your number and i willl walk u threw it again!


Hope my advice and daviets advice helped!

 

[rodbolt]

Re: Yamaha F100AET intermittent loss of revs

the 4 stroke yamaha DOES NOT use crank pulses to operate the fuel pump.
if the 4 stiroke 100 yamaha pump diaphram leaks it leaks directly in to the oil sump.
wont flood any cylinders.
DO NOT load that engine in reverse.
its not designed for continuous thrust in rev and you can damage the gearcase.
if it sparks at all spark is good.
no worries there.
this is a waste spark engine, 1 and 4 fire every time as does 2 and 3.
if the fuel pump is shot its simply shot and all 4 carbs are going to be affected.
but the description isnt a bad fuel pump.
seanymphstriper, get a manual for an F100 and read it, remember the F part is rather critical.

 

[wirlybird]

Re: Yamaha F100AET intermittent loss of revs

Ok gents i have set the TPS to .7 and it runs like a bucket of snot. back firing in the exhaust at idle and on acceleration i have a lean sneeze.

I have checked all the wiring for pinch and chafe points it all looks good

so whats the verdict lads ??????????????????

 

[rodbolt]

Re: Yamaha F100AET intermittent loss of revs

with the engine idling and the TPS set to .7V what is the idle timing?
have you used the manometer to correctly sync the carb shutters?
whats the pulser coil outputs while idling?
what is the CDI voltage outputs while idling?
your still describing fuel issues.
but its a quick test with a peak reading meter to eliminate or confirm a pulser,ign coil or CDI unit.

 

[wirlybird]

Re: Yamaha F100AET intermittent loss of revs

The idle is -9 warm and cold running and i have the carbs in sync

what colour cables to i connect the multimeter to to test the pulser coil as there are three going into the ECU?

And to test the CDI output should i just test off the back of the CDI or the back end of the leads where they connect to the spark plugs?

 

[rodbolt]

Re: Yamaha F100AET intermittent loss of revs

-9 is on the low side, pump your idle TPS voltage up to about .75 and see if it wont come up.
but first double check the timing pointer is actaully correct. wont be the first one ever been mis adjusted.
we need -5* plus or minus 2 with the engine warm at idle.
pulsers w/b-b (could be w/r)and the other w/b-b should see about 10v running.
CDI output at the ign coil primary connectors b/w-b andb/o-b should see 110 + volts any time the engine is running.
thats the one to monitor. if any CDI output fails you lose two cylinders.

 

[wirlybird]

Re: Yamaha F100AET intermittent loss of revs

ok i have a adjusted the voltage for the tps and set it to the timing and voltage its still a little out

i tested the CDI output at the ign coil primary and it fluctuates from100v to 116v


the pulsers had a reading of .02v - .01v

so i am guessing that's the problem?????

 

[rodbolt]

Re: Yamaha F100AET intermittent loss of revs

pulser coil voltage is way low, the CDI out is abot right.
what kind of meter or meter adapter combination are you using for testing?

 

[wirlybird]

Re: Yamaha F100AET intermittent loss of revs

A FLUKE 187 true RMS multimeter

 

[rodbolt]

Re: Yamaha F100AET intermittent loss of revs

RMS
Rootr Mean Square.
.707 working voltage.
wrong meter.
you need a PEAK reading DVA adapter.
thats most likly why your pulser coil outputs are so low.
RMS is NOT peak.
we need PEAK.
now in a jam I can check a know good output against a suspect output using the A/C voltage scale.
but I would rather see the DC peaks.

 

[wirlybird]

Re: Yamaha F100AET intermittent loss of revs

Are you sure its the wrong meter i can set this to measure peak DC

here is a pic of the meter

 

[rodbolt]

Re: Yamaha F100AET intermittent loss of revs

yep
I am positive.
nice meter, wont work for the application we need without a DVA adapter.

 

[wirlybird]

Re: Yamaha F100AET intermittent loss of revs

i have been banging my head against the wall for a while now and finnaly submitted to the fact that i would have this engine looked at by a yamaha dealer in the first half hour he found that the mixture screw had snapped off in the gallery. i now have the fun task of removing the snapped off brass peice or buy a new carby.

one question if you screw the mixture screw in does it richen or lean out the mixture?

and does this have any effect at the mid range of the throttle?

 

[rodbolt]

Re: Yamaha F100AET intermittent loss of revs

to check pulser coil or CDI output voltages you either must have a peak reading meter like a CD-77 or a digital meter with a DVA adapter.
sierra also makes the mercury equivalent analog meter that napa auto parts stores here in the states sell for about 120 dollars.
you can also use a Kv tester to check ign coil output voltage.
yes the F100 uses all carb circuits throuhout the RPM range, no its not going to cause bogging and stalling.
however each carb has a filter in the carb fuel inlet that can clog and the carbs MUST be correctly synched with a 4 channel manometer when your done.
NO WAY around it.
a broken carb mixture needle tells me untrained monkes have had a go at it.
beware the flying monkeys with tools.\

 

[wirlybird]

Re: Yamaha F100AET intermittent loss of revs

Rodbolt for some reason there is no filter in the carb. Nor is there a place for a filter to go???? see pic

I had my suspicions the mechanic had broken it when they told me that the needle had broken as it was ok when i stripped them down and cleaned them

FYI i have a DVA adapter on order.