1991 Yamaha 50hp, 3 cylinder, won't idle, pulling hair out

[One speed]

Hi all
i bought (in a rush due to lockdown etc) a 1991, 3 cylinder two stroke, DETO, got it home and it turns out the sellers idea of runs great is different to mine, ran on 1 cylinder , low compression on two out of the three cylinders etc. So....managed to find a powerhead second hand, good compression fitted that and it still ran on one, checked the coils and the reading were out of spec and the HT leads corroded as it was a saltwater engine, ordered three new coils fitted them and still ran on one, checked the CDI, it's toast, new CDi ordered, now when I start the engine she is running on three but once the choke circuit stops it just stalls out. I have now cleaned the carbs twice so sure they are good, all adjustments seem to be as the manual, another strange thing is if I back out the air pilot screws it runs better, seems 3 full turns out is the sweet spot) obviously this is way out of what Yamaha recommends (1 1/4 out) and even then it still lumps over and stalls out eventually. Carb butterfly's adjusted as per manual, while running on the choke circuit its roughly 5 Deg before tdc and once it drops into tickover circuit its 5 deg after tdc. I am sure I am missing something obvious, really annoyed as I have put in so much work(+money) and I seem to be getting nowhere- there are no outboard shops near me so would really appreciate any input and hopefully someone has an idea as I am stumped Sorry for the long post, just trying to explain the issue as well as I can.

[rejesterd]

I would guess either a weak fuel pump or weak spark. If you pump the primer bulb while it idles, does it help? If so, inspect/replace the pump.

Even though most of the ignition-related stuff is new, do a spark test with a spark tester to make sure it's jumping the gap specified in the service manual. You still might need new plugs, or maybe something is wrong with the pulser coil or the flywheel magnet.

[One speed]

Thanks so much for the replying, forgot to say I have fitted a new fuel pump fitted and bulb goes hard, I am convinced it's a timing issue but have set the wiper arm on the CDI as manual, and as far as I can see no adjustment under the flywheel.dont have a spark tester bit maybe flywheel magnet, honestly not much left it's bizarre and actually driving me up the wall, I can usually sort stuff but am utterly stumped

[99yam40]

what are the timing specs in manual for that 91 50 ?
how far off from spec is it?
does that motor have a choke or a prime start system?

[One speed]

Prime start system, runs ok on it then does as soon as it goes onto normal running, timing spec +5 atdc, it runs roughly -5 atdc on the prime start and then if I increase the throttle a bit runs but stumbles and coughs around +5 atdc as per the manual. I have the 703 remotes but no control cables currently and really don't won't to spend a dime more till it will actually idle.
thanks for replying

[99yam40]

Prime start system, runs ok on it then does as soon as it goes onto normal running, timing spec +5 atdc, it runs roughly -5 atdc on the prime start and then if I increase the throttle a bit runs but stumbles and coughs around +5 atdc as per the manual. I have the 703 remotes but no control cables currently and really don't won't to spend a dime more till it will actually idle.
thanks for replying

may want to read your last post and correct some of the mistakes
there is BTDC and ATDC, but no + & - ATDC
also missing a not in there too

if it is lean sneezing after the prime start goes away,
then I would think the carbs are running too lean with out the extra fuel from the prime start system
thinking the carbs are clean does not mean they are.

are the crank case recirculation check valves all doing what they should?

[ausnoelm]

Clean the carbs properly, I don't know how many Yamahas have had the carbs "cleaned" but are still dirty, there is no spray, wash or additive that will clean them.

[One speed]

Thanks for the inputs guys apologize for the typos, yes once the prime start turns off they do lean sneeze, and die, the fact that they run smoother (on start) with the pilot screws turned way out point to carbs.( I have checked the pilot screws incase they are deformed but they are perfect) I have no had the carbs apart twice, they are very basic and I have checked air circuit, jets, bowls, everything spotless but maybe it's time to invest in an ultrasonic cleaner I suppose. I haven't checked the recirc valves will do that today thanks should also say pulled the reed block when I did the carbs and they are perfect as well.
On these engine's I take it the only timing adjustment is on the wiper arm on the CDI?

[99yam40]

I would say yes that is the only timing adjustment, but I have not worked on a 91 50hp and I do not have a manual for it either.

on my 99 C40TLRX I had a problem with the CDI not setting the timing as it should at Idle when set as maual said so I replaced with a new one to fix that.
Did you get a new one or used?
seems it was retarted to 14 ATDC if my memory is OK, which cause the idle adjustment screw had to be set too high to get proper RPM

seems I remember that at cold start the idle timing is different than when it is warmed up

[One speed]

Ok guys,
Have had a look at the instructions from CDI electronic's where I got the CDI from and they say the timing for the 40hp is 4 to 6 degrees and the 50 hp should actually be 0 to 2 degrees, now I apologize here if this is a question how do I adjust that? Mine definitely seems to be on 40 hp timing as best as I can tell.
Again I am no outboard mechanic just trying my best to get on the water this summer!

[99yam40]

I would need to go look at a manual or my motor to see for sure, but am thinking adjusting the wiper linkage a little should move it.

but that will probably affect the WOT timing also
have you checked that timing also?
is WOT timing different for the 40 and 50?

looking at my manual it shows the same timing for the 40 and 50
7 ATDC + - 1 and 25 BTDC +3 -1


Aftermarket CDI may not be the same as factory so specs could be different

[One speed]

I have it bang on but as far as I can see it's running 40hp timing, is I adjust the wiper arm then it's not going to line up to the idle and wot marks on the CDI? Maybe I have confused myself and someone is going to point out where I am going wrong?

[One speed]

Here are the instructions from CDI electronic's

[99yam40]

it says to verify with a timing light, so if it needs tweaking a little, tweak it some until you get your desired timing.
after all it is just a starting point mark to get you close

logic would tell me if you advance the idle timing a few degrees it will also move the WOT timing the same amount, but a timing light will tell you exactly what you have

[One speed]

Ok update, manual I have states 5 degrees for 50hp fully retarded and the engine will absolutely not run at that, as per the sheet I received with the CDI it states 40 5degress and 50hp 0-2 degrees, I have now adjusted the wiper arm so I am at 2 degrees at tickover and success it now idles!!! Obviously now it's not pointing at idle on the CDI box, only other thing that's niggling me now is it really isn't happy at 1 1/4 turns out on the air screw, really wants to be around 2 to 2 1/2 turns, not sure why this is.
So to update, not sure if my specific year has different timing spec's or what the deal is as as far as I know the 6h4/6h5 engines 89 to 1994 where the same? I want to thank everyone for their help and if anyone knows if timing spec changed and any input on the air screw great, but looks like I will be on the water soon.
Thanks