Yamaha 40hp 2 stroke on old fishing boat

[Kirk Gibson]

Hello,
I haven't been on here a while, just too many other things going on, probably like most everybody else.
Both my F150s are doing great.
I have a mystery that I am working on and wanted to see if anybody here had any input. So here goes,
I am trying to help out a friend who has an old fishing boat (Carolina Skiff 17ft) with a 40hp 2 stroke Yamaha on it. I think it is a 1997 model.
Well of course he let it sit too long and couldn't get it started and I sort of knew right off the bat the carbs going to be crapped up so I pulled the carbs and sure enough they were BADLY crapped up. Soaked everything real good, ran thin copper wire through all passageways and jets, blew compressed air though everything, ALL passageways are open. All parts were clean enough to eat off of.
Re-assembled everything using Yamaha carb kit (floats, valves, gaskets etc.) measured the float distance to 15mm. Air mixture screws set at 1.5 turns. Reinstalled on the motor. Synched and linked per service manual. Also installed a new fuel pump (Yamaha) as the old one looked like the diaphragm was a little worn.
Started right up and purred like a cat in neutral. Set the idle speed to 800rpms. Raised the throttle lever (still in neutral) and she went right on up and sounded great. Put the engine in gear while on the muffs (I don't usually do that but just wanted to make sure it would not stall while in gear) and prop spun like a new engine. GREAT!! Problem solved, right? WRONG!
So we launch his boat (he just lives a few blocks from the ramp) and I was going to take his boat up the ICW to his dock. (His house is on the ICW) Backed out real slow, no problem, gave it a little gas, no problem. Gave it enough to get up on plane and it feels as though it struggled, then bogged down and stalls.
After I sit for a minute it starts back up, but will not take the gas so we limp up the ICW about 1/4 mile to his dock and tied it up.
I went out today to triple check everything, throttle linkages, idle stop (20mm) in neutral and CDI on 7 degree ATDC, full throttle CDI on 25 degree BTDC, both EXACTLY on the mark.
So we tried it again and it basically does the same thing.
(BTW this has fresh, non-ethanol gas in a new can and new fuel lines, gas mix is 50-1 ratio)
So we get it back to the dock. When we get back the engine didn't want to start. It would fire up and idle for about 5 seconds and stop (and not a smooth idle) eventually after doing this a few times it would not start at all.
I pulled the plugs and they looked wet but were gapped ok (.035) so I dried them and put them back. Still no start. I put a screwdriver in the end of top plug wire and held it close to plug...nothing. Same with the other two, nothing.
So we went from idling smooth, rev smooth, rev smooth in gear (all out of water) to... boggs down under load and now no start. No apparent spark. BTW cooling is working good, great pee stream always and no alarms.
Could it be the CDI or ignition coils? I did get a tiny tingle on the top plug but no real visual spark. Could the CDI maybe not be moving the spark when the throttle is open up and flooding it out? We are really puzzled with this one. Also one other part of the puzzle ... when it stalls there is a chirp which he says wasn't there before.
I know this is a little long winded but I wanted everyone to have all the puzzle pieces first. I'm just trying to help out a friend who is trying to get in a little fishing.
Thanks guys.

[Gemmini1]

Interested having a similar issue

[zenoahphobic]

This story is very typical and starts off appearing as if the cleaned carbs could have sucked in dirty fuel and therefore need to be cleaned again.
The culprit could be decayed fuel lines or tank contamination like water.
It would seem unlikely to immediately get an ignition problem after a very short time. But there is a possibility that wires (including ignition leads) were moved and failed or their connections had become unsound.
I would start at the fuel bowls carefully inspecting the contents. If there is debris then inspect the fuel lines (difficult to see inside them).
If there is water then your fuel tank needs to be cleaned out. Then clean carbys again.

[panasonic]

Older engine, no spark at all. Look at the dead man's switch. Or simply unplug it and see if the spark comes back.

[99yam40]

I agree, chase spark if you are not getting any on any plug,
peak voltages into and out of the CDI is where I would start.
once you have good steady spark then figure out the fuel issue

Bad kill switch or wires can bleed off spark voltage
My BILs 50 had debris in the #3 carb main jet that caused his motor to stall when giving it throttle.
never made and sense to me, but that is all I found when cleaning the carbs and it fixed his problem
one little flake hiding in the lines or pump can cause this

[Kirk Gibson]

Thanks Guys, I will temporarily (for testing only) bypass the dead mans switch. Also check CDI voltages and try and figure out why no spark first. The fuel and tank are new but the line to the motor from the tank is not. I will also check that. I also cleaned the filter before re-installing his carbs and there was no debris in there when I checked it when we got back to the dock (one of the first things I checked)
One thing I couldn't understand is when we tested it (it ran ok going almost at idle and stalled when giving it throttle) is was it starving for fuel or flooding from too much fuel? If there was (or is) a problem with the CDI not moving the spark with the throttle then it wouldn't it flood out? But out of the water in neutral it revs up great so that is what is puzzling.
Thanks for the advice. I have learned a lot from this site since I joined back in 2010. :-)

[99yam40]

the motor needs more fuel under load than when just reving with no load on it.
onboard filter should catch anything coming to the motor, but there are lines and the pump after the filter that could have stuff hiding and break loose after a carb cleaning

I once found a small thin almost like plastic wrap piece of debris in one of my carbs after cleaning my carbs that plugged up a main jet.
only thing I can think of it being was some dried up reside that finally broke loose from the inside of the pump or one of the lines heading between the carbs and pump.

timing light will tell you if the timing is in spec and advancing as it should.

how do you plan on bypassing the kill switch?
you do know that the switch grounds the spark voltage to keep it from getting to the coils

[Kirk Gibson]

I may have to repull the carbs and see if there is anything new in there. I will have him replace any and all fuel lines from the new tank forward. Also thanks for the tip on how the kill switch works, I always thought that it opened a circuit to kill the ignition, so all I should have to do is pull one lead off and that should work?
Thanks again

[99yam40]

those preformed little hoses around the carbs and pump get a little pricey

solve the spark problem 1st
then try to narrow down what cylinder has a problem with fuel if it still is a problem

[Kirk Gibson]

Makes perfect sense. Thanks again, may have to wait a couple of days as it's really hot out there today. Wonder why the little fuel lines are so pricey they don't appear to be anything special?

[Kirk Gibson]

OK, so I finally got back here to give the answer. Thank you 99yam40. I re-pulled the carbs and checked them with a fine tooth comb. Everything right on specs. Put it all back and started it and it ran perfect. We were going to take it out that day but it was so windy we knew it would be difficult to get it back in and aligned on the lift. So to make sure it would work under load we tied it to the dock and let it pull real good for about 30 seconds. Did great, thought we had it solved (although still didn't know what we/I did different).
So on a calm day he takes it out and it does the same thing as before.
When he brings it back in I notice / hear a miss in #1 cylinder. Long story short I found the plug wire to that cylinder had broke near where it snaps on the plug. (inside the plug boot) We replaced that wire and it now will run like a scalded dog!
99yam40 was right. It was a spark problem. Thanks again, I have learned a lot from your posts over the years.
BTW when we first start this engine it gives a little sneeze a few times but after running for about a minute the sneezing stops and runs and idles great, anybody had this happen? Seems I heard of this somewhere before. Not a big deal ... just was curious.

[99yam40]

since you never gave a model number, I would guess this motor has a prime start system not a choke.
chirp to me is a cylinder not getting enough fuel (lean sneeze) at cold start.
why who knows, but something to chase

make sure the red lever is in the normal/auto position and all the prime start system (, diaphragms, check valves and passages) are clean and good working order

and did you follow the link and sync procedures when you put the carbs back on?

[Kirk Gibson]

Thanks Yam,
Yes, I should have posted his model number (but I would have to walk out his 1/4 mile pier to get it now so I may do that later ...lol) and yes it is a prime start system ... idles high for about 15 seconds then drops to normal. Sneezes a couple of times but after running for a minute stops. Red lever on prime start solenoid/valve in normal auto position. Followed the link and sync to the letter when reinstalling. Carbs cleaned very well, screws at 1-1/2 turns out as per manual. Since it runs so good now (he claims it never ran this good even when new) I think I am going to let sleeping dogs lie and not mess with anything (like increasing screws to 1-3/4 or something) he says the little sneezing when starting is fine with him as long as it continues to run like this.
Thanks again for your input, as I said I have learned a lot from your posts over the years (2010) I have a 2011 256 Seafox with twin F150s and have been here since 2010 ... I know yours says Aug. 2022 but I know that is wrong since I have been reading your posts for a long time.
Take care,
Kirk

[99yam40]

Thanks Yam,
Yes, I should have posted his model number (but I would have to walk out his 1/4 mile pier to get it now so I may do that later ...lol) and yes it is a prime start system ... idles high for about 15 seconds then drops to normal. Sneezes a couple of times but after running for a minute stops. Red lever on prime start solenoid/valve in normal auto position. Followed the link and sync to the letter when reinstalling. Carbs cleaned very well, screws at 1-1/2 turns out as per manual. Since it runs so good now (he claims it never ran this good even when new) I think I am going to let sleeping dogs lie and not mess with anything (like increasing screws to 1-3/4 or something) he says the little sneezing when starting is fine with him as long as it continues to run like this.
Thanks again for your input, as I said I have learned a lot from your posts over the years (2010) I have a 2011 256 Seafox with twin F150s and have been here since 2010 ... I know yours says Aug. 2022 but I know that is wrong since I have been reading your posts for a long time.
Take care,
Kirk

Yea, I do not understand why, but every time I log in it puts that new date on my profile.
I started coming on here in 2008 when I bought my used C40TLRX and had problems to solve