Yamaha 175 2stroke- Hard to start.

Evan B · Feb 5, 2024

Hi folks-
Motor is a 1998 175 carbed 2stroke. Trouble I’m having is starting while cold.

Typically, I pump bulb, pull out choke on front of motor, advance throttle in neutral maybe 1/4 way, and turn it over.
usually get a stumbling start in the first turn or so then it simply dies and refuses to light off. Choke in or out, Throttle at idle or advanced (in neutral). Nothing.
I know it’s getting fuel and good spark.

One thing I noticed today is the choke butterflies remain closed after I push the choke back in to turn it off. When I manually reached behind the carbs and flipped them shut, it started right up.

Is that normal? Why do the butterflies stay closed?
Thanks!

Mustang65fbk · Feb 5, 2024

I think a bit more information is needed but a few questions and thoughts that I personally have on the matter would be... how many hours are on the motor? Has it ever been rebuilt? What's the history on it or the maintenance been like? Does it run fine when warmed up or are there other issues as well? It's now a 26 year old motor that's a 2 stroke, so if it has 2k-3k+ hours on her, it could be time to start thinking about doing some more maintenance and/or possibly a rebuild. I haven't owned 2 stroke motors in years, but they can be very finicky in the cold when trying to start, especially the first couple times of the season. I'd go out and try to start her up a few times a month at the very minimum. My uncle's old boat had twin 2 stroke 175 Mercury's on it and they would be difficult to start, especially the one, when it was cooler in the mornings or if you hadn't started them up the previous week. I typically would pump both bulbs until they were firm, choke to 100% as well as turn the idle up to at least 3/4 when starting them for the first time in over a week and/or cooler temperatures. The one motor was better at starting than the other and would usually start up the first or second try, but the other motor would sometimes take 4-5 tries or more. After starting both, I'd let them high idle for a few seconds until they sounded like they'd be able to keep running at a lower idle, then let them sit for a few minutes while we got everything ready on the boat to fish.

Evan B · Feb 5, 2024

3-400. I’d have to go look again, but it’s a pretty low hour motor.

Never rebuilt to my knowledge. It is new to me though.

Motor sat for years. Like 14 or 15 years. It had been winterized thankfully. Carbs and bowls drained, fuel tank drained.
I replaced fluids and fuel lines, filters, etc…

After it starts, it runs wonderfully. It just getting it to start when cold.

Since I know it’s getting fuel and spark, I think the choke sticking closed is choking out the 3rd element, air. Just not sure why or if it’s supposed to stay shut.

Thanks!

seasick · Feb 5, 2024

Do you know if your choke is purely mechanical or if it is electric? Sounds like something is broken, disconnected or way out of adjustment. I may have a service manual. What is the model type of the motor?

Mustang65fbk · Feb 5, 2024

Evan B said:
Motor sat for years. Like 14 or 15 years. It had been winterized thankfully. Carbs and bowls drained, fuel tank drained.
I replaced fluids and fuel lines, filters, etc…

I think you found the culprit right there. It's now a 26 year old 2 stroke motor, of which 2 strokes don't like to sit for a long time without being run, not to mention 14-15 years and especially not when it's cold. If this is the first, or first couple of times, that the motor has been started up in the last 14-15 years and especially when it's cold outside... I'd say that's completely normal. I would run the motor as often as you can, of which you can also tune up the carbs or rebuild them and do the other essential maintenance since it's sat for 14-15 years.

Evan B · Feb 5, 2024

seasick said:
Do you know if your choke is purely mechanical or if it is electric? Sounds like something is broken, disconnected or way out of adjustment. I may have a service manual. What is the model type of the motor?

s175txrw is the model. 1998
The choke is just the manual lever on the engine. The key does not seem to have a choke function.
A fairly quick inspection and everything looked good but I’m pretty sure the choke is not functioning properly.

I’ll pull the cover again tomorrow and see if I have the same luck flipping the butterflies open by hand and go through the linkage a bit more thoroughly. ‍

seasick · Feb 5, 2024

It looks like your motor has an electro-mechanical choke. There is a solenoid called a fuel enrichment valve that connects to a piece of linkage that ultimately connects to the carb butterflies. I assume that the valve(solenoid) when energized pulls the choke plates closed but I am not sure what opens them. It may be a spring or something like that on the choke shafts. I would also assume that there is an adjustment that sets the maximum choke plate position and I think it shouldn't be 100% closed.
Regardless, look for the linkage rod that connects to the choke plate shaft.

seasick · Feb 5, 2024

I did look at the service for a 1998 S175W model and it did have the fuel enrichment valve. It also shows the mechanical choke rod so what does the enrichment valve do? Perhaps it works to open the choke plates or maybe even the throttle plates. In any case it is a solenoid and if you ohm it out, it should read 3,000 to 4,000 ohms on its two leads. I suppose if you check the harness connection to that valve, you will see voltage at some point which causes the linkage to be pulled.

OceanSun · Feb 5, 2024

The good news is it runs great once started! Sticky choke is not uncommon and before doing a full rebuild on the carb I'd work the choke valves back and forth quite a bit with a liberal dousing of WD40 or similar. Your problem may be as simple to solve as that unless the aforementioned automatic solenoid is physically holding the choke closed. Back when I was running 2 strokes gummed up sticky chokes would act just as you described and was easily fixed. Full carb rebuild while paying special attention to linkage tuning and float settings may be a worthwhile thing to do on that age of motor irregardless of the sticky choke but a can of WD40 may be your quick fix for now.

Evan B · Feb 5, 2024

Thanks all!
Great info. I’ll get back into it tomorrow and see what I can sort out.

PointedRose · Feb 5, 2024

Wouldn’t hurt to try a seafoam treatment as well. When you say carbs and bowls were drained, were they cleaned at all? Next time you get on the water and started up, run with full throttle for several minutes to try to blow out any carbon buildup.

Gulffisher · Mar 5, 2024

The parts diagram I am looking at shows a solenoid as part of the fuel system and I can only assume this is for electric choke activated by pushing the starter key inward. I am guessing 1) the solenoid is stuck in the choked (butterflies closed) position or 2) the starter key switch in stuck in the choked position. In either case, the choke butterflies would remain closed and the manual choke (I assume there for manual rope pull starting, but I would NEVER want to be the one doing that) would do nothing. Otherwise, I can't see how what you are describing would be happening. I was confused a bit and hope you can clarify. You say choke remains closed, engine will not start/run but when you manually "closed" the choke butterfly from behind the intake/silencer box, the engine started and ran. Did you intend to say when you "opened" the choke butterflies?

Fishtales · Mar 5, 2024

If no luck, see if you can find a traveling marine engine mechanic in your area.

TMANN · Mar 6, 2024

I have seen broken or chipped reeds cause similar issues.

Electrically operated choke should not stick. Check linkage.

Starting procedure would be, pump bulb firm. Shove key in to activate choke and hold until running. Then bump the key as needed to keep the motor running until warm.

Sdfish · Mar 6, 2024

You should also check and possibly replace all fuel lines. The ethanol in fuel broke my fuel lines down and created havoc for an older motor I had. Motor ran like a top after they were sorted and carbs cleaned.

glacierbaze · Mar 6, 2024

If the solenoid is working, you should be able to hear a click when you turn the key on and push it in. With the cowling and the silencer box off, you should be able to see the choke butterflies move, and hear the solenoid.
I also thought that you meant to say, '..when you "opened" the choke butterflies by hand', which you seemed to confirm in post #6.

seasick · Mar 6, 2024

As stated as I see it, the solenoid does not connect directly to the choke plate. It is described as an enrichment valve and to me that means that is makes the air/fuel mixture richer which is what you need to start a cold motor.
I also don't think the issues is related to old fuel lines since the problem goes away when the motor is warm.
I suggest that you follow the linkage out of that solenoid and see what it connects to. Also check that it is able to move at all and especially if the ignition is turned on and the motor is cold.

enfish · Mar 6, 2024

If the OP is pulling out the choke on the front of the cowling, that's 100% mechanical, and the butterflies sticking closed, but easily pushed back open by hand, is likely just a function of them being gummed up a little bit, or there is a spring or something broken. I can't remember exactly how they work. I'm not sure if the linkage is connected to the butterflies or they just push the butterflies and they are spring loaded to flip back. On my motor, which is 3 years older, so it may not apply, I have 2 chokes... the mechanical one on the cowling and an electric one at the helm. On cold starts, I always used the mechanical one. On cool/lukewarm/warm starts, I use the electric one. If I try to use the electric one on a cold start, my motor does what the OP describes it will fire for a second or two, then stall out and won't start until I let it sit for a few minutes.

seasick · Mar 6, 2024

enfish said:
If the OP is pulling out the choke on the front of the cowling, that's 100% mechanical, and the butterflies sticking closed, but easily pushed back open by hand, is likely just a function of them being gummed up a little bit, or there is a spring or something broken. I can't remember exactly how they work. I'm not sure if the linkage is connected to the butterflies or they just push the butterflies and they are spring loaded to flip back. On my motor, which is 3 years older, so it may not apply, I have 2 chokes... the mechanical one on the cowling and an electric one at the helm. On cold starts, I always used the mechanical one. On cool/lukewarm/warm starts, I use the electric one. If I try to use the electric one on a cold start, my motor does what the OP describes it will fire for a second or two, then stall out and won't start until I let it sit for a few minutes.

That's interesting; local mechanical choke and electric remote activated.
Hve you looked at the solenoid on the motor to see if it activates when you use the helm switch?

enfish · Mar 6, 2024

seasick said:
That's interesting; local mechanical choke and electric remote activated.
Hve you looked at the solenoid on the motor to see if it activates when you use the helm switch?

I've never looked, but I can hear the solenoid click when i flip the momentary toggle switch. It's always been that way since I become owner of the motor 25 years ago when it was 4 years old.... the electric choke has never been good at being a cold start choke. It definitely works since it starts easier and the motor will bog down when warm if I don't release the toggle switch soon enough after it fires up. There's a bit of a timing art to it... key on, choke toggle activated, key to start, motor fires up, hold choke toggle on for a beat or two after motor is running and release. I hold the choke on probably a second or less after it's running, but I know when to release based on the sound of the motor.

The cold start mechanical choke is easier in that it's less artistic and more brute force, but requires a lot more movement... Choke closed, throttle forward some amount, primer bulb pumped, start motor, run back to motor to open choke before motor completely bogs down, race back to the helm to pull throttle back before it over-revs, keep it at high idle (1200-1500 RPM) for a minute or two before backing off the throttle to neutral. That method starts the motor within 3 or 4 seconds of the first key turn every time, even if it's been sitting for 6 months.

Yamaha 175 2stroke- Hard to start.

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