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Yamaha No Cold Start

Old 07-15-2018, 11:03 AM
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Default Yamaha No Cold Start

I have a 2001 90 Yamaha 2 stroke that is almost impossible to start when cold but starts with just a key bump when warm. I have found a red manual switch under the cowling that temporarily fixes this problem and probably can tell some of you what needs to be replaced or repaired. When the red switch is in the normal position the motor will almost run the battery down before it cranks and stays running. Once warmed up it cranks with a key bump the rest of the day. If I move the switch to the open position when cold it also starts with a key bump but soon begins to run rough. At that time, I can move the switch back to the normal position and the motor is good to go. I surmise that this may be a choke issue but as you can tell by the fact that I'm even asking this question, I am not mechanically inclined. I can replace most parts though.
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Old 07-15-2018, 11:19 AM
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That engine is going to have a electronically controlled needle valve attached to that piece you are fiddling with. The ECU makes that valve open when the engine is cold allowing more fuel in, and then as the engine warms up the ECU closes the needle valve and stops the extra fuel.

Your needle valve may be gunked up and you can take it apart and clean it, it may be bad, the temp sensor may be bad, or the ECU may have an issue.
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Old 07-15-2018, 11:37 AM
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Originally Posted by midcap View Post
That engine is going to have a electronically controlled needle valve attached to that piece you are fiddling with. The ECU makes that valve open when the engine is cold allowing more fuel in, and then as the engine warms up the ECU closes the needle valve and stops the extra fuel.

Your needle valve may be gunked up and you can take it apart and clean it, it may be bad, the temp sensor may be bad, or the ECU may have an issue.
Midcap may be correct about the needle valve. I was told by Yamaha tech that the sensor and ECU almost never go bad.
If you check my threads, you will find at least two attempts to find an answer to this problem. My motor is a 70hp and is set up exactly like yours. I have literally not left the dock without a spray can of carb and choke cleaner. I give the smallest shot into the air box and it starts fine.

Why the hell they got rid of the choke just makes me crazy. I own 4 Yamaha motors and will probably not buy another just over this issue.
OK rant over.

This may sound totally stupid, so forgive me in advance.
Remember when some ignition switches had a function where you pushed in on the key and it activated the choke?

The last time I started my 70 that has your issue, I pushed in on the key inadvertently while starting and the damn thing started right up. The weather was so awful I did not get to use the boat that weekend and have not been back to test.

I will report back, but nothing in my owners manual has any indication that there is a "choke". Sorry, more vent than help, but I feel your pain.
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Old 07-15-2018, 12:20 PM
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Originally Posted by muskrattown View Post
Midcap may be correct about the needle valve. I was told by Yamaha tech that the sensor and ECU almost never go bad.
If you check my threads, you will find at least two attempts to find an answer to this problem. My motor is a 70hp and is set up exactly like yours. I have literally not left the dock without a spray can of carb and choke cleaner. I give the smallest shot into the air box and it starts fine.

Why the hell they got rid of the choke just makes me crazy. I own 4 Yamaha motors and will probably not buy another just over this issue.
OK rant over.

This may sound totally stupid, so forgive me in advance.
Remember when some ignition switches had a function where you pushed in on the key and it activated the choke?

The last time I started my 70 that has your issue, I pushed in on the key inadvertently while starting and the damn thing started right up. The weather was so awful I did not get to use the boat that weekend and have not been back to test.

I will report back, but nothing in my owners manual has any indication that there is a "choke". Sorry, more vent than help, but I feel your pain.
You could always join the 21'st century and buy a 4 stroke. That way you won't have to carry ether on board any longer.
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Old 07-15-2018, 01:10 PM
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Originally Posted by muskrattown View Post
Midcap may be correct about the needle valve. I was told by Yamaha tech that the sensor and ECU almost never go bad.
If you check my threads, you will find at least two attempts to find an answer to this problem. My motor is a 70hp and is set up exactly like yours. I have literally not left the dock without a spray can of carb and choke cleaner. I give the smallest shot into the air box and it starts fine.

Why the hell they got rid of the choke just makes me crazy. I own 4 Yamaha motors and will probably not buy another just over this issue.
OK rant over.

This may sound totally stupid, so forgive me in advance.
Remember when some ignition switches had a function where you pushed in on the key and it activated the choke?

The last time I started my 70 that has your issue, I pushed in on the key inadvertently while starting and the damn thing started right up. The weather was so awful I did not get to use the boat that weekend and have not been back to test.

I will report back, but nothing in my owners manual has any indication that there is a "choke". Sorry, more vent than help, but I feel your pain.
As far as I know mine has the push to choke but it may not be working properly. Does anyone have a document available that explains how to clean the needle valve or a part # to replace it?
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Old 07-15-2018, 01:27 PM
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This video might help ya.

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Old 07-15-2018, 02:25 PM
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Originally Posted by twitch View Post
This video might help ya.

https://youtu.be/x35uqVMu2r0

Great video! Shouldn't I be able to pull the cover over the diaphragm and the plunger without pulling the carb and check them independently as the video describes? My motor is a premix 3 cylinder but the plunger and control look identical.
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Old 07-15-2018, 03:12 PM
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Originally Posted by BugDoc View Post
Great video! Shouldn't I be able to pull the cover over the diaphragm and the plunger without pulling the carb and check them independently as the video describes? My motor is a premix 3 cylinder but the plunger and control look identical.
if you can get to the retaining screws I believe so.
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Old 07-16-2018, 04:47 AM
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If I understand this system correctly, on a cold motor the plunger is in a withdrawn position which should allow extra fuel to flow to the carb. As the motor warms up the plunger extends to shut off the extra flow. Rotating the red lever allows the same extra flow. If this flow increases with the lever but is absent in a cold start, then the lever must open a different direction of flow than the plunger does. That must mean this particular problem has to be either blockage at the base of the plunger, a faulty diaphragm, or faulty reed valves. Am I missing anything in my analysis?
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Old 07-16-2018, 06:06 AM
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Originally Posted by twitch View Post
This video might help ya.

https://youtu.be/x35uqVMu2r0
He is very good, has an excellent video on cleaning/rebuilding carbs also. I had forgotten watching this particular one.

Unfortunately the prime start did not fix the problem. The plunger part is what the Yamaha tech said "almost never fails".
Just give me a f-ing choke.

I am no mechanic, but after seeing all that goes into this over complicated enrichment system, I bet the diaphram is too weak to do it's intended job. My motor developed this problem after only one season of use. I bought the motor new from a large dealer with a huge service department.

When i took it in after experiencing this issue the service manager said: " Lots of customers are just having their carbs rebuilt after each season to avoid this problem".

The reason I purchased another 70hp 2-stroke Yamaha was because the 1985 that I used for 30 years was totally dependable and required plugs and lower end fluid change annually.

Last edited by muskrattown; 07-16-2018 at 06:14 AM.
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Old 07-16-2018, 06:37 AM
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Originally Posted by muskrattown View Post
He is very good, has an excellent video on cleaning/rebuilding carbs also. I had forgotten watching this particular one.

Unfortunately the prime start did not fix the problem. The plunger part is what the Yamaha tech said "almost never fails".
Just give me a f-ing choke.

I am no mechanic, but after seeing all that goes into this over complicated enrichment system, I bet the diaphram is too weak to do it's intended job. My motor developed this problem after only one season of use. I bought the motor new from a large dealer with a huge service department.

When i took it in after experiencing this issue the service manager said: " Lots of customers are just having their carbs rebuilt after each season to avoid this problem".

The reason I purchased another 70hp 2-stroke Yamaha was because the 1985 that I used for 30 years was totally dependable and required plugs and lower end fluid change annually.
It very well may be the diaphragms. They are cheap and it's easy to work on....
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Old 07-22-2018, 05:21 PM
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Back at my boat today. This is all rant and no help. Forgive me.

Did some work on the house and thought the dogs would like a ride. Knew when I started the motor it was not right and strong. Sputtered to a complete stop after running strong to the mouth of the creek which is a mile or so.
No it is not fuel related. I will for the fourth time have to remove the f-n carbs and clean ever jet and passage. Then my motor might make it to November running right.

I would buy back the 1985 Yamaha 70 hp 2-stroke I sold when i bought this POS for $2000 right now. I sold for $500.

I have never seen or read a solution to this problem and I have tried for years to find one.
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Old 07-22-2018, 06:37 PM
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There is a solution. Install a fuel shut off, run the fuel out of the bowls and then drain the remaining fuel out of the bowls. I have a 150 2 stroke that I have to do that with or it runs like shit after a 2 week sit with fuel in the carbs. It's not a perfect solution, but beats the hell out of cleaning carbs.
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Old 07-23-2018, 11:16 AM
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Originally Posted by twitch View Post
There is a solution. Install a fuel shut off, run the fuel out of the bowls and then drain the remaining fuel out of the bowls. I have a 150 2 stroke that I have to do that with or it runs like shit after a 2 week sit with fuel in the carbs. It's not a perfect solution, but beats the hell out of cleaning carbs.
The bowl drain on my bottom carb is almost impossible to access. I have a source for no eth fuel and try to have that in the tank and carbs when the boat is not seeing regular use. I had today off so I pulled the boat and just re- cleaned all three carbs. I think only the bottom one was causing the problem because when I "choked" each one seperately under load the other two knocked down the rpms and the lower one did not.

Found the usual white powder debris in the lower bowls and no other real evidence of blockage. Ran bait rigging wire thru all jets and cleaned with carb cleaner. Re-assembled and it fires right up.

I did take the prime start apart just like the video. I am convinced that is not a part that will go bad, I think it is just poor design and these new carbs have too many tiny orifices that fuel must pass thru for all to be perfect.

On a side note, you can access the prime start and diaphram by removing the air box and the oil tank. Be very careful because there is a rubber gasket that seals the top over the diaphram and it is a MF to keep in place as you put the top back on.

I may just drill a hole in my cowl, 5200 a long screwdriver in a sleeve, and be able to turn the red screw like a f'ing choke. lol.
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Old 07-23-2018, 12:06 PM
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Originally Posted by muskrattown View Post
. I have a source for no eth fuel and try to have that in the tank and carbs when the boat is not seeing regular use..
It's the water that the alcohol is holding in suspension that makes it's way to the bottom carb when it settles out inside the fuel lines that is making the white powder(corrosion). Get off the eth and your problems will be reduced considerably.
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Old 07-23-2018, 02:24 PM
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Originally Posted by twitch View Post
It's the water that the alcohol is holding in suspension that makes it's way to the bottom carb when it settles out inside the fuel lines that is making the white powder(corrosion). Get off the eth and your problems will be reduced considerably.
Ironic that the only carb that is difficult to drain is the lowest one.

I agree totally about the eth. Maybe all my bitching would be the same with the old motor. It ran on mostly real gas. Talk about a motor you could count on!
I used to drift fish an inlet with lots of rocks and current ect. I could wait until the motor was needed and touch the key. Lots of guys never turned theirs off as the results could be bad.
Now I am with them, and I hate it.

Thanks for the input by the way.
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