Throttle problems: Engine only starts in slow (low) throttle

DAMatson

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  • / Throttle problems: Engine only starts in slow (low) throttle
Good evening all!

Mower has been working great the last few months, once I'm able to actually get it started. The starting problem I had recently appears to be fixed.

My newest problem is that the engine won't successfully turn-over on its own now. I have found that if I prime the carb with a few drops of fuel, it'll start up just fine, then sputters out. This makes me think that it is a fuel supply line issue. I've verified that the fuel itself is brand new, and that the hose and filter going to the carburetor were replaced in the last three months. This leaves the carberetor itself as far as I can tell. I've used a bit of carb-cleaner, with no change in symptoms.

I've also observed that the engine WILL start (again if primed) and NOT sputter-out, but only if I start with the throttle in it's lowest setting. The choke setting doesn't appear to impact anything, butI've confirmed that the choke linkage appears to be good, as it successfully moves the choke fin in the carburetor. Lastly, if I start the engine in the lowest Thottle setting with Carb primed, and it's working fine at idle speed for a minute, then attempt to move the throttle up to a faster setting, again the motor will sputter until it dies.

So, some kind of throttle-advance problem I presume?

ENGINE INFO: Tecumseh 15.5 HP Engine
Engine Model: OHV155 204509E
Engine Family: WTPSX.4902AA
Engine Displacement: 490

Any thoughts?
 

cpurvis

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  • / Throttle problems: Engine only starts in slow (low) throttle
Sounds like your low-speed circuit in the carb is dirty and needs to be cleaned. Engine is getting too much air, not enough fuel to accelerate.
 

DAMatson

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  • / Throttle problems: Engine only starts in slow (low) throttle
Thank you for the quick response cpurvis!

I too was considering taking the carb apart, but was just wondering how I might go about that. I'll keep an eye out for the low-speed circuit part and pay close attention to cleaning it.
 

DAMatson

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  • / Throttle problems: Engine only starts in slow (low) throttle
Boobala, thank you for confirming cpurvis' theory. Agreement on a recommended strategy always helps bouy one's resolve.

I especially appreciate the link for the carb tear-down article. Exceedingly helpful!!

-David
 

DAMatson

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  • / Throttle problems: Engine only starts in slow (low) throttle
Circling back to this conversation. I've not been able to resolve this carb issue, and I'm using the Series 7 Carb as shown here:

http://outdoorpowerinfo.com/repairs/tecumseh_series7_carb.asp

(Thank you for the link Boobala!)

While I've left the Carb itself still mounted, I have removed the fuel bowl from the main body and double-checked the following:

  • Seals are all in good condition.
  • No signs of holes or wear/tear.
  • Cleaned-out the fuel bowl, no water or other foreign contaminants present
  • I have not touched the welch plug yet.
  • Confirmed that float is intact and operating needle properly.
  • Emulsion Tube is clean, and holes shown on slide #10 are open & clean.

My problem is that the carb isn't delivering the initial burst of fuel to start the engine, thus requiring "priming" in order to start properly. ENGINE WORKS FINE ONCE IT IS STARTED, so not entirely sure where I need to focus going forward.

I'm getting confused at slide #11 & #12, but cpurvis mentioned the low-speed circuit, but not sure which holes to investigate further that are specific to the low-speed circuit. Slide #12 with blue highlight appears to reference this, but I'm unsure where it originates? The pink highlighted in slides #5 & #6?

Lastly, what is the best way to clear this low-speed circuit? Thin wire as shown in slide #6 entering pink highlighted port? Or air from compressor? Carb cleaner?

Love to hear your thoughts on this!

-David
 

cpurvis

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  • / Throttle problems: Engine only starts in slow (low) throttle
There is another aspect.

Maybe the condition of the engine is such that it doesn't develop low enough manifold pressure at starting rpm to pull fuel through the low speed circuit of the carburetor. That's one of the things a choke butterfly does. The primer bulb takes the place of the choke, so I guess one shouldn't be afraid to use it.

Lastly, what is the best way to clear this low-speed circuit? Thin wire as shown in slide #6 entering pink highlighted port? Or air from compressor? Carb cleaner?
All. Use whichever method(s) works best on each passage. Usually carb cleaner first (soak) then compressed air, then check each passage with thin wire.
 

DAMatson

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  • / Throttle problems: Engine only starts in slow (low) throttle
Thank you cpurvis!

I have the non-solenoid based drain plug as shown in slide #6. I'm still confused about the actual path of the low speed circuit that you were referring to previously.

I think it starts at the red highlighted port in that same slide, which leads to the pink highlighted port, which in turn leads-up to the "idle port" shown later in slide #12 highlighted in blue?

Can you confirm these ports mentioned in the URL what constitutes as the path of the low speed circuit?

Thank you for your time and assistance, it is greatly appreciated!

-David
 

cpurvis

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  • / Throttle problems: Engine only starts in slow (low) throttle
Yes, slide 12.

Clean them all.
 

DAMatson

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  • / Throttle problems: Engine only starts in slow (low) throttle
Good afternoon All!

So, I've soaked carb and parts in cleaner overnight, rebuilt the carb, and now the problem has gotten worse: I still cannot start the mower without using a little bit of primer gas in the carb, but now I can't even keep the engine going after starting it.


I've noticed that when I pulled back on the Lever highlighted in the first picture below, I *AM* able to start the motor, although only for a second or two.
Throttle Control Bracket-1.jpg


This in turn moves the linkage going off to the left on the top picture to what I presume is called the Throttle plate control, as shown in the second pic below:
Tecumseh Carb-1.jpg

I have a very high degree of certainty that I've rebuilt the carb correctly. I am now considering that the control linkage may be set incorrectly.

Any further thoughts on that topic?



Having said that, I'm also considering that the carb itself may have some other issues I'm not aware of, so I'm also really close to buying this carb replacement kit that also contains a new carb (with solenoid).

https://www.amazon.com/Carburetor-F...sr=8-1-fkmr0&keywords=tecumseh+OHV155+204509E

-David
 
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