49 TD20 Low-speed needle affecting high speed performance?

[John Gragg]

#282513

<!–more–>https://youtu.be/7MHBXdkA5-s?si=CoEl6KUraY7oGHDN

Newly overhauled motor and carb. New rings. Everything cleaned within an inch of its life. 2nd time running, 1st time water leak. That is resolved.  Here is the issue:

The service guide will tell you that the low-speed needle does not affect the high-speed performance. Not sure why the low-speed needle actually does affect the high-speed?

 

1.) I can’t get it to idle down to even the middle of the ‘Start’ on the mag plate indicator. It just dies.

2.) Will not start at the ‘Start’ position.

3.) Have to start it (warm or cold) about 3 or 4 clicks to the right of “Start”.

4.) I have a low-speed sneeze condition that I can’t adjust out of the carb.

5.) High-speed adjustment does almost nothing at high-speed. (really nothing, I can’t perceive any change once I open the HS needle enough to run the motor)

Take a look at the video please? Notice that the low speed adjustment raises the high speed performance.

Ideas?

I’m going to check points gaps tomorrow (cleaned and polished already) and take a look at the LS packings. Maybe swap out for some orings?

Help!

John Gragg
RIverside, CA

Just starting in the hobby, please be patient.

49 Sea King 5hp GG9014A
49 Johnson TD20
48 Johnson TD20
54 Johnson QD15
55 Johnson CD12

[steveh]

#282516

Hi John!

Given the low speed sneeze, along with other symptoms, it seems to me you have a fuel delivery issue. Is the fuel filter in the gas tank clogged? New leather o-rings? Check valve OK? Fuel lines clear?

On my motors, I have seen the low-speed needle have some effect, but it is usually minimal.

I am sure others will weigh in…

Steve.

[aquasonic]

#282517

Maybe focus on the high-speed side. As you mentioned, the high speed adjustment doesn’t seem to make any difference in the RPM’s. When working properly, the high speed adjustment will range from overly rich to overly lean and can shut the motor down.

Regarding the low speed packings, they are very durable and most of the time can be saved. The low speed system has a check valve that must be working properly to achieve an idle. Also, loosening the packing nut, removing the LS needle, and pumping the primer can be helpful in cleaning the LS system.

The Pochefamily website is very useful. Basic Carburetor Servicing Johnson H and T Series (pochefamily.org)

P.S. It’s good to see steveh on the forum!

[crosbyman]

#282519

John,

there is a good description also in the Johnson bible -red book  on adjusting TD TN carbs.   pages 87 and up

 

 

Joining AOMCI has priviledges 🙂

[lloyd]

#282586

Two things to check.  First of all what is the compression after installing new rings?   Should be 70-77 psi to idle down properly.

Second of all be sure to clean and test the one way fuel valve that carries fuel to the low speed orifice/needle valve.  231-929-7479

[John Gragg]

#282589

lloyd wrote:

Two things to check.  First of all what is the compression after installing new rings?   Should be 70-77 psi to idle down properly.

Second of all be sure to clean and test the one way fuel valve that carries fuel to the low speed orifice/needle valve.  231-929-7479

I haven’t checked compression yet. I was waiting for the rings to seat in. I will check tomorrow.

Check valve is good to go. There was a ton of junk in the gas tank that I thought I had cleaned out. I had to take the carb apart and clean again.  Tank has been acid washed, it’s immaculate now. I’m going to seal the tank with Por-15 tank sealer,  then try again.

Thanks

Best Regards

John Gragg
RIverside, CA

Just starting in the hobby, please be patient.

49 Sea King 5hp GG9014A
49 Johnson TD20
48 Johnson TD20
54 Johnson QD15
55 Johnson CD12