Initial Jetting on Yamaha 50hp 4 stroke outboards

[jcr6502]

Im mostly through the carbs and while the pilots are all 39's. The main Jets are
126/124/114 for carbs 2/3 and 4...[Top-down] havent opened 1 yet but will update when I clean that one. Did they arrive from the factory with a certain compliment. All different? Did the middle cylinders run richer due to heat considerations as opposed to the outer cylinders? None of the factory jetting info is in the manual.

 

[99yam40]

look up the parts to see what Yamaha says should be in there.
I have no idea what F50 you are talking about without a model #

 

[boscoe99]

look up the parts to see what Yamaha says should be in there.
I have no idea what F50 you are talking about without a model #

Folks guard the identity of their motors more closely than does the national security agency with respect to top secret documents.

 

[boscoe99]

look up the parts to see what Yamaha says should be in there.
I have no idea what F50 you are talking about without a model #

Are you saying "after all else fails follow the directions"?

 

[boscoe99]

Im mostly through the carbs and while the pilots are all 39's. The main Jets are
126/124/114 for carbs 2/3 and 4...[Top-down] havent opened 1 yet but will update when I clean that one. Did they arrive from the factory with a certain compliment. All different? Did the middle cylinders run richer due to heat considerations as opposed to the outer cylinders? None of the factory jetting info is in the manual.

Just for the sake of discussions, and at the risk of me making an ass of myself, I will assume that you have a 2003 F50TLRB.

The F50TLRB uses four different part number carburetors. Each using a different sized main jet. Each using a different float bowl. Hope you kept tabs on the latter as they are usually not separately identified.

From what I see the number 3 carburetor uses a different sized jet than what you mention above.

The parts catalog gives you the location for each carburetor, each main jet and each float bowl. Not the service manual.

The service manual does not state the idle mixture screw baseline settings. They are EPA protected. The procedure is to count the number of turns inward for each mixture screw. Make a note of it in your service manual. Upon cleaning and reassembly of the carburetors, reset the idle mixture screws to the number of turns that you wrote down in your service manual.

 

[jcr6502]

Thank you for the prompt reply, it was most helpful

Apologies, T50TLRB


Having completed and checked carb 1 the results are

1 - 116
2 - 126
3 - 124
4 - 114

Based on the info you had provided it looks like the PO swapped jets 1 and 3. All pilot screws were 2 1/8 except for carb 1 which was 2.0.

Thanks for the information. I found it further interesting int he manual that the measurments for the Prime start [COLD] are not asked for nor is the resistance between leads. In consideration that one is 19.9ohm and the other is 31.3ohms this may have zero impact on the performance but would have been a good baseline.

Incidentally the 31.3 carb 3 is cold showing 20mm and the 19.9 is cold at 22mm. carb 3 after 5min at 12v is 25mm and I havent yet tested carb 1...

 

[boscoe99]

The only thing that needs to be tested with respect to the prime start device is that it moves outward when heated by the application of 12 volts to the two leads.

 

[boscoe99]

The base settings for the idle mixture screws are as follows:

Cylinders one, two and three = 2.25 turns outward +/- .5 turn.

Cylinder four = 2.5 turns outward +/- .5 turn.

 

[jcr6502]

The valve on carb

The base settings for the idle mixture screws are as follows:

Cylinders one, two and three = 2.25 turns outward +/- .5 turn.

Cylinder four = 2.5 turns outward +/- .5 turn.

thank you, as it stands the valve measured 27mm after 5 minutes, so according to the manual its within spec, 2mm longer than carb 3. Thank you for the info it was most helpful.

 

[jcr6502]

As a side note, Ive noted upon assembly that the carb O-ring annotation 17 in the diagram for the manifold, 93210-35M-86-00 is too small to effectively seat on the carb for reassembly. I cant be the first person to notice this. A typo in the parts catalogue?