Tohatsu 3.5 hp 4 stroke OR 157...

[w2much]

Finally realized I needed a manual for the two of these motors I have. Should be here by midweek. I have a manual for 4/5/6 HP 4 strokes starting 1999. I dont want to use it as the properone will be here soon enough.I would like to get my ducks in line so that I can at least start an evaluation and parts list. This post may go on as needed or not. Right now simply the old compression question. Older manual says 42 pounds for the 4/5/6 models. What should the compression be on my 3.5's.

 

[pvanv]

Compression won't tell you much because of the decompressor feature. Year is irrelevant; exact model is critical.

 

[w2much]

Here we go for each of the two. I believe they are identical models:
Tohatsu
MFS3.5A 3BR
Ser# 016507XK
and the
Mercury
0R197503
June 2007
F3.5 M
And what is this decompression thing anyway. Tracking says Mondday delivery for the manual. Thanks for your help

 

[pvanv]

[h=5]SERVICE MANUAL - TOHATSU - 2/2.5/3.5A 4STR[/h]

Description

Covers 2A, 2.5A & 3.5A 4-stroke models

Part #: 003-21058-0
List Price (MSRP): $41.67

There is a weight on the cam that prevents fully seating the exhaust valve below maybe 1000 RPM.

 

[w2much]

Thank you. Manual tracking says tomorrow. Does the Mercury have the same feature?

 

[pvanv]

Yep. The Merc has a Tohatsu power head.

 

[w2much]

Will the Tohatsu and Mercury 3.5 s carburetors interchange ? I have not seen the Tohatsu carb listed as a whole carb, only parts. I will need one is the 3BR 03200 0 correct for this Tohatsu and Mercury ?

 

[pvanv]

3gv032000m

carburetor assy, f3.5b

$162.60

 

[w2much]

Thank you Paul. Where did you find it if you can say ? I am not familiar with the decompression sytem for the motor. What should I expect from a compression test ? Is it done as usual or do the valves need to be unadjusted in order to get a true reading. I did get the manual today but barely glanced through due to time constraints.

 

[pvanv]

I just looked it up in the Tohatsu parts catalog. The original 3.5A carb has been superceeded by the B version for EPA regulations. As a Certified Tohatsu technician, I have been to school in Dallas a few times, so I know these motors well. Decompression figures for the motor are in the Factory service manual, but that info is of little value, unless you are planning an overhaul of the motor; also the decompression-on figure will be quite low anyway, so the number is is of little, if any, value.

 

[w2much]

That explains the carburetor issue. Why it was not listed on my parts list. Just need the carb from the newer model. Makes sense. Seems like these motors all have the same issue, 60 lbs compression . Weird to me. The carbs were wasted on them. I dont know their history. I am going to purchase at lease one new carb or find a good used one and try it out to see what happens. I could just put them in the junk section but they look great and then I will have learned nothing. I will tear down at least one of them just for the need to know.
By the way I dont know if you have all of this info in your head or are taking time and looking some of it up but I appreciate your replies. Thank you again