used V6 has replaced powerhead, need guidance on carbs

[sly_karma]

I bought a used V-6 150 recently to replace the failed original power on my old Lund fibreglass 19.5 ft runabout. It was cheap, it had good compression (115 psi +/- 2) and the tilt/trim worked. Once it was rigged on my boat, I found it difficult to start and wouldn't idle. Diagnosed a bad switch box and replaced both, checked and fixed the timing. Ran better but still not idling, so decided carb rebuild was needed. Engine serial # is G000308, which indicates 1994 year, ordered carb gasket kits accordingly. As I was rebuilding the carbs, I found the only gaskets that fit were the carb base to manifold and a few O-rings for jet access plugs. Turns out this engine has WH-35 carbs fitted, which I think were standard equipment on the late 80s V6s. Then I hunted around and found the engine block date: 08/88. Huh, looks like this one got a replacement powerhead and the original carbs came with it. Jets in place are .050 main, .060 off idle, .094 idle/vent.

When I search online for WH 35, I get a lot of references to 'Mercury V-135 hp', but looking up carb parts for 'V-150 hp' lists jets for WH-32, 35, 38, 40. I'm new to Merc so this is a bit confusing for me.

And so to my questions:

• are the WH-35 carbs intended for 135 hp?
• if yes, can they be re-jetted for more power?
• is the jetting I have currently correct for the WH-35?
• can someone direct me to an overview or cross reference chart of Merc carbs and engine HP ratings for this period?

Thanks in advance for all responses.

 

[ondarvr]

I can't answer most of your questions, but will answer one.

​You can't re-jet for more power, jetting is set for the requirements of the motor as it sits, if the jetting is correct, meaning the motor starts and runs like it should, then changing the jetting will make it run worse.

​These carbs may or may not be used on different HP motors, if they are then you can find out the correct jetting fairly easily, if not you're on your own when it comes to dialing it in.

Hopefully someone can supply you with the info needed to answer your other questions.

 

[Faztbullet]

are the WH-35 carbs intended for 135 hp?

Yes and a few 150's ..most 150's have WH-40 and 48's

if yes, can they be re-jetted for more power?

Technically no........but you can fudge sometimes....

is the jetting I have currently correct for the WH-35?

Yes.....

 

[sly_karma]

OK so I guess what I got is a 1988 or early 1989 model year 135 HP. Engine serial is 0C110740.

Side issue: there is oil injection pump but it is disabled. I can't see any vacuum line to the fuel pump, just fuel in and fuel out. There is a fitting marked 'out' that is capped off, and another marked 'in' that appears to be factory plugged. Took the pump off its mounts and there's no hose behind it. Am I dreaming or did the previous owner plug the fuel pump's vacuum line?

 

[sly_karma]

Fuel pump vacuum line was blanked off at the pump and at the crankcase. WTF? Anyway all fixed now and delivering premix gas.

 

[jimmbo]

Technically no........but you can fudge sometimes....

Yes.....

Since most engines are jetted on rich side for many reasons, leaning them a bit will yield a bit more power, right till it grenades itself. Not really a wise idea

 

[ondarvr]

My answer was based on people thinking that by changing the jets to those in the higher HP motor they can increase the HP to that level. On some motors you can make minor jetting tweaks to make it run smoother or slightly better, but you aren't going to get 20-50% more power like many people think.