Switching from a MerCarb to a Rochester (1985 Mercruiser 140)

[ArkansasTim]

Hey guys,
I have a 1985 Mercruiser 140. I've been having issues with the carb for awhile now. It's a MerCarb 1389-8490 and I just haven't been able to set the mixture right and I'm constantly having issues with acceleration. I've fully rebuilt it and I still can't get it. I took it apart again to make sure I put it all back together again and the float was accurate and it all checked out. Also, it seems like the previous owner used some sort of lock tite on the screws in the throttle plates so I cannot get those screws out without damaging them because they are brass, so I could not take apart the bottom plate.

Anyways, I've found a great deal on Craigslist for a Rochester carb off another Mercruiser 140. The part numbers are 1351-4293A1 and 7040084. I was wondering if I will be able to switch to this carb or will there be issues with the bolts aligning? If I have to get an adapter plate, could you please show me which adapter plate I will need to get?

I've worked with a couple Rochester carbs before and I've liked them and found them easy to work on. I know the MerCarb I have is very similar, but rebuild kits for the Rochester are much cheaper than the MerCarb. Thank you for your help!

 

[old islander]

Re: Switching from a MerCarb to a Rochester (1985 Mercruiser 140)

I don't think the intake pad for the Mercarb will line up with the Rochester. And there is no adapter that I know of. Some of the experts will be along shortly for verification.

 

[achris]

Re: Switching from a MerCarb to a Rochester (1985 Mercruiser 140)

Merc call out a different manifold depending on carb (Mercarb or Rochester) for the 2 piece exhaust elbow, but not for the one piece. What is your engine serial number and do you have the 1 or 2 piece elbow?

Chris....

 

[fishrdan]

Re: Switching from a MerCarb to a Rochester (1985 Mercruiser 140)

I'm pretty sure a Mercarb for a 3.0L has a wider bolt pattern than a Rochester, bigger butterfly valves too.

Measure it and see.

Couple years ago, I bought a 3.0L Mercarb off Ebay for $10 (couldn't pass it up even if it didn't fit in place of my Rochester). Well, it wouldn't fit for the reasons mentioned above.

Also, it seems like the previous owner used some sort of lock tite on the screws in the throttle plates so I cannot get those screws out without damaging them because they are brass, so I could not take apart the bottom plate.

Don't mess with the screws holding the butterfly valves onto the throttle shaft. They usually stake the bottom of the screws to keep them from loosening and falling into the engine. There's no reason to take the butterfly valves off anyway, unless you're going to re-bush the throttle shaft, but I don't see any (many) of us having the equipment to do that type of work.