replace Mercarb on 4.3 with Rochester?

[13crazyhorse]

I have had continued problems with the original Mercarb 2 bbl on my 2002 4.3. I see a refurbished Rochester replacement on ebay for this application. Has anybody gone this route? I see it says minor fuel line modifications may be needed. Thanks for any help you can offer on this.

 

[Scott06]

I have had continued problems with the original Mercarb 2 bbl on my 2002 4.3. I see a refurbished Rochester replacement on ebay for this application. Has anybody gone this route? I see it says minor fuel line modifications may be needed. Thanks for any help you can offer on this.

Depending on where the fuelinlet on the mercarb is and where it is on teh rochester you may have to bend or make a new fuel line to meet up on the adjacent side of the carb. The two carbs shar a common lineage as merc started with the mercarb after GM/Rochester stopped making carbs in the late 80's or 9early 90's, so I would think it is relatively bolt up.

What are the continued issues you have with the mercarb? Just want to make sure it is not something else before you swap carbs as the mercarb generally works ok when properly cared for and set up

 

[13crazyhorse]

Depending on where the fuelinlet on the mercarb is and where it is on teh rochester you may have to bend or make a new fuel line to meet up on the adjacent side of the carb. The two carbs shar a common lineage as merc started with the mercarb after GM/Rochester stopped making carbs in the late 80's or 9early 90's, so I would think it is relatively bolt up.

What are the continued issues you have with the mercarb? Just want to make sure it is not something else before you swap carbs as the mercarb generally works ok when properly cared for and set up

I bought a rebuilt last year for 300 and it worked fine until this year then I had issues. Took it to a "carb guy" and he said the float was hanging up on the gasket. Worked fine for a few more months now won't start after running and sitting for a couple hours. I messed with it myself but now have gas pouring out of it so would just like to bolt on something that will work and move on very frustrated. I read these mercarbs can be troublesome not sure of their history.

 

[Rick Stephens]

The word 'refurbished' will always give me pause.

 

[Scott06]

I bought a rebuilt last year for 300 and it worked fine until this year then I had issues. Took it to a "carb guy" and he said the float was hanging up on the gasket. Worked fine for a few more months now won't start after running and sitting for a couple hours. I messed with it myself but now have gas pouring out of it so would just like to bolt on something that will work and move on very frustrated. I read these mercarbs can be troublesome not sure of their history.

gas pouring out could be needle and seat /damaged float, or you have too high fuel pressure or if mechanical fuel pump has a ruptured diaphragm

 

[13crazyhorse]

gas pouring out could be needle and seat /damaged float, or you have too high fuel pressure or if mechanical fuel pump has a ruptured diaphragm

I've checked things inside and cant find anything that's obvious anyway. I just wondered if anybody went the Rochester route. I'm tired of putting money in this mercarb just wanted to go a different route. I understand the "refurbished" hesitancy but I priced a new Mercarb and am not paying $903.

 

[Scott06]

I've checked things inside and cant find anything that's obvious anyway. I just wondered if anybody went the Rochester route. I'm tired of putting money in this mercarb just wanted to go a different route. I understand the "refurbished" hesitancy but I priced a new Mercarb and am not paying $903.

We wouldnt pay $900 either. Hesitancy others expressed is abut who is rebuilding it and what parts are being used.

Not trying to make this more complicated but would hate to see you have the same issue with another carb. Where exactly is fuel coming out of it? If you haven't measure your fuel pressure I would do that as you can buy another rebuilt carb but if your fuel pressure is excessive (more than 6 psi) you will have the same issue with a new carb.

 

[Lou C]

I'm agreeing with Rick, with a re-furburbished carb you might get good, might get bad. Even brand new, might be trouble, I had that exact experience, thinking my old Quadrajet was too old to rebuild, I tried a new Holley, had a lot of trouble with it, wound up pulling the Quadrajet out of the garage, carefully cleaning it, re-assembling with new gaskets & accel pump and it ran as well as it ever did, and 100% better than the Holley I wasted over $500 on! I took that Holley all the way apart and eventually found out what the factory defect was, something simple, I didn't look far enough when I was trying to make it work, so now I have a spare 4bbl carb sitting on a shelf in my crowded garage!
I'd go back at the Merc carb and really take your time, with carbs 95% of your success is in cleaning, replacing questionable parts and taking the time to get the adjustments correct. Keep in mind for any Rochester carbs, there have not been any "NEW" ones since 1990. I am lucky I have an original unmolested Quadrajet that was original to this boat.
If you absolutely want new the only other option, is a Holley 2bbl but that will require adaptation to make it work. Much cheaper than what Merc charges though. I think they take the parts that other suppliers make for them and double the price, Volvo does the same thing.

 

[13crazyhorse]

I'm agreeing with Rick, with a re-furburbished carb you might get good, might get bad. Even brand new, might be trouble, I had that exact experience, thinking my old Quadrajet was too old to rebuild, I tried a new Holley, had a lot of trouble with it, wound up pulling the Quadrajet out of the garage, carefully cleaning it, re-assembling with new gaskets & accel pump and it ran as well as it ever did, and 100% better than the Holley I wasted over $500 on! I took that Holley all the way apart and eventually found out what the factory defect was, something simple, I didn't look far enough when I was trying to make it work, so now I have a spare 4bbl carb sitting on a shelf in my crowded garage!
I'd go back at the Merc carb and really take your time, with carbs 95% of your success is in cleaning, replacing questionable parts and taking the time to get the adjustments correct. Keep in mind for any Rochester carbs, there have not been any "NEW" ones since 1990. I am lucky I have an original unmolested Quadrajet that was original to this boat.
If you absolutely want new the only other option, is a Holley 2bbl but that will require adaptation to make it work. Much cheaper than what Merc charges though. I think they take the parts that other suppliers make for them and double the price, Volvo does the same thing.

I appreciate the inputs. I'm getting the same results with two different electric fuel pumps so the pressure is not the issue. I'm going to try the Rochester later this week and will post my results. Thanks again for the input.

 

[Lou C]

that old Rochester 2bbl is a pretty simple carb. We had one on our '72 Chevrolet my parents bought new. Back then I remember my motor head friends saying that Quadrajets were hard to rebuild, too tricky for a beginner but I did not find that to be the case, all these years later. I had mine apart and back running in about 3 hrs.

 

[Rick Stephens]

I appreciate the inputs. I'm getting the same results with two different electric fuel pumps so the pressure is not the issue. I'm going to try the Rochester later this week and will post my results. Thanks again for the input.

Unless you measure pressure, you don't know if something is effecting fuel pressure - pump, lines, vents, valves, pump(s).