New Carb Suggestions for 5.7 350 Mercruiser

[dipthenet]

Hey all,

In some of my previous posts, I mentioned that I had a Rochester Q-Jet. Seems like lots of negative feedback for those. I am open for some ideas for a new carb. Any Suggestions? Or what is everyone else running on there engines with success? Thanks in Advance

 

[Fishermark]

Re: New Carb Suggestions for 5.7 350 Mercruiser

Edlebrock 1409 Marine carb. Great right out of the box.


You can buy it several places, but here is a good spot to begin looking.

 

[John_S]

Re: New Carb Suggestions for 5.7 350 Mercruiser

First off, are you having problems with Q-jet that you want to change it? If so, what are they? Q-jets are good carbs, when adjusted right. If its worn out, and needs more than cleaning and kit, then time for new carb.

The Edelbrock 1409 is a simple carb to replace and tune. Depending on your current set-up, it may require a intake manifold chane or require a square bore to spreadbore adapter (not recommended), along with a fuel line change.

Holley sells a marine Q-jet replacement (about $50 more than 1409) which will not require a manifold change. Fuel line might be good too. Holley also makes some 600cfm marine carbs, but requires the same changes as Edelbrock.

 

[wca_tim]

Re: New Carb Suggestions for 5.7 350 Mercruiser

the edelbrocks are easy to set up but in addition to what don mentioned above, for drop on replacement of stock qjet, they're not always a straight drop on. also since they're square bore - primaries and secondaries the same size, compared wot the qjet which has smaller primaries, you may get better fuel economy with the qjet. qjets are great carbs if set up right and not worn out. imho

 

[captmello]

Re: New Carb Suggestions for 5.7 350 Mercruiser

I faced this decision in the spring. I had the stock Qjet. Wouldn't idle well, idle/air adjustment screws where froze up. I know it needed to be gone through.

I found a local mechanic to rebuild the qjet for $100, plus $40-$50 for kit and brass float. I bolted it on, set the idle speed and have not touched it all summer. Runs perfect. The mechanic knew what to look for to make sure it was worth rebuilding in the first place.

Saved $200 plus no adapter or new manifold.(Even though I have an edelbrock manifold already and wouldn't have needed)

I don't know what RPM you cruise at but my boat will plane out without the secondaries opening and i believe that helps in fuel efficiency. If your running 80% WOT all the time, probably doesn't make any difference.

If money was not a concern, I would have bought the new Edelbrock.

Let us know what you do and the improvements you find.

 

[dipthenet]

Re: New Carb Suggestions for 5.7 350 Mercruiser

As for problems with the Q-jet. None really, just what I have been reading regarding my tulliped valves. Hot detonation, and other stuff that the carb could have caused. The q-jet was new in August of 06. I guess the real issue is my lack of knowledge on the subject. Far as I could tell the carb seemed to function fine, idle was good and it seemed to operate fine. I have no problem staying with the Q-jet, it will save me money if I do. But if spending the money helps me in the long run than I will do it. Thanks again to all. This site is great.

 

[gadget73]

Re: New Carb Suggestions for 5.7 350 Mercruiser

I personally like the Q-jet. The AFB family is fairly simple to tune, but to be honest with you I've never had one start or run as nicely as a properly set up Qjet. I also like the spread bore design for its spectacular low RPM torque and big secondaries for higher RPM airflow. The other problem is going from the spread to square intake. If you use the adapter, I strongly suspect it causes some performance issues with the way it necks down and bends around to make the primaries on the Eddy mate up to the much smaller openings on a Qjet intake manifold. Honestly I find that swapping like for like to be the easiest route 90% of the time. Going from one carb to another, especially if you don't happen to be versed in the proper incantations and have a sufficient number of dead chickens to wave over the new carb to get it tuned right, is probably not a great idea.



When you got the new Qjet, did you use the ID numbers off the old one to get the correct new carb? If not, you may have the wrong jets or metering rods. If you don't mind buying a carb kit (or if you're very careful) and have the old carb still, it might be worth pulling the tops off both and comparing the numbers on the metering rods and main jets to see if there is any mismatch.

 

[proxyx]

Re: New Carb Suggestions for 5.7 350 Mercruiser

carb performance goes hand in hand with ignition, if you have detonation either carb is not adjusted or ignition timing/spark quality/spark plugs may be an issue. Why dump the money on the carb/unknown problem. Diagnose it properly. I have no issues with my Rochester Q-jet... when clean, LOL.

 

[John_S]

Re: New Carb Suggestions for 5.7 350 Mercruiser

just what I have been reading regarding my tulliped valves.

Was there another thread on this?

Carb could be the issue, but over propped and other things could be as well.

 

[sbbamafan]

Re: New Carb Suggestions for 5.7 350 Mercruiser

Mine came with a Holley 4150. VP # 855750-6. I have been through some of the same issues as you. Specifically, I had carb problems 6 or 7 years ago.

It ended up costing me virtually an entire summer (and a load of money) getting it sorted out. I paid a 'reputable' mechanic (JOA Marine in Atlanta) nearly $1000 to build the carb (and do some other stuff). Everything they did was wrong and every time I took the boat back to them, they put me at the end of the line - waiting 2-3 weeks each time. They rebuilt the carb 3 times and finally told me it should be replaced. I finally told them how bad they sucked and looked elsewhere.

I then found a guy locally that does a lot of hot-rod / performance automotive stuff and is 'into' boating. I spent another $250 (and about 2-3 weeks) with him and he did NOTHING. He is out of business now - no wonder. He said it was not a carb problem but that I needed a NEW ENGINE! I told him no thanks, picked my boat up and felt remarkably screwed.

By this time I was bad-mouthing Holley and everybody else. I seriously looked at changing carb brands and looking for a 'cure-all'. A friend of mine told me what a good experience he had with a company called Carburetor Specialists in Smyrna, GA. I figured I would take a chance and go one more place. I dropped my boat off around 8 in the morning expecting to have to wait weeks again. They called me by about 11 on the same day and said it was all ready and everything was fine. They said whoever worked on the carb was clueless and all adjustments were waaaaay out. They charged me less than $100. I was somewhat doubtful when I picked up the boat and took it to the lake the following weekend. IT RAN GREAT and has every day since (about 300 -400 engine hours). If in/near Atlanta go to Carburetor Specialists! I don't work there or know the owner or anything like that. I am just a very satisfied customer that only had to go there ONE time to feel this way.

I don't mean to ramble but here is my point. I think all the carbs that come on engines, generally speaking, run well and operate as intended. Otherwise people would not buy them to begin with. The key is to find someone you can trust to maintain it if you can't/don't do it yourself. That being said, I recommend you find a trustworthy shop instead of trying to change equipment unless you are really trying to do something special with your engine. Good luck!

 

[180shabah]

Re: New Carb Suggestions for 5.7 350 Mercruiser

Was there another thread on this?

Carb could be the issue, but over propped and other things could be as well.

I agree, we need ALOT more background here. Replacing a carb, if it doesn't need it is pretty wasteful IMHO.

 

[proxyx]

Re: New Carb Suggestions for 5.7 350 Mercruiser

...
I don't mean to ramble but here is my point. I think all the carbs that come on engines, generally speaking, run well and operate as intended. Otherwise people would not buy them to begin with. The key is to find someone you can trust to maintain it if you can't/don't do it yourself. That being said, I recommend you find a trustworthy shop instead of trying to change equipment unless you are really trying to do something special with your engine. Good luck!

Well said. I had carbs adjusted on a flow machine straight from a rebuilder that sucked really bad. Not that they did not do a good job. The adjustment was correct according to the machine, but flooded the engine. 2500 RPM was max. Took me a day to address it as the carb was the last thing I wanted to look at, after all it was "professionally" redone and set... turned out the idle screw was well over 2,5 turns out. After setting it at around 1.5 turns the boat took off like a rocket. Could not believe how poorly adjusted it was. So carbs alone (or the design) may not be at fault regardless of manufacturer. So many great running boats out there whether on Rochester or something else. Need to eliminate human error that may be buried somewhere, deep and hidden.

 

[jtybt]

Re: New Carb Suggestions for 5.7 350 Mercruiser

Words of wisdom from sbbam! There are tons of 'mechanics' that don't know how or what to do to adjust any carb.