2 bbl to 4 bbl swap or rebuild

[Chris611]

I have a 1996 Conquest boat with a 350 Merc and a 2bbl MercMarine carb. I had it to the mech and he says it needs rebuilding due to raw fuel sitting in the intake. He want's $375 to do that and says that he can't guarentee that will fix it. Says that sometimes there are cracks in the carb or the well plugs are leaking (well plugs can be epoxied). So my thoughts are to rebuild it myself or replace it and the intake manifold with a 4bbl. Can anyone give me advice on either. Where can I find the rebuild kits and if you were to replace with a 4bbl, which intake and carb should I get? Any help would be great.<br /><br />Thanks<br />Chris

 

[achris]

Re: 2 bbl to 4 bbl swap or rebuild

Chris,<br /><br />4bbl. MORE POWER <br /><br />Check out this thread<br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=24;t=007451 <br /><br />Chris..............

 

[Northern Eclipse]

Re: 2 bbl to 4 bbl swap or rebuild

Chris I just did that to my 350 last May I bought a Edelbrock Performer model 1409 marine carb, it's 600cfm electric choke, I mated it to a Edelbrock performer intake which is sqaure bore dual plane design. The EP carb is really a Weber and is easy to set up and rebuild, You can actually get a kit from Mercury, here's what you need to do the conversion Carb/Intake you can order a new fuel line from Merc for a Weber Carb, Throttle cable bracket along with cable mounting studs and nuts/washers, you'll also need new carb stud/nuts/washers all available from Mercury and a new Flame arrester, Felpro black gaskets for intake and carb base gaskets also. I bought fuel line and hardware/throttle cable bracket and Flame arrester from Merc everything mated to the intake and carb to a factory fit, Just remember when ordering a Intake that you probably have Vortec heads if your motor is a 1996, I suggest you run the engine serial number by Merc dealer to be sure. I found the that my low end Torque and midrange response was greatly improved and Fuel consumption did not vary to much, well worth the upgrade. Good luck

 

[John_S]

Re: 2 bbl to 4 bbl swap or rebuild

Chris_P,<br />I'm not trying to hyjack your post, but I have interest in this same mod. I have a '97 350 2brl, which is 210hp. I think this is the same as your '96. From the sniffing around here, I thought that I read somewhere that the 2 brl model went to 250hp when Merc changed the cam and lifters. Also, sounds like from this, there was a head change. Not sure, but thought these changes happened w/'98 models. <br /><br />Northern Eclipse,<br />My asumption to this point was, just changing the intake and carb, but not cam, would only provide a minor improvement. Did you do this mod to a 2brl motor or was this a 4brl swap? From your profile, I suspect the latter, but maybe it was a different boat. It would also make sense given the improvement areas you said. With just a 2brl to 4brl/intake change, I would think the improvement would come at the top end. Maybe I'm relating this too much to car engines, but just the carb/intake change would be maybe 10-20hp increase, but its been awhile. There is much in this water world, I still need to understand. For instance I thought a 600cfm was good for 5-6K RPM in a car, but most 5.7L specs show WOT 4-5K. So not sure how a boat engine gains with carb with more flow, without the higher rpms. OK, I'll put a cork in it!

 

[Chris611]

Re: 2 bbl to 4 bbl swap or rebuild

Thanks for the replies. I brought the boat home yesterday and took the Merc 2bbl carb off. It does apprear that there is an internal leak. It leaks out of the small slits in the bores. I have heard of fixing automotive well plug leaks with epoxy, but this carb, there is no base plate to take off to get to that area. So I guess its junk right? I have found rebuild ones for sale for $180, but seems like for that money I should switch to a 4 bbl system like Northern Eclipse did. Is the marine version of the Edelbrock carbs worth the extra money of the auto version?<br /><br />Thanks

 

[akriverrat]

Re: 2 bbl to 4 bbl swap or rebuild

every penny and more if the auto carb ever causes a fire.

 

[Northern Eclipse]

Re: 2 bbl to 4 bbl swap or rebuild

John your questions are well received, my motor is a 1994 350magnum which was rated at 260hp propshaft, when I purchased the boat somebody had put a 2bbl carb and intake on it, (350 replaced the orginal 305) The 350 suffered badly with 2bbl, so I swapped out to 4bbl, I also installed thru-hull exhaust. I did gain improvement to top end, but due to the Intake I used, low end torque and midrange (3000rpm and up) throttle response was more noticable, I'm not sure when Vortec heads came into the marine world, but have been in the automitive field since '96. The 600cfm carb is most popular for small block marine.<br /> I used the Edelbrock carb due to its tuning capabilities and reliability, Chris You most use a marine carb, they are different than a automotive, such as Fuel bowl overflow vents down the carb and throtte shafts are sealed to prevent external leakage, onto the motor or into the bilge, I bought my edelbrock carb off e-bay, it was brand new out of the box for $175 you can find remaned carbs there also, using a automotive carb is a fire hazard.

 

[John_S]

Re: 2 bbl to 4 bbl swap or rebuild

Northern,<br />Thanks for the additional info. I assume yours has the cam referanced in the Seloc manual. Note: 5.7L engines with roller lifters and steel cam. Which has 0.024 higher lift on intake, and 0.031 higher lift on exhaust, than "standard" cam. No duration specs, but assume they would be at least slightly different.<br /><br />Chris,<br />Like you, I wouldn't consider the mod, unless replacing a bad carb. Adding cam & lifters, and timing chain & gear, starts to add up. Haven't looked or measured, but a cam may mean engine out of boat. HP would start to creep closer to 300, which might mean an outdrive upgrade from Alpha to Bravo, and a prop change. Brovo may mean some cooling system changes... Maybe boats are like cars. One change leads to another, and another, and.... ;-) <br /><br />I am currently happy with my boats performance. (easier to say when I start to add up that cost) But by the time my carb needs major repair, who knows? If you go the 4brl route, keep me posted. Would like to hear what the improvements are with the 210hp cam. Are there better 2brl marine carbs that flow more than stock? If so, might get some gain without the cost of intake manifold or additional work to replace. Anyway, just a thought.

 

[Chris611]

Re: 2 bbl to 4 bbl swap or rebuild

Thanks again. I have decided to go with the Edelbrock #1409 Marine 4 bbl carb and Performer Intake to fit the vortec heads. Here is a newbie question. How do I drain the water from the heads? I see two brass plugs (one on each side) on the sides of the engine block. Are those to drain. Since I already have the intake off, and some water got into the galley, I assume now I will have to also change engine oil. It didn't seem to go too bad. Took about an hour to remove. I did remember to put engine at TDC on #1 cylinder compression stroke and to mark the dist. Any other advice on reassembly, break-in, or adjustment. Also I thought that the 2 bbl Merc 350's were 260HP. Where is the 210hp coming from? I know that the auto TBI 350s around 1993 were 210hp. Just looking for a little history lesson. <br /><br />Thanks to all<br />Chris

 

[John_S]

Re: 2 bbl to 4 bbl swap or rebuild

Chris,<br />From my '97 Merc Op & Maint manual:<br />5.7L = 210Hp (2brl, what I have)<br />5.7LX = 250Hp (I think this is a 4brl)<br />350Mag = 250Hp (definitly a 4brl)<br />5.7L EFI = 220Hp<br />5.7LX EFI = 250Hp<br />350Mag EFI gen+ = 280Hp<br />Note: these are BSO/SAV ratings for propshaft hp<br />Seloc manual doesn't list hp<br />I believe the current 5.7L 2brl is 250hp.<br /><br />As an I/O newbie myself, the only other answer to your questions I can give, with confidence is, yes, you will need to change the oil. Sorry.

 

[xltier]

Re: 2 bbl to 4 bbl swap or rebuild

i have a 88 merc 350 4 barrel and its 260 hp.hth

 

[jimmbo]

Re: 2 bbl to 4 bbl swap or rebuild

Holley makes 650 spreadbore marine carb http://www.holley.com/HiOctn/ProdLine/Products/Marine/FMS/FMSC/0-80552.html <br /><br />BTW Automotive carbs on a boat is againt USCG regulations. Can you say ILLEGAL!

 

[John_S]

Re: 2 bbl to 4 bbl swap or rebuild

Chris,<br /><br />Hopefully this post will find you are already back on the water, with maybe just some final carb adjustments to make. When you do find some time, like to hear about any improvements or issues you encountered. I'd like to know which Conquest model and prop you use, as well. ie calculate how much it might apply to me. Thanks.

 

[Chris611]

Re: 2 bbl to 4 bbl swap or rebuild

John_S, I have a 1996 Conquest 2100 Sport. I have a 23 prop on it. I bought the boat used a month ago and have only had it on the water a few times, so I have little experience with the "stock" setup. I got the carb and intake installed this weekend (Edelbrock Performer intake & Marine carb #1409). Only non bolt-up issues were the bracket for the throttle cable and 50A circuit breaker. I fabricated a bracket at work and it works good. Boat fired up after the install, and now I am taking to the boat mech (local guy) to set the timing and change oil. I have a timing light, but wasn't sure if I needed to disable the timing advance part of the dist to take the readings. I will keep you updated on the performance aspects as soon as I get it in the water. Hopefully soon!

 

[Northern Eclipse]

Re: 2 bbl to 4 bbl swap or rebuild

Good job Chris, I'll be watching for your results along with John. So I may compare my results to yours. happy boating

 

[broark01]

Re: 2 bbl to 4 bbl swap or rebuild

For a recent award winning article pertaining to the above mods:<br /><br /> http://www.boatingmag.com/article.asp?section_id=8&article_id=501&page_number=1&preview=

 

[John_S]

Re: 2 bbl to 4 bbl swap or rebuild

Thanks Cap'n,<br /><br />Lots of great info. While the "tips" are too late for Chris, he should be happy to know he has choosen a proven combo. <br /><br />This quote has me confused, when I look at the last page with the test data.<br /><br />Quote "The new setup will also use more fuel, which I expected at the upper rpm range but not at 2000 rpm and under. Edelbrock says this is because the individual barrels in a two-barrel carb are larger than the two primaries in a four."<br /><br />The data shows better fuel economy at 2K rpms and below for the 4brl vs 2. Data or quote typo? My off the cuff analysis, says that the two primaries in the 4brl only flow 300cfm vs the 425 for the two barrel. So it might get better economy in this range??? Also if you compare fuel economy at the 25 - 35mph range, the 4brl is same or better than 2 brl. Not that fuel economy means much in boats!<br /><br />No mention of idle or hesitation/accel issues - good!<br /><br />Now if they only provided time to plane and time to top speed compare.. ;-) <br /><br />On the cam front, I found some data that may indicate the roller lifters are in the '97. I found the '97 Mercruiser brochure that says all v6 and v8s have roller lifters. Seloc says roller lifters mean the better cam?? I don't think this will be settled till I receive the Merc manual for my serial number. I'll post the info incase there are other inquiring minds ;-).

 

[Chris611]

Re: 2 bbl to 4 bbl swap or rebuild

Well I finally got the new setup in the water. The first thing I am glad about is that my hot start problem is fixed! The 4 bbl seems to have helped some. Its not night & day difference, but subtle differences. Although I didn't do much running with the 2bbl and never pulled a skier. One thing I am surprised about is the top speed. Its not much different from the 2bbl, maybe a few MPH. I have a 23 pitch SS prop (quicksilver LaserII..) on a 21' open bow boat (don't know weight) with a 350. My WOT is 4600 RPM and my top speed is 54-55MPH, speedo...I don't have GPS or another boat to compare to, so speedo may be off. Does that speed seem right? <br /><br />Another question: Whats the difference between a 350 MAG and a 350 with a 4 bbl?<br /><br />Thanks for all the help with this change over. This message boat has been a lot of help.<br /><br />Chris

 

[John_S]

Re: 2 bbl to 4 bbl swap or rebuild

Chris,<br /><br />NADA reports that your boat weighs 3150 with standard 190hp engine. The 5.7L is about 100lbs more. If you go to www.boattest.com, you should be able to find comparable boat/motor combinations and compare the results. I think mid-fifties is about right for a standard v boat. There wasn't a pic on NADA of your boat, but if it is a more sporty hull, like the baja, then you might expect a little more. <br /><br />Your boat weight is about the same as mine, but I haven't done any WOT tests yet. I have easily hit 45 with six 17-18 year old boys, myself (250+), plus gear and full gas tank (28gal). I expect to hit low 50's with just a couple in boat and trimed out on calm water. Most likely, I won't get to that until thee 2nd week in August (vacation). Much less boat traffic during the week. I will let you know what it is.<br /><br />Your WOT rpm is right where it should be for the 5.7 2brl(4200-4600). The 4brl/250hp is 4400-4800. If you were on the low range of the 2 brl spec before mod, the prop might be a little too high in pitch. I would do some more test runs, and trimming out before trying another prop. <br /><br />BTW, given your prop pitch, I assume your Alpha drive gear ratio is 1.47, vs mine of 1.62 with current 14x19x3 alum prop. The 1.47 is standard on the 250hp 5.7L, according to the '97 brochure, while on the 210hp it was optional. Good for you, bad for me. If I do any upgrades, it means upgrades in the outdrive, as well.<br /><br />The Seloc manual does not provide any details on differences between magnum and other versions of the 5.7. The brochure specs are the same for the 5.7LX and 350 Mag. The only thing the brochure alludes to, is stainless steel exhaust elbows, in the magmum v8s. I am sure there are other differences.<br /><br />BTW, what flame arrestor did you choose?<br /><br />PS: I am still waiting for Merc manuals from Merc Pubs. Sent email this weekend to find out status.

 

[Chris611]

Re: 2 bbl to 4 bbl swap or rebuild

I bought a Holley flame arrestor off eBay for $40. Problem when I got it was it was flat on the bottom so it hit some of the linkages on the carb. I was able to find a piece of tubing at work with a 5.06" ID and turned it out to 5.125 and the OD was 5.56? I made it an inch tall and now it clears all the linkages and allows the engine cover to close.<br /><br />I will have to check out the boattest website, sounds like a cool site.<br /><br />Thanks<br />Chris