17059286

[1mainiac]

I have a 26ft boat with this carb recently replaced the 350 with a 383 long block boat performance has gotten worse. Mid range has improved however top end is lower. Idle is way too lean so it stalls on every shift out of gear I have to send the rebuilt carb back as it is messed up and they will replace it however what jets should be in this setup. I am going to rebuild my stock carb over the winter since I have a second boat with the same engine setup which I will be getting ready for next season. The 383 long block was installed by a  shop and nearly everything was replaced during the upgrade. Which included new fuel pump new Distributer new water pump and belts it has no vacuum leaks. The issue is it runs much worse with the rebuilt carb than with the 26 year old stock carb since I will have 2 carbs I have some room to play around and dial it in. However I want to be fishing not working on the boat. The  rebuilt carb has damaged idle mix screws and they are replacing  the carb what bothers me most is I should get more top end out of the new engine, it has 30 hours break in on it. the motor will not make over 4000 rpm I swaped  props from a 17 to a 15 and all I got was lower speed it still would not go over 4000 rpm. My thought is the carb does not have jets enough to provide the CFM needed The old 350 would run about 4300 with this carb which if my math is correct is about 440 cfm the 383 runs 4000 which is  436cfm by my math. To get where I want I need 650 cfm running correctly what should I use for jets and adjustments?

[StillLearning]

Welcome to the blog!
  With all the new stuff and changes to your engine take some time and make sure some of your basic settings are correct. A lot of what seem to carb problems can be ignition timing, fuel pressure or some other thing that was overlooked.
 That said, most commercially available "rebuilt" carbs are not all that good. Each one is built for several different applications and usually are marginal for said applications. You would be much better off taking the original unit and building it with Cliff's parts. Most rebuilts use some pretty cheap innards.  With Cliff's parts you get the right parts and the newer alcohol containing fuel won't be a problem. Consult with Cliff to find out what changes you need to make to your Q-jet. He also has a rebuilding service if you don't want to try it. Believe me it will save you time and hassle in the long run. Happy fishing!

[1mainiac]

I have no problem with rebuilding my own carb what I don't have is experience with Quadrajets frankly I am one of the guys that always tossed them out and installed a Holley. Not that I thought they were junk but I grew up with Holley carbs and could tune them in my sleep years ago. So what I need is a base line to work with. I would prefer fat and happy til I get some more hours on the engine. Not really looking for huge performance but I expect it to make decent power and be able to hit upper RPM when needed. On paper this setup should run 5200 to 5500 pretty easy which a friend of mines similar setup does with a stock 350. I have a few more weeks to sort this out before I put it to bed for winter. If it does not start to behave soon it will have a TBI on it next spring.

[77cruiser]

Do you have Cliff's book? It has some baseline combos in it.

[Cliff Ruggles]

The problem is going to be with the "rebuilt" carburetor.  I do this for a living and will NOT work on them, and don't even want one sent to my shop for any reason.  I'd send it back and completely/correctly rebuild the original carburetor with one of our kits.  I'm betting at this point your carburetor issues will disappear.....Cliff

[1mainiac]

I guess my original post of this did not get worded or understood correctly. My question is what parts should I order to get my carb jetted for this engine setup?, I have the idle mixture screws backed out around 6 turns to get it to idle and it is way lean thru the entire throttle range I can't find any numbers on the jets or rods on the original carb which I would prefer to rebuild and as such would like a idea of which parts to get so I can rebuild it one time and use the boat.

[Cliff Ruggles]

We can supply tuning parts wit the rebuild kit.  It will need a slight modification to the idle system as well, since it appears a larger than stock cam is being used.  Marine carburetors are not emission calibrated, and actually pretty generous for fuel delivery everyplace. 

If the engine vacuum is lower at idle and low rpm's than the original engine, it will still need a little help, but it will work fine for the larger engine once you get it tuned correctly......Cliff

[1mainiac]

Can you put a kit together and price it for me or secondly what would you charge if I sent you the original carb for a rebuild and rejet.  Here are the basic specs for the engine
Block GM 4-bolt 1 PC rear main seal
Crankshaft Scat steel 383 crankshaft
Connecting rods GM 3.750 w/ARP 150,000 bolts
Pistons Speed Pro Hypereutectic flat top 9:1 comp ratio
Piston rings Mahle plasma moly piston rings
Camshaft Comp marine .462/.477 - 218/224 - 112 specs
Lifters Speed Pro hydraulic
Oil pump Melling high volume oil pump
Timing set Cloyes HD double roller timing set
Bearings Clevite/Mahle HP "tri-metal" rod & main bearings
Flex-plate Pioneer 14" 168 tooth
Harmonic balancer GM externally balanced
Freeze plugs Brass deep dish
Heads GM 76CC 1.60/2.02 cylinder heads
w/hardened valve guides, seats, guide plates & screw-in studs
Valves Stainless steel swirl polished 1.60 / 2.02
Springs Comp series valve springs .530 max lift
Push rods Elgin hardened push rods
Rockers GM 1.5 ratio rockers arms, balls & nuts

The boat ran 4200 rpm at 40mph with the original engine which had 2 dead cyl before it dropped the 2 cyl it would run around 43 at 4800rpm that was a stock 230hp OMC. This motor should make between 350 and 400hp It was listed as 390hp at 5200rpm I am rev limiting it at around 5500 which is plenty fast for a fishing boat.

[Cliff Ruggles]

Best to call the shop to order parts.  We can discuss rebuild options if you want to send the carb here and have us do the work.....Cliff