Rochester 2GC Jet Size?

[cionjay]

I purchased a 1989 19’ Sea Swirl Sierra Classic with an OMC 4.3 liter 2 barrel Rochester 2cg carburetor in non-running condition. The previous owner purchased a rebuilt carburetor and could not get the motor running. After I purchased the boat I installed a new ring gear on the flywheel, new OEM starter, new OEM spark plugs all new fuel (no ethanol), fuel lines, all new fluids, new water pump on the drive and Pertronix electronic ignition. I still could not get the motor running so I purchased a remanufactured carburetor from I-5 Components and installed it on the motor. I got the motor running and it sounds great on earmuffs. It will idle at 600 rpm and rev up to 4500 and does not miss a lick. I put it in the water and the motor runs bad above 3000 rpm and has a sporadic hard knock. I put the boat back on the trailer and looked at the spark plugs and they are very black with dry carbon. I bought another set of plugs, a timing light and vacuum gauge to try and diagnose the issue. I found that the vacuum would fluctuate between 18 and 20. The timing is set at 28 degrees at 600 rpm. I have read that it should be at 6 to 8 degrees at 600 rpm. If I try and retard the distributor it will run bad and the engine shuts down. I adjusted the carb metering screws to 1.5 turns out and still have the same issue. I checked the TDC on the #1 cylinder and the timing mark is set properly with the rotor pointing toward the #1 cylinder and double checked the new Mallory marine 8mm spark plug wires were in the correct firing order starting with the #1 wire above the rotor and then 6-5-4-3-2 in a clockwise order. Again the engine ran great on earmuffs and terrible in the water above 3000 rpm. I pulled the plugs and found them very black again. I am beginning to think that the jets are incorrect. What size jets should be installed on a stock motor and will smaller jets allow me to retard the timing to 6 degrees? What else should I look for in the carburetor such-as power valve size once it is apart? Any help or ideas would be very much appreciated.

 

[alldodge]

Unable to find the jet size for your motor but I think you have something else going on here. Your unable to get the timing set correctly so that is where I would start, something is wrong. Need to be able to get timing a 8 BTDC.

Suggest doing a compression test

 

[cionjay]

That is exactly what I want to do. My thinking behind this is that the current jet sizes are too large making a very rich environment. because it is so rich I have to advance the timing 28 degrees BTDC in-order to keep the motor running. If I can lean the motor out, I may be able to retard the distributor 8 degrees BTDC. I just do not know what size jets to order. They are about 5 bucks a piece so I would hate to buy every size and a box of gaskets. I was hoping maybe someone either knows or has an old carb laying around and look at the jet and power valve size.

 

[alldodge]

Your carboned up plugs is not from over size jets IMO, there is something else going on. The entire jet sizes I'm finding is from .040 to .062 which is not much overall

 

[cionjay]

Thanks, I will keep digging. any other suggestions from anyone is welcomed.

 

[Bondo]

The timing is set at 28 degrees at 600 rpm. I have read that it should be at 6 to 8 degrees at 600 rpm. If I try and retard the distributor it will run bad and the engine shuts down.

Ayuh,...... Something is very wrong if it runs at 28?btc,.....

Either yer not on cylinder #1, or something,.....

#1 is the port-side front cylinder, not the starboard-side,....

 

[cionjay]

I will double check the distributor position. I may be one tooth off or something. I started to dig around the coil side of the distributor. Here is what I found.
I have the pertronix igniter with a 3 ohm flame thrower coil. When I tested the coil I only get 6 volts with the ignition key on. I thought it should be 12 volts. I took the coil out and tested the ohms and I do get 3 ohms. I read somewhere that I should disconnect the red/purple resistor wire on the + side of coil but I think that is where my power is coming from. I have no idea where those wires go and looked in the manual and can't find a good wiring diagram that shows the color of the wires and the location that they terminate. All of my black spark plug problems may be caused by the coil and distributor issue and my carb may be perfectly fine.

 

[Darringer]

I have an 85 Seaswirl with the 3.8 V6 that I recently put a rebuilt 2GC carb. Had the exact symptoms as you describe. Ran perfect with the old carb, but developed a leak as it was badly corroded. Replaced the carb and ran poorly above about 3000-3500 rpm. It had #63 main jets but was extremely rich. My old carb had 70s in it which was weird, and it ran well. I ended up dropping the mains to #53. By the way, there were no powervalve numbers on either valve from both carbs, old and new. So I kept leaning it out until it ran well. I didn't change the top gasket while making the changes and have no leaks. It took 3 times to get it right, as I swapped the jets with the carb on the motor and the boat in the water. I hope this helps.

 

[cionjay]

Thank you Darringer, I will try this and update my solution as soon as I get this running properly.