New to the OMC Sterndrive forum

Allow me to start over. I have been a member of the marineengine.com forum for many years. I owned a 21ft Fiberform boat powered with a 318 Chrysler engine. I live in the Rocky Mountains and enjoy spending my time on a boat on reservoirs like Blue Mesa, Flaming Gorge, Ruedi and of course Lake Powell. A year ago I found the boat I was looking for on Craigslist. A 1982 Sea Ray 245 Sundancer with twin 3.8 liter OMC Sterndrive power plants. It is a one owner boat with well maintain completely from the factory stock motors and stringer out drives. How lucky am I... The perfect boat with a triple axle trailer that can handle the 4 and 5 hour drives to the reservoirs I enjoy spending time on. The boat sat for a couple of years unused and from the cosmetic shape of the boat in questionable storage facility. I have worked through all of the typical problems when a boat has not been used consistently-- electrical problems,tilt motor, select trim hydraulic leaks etc. I finally was able to get the boat and all of its systems up and running consistently, until a couple of weeks ago. The port motor will not go over 3300 rpms. I'm not sure what has changed. The biggest thing I have seen is that when the boat gets up on plane the Rochester 4barrel carb secondary is still spraying fuel even when it's is planed out and dialed in. The starboard motor when up on plane is only running on the primaries. I have done some research on the forum and ended up doing a distributor points,condenser,cap and rotor tune. A Rochester Quadrajet rebuild and a fuel pump change. I still have the same problem. The motor is timed, dwell metered and tuned by the numbers. Runs well at idle, distributor advances exactly when it should under power, but the motor will not go over 3300 rpm and the secondary is spraying fuel even when planed out. I'm starting to think the motor and carb are fine and I have a stringer out drive problem. Is there something that the Sterndrive can be doing to make the carb think it need s the extra fuel in the secondary when at cruising speed? Any thoughts would be helpful I am out of my troubleshooting bag o tricks

Possible vacuum leak? Are all the plugs the same color? I would first do a complete diag of the engine. Compression test and leakdown if necessary, Check for slop in the timing chain and use a piston stop tool to check for true TDC.

Are plugs fouling, Is carb mounted snugly,vacuum hoses intact. Do both sterndrives have the same props on them?

I did vacuum tests at idle with both carb cleaner and propane with no idle response for either. Props are the same on both port and starboard, this boat has run with this set up. Pulled 4 of 6 plugs they all woulld be called normal on a plug color chart. I did top dead center with a depth caliber feel I got it pretty close to dead on. Motor timed well and purrs at idle. Thank you for your help.

The motor runs smoothly at idle, and the vacuum operated choke piulls in, at around 1800 rpms the secondary's open and the vacuum to the choke goes away and the motor sounds real boggy , I manually pull the choke actuator in and the motor smooths out , the secondary air valve is open about 3/4 of an inch, the motor will not go over 3300 rpms.

Has compression test been done yet? post#2

I have not done a compression test, I have an older test gauge , looking for something better to do the test. I'm taking the boat this morning to be put on a dyno

First of all, those 30 year old carbs are probably not doing you any favors. If it were me, i'd be shopping for new (NOT remanufactured). Second, did you replace all the fuel hoses from tank to carb with new alcohol resistant hose? Have you had the tank(s) flushed and polished? Have you replaced the filter/separator elements? It seems that there is a bit of fuel starvation going on that may be from one of the fuel delivery system components being fouled.
Doubt you have compression problem since boat engines rarely get run enough over the years to actually wear them out, but it can't hurt to check anyway.

Hoses from the 100 gallon tank are new, I replaced both fuel filters, the canister element and the smaller filter on the carb inlet. I cut the canister filter apart and it was very clean. I have run through 5 or 6 full tanks of gas and feel like the tank is surprisingly clean.

O2batsea, what is the relationship between throttle position, secondaries opening, getting up on plane and just running on the primaries? Is it the amount of torque, is it vacuum in the intake? What is the trigger for the quadrajet to know to back of the secondaries and run efficiently on the primaries? Thank you for your response.

Post #9 30 year old carbs,he might have something there,worn out parts,many vacuum leaks. compression tested yet???

I know nothing about Q-jet carbs. I put a new Edelbrock Performer marine (Weber) on my engine a couple years ago.