Carb and shift prob

Hello techs, I need some training. I have a 1995 5.7 mercruiser with remanufactured basic edelbrock 4bbl. I installed it and it didn't run good initially (at home with the water hose). I adjusted it until it idled at 650 rpms and was running smoothly. I have no real carburetor experience but some mechanical inclination. I adjusted the fuel/ idle mixture screws and the idle speed adjustment until I was satisfied that the idle was right and it shifted from forward to rev smoothly. This was all in the yard. I put it in the water under load and everything started off good (Idled great shifted great). Got underway and after about 10 minutes of running in the 2000 to 3000 rpm range I stopped to test everything. Going through neutral to reverse and visa versa became a problem. It was hard to shift and when it did it was a hard clunk. It would sometimes jump neutral and straight into reverse so I decided to bring it in. On my way in while cruising at 2500 rpms it started fluttering and the rpms would fluctuate back and forth down about 300 to 500 rpms. To avoid any further problem I brought it down to about 15-1800 rpms and cruised on in. It still performed slightly funky but not as bad. When I got back to the ramp it still would not shift into neutral. When I got home I checked the basic things and saw no obvious problems such as trash in carb or filters. I think I need a lesson on basic carburetor adjustment and it would be highly appreciated if someone with some patience would send me some guidance. I don't want to continue and make it worst on my own. Today is July 3rd and between the holiday visitors and my crazy work schedule I don't see getting back to the water again for about a week but I will make time to make the adjustments. It needs to tach correctly, shift right and run smooth. Thank you anyone who has the patience to assist me with my problem. I have almost all new and remanufactured parts on this engine and trying to get it 100% before getting away from the ramp. It still runs and shifts great in my back yard on the clam shell but I can't find any fish back there.

Re: Carb and shift prob

Looks like you have a few problems so I would suggest going back to basics. You need good fresh gas, clean filters, correct fuel pressure and going to need to look at adjust and/or replace the shift cable. I say adjust or replace the shift cable because it probably loosened up on you but may also be damaged, just don't know right now. Ajusting the idle on a carb is a good thing to do but you have runability issues which need to be looked at first. Idle ajustments are for idle only and are not used much above an idle.

What shape is the engine in. and has anything been replaced other then what you have mentioned?
How long has the fuel been in the tank?
Has the fuel filter(s) been replaced?
Have you check fuel pressure?
What is the engine serial number?

Re: Carb and shift prob

Serial # doesn't exist but local marine dealership has determined it's 87-95 but more like 95 so that's how I buy parts. Fuel pressure checked prior to the bad run and was 6.5. All new fuel filters and water separator. 75 gallons of new fuel installed on 6/29/13. Drained all of old fuel. Engine in excellent shape. Brand new shift and throttle cables installed. Fuel pump is new. Shift interrupter is old type and is used. Works fine.
This is my story in brief. Had an minor engine fire, replaced everything that even resembled damage and most stuff that didn't. All electrical rubber hoses and anything plastic. Even if it didn't look bad I replaced it anyway. The outdrive had slop in it and I had it repaired the correct way as well. New (remanufactured) carb. Prior to my fire I did have this problem though. After travelling about 10 miles the engine would cut back the rpms to almost shutting down. I would wait about 2 or 3 minutes and get back to normal. After a while it would happen again. That was last year and I took it out of the water and vowed to not go back until I got it corrected. In the meantime I had the small fire (which had nothing to do with that, but was caused by my negligence) and repaired/ replaced everything. The problem is different now because it ran great at high rpms before for about 10 miles and now it's fluctuating and it never did that. I think it's the carb because I was just turning screws, watching the tack and listening for a smooth sound. It idles great. I have no leaks, new oil and filters. I have all new gauges and wiring. New steering wheel and rack.

Re: Carb and shift prob

jacklegmech said:

Serial # doesn't exist but more like 95 so that's how I buy parts. Fuel pressure checked prior to the bad run and was 6.5. All new fuel filters and water separator. 75 gallons of new fuel installed on 6/29/13. Drained all of old fuel. Engine in excellent shape. Brand new shift and throttle cables installed. Fuel pump is new. Shift interrupter is old type and is used. Works fine.
This is my story in brief. Had an minor engine fire, replaced everything that even resembled damage and most stuff that didn't. All electrical rubber hoses and anything plastic. Even if it didn't look bad I replaced it anyway. The outdrive had slop in it and I had it repaired the correct way as well. New (remanufactured) carb. Prior to my fire I did have this problem though. After travelling about 10 miles the engine would cut back the rpms to almost shutting down. I would wait about 2 or 3 minutes and get back to normal. After a while it would happen again. That was last year and I took it out of the water and vowed to not go back until I got it corrected. In the meantime I had the small fire (which had nothing to do with that, but was caused by my negligence) and repaired/ replaced everything. The problem is different now because it ran great at high rpms before for about 10 miles and now it's fluctuating and it never did that. I think it's the carb because I was just turning screws, watching the tack and listening for a smooth sound. It idles great. I have no leaks, new oil and filters. I have all new gauges and wiring. New steering wheel and rack.

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Engine prior would cut out and in 2 to 3 minutes it would run again, then do it again later (Fuel delivery). Replace both throttle and shift cables, and in first post could not get it into netural (May need adjusting). It idles great but will not perform (Fuel delivery).

My thoughts are you have your shift/throttle cable which needs to be rechecked. The engine would die before and then restart later which leads me to think you have a tank which is not being vented properly. The gas cap vent is not working or tank vent is stuck and after a while the fuell pump creates a vacuum in the tank. You say it is worste now then before which may mean you have a fuel pump issue as well. It could be other things but this is what my thoughts are so far.

Re: Carb and shift prob

Ok i 'll recheck the cables. I changed the tank vent last year but just to be thorough i'll check the line from the tank to the vent. Thank you again. I'll post my results ASAP.

Re: Carb and shift prob

Carefully adjust the lower shift cable. When it's right it causes the interrupt system to briefly shut down the spark when pulling the drive out of gear. The gears are shaped in a way that won't allow them to disengage under load, so the shift interrupter stops power to the plugs just til the drive goes to neutral, then it renews the spark pulses before the motor stops spinning and it keeps running. It's no longer in gear though.
To correct the hot stumble and stall, maybe get the engine compartment cooler by running the blower at low rpms. It could be something blocking the fuel tank vent, try releasing the fuel cap when she stumbles and listen for vacuum/sucking sounds.

Re: Carb and shift prob

Thank you, I'm gonna go hard on it today and hopefully with the advise I've gotten from you guys I'll solve my problem.

Re: Carb and shift prob

Hey guys; since I last requested help my job sent me out of town to work. Before I left I corrected everything except the shift issue; couldn't seem to get it right even with the instructions and the correct tools. The carb just needed an extra inline filter. When I returned I took the boat to someone that was recommended to me and after checking everything he had to remove the remote shifter and totally readjust it. It's performing excellent now. The engine is performing great as well. I'd never thought remote end of the cable was my problem. The original mechanic I paid to do all my work messed that up to. I've learned a big lesson and won't be dealing with mechanics that can't keep a job at a shop anywhere anymore. Thanks for the help.