mrsaundep
Seaman
- Joined
- Jun 9, 2009
- Messages
- 55
Mercruiser 3.0, MCM 140, No. 5568367, 1982, Alpha one (Boat maker Sealine)
Sorry for the long post but I’m at the end of my knowledge/tether and want to give as much info as possible in the hope that some of you knowledgeable guys can help me to solve this.
The existing Carb (Rochester 2BBL) has the following markings: GM 2 Jet, Bay City, 7041110, 23 1-CF (2 idle jets screws), Distributor is electronic DELCO EST distributor kit.
I have owned this boat 11 years. I performed a full overhaul myself some 6 years ago with the engine and leg fully serviced. The main Engine work included: engine out of boat, pistons out, liners honed, new rings, head stripped cleaned and lapped in valves, new engine mounts fitted (2 rear 1 forward). Rebuilt carb with overhaul kit. New throttle and shift cables. At this time I also fitted an electronic distributor - a new 3.0L DELCO EST distributor kit 107-A and coil, new HT leads and plugs. I also took out the automatic choke and fitted a manual conversion. Engine has run ok since then, the odd tweak now and again to keep it idling / starting o.k. The boat is not used a lot, some 300 running hours accrued since this big overhaul.
Earlier last year (2019) the engine would not start. After some trouble shooting found a lot of fresh water in the fuel tank. Assumed it was rain through the fuel filler screw cap, it was found loose (never had this problem in 11 years). Drained, cleaned and dried, new petrol, new filters x 3 (water separator cartridge, filter in the Carter (low volume) fuel pump, and the small one in the carb filter nut fuel connector. New spark plugs (gapped correctly). After flushing through the fuel line and reconnecting it, the engine would start and run ok at high revs but would run rough below 1200 rpm and stall around 800. Tired adjusting idle stop and idle mixture screws, no success. I decided to strip and rebuild the carb, and done this with a genuine rebuild kit. Float adjustment set as per specs. Engine run o.k for half an hour. Took the boat out to set the idle mix up in gear at low RPM, done this, then suddenly found I had no drive (engine would run and rev but prop not turning). Rowed back to the staithe. Found the drive coupler was shot. Hauled the boat, removed engine, ordered and fitted a new coupler, aligned engine, relaunched boat. Run the engine up and drove the boat from the launch ramp to the staithe, about 20 mins – all well. I came back about 2 weeks later, engine run ok for a few mins then stalled. Long story cut short – fuel in the tank again! Turned out some local was going around trying to syphon out fuel and swap it with water. So I fitted a lockable fuel filling cap and to date (some 3 months now) not a drop of water in the fuel tank – so that one is solved.
Anyway, over the next few weeks I repeated the previous exercise (fuel/water out, clean and dry tank, fresh fuel, new fuel filters x 3. Engine starts OK and runs fine above 1200 RPM, as soon as I drop below that it hunts – it revs up between 900-1400 over about 30 seconds, then down again, and wont run steady below 800, and then stalls. This happens both with the throttle remote control cable fitted, and with it disconnected and operating the throttle by hand.
So I decided to strip the carb again. I got the 2 main metering jets and the power valve assembly out and cleaned the lot in carb cleaner and also in an ultrasonic cleaning tank. Note I could not (and never have been able to) remove the power piston! Rebuilt with new carb kit including needle and seat, accelerator pump, float weight was fine (10.9g) and set the float drop etc all as per the manual. Refitted the carb, same symptoms, hunts and runs rough below 1200rpm, stalls below around 900-800. What is also odd is I can sometimes get the engine stable at around 1000 rpm and it will run for several minutes and seems like it will run forever but, the revs drop and the engine dies if someone (my or my assistant) move transversally in the boat and the boat heels over – what could be the cause of this?
I have checked the following and have found nothing wrong: Compression check - (140/135/134/140), borescoped all cylinders - tops of pistons all look good (can’t see valves), removed rocker cover and observed push rods and valve operation whilst cranking – all look good, check the timing with timing light (as it does not idle its not that accurate but looks advanced enough to be just about right for 1000 rpm. I have also tried adjusting the timing by moving the electronic distributor back to the point where the engine wont even start, and then round and through the range to the next point where the engine won’t start, but nothing changes throughout that range. By the way, I have bypassed the boat fuel tank and water separator / filter by placing the fuel lift pump suction hose direct into a 5 litre can of fresh petrol, and has the same issue.
My thoughts are the carb is knackered. Research shows that , “Bay City” was a company used as an ‘overflow’ manufacturer by Rochester when they needed extra capacity, and that this carb number was cast in 1971 - noting the engine is 1982! With hindsight, when I overhauled the carb I noted the following, which at the time I did not think significant, but now feel these may be the issue:
Thanks in advance for any advice,
Paul
Sorry for the long post but I’m at the end of my knowledge/tether and want to give as much info as possible in the hope that some of you knowledgeable guys can help me to solve this.
The existing Carb (Rochester 2BBL) has the following markings: GM 2 Jet, Bay City, 7041110, 23 1-CF (2 idle jets screws), Distributor is electronic DELCO EST distributor kit.
I have owned this boat 11 years. I performed a full overhaul myself some 6 years ago with the engine and leg fully serviced. The main Engine work included: engine out of boat, pistons out, liners honed, new rings, head stripped cleaned and lapped in valves, new engine mounts fitted (2 rear 1 forward). Rebuilt carb with overhaul kit. New throttle and shift cables. At this time I also fitted an electronic distributor - a new 3.0L DELCO EST distributor kit 107-A and coil, new HT leads and plugs. I also took out the automatic choke and fitted a manual conversion. Engine has run ok since then, the odd tweak now and again to keep it idling / starting o.k. The boat is not used a lot, some 300 running hours accrued since this big overhaul.
Earlier last year (2019) the engine would not start. After some trouble shooting found a lot of fresh water in the fuel tank. Assumed it was rain through the fuel filler screw cap, it was found loose (never had this problem in 11 years). Drained, cleaned and dried, new petrol, new filters x 3 (water separator cartridge, filter in the Carter (low volume) fuel pump, and the small one in the carb filter nut fuel connector. New spark plugs (gapped correctly). After flushing through the fuel line and reconnecting it, the engine would start and run ok at high revs but would run rough below 1200 rpm and stall around 800. Tired adjusting idle stop and idle mixture screws, no success. I decided to strip and rebuild the carb, and done this with a genuine rebuild kit. Float adjustment set as per specs. Engine run o.k for half an hour. Took the boat out to set the idle mix up in gear at low RPM, done this, then suddenly found I had no drive (engine would run and rev but prop not turning). Rowed back to the staithe. Found the drive coupler was shot. Hauled the boat, removed engine, ordered and fitted a new coupler, aligned engine, relaunched boat. Run the engine up and drove the boat from the launch ramp to the staithe, about 20 mins – all well. I came back about 2 weeks later, engine run ok for a few mins then stalled. Long story cut short – fuel in the tank again! Turned out some local was going around trying to syphon out fuel and swap it with water. So I fitted a lockable fuel filling cap and to date (some 3 months now) not a drop of water in the fuel tank – so that one is solved.
Anyway, over the next few weeks I repeated the previous exercise (fuel/water out, clean and dry tank, fresh fuel, new fuel filters x 3. Engine starts OK and runs fine above 1200 RPM, as soon as I drop below that it hunts – it revs up between 900-1400 over about 30 seconds, then down again, and wont run steady below 800, and then stalls. This happens both with the throttle remote control cable fitted, and with it disconnected and operating the throttle by hand.
So I decided to strip the carb again. I got the 2 main metering jets and the power valve assembly out and cleaned the lot in carb cleaner and also in an ultrasonic cleaning tank. Note I could not (and never have been able to) remove the power piston! Rebuilt with new carb kit including needle and seat, accelerator pump, float weight was fine (10.9g) and set the float drop etc all as per the manual. Refitted the carb, same symptoms, hunts and runs rough below 1200rpm, stalls below around 900-800. What is also odd is I can sometimes get the engine stable at around 1000 rpm and it will run for several minutes and seems like it will run forever but, the revs drop and the engine dies if someone (my or my assistant) move transversally in the boat and the boat heels over – what could be the cause of this?
I have checked the following and have found nothing wrong: Compression check - (140/135/134/140), borescoped all cylinders - tops of pistons all look good (can’t see valves), removed rocker cover and observed push rods and valve operation whilst cranking – all look good, check the timing with timing light (as it does not idle its not that accurate but looks advanced enough to be just about right for 1000 rpm. I have also tried adjusting the timing by moving the electronic distributor back to the point where the engine wont even start, and then round and through the range to the next point where the engine won’t start, but nothing changes throughout that range. By the way, I have bypassed the boat fuel tank and water separator / filter by placing the fuel lift pump suction hose direct into a 5 litre can of fresh petrol, and has the same issue.
My thoughts are the carb is knackered. Research shows that , “Bay City” was a company used as an ‘overflow’ manufacturer by Rochester when they needed extra capacity, and that this carb number was cast in 1971 - noting the engine is 1982! With hindsight, when I overhauled the carb I noted the following, which at the time I did not think significant, but now feel these may be the issue:
- Both idle mixture needle screws have slight radial scores about 4mm from the tip (as if they were probably screwed into the seat too hard at some time in the past),
- I could not get the power piston out when cleaning it,
- The beading on the float bowl gasket surface is worn away in some places,
- Power valve has no check ball fitted - the book says only later models have them and mine is apparently 1971, (so should have one?),
- Accelerator pump shaft lever bush is worn and the shaft is slack in the bush (maybe allowing to suck air in?)
- The baffle that fits around the float needle and seat is missing (this was not there when I Overhauled the carb in 2013 and the engine run ok for several years thereafter).
Thanks in advance for any advice,
Paul
Last edited: