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  #1   IP: 167.136.235.247
Old 08-16-2005, 02:39 PM
Jeremy Thompson Jeremy Thompson is offline
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Low RPM's Under Load

The engine starts fine, idles fine, has good RPM's in neutral, but has a top RPM in forward of 1200. So what's changed?

2004 Season
3 bladed Indigo 10x7.4 prop.
2400 Max RPM's

Before 2005 Launch
1) Replaced propeller with 2 bladed 12x8 folding.
2) Installed a dripless shaft seal.

Launch 2005
2100 Max RPM's. Assume drop in RPM's is due to different propeller.

Spring 2005
1) Installed Ignitor electronic ignition (Moyer).
2) New distributor cap (Moyer).
3) New spark plug wires (Moyer).
4) New spark plugs.
5) Installed new water temp sending unit (gauge was fine, sending unit was bad).
Same 2100 Max RPM's after installation.

Summer 2005
Max RPM's seems to gradually decreased to 1200. One day out it was 1900, next time it was 1700, then 1200.

Round 1:
Noticed a small amount of oil on top of coil. Replaced coil with Moyer coil part IGLM_05_31.
Still 1200 RPM's max.

Round 2:
Decided problem may be fuel related, so:
1) New fuel line from the gas tank (Moyer).
2) Installed manual in-line primer bulb on the gas line just before the Racor filter per Moyer web site suggestion.
3) Added a Racor fuel filter (Moyer).
4) Added a engine mounted electric pump (bought Moyer kit FPMP_10_52).
5) In-line gas filter (came in Moyer kit).
6) Oil safety switch. (came in Moyer kit). Engine didn't have one before.
7) Also replaced the oil pressure adjustment with an early model style (Moyer) as oil pressure has always been erratic. Press is steady now at 40 pounds. (The one thing I was able to correct!)

After all of above, still max RPM's of 1200. One change... engine now stalls under load after a few minutes. Just stops running like the key was turned off. Will restart either immediately or after a minute or two. I've run it at about 1200 RPM's in neutral for more than an hour with no stalling. When running wide open at 1200 RPMs, it sounds like its laboring.

Round 3:
Then I checked compression.
#1 = 130
#2 = 90
#3 = 130
#4 = 130

I put some MMO into #2 and it retested at 130.

Round 4:
Then I checked timing. Under load pulling at the dock lines, I made a very slight adjustment to the timing which improved the RPM by a very small amount. Now at about 1220.

The engine does have a small amount of blow by at times with exhaust coming out of the oil filler cap. It has had this for a few seasons.

I added 10 oz of MMO per 10 gals of gas and ran the engine in neutral at 1200 RPM's for an hour.

Rechecked TDC of #1 piston and rotor was positioned at #1 plug wire. Then check that order, going clockwise, is 1,2,4,3.

Tonight I got the boat out from the dock far enough to be in clear water and checked the prop and shaft underwater. There is nothing wrapped around it. The shaft turns freely in neutral. It does take quite a bit of force to shift into forward, but then the shifter has always been fairly stiff. With the shifter in forward, I can easily hand crank the engine and shaft.

The engine stalled 3 times in the ten minutes of running under load (may be the oil safety switch?). It runs fine at about 1/3 to 1/2 throttle, past that and it sounds like it's laboring and bogging down.

I'm out of ideas.
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  #2   IP: 216.54.200.157
Old 08-17-2005, 04:39 PM
jkenan jkenan is offline
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Can you increase RPM's by pulling the choke out halfway or more while under load? You have lots of issues listed, but bascically you say it runs fine in Idle, and under load RPMs drop and eventually engine stalls, right?

If you can improve RPMs with choke out, it is likely a fuel starvation issue, so I would first check main jet in carb for dirt.

Good Luck!

John
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  #3   IP: 167.136.235.247
Old 08-22-2005, 02:24 PM
Jeremy Thompson Jeremy Thompson is offline
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No increase in RPM's with choke (I have installed a new carburator). I removed my exhaust over the weekend. RPM's increase slightly to about 1400 RPM's. Also have checked for coil spark, which looked good.

The top of the carb, where it meets the manifold, get cold and condensation forms when the engine is running. I do not have a restrictor ring in the manifold. Has anyone else experienced this?
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  #4   IP: 70.25.215.153
Old 09-14-2005, 11:40 PM
James Supple James Supple is offline
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Cool Spider in fuel tank vent

I had same problem with 1975 C&C27 Mark II that it would start, run for seconds to minutes then stall when fuel in carb was used up. This was after other problems too long to detail, including rusty fuel guage sender, lots of dirt in fuel tank, weekly disassembly of carb (I can now take it off, disassemble it, clean it, reassemble it and remount it in 27 minutes), pump-out of fuel, cleaning tank with rag-on-a-stick, and routine cleaning of the fuel sediment bowl and and filter (rust comes off easily with water).
Turns out that there was a spider with a 1/4 in abdomen, and his web containing his lunch living in the fuel tank vent. My swiss army knife pursuaded him to come out, whence he went for a swim, and the engine immediately gained power. I suspect this might be your problem, since the only thing you havent changed in your fuel system seems to be the line from tank to vent. Try opening the fuel filler plug while running.
Myself, I still have problems caused by dirt & rust in the fuel tank, which is built in and would require removing the galley to get out. I'm looking for suggestions on cleaning the tank. Also my fuel tank is a cylinder, and the new sender is for a rectangular cross section and is correct only for full, half and empty, and I would like to find a sender for a cylindrical fuel tank.
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  #5   IP: 38.118.55.228
Old 09-15-2005, 05:03 PM
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Don Moyer Don Moyer is offline
 
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James,

Thanks so much for your input. I continually forget to mention the importance of having a wide open fuel tank vent line.

Don
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  #6   IP: 142.68.235.182
Old 10-04-2005, 09:52 PM
DaveHackett DaveHackett is offline
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Jeremy...

I'm wondering if you solved your problem?

I have a '76 Ercison 32 with an A4 that has the exact symptoms that you decribe. In neutral I can rev past 3500 RPM but in gear under load I can't get above 1100 RPM. Prop is free and clear and the ignition wires are correct. I'm about to disassemble the whole fuel system even though I'm getting good fuel delivery.

Any updates to report?

Thanks
DaveH
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  #7   IP: 69.177.39.122
Old 11-15-2005, 12:10 AM
mmsher2 mmsher2 is offline
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Jeremy
I've run my At 4 for the 18 years I've had the boat @ 1200 rpms. It runs fine, always has, races in neutral to about 2800 rpms, but under load with 2 blade fixed 13/6, 13/8 and 3 blade12/7.5 always runs at 1200rpm. Pearson Vanguard moves at 5 to 6knots in still water. New sp wires , old s p wires, whatever , 1200 rpms under load but no problem.
Mark

Last edited by mmsher2; 11-15-2005 at 12:12 AM. Reason: spelling, grammer
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  #8   IP: 68.60.84.181
Old 11-18-2005, 06:10 PM
Jeremy Thompson Jeremy Thompson is offline
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Dave,
What size propeller do you have?

Jeremy
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