weak firing lower cylinder 76 55hp

[rickryder]

Hi
I am trying to get my old 55 HP 557 hg to run properly. I could hear it wasn't really running on both cylinders so I started trouble shooting from the plugs back. I did a compression test and read the plugs,top plug looked great bottom looked almost new not much burn going on. My compression is 127 in both cylinders. Next step was to ground out each plug,top made motor miss bottom was no change. Checked switching wires same results,switched coils same result when bottom cylinder is grounded there is no change in motor run-ability. My question where should I go next?? Points? Only strange thing is if I test for spark with a screwdriver in the lower wire to ground I have spark Anyone have a suggestion?? Thank You

 

[rickryder]

Re: weak firing lower cylinder 73 55hp

Re: weak firing lower cylinder 73 55hp

No one has any ideas?

 

[treemaker]

Re: weak firing lower cylinder 73 55hp

Re: weak firing lower cylinder 73 55hp

Are you sure the spark plug is good? New is not allways good.

 

[rickryder]

Re: weak firing lower cylinder 73 55hp

Re: weak firing lower cylinder 73 55hp

I even went as far as to swap the plugs between cylinders and no change....I'm baffled I'm missing something perhaps fuel related something in the reeds?

 

[rickryder]

Re: weak firing lower cylinder 73 55hp

Re: weak firing lower cylinder 73 55hp

I really need some advice on what else to look for on why this motor is running the way it does.....

 

[jerryjerry05]

Re: weak firing lower cylinder 73 55hp

Re: weak firing lower cylinder 73 55hp

Check the fuel pump diaphram.J

 

[rickryder]

Re: weak firing lower cylinder 73 55hp

Re: weak firing lower cylinder 73 55hp

Thanks for the reply Jerry. I am trying to learn about these o/b's Would the diaphram cause just 1 cylinder to miss on a single carb motor? I come from an automotive backround so this is all Greek to me

 

[tater76]

Re: weak firing lower cylinder 73 55hp

Re: weak firing lower cylinder 73 55hp

Try new condensors, I had the exact same issue. This fixed it immediately! Unfortunately, in diagnosing this problem I rebuilt the carb, fuel pump, new plugs, new points, etc to find out it was a ten dollar part!. I found mine at my local NAPA auto parts store, part# FM200. Hope that helps?

 

[rickryder]

Re: weak firing lower cylinder 76 55hp

OK an update... I was looking at the motor and really cleaned the motor tag. I was told it was a hc =73 but I found its an hg I guess that would make it a 76. I was cranking the motor over by hand and covered the single carb....seems when the #1 cyl. pulls for fuel through the Carb on intake stroke it's more than the #2 cyl.. Can someone tell me what might cause that to happen?

 

[asm_]

Re: weak firing lower cylinder 73 55hp

Re: weak firing lower cylinder 73 55hp

Keeping an eye on your thread. Don't have solution for you, but I have a very similar problem with my 82 I6. Lower two cylinders is been lazy. Sparking with good compression, but not sucking air.

By the way, you want to get one of those spark plug tester from your local auto parts store. It connect inline to the plug wire. The light bulb lights up every time the plug fires. This will allow you to tell if the plug actually firing while running.

B

 

[rickryder]

Re: weak firing lower cylinder 73 55hp

Re: weak firing lower cylinder 73 55hp

Thanks ASM

 

[Frank Acampora]

Re: weak firing lower cylinder 73 55hp

Re: weak firing lower cylinder 73 55hp

If it is a magneto or battery and points ignition engine, the first thing you need to do is pull the flywheel and clean and regap BOTH sets of points. Dirty, pitted, and improperly gapped points are probably the number one cause of misfiring. They should be set to .020 and as equally as possible since a difference of only .0015 equals one degree of timing.

Condensers rarely go bad but they can. If they show visible cracks or frayed insulation then yes, they need to be replaced. also check for an intermittent short on the kill wire (brown on the magneto ign.) for that cylinder

 

[rickryder]

Re: weak firing lower cylinder 73 55hp

Re: weak firing lower cylinder 73 55hp

I have pulled the flywheel and set up the points as per the shop manual. I have a battery/points type ignition. I am a little confused with the setting when they say to set to highest point of cam...seems the cam has a very long high spot plus the 10 degrees atdc hard to judge without the timing tool. Do I need to get that tool to get the setup correct?

 

[jtbull]

Re: weak firing lower cylinder 73 55hp

Re: weak firing lower cylinder 73 55hp

Here's my take,
Does sound like a points or condenser problem. You have eliminated all of the other components. I think you are getting spark, but it is weak. The spark should be blue and not orange. When the spark plug is under pressure, it won't spark. You could try switching the condensers and see if the problem moves to the other cylinder. Also, the coils spark at the instant the point open. By setting the gap at the highest point on the lobe you are only adjusting the spot lower on the ramp of the lobe at which the points open. The most important thing is to have both points set the same. The actual timing is set by using a dial indicator to find top dead center (TDC) and a light or buzzer to determine when the point open and adjusting the advance linkage so the points open at the specified degrees before TDC. As for the fuel issue, if one side of the reeds were bad you would get excessive blow back out of the carburetor on heavy acceleration and the good cylinder would run rich (foul out). It is possible that your lower cylinder is scored or worn at the lower part of the cylinder causing it not be able to push the fuel charge up into the combustion chamber but still show fairly good compression. Although it is unlikely that only one cylinder would be this way that, this is a problem more likely when the motor is just worn out and usually has low compression as well. I have a manual for a 1972 55 and it calls for compression of 145-155 psi. I am not a boat mechanic but have many years experience with 2 stroke motors.

Hope this helps

 

[Frank Acampora]

Re: weak firing lower cylinder 73 55hp

Re: weak firing lower cylinder 73 55hp

On those engines there is almost nothing you can do to change the timing. The link between the tower and magneto plate will only adjust about 2 degrees. If you set the points correctly, the timing will almost invariably be correct.

IF the cam has an arrow on it, the arrow needs to be UP. (flywheel direction) It may also have a mark stamped into it indicating high spot--some do, some don't

Turn the engine by hand and eyeball the points. They open rather rapidly so after they do start to open, watch for the widest gap, the high point will be there.

 

[rickryder]

Re: weak firing lower cylinder 73 55hp

Re: weak firing lower cylinder 73 55hp

Thank you guys for the info. I will be buying new points and condensers just to take them out of the equation and I will set them up again making sure they are both gapped at the same setting. I'll let you know how I make out in a few days. Thank you again for your time!

Rick

 

[tater76]

Re: weak firing lower cylinder 73 55hp

Re: weak firing lower cylinder 73 55hp

Ok, so here it is from the horses mouth, I took my boat that has a 1973 55hp Chrysler on it out last weekend. It ran great for about 5 mins then lost power, and was running on only one cylinder. Got it home and found the new condensor i had just put in was mangled. It came loose from the mount and got chewed up pretty bad, thus causing it to run on only one hole. A few weeks earlier it was running with alot of missing. I pulled the flywheel, checked for loose connections, found that one condensor wire was actually loose inside the condensor itself. When I pulled very gently on the wire going into the condensor it pulled out entirely. Seems it was hanging on by a thread. I put a new one on and it ran beautifully. Then the exact same thing happened to the other condensor on the next trip out! So don't underestimate these little guys, and pay for good quality parts! I literally just installed a new set not 15 mins ago, and its running awesome!

 

[rickryder]

Re: weak firing lower cylinder 76 55hp

OK got new points and condensers,OUCH! $126.00 did the set up by the book(oem shop manual) I have the points gapped at .015 10 degrees past the highest point of the cam. I started working on getting the timing set as per manual,throttle at WOT and adjusted the plate rod untill the points were at the exact spot when the point brake connection...ran out of daylight so back to it tomorrow. I hope this sounds like the right thing to do....I cleaned every wire connection I could find too

 

[rickryder]

Re: weak firing lower cylinder 76 55hp

OK now I'm really stumped.... I rebuilt the fuel pump,cleaned everything,new diaphram and gasket...set timing per manual and fired up motor. It sounded a little better but when I checked the 2 cylinders by grounding each one I still have the same problem big change in the top one and very little change in bottom one... Ok now where should I go ....Fuel problem? Reeds? I read a few times about puddle valves but I am unsure where they are or what they do....Could it still be a weak coil? I did the old screwdriver in the plug wire to ground to jump a spark and its not all that great maybe a 1/4 inch jump not bright blue...I am at an end here any suggestions??

 

[rickryder]

Re: weak firing lower cylinder 76 55hp

Well I'm going to take the boat out tomorrow to go crabbing. I'll see how it performs under load....still not sure if it will run well or not....I will report back on how it went...untill then if anyone has any other ideas what is causing the misfire in the #2 cylinder please post it. Thanks for all the help so far,I know we will figure it out at some point.