Help interpreting compression test results

[redart]

Hi,
STILL trying to get my '81 6hp Sea-Horse to start. Just run compression test and got the following results - top 90 psi, btm 73 psi. After I put some engine oil in each cylinder I got top 105, btm 125 ! Can anyone help me interpret these results ?. I did the tests with both spark plugs removed and I also had the carburettor off at the time. Stumped as to why it wont start! Sparks are good (over 1/4" to block), fuel should be good. Only thing I haven't been able to check is timing, but would this stop it firing completely ? Is there a way to check the timing without removing the flywheel ? I've also just tried adding some fuel directly into the cylinders and still nothing - not a pop !.

 

[tashasdaddy]

Re: Help interpreting compression test results

did you clean and rebuild the carb? http://shop2.evinrude.com/Index.aspx?s1=429c8fdd776bb2399ec4b10b79b86499&catalog_id=0&siteid=1

 

[JB]

Re: Help interpreting compression test results

Put your carb back together and back on the engine.

Go to the Top Secret File and do "Outboard won't start."

Once you get it running, do a decarb.

Compression is too uneven now. If it is still more than 10% uneven check for blown head gasket.

Do one thing at a time, mate. Finish that before starting something else.

 

[redart]

Re: Help interpreting compression test results

Put your carb back together and back on the engine.

Go to the Top Secret File and do "Outboard won't start."

Do you mean the "Why won't it start" link ? If so I've already been thru it. Only thing I haven't done so far is check the flywheel key isn't sheared. Got the nut off today and will get some sort of puller organised tomorrow. Still not sure what size bolts I need to thread into the 3 holes (see my other thread "Bolt size for 6hp flywheel puller?" - got 2 different answers so far!).

As for the carb, I've had it apart and cleaned it up. Float, bowl, main jet, idle jet, all look ok. One question regarding the main jet....when you remove it and look inside the tube there appears to be another tube inside it with a slotted head. Is this meant to come out?.

 

[redart]

Re: Help interpreting compression test results

100% stumped now. I think it's a fuel delivery problem, but I've had the carb apart and cleaned it out, and I know for certain fuel is getting up to and into the carb (clear line between fuel pump and carb inlet). I've also had the flywheel off and the key is intact, therefore timing should be ok. If I remove the spark plugs and crank the engine over several times, I would have thought if fuel was getting into the cylinders then a naked flame held to the plug ports would ignite whatever fuel was left after I stop cranking, but there's nothing there. I'm positive the main jet in the carb is clear. What's left ? Crankcase seals ?.

 

[AlTn]

Re: Help interpreting compression test results

from the site.... shop2.evinrude.com......looking at the carb diagram for a 1979 6hp...if you remove part no.29 after pumping up the bulb...fuel should come out of the bottom of the bowl. If it doesn't, you still have a problem in the float/needle valve seat area. If fuel does come out...an amount you think would indicate a full bowl...spray some fuel mix into the carb throat with both the choke butterfly and throttle butterfly open. Pull the starter slowly through a few times with the plugs out. Spray a little mix into each hole, reinsert plugs and attempt to start in a normal fashion,..choke closed and throttle in start...or as advanced as possible while in neutral. The motor should at least sputter. If it doesn't...you may have to revisit the points under the flywheel and puzzle out if they are opening at, or near, tdc.

 

[Wover98]

Re: Help interpreting compression test results

Has engine sat dormant for a long stint? You my possibly have "Frozen" reed valves. This would prevent fuel from getting to cylinders.

 

[redart]

Re: Help interpreting compression test results

from the site.... shop2.evinrude.com......looking at the carb diagram for a 1979 6hp....

Thanks again for the replies, but that's not the carb I have. Mine is like the 1981 7.5hp diagram. Also there are no points under the flywheel - it's a CD2 type ignition.

Not sure what the history of the motor is as it was bought by a friend as a non-runner and I'm fixing it (or at least trying to) for him. It looks in reasonable condition though. I've had the head off and the cylinders and piston tops look ok. How much of a job is it to inspect the reed valves ?.

 

[AlTn]

Re: Help interpreting compression test results

with a spark checker set at 1/2" you should have a bright blue spark...easiest to observe in dim light...check this first to rule out ignition problems...no chance you have the plug wires crossed?....if you have adequate spark,the motor should try to start with the spray mixture

 

[redart]

Re: Help interpreting compression test results

With a home made spark tester I have sparks able to jump 1/2", and no chance of the plug wires being crossed - they're too short to reach the wrong plugs. I've had the reed plate off and all looks fine there too. Held a business card over the inlet manifold openings to check for suction and could see it pulsing back and forth when I cranked the engine. There's definitely fuel getting to the cylinders as I can now get a pop out of them if I crank the engine with the plugs removed and then hold a naked flame to each port. I'm also getting the occasional pop when the plugs are installed, but it's still nowhere near starting. I'm at a loss as to what to try next. I'm in need of inspiration...divine or otherwise !

 

[AlTn]

Re: Help interpreting compression test results

welllllllllll....looks like it's time to rebuild the carb with a new kit...this includes removing the welch plug on top of the carb and cleaning the idle circuit holes you'll find underneath..the idle mixture screw needs to be removed and examined as well.Numerous <understatement> posts and pics of carb rebuilding are on here..then do the link and sync of the carb to ignition timing...don't throw in the towel just yet

 

[ezeke]

Re: Help interpreting compression test results

I would suggest you deal with the uneven compression first, as recommended. You may have a bad head gasket, but you should at least pull the cylinder head and check it out.

 

[Fuzzytbay]

Re: Help interpreting compression test results

I would suggest you deal with the uneven compression first, as recommended. You may have a bad head gasket, but you should at least pull the cylinder head and check it out.

If you ignore this advice, then you may just be throwing good money after bad, it won't run pretty on that uneven compression. In fact it might be a pain in the a** just to start.

 

[redart]

Re: Help interpreting compression test results

Already had the head off. Gasket was intact and the cylinders looked ok, so I put it back together re-using the old gasket for the time being. As I understand it each cylinder is independent of the other, so even though compression is uneven they should still be able to fire even if it doesn't 'run', as such. It's the complete lack of even an attempt at starting that baffles me. I have spark, I have fuel, and I have compression....that's meant to be it !.

 

[AlTn]

Re: Help interpreting compression test results

in rereading your posts....did you ever try Zephyr's suggestion of placing your motor on the ground with the carb facing up, and pouring a cup of premix down the carb throat with the throttle plate open?...you'll have to turn the flywheel over a few times, but this procedure should help cleanse the buildup out of the crankcase while helping to recoat the piston skirts and rings with some oil...it's cheap and it won't hurt it. You'll need to drain as much as possible of this mix back...from the spark plug holes as well as the carb

 

[Fuzzytbay]

Re: Help interpreting compression test results

As I understand it each cylinder is independent of the other, so even though compression is uneven they should still be able to fire even if it doesn't 'run', as such.

Uneven compression means uneven fuel mix. The low cylinder may not draw enough fuel in to even have a chance of firing. The higher pressure cylinder may splut the first time round, then get wet on the second pass. The cylinders are seperated from each other yes, by the cylinder walls and crank shaft seals. Its possible that your center crankshaft seal is also leaking, as could be the upper and lower seals, have you noticed any oily residue under the flywheel?

 

[redart]

Re: Help interpreting compression test results

Yep...cleaned it out last week by pouring fuel mix into the carb with the engine on it's back and turning it over, then draining it. No signs of oil under the flywheel so top seal should be fine. Does this suggest middle and bottom seals should be ok too ?

 

[AlTn]

Re: Help interpreting compression test results

I can't answer your seal question...if I had this engine at home, I'd get someone to observe the spark tester as I pulled the motor over several times, looking for intermittent spark. If this exist, I'd clean and tighten every ground connection. If sparks were steady and always present,I'd reinstall the spark plugs, attach the wires, and check for spark leaking to the block...a spray bottle to "mist" the wires facilitates this...as does very dim lighting.If this revealed nothing...I'd call it a day...order a head gasket...take the head back off and begin to resurface it with some #120 emory cloth on a smooth, flat surface <glass is suggested>, you move the head in a figure 8 pattern until the head surface is the same uniform color. A final polish is done with #180 grit. When that head gasket arrives, I'd install it, torque the head back down...put some 2 stroke oil in both cylinders, pull it through a couple of times, reinstall the plugs, spray fuel in the carb throat while the throttle plate is open, close the throttle plate, pull the choke on, insure the link and sync is right and pull that starter rope in full anticipation of success. If 4 or 5 attempts prove to be unsuccessful, I'd sit down and eat a popsicle and mull things over a while longer.

 

[redart]

Re: Help interpreting compression test results

Well dip me in dogs droppings....I got it running Thanks to all those who helped me get to the answer, especially those who suggested the plug wires might be reversed. They weren't, but the coils were!. Swapped the coils over and she fired up 2nd pull. Should have tried that 2 weeks ago Running pretty sweet, albeit in an esky (chilly bin) at the moment and without it's prop. Mmmm...I might just have that popsicle anyway. Thanks again to everyone. Now then....on to tuning......

 

[AlTn]

Re: Help interpreting compression test results

congratulations!!...get a head gasket, waterpump kit <check Ezeke's recent post for number>, surface that head, and "gods willin'" the remainder won't be as "trying" as getting it to start has been