90 psi compression?

[huntxtrm]

I have a 73 rude 50 hp, I've been working on. It has set for about 6 years, outdoors. I got it sparkin on all 2 cylinders, checked compression, 90 psi or real close on both. Maybe 95. Is this too low for this motor, shouldn't it be more like 120 psi? Is it ok for the season? Am I scared for no reason? Will the compresson come up after I run it for a while, and get it used to running again? Maybe the rings are dry and not sealing good till I get some fuel in there? Please help. Oh yea and anybody know what mix this engine uses? 50:1?

 

[samo_ott]

Re: 90 psi compression?

It is 50:1

90-95 psi is not bad. it should run ok, just not stellar. You could try a de carb to try and bring it up once it's running. (search forum for links on decarbing)

 

[huntxtrm]

Re: 90 psi compression?

I appreciate it, I will search into decarbing. Thanks.

 

[R.Johnson]

Re: 90 psi compression?

Try a different valve stem in your compression guage, and see what you get. Every couple of days' we go thru compression guages', and their readings'. Try different guages' til you get a reading you like.

 

[huntxtrm]

Re: 90 psi compression?

Are you saying my gauge might be bad? What valve stem?

 

[airframer]

Re: 90 psi compression?

those gauges get sticky from humidity and what not. he's suggesting to try another to see if the outcome is the same. we go through aircraft tire gauges monthly cause of their lack of calibration.
the valve stem going from the cylinder to the gauge

 

[R.Johnson]

Re: 90 psi compression?

huntxtrm: Your guage might be reading a little high, but! than again.

 

[huntxtrm]

Re: 90 psi compression?

A little high! I hope it's reading a little low if anything. Thanks for the info, I'll buy another gauge tomorrow, could use a back up anyways. Thanks.

 

[R.Johnson]

Re: 90 psi compression?

I was joking with you about the guage, and I apologize. Every few day's a thing about compression readings' come up and the confusion never ends. Quality of the guage, cleanliness of the valve, and stem, cranking speed, seal around the screw in connector, you can go on, and on. An even reading is what you are looking for.

 

[jay_merrill]

Re: 90 psi compression?

Well, actually, 2 psi per cylinder is ok as long as the readings are even!

OK, OK, I'm kidding. Yes, you might get a bit of variation between gauges but it shouldn't be much unless you are using a very cheap or defective gauge. I like to see 100 psi or better but 90 to 95 is workable. If the values are more than 10% apart, you might feel some roughness in the engine, with the degree of that problem increasing as the spread gets higher.

 

[tashasdaddy]

Re: 90 psi compression?

this is a simple way to decarb that i use.
Decarb, take a can of seafoam put 3/4 of it in the gas tank, with only 1 gallon of premixed gas. put the rest in a spray bottle. start the engine, and let it come up to temperature. then remove plugs, and them some real good shot of seafoam into the cylinders, replace plugs, let sit 15 minutes. restart, and spray the rest of the seafoam into the carbs, so the the motor almost stalls, wait and repeat until the seafoam is gone.then take for a wide open spin. then put in new plugs, ad premixed gas to the tank, and take it for a wide open throttle spin. it is going to smoke like a house on fire, during this process.

afterwards compression.recheck

 

[patrick4266]

Re: 90 psi compression?

can i decarb in my yard without taking it for a spinI I live 30 miles from the water and I am not quiet ready to take it out yet. I still have some boat work to do.

 

[tashasdaddy]

Re: 90 psi compression?

you can, but do not rev over 1500 rpms, chance of a runaway motor. also don't do it on the drive way, as it expells uck out the exhaust.

 

[wavrider]

Re: 90 psi compression?

Pat,

I decarb in a barrel at the shop, Keep a set of good plugs as you may foul the ones you are using to decarp as can not go past 1500 rpm.

It will work just need to let it high idle for a while until the white smoke clears up, and it will smoke like a banshee.

 

[huntxtrm]

Re: 90 psi compression?

Every body want to have fun with the new guy! I appreciate the help, thanks for giving me that decarbing procedure, I'll try that. I was wondering how my sun gauge was crap. probably still going to buy a backup, mine is 20 years old. Thanks again,

 

[Ranger 330V]

Re: 90 psi compression?

hey just to ease your mind a bit...my 78 140 crossflow has 95psi on all four. pushes my 17ft bass boat 52gps...and shes not dialed in yet. That should make you feel a bit better about your reading..lol. I think i've read that some have even run down into the 80's with decent luck. good luck

 

[huntxtrm]

Re: 90 psi compression?

I appreciate the input. I am hangin this thang on my transom, gonna see what happens. Thanks.