Compression check question
 

When performing a compression check is there any way to keep fuel from being pumped into the cylinders when you have a mechanical fuel pump? I'm having a problem with fuel in my oil and do not want to add to the problem while troubleshooting it, if at all possible.
Thanks
Trueoo7

Unhook fuel line from carb, run into quart gatorade bottle. Just assuming that might be the easiest answer. That's how I primed my fuel line and made sure the tiny rubber and stainless bits that went in the tube from cutting it w/ a whiz-wheel were completely out.

Depending on your fuel line setup that may be a pain in the butt, but if it's easy, that's probably an easy solution......

Just my $.02

This is a question better suited for Thomas than me. My knowledge on the subject is rather limited compared to him. But I will take a stab at it.

I don't think too much fuel will go into the engine if you don't open the throttles when you crank the engine over. If you are really concerned, you can always disconnect the fuel line and plug it off. You need to make sure you throughly check the line fittings, JIC, SAE, Tube, etc. and then put on the appropriate plug. Of course, if your carb is working correctly, then the needle seats will have shut off the flow of fuel to the carb so I am not sure this will acomplish much either.

Of course, if your needles aren't seating, then I have seen truly outrageous amounts of fuel being dumped down the engine--maybe this is where your fuel in the oil problem is coming from.

More importantly--safety.

Be very careful not to pump raw fuel anywhere and make sure you don't have any leaks. I have seen more than my fair share of "haircuts" from leaking fuel lines, carbs catching fire and giving you an unexpected hair cut...or worse.

Soak up any raw fuel with some rags and dispose of them properly and away from any sources of ignition...water heater pilot lights, spark plugs, wires, hot parts, etc. Don't laugh, I have put out more than my fair share of engine fires, (fortunately, none of them were my fault.) I once put out a fire at BYU where an oil pressure line came apart and sprayed oil on the exhaust manifold...you wouldn't think it would have went boom, but it did. What a mess that one was. Fuel is way more dangerous than oil.

Always keep a friend and a fire extinguisher handy when working on fuel systems--and make sure it is the right kind of fire extinguisher.

Be careful and have fun. It will all be over soon and you will be driving with a big smile on your face.

David:) :) :)

Trueoo7,
Discontect the fuel inlet line and plug it. A 3/8 bolt works great. Then disable the igntion,remove fuse, disconnect the wires, ground the coil wire with a jumper wire,whatever works!! A few years ago an older gentelman I know got 3rd degree burns doing a compression test. NOT FUN!:( Safety first! Dont forget the wet test, a shot of oil to seal up the rings.:)

Thanks everybody for the suggestions. Decided to just completely disconnect the fuel line (from tank) into the fuel pump and took distributor cap completely off. Was able to do the test without incident (extinguisher was handy just in case) What I could use now is some interpetation of the results.
cyl 1 - 130
cyl 2 - 160 1st time.... 150 2nd time (I'm guessing it might of had some left over fuel in it.
cyl 3 - 135
cyl 4 - 140
cyl 5 - 137
cyl 6 - 135
cyl 7 - 135
cyl 8 - 142
Did not have time to do a wet test as cyl 7 took me about an hour to do due to the dip stick being in the way.
So for a 302 does this look OK?
Thanks again !!
Trueoo7

You shouldn't have fuel going to the cylinders.
1) The fuel pump shouldn't be able to overcome the needle and seat if the bowls are full, so pumping gas out the boosters shouldn't happen.
2) Gas shouldn't be sucked out of the boosters either, as all sparkplugs should be out so it isn't going to have any vacuum signal going to the carb with such a major vacuum leak in each cylinder.

True,

That looks pretty good to me if your engine is stock. The difference in the reading between cylinders is as or more important than the actual comression. for example my B/B reads 167 to 175 between all 8 cylinders with four of them reading 170.
My stock 289 comet reads less but all are within 12 pounds of each other and most are within 10 pounds.

Ron

Mr. Fixit,

You are right...the fuel pump shouldn't overpower the needle valve.

We have one here right now with that very problem. Seems dirt or gunk of some sort must have gotten sucked up. Who knows how as the filter is only 12 inches away...

Symptoms,

Driving along fine and dandy, and then the engine just bogs down terribly and dies no matter what you do. Sometimes you can save it and start it back up but it runs like crap. We saw it pumping fuel out of the vent tube once and filled up the carb...and then the cylinders. Out came the plugs and each cylinder sent out a geyser of fuel. (Where is the Taliban when you need them).

Later, new test drive; everything fine and running hard when a fuel air bomb goes off and sprays fuel everywhere out of the air cleaner and onto the fenders with a huge backfire. (Where's the Taliban...) Take the plugs out, pump out all the fuel from the cylinders and repeat the process.

Driving me crazy. Anyway, any suggestions? I would love to figure this one out.

Many thanks in advance for any help.

David:) :) :)

True,
The rule of thumb I remember is all cylinders within 10% of each other, and over 100 psi. So your good. I think your #2 cylinder reading is just a fluke. Back to the problem, gas in the oil. Fuel pump diaphragm is bad, change the fuel pump! ;)