engine question, please read.

Here's some info about the leakdown test.

The essence of a leakdown test is to determine (1) how fast compression leaks out of the combustion chamber, and (2) determine source of the leaks.

With the engine not running, air pressure is pumped through the spark plug hole into a cylinder combustion chamber.

There's a gauge that shows how fast the pressure leaks out. An engine in better condition loses pressure slower.

Generally four places where the compressed air can escape the combustion chamber.

Through a leaking (non-completely sealing) intake valve -- can hear air coming out the carb intake;

Through a leaking (non-completely sealing) exhaust valve -- can hear air coming out the exhaust;

Down past the pistons and rings -- can hear air coming out the crankcase vent;

Out a leaking or blown head gasket -- can hear air hissing past the head gasket (where leak is to outside, often where there's visible evidence of leakage, as opposed to leakage inside to the crankcase).

Where the valve clearances are correct, and compression psi test figures are within specs, there's usually not much leakage to be heard anywhere.

But where the valve clearances are correct, and compression psi test figures are lower than specs, there's usually some leakage to be heard at one or more of the four mentioned locations.

Where compression test figure is low, the technique of putting some oil through the sparkplug hole into the combustion chamber and re-testing will show either the same compression psi or a higher psi.

If the added oil causes no change, likely one of the valves isn't sealing or the head gasket is leaking or blown. But without hearing where air pressure is escaping, it's difficult to determine which valve or headgasket.

If the added oil increases psi, the valves are likely sealing okay, and the extra oil is keeping the air pressure from escaping down past worn piston and rings into the crankcase.

Imo, a leakdown test should be performed before disassembling the engine top end, as it helps to better know what you're looking for.

If a leaking head gasket is suspected, it's imo best to first re-torque the head nuts for possible quick easy remedy.

One last thing -- a fuel fouled sparkplug, even if relatively new, and sparking okay outside the cylinder, may actually be ruined beyond recovery, and should be replaced with a brand new plug.

Final last thing -- would use clear plastic tube test to determine and assure fuel level inside floatbowl is correct. A too high fuel level may cause excess richness in an otherwise perfect carb, and flood out the plug.

Good Luck!

Silly thoughts. Define "flooding out", Gas on the floor would logically indicate carb. a fouled plug,could be a tight/brnt valve, faulty coil wire/plug cap. need more info. a compression check/ leakdown/valve clearance check, would help. g

Could use more info about the oil leak and why the oil is suspected of leaking into #1 cylinder.

Good Luck!

you know I remember that we cleaned out the tank and lined it with this blue stuff not to long ago so my guess is that the tank is still clean but I'll check, thanks guys.

badboie wrote:

you know I remember that we cleaned out the tank and lined it with this blue stuff not to long ago so my guess is that the tank is still clean but I'll check, thanks guys.

The blue stuff you speak of, if not completely adhered to the inside of the tank, can get into the carbs and and cause flooding like you describe.

If you have a vacuum petcock, don't forget to check that too. It might need a rebuild to keep the fuel from constantly flowing into your carbs while parked. I know the float needle is supposed to do that but it rarely does. Just make sure there is no fuel coming out of your petcock when it is in the "on" or "res" position. "PRI" should flow gas at all times.

It it's not a vacuum petcock, nevermind! :laugh:

badboie wrote:

next thing we checked was the carbs. we found that the carb associated with that cylinder was in fact stuck open and all the carbs were dirty so we stuck them in a carb bath and did a rebuilt on all of them. Droped them back on and it ran fine for about a day or 2 and same problem showed back up.

My first guess was either a sticking float or crud at the needle face. Definitely would install inline filters, take bowls off and reclean. Polish tapered end of needles and clean floats.

FYI, crud always accumulates in the bottom of gas tanks. You need to clean them periodically.

all but one head bolt has been re-torqued to spec, the one that wasn't is because it is stripped. This bolt is for number 2 piston and is next to spark plug. We did the clear plastic tube fuel test and set it to spec. We did a compression check, all passed but number 1 barely passed, number 1 is on the low end. Should do leak down test to determine where its leaking. We have put new plugs in and it will run good for a day before it goes bad. Also number 1 cylinder starts firing at higher RPMs.