is my compression to low

I am no way a expert, they will be here in a few minutes. What I have heard is that all cylinders should have similar compression, so you have that going for you! Not sure whether 55 is goo but you dont have one that is 10!
 I just had similar engine start up issues and mine turned out to to be the bottom end of the Marvel carb. Yep I had it off 5 times at least. Called Sandy Lake and had my Allis expert Gary G look at it. I changed the carb base, which has a small jet way down at the end of the emulsion tube and the tractor is working way way better! I had to run it on half choke to keep it from faltering when trying to accelerate. No it is very responsive!
 Don't give up the answer is there somewhere.
Regards,
 Chris

There is one small jet that I couldn't remove but it doesn't seem clogged.
I double checked for vacuum leaks, I didn't find any.

Edited by gtorick1 - 08 Jan 2015 at 5:36pm

Carburetor rebuilt? Needs tuning. The shop manual settings are only close enough to get it to run enough to allow further adjustment. Idle is often an air adjustment, needs less air.The main jet needs more fuel. A leaking intake manifold gasket makes an engine run lean.

Compression is low for an engine that new. You get a low compression reading if you only pull one plug at a time. if you don't  make sure the throttle and choke are full open, or the battery isn't fully charged.

With the rings dry and if new rings haven't seated compression will be low. With the plugs out squirt a half teaspoon of oil in each cylinder and spin it over a few seconds, then check compression again. The oil will make the rings seal better and if the compression (with all the other details above) isn't better, then the valves are suspect. Make sure the valves have clearance when closed.

Gerald J.

when you rebuilt the carb you turned the screws all the way in till they were snug. then backed them out one and a half turns. this will be a good starting point.

I will try that trick.
What's great about this and other forum web sites is that I can research all the threads that pertain to my problems so I don't have to bother the pros prematurely

always do compression test withwide open throttle

Like Gerald said, put oil in the cylinders and take a pressure reading. If the pressure comes up the rings are the problem. If it does not come up you still have valve problems.

As stated above check gas flow out the bottom of the carburetor. If you good constant flow readjust the carburetor.
O this carburetor you want to set the idle first. The engine idle RPM's are set with the stop screw on the back. In the idle circuit fuel is drawn thru thru to the engine. The idle adjustment screw adjusts for the proper amount of air to make the engine run smooth at your desired idle RPM. After the engine is running above idle you make small adjustments to as you bring the throttle lever back to the idle position. After the idle is set with choke off and lever back you then move the throttle lever to wide open. you then adjust the power jet to cause the engine to run at the highest RPM. You then turn in the power jet in until you notice a slight lower RPM. This will be the best you will get with out having the tractor under load which is not necessary unless you are going to tax the engine power.
Make sure you have the .012 clearance under the rocker arms.

The measured compression depends on the volume of air taken into the cylinder on the intake stroke. Any restrictions (air cleaner, choke, throttle) limit the flow on the intake stroke and so limits the pressure at the top of the compression stroke. If the cylinder drew a perfect vacuum of -15 psi and it only filled half way to -7.5 psi, on compression it won't make anywhere near the rated pressure.

Then when the shop manual lists a compression pressure the most consistent measuring condition is with choke and throttle full open. Choke and throttle partly closed is not a reproducible condition.

I've never seen an engine make the compression pressure on the first compression stroke, it takes a few strokes and how many is also an indication of engine condition.

When tuning a carburetor, the idle and main jet adjustments interact so it takes more than one refinement on each to get tuned right. Start with idle, then high speed/power, then idle, then high speed and repeat until neither changes. The governor will hide the effects of tuning so it has to be overridden or observed that as tuning improves it closes the throttle. Idle tuning is most effective with the throttle plate closed as much as possible by backing off the idle speed screw on the throttle shaft quadrant. That's because when the throttle plate is tightly closed the only fuel comes from the idle circuit and as the throttle plate is opened even slightly some fuel comes from the high speed jet and circuit.

Gerald J.

Dick L wrote: mattb wrote: always do compression test withwide open throttle Not throwing rocks but have read this before can no understand the theory. The question I have is if you seal a can with a lid in the house how would opening a window change anything on the inside the can.

Or an easier way to put it:

When you measure pressure with a compression tester, you're essentially doing what a tire gauge does to a tire... it compares pressure inside the tire, against pressure OUTSIDE the tire. It's not actually measuring absolute pressure, it's comparing it against atmospheric pressure.

Let's say you take a pressure reading of a sealed vessel at sea level... and the indicated pressure is 15psi. At 10,000 feet, you should still have 15psi, right? Not if the gauge you're reading, is comparing ambient pressure against the vessel... it will indicate HIGHER, because ambient pressure at 10,000 feet is much lower.

The difference of having a closed throttle is twofold:

First, it causes the engine to become a vacuum pump... it is REDUCING the ambient pressure being drawn into the cylinder. That means that the relative pressure you're measuring at the gauge, will be substantially skewed... it will read dramatically lower. A simple (but dangerous) demonstration, would be to cap off the intake of your shop air compressor and see how much it's output is affected.


Second, the throttle is not a 'consistent' device in terms of applying drag... it rattles around... so the readings you'll get, will be rather unrepeating.

Hence, the standard is to hold throttle full open when doing a compression test.