Yes, one tooth off will be fairly obvious. For example, if your engine’s timing gears have 24/48 teeth, each tooth will be 15 degrees of crank rotation.
Just did a vacuum test off the carb. 10 inches at 1000rpm and 15 inches at 2000rpm. I think that is about right. I also think that eliminates a misaligned timing chain as the problem. I also put a fuel pressure gauge on it. It reads 3.5 psi at 1000rpm and 3.5 to 4 psi at 2000rpm. That seems low to me.
I just did a compression test.
- 115psi
- 105psi
- 105psi
- 105psi
I don’t know what these numbers are supposed to be, but they are all pretty even.
It is good they are close like that but they are low. More confirmation that the valve timing is off. The compression should be around 160lbs I would guess.
Would valve timing cause my timing to move around or stick at 2000rpm like its doing?
10 inches at 1000rpm is too low. With no load it should be ~15 inches from idle on up.
Have you cleaned up and lubricated the mechanical advance mechanism? The the distributor should advance the ignition timing smoothly going up and coming down in rpm.
The 10 inches at 1000 rpm (I am assuing this is no load) is way too low. Make sure you are actually on a nib that is reading manifold vacuum not venturi or ported vacuum. If the 10" is actual you do have an ignition or valve timing problem. If this has mechanical lifters, hand crank the engine over until the valve clearance on the intake of #1 starts to close up. See if that is occurring close to the specified crank angle for Intake Opening Before Top Dead Center. You may have to mark up a scale to tape to the vibration damper as a poor man’s degree wheel.
Still interested in what is going one here so continue with the postings.
The engines compression pretty much rules out “Jumped Timing” I think. Check the engine vacuum at a manifold fitting, not a carb fitting. You can check the mechanical ignition advance by turning the ROTOR with your hand…It should rotate a fair amount against it’s advance springs, then snap back when you release it…
OH!! Have you checked for an exhaust obstruction??? Right at the point where the “Raw Water” is injected into the exhaust is a FAVORITE spot for corrosion to restrict and eventually choke off exhaust flow…Open the exhaust at that point and check that the cast iron “heat exchanger” is not packed with rust…
The way I see it, the low RPMs, vacuum, and compression readings all add up to bad valve timing. I suggest you check that out.
I have already checked and lubed the mechanical advance(appears to operate correctly).
I get no vacuum at all from the manifold, only the carb. There is only one vacuum line on the motor(carb to intake).
You have the CLASSIC symptoms of exhaust restriction…This is COMMON in marine engines with their water injected exhaust pipe…Open the exhaust manifold to exhaust pipe joint and check it out…
The mechanical advance has to do with ignition timing, not valve timing. Valve timing is achieved with the proper alignment of the crank and valves that are tied together with a timing chain or belt.
Caddyman brings up a good point about the exhaust flow as being the problem but since the compression is low I still think it is a valve timing issue. I may be wrong though.
I’m getting ready to check out the timing chain. It looks like I have to remove the motor mount and the balancer to get to it, although I do not see any bolts on the balancer. Anyone know how to remove it?
Usually there is one center bolt that threads into the crankshaft.
I don’t see any bolts
From http://www.geocities.com/alberg22/motor.html ?
The propeller has several parameters to be considered, but two in particular: its diameter and its pitch. The pitch is the distance that a propeller with no slippage would advance in one full turn. These two parameters are usually expressed in inches and as “(diameter) x (pitch)”. Thus, an “8 x 7” propeller would have a diameter of 8 inches and a pitch of 7 inches.
The diameter is determined by the HP (actually, the torque, I believe) of the motor and the need to minimize drag particularly in sailboats when operating on sail.
The pitch, on the other hand, is a function of the maximum hull speed of the boat and the recommended operating RPM of the engine at maximum throttle. A pitch below optimal will cause the motor to deliver less than its maximum power at maximum throttle while a pitch above optimal will cause the motor to operate below its intended RPM (my Italics) which [in an outboard] will foul spark-plugs and fail to charge the batteries. It will also cause the boat to accelerate to maximum speed even at low throttle. This makes difficult the maneuvering of the boat at low speeds, which can only be attained by bursts of power at low throttle interspersed between intervals in neutral.
Ideally, at maximum throttle the boat should reach maximum speed and the pitch * RPM (prop) should be covering the same distance as the hull speed - or a fraction above it due to slippage of the propeller.
About this ‘maximum hull speed’ idea; the way I explain it is like this: Air is so much easier to push out of the way that you don’t see this effect until you get an airplane up to around 700 MPH. It’s called the sound barrier. With water, you can only push it out of the way so fast (depending on things like the shape of the hull and the length of the waterline) so Imagine instead of driving the boat with the engine, towing the boat instead at this maximum speed. Leave the propeller freewheeling. The water pushes on the prop, making it spin. The speed that the prop spins at this maximum hull speed is supposed to match the maximum RPM of the engine at full throttle. The way to adjust this is by varying the pitch of the propeller. It must be designed to match speeds between the hull and the engine. The key concept is that while the prop pushes on the water, the water also pushes on the prop, and fitting a propeller of too high a pitch will load down the engine. Of couse it will. No matter how powerful the engine, it is fighting the entire ocean - or, the entire mass of the water moving past the propellor, which is a lot more powerful than any engine.
Um, ya think maybe since 2008, he might have either figured it out by now or dumped the boat??? Huh?? Nothing like being late to the party, like three years late. He could be even dead by now.
Still enjoyed the thread again!
Not to be smart or anything but if you like to read old posts, there are 2015 pages of old posts dating back to 2007 for your reading pleasure. They have the usual stuff such as “car stalling”, “funny noise”, “coolant loss”, and so on but most people don’t like to wait three or four years to solve a car/boat problem.
Being ‘smart’ I was NOT the one who dredged up the post, But I even enjoyed your response!