My motor gets up to about 3700 bogs and dies . Started about 1200 and died but, rebuilt carbs got to about 2200 put new switch boxes now 3700 and dies????other ten rebulding the powerhead anything I can do to bring up compression
How long have you had the motor and when was the last time you decarb'd it. A SeaFoam decarb might clear some of the carbon out of the ring lands and give it a little more life.
The compression is low. These engines like to be in the 130-135 psi range. You're off more than I would like to see in a motor. The idea of even within 10% of each other is fine up to a point but if you've lost 30lbs it's going to cause a pretty significant power loss.
Unless the compression gauge you are using has been calibrated. I wouldn't take the 90psi value at its face value. All it is saying is all cylinders have about the same compression.
The carbs have been rebuilt once this year by me when I first took it out. That did not help then I put two cans of seafoam in the tank ran it for about 3hrs before I took it out. only helped that it would run up to about 2200 RPMs then die. took it to a marine machanic he rebuilt them himself and fould that they did have some clogging.After he rebuilt them now it will get to about 3700 then die. then fual pump was new last year.Will the diaphamin the pump streitch and not pump right??
If the compression is low because of normal wear and tear like it sounds then it's likely that your also not building adequate crankcase pressure. This will result in a weak pulse signal to the fuel pump and you'll simply not have enough fuel to get past the point your at now.
You can do a leak down test to check this as well as a primary compression test of the crankcase to see if this is actually the cause. If it's not, then you can eliminate that as the problem and move on with the trouble shooting. I'd highly recommend this as the next step. The procedures are in the merc service manual or you can take it to a good marine mechanic and have it done.
Squeeze the primer bulb which will 'assist' the fuel pump. If the fuel pump is limiting fuel flow then your hand should make a difference.
'Bump' the Choke to artificially richen the fuel mixture. If the fuel system is limited then adding fuel should make an improvement.
These test should prove if your problem is fuel related.
What is the WOT Ignition Timing set at?
Take along a timing light and verify WOT Timing.
Also, check that the timing light FUNCTION at WOT on EVERY CYL.
A weakening stator can limit WOT RPM as it may not be generating adequate voltage to fire the ignition at that load, yet seem to run just fine at lighter throttle settings.
Attach a DVA Meter to the stator wires and test run at speed, observe voltage raising from idle to your max RPM. What is it?
Good point Charlie, I was concentrating on the effects of low compression but a stator could also be at the root of the problem. He may just be correcting other problems as he goes and discovering new ones along the way.
