15 May 10 14:09
If the slow down is proportional to the increased load, that may indicate that the fuel stop has been tampered with.
Erratic slow downs that I have encountered are usually fuel related. Have the fuel filters been changed lately?
An anecdote; A worker filled the fuel tank on a small diesel generator with fuel from a tank with a lot of standing water.
He got a couple of quarts of water into the fuel tank. The filter plugged and the set stopped. He correctly diagnosed the problem as a plugged fuel filter and changed the filter. The fuel pickup was still sucking water. The new filter plugged up immediately. He had just changed the filter so he "knew" that the filter was good. He then suspected the oil pressure switch and destroyed it. The over temp was the next to go. I forget what all was on the set, but he managed to destroy everything, including the remote start. Finally he found the water, cleaned the tank, changed the filter and started the set. In the next few months it turned out that the safety stops were not needed. An oil line broke.No problem, the set eventually stopped on its own. Over temp, stopped on it's own. Another oil leak, no problem it'll stop.
When the set could not be started at all, it was sent to the dealer for repairs.
The dealer evaluated the damages and then asked what our tax situation was. The repairs would cost $4600. If we were not in a position to write the repairs of against taxes a new motor could be supplied for $4000.
The moral is; Just because you have changed a filter, the fuel may be still contaminated.
This really sounds like a fuel related problem. But the motor may be failing, or you may have a cable going bad.
If you have an ammeter, see if the amps are going up above the rated output of the set when it slows down.
"Why not the best?"