volvo penta 431a bad surge under load

Skybreeze

Seaman Apprentice
Joined
Jul 14, 2010
Messages
44
Hi all am new here. Found this site as I was searching for answers to my surging problem. Found alot of people having similar problems but no real posts on what was finally found to be the cause. Sorted my problem so thought it might be benificial to others as to the cause.
First the history: Boat started easily all the time, idled nicely and ran well up to about 3000 revs when it started surging. It really felt like a fuel problem. Rebuilt carb changed filters checked fuel pump. All seemed good.Took boat for a run and same problem. Checked with a timing light on all cylinders at idle and all were good. We then ran the boat till it started surging and checked all cylinders again. One cylinder was firing intermitantly causing a surge sensation. Conclusion: Coil must have been okay otherwise it wouldn't have just been one cylinder. Tried new HT lead with no difference. Changed Rotor and surge went away. Inspected old rotor against new and found that the tip had worn down on the old one. As rotor was rotating at idle there was no problem but as the speed picked up eventually the spark was unable to jump the gap inside the distributor cap and dropped off one cylinder. Why not other cylinders you ask? I would suspect that caps are not perfect so the gap for the spark to jump on that cylinder was probably slightly larger than the others. Eventually it would probably drop off on another as it wore more. So if you think that it feels like a fuel starvation problem it may well not be?
 
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