9.9 powerhead swap mystery

[Duckpond]

I recently did a powerhead swap on a late 90's Force 9.9hp--found a nice one on eBay. New one starts great, idles-runs nice, revs up nicely in neutral. WON'T reach full rev under load. <br /><br />New power head come from a points-type ign. Mine was newer magneto-type. swapped plates-went together fine.<br />There is a possibilty that new p-head is off a 15hp--they're interchangeable.<br /> <br />Is there a possible problem with timimg advance between the two types of ign.? Could jetting of carb have to change? What else?

 

[12Footer]

Re: 9.9 powerhead swap mystery

Welcome to iboats, duckpond.<br /><br /><br />Could be a timing issue. But make sure the throttle plate opens fully with the helm at WOT. You can do this with the motor off in the the driveway.<br />If it is opening fully, it could be timing ,porting ,or prop pitch. The timing tracking is identical if the linkage is identical. I think carb jetting is larger on the 15 (.045"???).

 

[FlyBoyMark]

Re: 9.9 powerhead swap mystery

On these particular motors there are a 7.5 HP, 9.9 HP and 15 HP. The power heads are IDENTICLE on all. The carbs are gradualy bigger for each HP AND the induction manifold is different for each model(the reeds and forward..). These are the ONLY differences. Another words, the 7.5 HP can be converted to 15 HP by simply bolting on the 15 HP manifold/carb assembly. There are no special exhaust tuners in any of them. These motors are very strong for their class, they have a lot of cu. inch displacement and weigh only about 70 lbs.<br /> You may NOT have the HP powerhead you think you have. Only close examination of carb and manifold numbers will tell.<br />The sync of the carb and spark advance on these engines is very easy to disturb by accident. You need a manual to figger this out properly.<br /> Different jets WILL NOT increase HP, only flood the engine.