Seadoo rough low end

[JPSkier]

I have a Sea Doo 650 with a NEW SBT short block. We have gone through the break-in instructions, but still the low end is rough. It runs great when it is wound up a bit, but does not want to go slow? Any Ideas

[Bryan Glynn]

Check the condition of the rotary valve, the cover, and it's clearance.

What happened to the first engine?

Has anything been done to the carbs?

[JPSkier]

The old engine got full of sand and the oil pump failed, locking up the rear piston (after 7 years!). I did a top end and it ran for a few weeks before it threw a rod. The new engine is an SBT 650X. We replaced the rotary valve and installed two new carb kits. We installed an oil block off kit. Otherwise the carbs are stock.

I do not know anything about the rotary valve clearance. The cover seemed to be fine. We tried to follow the timing set-up from the SBT website and used a timing disc bought from SBT.
It all runs GREAT over 4000 RPM or so. It also idles fine. Its just the mid range that is rough. We need to ride out at medium speeds some of the time due to local conditions. It seems like it will stall if you don't gun it up and down until you take off.

Thanks in advance. Also, the speedo is intermittant. In don't know it that is related.

[Bryan Glynn]

What did you set pop-off to?

[Bill O'Neal]

That is a symptom of a leaky needle and seat or low pop off pressure. Make sure it pops off somewhere over at least 25 lbs, without leaking. Have you tried leaning out the low speed adjusters on the carbs?