half speed

hi guys , i have a 1970 evinrude 9.5 twinstar model9022c that starts 1st pull idles good but wont rev to full rpms under load runs about half throttle ,butterfly in carb seems to be opening fully . Where should i start looking?

I would start with spark and compression test. It may be running on one cylinder.

After running at full throttle for a few minutes, shut the motor down and remove the cover. Use your hand to compare cylinder head temperatures between the top and bottom cylinders....if it is running on both cylinders, the temperatures should be almost identical. If one cylinder is not contributing (cold ), check for spark and do a compression test. While the cover is removed, try running at full throttle again...these motors are prone to exhaust leaks and any exhaust leaking under the cover will contaminate the intake mixture and cause a low power situation. If it runs better without the cover, check for an exhaust leak.

thanx for the quick replies , i will try your suggestions and get back to you

hi ,compression is only 70 lbs each cyl is that to low ?

Gauges vary a lot --------Do you have spark that will jump a gap of at least 1/4" on both leads ?

yes verygood spark taking boat out today i will write back thanx