98GTX top speed lower after new engine

[moziomek]

I finished the break in period on my first 951 SBT engine and max. speed is 13 mph lower than the 65 I had before replacing engine. I know the speedometer is not perfect but I didn't change the speed sensor wheel or the MPEM. It doesn't have the open throttle torque from a standing start like it used to. I didn't do anything with the carb. during install. Just bolted back on.

Maximum RPM is 6000. I replaced the spark plugs as directed in breakin notes and know the fuel/oil ratio is 40:1. I blocked off the oil pump and capped the small oil tubes that passed oil to the carb. What kind of pressure is seen inside those small tubes? I can't get to them now but if high pressure exists inside carb I suppose my tube caps could have blown off. I need logical things to check. Help!!

[Technical Support]

Re: 98GTX top speed lower after new engine

There is no pressure, there is vaccuum.

What caused your original engine to fail and what other repairs were made otehr than replacing the engine?

[moziomek]

Re: 98GTX top speed lower after new engine

Part of the piston broke off and knocked a couple of holes/cracks in the casing. There were metal chips in the casing and in the bottom of the hull. The reed valve assembly for that piston was totaled as well. I bought a new reed valve assembly. I pulled the cylinder section off the two pistons and the sleeves were in great shape. The failed piston head looked good except for a section gone on the non-compression side. This just seems to have flaked off. It showed no evidence of scoring due to lack of oil. I sent the engine back as a core.

I did take it to a local dealer for an estimate and he said compression was good on both cylinders but pointed out the small hole in the bottom of casing where the case oil and chips fell out. He wouldn't even quote on repair.

Extra I did:
Your tech guys recommended blocking off the oil which I did. I removed the oil pump and the linkage from the oil pump to the carb. I put caps on the two small oil tubes leading into the carbs. I used the caps that came with the block off kit. I didn't use zip tie to secure as they fit pretty snug without it. There was a 6" piece of fuel line between the two carbs that looked kinked which I replaced. I used engine alignment tool to get things back in alignment.

That's all I did.

[Technical Support]

Re: 98GTX top speed lower after new engine

Pistons don't just break - they get broken. I would suggest rebuilding your carbs as a first step, including checking pop-off pressure. Most likely your original problem is still present.