hey Ive got an STS .21 T Dadders mod stage II, and it just wont transition. Top end is fine, idles fine, but will NOT transition. Used brand new OS p3, and p7's. 20% trinity platinum. Mixture seems to be fine, only runs 3-5 seconds when fuel line is pinched. when throttle is applied, seems to be MEGA rich, but any leaner it quits and temps shoot up. No air leaks. Whats up?

how much fuel thru the motor ?

How much oil%? Also Have you tried changing fuel brands?

not sure how old it is. Bought it used, was Racernine.com's backup engine, told it was broken in but not raced. 12% oil. Trinity monster HP has same effect.

I'm not sure with your .21 STS but I just got the D30M STS engine and it uses a long plug and I thought I had been reading that the O.S. plugs are incorrect for it. Just a quick thought I had.

yeh stay away from the os plugs in the STS engines. you can run a MC8, and I run the OFNA/PICCO med plug in both my STS 21B and STS 30

it needs a turbo plug.

okay my guess is the motors not broken in... take the glow plug out of the motor.. then turn the motor over slowly off the end of the crankshaft.. if its sticks at TDC its not broken in.

it is broken in.

sorry about that wasn't paying attension. don't know about the os turbo plugs.

does it rotate over TDC with no plug effortlessly ? please double check, dont just assume

without the plug it rotates effortlessly...

Sell it on Ebay and get a real engine. RB Concpet, Novarossi or O.S.

I have a "real" engine. I have a Lamberto Collari by Werks and it was perfect until the piston skirt shattered (?????) new p/s on the way. The only reason I tried the STS is becuase I had it on hand...

any engine that runs and moves the car is a REAL engine, because if it works then its not fake, and if its not fake then its real.

Do the normal procedures to RTV seal your engine. This is a good practice, no matter what the engine or how many gallons it might have run through it. Always attack all air leaks and all possible causes for air leaks. Doing this will allow you to rule out certain factors (punctured fuel tanks, pierced fuel lines, engine screws not tightened properly, etc.).

While RTV sealing your engine, dismount the carb and thoroughtly inspect it. Take out all the needles and apply Associated Green Slime to the o-rings. In particular, check the LSN ant its o-rings. Does the LSN have a proper fit and feel when Green Slime is applied? Does it screw in and out normally?
Inspect the tips of all the needles and make sure they are not damaged in any manner. If any of the needles and o-rings are faulty, replace them.

Once you have done these simple things, reinstall the carb and try running it again. Does it still run away once it warms up? If so, check the LSN fit again. STS might have installed a faulty carb on your engine. The LSN hole might have been milled to big; I think teflon tape on the outer LSN o-ring could correct this. If not, try to call STS and get a replacement carb. They should send you a properly milled and machined STS big block carb.