I don't think they are completely broken in even with the race prep...

From what Iv seen, u should take your carb apart n clean it, or take a carb off another b5 or star LM engine n try it out, if you have a os or ninja carb your money n u should have no problems, i really am starting to see these little micro engines have ultra sensitive carbs. We just need fuel injection haha.

If you picked up one if the race prep engines then Incan say with 100% certainy that there is absolutely nothing possibly wrong with the engine or the carburetor because it was run together. We do use our fuel and a 2058 for break in so the engine is tuned for that so you will have to adjust the tune for the configuration that you are running. What exactly does the top end breaks up mean? If you give me a more detailed description of whatmyou are seeing I'll try to help you out.

when you are at full throttle its almost a crackling sound... wont clean up... i had a guy that is very familiar with b5's mess with it and he couldnt get it to stay in tune either.. he thought maybe we had a fuel tank issue even though it was a new AE tank(lots of problems).. so i put a D8 tank on and still no better.. what are stock needle settings ?? one concern he had was the hs needle stuck out really far compared to his and others... ive never had an issue like this with any engine... purchased race prep motor to insure proper break in and now i just feel like throwing it off a bridge....

No offense but rather than feeling like throwing your engine off a bridge, just take the time to learn how to tune it. Race prep engines are jsut like RTR cars, just because the car is pre built does not mean that you dont have to know how to set it up lol. Stock needle settings are flush on the HS and flush on the LS and are where the race preps come set out of the box. So... if the HS is far out from flush as you mentioned then one of the people helping you set it there. The bottom line though is that tuning an engine is not rocket science. If the HS needle is far out from flush and the engine will not clear out on the top end then obviously the HS needle is set too rich. Just read my tuning guide on post one and set the idle gap back to where it was when you got the engine which is aproximately 0.5mm, set the HS and LS to flush and then tune from there. Right now as i mentioned you are just too rich on the HS and I would guess probably also too lean on the LS.

wht brand of fuel are you trying to run ? what glowplug ?

I must say Im impressed with the b5 so far. I bought one with a true 1 gallon on it from a fellow racer and this engines runs great. Idles awesome and has great power. I helped a guy yesterday having problems with his b5. Was kind of back firing a little when giving full throttle and would flame out often. Turned out to be the lsn was to rich and we put a new plug in it and he ran the 20 min main with no issues.

mine wont tune worth a crap, wont idle worth a damn. In about another gallon i will have a paperweight.

mine flames out repeatedly not matter how i tune.

i am will throw in my ninja carb and see if it helps.

I've had 3 stock b5's & 1 b6 as well as 2 clocked b5's & I've not had to ever use another carb. There is most likely an air leak in tank,fuel line orings somewhere . Or the usual case of the tune being off.

Problem fixed. Thanks Neil! Ur the best!

So what was wrong?

99.99 % of the time its a underlying mechanical issue causing an engine to act funny......These nitro engines are very very sensitive and it doesn't take much to throw them off.....As a rule if an engine is being picky to tune there is a underlying mechanical reason behind it....

If anyone can get the "Poster Child" of rc straightened out, it
would be you Neal.
Good job, as usual buddy.