HELP! OS .21RZ(VO1B) problem
 

Ok, here is the full detail scoop. I am not a novice, but this one just has me stumped. Any help would be greatly appreciated.

Engine: OS Max .21RZ(VO1B)

Piston/sleeve/conrod are about 3/4 gallon old.
Carb was rebuilt about 1/2 gallon ago.
30% odonnell - 280 avg race temp

During the middle of a race, the engine began acting up and has not ran right since. Here is the problem:

Engine gives indication that the LSN is set EXTREMELY rich. LSN and HSN settings were not adjusted, problem came up on its own. Acceleration from a stop is extremely sluggish, there is plenty of smoke from the exhaust, and it sounds rich. once up to speed, drives nice and has power, but much LESS power than before the problem. When at idel, or coming to a stop, the engine will not run, and stalls. Will stay running at a stand still if throttle is constantly blipped to keep the RPMS up.

Took the carb apart and inspected all parts. Everything is okay, all o rings and seals are in good order, and needles are not damaged. Replaced carb and returned needles to std race settings (2 1/2 HSN, 2 1/2 LSN). Problem is still the same. Leaned the LSN in almost completely, no change. Richened it to 4 turns out. No change.

Checked the clutch to make sure it wasnt engaging early. It wasnt, and is in good working order.

you might want to check for any air leaks.

But wouldnt an airleak cause an overly LEAN condition? Not an overly rich condition?

yes i know it happens in overylean conditions. Have you checked any of the engine parts? Is compression still strong? The v01b should be good for 5-6 gallons if tuned well. Its hard to say what is wrong with engine without being there.

yeah, compression is fine. i replace the piston/sleeve/conrod and do a carb rebuild after every race season.

Your LSN should be at 3 1/4 to 3 1/2 out and the HSN 2 1/2 out. Once you set it, you shouldn't have to turn more then a few hours. It sounds like it's lean on the top AND bottom. As SK said, it might have an air leak too. Did you seal the carb base?? How about the back plate and boost fittings?? Also, what shim/shims did you use? How are the bearings?? Dry?? When you checked the o-rings on the carb, did you use some type of grease to seal them when you put them back in??? All of these could be a cause of the way it's running. Check those things out and let us know.

i just realized that i am using an OS8 plug with 30% - could that be the problem? i am gonna retest everything in the morning after i do what everyone has suggested. i will give an update then.

Try an A5. That's what I used under any condition and had great luck with them.

Matter of fact, I got over a gallon from each A5 I used. Had over 4 gallons through the engine before I sold it. Still ran great too.

Does it feel rich all over the powerband, or just at low RPMs? That sounds pretty hot for 30%, even for that engine. Check for air leaks, seal it up anyway(it's a good idea to, anyway). Has weather changed a bit since the last time it ran well? When you accelerate hard from idle, does the engine bog, then take off at higher RPMs, or is it a "burbly" bog?

i use mc- coy mc-9 cold plug with 20% odonnell fuel.

You should NEVER run an O.S. at 280. Thats really hot, try running around 230. I wouldn't even run any of my RB's that hot. O.S's like cooler temps better anyways.

this has got to be a typo. I also have RB engines, they run cool, not hot. run about 215. all 5 of my os engines have always run hot and everyone else i talk to says the same thing. 230, and a RZ wouldnt even run it would be so rich.

Hmmm, must be the air over here. Optimum running temps for my RB's is about 240.

hmm. Mine is a RODY though, extra cooling fins may have something to do with it. 30% nitro also. and head shims.