Charles, if your 420 is still running well, take care of it and don't make a move for a while. I've become very disgusted with some of the Stihl products recently and back pack blowers are one of them. We have not sold a ton of these 4mix back packs, in part because we don't push them due to problems we've seen. I think the sale count is currently6 and 4 have had authorized short blocks installed. All removed short blocks have been returned to the factory and none have we been told we errored in our determining that they were warrantly.

The 4 mix back pack is a heck of a unit when it runs right so i am hoping they correct the problem cause it has potential of being a dynamite product if they work it out. Reasonable weight, blows like Katrina, quiet and smooth, just not yet reliable.

Actually the last year of production we had maybe a 25% failure of the 420 as well. If your 420 has commercial hours on it and has over 6 months of use you prbably won't have any problems so hang on to it and take care of it so it will last until they correct the 4mix. Try to get another year out of the 420 and hopefully the 4mix problems will be resolved ny then.

I agree. I am not sold on the 4-mix either, there do seem to be reliabilty issues. The valve adjustment is not difficult but what a pain to get access to them. I recently replaced a throttle control which includes the cable and shutoff wires and it was not a fun job.Like n/v says it is a heckuva unit when it works.

Thanks for the responses. I noticed Redmax states on it's web site their backpack uses "Pure 2-cycle Technology". That, I'm sure, is directed towards STIHL. STIHL better do some real homework to correct the maintenance problem. I do like the specs for the BR600, especially the weight. It is only about a half pound heavier than the 420C. I still can't imagine how someone can know when they have reached the 139 hr point for maintenance. You would have to keep a written log of when you started and stopped the engine. That would drive anyone nuts. Charles Ranheim

I bought the BR600 in March. Tested both it and the RedMax EBZ8000. Both seems to blow about the same, which is to say a heck of alot, but the Stihl was alot quieter (sounded about 1/2 the rpms too) and felt alot lighter. I think its only 5lb lighter but it was very noticable.

I had read about the valve adjust. Many I've talked to have blown by the 139hrs with no adjustment and no problems. Heard it's relatively easy to do and Stihl sells a cheap kit with valve cover gasket and feeler gauge. Video of the simple procedure here: http://www.stihl.ca/4mix/english/stihl4mix/service1.htm

Didn't know about the "decoking" until you mentioned it. My manual says 139hrs or if required.

I plan to run it until I notice a performance problem. I run synthetic oil at 80:1 in it, and everyting else, and have had no problems in maybe 20hrs of use.

nevada_walrus: What was the short block problems you were seeing? Only problems I've heard on them was the plastic handle breaking for landscapers using trailer hangers that weren't designed for properly for them.

In short, I love it. Saves alot of time in cleanups over my handheld. At idle it moves as much air as my echo handheld. At full throttle it will move a brick across my driveway and I've got to be careful not to point directly at the ground or dirt and grass will fly.

The video shows it being done on a brushcutter which is simpler than the blower. The blower shroud could be a lot easier to deal with. We have seen a couple of cam failures which destroyed the engines.

Primarily dirt injestion caused heavy combustion chamber carbon problems along with related dirt problems in crankcase. Cause, leaky crank seals.

Our service distributor keeps saying they haven't seen it but problem units have very obvious leakage at the crank seals. Like I said, even though they keep denying seal problems, every short block has been returned for their inspection and not once have they called us to say we were wrong.

I wrote to STIHL about my concerns with the required maintenance procedures on the BR600 4Mix engine. I was told it is not a difficult thing to do (Decoke & adjust valves). The person said I did not have to take it to a dealer if I am mechanically inclined. I wrote back and asked where I could find the valve specs and the procedure to decoke the engine, because it is not in the Operator's Manual. He said the procedure is not available on the internet or in the owners manual. I would have to contact a dealer to see if he would be nice enough to order me a shop manual on how to do it maintaining the proper clearances and torque specs. So much for the first statement saying I can do it myself. These answers are turning me off on buying the BR600, even though I like STIHL products. Charles Ranheim

Seafoam would decoke that engine and clean the valves without dissassebling the entire thing

I have a BR550 and i think its a great machine. Its quiet, powerful and easy to start. I used mine about a total of 10-12 hours last year including helping my dad with his yard. Since I'm not using mine for business only personal yard clean up, it will be over 12 years before I need to perform that maintainence which is ok with me.

Ive had a br550 for 11 months now,and it just quit just working.Its under warranty but not covered.They say carbon build up has caused a burnt valve.I wish my dealer would have told me about these adjustments and maintenece.But of course I would have bought another blower instead.Forget 4 mix!!! Never again!!! Dont do it!!!