Kim - personally I think this whole bit about removing varnish and ruining an engine is nonsense. 

I have had many older Fox 35s that were totally loaded - pistons black, exhaust port partially blocked, etc.

I ran them HARD on both Powermater 10/22 and Brodak 10/23, both 50-50 castor/synthetic blends. I NEVER had a situation where the engine performance degraded, even though they were noticeably cleaner, including the piston looking new.
In fact, ALL the engines ran better on the blend. I now use the Brodak fuel in all my engines, including my 1950 Atwood.
Whenever I break in an engine, I use the same Brodak fuel.
No problems at all.

Bob Z.

Randy,
Today this statement was made on Stuka:
 
"All fuel with castor will eventually cause varnish formation, see Randy Smith's article at the top of the engine column on the 'other forum' for a full explanation."

"All fuel with castor" includes castor/synthetic blends.  As I read your article, not only does blended oil NOT cause varnish formation, but it actually REMOVES varnish already formed from running all-castor fuel so effectively that it can ruin the compression of a heavily varnished engine.  (Obviously varnish removal won't happen instantly, but over time running the blend).

Am I reading your article correctly?

Thanks,
Kim Mortimore

Hi Kim

Yes you are reading correctly, All castor fuel will varnish up motors, part synthetic will most all times  keep the inside much cleaner, and will , most all the time will also clean the varnish that is there from castor fuels.
I have never seen a synthetic blend varnish a motor.
I have never seen a blended synthetic fuel that varnishes up an engine like all castor will.
And  doesn't matter who thinks its nonsense, the FACT is sometimes a motor that has been heavily varnished will be degraded by cleaning the varnish off of it.
I have seen this many many times over the years and it does happen. I have had a couple of my personal old engines with this problem that were heavily coated.
 You can't remove a thick coating of black burned on film from the sides of a piston and the sleeve  and  not increase clearance and decrease compression. Decreased  compression  WILL  degrade  most engine. however  this  does not mean it will happen  to all engines that are varnished...it depends on how much is in the engine.

Regards
Randy

Thanks for your replies.  I didn't intend to    but sometimes it seems unavoidable on message boards. 

  Indeed.

    BTW, even partial castor will cause some varnishing or other carbon buildup. It's just less (a lot less) than all-castor. Back in the bad old days the varnish seemed to only hurt on 049s and the like, but I can report that even on Powermaster 18% R/C fuel (castor/synthetic blend) you can get enough varnish buildup on 60-sized AAC motors that it affects the run (negatively). I had a slow power degradation on the RO-Jett, just like it was getting worn out. At Richard Oliver's suggestion, I ran a few tanks of straight synthetic through it, and it improved drastically in both power and responsiveness. I went back to my regular fuel, and it was like it was new again. If I could get a decent quality straight-synthetic fuel at the local hobby shop, that's what I would use all the time.

     Brett

Kim

There are problems with blanket statements about "all" fuels, there are synthetic blends that will not build up carbon coatings and there are some that will.
Many fuels have detergent additives in them, or packages you can buy to add to fuels. Some syn-castor blends do not have any cleaning agents in them and will slowly build carbon build ups.
 A major fuel maker for example used to use Lubricin as an additive in their fuel to help keep the engine clean inside, Lubricin is a "detergent", however with the castor of the past couple of decades it flecks castor very badly and causes major problems.
 I am personally running 10% oil content fuel that is 75% synthetic, 25% castor and has an ounce of my additive package in it .
I have a PA 40 that has a very bright shiney piston top after over 900 runs, My 51 still has mostly shiney metal with only a partial brown stain on the piston top. The sides are very clean and bright. The 51 has over 600 flights on it.
On the other hand I have also seen all synthetic fuel that was used in a 65 that does have a slight carbon build-up on it.
 So take the information and use it to help guide you through this, just remember there are no "absolutes" in fuel.

Regards
Randy

Hi Randy - I have been running a pipe mix in piped engines, 20% oil, 50-50 castor and Klotz.  This seems to give less varnish than 10-22 powermaster, which I use as a generic fuel.  Do you think the powermaster contributes to varnish formation more than others, say Sig or homebrew?  Tom H.

Hi Tom

I can't say, as I have not ran enough of their  fuel to tell one way or the other. I will tell you that with some fuels if you don't run a very rich needle, many will varnish very up badly. And  some people use a very rich setting others run hotter in a  more of a high switching 4-2 cycle. I have also seen a wet 2 cycle produce very heavy varnish, on many engines.

Regards
Randy

Hi Randy - I have been running a pipe mix in piped engines, 20% oil, 50-50 castor and Klotz.  This seems to give less varnish than 10-22 powermaster, which I use as a generic fuel.  Do you think the powermaster contributes to varnish formation more than others, say Sig or homebrew?  Tom H.

   I have run Powermaster 18% oil "Sport" fuel for quite a while, and it's not any different from SIG as far as varnishing goes. One thing that is different is the lack of a tendency to form "taters" on the plug element. It varies from engine to engine, but with SIG we were getting as little as 30 flights on a plug before the plug formed a tater and the power went over the hill. You could scrape them and see that they were carbonized black on the outside but sort a plastic-looking tan underneath. I think it's something to do with the anti-foam additive (some sort of silicone, I speculate) but with Powermaster I get almost none of it and run the same plug for a full season.

    Brett