Build up on piston

[Tim kapopoulos]

Ok this is what Im running 50 cc, malossi crank 85 mill rod aluminum drr cyl slight port on exhaust .25 squish ngk 7hsa plug drr 90 pipe 21 carb 35 pilot 2 turns out 112 main needle middle 40:1 royal purple oil 101 vp mixed leaded fuel. Top of piston is real dirty about a mill thick of what looks like carbon build up. I think I need to lean out oil mixture ang go 50:1 maybe with amsoil dominator what do you think ?

[fomospede]

did you run it wide open prior to disassembly ?
if it was idled prior might have more carbon

we run 40to1

and i only look at the plug for info on burn

[Tim kapopoulos]

Yea It was run wide open we were testing roller weight and spring combos . I let it idle but I Think it's a lot especially since we were taking full throttle runs .

[woodsracer22]

leaded fuel and royal purple i say. Try some 93 superclean unleaded & Klotz R50 mixed 50 to 1

[asadad00]

The 21mm carbs on the stock 50's tend to load up on the low end and idle and choking the carb for more than a second or two will build up alot carbon quick . The stock exhaust doesn't do a great job of burning the charge fully , a good pipe will keep the piston much cleaner when tuned well. Like said above the plug is best way to read the jetting concerns, how does it run? what rpm?

[Tim kapopoulos]

Unfortunately we are restricted to the oem pipe, we run the limited class . We are allowed to interchange pipe with the apex's but not sure If its any better than the drr 90cc we curently run. It runs well launches hard stalls at 6800-7000 range pulls and shifts out at 10500 . With 4.5 rollers , 1500 spring and 782 belt with 2mill shims I get full travel with belt . Plug always looks a little lean after running a while i pull the plug cutcoff the threads to the base of the porcelain im getting a 1 to 2 mill thick band grayish in color. Heat range is correct half way discoloration on electrode. I have noticed the 21 carb is not as responsive as the 20 PE on our other drr I did this motor over with intent to make some power down low. Im just confused as to why my plug looks a little Lean but piston looks dirty.

[fomospede]

Try what woodsracer said
Atleast try an unleaded fuel

[Tim kapopoulos]

Will do. Going to first change oil brand and go from there. Its great to get some info from all you guys.
Thank you .

[woodsracer22]

Tim sent you a pm

[Woodsrunner]

I'm in the same boat Tim. I bought the 50 limited the won the national championship last year and my boy has won every woods race we entered on it plus we ran about 8 flat tracks with it. I cannot get a nice color on the plug, I have tried different oil, fuel, nothing changes. I use the same oil and fuel in two 90's and they have good plug color. If I jet to get color on the 50 it's too rich. So I just jet what it likes and run it. So far we have not had any issues but I dont like not having some color.

[woodsracer22]

There is another pipe for the 50 limited

[Tim kapopoulos]

Sent pm

[woodsracer22]

pmed you back

[woodsracer22]

pm sent

[redonkulousruntsracing]

Tim,
we always used Klotz R50 @ 50:1, and still do with straight CAM2 110 in our 50 limited, then our 50 mod and now in our 70. I don't get a build up on the piston, just a blackish discoloration on the top of it. Your DRR 90 pipe is about as good as it gets on a OEM 50 cylinder. 40:1 is too much oil in my opinion and could definitely be the cause of the build up. Is the tip of you silencer black too? As for the plug, I liked the BR8ES and BR9ES. I have never seen anyone use a 7. I am pretty sure that we pitted across from you at MX101, we will be at Capeway. I always like to jet as lean as possible, I guess that's why I keep 2-3 pistons on hand just in case I go to far, but knock on wood, I haven burned a hole in a piston yet. I remember people would think I was crazy when I told them that in my PWK 21mm that i ran a 48 pilot and a 98 main jet, but it worked for me for 3 years!

[Tim kapopoulos]

Yea that was us at mx 101 . We're leaving for cape way sat morning. See ya there . I switched to amsoil dominator and 50:1 and no more build up .