Need help from supertuners reed valve issues!

[mountain80]

Like it says, I rebuilt my 66 cc new gaskets and seals, I run a puch head and a dellorto 16mm phbg with a rock soild reed kit. I am running a sbp pipe. I have previously ran withot the reeds with the pipe/carb/head setup for 2000 miles no problem. This is going to be a long/multiple post so hang in there.

I was running a 60 main and 40 pilot previously and I changed the main to start rich with, I believe an 80 to start. Fired it up on 20-1 oil gas mix for break in. Changed idle to #38 and 1 1/2 turns, idles smooth. W3 needle but left it on top (#1 groove) flat etc through midrange and 4 stroking blubberly on main jet. I am running a cyinder head temp gauge(cht) And the temps wer getting up around 380 f on the hill i use to provide a full pull followed by a proper plug chop. Came home plug black BUT their are light cylinder score marks- crap. Started with a new cylinder and gaskets and opened up needle to #3, nice and blubbery/safe/4 stroking. Ok no problems but I ordered newer richer needles so I sarted working on jetting the mains.
Started jetting down in small increments, plug went from black to grey and than strted seeing dark chocolate brown BUT the dark brown was only on the center porcelain and a little of the groundsrap but not on the bottom area around the threads. Watched my cht and it was making good power continued jetting down with proper plug chops then i heard a small rattle and yes when i pulled the head it was small balls of alumium off of head BUT the plug is stall chocolate brown.

Continued in next post

 

[mountain80]

I checked with Dellorto to see what their carb angles are allowed and they say 40 degrees max, I am running 30 degrees. To further add more info I have machined 2 vetical slots on the intake side of the piston aproximately 1/4 wide with a 1/4'' wide wide bridge between the 2 as well and have nice radius made by the milling cutter. I am almost running a full 360 degrees intake duration. Their are no leaks anywhere i spayed with wd40 not a single change in rpm. My problem is that the plug is not accurately showing me what is going on, the carb is clean and running perfectly but I have scored(allbeit lightly) 2 cylinders and have no idea why. Is it the piston that is causing this issue?? My head and pston show no carbon after an hour and it can't be washing from too much fuel as i jetted down and its starting to ball aluminum yet the plug (which is a new ngk b6s) shows no indication.
I do a nice cleanup/matching /blending on all my cylinders and my head runs about 160 psi cranking pressure.

I am completely stumped so if anyone can point me in the right direction or needs further info from me to help I will provide it.I am all ears as I have ground to a stop.

Thanks a bunch.

 

[mountain80]

Eureka!! some problems found. Intake port Must be machined, found the post somewhere as the top reed hits the top of intake port AND piston was incorrectly machined along with possibly too hot of sparkplug. Stay tuned.....

 

[dmb]

use a ''8'' plug. did you have full throttle on the compression test? [needs air] if your 170+psi i'd run some hi test mixed. 185+ use 100 oct. and a ''9''plug. hot plugs and hi compression dont mix. you know that! in that nice cold air it should run good once warmed up. the best intake is 180 and almost 180 transfer. with no adv/retard timing. good luck dennis

 

[mountain80]

Yes running an 8 heat range plug and yes 170 psi with throttle open on premium fuel. Will be machining a new piston this week for the intake slots, as it sits I am running 360 degree intake , by any chance are you able to translate that timing into an intake window length????

Cheers.

 

[dmb]

i'm no expert on the ht engines. but a big window in the intake on these chinese cast pistons is asking for trouble IMHO. i dont know but i think arrow went the case induction to try to save pistons and more port space vs big holes. im just guessing so leave it at that. norm at venice motor bikes does piston porting and can tell you what will last and what wont. good luck dennis

 

[mountain80]

I don't use windows I use 2 vertical slots with a 6mm bridge between the two.

 

[ivan H]

Hi, b4 doing reeds/mods I was running 75main 27.5pilot in 16mm mikuni. Now its 97.5main, 32.5pilot. If u had a 40 pilot in b4 dont go smaller, its a considerable upjet. Use starndard needle 1st, get main right @wot then pilot then needle. Plug chop with new plug, read porcelain insulator, center electrode & flat of the earth strap, it'll b darker on the curve of the strap. Nother post

 

[ivan H]

Dont read the end of the threaded portion of the plug, it'll probly b near black when its jetted right. If the porcelain insulator was grey it was already dangerously lean. Also wot CDI r u using. Stock item just keeps advancing as revs increase, & its getting much more charge into the cylinder now so u really want a CDI that retards at higher rpm. Cheers

 

[ivan H]

FWIW, I use an NGK B6HS plug 4 just running round & B7HS 4 long rides with RSE head. Havent put a compression guage on it buts its pretty Hi Comp. Rule of thumb regarding heat range it if the end 3 threads of the plug show blackening from heat ur using the right plug. The end of the threaded portion will b same sortta color. Again, use new plug 4 each plug chop, & do a plug chop 4 each area of the throttle ur trying 2 tune. I think ur way lean. Cheers

 

[ivan H]

Hi again. My ports in piston r 17mm in height. The top edge of them r 18mm down from the top edge of the piston. 9mm wide with 6mm between them 2 match 3mm widened intake port. 5mm removed from skirt 2 match. Starving up top could b mistaken for 4 stroking. I'm not familiar with the dellortto but my mikuni main went from 75 to 97.5. I cut carb side of intake port roof horizontal 2 a depth of 8.5mm, 21mm wide for upper reed clearance. Hope u get it sorted. Cheers

 

[mountain80]

Some good reading!! One question though??? Why will the plug be black if close to jetted correctly??? Why Can't the plug be read as per usual I am puzzled?? Btw I am running a stock ignition with the woodruff key machined to retard the timing 3 degrees static only as I am not able to find an aftermarket ignition right now as the jaguar cdi is sold out.... Thanks for the help so far.

 

[ivan H]

The plug is read as normal, looking for the normal chocolate/tan color, but only read the porcelain insulator, center electrode & side (earth) electrode (which will probly have darker color on the curved part). Dont read the end of the threaded portion, (which will probly b near black). Cheers