Help needed: Am I running too lean ?

Discussion in 'Full Rebuilds' started by Shobos, Nov 27, 2022.

  1. Shobos

    Shobos Member

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    Hello, basically I did the 18cc hemi head mod, porting from KOR videos, airbox lid off, 1mm exhaust port raise mod on an otherwise stock blaster. I installed 260 main and did the break in but after opening throttle I think I can hear loud pinging on higher rpm's and on top of that after I come to stop and put into neutral, the blaster shoots up in rpms like its an airleak, strange thing is that when I panic and turn the ignition key off, it still revs up and take 2-3 seconds to shut off( this doesnt happen if I havent been in high rpm's prior to stopping) . I did take a look at piston through exhaust port and I believe I can see scoring on the brand new vertex piston.

    Specs of the mods
    squish distance set at 0.86mm or 33 thousands
    18 cc volume
    0.05mm piston to cyl clearance
    260 main
    gutted stock pipe
    no lid
    european 98 octane fuel wich in usa equals to 93 ? \
    premix at 32:1
    engine has all new gaskets and oil seals
    200 feet elevation, outside temp minus 5 celsius or 23 farenheit
    compression at 160 psi

    If more info needed ill try my best

    thanks in advance
     

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    Last edited: Nov 27, 2022
  2. Larry's Shee

    Larry's Shee Active Member Technician

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    First off, what fuel are you using?
    Where’d you get the 18cc spec ?
    Did you do a leak down test and heat cycles and re-torque?
    No mention of what pipe !!
    260 is way too small !!
    That’s barely enough to cover a good filter with no lid. Not to mention the cold weather. Don’t use any kind of bean oil in those temps !!
     
  3. Shobos

    Shobos Member

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    Hello Larry! Please read bottom part carefully - I mentioned all those things.
    As for the 18cc head thats what i basically came up to when I cut the dome and after reading about head rechambering I shouls be ok with 98 gasoline at 160 psi comp.
    And yes leakdown test was done and retorque too (had new crank seals and gaskets)
     
  4. Larry's Shee

    Larry's Shee Active Member Technician

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    I guess gutted stock pipe didn’t jump out to me.
    Reason I ask about your head design/specs. 160 psi is right at the edge of needing race gas or least 50/50 blend. And that squish is pretty tight. Are you sure it isn’t tighter towards the center than the outside?
    Have you done a plug chop? What plug are you using?

    The auto ignition is troubling. It indicates either a hot spot or extremely lean conditions . What size pilot and turns on air screw?
     
  5. Shobos

    Shobos Member

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    I have dismantled top end and currently redoing hemi to about 20cc's to drop down the comp. The squish part was cut at 11 degrees and confirmed its all pretty much the same towards the center(measured with solder at the side of the piston). Havent done a plug chop but will do it when I put it back together ( BR9ES plug)
    I did change to 290 main before dismantling the engine and did drive it a bit and the auto ignition was gone completely and I didnt hear any strange noises at high rpm's too.
    EDIT: one more thing I forgot to mention I have on the quad is vforce 4 reeds.
     
    Last edited: Dec 1, 2022
  6. Larry's Shee

    Larry's Shee Active Member Technician

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    What prompted you to tear it down?
     
  7. Shobos

    Shobos Member

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    To see how bad the scoring was and to increase hemi volume.
     
  8. Larry's Shee

    Larry's Shee Active Member Technician

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    I must have missed something.
    Why do you think it’s scored?
    Hope you aren’t increasing volume because of me. Or did you have symptoms of detonation ?
     
  9. Shobos

    Shobos Member

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    Have You seen the attached picture of piston trough the exhaust port? That piston has at best 50 minutes of run time. I increased volume as I was noticing some weird dings when i was in high rpms

    EDIT: after putting it back together for second time it starts dieseling( auto ignition) at max rpm after it has gotten up to running temp, luckily I was thinking fast and I slammed into 3rd gear and dumped clutch while holding the brake. As far as I understand this all points to air leak. Will update when I get do a leakdown test
     
    Last edited: Dec 6, 2022
  10. Larry's Shee

    Larry's Shee Active Member Technician

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    Small phone and old eyes don’t go together
    I thought that was just a picture of your port work. Yeah that piston doesn’t look good. What brand piston? Clearance ? Ring end gap? Fresh bore? If so, was cylinder white glove clean for assembly ?

    Picture of piston crown? Any possibility of crown material being shed as molten debris?
     
  11. Shobos

    Shobos Member

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    Piston make was Vertex (cast) piston to cyl clearance was 0.0015. forgot the exact number on the ring gap but I didnt need to adjust it ( ring gap was already set dead on in the factory) Bore wasnt fresh but I did hone the cylinder with 260 grit sandpaper using 3 leg honing tool and wd-40, cylinder had equal wear and wasnt conical or anything....I still have the same problem where it starts to auto-ignite after extended periods of WOT. Could this be caused by lean pilot circuit ? as of now I have installed 35 pilot jet as I have suspicion old one was clogged up beyond possible cleaning... I havent had time to test out this 35 pilot tho.

    EDIT: piston wasnt actually that bad... all that scoring in the picture was just oil residue lines. No melted sides or crown
     
  12. Larry's Shee

    Larry's Shee Active Member Technician

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    Out of many Wisecos over the last few years I think I only had to file rings once.
    I’ll have to read this post again because the auto ignition is bothersome
     
  13. Shobos

    Shobos Member

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    Im still struggling with the auto ignition the harder You ride it the higher the idle gets and eventually starts dieseling. I have done leakdown test again and it shows no leakage from seals or gaskets anywhere. Only thing i havent tested for air leaks is top cap on carb... Will try that next.
     
  14. Shobos

    Shobos Member

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    @Larry's Shee Might this all be caused by air leak at the exhaust flange ? I installed brand new fmf fatty with silencer but I was surprised that there is no O ring on the exhaust flange slip on part. There is unburnt oil all around the flange. Im thinking on just welding the flange onto the pipe
     
  15. Larry's Shee

    Larry's Shee Active Member Technician

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    Clean outside of flange and inside of pipe wit brake clean or something that will get the oil off. Install pipe with high heat silicone https://www.amazon.com/dp/B00ID8IUJY/?tag=jyj356j5-20
    Also what main jet are you using now? FMF calls for 270 MINIMUM !!

    Clean the carb again. Make sure to clean the main jet holder/emulsion tube. In the intake side is the passage for the pilot jet/air screw. Make sure you can blow air though it when air screw is out 1 1/2 turns.

    Far out in left field but maybe try a different plug plug. Maybe there’s a defect causing it to heat up. Something is getting too hot
     
  16. Larry's Shee

    Larry's Shee Active Member Technician

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    Sorry I took so long, things are busy right now
     
  17. Shobos

    Shobos Member

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    Carb is spotless, had it sitting in ultrasonic cleaner for a while and blew all passages. I am currently on 290 jet. I will try to make all cadb circuits rich (main jet mby 330? Raise needle, richer pilot) and I have already tried brand new spare plug but no change.

    EDIT: one thing i noticed is that it doesnt have the distinct motul 710 exhaust smell. It instead has this very eye stinging smell wich I believe is from running lean
     
    Last edited: Dec 21, 2022
  18. Shobos

    Shobos Member

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    UPDATE: problem is fixed... it turns out I was way too lean on needle and main jet, im currently at 350 main, second from bottom needle clip position, 35 pilot with 1.5 turns out and its running like champ with incredible amount of power and no auto ignition or pinging noise. I still need to fine tune main jet size but it seems im almost on the right size. Im still thinking why the heck this engine needs so much fuel ? I was looking at jetting thread and most people are 260-300 range with almost the same mods.
     

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