sounds like marbles in my top end

[blaster240R]

i have a 240 vitos big bore with a 35 pwk carb. at 3/4 to full throttle after 3rd gear i get this noise in my top end that sounds like preignition but slightly diff. when the noise gets really bad engine will stall. it will refire and noise will be gone until i do as described above. i also notice alot of unbunt gas/oil on my a-arms and exhaust flange. when its in neutral i can rev it completely out with no noise. only starts after 3rd grear and only when 3/4 to full throttle. i'm getting very frustrated and have tried many diff combos of main jets and needles. if anyone has experienced this please give me some ideas of what it might be.

 

[245stroker]

Have you done a comp test? Plug chop? I'd do a comp test to see where its at first. What are you running for a main and wheres the needle at?

 

[blaster240R]

havent done a comperssion test. i just got through the break in process. its all brand new. my carb is 35pwk 150 main, 52 pilot, dek needle on middle pos. its the weirdest thing if im just cruisin it runs fine but the second i get on it, it makes this noise. and severly affects perfomance. the longer i keep it pinned the worse it gets

 

[xmous3yx]

sounds like its beyond pre-ingnition. more like detonation u might wanna try running higher octane fuel. and do as the person above me said. and if worst comes to worst u pull ur head off and check if everything is alright(check on the marbles lol).

 

[xmous3yx]

hey i was thinking try skipping 3rd, throw it in 4th, 5th or 6th. could be a f*cked gear. lol i was just hit by the idea. i dont think this could happen but u said it was third. so u might as well give it a shot.

 

[fmxr47]

i would say try the highest octane fuel you can easily obtain in your area and try that, the higher the octane the more resistance the fuel has to detonate.

 

[fmxr47]

where abouts do you live, im from lodi area, if worst comes to worst i could take a look at it for you.

 

[blaster240R]

did a comp. check today and found comp. good at 120. maybe its a combonation of my needle and main jet not being right. its kinda hard to do a plug chop right now when i cant run it very hard at 3/4 to full throttle like you supposed to.

 

[245stroker]

on my carb I'm running the needle on the top clip with the 150 main. Have you tryed adjusting your air screw?

 

[blaster240R]

yeah i've tried that. it idles perfectly. i think i'm gonna try a cgl needl and richin up my main jet and see what happens.

 

[03blasteryfs03]

dump a lil lucas octane booster that is wat i did to mine

 

[1997blaster]

what gas you running

 

[blaster240R]

93 octane and i've tried diff.brands of gas.

 

[245stroker]

Just curious, but have you checked your reeds since the build? Almost sounds like you've got a bad reed thats fluttering in higher rpm's

 

[370]

you need to do a leakdown test on that thing.. has it done this ever since you built this engine? you may a mixture of problems here.. an airleak will lean you out... and the leaner mixture will accelerate the cylinder temp causing detonation.. trying to jet this problem away will probably not work.. so.. do a leakdown test and see what you find.. if you find nothing and that thing is sealed up tight.. then look inot the igntion system... how much advance are you running? you'll want to check the resistance in the source and pickup coils..

 

[Blasterdude27]

Just curious, but have you checked your reeds since the build? Almost sounds like you've got a bad reed thats fluttering in higher rpm's

I had that happen once.. it drove me crazy trying to figure out what it was.

 

[blaster240R]

i put new reeds in. they are ok. i've tried to go as high as a 170 main no diff. have replaced the coil and stator. 4 degrees advance. one other not if i am doing donuts in first or second gear with the throttle pinned i hear no noise. if i take off from a dead stop throttle pinned by third or fourth gear it starts and gets worse the longer you go. maybe my carb bowl is running out of fuel. maybe that screen in the petcock has some dirt or somethin on it and wont allow sufficent fuel flow.

 

[370]

how much compression do you have? whats the squish clearance?

 

[blaster240R]

compression is 120 i havent had the head cut. i put some .060 solder in there and couldnt smash it. so i should have any problems with fuel octane.

 

[370]

i highly doubt your sucking that bowl dry..

checkign the petcock screen is a pretty good idea.. but you NEED TO leakdown test that engine.. if you dont; own a leakdown tester i wrote an article on how to build one for around $20... and then i wrote another article on how to use that tool
properly