Super Jet Odd sound from a fresh motor?

[zzylstra]

I just recently finished my motor build, 718cc freestyle ported, ADA with 33cc domes, dual 44's, Cheater B pipe. And I did the proper break-in procedure, and have it tuned in pretty good. But tonight I was running it, and noticed when I was setting up wakes and "braaaping" the throttle from 1/4 to 1/2 and as soon as it started to drop RPMs, I noticed a ringing noise? didnt think it was good so went back to trailer. Idling or High RPM, the sound is not heard. ONLY when you brapp it. Kinda wierd. I eliminated the sound to the flywheel/starter area. Any suggestions to what it is? This motor was built from ground up with ALL brand new components besides hard parts (crank, rods, etc.) properly and all clearances/gaps where exact. Any help is appreciated, I dont notice any performance being affected by this sound, still rips hard. 32:1 mixture for break-in. Highs are at 1 turn out, Lows 3/4 out. Plugs have nice tan color on the electrode, and are not bathed with fuel/oil.

Thanks, Zzylstra

 

[Sospikey]

Worn bendix not retracting properly, could be midshaft bearings (probably not) or some other part that would start to rattle at certain rpms. Check the engine bay for loose parts!

 

[zzylstra]

I checked for loose bolts and stuff. It only does it when the rpms signoff from a good braap.wierd

 

[zzylstra]

Update: bednix is good nothing abnormal as far as wear or anything, did find the handlepole bolt nut wedged inbetween the gas tank and waterbox? idk if that would cause it but we will find out tomorrow night

 

[Carbon Blaster]

Found 2 issues possibly similar in sound to your noise on a couploe of skis we worked on.
One was the b-pipe chamber just hitting the side of the hull at the same rpm your refering to & sending a metalic rattling sound back to the flywheel cover area.
The 2nd was kenny keepers that are adjusted for not enough clearance & at that same rpm range would vibrate the motor in such a way that engine cradle would rattle against the kenny keeper arm & send a metallic rattle sound to the motor.
Check both these things as you rev it on the trailer to see if it could be either

 

[vomitspot]

i had pump bearings failing om me once that i could hear whispering when i let off throttle once

 

[Waternut]

Bendix may be good but is the spring in place? Letting off the throttle will sling the bendix forward into the spinning flywheel. Just a thought.

 

[zzylstra]

Found it!! chamber hitting manifold, faaauucccckkk scared me for a second

 

[Tyler Zane]

i had a similar issue with my chamber hitting the hull.

 

[sjetrider]

Anyone ever have a b-pipe headpipe rub the manifold before. I had one headpipe that did this no matter what manifold it was bolted to. Like the triple holes were drilled in the wrong freakn place causing it to be twisted inward too much and it litterally sat right on the manifold causing this same issue / sound and wearing into both the mnfld and headpipe.
I ground them down (both) to allow for more clarance and still only had about .015 clearance.
Freakn HIG $ FP and they screw them up. I really wish there were another option on pipes, evem PF relys on FB. Pour service and occasional sketchy quality. Sad thing is , because I ported the brand new headpipe the warranty is VOID!!!! Even though it was a MFR error!!!!
RANT OVER!!!

 

[Tyler Zane]

thats shatty!! ^