Detroit Muscle Posted April 15, 2009 Report Share Posted April 15, 2009 Okay well first off, this is going to be a long post and I'll try to keep it as simple as possible. I have an HJR built stock cylinder 4mil w/ a dune port. 35mm pwk's, 170 mains, needle in center, air screw 2 turns out, @ ~800ft elevation in SW Michigan. It's got a cool head with 25cc domes running 120psi in each cylinder. (Brand new motor with maybe 5hrs). I started out with 24cc domes set up for running premium 92 octane. I had a plug back out on me a few times, then for an unrelated issue I blew one side via a cracked piston. After talking it over with Kevin we decided that maybe it be best for me to go up to a 25cc dome to drop the compression some since I don't want to have to run 110. This dropped me from 155psi before the rebuild to 120psi after. I have since ridden it some and am still having an issue with plugs backing out. Mostly on the right side. My timing is set at +5. Today I tried some 100LL which made the bike run a little better but after only about 15-20min of riding, including 4-5 passes down our ~300ft strip I stopped to check plug tightness, the left side was tight, and the right was loose enough to spin it with a finger. I immediately called Kevin to update him that the 100octane still didn't solve the problem even with 120psi compression. There are no air leaks, the bike is seemingly running perfect save this issue. We are both stumped as to how or why this could be happening given the circumstances. I realize it is indicating detonation, but neither of us can figure out how that's possible with 120psi on 100octane. I should have time to do a squish test this evening and will post the numbers if I can, if not probably tomorrow morning. Have thought of retarding the timing a few degrees, but it doesn't seem like that could be the cause because I should be able to go to 6 or 7 even with this low of compression on 100octane. Again sorry for the long post but I'm desperate. If I've forgotten anything that you'd like to know let me know. I need ideas!! Quote Link to comment Share on other sites More sharing options...
sheefreak Posted April 15, 2009 Report Share Posted April 15, 2009 Excessive squish and oring or head gasket leak would be the two things I would be looking at next. That is assuming you don't have an air leak. There is no way you should be having this problem because of the fuel you are using w/the low compression ratio. Are these off the shelf domes I am assuming? Not something Kevin cut for you... Quote Link to comment Share on other sites More sharing options...
Dinner Posted April 15, 2009 Report Share Posted April 15, 2009 Are you tightening down the plugs properly? Stupid question I know but some people stop as it just gets snug, to only find out they haven't seated the washer yet.. Quote Link to comment Share on other sites More sharing options...
Detroit Muscle Posted April 15, 2009 Author Report Share Posted April 15, 2009 The domes are custom cut for my set up, as were the 24cc ones I had in before these. Kevin did the first ones, and I believe he had Dave Noss do these with his design. And I am tightening the plugs down the same as I always would, I am afraid of overtightening them if I go any further. Quote Link to comment Share on other sites More sharing options...
wesw Posted April 15, 2009 Report Share Posted April 15, 2009 what intakes are you running i had a motor do the same thing took timing out and blah blah it was massively lean in the mid range try raising your needle up and lowering your main down some. wont hurt to try it. Quote Link to comment Share on other sites More sharing options...
RUDEDAWG Posted April 16, 2009 Report Share Posted April 16, 2009 I am curious how much squish you ended up with, thats one of the most important #'s you should know on your motor. I have the same set-up as you except with 22cc. domes and 150 psi. @ 4800'. My squish is .040. Quote Link to comment Share on other sites More sharing options...
flotek Posted April 16, 2009 Report Share Posted April 16, 2009 do the plugs show signs of detonation ,any little flecks of aluminum and look lean ? keep in mind there is much more to detonation than static compression alone: squish clearance ,dome volume,squish band width squish angle ,ignition timing, fuel choice,exhaust port shape exhaust port height and design, plug heat range, ect.. Quote Link to comment Share on other sites More sharing options...
Detroit Muscle Posted April 16, 2009 Author Report Share Posted April 16, 2009 I am running BR8ES plugs, nothing on them, and they look good. Wet even from the 170 mains. Quote Link to comment Share on other sites More sharing options...
dlnoss Posted April 16, 2009 Report Share Posted April 16, 2009 Is it possible the timing plate, key, dyna isn't working or calibrated correctly? I would set it back to stock and try it. Maybe the +5 is really +10. Just a thought... -David Quote Link to comment Share on other sites More sharing options...
KEVSWS6 Posted April 16, 2009 Report Share Posted April 16, 2009 I'm stumped at this point. .050 squish on 120 PSI with 100 octane. It is on a rediculus 25cc dome cut at .115 depth on a 13 degree angle by NOSS. The next step was to try and set the timing to zero. Thanks for the input guys. Quote Link to comment Share on other sites More sharing options...
shee23 Posted April 16, 2009 Report Share Posted April 16, 2009 do u have a noss head? casue thats wat i have and it does the same thing to me. maybe its just the head.. not sure Quote Link to comment Share on other sites More sharing options...
KEVSWS6 Posted April 16, 2009 Report Share Posted April 16, 2009 The spark plugs actually are threaded into the domes. I have had issues with people not tightening them all the way. If you do a leak down test and air is coming out of the spark plug tighten them down until they seal up. That Quote Link to comment Share on other sites More sharing options...
jbooker82 Posted April 16, 2009 Report Share Posted April 16, 2009 Didnt Brandon (Wild Card Racing) aka slobanshee06 have a problem with detonation on a customers bike and he couldn't figure out what it was. Same type of deal only he donated a top end or two. It turnd out to be a faulty fuel cap. If you have a stock cap you might try gutting it. http://www.bansheehq.com/forums/index.php?...=101648&hl= josh Quote Link to comment Share on other sites More sharing options...
flotek Posted April 16, 2009 Report Share Posted April 16, 2009 typicaly if its starving for a steady fuel supply it will be evident on the plugs and fall of the pipe as well as hesitate at high rpms ,not saying thats not the problem here but if it was me id investigate into the electrical system more and figure out what kind of actual igntion timing your getting. :geek: it defies logic that the domes/clearance are causing the issue at this point. Quote Link to comment Share on other sites More sharing options...
dajogejr Posted April 16, 2009 Report Share Posted April 16, 2009 Has this motor been completely leak down tested. Have you tried different ignitions. Tried Fresh fuel? Taken the fuel valve out of the gas tank and checked for dirt/debris. Gut the gas cap and drill the vent tube out to .125 With those domes, angle, squish...octane and fuel will not be a problem. You should damn near be able to run it on pump gas. Is it rattling both sides out? Seeping coolant into the chamber will make it deto real quick, been there done that. Quote Link to comment Share on other sites More sharing options...
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