Wildcardracing Posted September 30, 2008 Report Share Posted September 30, 2008 Well, here goes. I have a 93' of a customers that I did a full build on. The bike screams, but keeps detonating and backing out the plugs. I have allready bought him one top end. I am running out of ideas on this one. The setup is as follows. Aggressive dune port 64.5mm bore Wiseco pro-lites CPI's ported cases trued/welded crank modified stator plate (was at +4, now at +0) Pro-design head w/19cc noss domes (150psi @5000') on 91octane@40:1 Squish at .045" exact billet w/p impeller Ported cages w/boyesen dual stage reeds stock carbs w/k&n pods...320mains,25pilots, 1.5 turns out, stock needles 4th clip...@65-70deg plug chop verified So far it has passed two leak down tests and held 6psi for 6+minutes, it has passed a coolant system pressure test, I have gone down one heat range on the plugs to BR9ES, I have backed the timing advance from +4 back to +0, I have tried fuel from 3 different gas stations, I have verified that the crank key is intact. The pickup gap is exactly .020". This is the fifth engine that I have setup to these exact specs, none of the other 4 have had any problems. Is there anything that I am missing. I suspect the CDI is not backing off the total advance at high rpms, but have no good CDI with the round connectors. Any help is greatly appreciated. Thanks, -slo Quote Link to comment Share on other sites More sharing options...
THE GRIM RIPPER Posted September 30, 2008 Report Share Posted September 30, 2008 Sounds like you got everything covered.... did you try a higher octane?? I'm no pro or anything but I know some shit Quote Link to comment Share on other sites More sharing options...
4stroker Posted September 30, 2008 Report Share Posted September 30, 2008 sounds like a faulty cdi, apparently it can happen. i would try a new one. maybe you could also try checking the timing with a timing light. Quote Link to comment Share on other sites More sharing options...
BellicoseBanshee Posted September 30, 2008 Report Share Posted September 30, 2008 Well, I would suspect the CDI as well. It sure sounds like everything else is in order. At that elevation, 19cc domes and +4 timing should be no problem... I am curious to hear what is causing the problem if it is not the CDI... Quote Link to comment Share on other sites More sharing options...
Wildcardracing Posted September 30, 2008 Author Report Share Posted September 30, 2008 Thanks for the input guys :thumbsup: I'm also looking into the fuel cap for propper venting. If that's not the problem, I guess we'll have to look into the CDI. If anyone else has any suggestions I'm open to them, I hate to tell the customer it's the CDI before all of the bases are covered. But, I've tried every possible cause I can think of. Most of the time when I've seen a CDI go bad the bike won't rev or won't run at all. I may even swap in some 20cc domes I have on the shelf before I conclude it's the CDI, but like I said this is one of five with the exact same setup and the other 4 have run just fine on pump premium :shrug: Quote Link to comment Share on other sites More sharing options...
lowbuckracing Posted September 30, 2008 Report Share Posted September 30, 2008 Did you jet the carbs?May need a bigger main...Had a bike do the same untill I went to bigger mains..Good luck Quote Link to comment Share on other sites More sharing options...
magz Posted September 30, 2008 Report Share Posted September 30, 2008 Did you jet the carbs?May need a bigger main...Had a bike do the same untill I went to bigger mains..Good luck sounds lean to me, i got the same setup but im running 350 jets and 25 pilot. with no problems Quote Link to comment Share on other sites More sharing options...
BellicoseBanshee Posted September 30, 2008 Report Share Posted September 30, 2008 Well, that may be a solution, for excessive heat in the combustion chamber can cause detonation. Quote Link to comment Share on other sites More sharing options...
Tim Potteiger Posted September 30, 2008 Report Share Posted September 30, 2008 I have been getting detonation running 18cc domes and +4 timing, while running 111 octane fuel. It is also tuned too rich, but yet still doing it. It doesn't make sense to anyone I have talked to. I turned my timing down to +3 and switched out to B9ES also. It seems to have cured it, but then again I only have about 2 tanks of fuel so far through it. I can't imagine why that would detonate with no timing advance. I would say go to 20cc domes if he wants to run pump gas, or go to 18cc domes and run 111. My experience with CDIs is they work or they don't. I haven't seen an in between (I am not saying it doesn't exist, i just haven't seen it). Quote Link to comment Share on other sites More sharing options...
BellicoseBanshee Posted September 30, 2008 Report Share Posted September 30, 2008 I tend to agree Tim, CDIs usually work or completely fail... :ermm: Quote Link to comment Share on other sites More sharing options...
Wildcardracing Posted October 16, 2008 Author Report Share Posted October 16, 2008 I just thought I'd post on here to say thanks to the guys who tried to help out on this one. This info may help someone. It turned out to be a faulty fuel cap not venting properly so it was starving the carbs at high rpms. It ended up costing me quite a bit of time and money, but in the end the customer was very happy. I just hope that for the $$ I lost on something that wasn't my fault, I will have earned his future business. Quote Link to comment Share on other sites More sharing options...
jbooker82 Posted October 16, 2008 Report Share Posted October 16, 2008 Glad to here you got it going. Hopefully he realizes that you went above and beyond to fix a problem that wasnt related to the work you had done. Was it a stock cap that quit venting? I took all the balls and drilled the passages out on my stocker. I now have an aftermarket clear gas cap. I just use a pice of fuel line for the vent hose. I have herd of those little gas cap vents (short vent tub with billit aluminum top) going bad and starving the engines too. josh Quote Link to comment Share on other sites More sharing options...
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