Bobby Banshee Posted December 2, 2007 Report Share Posted December 2, 2007 Hey guys... My bike has 190psi compression in each cylinder. I'm running 100 octane with 20cc domes, advanced 5 degrees on the timing. I've had alot of stuff done to this bike. It has a vito 4mil crank bored 100over with a trail port. I'm having a really hard time getting the jetting right on this bike. Could this high compression be causing the problem/faking a carb issue. I have a set of 21cc domes coming so i can get the compression down. Quote Link to comment Share on other sites More sharing options...
Snopczynski Posted December 2, 2007 Report Share Posted December 2, 2007 (edited) at 190 psi, I would be running at least straight 108-112 race gas. Something here is not right though. does this bike have a spacer plate or what? How did they setup the stroker crank. There is no way it should have 190 psi with a 20cc dome. Edited December 2, 2007 by Snopczynski Quote Link to comment Share on other sites More sharing options...
Bobby Banshee Posted December 3, 2007 Author Report Share Posted December 3, 2007 at 190 psi, I would be running at least straight 108-112 race gas. Something here is not right though. does this bike have a spacer plate or what? How did they setup the stroker crank. There is no way it should have 190 psi with a 20cc dome. Kevin Jerr built my motor and it doesn't have a spacer plate. He had to special cut my domes, it has 20+2 etched on my domes. Quote Link to comment Share on other sites More sharing options...
badassbanshee479 Posted December 3, 2007 Report Share Posted December 3, 2007 did you happen to check the squish when you put it together?? did you check the comp with a couple different gauges?? what is it doing that you think its jetting? Quote Link to comment Share on other sites More sharing options...
FASTOYS Posted December 3, 2007 Report Share Posted December 3, 2007 I would call Kevin and he will get you figured out. As always , it is best to go straight to the builder... Quote Link to comment Share on other sites More sharing options...
Bobby Banshee Posted December 3, 2007 Author Report Share Posted December 3, 2007 I have talked with Kevin about the compression. He's going to send me some more domes, size 21. I asked him about the squish and he said he checked it and it was ok. I'm having low end bog issues. I've tried everything from 25 to 30 pilots and moved the needle clip several places. I've moved the time plate adjustment from 0 to 5 plus degrees, still get the same results. What issues will high compression cause??? Quote Link to comment Share on other sites More sharing options...
Snopczynski Posted December 3, 2007 Report Share Posted December 3, 2007 ok, so I would think he could figure this out. Basically you probably have 795m pistons, then he had to machine your domes 2mm. You can't just take a 20cc dome and cut it, the piston sits higher in it, so realistically it makes it about a 16cc dome if you just cut the 2mm recess. My motor guy usually just buys 16mm domes, cuts the 2 mm recess, then reshapes the entire area of the dome that's left to make it the proper cc size. So then you can get the proper compression and squish. Quote Link to comment Share on other sites More sharing options...
fixitrod Posted December 3, 2007 Report Share Posted December 3, 2007 I've had low end bog issues for a lonnnnnngggg time. I had went super lean on my pilot and it helped but not fixed. Tried several needles and at all heights. Believe it or not leaning my main helped it a ton. I was way too rich and it was screwing my bottom end. Sounds nuts, try it though. If it scares you just dont rap it out at high rpm right away. Try it at low rpm where the bog is. May or may not help... did mine and I couldn't believe it. All simple theory goes against it but when you think about it .... kind of makes since. I'm right at 190psi also. Quote Link to comment Share on other sites More sharing options...
Bobby Banshee Posted December 3, 2007 Author Report Share Posted December 3, 2007 I've got the 4mil crank with standard rod lenth not the 795 series piston. There's not a plate at the bottom of the cyclinders, Kevin said he had the domes special cut for the 4mil crank i wouldn't run into the leakage problem with that plate everyone's talking about. I've tried all kinds of different jets. Is it possible that to much compression would cause a issue that would resembles a jetting problem. Want about Pre-detonation, would that be a factor. Quote Link to comment Share on other sites More sharing options...
Snopczynski Posted December 3, 2007 Report Share Posted December 3, 2007 The only other way I can figure he did it without a spacer plate is with blaster pistons. Pre-ignition or detonation would damage the piston dome and head domes. Quote Link to comment Share on other sites More sharing options...
flotek Posted December 3, 2007 Report Share Posted December 3, 2007 I agree something is not right or calculated correctly with your setup . having 190lbs is going to reduce your peak rpms by a great deal and will be hard on bearings and as we all know the vitos cranks arent known for holding together to wel l in the first place,i would check the squish clearance and those domes for the correct trapped volume Quote Link to comment Share on other sites More sharing options...
spurdy Posted December 3, 2007 Report Share Posted December 3, 2007 The only other way I can figure he did it without a spacer plate is with blaster pistons. Pre-ignition or detonation would damage the piston dome and head domes. You can use stock pistons with a 4 mill crank if it isn't a long rod crank. Then all you have to do is run cut domes. You should only have to run 795 pistons and cut domes if your crank is 4 mill and long rod. I am pretty sure this is correct, and I believe this is what Kevin runs in his bike and offers as a 4 mill set up. Quote Link to comment Share on other sites More sharing options...
fixitrod Posted December 3, 2007 Report Share Posted December 3, 2007 You can use stock pistons with a 4 mill crank if it isn't a long rod crank. Then all you have to do is run cut domes. You should only have to run 795 pistons and cut domes if your crank is 4 mill and long rod. I am pretty sure this is correct, and I believe this is what Kevin runs in his bike and offers as a 4 mill set up. Some do use stock length rods on the 4 mil cranks. Puts some extra angle on them but it can be done. I thinks it's the 7mil that is 100% in need of longer rods. Quote Link to comment Share on other sites More sharing options...
Snopczynski Posted December 4, 2007 Report Share Posted December 4, 2007 You cant run stock pistons if you dont have a spacer plate. I have never seen someone cut a dome 4mm and then rechamber it to be the right size. This guy says he doesn't have a spacer plate. Quote Link to comment Share on other sites More sharing options...
spurdy Posted December 4, 2007 Report Share Posted December 4, 2007 (edited) You cant run stock pistons if you dont have a spacer plate. I have never seen someone cut a dome 4mm and then rechamber it to be the right size. This guy says he doesn't have a spacer plate. The connecting rod between the web is moved outward by 2mm. This changes the top dead center by 2mm as well as the bottom dead center by 2mm giving you 4mm of increased stroke. However far you move the piston at the top position is also done at the bottom position. Therefore no spacer plate is needed unless you increase the rod length as well. Please correct me if I am wrong, but I think I have this correct. Edited December 4, 2007 by spurdy Quote Link to comment Share on other sites More sharing options...
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