Carb (?) problems
07-04-2008 | 05:16 PM
#1
Thread Starter
Member
Squid
Joined: May 2007
Posts: 99
From: WA
Carb (?) problems
Since i got the motor rebuilt (last years lowside) I have been having issues with it surging, with choke on and riding. and it just wont run at WOT. I know my chain has a couple of suspect spots, but that obviously wont have anything to do with the surging when it is on choke (never surged on the choke before)
It was running like a raped ape, just screaming before I wrecked. I rebuilt and the only new item was the JE drop in pistons and the 4 deg advancer. (KN, Leo Vince, and moriwaki stg 1 cams with dynojet kit with the recommended 190/195 mains and needle at 5th position were in prior)
Now it will surge when the choke is on and it sounds like a rod knock when the surge happens. It also sound like a knock when taking off in first and second gear. No sounds in higher gears. I know it cant be a rod as it would do it all the time if it was. I have had the covers off 3 different times trying to push/pull/pry etc to see if I can find something, anything loose, but I cant find anything. Everything plastiguaged within specs when I put it together
I have the valve covers off again rechecking the cam timing. (yes the intakes are on the intake and exhaust on the exhaust side) I tried loosening/tightening the APE CCT's, but that does not change the knock sound.
It runs strong at 1/4, 1/2, 3/4 throttle, but as soon as I twist it to WOT it just bogs down and dies out. Doesnt matter what gear. I took it to a track day 2 weekends ago and 110 ~ 115 was as fast as I could get it. (before the speedo could hit ~140+) it ran great and pulls hard at 3/4 throttle, but at WOT it just wont go.
I pulled the carbs off again this weekend, and resprayed carb cleaner and looked at the floats (I dont have a float guage but they both drop the same amount) I have also been putting in a ounce or 2 of carb cleaner in the tank every time I fill it up, so if there was varnish, it should have been cleaned out a long time ago.
I tried covering 1/2 of the airfllter with tape to see what would happen, but it died at WOT, I then took the air filter off and it still bogged/died at WOT. The slow and mid speed circuits of the carbs seem to be working quite well, its just WOT that wont work.
I had the 4 deg advancer on it, but took it off to see if that made a difference, but it didnt.
I still have my trailer park flex pipe on the left mid pipe where it was crunched. I could see where that would be a issue at a specific rpm. But, the bike will bog at any rpm that I twist it to WOT. ie: if I punch it in first, it will be 5500rpm when it dies. If I get it up to 7000rpm at 3/4 throttle, then WOT, 7000rpm is where it dies at WOT. So I cant really see it being the exhaust doing it at a range of rpms. but it is possible I guess. (I received the wrong replacment pipe and now am waiting for the new one to come from Italy)
So, has anyone put in JE drop in pistons and experienced carb issues? or experienced any issues like mine? Id pull my hair out, but I dont have any left on top
.
It was running like a raped ape, just screaming before I wrecked. I rebuilt and the only new item was the JE drop in pistons and the 4 deg advancer. (KN, Leo Vince, and moriwaki stg 1 cams with dynojet kit with the recommended 190/195 mains and needle at 5th position were in prior)
Now it will surge when the choke is on and it sounds like a rod knock when the surge happens. It also sound like a knock when taking off in first and second gear. No sounds in higher gears. I know it cant be a rod as it would do it all the time if it was. I have had the covers off 3 different times trying to push/pull/pry etc to see if I can find something, anything loose, but I cant find anything. Everything plastiguaged within specs when I put it together
I have the valve covers off again rechecking the cam timing. (yes the intakes are on the intake and exhaust on the exhaust side) I tried loosening/tightening the APE CCT's, but that does not change the knock sound.
It runs strong at 1/4, 1/2, 3/4 throttle, but as soon as I twist it to WOT it just bogs down and dies out. Doesnt matter what gear. I took it to a track day 2 weekends ago and 110 ~ 115 was as fast as I could get it. (before the speedo could hit ~140+) it ran great and pulls hard at 3/4 throttle, but at WOT it just wont go.
I pulled the carbs off again this weekend, and resprayed carb cleaner and looked at the floats (I dont have a float guage but they both drop the same amount) I have also been putting in a ounce or 2 of carb cleaner in the tank every time I fill it up, so if there was varnish, it should have been cleaned out a long time ago.
I tried covering 1/2 of the airfllter with tape to see what would happen, but it died at WOT, I then took the air filter off and it still bogged/died at WOT. The slow and mid speed circuits of the carbs seem to be working quite well, its just WOT that wont work.
I had the 4 deg advancer on it, but took it off to see if that made a difference, but it didnt.
I still have my trailer park flex pipe on the left mid pipe where it was crunched. I could see where that would be a issue at a specific rpm. But, the bike will bog at any rpm that I twist it to WOT. ie: if I punch it in first, it will be 5500rpm when it dies. If I get it up to 7000rpm at 3/4 throttle, then WOT, 7000rpm is where it dies at WOT. So I cant really see it being the exhaust doing it at a range of rpms. but it is possible I guess. (I received the wrong replacment pipe and now am waiting for the new one to come from Italy)
So, has anyone put in JE drop in pistons and experienced carb issues? or experienced any issues like mine? Id pull my hair out, but I dont have any left on top
.
07-05-2008 | 04:07 AM
#2
Slacker
Superstock
Superstock
Joined: Jun 2005
Posts: 489
From: San Antonio, TX
1. The high compression pistons will necessitate premium fuel. Do you have 93 octane gas in the tank? If not , this could account for the "knocking" sounds you hear. This would be very BAD.
2. As for the full throttle bogging out, I would imagine that with the new pistons sucking in more air through the same carburetor with each intake stroke, thus causing an increase in air velocity, that a SMALLER MAIN JET will be needed. Other members have gone your route before, and will surely give suggestions for you. I remember reading something about mains going smaller than stock sizes? At any rate, you seem have a massive rich condition on the main jet circuit.
2. As for the full throttle bogging out, I would imagine that with the new pistons sucking in more air through the same carburetor with each intake stroke, thus causing an increase in air velocity, that a SMALLER MAIN JET will be needed. Other members have gone your route before, and will surely give suggestions for you. I remember reading something about mains going smaller than stock sizes? At any rate, you seem have a massive rich condition on the main jet circuit.
07-05-2008 | 07:03 AM
#3
Senior Member
SuperSport
SuperSport
Joined: Dec 2006
Posts: 880
From: Victoriaville, Quebec, Canada
Some plug reading would help here, a pic of the plugs after a WOT pull would tell more about your problem.
You may just run pig rich as said above, but can't explain the knock sound.
You may enter heavy detonation when you go WOT or worse pré ignition. Detonation will not bog down the engine as much as pré ignition and will generate a hell of a rattle trying to compress an already burning mixture.
Remember that the Hawk fires twice per cycle, the wasted spark 30°BTDC should not ignite any fuel, but with different cams phasing, I'll check the intake opening point to make sure it's still closed by the time the plug fires it's wasted spark.
Why at WOT, gases velocity pull more air at overlap, it sould concentrate around torque peak (highest VE)
As for the choke it make no sense with pré ignition, it may be a different problem, that make it so hard to troubleshoot.
Good luck, feel free to ask more questions I like engine dynamics.
Question, is the WOT problem worst with the choke on once you past the initial bogging ??
You may just run pig rich as said above, but can't explain the knock sound.
You may enter heavy detonation when you go WOT or worse pré ignition. Detonation will not bog down the engine as much as pré ignition and will generate a hell of a rattle trying to compress an already burning mixture.
Remember that the Hawk fires twice per cycle, the wasted spark 30°BTDC should not ignite any fuel, but with different cams phasing, I'll check the intake opening point to make sure it's still closed by the time the plug fires it's wasted spark.
Why at WOT, gases velocity pull more air at overlap, it sould concentrate around torque peak (highest VE)
As for the choke it make no sense with pré ignition, it may be a different problem, that make it so hard to troubleshoot.
Good luck, feel free to ask more questions I like engine dynamics.
Question, is the WOT problem worst with the choke on once you past the initial bogging ??
Last edited by gboezio; 07-05-2008 at 07:06 AM.
07-05-2008 | 03:09 PM
#4
Slacker
Superstock
Superstock
Joined: Jun 2005
Posts: 489
From: San Antonio, TX
one more thought
It is possible that you have the valve timing out of phase? The crankshaft turns 720 degrees in order to completely cycle the cams. The front cylinder should follow the rear by 450 degrees, but it is very possible to set the front to follow at 90 degrees crank rotation. This has been discussed more than once here in the past.
07-06-2008 | 08:56 AM
#5
Senior Member
SuperSport
SuperSport
Joined: Dec 2006
Posts: 880
From: Victoriaville, Quebec, Canada
It is possible that you have the valve timing out of phase? The crankshaft turns 720 degrees in order to completely cycle the cams. The front cylinder should follow the rear by 450 degrees, but it is very possible to set the front to follow at 90 degrees crank rotation. This has been discussed more than once here in the past.
07-06-2008 | 02:55 PM
#7
Thread Starter
Member
Squid
Joined: May 2007
Posts: 99
From: WA
Thanks for the replies.
I use premium gas all the time. I wondered about the cam timing, but IIRC, if it is out, it runs like a 1 cyl ?? It runs great untill I hit the WOT circuit on the carbs, thats when everything goes to hell in a handbasket.
I wish I had the gastester (on order) and my midpipe(on order)
I will try to go down on the main jets 1 size and see what happens.
Going WOT the shutting down and checking a plug sounds like agood idea.
I use premium gas all the time. I wondered about the cam timing, but IIRC, if it is out, it runs like a 1 cyl ?? It runs great untill I hit the WOT circuit on the carbs, thats when everything goes to hell in a handbasket.
I wish I had the gastester (on order) and my midpipe(on order)
I will try to go down on the main jets 1 size and see what happens.
Going WOT the shutting down and checking a plug sounds like agood idea.
07-07-2008 | 03:33 AM
#8
Junior Member
Squid
Joined: Jul 2008
Posts: 22
I have the same problem with WOT and still struggling to find whats wrong. I bought the bike this winter so I had no possibility to take it for a test drive and now I am not sure if the problem came with the rebuild to Street fighter or if it was there before. I have heard that the cct:s were replaced after break down by the earlier owner, and thinking that the cam timing could be wrong.
I will follow this thread closely hoping to get some good ideas!
I will follow this thread closely hoping to get some good ideas!
07-08-2008 | 05:40 PM
#9
Thread Starter
Member
Squid
Joined: May 2007
Posts: 99
From: WA
Well, I went down from 190/195 to 185/190. That helped alot, so maybe this weekend I will go down to 180/185. I will probably try to go down on the pilot jet to. I went to the dealer, and of course, there are 2 possible styles 
So progress is slowly getting made
So progress is slowly getting made
07-08-2008 | 07:19 PM
#10
Senior Member
SuperBike
Joined: Aug 2005
Posts: 1,858
From: Fort Wayne, IN
Back on topic - I had a similar thing happen one time when my cams were out 360° of crankshaft rotation. You need to check the cam timing on both heads at the same or you will never find this. I learned that the hard way!
07-08-2008 | 08:34 PM
#11
Senior Member
SuperSport
SuperSport
Joined: Dec 2006
Posts: 880
From: Victoriaville, Quebec, Canada
If you increase VE by putting an exhaust to 85 % for example, each cycle will draw an extra 50 cc of air, specially at higher rpm where the VE drops rapidly.
AS for the knocking sound, there were no harm then, a pig rich engine will not knock or pre ignite, mostly crap the plugs with carbon
Edit : I just read this thing again and I realized that it was a piston question, the pistons only don't affect the VE, induction and exhaust do.
Last edited by gboezio; 07-09-2008 at 07:42 PM.
07-09-2008 | 08:59 AM
#12
Senior Member
SuperBike
SuperBike
Joined: Jun 2007
Posts: 1,031
From: Los Angeles ish
I'm with Jamie on this. Only changing to a high compression piston won't increase the charge velocity. If anything, it would reduce it. Most high compression pistons reduce the displacement slighlty, so a 996 might be a 995. Changing the intake runners and maybe a different cam profile would be the direction I'd go.
07-19-2008 | 07:04 PM
#15
Thread Starter
Member
Squid
Joined: May 2007
Posts: 99
From: WA
Well, put 42 slow jets in. At idle, it was 2.2% co, 
but at 2500 it went down to 1.1%. so I took carbs off ~again~ and put the clips of the needle on the 6th slot (they were on the 4th) the co went to around 4% at 2500 rpm, so I left it there and went for a ride 
nice power now
It still has a knock like sound when first starting out in 1rst and 2nd gear, unless I really let the clutch slip.?
but at 2500 it went down to 1.1%. so I took carbs off ~again~ and put the clips of the needle on the 6th slot (they were on the 4th) the co went to around 4% at 2500 rpm, so I left it there and went for a ride nice power now
It still has a knock like sound when first starting out in 1rst and 2nd gear, unless I really let the clutch slip.?
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