high rpm surging

jabber800

jabber800

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Joined
Jul 8, 2007
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686
Age
62
Location
Coniston Ont.
I thought I'd throw this one out to see if anyone has experienced this problem. I have a 600 SRX mod that surges at hight rpm's, it has high rpm pipes and cdi with race porting and 38mm flat slide carbs.. engine pulls great to 9400 then falls flat and picks back up after the rpm's have dropped.. It is not a clutching problem as the problem occurs on the engine dyno aswell.. Any thoughts?? We will be testing a couple ideas this week but I wouldn't mind some other thoughts on what could cause this problem.. We have already eliminated the electrics as we have tried 3 different CDI's and 2 known good stators and wiring harnesses..
 

Not enough fuel?? Or maybe too much? I had an old phazer mod that would do something similar when I swap to a psi pipe. I kept adding fuel till I ran out of jets and it got better each run, but I never did get it. Finally went back to my known set up and just rode it. I don't know, but something to think about.
 
Air fuel readings on dyno where good, but we will be trying smaller carbs this week as I think it has something to do with air flow.. Carbs or reeds.. maybe both!!
 
Cases are ported, webbing removed.. Should have decent volume but will try another set of cases with more porting after carbs and reeds..
 
When is test day? I have a call into Peter Duncanson to pick his brain over this issue. He's run every carburetor combination known to man, so I wouldn't be surprised if he ran into this issue at one time. Hopefully he calls back someday soon. :)
 
engine is out of sled and light weight parts being install.. I ordered rings for the new cylinders, should be in wed. I'll build the second engine and test at legges dyno on weekend of the 10th.. Should have a little test area aswell to dial in 60ft... I'll keep you posted...
 
jabber800 said:
I thought I'd throw this one out to see if anyone has experienced this problem. I have a 600 SRX mod that surges at hight rpm's, it has high rpm pipes and cdi with race porting and 38mm flat slide carbs.. engine pulls great to 9400 then falls flat and picks back up after the rpm's have dropped.. It is not a clutching problem as the problem occurs on the engine dyno aswell.. Any thoughts?? We will be testing a couple ideas this week but I wouldn't mind some other thoughts on what could cause this problem.. We have already eliminated the electrics as we have tried 3 different CDI's and 2 known good stators and wiring harnesses..
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What about too much port timing?
 
how do you know that the cdi is good? Are the other cdi's race ones as well?Also what about coils, I have heard of guys using high output ones and obviously you are running this thing at quite higher rpm's
 
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Dan port timing is pretty wild but I have a second set of cylinders with equal timing that ran fine on another engine so I thinking where Ok there...
Josh we tested 2 different known good electrical systems and 3 different high rpm cdi's. Justin Fuller was good enought to bring me one to test with that he had run on his 700 improver.. Tried 3 coil packs, 2 on the ice last season and one on the dyno.. Have not tried high output coils but may have to give that a shot.. Did you run at boyle on Sat??
 
asphalt track and skis had no hook on the clay but I was there.. Ask Fuller how he is coming along with making things right on my buddies 2 xr1200 turbos that went south the next time you see him, seems he never answers when they call...
 
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If I was as close as you guys are to him and having problems I'd probably drive down to his shop to get them resolved..
 
you would eh? Well dont think that we wouldnt either but there are some border concerns to deal with on that, but if this drags on much longer it will happen. There is alot of money involved.
 
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Dan, we are running stock coils on a SRX at 10600 with no issues on the dyno however, we did need to upgrade the coils on the max4's to spin 10+

Killer Josh,,,,,give cousin Luige from Chicago a call
 
Hey Josh Why you getting on me here?? I have nothing to do with this.. Never seen a 1200 turbo nor do I care to. I don't get the attitude, all I'm trying to say is sometimes you get better results when there is a problem if you talk it out face to face.. Doesn't have to get violent..
 
Dave are you running the coils in series or parallel?? I have tried both aswell as both the 99 ignition and a 2001 ignition..
 
is it something wierd w/the servo motor for the valves?? where like they open properly @ 1st (rpms come up fine) and then they close (rpms drop/go flat) and then re-open again (rpms come back)?? if the valves were closing for some reason, that would make sense that the engine drops in rpms, as the duration of the exhaust port and time area would be too small for that higher rpms?? then when the valves come back open, you get enough duration and time/area to allow the engine to turn the higher rpms??
 
dan not getting on you but there is a whole story here that is not mine to air on the internet, if you want the scoop you can call me at work.
 
jminor1 said:
dan not getting on you but there is a whole story here that is not mine to air on the internet, if you want the scoop you can call me at work.
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seems we are getting a bit off topic.....
 
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