Have a 2006 Apex motor installed into a Polaris RZR UTV and the motor backfires when I let off the throttle as the engine rpm's backdown. I checked to make sure the exhaust pipes don't have any leaks, similar to having a donut gasket go bad but there isn't any leak so I have an exhaust gas temperature probe in the header pipe collector as its a four into one exhaust and the gauge reads 14.7 at start-up and goes to 15 at the high end. I was told it should be around 11.2 to 11.8 yet I get these higher readings. The header collector is 2" in diameter and I opended the exhaust silencer to a 2" inlet and 2" outlet.
My question is do I need a custom adjustable fuel management to get the motor to stop the backfire when letting off the throttle and to bring the exhaust temperature closer to the 11.2 to 11.8 EGT reading?
Any help on this issue would be appreciated.
My question is do I need a custom adjustable fuel management to get the motor to stop the backfire when letting off the throttle and to bring the exhaust temperature closer to the 11.2 to 11.8 EGT reading?
Any help on this issue would be appreciated.
yamadog1
TY 4 Stroke Junkie
fuel
i would check with allen ulmer he may be out farming, also could it be to much back pressure.
i would check with allen ulmer he may be out farming, also could it be to much back pressure.
nate007
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You've actually got too little back pressure, which is why it's going lean and popping under decel. Not a problem to deal with, but will need to do some fuel tweaking.
The factory header is approx 1 3/8", and the air box is likely more restrictive than what you have in your set-up, so it's actually flowing more air than it would originally. The sled doesn't do much at all for air flow calculations, so it's feeding your motor the same as it would in a cold environment with stock int/exh. The popping comes from unburned decel fuel igniting in your header/exhaust, and although it's kind of hard to explain, it's escaping at a higher rate and a hotter temp and igniting there.
For the time being, you could try a restrictor in the muffler to add a little backpresure, and help with the lean condition.
The factory header is approx 1 3/8", and the air box is likely more restrictive than what you have in your set-up, so it's actually flowing more air than it would originally. The sled doesn't do much at all for air flow calculations, so it's feeding your motor the same as it would in a cold environment with stock int/exh. The popping comes from unburned decel fuel igniting in your header/exhaust, and although it's kind of hard to explain, it's escaping at a higher rate and a hotter temp and igniting there.
For the time being, you could try a restrictor in the muffler to add a little backpresure, and help with the lean condition.
Wait a minute. Is the a EGT reading, or a AFR reading??????? Sounds more like AFR, which yes 11.5 to 12.5 would run very ideal. 14.7 I beleive is considered ideal for emmisions, but not for performance from a small engine. If what you are telling us is correct, and you have no exhaust leaks, than Nate's explaination is good. You could see if Ulmer could help to map a fuel controller to help correct, and richen, also you may need to get a ACV (air cut valve), so that the engine does not continue to pump excessive air on decel. I beleive that yami even has this set up on some bikes. For more reading on popping on decel, google search it on "THUMPERFAQ.com". enjoy 
FireStone
Pro
best AFR for Apex motor is 12,8 to 13,0
nate007
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A PCIII would be an easy fix for it, with lots of info available to help you tune it, so if you'd like to try that, I can create a map for you to start with and it should get you pretty close.
Not sure if you're familiar with the programming, but I'd start with a map that add 10-12% at full throttle (70-100%) in the top 10% of your rpm range, tapering to no more than 3-5% just above idle. That way you're not running so lean during decel and causing the popping.
Not sure if you're familiar with the programming, but I'd start with a map that add 10-12% at full throttle (70-100%) in the top 10% of your rpm range, tapering to no more than 3-5% just above idle. That way you're not running so lean during decel and causing the popping.
PCIII
Who makes this PCIII fuel controller? website? Also I will be replacing the Hyabusa silencer that I modified to allow less restriction with another Hyabusa silencer that hasn't been modified so it should address the back pressure issue. I have run the air intake side with a 3" diameter tube and a Donaldson air filter element and a Uni-filter to prefilter the air
I have also ran the RZR without any filter to see if I am restricting in intake with the filter and it doesn't seem to affect the performance or EGT.
Who makes this PCIII fuel controller? website? Also I will be replacing the Hyabusa silencer that I modified to allow less restriction with another Hyabusa silencer that hasn't been modified so it should address the back pressure issue. I have run the air intake side with a 3" diameter tube and a Donaldson air filter element and a Uni-filter to prefilter the air
I have also ran the RZR without any filter to see if I am restricting in intake with the filter and it doesn't seem to affect the performance or EGT.
swappped exhaust silencer
Just installed a stock Hyabusa silencer on the RZR-X project and that seems to stop the engine from backfiring when I decelerate. Guess it really was a too little back pressure with the modified Hyabusa silencer. The real test will be in the deep sand as that always calls for more HP. So far so good, it even seems to have a better low end response, just hope it doesn't fall flat in the upper rpm range. Will report the results after this weekend on the trails.
Just installed a stock Hyabusa silencer on the RZR-X project and that seems to stop the engine from backfiring when I decelerate. Guess it really was a too little back pressure with the modified Hyabusa silencer. The real test will be in the deep sand as that always calls for more HP. So far so good, it even seems to have a better low end response, just hope it doesn't fall flat in the upper rpm range. Will report the results after this weekend on the trails.
