The dreaded intake backfire cure.

Whilst I have in the past advocated advancing the static TPS set up value of .64V I still had some very rare and occasional intake backfire I have totally cured the issue recently and below is what has worked for me.

I recently had my TPS sensor fail causing an erratic very low part throttle behavior where the TPS movement was jittering between 0 and 3% when pulling away or when cruising causing backfire running lean then rich and everything in between.

Upon replacing the TPS and doing the standard TPS/ISCV set up of .60V to .74V the TPS was lagging behind throttle movement by about 1-1.5% causing the dreaded intake backfire and rough running at very low throttle movement in the 1% to 3% TPS range. To correct this issue I have through trial and error manage to sync the smallest throttle movement with TPS movement.

My static setting for the TPS is now .66V and the ISCV setting is .78V I now have instant TPS movement as soon as the throttle (and RPM) starts to increase, therefore the low speed and cruise AFR is balanced and in sync with mapping, no more intake backfire and smooth transition when rolling on the throttle during coast and cruise.

Blipping the throttle results in an increase in RPM without the dreaded backfire.

I am not professing this is a fix for all but in my case it has cured the TPS lag and the resultant backfire.

A really important element to a smooth running engine is ensuring the throttles are balanced well - spend the time to match and balance the throttles your engine will respond well.

Shared information like this is what makes this place so worthwhile.

John Miller said:

Whilst I have in the past advocated advancing the static TPS set up value of .64V I still had some very rare and occasional intake backfire I have totally cured the issue recently and below is what has worked for me.

I recently had my TPS sensor fail causing an erratic very low part throttle behavior where the TPS movement was jittering between 0 and 3% when pulling away or when cruising causing backfire running lean then rich and everything in between.

Upon replacing the TPS and doing the standard TPS/ISCV set up of .60V to .74V the TPS was lagging behind throttle movement by about 1-1.5% causing the dreaded intake backfire and rough running at very low throttle movement in the 1% to 3% TPS range. To correct this issue I have through trial and error manage to sync the smallest throttle movement with TPS movement.

My static setting for the TPS is now .66V and the ISCV setting is .78V I now have instant TPS movement as soon as the throttle (and RPM) starts to increase, therefore the low speed and cruise AFR is balanced and in sync with mapping, no more intake backfire and smooth transition when rolling on the throttle during coast and cruise.

Blipping the throttle results in an increase in RPM without the dreaded backfire.

I am not professing this is a fix for all but in my case it has cured the TPS lag and the resultant backfire.

A really important element to a smooth running engine is ensuring the throttles are balanced well - spend the time to match and balance the throttles your engine will respond well.

Click to expand...

John- for a lot of us that .60 and .74 standard setting is something we adjust as specified because, well, we're told to, but have no idea why or how it works.

I understand that you are not recommending that everyone use this particular setting- it's something that you arrived at for your bike, but can you explain what happens, or the "why," when you increase either of those values and lower vs. upper, etc.?

Btw, I believe some time ago that I also saw where @Claviger recommended another setting.

Journeyman28778 said:

John- for a lot of us that .60 and .74 standard setting is something we adjust as specified because, well, we're told to, but have no idea why or how it works.

I understand that you are not recommending that everyone use this particular setting- it's something that you arrived at for your bike, but can you explain what happens, or the "why," when you increase either of those values and lower vs. upper, etc.?

Btw, I believe some time ago that I also saw where @Claviger recommended another setting.

Click to expand...

Going slightly above .6 helps, taking some the over the top ignition advance out of the 0-5% throttle range from 1000-2500 can also help, it's lighting the mixture while overlap is occuring, then add in imperfect ecu data from desyncronized TPS sensor vs mapping vs throttle blade movement and it can create the perfect afr in the intake tract to ignite and backfire.

Raising the TPS to .64 or .66, or wherever your ECU registers the very first bit of blade rotation as actual increase in voltage, as John has done, usually fixes it completely.

Claviger said:

Going slightly above .6 helps, taking some the over the top ignition advance out of the 0-5% throttle range from 1000-2500 can also help, it's lighting the mixture while overlap is occuring, then add in imperfect ecu data from desyncronized TPS sensor vs mapping vs throttle blade movement and it can create the perfect afr in the intake tract to ignite and backfire.

Raising the TPS to .64 or .66, or wherever your ECU registers the very first bit of blade rotation as actual increase in voltage, as John has done, usually fixes it completely.

Click to expand...

I understood a fraction of what you said in the first sentence , but thanks. I'll focus on the second part for now.

Ok, maybe not- why change the second value?

Claviger said:

Going slightly above .6 helps, taking some the over the top ignition advance out of the 0-5% throttle range from 1000-2500 can also help, it's lighting the mixture while overlap is occuring, then add in imperfect ecu data from desyncronized TPS sensor vs mapping vs throttle blade movement and it can create the perfect afr in the intake tract to ignite and backfire.

Raising the TPS to .64 or .66, or wherever your ECU registers the very first bit of blade rotation as actual increase in voltage, as John has done, usually fixes it completely.

Click to expand...

Glad you're back/posting again.

Put simply as @Claviger has indicated.

By lifting the static voltage above the standard setting from .60V to .66V I have now matched/synchronized TPS movement with initial throttle blade movement.

In my case the std. .60V setting was not in sync. with throttle blade movement and the TPS was lagging - causing a hesitation / lean condition, a bit like a flat spot when you gently or slowly roll on the throttle.

I hope that explains the condition caused by an out of sync. or lagging TPS and why lifting of the std. value is necessary to correct it.

The bottom setting position on the TPS (.66V) sets the closed TPS position whilst +.12V (.78V) sets the position for the ISCV. stepper, I have always stuck to adding .12V above the bottom setting to obtain a smooth idle. this gives the stepper a range of operation above the closed throttle position to permit idle operation.


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Journeyman28778 said:

I understood a fraction of what you said in the first sentence , but thanks. I'll focus on the second part for now.

Ok, maybe not- why change the second value?

Click to expand...

This information its excellent and very specific.

The way I could explain this (from some IoT knowledge) is that you have different stepper motors

controlling the TPS, ISCV, and probably more in other places.
All those little stepper motors receive X voltage as a signal and depending on that voltage, they are supposed to turn an X amount. And because precision, material, temperature, quality, whatever, there are differences, like X voltage should make it turn Y times/degrees, but instead turn Y +/- z%.
if you want them to work correctly and synchronized as they were imagined (or maybe even just dream of because individual labor will be so expensive), you can adjust one, or both, depending on tolerance (maybe can only be adjusted w% more or less not just infinite)

Jmo
When the bike is new they set the throttle plates a little off off fully closed because they tend to stick when they r fully closed then they needed a tps value so they picked .60 volts then they wanted to open the throttle a little to a place where the ecu could
control gas to air mixture so the ecu sends signals to the stepper motor to come out till the tps reads .072 then ecu cotrols fuel keeping the motor at the desired rpm by reading the oxygen sensor and adding or subtracting fuel.
All that is great when your machine is new but mine has 53,000
So i figure my linkage is wore a little.
Now i do not know if the plates r closed or open more.
I have been thinking of doing something to mine so have been watching all these threads.
I think when u increase tps value the ecu puts more fuel and cures a lean condition making it run better..
Because of this post i tend to believe when the throttle plate linkage wears out it is opening the plates and there fore u need to add fuel (aka tps signal)

"it's lighting the mixture while overlap is occuring, then add in imperfect ecu data from desyncronized TPS sensor vs mapping vs throttle blade movement and it can create the perfect afr in the intake tract to ignite and backfire."

"I understood a fraction of what you said in the first sentence" was a compliment to @Claviger and those who understood the above, in case there was some doubt. I appreciate all the clarifications. I plan to do some tweaking soon, based on this information.