closed throttle fuel cut - fact or fiction?

[trepetti]

Years ago I drilled the stock exhaust on my 05. After that it began to burble on decel. Lived with it for a while, kinda liked it. But now its time to go.

I have a PCFC installed so easy fix. Added about 15% addl fuel at 0% throttle from 2500 rpm to 14000 rpm. Extra fuel lowers the exhaust temp eliminating the burble.

But wait a minute! If the ECU turns off the injectors when closing the throttle at higher than idle speeds, I am adding an additional 15% of nothing. But the burble is gone!

I believe this whole fuel cut thing is a hoax.

In all seriousness, does anyone have a theory? I was thinking of back pinning one of the injectors and hooking up the oscope, but too busy right now to futz with it.

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[TownsendsFJR1300]

My Gen 1 (2004) Yamaha FJR shop manual had a chart for fueling.

There was indeed a de-cel, "fuel cut" off for the engine (fueling map).

I suspect the FZ is the same however I've never seen a chart for it.

 

[trepetti]

My Gen 1 (2004) Yamaha FJR shop manual had a chart for fueling.

There was indeed a de-cel, "fuel cut" off for the engine (fueling map).

I suspect the FZ is the same however I've never seen a chart for it.

I am hard pressed to explain the PCFCs effect. I need to do a more controlled test by resetting the 0% throttle fueling to 0 and take a controlled ride to establish that the burble is back then re enrich that range.

but because the PCFC simply lengthens the injector pulse width of the ECU signal, if there is a fuel cut there is nothing to lengthen. I think

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[Motogiro]

I was told by my tuner(reputable) that there is cut off and you set the PCllll to overide the cutoff.

 

[TownsendsFJR1300]

The ECU re-programmers usually eliminate that de-cel issue...

No need for add on tuners as they custom tune your ECU (remove limiters, change ignition advance, etc)

 

[trepetti]

Thanks everyone, I get it. But isnt anyone else perplexed how a device that adds a percentage of current fuel can have any measurable result when the current fuel is zero? I have been tuning ecus for years (Subarus using open source RomRaider) so I understand the tech. That's why to me, the results of the fueling change doesn't jive with the fuel cut.

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[TownsendsFJR1300]

Thanks everyone, I get it. But isnt anyone else perplexed how a device that adds a percentage of current fuel can have any measurable result when the current fuel is zero? I have been tuning ecus for years (Subarus using open source RomRaider) so I understand the tech. That's why to me, the results of the fueling change doesn't jive with the fuel cut.

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Nope, doesn't bother me, nor ever thought about it.

Bike runs great, it ain't broke, just go ride....

 

[trepetti]

Nope, doesn't bother me, nor ever thought about it.

Bike runs great, it ain't broke, just go ride....

[emoji3] Yep. Except I have always needed to know why.

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[TownsendsFJR1300]

If somethings broke/ malfunctions, I'll be first to cut it up and find out why. If it isn't , I don't touch it..

Starter relay from my Yamaha F150 4 stroke OB that failed:


T&T from same engine:

 

[trepetti]

If somethings broke/ malfunctions, I'll be first to cut it up and find out why. If it isn't , I don't touch it..

Starter relay from my Yamaha F150 4 stroke OB that failed:


T&T from same engine:

I have been involved with engines since I was a kid. I was born BN, before Nintendo [emoji3] I was the neighborhood Holley guy. I would fix the neghborhood 'racers' engines after they jerked around with adjustment screws resulting is an awful off-idle transition. Once everything wenf fi, things got more complicated as you know. Trying to reduce the throttle snatch on the FZ like I did on the Subaru. https://www.highpowermedia.com/blog/2900/wall-wetting-the-tau-factor

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[TownsendsFJR1300]

Same here... I was tearing into two strokes, YZ's, Kawasaki 350 "Big horn"-cracked case, fixing transmissions, blown crank rods(the YZ's, racing MX), etc since 15.

Still am! Just resurrected a Husky, 52cc chain saw, fixing (waiting on a carb kit, today) to crank up an OLD "PARTNER" brand concrete, 2 stroke saw(never heard of till a customer brought it over), etc.....

 

[Motogiro]

The cutoff is likely a result of meeting emmissions. The tuner likened it to an accelerater pump on a carb. When you eliminate the cut off it allows the extra bit of fuel right at throttle plate opening. When you get a bike tuned your tuner may require confirmation that the bike us being used for track only.

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