Loping idle after cat cut.

zdrinkwine70

New Member
Hello,

Thank you for taking a look at this thread, take the information you may find helpful and use it, and post anything that may be helpful for the problem being expressed. I currently have a 2007 Yamaha FZ6 S2. I recently purchased a de-cat to go with my Delkavic slip ons. Currently the bike has Delkavic slip ons, K&N air filter, and a de-cat from Delkavic.
Upon installing the de-cat I started the bike being completely cold and during warm up it ran perfectly fine. After it was 120f the bike started to lope and the RPMS would jump maybe jump at max 100 and before when warmed up it would never do that. Another thing to add is that during installation of the de-cat, I did replace the spark plugs which were at 12,000 miles. I double checked the seat and click(seating of the spark plug cap) to make sure the bike was not misfiring and I came up with no signs that the bike was misfiring.
IÂ’m pretty in tune with my bike as far as being able to tell when somethingÂ’s wrong because itÂ’s not sounding normal. I read other threads and saw that the lack of back pressure some how makes the bike idle differently? I do have the DB-killers in the slip-ons as of right now. Another thing to add is that the bike is still very responsive throttle wise and doesnÂ’t jump RPM when held at a higher rev. With all the mods that affect air flow, would a power commander be an advised option to fix the loping idle? Does the lack of back pressure have a negative impact on performance? Is it something that IÂ’m just going to have to deal with? I might be able to tell if there was a lack of power but I live in Minnesota, so the option of riding is out of the picture for at least a month.

Thank you reading my post. Please leave a comment if you have any knowledge about this problem and if you were able to fix it .
 

TownsendsFJR1300

2007 FZ6
Site Supporter
As you noted / discovered, too much air free flow (not enough back pressure) WILL cause loping at idle.

It's smooth at start up due to the enrichment process (cold start), but once warm, the stock computer can't compensate, thus your lope..

IMO, the easiest fix would be to replace the cat (and get some back pressure in there). Opening the air box for more flow ALSO exacerbates the issue.. Simply too much air flow for the stock ECU to adjust to..

If not, an aftermarket fuel controller should help however I'm not familiar with the advanced tuning required (lower fuel mileage), etc.

IMO, KISS (keep it simple stupid). One less thing to break / adjust, etc..
 

zdrinkwine70

New Member
As you noted / discovered, too much air free flow (not enough back pressure) WILL cause loping at idle.

It's smooth at start up due to the enrichment process (cold start), but once warm, the stock computer can't compensate, thus your lope..

IMO, the easiest fix would be to replace the cat (and get some back pressure in there). Opening the air box for more flow ALSO exacerbates the issue.. Simply too much air flow for the stock ECU to adjust to..

If not, an aftermarket fuel controller should help however I'm not familiar with the advanced tuning required (lower fuel mileage), etc.

IMO, KISS (keep it simple stupid). One less thing to break / adjust, etc..

Thank you for the information! I’m just digging around trying to confirm what I thought and see what some solutions might be. Unfortunately I cannot put the cat back on because the bottom clamp closet to the headers is broken and it’s tack welded onto the cat. I know that the power commander fuel controller allows for adjustments at low, mid, and high RPMS with an increase of fuel up to 10%. I don’t know if that would help? Or to download a map onto the power commander that has slip ons and an after market air filter worked into and then adjust from there? Yeah I understand your unfamiliarity with the lower fuel mileage and how to get rid of the lope but also hit the good fuel mileage. Thank you again for your response!
 

FinalImpact

2 Da Street, Knobs R Gone
Super Moderator
Site Supporter
You said it's an S2, yes?
So you still have the cats in the header.

Two ways to solve this;
Turn all of the TB sync screws an equal amount until it idles right and then balance them if you feel the need or jumper the ECU with a wire to ground (I prefer an test lamp having an incandescent lamp), then go into diagnostic mode, CO mode and bump the C0 C1 values up equally to richen it up.

My 08 was at 0/0 and I ran them up to 25/25. You may not need to go that far. You can the details on both of these with a little search.

I also advanced the ignition from its stock 5.0° to 11.5° and mine has a lope for excessive ignition advance at idle but its so happy above 5k I just don't care!
It also has a fuel controller and S1 header so breathes pretty well cat free.

Let us know if you need more input.
 

zdrinkwine70

New Member
Makes sense! The timing is a little over my head, but definitely a consideration. The thing I know the most is the throttle body syncing. To get the TB in sync, so I first have to get the idle stable by adjusting each one equally until I reach a stable idle, but won’t it fall into a lope again when I adjust them to be in sync?

Another thing I’m curious about is that since it doesn’t bog down or lope at higher rpms could I just leave it? And would the bike not negatively impacted in the future? Will a loss of back pressure damage the bike is really what I’m asking.
 
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FinalImpact

2 Da Street, Knobs R Gone
Super Moderator
Site Supporter
The only wear item I can think of the timing chain tensioner.

The CO adjust is easy.
The sync thing, just saying if turn #1 a 1/2 turn turn them all a 1/2 turn. A quick fix.
 

zdrinkwine70

New Member
Gotcha!! Thank you so much for the helpful input I’ll defiantly look in the CO and see what that does but I’m interested to see what the throttle bodies would do to it.
 
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