Low end sputter, hesitation

[NHCB_imp]

So you think its ok at 11.2:1? Im new to getting into these ratio numbers so dont know what is ok or extreme. It runs great and smooth so im happy about that. I havn't gone on a long ride yet so wonder how mileage will be. I'm not looking to get the best mileage. But don't want to be stopping for fuel excessively.

[tomas_imp]

Good info here on the 02 sensor eliminator. I ordered one today to see if it makes a difference on my "13". The bike runs great, but I do have a Staintune slip-on exhaust and K&N air filter installed on it. I'll report back on how it all worked out.

[Siggy Javotnik_imp]

Zombie post: I removed my O2 eliminator (resistor) and plugged the O2 sensor cable back in to the ECU. I found that (1) the PAIR valve mod gave me the tractability gains I wanted; and (2) that, combined with the O2 eliminator made the throttle's responsiveness too soft. Not snatchy enough, for lack of better words. I'll still hold on to the eliminator -- when the O2 sensor fails (and it will), I'll probably just plug in the resistor rather than dig out and replace the expensive O2 sensor.

I'd made the mistake of doing both mods -- PAIR valve and O2 eliminator -- at the same time. Once I realized I wanted more responsiveness from the throttle, I had to choose which mod to undo. The PAIR valve is [modified after comments below and reading the service manual] causing secondary combustion in the exhaust port, which makes for a hotter engine and headers, so I'd rather leave it plugged. The only benefit I can see to taking it back to stock (unplugged) is if I lived in a really cold place and only rode 3 miles at a time -- stock, the engine would warm up quicker. [Also, less chance of fouled plugs, especially on #2 and #3. Probably not a problem with this bike, but it sure was with my '79 CB650! In short, the exhaust port and headers will heat up quicker and be hotter with the PAIR valve stock -- because it's causing secondary combustion there. If plugged, no secondary combustion, less heat].

[Pterodactyl_imp]

My understanding of the PAIR valve is that it allows ambient air into the hot exhaust ducts, via reed valves, to assist in full burning of any unburnt fuel exhausted, particularly in the overrun. Another "green initiative", so to speak. Correct me if I am wrong.

Cheers

[Gumby 1100_imp]

My understanding of the PAIR valve is that it allows ambient air into the hot exhaust ducts, via reed valves, to assist in full burning of any unburnt fuel exhausted, particularly in the overrun. Another "green initiative", so to speak. Correct me if I am wrong.

Cheers

Correct! It injects filtered air into the exhaust in order to burn off noxious emissions that were not fully burned off in the combustion chamber. It does not, as Siggy suggested, inject anything into the combustion chamber, and, as a result, the PAIR mod does not impact performance in any way. The only benefit you will experience is less decel popping and a cooler running exhaust.

[Pterodactyl_imp]

Hey Gumby, let's give ourselves a couple of cigars. .

Cheers

[Gumby 1100_imp]

Zombie post: I removed my O2 eliminator (resistor) and plugged the O2 sensor cable back in to the ECU. I found that (1) the PAIR valve mod gave me the tractability gains I wanted; and (2) that, combined with the O2 eliminator made the throttle's responsiveness too soft. Not snatchy enough, for lack of better words. I'll still hold on to the eliminator -- when the O2 sensor fails (and it will), I'll probably just plug in the resistor rather than dig out and replace the expensive O2 sensor.

I'd made the mistake of doing both mods -- PAIR valve and O2 eliminator -- at the same time. Once I realized I wanted more responsiveness from the throttle, I had to choose which mod to undo. The PAIR valve is [modified after comments below and reading the service manual] causing secondary combustion in the exhaust port, which makes for a hotter engine and headers, so I'd rather leave it plugged. The only benefit I can see to taking it back to stock (unplugged) is if I lived in a really cold place and only rode 3 miles at a time -- stock, the engine would warm up quicker. [Also, less chance of fouled plugs, especially on #2 and #3. Probably not a problem with this bike, but it sure was with my '79 CB650! In short, the exhaust port and headers will heat up quicker and be hotter with the PAIR valve stock -- because it's causing secondary combustion there. If plugged, no secondary combustion, less heat].

No problem, but I think what may have gotten you off course could have been confusing the PAIR system with the EGR (Exhaust Gas Re-circulation) systems that carbureted cars used to use.

If you check your service manual, you can see the plumbing required for the PAIR system to take filtered air from your air box (not super-heated exhaust), then inject it into the heads AFTER the exhaust valve. This clean, relatively cool, oxygenated air, when mixed with the heat of the exhaust, helps to burn off the noxious fumes the EPA is worried about. This burning (actually small explosions) takes place in the exhaust, which is the reason for decel popping.

After seeing how the PAIR system works, it should also be the case that doing the PAIR Valve Mod would have little to no effect on how fast your engine warms up (other than the exhaust system getting hotter with the PAIR system functioning). The use of the O2 Sensor Eliminator Plug, however, may affect warm-up time as it should richen the mix at idle and low end. Then, after the engine is running well, the richer mix should actually allow the engine to run cooler and more efficiently (but, not 'efficiently' according to the EPA!)

[Siggy Javotnik_imp]

Thank you for walking me through that, and referring me to the service manual! Some kind soul posted the PAIR valve page on this site, here: http://i.imgur.com/cSu7e1X.jpg

On the CB600 forum, I also found this explanation, which made sense and explained popping on decelleration: "The system only activates under negative load (throttle down). this would not [a]ffect throttle up operation, which is what dyno tuners tune to, sooooo........"
In other words, unless I mind the popping from the Yoshimura slip-on that came with the bike (I don't) or am concerned about engine heat it's fine to just leave the valve as-is. And, of course, my idea that blocking the PAIR valve affected throttle smoothness doesn't make sense. The one way I've found to do that is the O2 eliminator, which has the fueling effects outlined expertly by Gumby 1100. This forum is great for this kind of knowledge, thank you!

p.s. Gumby was right, I have dealt with 1980's era automotive EGR. Although modern Triumph classics have SAI (Secondary Air Injection) with a port directly into the head that is maybe closer to EGR than Honda's PAIR valve. Removing SAI on a Triumph makes the engine run noticeably cooler and (seat of the pants) smoother -- but I've been wrong on that before, see above.

[lemontree_imp]

So what was the conclusion of the OP?

[Siggy Javotnik_imp]

So what was the conclusion of the OP?

1. Installing an O2 eliminator (a resistor) can soften snatchy throttle response, especially at small throttle openings or on/off throttle. It can also fix the hunting/surging that some folks experience at small throttle openings.

2. It is not necessary to physically remove the O2 sensor, and it's a royal PITA to do so unless you have the right slotted wrench. (This is somewhat controversial -- some people posit that physical removal is smart because the O2 sensor will "fail" if it's not connected to the ECU. I respectfully disagree, because I can't see why that would be true. The O2 sensor is not heated or cleaned by dint of being hooked up to the ECU).

3. Installing an O2 eliminator will make your bike run richer and therefore cooler and may slightly adversely affect fuel economy (I found it negligible or non-existent, but YMMV. In fact, I experienced a slight increase in fuel economy, but that makes zero sense and I can't explain it so I chalk it up to user error).

4. If your bike fuels nicely with the stock setup, don't bother with the O2 eliminator. If, on the other hand, you have fueling problems at low throttle, it's a cheap experiment to see if it fixes the problem (it seems like it usually does).

5. Many aftermarket or race exhaust systems require or include an O2 eliminator, and simply do not have a physical threaded hole for the O2 sensor.

I'd welcome disagreement on any of those ideas, but that's what I got from reading the thread and my own experiments! Ride safe and have fun.