Popping on decel and constant partial throttle at 3-5k RPM

[al_roethlisberger]

Well, after the move to NC last Summer, believe it or not, I have *just* now gotten around to a lengthy ride on the bike when a friend rode over from Texas this weekend.

 

I have lots of excuses why I haven't been riding this year(and I swear, some are GOOD ONES ), but let's just leave it at that

 

 

So anyway, here are my observations and questions:

 

First, as you may recall, last year the bike got its defective fuzzy cases swapped, and at the same time in went a Megacycle cam and MR pistons.

 

The bike now runs like "stink" as Pete would say, and has never idled or generally run so well. So that's good news. It also starts right up every time, with no fiddling of any kind

 

 

But after riding about 200 miles yesterday, I noticed that between 3-5k(mostly), on constant partial throttle(maybe 20%?) after a few seconds, the bike wanted to pop out of the exhaust. This popping was just like the pops/report you hear from the exhaust of many race bikes and the come off WOT into a curve or down a cork-screw.

 

And it wasn't just audible, it often could be felt, almost like "miss", but I don't think it was missing per se.

 

Now, this wasn't constant, and could be managed with some variance in throttle position. But it was quite annoying when going through towns where the speed limit was 35-45mph, and the bike just didn't seem happy once good and warmed up(about 90 degrees F).

 

 

Now, the bike has always hated to run at that 3-4k RPM range, even before the mods, and as we all know, that is a little low on the RPM range anyway, so I do avoid it. But every so often, you just get stuck there for a bit, and don't want to wind the engine out to go 30 mph

 

So, I'd like to get some ideas on why I am getting this popping/backfire thing on constant partial throttle in this RPM range.

 

And BTW, it does it a bit over 5k RPM every so often, just not as much.... kinda rare actually.

 

I have also attached a photo of my plugs following the ride, right and left respectively. I think they look a tad rich, but still well within "OK". See if those add any clues.

 

I will say my exhausts seemed a bit dirtier following the ride, so maybe a bit rich?

 

 

Other than this one issue, the bike ran like a champ.

 

 

Thoughts?

 

 

Al

[dlaing]

This type of popping can usually be fixed by adding fuel to the appropriate map area....

But it seems like you are already running rich.

Have you dynotuned with tuning link?

A nice even lambda should keep it from getting too hot, but also help reduce carbon build up.

[Guest scooterneal]

Sounds really similar to problems I just worked out on my bike. I had it into a dealers more than twice. The first time they tuned it to spec's and sent me on my merry way. It ran worse than when I took it to them. It ran though. This summer though it started running like crap at constant throttle in the rpm range you mentioned in your email. It ran fine accelerating. I took it to a different dealer and they did the same thing. They rode it a few miles and didn't have a problem (so they say). I took it out and 15 min later it was doing the same thing. I rode it back to them and insisted that they ride it and they came back admitting that something is indeed amiss. They wound up taking over a month before they gave up and replaced my entire fuel system. It runs fine now but it cost me my first born (at least it would have if I had a first born). I really suspect the throttle positioning sensors wer screwed up. I'm going to buy the software to do my own diagnostics. I won't get caught going through that misery again.

[v50man]

Al, Al, Al.............

 

A little popping of the exhaust never hurt anybody.

 

Get out and ride in NC -- it's the best time of the year.

 

If it'll make you feel better, dump half a bottle of Seafoam® in your tank -- go for a long ride -- and call it a day...

 

It's a Guzzi, for God's sake. If you wanted perfection, youd've bought a Buell!!!

[dlaing]

It's a Guzzi, for God's sake. If you wanted perfection, youd've bought a Buell!!!

I guess you don't visit the forums that discuss Buell problems Atleast your mechanics are better looking than Luigi

sourced from http://amifastorwhat.ning.com/detail.php?DetailID=501306

[al_roethlisberger]

Heh, yeah yeah yeah....

 

Anyway, for those that asked, yes it has a custom map via a PCIIIusb, and a custom ECU ignition mapping by TLM for the dual-plugged heads. I'm thinking this is just a minor tweak to the map I'll need to make in this RPM range on the PCIII, or maybe the air-bypass screws?? Not sure where to start.

 

And BTW, it's not just the POP that drives me nuts, its the slight lurch I get with each POP, so again... riding through a 35mph township isn't the most fun

 

I'm going to put the K&Ns that were hanging directly off the TBs back and see if that makes any difference, as I don't really remember this doing this with them on before I put the velocity stacks from Sport Cycle Pacific for this ride

 

I can't imagine they made any real difference though, but I guess it is worth a test.

 

Al

[dlaing]

the stacks could be making it just enough richer to make it pop.

Tuning the PCIII is a piece of cake....just requires a little patience and subtle changes.

[quazi-moto]

A tuner/mechanic guy I met at a dealership told me that doing plug chops with today's fuel and fuel systems really doesn't tell you much. I don't know myself how much truth is in that, but he tried to fatten up the map on my PCIII to get rid of the mid-range popping that Al described and it just seemed to make the overall map too rich yet it still popped at part throttle/mid-RPM's. I'm now running with the My15M and putting it through its paces. I'm going through some growing pains, but I feel optimistic that I can get it just about spot on with some more tweaking and I'm only running open loop for now. On a street ridden machine the mid-range performance is crucial. At least it is to me anyway. With the amount of torque that this bike has it seems rather ridiculous to have to keep the engine spinning above 4000 RPM all the time. These bikes have the potential to be great road machines, but the fuel management issues are a nuisance.

[v50man]

I guess you don't visit the forums that discuss Buell problems Atleast your mechanics are better looking than Luigi

sourced from http://amifastorwhat.ning.com/detail.php?DetailID=501306

[luhbo]

I assume you have to change the spark advance a bit in this area. This is the best solution I think.

 

The last carburetor cars, already suffering the oncoming environmental laws, were eliminating this low load poping by retarding the spark advance a bit. To go at constant speed you had to open the throttle a bit more so the engine came out of this difficult to tune area.

 

Using the proper tools you can do this yourself, without sending it to TLM (and you can get some money for your PCIII by the way).

 

What I found working also is to give more advance, albeit this can lead to some anoying to'n fro what sometimes must be interrupted with a short clutch feathering.

 

Changing the advance gives "instant action", the attempt to drown every possible fault easily leads into frustration. Times are a'changing

 

Hubert

[Skeeve]

...

First, as you may recall, last year the bike got its defective fuzzy cases swapped, and at the same time in went a Megacycle cam and MR pistons.

 

The bike now runs like "stink" as Pete would say, and has never idled or generally run so well. So that's good news. It also starts right up every time, with no fiddling of any kind

But after riding about 200 miles yesterday, I noticed that between 3-5k(mostly), on constant partial throttle(maybe 20%?) after a few seconds, the bike wanted to pop out of the exhaust. This popping was just like the pops/report you hear from the exhaust of many race bikes and the come off WOT into a curve or down a cork-screw.

 

And it wasn't just audible, it often could be felt, almost like "miss", but I don't think it was missing per se.

 

Now, this wasn't constant, and could be managed with some variance in throttle position. But it was quite annoying when going through towns where the speed limit was 35-45mph, and the bike just didn't seem happy once good and warmed up(about 90 degrees F).

Now, the bike has always hated to run at that 3-4k RPM range, even before the mods, and as we all know, that is a little low on the RPM range anyway, so I do avoid it. But every so often, you just get stuck there for a bit, and don't want to wind the engine out to go 30 mph

...

 

First, the good news: I'm willing to bet your bike pulls like the Borax 20 Mule Team from 6k to redline. Next, the bad news: at 50% revs of the powerband, the intake & exhaust harmonics give you a flat spot. It's always been this way, & only recently *not* been by tricks like the path-doubling exhaust valves used by the Big 4, etc. So, short of changing your exhaust or cam around (more/again) about all you can do is live with the popping. If it is missing due to lean stumble, then going richer in that range should eliminate the popping in the exhaust & herky jerks; if it's missing because it is already too rich, then you'll just have to lean it back out & live w/ the hole in the powerband. That's life...

 

[luhbo]

That's not really satisfying, is it?

 

Hubert

[Skeeve]

That's not really satisfying, is it?

 

Hubert

 

Nope. The alternative is to tune for a lower, broader power peak. That's not really satisfying either, for us speed freaks...

 

Alternative: put in an EXUP-style exhaust valve to alter the resonance of the exhaust to better suit the engine in that 3k-4.5k rpm range & banish the hole in the powerband. Or, less ideal [but more easily implemented], put on a front x-over like on the 2003+ V11 bikes, which doesn't exactly banish the hole in power-band but fills it in to mostly flat. [Which is why Guzzi did just that for the 2003 & 2004 V11s... ]

 

I don't know which model year bike Al has, but if it's from 2002 or before, I suspect he'll start prowling for the front x-over from somebody's later model V11 to help sort out his powerband (unless he just hates the look, as some people have stated when prior threads on the front x-over came up...)

 

[docc]

(and you can get some money for your PCIII by the way).

 

 

Hubert