Backfire/coughing

[Daveguzzi1]

I have a 2003 v11 Lemans. I have an off idle cough/backfire through the intake that is consistent to 3000 rpms. It is worse when the bike is fully warmed up. When rolling on the throttle and going thru the gears it doesn't occur but holding the throttle steady at 3500 or below it hiccups and coughs. New plugs properly set valves clean air filter. Plugs look good when pulled after running. The exhaust crossover has the special seals so it doesn't leak and headers are tight and not leaking. 23k on odo. She's done this for a while but getting worse. We have a dealer in our town but I have a factory service manual and would prefer to fix myself.  Thoughts????? DaveG

[Pressureangle]

Man, you stepped in it on your first post lol

We've all had it, seems like there is no 'patent' sure cure

Everybody will be along soon enough to pile on the thread and direct you to the appropriate historical threads to read.

My '97 1100 Sport-i had stock cans with a Feracci crossover- nearly undrivable at 3k rpm. After months and miles of proper tune-ups, replaced sensors, and an aftermarket tunable ECU I could never completely tune it out. Minimal yes, and mostly ok but I'm a perfectionist for drivability. Mine finally completely resolved only with the installation of a cam drive gearset replacing the chain and weak-suck stock chain tensioner. i don't know that anyone else has reported the same, though more than a couple here have the gearset. Put your reading glasses on and your warm garage socks and settle in to the comfortable mindset that it will never be resolved, then you'll be extra happy when you hit the combination that your particular bike needs. 

[guzzler]

Yeah, I reckon you're right mate.

I also think it's a combination of things that finally sorts it out!

Cheers

Ps getting rid of the crap standard tensioner was definitely a factor and the correct gap on the phase (?) sensor plus ......ha ha 

[Daveguzzi1]

I run one hundred octane sunoco fuel except when on a long ride. I drain her and refuel with same as California gas is hideous when it sits. Methanol is a curse. I think I will yank the tank  and replace all the hoses as well as replace the filter bag thingie in the tank that passes for a filter. I've never serviced it and I have owned the bike since new. Mileage is low but I rotate thru multiple bikes. Don't know much about setting electrical values and such for the  tps but will try to figure out how to get the readings and see what that means 

[Lucky Phil]

56 minutes ago, Daveguzzi1 said:

I have a 2003 v11 Lemans. I have an off idle cough/backfire through the intake that is consistent to 3000 rpms. It is worse when the bike is fully warmed up. When rolling on the throttle and going thru the gears it doesn't occur but holding the throttle steady at 3500 or below it hiccups and coughs. New plugs properly set valves clean air filter. Plugs look good when pulled after running. The exhaust crossover has the special seals so it doesn't leak and headers are tight and not leaking. 23k on odo. She's done this for a while but getting worse. We have a dealer in our town but I have a factory service manual and would prefer to fix myself.  Thoughts????? DaveG

Inlet manifold rubbers leaking/cracked. Worse when at operating temp because the engine is off the cold enrichment trim and onto the normal fuel mapping and so the air leak makes it lean. The cold enrichment trim helps cover the leanness caused by the manifold leak. I was the first to fit cam gears and it didn't cure my 2800-3200 hick up. A Daytona engine cured that.

 

Phil

 

[Steve S]

I’ve just replaced 2 throttle position sensors on my bike and a friend’s, they both had a misfire at 2k rpm when riding slowly, open the throttle and you could pull through it 

[audiomick]

8 hours ago, Daveguzzi1 said:

...electrical values and such for the  tps ...

157 mV measured across the TPS with the throttle completely closed...

 

Yeah, I know, that doesn't help much.

If you are only just starting in on working on the bike yourself, I would suggest looking at these three threads first. I only bought my 2002 V11 Le Mans about 18 months ago, and found them very helpful in quickly getting to a point where I can start to do sensible work on the bike (which needed it, and still needs a bit more...).

 

 

read that one first, then look at these

 

 

A tip for getting the tank off: your 2003 V11 should have the "click-on" connectors for the fuel lines. Be careful there: the plastic elbow coming out of the tank is fragile, and about as easy to find as hen's teeth. What helps a lot: pull the plug on the fuel pump, start the bike and let it run until the motor dies. This relieves the pressure in the fuel line, and makes it possible to disconnect as easy as it is possible to get it. To disconnect, push the connector firmly towards the tank, pull the ring back and pull the connector off.

 

PS: mine coughs too. Pretty much as you describe yours. Going through the "decent tune up" helped quite a lot. Further research remains to be done...

[p6x]

Mine was recently cured with a TPS and new ECU mapping.

The infamous 3000 misses have completely gone, at least for now. This will need to be confirmed when the weather starts to become more Texas. I am guessing Florida is not so different, maybe a tad less humid?

One of the side effects is that my gas mileage has drastically changed. I used to be in the +40ish, such as 42/44 stable highway posted speed. I am now around 38 MPG in the same conditions. Again, insofar the temperatures in Texas have been forgiving.

My idle was low, around 800 rpm instead of the preconized 1200 rpm which has now been adjusted. However, before my 800 rpm were like clockwork. Today, my 1200 rpm is steady for the most part, but from time to time, it drops and comes back up.

This happens when the engine is well in temperature.

 

[Daveguzzi1]

I have thought the intake manifold could be the issue as this was a problem on another bike I had. I've had the tank off before and know how tricky the fuel connections are. Not my favorite part of the bike to deal with. Rainy this weekend so I have time to investigate. If I spray starting fluid on the manifold while running and warmed up it should be noticeable I would think. 

[audiomick]

10 hours ago, Daveguzzi1 said:

... If I spray starting fluid on the (intake) manifold while running and warmed up it should be noticeable I would think. 

Yes, that is the method that I have seen recommended by any number of reliable sources for looking for air leaks in the intake passage. If you spray and the revs go up, there is a problem.

[thumper]

Daveguzzi1 have you solved the problem? If so what was it?

[GuzziMoto]

Come in @Daveguzzi1 Any news?

He has not been on site since March 22nd. That is only a couple weeks, though. Likely not enough time to resolve the 3k stumble.

[thumper]

10 4

[Daveguzzi1]

I have been sidetracked with other vehicular issues on other vehicles. I did order a fuel filter bag thingy and a gasket so when I take the tank off I could pull that off and check it and replace it. My intention is to replace several vacuum hoses and lines that are under the tank and in front of the seat area because I can see visible cracks. I haven't forgotten to respond I've just been a little busy. I will post what I know more

[Rox Lemans]

I've had this....  few things trying before you go crazy and ripping stuff apart: 

What gas you using? If you're not using Super, that can be it. I know. It's silly. But even I tried using 89. It'll be fine for about a tank or two, but eventually, your bike will cough. 

When was the last time you got the throttlebodies synched?  Yeah, yeah.. I know...

Your throttlebody cups too loose? Too tight? Cracked? Been there. I had a crack in one of mine you couldn't see when the bike was off. But when idling, I saw it. $25-$30 at MG Cycles. Change and synch the throttlebodies. 

It looks like you hit most of the common things. Plugs, checking the rubbers, etc. I'm sure it's simple. Could be dirty throttlebodies. I ran fuel cleaner which has worked. But you gotta burn that tank up on the freeway or something. You don't want that fuel cleaner sitting in the tank. I ran it 80-90miles which seemed to do the job and then topped off the tank to dilute the detergent. I can already see the veteran readers here facepalming.... Hey, it worked..  

But a big silly one is the gas. Don't try using 89 octane. Run super. It'll make these bikes cough like unbalanced throttlebodies or bad plugs.