Modern Vespa

We have two Vespa 2007 250's-a GTV and GTS and as the heat rises in the Carolina's both scooters are doing a lot of backfiring as we back off the throttle. In the winter, we don't experience the backfire and even fill with regular gas. In the summer, we fill with mid-grade and premium and still hear the engine backfire. is this normal? Will it hurt the engines? Is there anything we can do? Thanks for any thoughts-B&B

I noticed the same thing this last weekend. Tempature was over 100. They were muffled backfires and didnt experience any performance issues.

I've got a Prima pipe on my Gts (nearly 3000 miles on the pipe) and it backfires when coming to a stop in the first 5-10 min after start up. No more after it gets up to temperature. I love the sound!

I could be wrong, but...

Backfire is caused by valves opening and closing at the wrong time. It has to do with the timing of when the valves open and close.

Now this might possibly be an electrical issue, because if the spark from the spark plug is not happening at the proper time, you will get backfire.

My BF's motorcycle was backfiring due to a poor connection at the battery. Once that was fixed, no more backfire.

It may be time for tune up.

The GT 200's AND the GTS 250's have this problem when they aren't warmed up. One way to correct it is to not just release or roll off of the throttle completely when coming to a stop until the motor gets warmed up. Once the motor gets up to operating temperature the backfiring goes away.

Do a little reading: https://modernvespa.com/forum/topic13223?highlight=backfire

In my case I believe it had more to do with the high air tempature. The temp on the vespa read 107 but I think the real tempature was around 102 or 103. It doesnt backfire when the tempature is more moderate.

Interesting, I am down here in Aiken just across the river from Augusta and it has been very hot these last couple of weeks. Thus far, I have not experienced any backfiring, ... now staying cool at a stop light is another matter.

take the gas cap off and put it back on
Sometimes the heat causes it to build up pressure

Dear-"imwithhappy"-I did do a search for backfires and found this same article that talks about warming up the engine, but my issue happens way after the engine has been warmed-up and running for some time and on both bikes. In fact, after riding for well over an hour yesterday, the backfire continued. I do not experience any backfiring until the engine has been running for some time. It runs great for the first 5-10 miles. Both bikes went through a tune-up and oil change this Spring at my local Vespa dealer. And the techs at the shop didn't really have an answer for me. Both bikes still have the same pep and run well otherwise. Seems it only happens when the air temperature exceeds 90 degrees. We are taking both bikes from the Piedmont to the cooler mountains next week. Should be interesting to see if the change in temperature has any effect. I'll keep you posted.

i have backfire when using a pm pipe on my gt
& i had it always on my last motorbike, honda ntv 650
it appears when decelerating & it's due to a bad combustion of the gas
i think the high temp should have the responsability of it,
do not panic, it won't damage your vespa

regards

Backfires are usually a result of exhaust leaks.

Possible causes of backfiring

*Exhaust leaks........The muffler bearing that is made of a graphite material (where it joins to the exhaust pipe) is notorious for disenigrating and leaking..............OR,

*Valve clearances not adjusted to spec........OR,

*Engine running hotter than normal and ECU not compensating for the extra heat by adjusting timing and air/fuel mixture ratio to the fuel injector........ergo...... backfiring

I have this issue too, and in my case I'm convinced it's a gasket/poor exhaust design issue.

My factory exhaust backfired all the time, then I realized it had a very fine crack in the bottom, this allowed cool air into the exhaust system which created the popping noise. The next question is why was there a crack? I think this relates to the design of the exhaust system on the GTS 250 - it's just too hot for that exhaust system.

now I have a leo vince 4road, it did not backfire at first, but now as you can see from my other post i am having serious issues with this setup however prior to that I still notice the popping back fire issues even when the Vespa has been running in 100 degree plus weather for 45 min or more. This leads me to think there is a gasket issue, or the exhaust is just not engineered correctly for a scooter to run 70 MPH in 100 degree weather.

A few days ago my BVC did the same thing.

It's new, 2100 km... had the most recent service, and it wasn't very warm

So... who knows.

Just got back from a ride and I'm convinced it has a lot to do with the outside temperature. I rode backfire free with virtually no stops on my way-about 20 miles and 30 minute drive going through city traffic as well as cruising around 60. On the way home, I seemed to get caught at every light and as soon as the temperature on the dash on my GTS got to 100 degrees, the backfires started. As soon as I hit the shady open road and the temperature gauge dropped to 95 degrees-no more backfires. I don't think this is hurting my engines, but... I'll be sure after the trip to the NC Mountains next week. Glad I'm not the only one experiencing this.

I have the same backfire trouble, I put the gt 200 (2006) on the center stand gas it a little let off and it backfireds (this was after it was warmed up....I turned the gt off and heard it wineing???? I opened the gas cap and it just about blew out of my hand...so I left the cap loose and no more backfireing (0: .................................................................. I wonder if theres a vent pluged?? anybody Know????? OLDMAN.

Its common place on modern fuel injected engines, as they program the ecu to shut the fuelling off on sudden throttle closure to reduce emissions, this sudden weak mixture gives the popping and is completely normal.

On most modern non injection machines they run a pulsed air system that forces fresh air into the exhaust to fake low emissions at the tailpipe, this also causes the popping and again is normal.

maybe so but why is the fuel tank under pressure.....anybody??? OLDMAN.

oldman: If pressure is building up in your gas tank, you would be wise to disconnect the evaporative canister system. That will stop the problem. I've done this on four modern Vespa's that we have owned. If you decide to disconnect it and need some help, pm me with your email address and phone number and I'll walk you through the procedure. It's very easy to do.

ADDICTED, I pulled the return line off the top left side of the carb. and blew through it , it was open... is this what your talking about? OLDMAN.

Nope! Your scooter has an evaporative canister system that was installed at the factory with the purpose of stopping gas fumes from being released into the atmosphere. It's a very poorly designed system and can cause a myriad of problems. See this thread: https://modernvespa.com/forum/topic86

It can cause pressure to build up in the gas tank. It's an easy fix if you don't mind getting your hands dirty.

Your exhaust gasket where the muffler meets the tail pipe may be deteriorated (common problem) and this can cause backfiring.

Me too. Hot day. A little sputter and backfire. Benito said that it is common, but because of the stock pipe, you just don't hear it a lot.

Otherwise, my scooter is running just fine. Not sweating it, but I feel relieved to know that it's other peeps too. I'm a year into my scoot with 4500 miles on it. It's been hot as balls in Sacramento, 100+ for the last few days.

Mine always pops a little when its cold but a month or so ago, was doing it WAY more than usual. Found a post here that recommended I disconnect the battery for about 10 minutes and let the ECU reset. After doing that, it ran significantly better and the popping virtually disappeared.

Ok I have to weigh in on this too. My wife's GT200 does the same "popping/backfiring" after it is warmed up, releasing the throttle to slow down.
On Thursday my local shop took the carb off , cleaned it, noticed gunk (possibly from ethanol) in the idle jet. The exhaust pipe hook up was not very well managed either. we checked it and noticed a lot of corrosion. Only 2800 miles, garage kept scooter.
Ok, after cleaning the carb, checking the valves, and spark plug, we noticed that it was running real lean. Apparently piaggio doesn't want anybody to adjust these carbs because there is a special tool to adjust flow.

Point being now scooter runs rougher, pops more, and does build up lots of pressure in the tank.

If not enough we are having cranking problems, maybe related to one of above mentioned.

Try relieving the pressure in your tank by unscrewing
the gas cap and letting the pressure escape before your take off.

They really need a better breather tube on these scooters

Use to have that problem before on my old "Modern Scooter"

My GT 200 pops and burbles on the over run all the time and it doesn't bother me at all.

Bill X

Just back from Boone NC and a wonderful two-day ride in 70-80 degree weather. Both bikes drove like dreams at 70 mph with no problems and no backfiring and little popping when the temp. gauge on the GTS stayed in the low 80's. What a joy to do this ride on the Vespas! I do believe the "popping" is normal and that higher temps help create the backfiring and that neither hurts the engines. Done. Bob

Backfiring should not be considered normal under any circumstance. The unburned fuel is re-igniting in the exhaust causing back pressure on the valves, etc. More than likely, the pilot screw (minimum flow) screw is too lean. The pilot jet controls up to 1/3 throttle, then the main jet takes over. If you're noticing that it's popping/backfiring on deceleration as you completely roll off the throttle, then there's a good chance this is the problem. Some people get away with upping the RPM's, but you're only masking the problem. The minimum flow screw needs to be adjusted for proper air fuel mixture. The piaggio/vespa's are made to run super lean to conform with certain state regulations. Lean is not good. My fly 150 that I just got is doing it. It only has 1600 miles on it. My old fly never did it, so I know it's not normal. I have checked everything except the valves at this point. The insulator on the plug was white, which is a strong indication of lean running.

The GTS/GTV/GT60 don't have carbs. With fuel injection the ECU and Oxygen sensor determine the mixture. Also the idle is set on the computer, not by turning a screw or adjusting the cables or stops.

Oh, welcome to MV. Killer deal on your Fly.

cheers

Okay, here's my thought: I've been wrenching on modern Vespas over four years and found that at least 95% (or all) of them do this to some degree. Maybe it's just more common here in Texas where it's warm in the winter and much like the surface of the sun in the summer. (We only have two seasons here, you know.) I attribute it mainly to the Secondary Air System. The SAS pumps fresh air into the exhaust, either directly into the header or into the exhaust manifold just before the header. They do this for a claimed "more complete burn" of fuel making its way into the exhaust, thus reducing unburned hydrocarbon emissions, although I sort of suspect that it mostly works by effectively diluting the exhaust with clean air. Big manufacturers have been known to do funny stuff when it comes to emissions, after all. Accelerator pumps are a good example of this. But that's neither here nor there.
The point is the SAS pumps clean air into the exhaust, to complete the combustion. I guess it must work, thus the pop when you shut the throttle, just like with a regular, non-oem exhaust leak.

My new 250 GTS was backfiring some too, and I started burning 92 or 93 octane in it - whatever was the highest available when I'd stop to gas up (as I had been using 89 octane, forgetting that it is supposed to be at least 90), and that seems to have stopped the backfiring, but someone already suggested using the higher octane fuel. Other than that, I don't have any other suggestions.

I do feel that the "popping" is normal and not a detrimental thing to my 250's engine. What was curious to me was the backfiring that only seems to rear it's ugly head when the outside temperature exceeds 90 degrees and the engine gets even hotter because of stop and go traffic. I experience backfiring on both bikes with high octane fuel only when I'm cooking slowly along hot, humid Carolina roads. If there are no temperatures over 90-no backfiring on either bikes. But I do hear the "popping" in just about any temperature and riding situation. I'm not too worried about it, but...

With 300 miles on my GTS 250ie, today was the first time I've ever heard the popping/backfiring. Coincidentally, the temp here in SW Florida is 80 and humid. I have to guess that it is related to temperature. But, my guess and about 75% of the others here seem to be wrong. I pay attention to the experienced mechanics here and appreciate their input very much. Thanks!

the little popping sound you hear when letting off the throttle is normal when breaking in a new engine. It will taper off as you get up to 1000 miles on it. nothing to worry about. In fact if you ride it hard and fast the popping goes away faster.

Just popped (no pun intended) onto this site. This info about backfiring is interesting. I live in the piedmont area of NC too. This summer has been particularly hot. If I'm lucky this is the only reason mine would do that.
I tend to think my 08 GTV250 (7k miles) needs some tuning but it could simply be the heat.
**I would like to add a comment though- The 08 GTV250 does not have the worthless gasket in at the header pipe/muffler connection. At least mine doesn't. Now, my wife's GT200 does and it has failed repeatedly over its 12k mile lifespan. I finally got tired of this and located a solid metal (copper or brass I believe) bushing/gasket somewhere online. It has lasted several years and seems to be holding up well. I was to the point of having this connection welded.

No backfiring is caused when hot unburnt gases meet air, which can be sucked into the muffler on deceleration on a system with no leaks.

So in theory I have an air leak somewhere.

Nope, air can be sucked in thru the back of the muffler. Back firing to an extent is normal, unless it is excessive.
I was at a light the other day listening to my stock BV350 pop very quietly at idle.

However, it'll sound a lot louder if there's a hole - and this may be the only time it's noticed.

I did find that the clamp at the header pipe and muffler had slid forward 1/4" and was just a tad loose. This seems to have helped.