Airbox backfire.

[mart3442]

My VTR will backfire into the airbox occasionally, first time it did that, I s##t myself, thinking something had blown in the engine!
I balanced the carbs which were quite a way out of synch, hoping that this would be the end of it. Engine is running very nicely but the backfire remains, anyone have any solutions?
Cheers.

[VTRDark]

There's a few things that can contribute to this including carbs being out of sync. Basically it's down to tuning/timing. You could be running to lean. What air filter are running and have you got de-baffled aftermarket cans. You may require some some carb re-jetting. Adjusting the TPS to 500 ohms also helps. At what point in the revs are the carbs spitting back. The recent cold spell we have had probably does not help either as the cold weather will make things run leaner as the air is more dense.

(:-})

[alternative_vtr]

Yes good point Carl, so really this weather is the leanest the air fuel ratio can get, once it warms up a bit in theory the mixture will richen.

[VTRDark]

The theory being is it going to warm up

(:-})

[edds11]

the only downfall with that one is that the fuel is also cold and hence denser, is it possibly the same density increase as the air ? I don't know, without researching into the relative density of air and fuel and its coefficientcy of expansion and contraction, but I think that might be taking things a little too far.

[VTRDark]

If that was the case then we would not have problems with altitude. Also Fuel is liquid and air is a gas so they must have different comparisons to how they expand and contract to pressure and according to Charles law pressure and temperature are related. It's down to the quantity of air particles that are compacted together within a given space.



(:-})

[benny hedges]

turning the idle speed up to 1200 - 1300 rpm near enough stops the carb fart issue.

[sirch345]

Also when the spark plugs are getting past their best the bike will do it more,


Chris.

[edds11]

air thinning at altitude is far more drastic than a few degrees temp, i.e. half the molecules of air due to the lack of compression of the atmosphere above it, thats why air thins out at extreme height. having never taken a VTR to the top of the Himalayas I would not be able to comment on the practical side of such a test. r.e. gases and liquids, reference to my comment on the coefficient of expansion and contraction, you could work it out with the correct figures, but like I say its a bit extreme, gases and liquids expand with heat and contract with cold. (awaiting for the referance to water pipes in winter)

[edds11]

p.s. has anyone ever put an aerosol onto an open fire.....

[VTRDark]

(awaiting for the referance to water pipes in winter)

or even carb icing

Your right it's a lot more extreme when high altitudes are involved. But I think the weather conditions at 1 ATM have an effect on it as well though not as drastic. I suppose it's down to how finely or not the carbs are tuned. I have moved my needle clip before from 1 clip or a 10 thou shim and it's gone from a bit of lean spitting back to not spitting back. I have also had a bit of spitting when I have first started the bike up in the morning but once fully warmed up it runs great.

A bike could perform great on a hot day riding about and when it cools down towards the evening and riding home it does not feel quite as good or vica verca. There is a very noticeable difference to a hot summers day and dropping below zero in Winter. But like I said it depends on how finely or not the carbs are set up. Just tweaking the fuel screw 1/2 turn could be the difference between it spitting or not.

The carbs are just one contributing factor that can cause this issue. And it's also down to timing/ignition.

(:-})

[edds11]

E =MC2 .........every action has a negative and equal reaction ......pige DO fly .....it never rains in central spain, DONT FRIKIN GO THERE THEN.

[bluestoesonnose]

To be honest I quite liked it on the Storm, my TransAlp 650 did it and my SV1000S (injected) does it. My mates TL1000s and his TL1000R do it, thought the better half's Ducati M750 Monster doesn't, I think it's a Jap Vee Twin thing.

I did a full service on the my (standard can's and intake) Storm (when I had it) and even checked the Vv clearances and it's didn't make any difference, putting the tick over up just make the bike a little odd around town as it always wanted to go faster than I wanted at lower speeds.

Live with it, accept that it's part of Vee Twin ownership, heck the Storm has some huge carbs I'd be upset if it didn't do it...

[VTRDark]

I think it is defiantly more of a V-Twin thing especially with the ruddy great carbs we have. And we all now how sensitive they are to changes, especially with the airbox and filters.

When I first got my storm it had microns on that where designed for the storm unlike my current ones, and had a BMC street filter. My bike was terrible for carb farts and it used to cut out for no reason while idling at lights from time to time. The first thing I done was raise the idle speed which like you say doesn't feel right riding around town and pulled to fast (less control) from the lights. Also it just increases the amount of wasted fuel burnt while idling at lights etc.

I decided next to pull the carbs and clean and investigate what was going on inside. It had a standard setup with the exception of the emulsion tubes the wrong way around, so I cleaned and put everything as it should as standard according to the manual, and re-balanced the carbs, The bike idled a little better but not much improvement and it still had the odd carb fart. The next thing I done was adjust the TPS and this had an immediate improvement, carb farts went and the bike idled even better at 1000rpm with no fluctuations. It also pulled from low down a lot smoother.

The only time I ever get them now is when I have been messing around with jetting and it's running to lean. Right now I have it running nice with no carb farts and power and smoothness is good throughout and I have it set to idle at 1000rpm when fully warmed up. I could set it lower as it idles from about 2000-3000 before it stalls. When I first start it in the mornings a tiny bit of choke for the initial start on really cold days or it generally does not require it. It starts idling at around 2000 and as it warms up to running temp it idles at 1000 with no carb farts through the range.

(:-})

[tony.mon]

(:-})

But why is the piston lifting green handbags?
Is this the latest Kermit accessory?