Topic: Replaced your 750 airbox rubbers?

[Tim2005]

Who's changed their airbox rubbers (i.e connectors between carbs & airbox)? Did you notice any change in mpg afterwards? When I stripped my 750 to repaint the frame last winter I noticed they had gone hard and were a little bit loose in the airbox, so got a new set.

The rest of the rebuild was mostly paint and gearbox - nothing that should affect mpg- and I've since double/treble checked everything carb & ignition related etc-  and it is running beautifully, plug colours are aok etc too. No fuel leaks either.  However my mpg is under 40 now and before rebuild for years it has been an incredibly predictable 45 - always used to get 120-122 miles before reserve, now it is 98-101. Same fuel, same rider, same roads.

It's hard to accept it was drawing that much extra air, the old rubbers weren't terribly loose, but weren't tight, and I don't rememember the plugs being lean etc., but if others have noticed this effect too then it would explain it.

Any other ideas welcomed too.

[scottly]

Any other ideas welcomed too.

It's very hard to judge the fuel level in a Seeley tank by peering into the fuel cap; 1/4" error might be equivalent to two liters. The last time I made an accurate measurement of my fuel usage, I made a "dip stick", and checked the level with a nearly full tank. After 700+ miles, I filled the tank up to exactly the same level, and tallied the numbers.   

[HondaMan]

Take note: this year the EPA has forced new fuel regulations upon all of us. Those new regulations include fuels that burn with less heat, which equals less power and MPG, to supposedly create less CO2 (it does not). It is not the airbox rubbers: my cars have all lost 10%-15% of MPG since this time last year. They are being driven the same way, the same daily trips, etc., but even the built-in MPG computer displays are showing 1-3 less MPG in the long-term readings as compared to the previous 6 years that I have had them.

Write/call/e-mail/text/YELL at your congressman: they are not even paying attention to the damage this is doing to all of our vehicles' engines, let alone our wallets.

[Tim2005]

Thanks Scottly, but yes I've done best part of 1000 miles and am rather certain the mpg has dropped to this. And yes Mark, I agree that the new ethanol fuels are a problem- saw your other post too- but I'm in UK where we are still on 5% ethanol and although there are other changes to our fuel my other bikes are consistent on mpg. Hopefully someone else has changed their airbox rubbers...   

[scottly]

I can't see how the airbox rubbers could affect mileage, unless they have a smaller bore or some sort of restriction? Do they fit over the carbs the same as the originals?

[flybox1]

New boots...Yes.    Better mpg...No.
It only makes getting the top half of the box on and off easier.
My consistent 45mpg is contributed to the knowledge of the forum and my OCD when it comes to maintenance   

[Tim2005]

Scottly, what I mean is the old ones were a bit loose in the airbx- so there could have been a slight air gap (causing it to run lean, perhaps),  which fitting the new ones would have selaed up. Thanks Flybox, yes 've always been consistent on mpg too, hence why I'm rather baffled by this.

[flybox1]

It sure is possible 
Now that everything is tight, IIWM, i'd proceed with a (new plugs) idle plug shop, and go from there.
Adjust your IMS as needed based on your plug color.