Hey guys (I hope this is in the right thread) I have noticed recently that my petrol mileage on my 2004 yamaha Dragstar Classic has gone crap recently. The only contributing factors I have are that I have been using the choke a lot more to warm her up (as it has been cold lately) and that I have modified the air intake system. The current setup has a k&n air filter, cut open stock airbox ( more air flow) , silvertail k02 exhaust pipes (with the baffles) and jetted carbs (127.5 main jets) I am aware that there is a sacrifice of fuel economy for a few more horsepower however I am barely scraping 100 miles on a full tank! From a bike that (stock) claims to do 170! My only guess is that either I am using insane amounts of fuel by having the choke out for 5 minutes or that the main jets are too big and I am running very rich - in which case I can either downsize the carbs or purchase a RAM air kit (or a hyper charger) for more airflow - or maybe more free flowing exhausts? I know the logical thing to do would be take it to a rolling road dyno centre however here in the south they are pretty expensive. Any advice would be greatly appreciated. Thanks

take it to a rolling road, there's no magic panacea we can offer, each bike behaves differently.

why are they so expensive? usually about £40

You should not need 5 minutes of choke to warm the bike - 30 seconds, to perhaps a minute at most...!!

Have you tried altering the idle?

Most carbed bikes seem to need it turning up a touch during Winter.

Also, have you balanced the carbs?

Cleaned the carbs? Checked the diaphragms?

Got the right tyre pressure?

Lots of little things can kill your mileage...

Took it to the local mechanic who told me there two options, use smaller carbs or pull the baffles out, he reckoned that the air flow was being messed up at the rear end. Tried doing that and it is WAY too loud. As the pipes have NO aftermarket baffles available (Silvertails are a weird size), I am going to have to modify the current ones. I have attached the options that I have - Can anyone give me an opinion as to which you recommend and why? (i have already removed the packing as running too rich has wrecked it.) Thanks very much

Cut it in half if it was mine & repack the wadding at the back end to keep the rasp out of the noise it makes.

I'd definitely get it dyno'd first (£40-£45) to see what's what. But yes, sounds like she's way too rich. What size are the stock jets compared to the 127.5's? Maybe you just used too large a main jet? If the jets are too large and you're running quite rich, you'll actually have a drop in hp. I'd start with a dyno and then possibly reducing the jet size, as you may have put in larger ones than the motor + silvertails can usefully turn into power.

Edit: just did a search and stock jets are about a size 91. So I'm fairly certain the issue is with your main jets being way too big.

I'd say combine going with option 1 (drill hole through plate) plus repacking baffle with fresh fibreglass, with going down to a size 110. Possibly lower. Also check your plugs for colour. If black then yep too rich.

Straight through pipes are the ones that have the potential for the biggest gains in hp, but as you have found out, they're too feckin loud! The baffles on the silvertails have this weird metal plate in the middle, forcing all the gasses to go through the padding, creating a lot of back pressure. Combine that with those very big jets and I don't like to think how much unburnt fuel has gone through that packing (hence why its ruined). So the next step is to drill a hole in that plate. Basically as big as you can make it, 20-30mm. This will louden up your silvertails, but the packing will take the edge of the noise, an in any case, won't be anything like as loud as with no baffles!

With that done I'd expect you'll still be running too rich, if less so than before, so I'd advise you to fit smaller jets, and possibly plug up that hole you made in your airbox.

The hole has a similar effect to that of a Hypercharger - as I am not rolling in it i decided I would save myself 300 quid and do it myself. It is now similar to a Ram Air Kit - Here is a link to the basic principal of it.

http://650ccnd.com/mods/RAK/rak.htm

Which diagram option do you all recommend then because now I am stuck between cutting it in half and repacking it with the wadding or drilling the metal midway plate out.

Thanks again for all of your help

Looking at Touts post I would go with the "drill the centre out" method he suggested, makes a lot of sense.

Thanks for all your help guys fixed her up a treat

Yeah, so what did you do?

I bought some aftermarket baffles or "motorcycle decibel killers" from ebay, they were slightly too large so I grinded them down to fit within the pipes. They are essentially the silvertail baffles cut in half ( i didn't want to modify the silvertail ones as replacement baffles are expensive and hard to get hold of plus I have no tools that could drill out the piece as of yet) - I then bought a hypercharger for £40 (Unbelievably Cheap Price Right???) jets are still the same at the moment.

I personally believe she is running one hell of a lot better now and after doing a round day trip (more or less 80 - 100 miles ) i filled her up to the brim again - only took 6 litres, so the fuel consumption has definitely improved

That being said, I do plan to go forward with taking her for a dyno run and also downsizing the main jets - in addition I will hopefully continue with the drilling of the plate in the silvertails as the decibel killers make her sound beautiful at idle, however doing 60+ mph she sounds like a WWII V1 BUZZ BOMB haha! Not pleasant.

Im guessing Tout that you have silvertails yourself as you seem to know a fair bit about them - have you modified yours?

Good to hear mate, 6 litres for 80 to 100 miles is now in 60+ mpg territory! But if that's what you're getting maybe you don't need to downsize your jets after all...

I have Vance & Hines Cruzers fitted, with baffles which are quite free flowing, so they're quite loud. At motorway speeds I really need to wear earplugs! At more normal speeds she's pleasantly loud and turns a fair few heads...

Edit: forgot to ask, do the new baffles have packing of any kind? If not, wrapping some fibreglass around them will quieten them down a wee bit.

The new baffles didn't come with any packing at all actually, I tried wrapping some around them and they sounded exactly the same as the stock silvertail baffles . I do like the idle sound with them however when revving high (especially when riding) the sound is what i'd call "hollow" or "tinny". I am still planning on drilling out the plate in the silver tail but the bugger is very far down in the pipe - but if this is done, and repacked with fiberglass, my GUESS is that they will have a lot deeper sound than they do now .

Hi guys similar problem here with my husband’s bike yamaha dragstar classic 1100 , it only did 60 km with a full tank .We checked the air filter - it is clean, checked the sparkplugs -all good , the only problem that we think it may be is the carbs -maybe the settings are not right . Also it is having a lot of unburned gas ,and when u drive sounds like a storm behind u .any advice before we put in again in service ? Got it second hand for 3000 so far spend another 1500 on it for service really getting   furstraited here .Any advice be highly appreciated . 

You have tacked on to a very old thread which will for the most part get you ignored.

Start a proper thread of your own, after saying hi briefly in the new members area.