Backfiring!

[F0ul_Oli]

We had a lovely day yesterday - it was like summer so I went for a spin with a mate.

The Baggy was great, it kept up with a TRX850 on all the smaller roads, but wasn't too good on the bigger roads but neverthelesss ..

I found it was backfiring a lot - is there a way to stop it from doing this?
It seemed to be doing it on decelleration - coming up to a corner, I would twist the throttle closed, and it would go bang a few seconds later.

Will this damage the bike and is there a way of stopping it happening?

We were thinking that it might be running a little lean, but before I start fiddling, I thought I would be better off asking the people who know!

[oldboyonrgv]

they all do that sir !!, they are set up really lean standard, it won't do any intial damage but i wouldn't want to leave it like it.
Get a dynojet kit for a Yam660 http://www.tts-performance.com/ that will sort it.

[oldboyonrgv]

Here's the kit http://www.tts-performance.com/catalog/product_info.php?cPath=383_385_389&products_id=2581&PHPSESSID=33b60547365703eca88efae1bac954f2

[keithcross]

Hiya.

Forgot where I put the info, could you e-mail me teh infoyou used to have on your old MZ web site on carb set up please.

keithcross55@hotmail.com

Ta

Keith

[oldboyonrgv]

Ahhh , I was looking for the same thing ... I will have a look on the home P.C tonight.

[oldboyonrgv]

Nope its gone !! sorry, I could probably remember though .

[oldboyonrgv]

carb modifications. The mixture screw gets backed out(holeshot performance recommends 7 1/2 turns out from lightly seated),the main jet isn't adjustable, you replace the 130 main jet from the left side (as you're sitting on the bike)carb with a Kehin 135 and screw it in all the way tight. The midrange jet needles (both sides) get raised 1 notch, (this means the cirlip goes in the second groove from the pointy end) cut 2 coils from the constant velocity slide spring (right side)and re-install cut side down. Be sure to line up the diapraghm correctly, there is a little tab on the edge of it that fits into a recess cast into the top of the carb. At low altitude (below 5000 feet), you can drill the right carb's main jet with a #51 drill bit, just twist it between your fingers, no need for the drill press and re-install with a new P/N 90-20.142 crush washer. For around town riding this last step isn't really nessesary, you'll foul plugs more often and you should definatly keep a stock main jet (P/N 90-20.146) handy if you plan on doing any riding up in the mountains. The sync screw on top of the carb bank controlls the point after the low speed carb carb starts opening that the high speed carb begins to open, crank it in a turn or two so that as you twist the grip, you'll feel the freeplay take up, then the low speed carb start to open, then the added resistance of the high speed carb opening. You want the high speed carb to open just after the low speed opens, without as much of a delay as with the stock setting. This obviously needs to be set with the carbs reinstalled on the bike before the gas tank is replaced. Lastly, if yor bike is a Skorpion (Sport, Traveller, Replica Etc., not a Mastiff, Black Panther Etc.) Remove the black rubber snorkel from the top of the airbox. Of course, all these modifications are recommended for closed course, racetrack use only. Wink.

[oldboyonrgv]

By the way, You can also drillout the air damper hole on the CV side (its the hole next to the needle) to 4MM, this allows the air to move faster so the slide comes up qucker. and I also recall installing a larger pilot jet, but there again I was running a race exhaust.

[keithcross]

Thanks

All usefulstuff. As Iamgetting aspare set of carurettors (£20 froma guy I brought some gear off of on EBay) I might tryout some of the mods.
Any body else got tis on Carbs mods?

Keith

[F0ul_Oli]

This mod looks really good - but I think I'm going to have a go at getting an exhaust and a dyno jet adaptor sorted out first.

How much does this affect the fuel economy?

[Whysub]

[boysie]

Hi Kieth, yes mate I have also been running a similar setup for a number of years now, I seem to remember you have to order the pilot jet form a Yamaha dealer for an XT, as MZ don't supply pilot jet options, also you can modify your CV side main jet by drilling and taping it to accept Dynojet jets this gives more options for adjustment..

Oh yes, don't forget to drill some stonking great holes in the airbox;-

[keithcross]

Cheers to all. Boysie. when we gunna see your bike now its had te engine mods done?

Keith

[F0ul_Oli]

[quote="Whysub"]

[oldboyonrgv]

F0ul_Oli where did you get that from ? getting em to run right makes them more economic as they are more efficient so you dont have to use so much throttle for the same result.
its only when you tune for speed you start to have an effect on the economy.[/quote]