Help needed!!

[xs650mark]

Hi all,
I need some expert advise, I have a few issues with my xs bobber, she is an 81 special with stock carbs and I have very short pipes. If you done mind I will list the issues I have and hopefully someone will point me in the right direction:
1) Backfiring on decelaeration (I have read that this may be due to the short pipes and the holes in the pipes not sealed correctly or is this linked with the problems below ???)

2) When I reach 60/70 mph (I have no clocks on my bobber so cant tell you revs) my bike begins to chug for want of a better word, and wont go above that speed. Also I have had petrol flood out through the filters on both carbs (I had carbs apart today and they are perfectly clean and the floats are as free as a bird), also sometimes when I rev and release the response is very slow and she seems to hold the high revs and slowly return to tick over.

Thanks in advance, much appreciate any advice.
Mark.

 

[ember]

Jetting and you need a little back pressure in the pipes.
Search "lollipop" and you will find info on using a washer inside the pipes to aid in back pressure. Will help decel popping, but it is most likely at the carbs with jetting and possibly carbs not synced.
What size main and pilot are in the carbs? Are you running pod filters?
Forgot to ask, did you check float height is correct and that ALL jets are clean and clear?

 

[DogBunny]

If you never re-jetted for your short pipes, then you are lean.
Read the carb guide:
http://xs650temp.proboards.com/index.cgi?board=carbfaq

Leaking gas is a float valve issue. A piece of dirt on the float valve is preventing the float valve from completely closing, or float height is way wrong, or floats have holes in them and are full of gas.

And yeah, your bike will work a lot better with a baffle or lollipop or something.

 

[littlebill31]

"When I reach 60/70 mph, my bike begins to chug for want of a better word, and wont go above that speed." Check to see what position your throttle is when this happens. These carbs work on throttle postion, not so much speed. 1/2 to 3/4 throttle would lead to the needle jet/jet needle or diaphragm tear/not positoned correctly. Full...probably main jet.
"Also I have had petrol flood out through the filters on both carbs" Most likely float height. The BS34 had 2 floats, both had different heights. The '80 had brass floats and are set at 27mm. The '81 and up had foam, which are 22mm. You only have about 1mm +/- with these or they will cause problems.
"Also sometimes when I rev and release the response is very slow and she seems to hold the high revs and slowly return to tick over." Hanging throttle is a lean condition. Check your plugs too. Short pipes and pods need a bigger pilot. As an example, my '81 with short pipes and pods runs 145 mains and 45 pilots. BUT make sure you have adjusted your mix screw correctly also. They have a huge effect on mix. Did you replace the mix screw o-ring and washer? Throttle shaft seals?
Double check your exhaust head pipe to see if it is tight. This, carbs out of sync, holes in exhaust, can all cause backfire.

 

[xs650mark]

Thanks guys, really appreciate your help!

 

[xs650mark]

Just one question with regard to the "lollipop", does that have to be placed on the exhaust end, could I insert a lollipop/baffle into the engine exhaust port, and roughly what size should the hole be?? My exhaust are 3ft long approx.

 

[DogBunny]

http://www.xs650.com/forum/showthread.php?p=158413#post158413
Take a look at the above link which explains the picture.
I would make ones like in the picture, as long as possible, which will be about 10" -- any longer and you won't be able to fully insert it because of the curve in the header. AND, I would put 3 nuts and bolts through each one, each nut and bolt on a different axis, instead of just the one in each like in my picture. So, what I am suggesting is that with your super-short open pipe you make a substantial obstruction. This will go a long way to restoring your low-end power, and will make jetting a whole lot easier. Your bike will still be loud as hell.