Splutter at full throttle

[solly]

hey all - newbie here so treat me gently if i mess it up !

i have an xs650 hardtail bobber - not sure of the age of the engine but the v5 says 1974!

not sure which carbs i have either !

basically starts ok but when going past 3/4 throttle she starts to splutter

someone has said it is running lean - open exhaust pipes and cheap k&n filters

they have suggested going up to a 140 main jet and lifting the needle a notch

wanted to check with the experts before making expensive mistakes!

can anyone help with the following

what carbs are they mikuni.........?
will changing main jet make any difference?

thanks

here are some pics and i throw myself open to ridicule ...........

 

[TwoJugs]

Looks like BS38 carbs. If you have points check them too. Those filters have a problem of blocking air holes on the carbs flanges if installed too tight. With free breathing filters and open pipes you usually need to step up the jet size. After doing all the basic, timing, compression, valve lash, cam chain stuff try a bigger main jet. You can access it through the bowl plug and if they are not stuck and you have a good fitting tool you can change them out while mounted on the motor. If you have not done this before it might be best to remove the bowl or carbs and do it first on a bench. Having a super good fit into the jet slot will assure you dont chip away the slot and create new problems. Make sure your tank is venting properly too.

 

[solly]

that was a quick reply!

thanks for the advice - I will get myself a haynes manual and check the timing etc first before getting carried away

David

 

[grizld1]

Right, the first rule of carb tuning is simple--do everything else first.

And right again, your present problem may have little or nothing to do with jetting or but much to do with internal flanges on those cheapo pods. 5twins and I wrote the XS650 Garage Carb Guide once, and I for one am not going to write it again a piece at a time. Go to the Tech section and follow the link or register at XS650 Garage and go to the source.

The Carb Guide has material that will help you identify your carb set. Judging by the plate between the carb tops and the single cable setup, it's either 76-77 or 78-79. You'll need to pull the filters and look at the intake bells to tell which.

 

[angus67]

get these.
http://www.motorcycle-superstore.co...ID=AvantLink|NA|55963_d3fe7c65&WT.MC_ID=54020

 

[solly]

What can I say - thanks chaps for all of the splendid information - just got to find a UK supplier for those better air filters - started to go through the carb guide in the tech section.......

Will post some burnout pics when she is running properly.....!

 

[taggat]

Definetly do all that was mentioned above.
Quick way to tell if your running lean or not is to hold the choke down at full throttle.
If it gets better your lean if it gets worse your rich, now this is just to get you into the right direction of which way to go on your jetting.

Youll need to cut away the lip on inside of those cheapo pods as your covering inlets or get the better uni's and call that done and resume synching and tuning and jetting.

 

[solly]

thank you taggat - all good advice - I have ordered some decent air filters now and the haynes manual is on the way....happy days......

 

[scabber]

Welcome to the site. Not much to add on the advice already given. Nice bike like the tank and the rest looks great. Should be a blast to ride once you get it sorted.