Bs38 blow off engine, Maybe time for injection?

[74-Chop]

Hey guys, My chop runs std Bs 38 carbs and when you start her up they blow off out the rubber manifold

I know this is down to ignition timing right?

Well arent they 2 heavy anyway?

Xs 650 chop with K&N filters, Nothing holding the carbs other than the rubber mounts.

The carbs tend to lean downwards a bit cuz i believe theyre too heavy,


Ive always been dead set against using BS34's as from past exp on a std XS, BS38s were always way better!

But ive heard u can turn Bs34's into Injection throttle bodies?

Is that an easy take?

And make it Mechanical fuel injection instead of EFI

 

[weaselbeak]

If they blow off you either have no pressure on the clamps or you are getting backfires. Either way, it wouldn't hurt to support the weight of the carb bank with a bracket of some sort. Fix your problem, don't blame the carbs.

 

[74-Chop]

I did contemplate making a bracket mate as they are quite heavy compared to Bs 34's

Just not had much look with carbs on this bleedin bike. Being hardtail im sure doesnt helo, With all the Vibration!

The clamps are tight down,

And yea its back firing through the carbs which im sure is down to Ignition timing. But i cant get it perfect.

Ive user a strobe light and still back fires, So maybe im jumping the Gun? And should be looking elsewhere?

 

[grepper]

Those clamps were never meant to fully support the carbs, the stock air box assists in that. So another support may be necessary.

Or you can use these manifolds http://www.tcbroschoppers.com/xs650-billet-aluminum-intake-manifolds.html. I have them for my mikuni round sides and they work great.

 

[NONclow]

Valve timing adjustment? Maybe the weight of carbs, the rotten boots, and a stretched timing chain are contributing to a lean contition

If you're any good with a welder (or know a guy)....

http://www.xs650.com/forum/showthread.php?t=35424

 

[ippytattoo]

Or just take a good hard look at the cvk34's from the ex500 or I believe a gpz500 (verification required). They are lighter and perform better than the older stock carbs.

 

[74-Chop]

Ive had a set of them ippytattoo but they never seemed to run as sweet as my BS38's

NONclow thats awesome! Thank you!

 

[scabber]

Curious as to the jets and needles you were running in the CVK carbs.

 

[DIRTY DOG]

the only time I had a problem with bs38's blowing off was a had points and had a bad coil
and weak spark out put and a bad condenser and it would back fire and blow the carbs off,( hot or cold ) I had a 81 charging and ignition system i installed on it and the problem is gone and it ran great so you problem may be ignition but not necessarily the timming/lean jetting could allso cause the back firing

 

[74-Chop]

Cheers for the Advice Dog, I plan on renewing everything soon anyway as its older than gods dog so your probably on to something there!

 

[cowboy3669]

I had a problem like that when starting,the mech. advance was stuck in the full
advance position. Might want to check that.

 

[gggGary]

Yep on the list is sticky advance shaft and or weak advance springs.
I suppose a sticky intake valve or loose cam chain could cause it too. Many guys no longer realize that the points mechanisms wear out too, then they can no longer be timed accurately, the ignition just randomly wanders around. I've had a few points, mechanical advance bikes blow their carbs off. But not after I installed a Pamco......