Popping through the carb

[EDub]

Need some help...   04' gs500f (not california model

I am getting severe popping (almost like backfiring) through the carburetors at low rpms ( below 5k).  I checked that plugs, they seem fine.  From the research I have done, I have found that this is probably due to a vacuum leak.  Am I correct in assuming this?

This all started after i did a k&n filter and exhaust upgrade.  So it is very possible that I reinstalled some of the vacuum lines incorrectly.  I tried using the parts fiche, but it was somewhat unclear as to where some the lines went.  Does anyone have some clear pictures or a clear diagram of the vacuum hose routing that I could look at? If not I will try to take some pictures tomorrow of my configuration.

Note 1:  I used the rejetting recommendations found on this site so the sizes should be spot on, or close enough that it shouldn't be the problem. 

Note 2:  I had to use a plastic (polyurathane?) washer to shim the needle.  The #4's that are recommended on this site dont fit the gs500f models.  It was a pretty tight fit, so im not sure if this could be causing my problems.  I'm in the process of ordering the correct washers.

Any other suggestions would be greatly appreciated.

Thanks,
Kevin

[EDub]

bump

[ben2go]

I had the same problem and had to change carbs.Luckily I had the original unmolested set that was on my bike from the factory.I changed the jets over and I will be trying them soon.I had no vacuum leaks,no ignition problem,and no fuel problems.I still have found no reason why my bike done this.Take your carbs apart and check the diapghrams.Mine back fire thru the left carb and blew off the lunch box and blew the carb out of the intake boot on the left side.I stripped my other carbs and can't find any problems. 

Could be a sticky intake valve. 

[EDub]

thanks for info, glad im not the only one.  This all started after i did some modifications though (pipe and intake).  So im fairly certain it has something to do with that.

any more guru's out there wanna chime in? 

[EDub]

http://www.hillsboromotorcycles.com/fiche_section_detail.asp
carburetor model k4/k5/k6

So looking at the parts fiche i think i have all the hoses in the right place but im unsure about #43... does this connect to #47?  Also, does #73 lead to the petcock?

[ben2go]

http://www.hillsboromotorcycles.com/fiche_section_detail.asp
carburetor model k4/k5/k6

So looking at the parts fiche i think i have all the hoses in the right place but im unsure about #43... does this connect to #47?  Also, does #73 lead to the petcock?

That's an 04 with emissions equipment.I do not have experience with those.It may be a good idea to buy a Haynes repair manual for 89-06.They're $20-$25 for paper back and $70-$100 for hard back depending on reseller.

[EDub]

So I opened up the carbs and pulled out the membrane/needle assembly and got two surprises.  The smaller spring that pushes the needle down into the jet hole was bent, and now where it should have been.  Also, the shims that i put under the needle a long time ago were much larger thicker than i remembered.  So i took the shims out and straightened the spring.  The kicker is... when i went to put the upper carb cover back on, i stripped the threads... arg!!! o well... ill fix that tomorrow and fire her up.  I'll let you know how it turns out.

[EDub]

wow my grammer is amasing

[EDub]

BTW still need to know about that hose routing as stated above if any could chim in.

Thx

[arbakken]

http://cgi.stanford.edu/~sanjayd/gs500/Main/HoseRouting

like so?

[lamoun]

Try this...



Also look here http://www.mikuni.com/fs-tuning_guide.html for the backfire. My 06 does it to.

[EDub]

thanks lamoun, that helps alot

[EDub]

so i made a few minor changes and it is still doing the popping through the carbs... can someone look at these pics and tell me if my hose routing is correct?  Another symptom it has is a very slow return back to idle and virtually no power when i try to take off.








thanks,
Kevin

[EDub]

bump

[lamoun]

It looks fine to me!
The fuel hose goes to the brown T, on the lower part of the carburetors... (just in case... )

[EDub]

wonderful so im back at square one. Grrr!

[lamoun]

Still popping eh?

How do you feel about valve clearance inspection?? 

[EDub]

Hmmm... It has done this even after several valve checks by certified mechanics... so that one is out.  I just cant get my head around there must be a vacuum leak

[EDub]

welp, goin on vacation for a week guess ill deal with this when i get back.

[darb85]

Check your jetting, make sure that the butterflys are closing in sync.  I have a Corvair with 4 one barrels, i Get this everyonce in a while on high lean conditions.  you said you changed out your exhaust and such?  make sure that the jetting is right, then check your idle circuit, make sure both circuits are excatly the same turns out.  I thend to get it when my secondaries get thrown in slightly and then off throttle, though we dont have secondaries on these so...  dont know excatly whats going on with your carbs, but hopefully this gives your an idea?

Good luck!

Have a good vaca!