help me identify these gs500 symptoms

[MongMan]

Hi, i feel so close to getting my gs500 running but its just not quite right. What could be all the possible causes of these symptoms:

bike starts quick with full choke but the rpm is very very low, which is not normal for me as i always thought full choke gives very high rpms. It barely stays alive though, and after warming it up i can reduce to almost half choke but anything less than half and it will die from too low of an rpm. After its warmed up if i give it throttle it will bog down and almost die unless i  start giving a lot more throttle and when i reach high rpms the throttle response is there. So basically it only runs with choke at low rpm probably below the idle rpm, and initial throttle response is boggy. I cant twist the idle screw in much or it wont even try to start.

new spark plugs
new intake manifold gaskets
valve adjustment in spec
did the carb a bunch of times because from research it sounds like the smaller 37.5 jet is the problem, but after using some wire in them and putting them back in, same problem so i took them out again and i could still see through the hole, was not clogged, put them back on still same problem. hmmpfh
If i watch the slides in the carb while i give it a little throttle they spaz and jiggle (thats when the bike bogs and wants to die) but giving a lot of throttle they slide up normally.

[Snake2715]

Someone else with waaay more experience will hopefully chime in..

Did you lose the oring in the tops of the carbs (under the cap) when re assembling?

[MongMan]

got those on there, they arent original but some o rings i used that seemed to fit.

[Janx101]

got those on there, they arent original but some o rings i used that seemed to fit.

... im no carb expert... or even a novice .. but ...



but .. they could be good .. ?! ... just ive heard "it fitted pretty close so we went with it" a lot of times over the years on various mates vehicles projects ... its also known as pot luck mechanics 

[demonsavatar]

Did you lose the oring in the tops of the carbs (under the cap) when re assembling?

Correct me if I'm wrong, but if the o-rings are missing/wrong, the carbs would be getting more air, and likely increasing the RPMs, not killing the engine like OP said.

I would start checking if fuel is getting to the carbs.  Maybe remove the frame petcock, and feed some gas via a funnel directly into the fuel line going to the carbs and see if it runs.  Similar procedure to a carb sync.  In fact, if you're doing that, might as well do a carb sync too.

[RossLH]

I would start checking if fuel is getting to the carbs.  Maybe remove the frame petcock, and feed some gas via a funnel directly into the fuel line going to the carbs and see if it runs.  Similar procedure to a carb sync.  In fact, if you're doing that, might as well do a carb sync too.

Easier yet, put the petcock on prime and open the float bowls one at a time.

[MongMan]

i forgot to mention i have bypassed the petcocks and used a different motorcycle gas tank that works on a running motorcycle connected to the carbs to be sure. So i am guessing the symptoms i described are not obvious to a specific problem with the motorcycle? I was thinking it has got to be something really really simple. I should also mention with the original gas tank i did only run it on prime setting, and i dont have the vacuum line to the left carb hooked up either. All i have connected is the choke cable, the throttle cable, and a gas line. And....... i haven't done a carb sync, could a carb sync be causing these kinds of problems?

[Courtice_GS500]

Is the vacuum line off the carb plugged or is it an open line?

[MongMan]

the one that is supposed to go to the left carb? i left it open.

[bombsquad83]

You can't leave that open if you aren't using a vacuum line.  You have to cap it.

[Courtice_GS500]

+1

Bomb is right. That line being open is going to cause a massive vacuum leak.
Cap it like the one on the right or even use a piece of hose folded over and zip tied then try running and see what you get.

Vacuum leak= running like crap

[bombsquad83]

I used a rubber cap and metal clip the same as the ones that are used for the sync ports on the diaphragm caps on our carbs.  I think you can find caps that will work at an auto parts store as well.  I don't use the vacuum line because I replaced my petcock with one from an '07 Honda CRF250X which does not use vacuum. 

[Snake2715]

Yeah a pack of various size caps is 2-3 at the auto store and put the smallest one that you can manage to fit on it. Dont put one that slides on easy.

[MongMan]

wow thanks guys, that definitely changed my gs500's behavior! now it revs up way high with full choke! 4000+ It doesn't bog anymore when giving throttle either. And i can get the choke position very close to off but not quite lol. But grrrr now other problems have surfaced, now that i have the vacuum plugs on both carbs, The idle is surging up and down and the throttle response is delayed plus it takes a while to drop back down if at all, a lot of back firing too. Im very reliant on you guys lol, where should i look next. Thanks so much for the vacuum leak info, i knew you guys would show me that it was a simple simple thing like a plug .

[Courtice_GS500]

Bouncing and hanging idle is generally a vacuum leak. Have you tested everywhere with WD-40?

Have you checked the plugs? Are they showing lean or rich?

Do you have stock jetting in the carbs? Stock exhaust and air filter?

The backfire is probably due to your air/fuel mixture.

Make sure you have no vacuum leaks anywhere and pull the plugs. They will tell you what your A/F is.

[Snake2715]

a common pla e to leak is the boots between carbs and head.

[MongMan]

stock jetting, mixture screws 2.25 turns out, stock exhaust, no air filter on carbs atm while testing, damn another vacuum leak? i replaced those intake manifold boots already and put new gaskets on them. I'll pull the plugs n report back, but they tend to be black because of the choke always being on.

[Courtice_GS500]

Try putting the air box and filter on while your testing.
Run it until you can turn the choke off completely then pull the plugs.

I would hazard a guess and say that you are running lean.

[MongMan]

wow think your right again the plugs are white, i didnt know lean running could cause such havoc. Should i turn the mixture screw out a bit?

[Courtice_GS500]

Were  they showing lean with the airbox and filter installed on the carbs?

If so then you can try the mixture screws or you might need to jet up.

I will leave that call to the the carb guru's.

If your still testing without the filter and box your going to show lean no matter what you do.