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.
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?
got those on there, they arent original but some o rings i used that seemed to fit.
Quote from: MongMan on July 10, 2013, 09:05:15 PM
got those on there, they arent original but some o rings i used that seemed to fit.
:icon_eek: ... im no carb expert... or even a novice .. but ...
(http://upload.wikimedia.org/wikipedia/commons/thumb/3/3b/Paris_Tuileries_Garden_Facepalm_statue.jpg/300px-Paris_Tuileries_Garden_Facepalm_statue.jpg)
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 ;) :D :thumb:
Quote from: Snake2715 on July 10, 2013, 08:55:11 PM
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.
Quote from: demonsavatar on July 11, 2013, 03:20:12 PMI 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.
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?
Is the vacuum line off the carb plugged or is it an open line?
the one that is supposed to go to the left carb? i left it open.
You can't leave that open if you aren't using a vacuum line. You have to cap it.
+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
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.
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.
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 :).
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.
a common pla e to leak is the boots between carbs and head.
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.
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.
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?
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.
Quote from: demonsavatar on July 11, 2013, 03:20:12 PM
Quote from: Snake2715 on July 10, 2013, 08:55:11 PM
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.
Just quickly read through this thread... In my mind, with solving one lean issue and still stuck with another lean issue... this quoted above throws out a red flag again... We certain they work as intended?
If you mess with mixture screws, set them to the general starting point at three turns out from lightly seated and don't stray far from it... I doubt the mixture screw is causing the issue and changing it much will move your target... no one likes chasing a moving target... I personally wouldn't mess with it other than ensuring its not on the extreme ends to start with... just until you get a noticeable change for the better elsewhere, then dial in on the mixture screw.
Also, I might have missed it but, did you check the carb boots for leaks? most common place, and super easy check with WD40... I know you mentioned you replaced them, but double check they are seated well if you haven't, and triple check with the WD40.
- Bboy
Try mixture screw 3 turns out from lightly seated. I mean, really light, like tinger tip in the bit of the screwdriver light. If not working, sync carbs. It can be done by measurement, or with the vaccum meter. No need for a very precise sync to begin with, just to be sure that there is not a big difference between them.
You didn't mention the generation of the carbs but I'm assuming since you mentioned 37.5 that they are the older ones with less vacuum line bullshit.
Anyway, it's not imperative that the o-rings between the slide caps are of a specific diameter - just that they are of sufficient thickness to seal the area when the cap is tightened down. The ones that were in my perfectly functioning 97 carbs were really loose but did not affect it at all.
I would check to make sure you haven't accidentally snapped off one of the mixture needle tips. Tightening while dirty (not saying you did, but possible) can cause the tips to snap off.
Additionally, stock, my bike would not run AT ALL with 2.5 turns out on the mixture needles. I ended up with something like 3.5, so try 3 and see if that improves anything.
Finally, you may end up going to #40 pilot jets. I know it vastly improved things for me. Here's a video of my bike starting from dead cold with the #40 jets: http://www.youtube.com/watch?v=x5vidyo2_iw Keep in mind it was barely 50°F and the bike was stone cold. It started with no choke at all and then after about 15 seconds at 20% choke it ran perfectly with no choke at all. You'll notice it also didn't do that surging crap that you are likely to encounter without them.
Thanks for all the great tips and advice guys! I have been putting things back together to get the conditions recommended in this thread, but haven't got a chance to start it yet. So far i have taken off the carbs and turned the mixtures 3 turns out from very tightly seated. Dohhh now i read from lightly seated >< ill still try it out though, got the airbox back on with the air filter (its always a tuff job for me lol), just need to hook up the tank and ill give it a test tomorrow and report back. Its a 91 bike that has tags from 2003 so i am assuming it has not been run for a very very long time. Im not exactly sure how long though (bought it like that) oh yea and the carbs are not synced i only eyeballed them to get them as close as possible when rebuilding them.
0A big tip with the carbs and air box.
Put the carbs on the airbox get those boots tight and mounted.
Then install the whole combo in the bike and the front boots. Makes things a lot easier. It will fit as a unit, just get it between the frame with a little finesse and go from there.
Another small tip...you can use feeler gauges to bench sync the carbs.
Quote from: Snake2715 on July 19, 2013, 06:37:35 AM
0A big tip with the carbs and air box.
Put the carbs on the airbox get those boots tight and mounted.
Then install the whole combo in the bike and the front boots. Makes things a lot easier. It will fit as a unit, just get it between the frame with a little finesse and go from there.
I actually find it easiest to take the air filter out and use my hand inside the airbox to make sure the carb to airbox boots are completely outside the carb mouth while you slide the airbox on.
?| I should have clarified that, yes without the filter in the air box.
thanks for the tip much easier that way.
Ok i started it up today and here is what happened: on first startup i had the same problem i was having without the airbox and filter. the rpm was surging between 2-4k after warmed up and requiring choke to stay alive. So i sprayed WD40 all over the intake boots and nothing changed either. I expected this much though because i changed the boots and put new gaskets. So after reading about the mixture screws position relative to force, i turned them out 2 extra turns though it might have been 3 turns i forgot lol. So i am thinking i was around 6 turns out from bottoming them out originally. Started it up and the surging was gone! it stayed at 2k rpm with choke on. So i turned in the idle screw until the rpm went way up high, then dropped the choke a little to get rpm back down, then turned the idle screw in some more to get rpms way high, then the choke down some more, continuing this routine until the bike ran at 1.5k rpm with choke completely off. I would love to say success story right about now but the last problem about the throttle response is not completely normal.
Now with the choke off and the bike idling ok, on initial twist of the throttle the rpm rises in a somewhat responsive way, except it takes a long time for the rpms to drop back down after letting go of the throttle. So this is where i am at currently, i didnt get to remove the spark plugs sorry it got too dark out when i finished, and also another thing i noticed is that i am not using the two gas vapor hoses connected to the bottom of the carbs. I plugged them in, but i didnt notice any difference, so i just left them off for now, because i am not using original tank yet. I think they are just for recycling the gas vapors from the tank, i just hope leaving the holes open in the carbs isint a problem is it? S