1981 GSX250 carb problems

[CafeGSX]

Hi, first of all let me say this is a great forum and there is certainly a lot of information available.
I have a 1981 GSX250E, which to some of you is a GS250. About 4 months ago, while the bike was running quite well, I began to strip it down and restore it. I had the frame sandblasted and gave it a nice black powdercoat finish. I cleaned the engine up and gave the side covers a polish and painted the barrells and head black. Looks quite good. Had to modify the electrics abit, but only by shortening it a little.
Yeah yeah all nice and good, but what's the problem you say? Well let me just say that I have read quite a few articles and yes even conducted a number of searches to find out what I can do.
While separate from the engine I gave the carbs a really good clean and tried not to disturb anything as it was running quite alright. Yes opened them both up and removed each jet, float etc and gave a good hit with carby cleaner and then compressed air. Fitted it all back together waiting for the frame to be finished. I did purchase some new O rings that fit between the inlet manifolds and the engine, however saw that they were too 'fat' and the manifolds did not sit flush. Thought though that it was a pretty good fit.
Put the engine back in, fitted all the electrics and mated the carbs back with the engine, taking great care to put it all back together correctly. Fired the engine up and it started nearly straight away, needed to prime each carb so that fuel got into the engine.
Anyway, I backed the throttle off and the engine cut out. No problem, but it took a while starting, needed to hand prime each carb to get it going. At this stage I have not got to putting the cone filters on so the carb inlets are directly exposed to the outside air.
Had the engine fire up again and yet again it would not hold above 1500 revs having to keep throttle open in order for it to run. After reading a few forums and seeking a bit of advice from local motorbike shops I am at the point now where I have changed the O rings back to smaller size so that they now fit flush with the engine. I have put 120 size main jets in for when I can put the cone filters on. I had also found that the left intake manifold had quite a big slit in it and it was drawing in extra air, new boot bought and replaced.
Today, fired the bike up with all the new changes and yet again the bike does not want to idle at all. I have pulled the carbs apart at least 6 times and cleaned them as best that I can.
I am really hoping that someone can shed more light on what else I can look at. I realise that the pilot jet is responsible for idle at low rpms, I have removed each of them and they are as clean as a whistle.
Hoping someone can help.
Steve

 

[hillsy]

....I have not got to putting the cone filters on so the carb inlets are directly exposed to the outside air....

That would be part of your problem.

Did the bike have the stock airbox before you disassembled it? If so, you will be running very lean without this - and worse still without any form of filtration.

I know you said you changed the main jet, but this only comes into play at higher RPM's. You will need to richen up the idle circuit at the very minimum (and possibly step up the pilot jets). There should be a screw on the top of each carb between the manifolds and the slides to adjust the idle circuit. Start at 3 turns out and adjust by 1/4 turns to get the best running condition. Although you are probably best off getting air filters on there first before you start messing with the carbs any more.

Good luck with it

 

[tas850g]

check to makesure you're petcock is working well. I had similar problems with mine and the petcock was not allowing fuel to the carbs. Not sure what type of petcock you have but i put mine on "pri" and it ran great.

I have a chance to buy a gs250. cheap, around $100. Not sure about it. just something to tinker on. I guess one of the coils is not working.

 

[KitKat]

http://members.dslextreme.com/users/bikecliff/ - look for carb cleaning guide.

if you havn't cleaned the carbs by soaking each for 24 hours, i recommend you do try that, and also

new orings from www.cycleorings.com (run by fellow gsr user) are great!

 

[CafeGSX]

Thanks guys for your input. I did have the original airbox on so I guess it helped it breathe a bit better, but I don't want to go back to that airbox as I have modified the bike for a cleaner look. The petcock is the two stage type where there is no PRI mode, there is a screw that is loosened to help prime the carbs, then tightened once done. The petcock is always on basically. I have a clear in line filter and I can see that the fuel is running freely. There is a pulse line from the right carb to the petcock to make sure the fuel is drawn to the carbs.
I haven't soaked my carbs, that may have to be the next step, and I have already replaced all the O rings.
I managed to start the bike yesterday and hadn't noticed it before but the bike did idle (breifly) at low RPM's and it sounded like a misfire. When the bike engine revs got to aboe 2000 the misfire disappeared. Any ideas on this? I've had a look at the timing and there isn't a great deal of manipulation of the timing to be that far out of sync.

Steve

 

[KitKat]

most people don't run inline filters on the gs because the petcock already has a filter and the extra in - line may restrict fuel flow; however, with your after market petcock... does it have a built in filter? if it does, i would recommend taking out the inline

 

[doctorgonzo]

Inline filters are fine as long as they are made for a bike (or a lawnmower) and not a car (which has a fuel pump).

If you don't want to run the stock air box, then go ahead and rejet the carbs while you're cleaning them because that is the only way it will run right. That 120 main MIGHT do it, but it also might not be big enough. Also, you'll have to raise the needles, and turen the pilot fuel screws out a fair bit (which is propbably your idling problem).

Will it hold idle if you keep it on choke?

 

[CafeGSX]

Thanks once again guys. So far I have taken the inline filter out, it was a clear one and it was easy to see if fuel was flowing, which it had been. I've taken it off and connected it all back up. Might do as you have suggested doctorgonzo and raise the needle. I pulled the spark plugs out and saw that the right pot was running lean so I adjusted the mixture on that carb to a bit richer, the spark plug on the left pot was black with soot, I leaned the mixture a little in this carb.
I don't think it is an issue with syncing the carbs as last time I had the carbs off I did as suggested in other posts and got the butterflys pretty close on the bench.
The engine doesn't run long enough to really get a feel for much. Next I will raise the needle and see how that goes.

Steve

 

[CafeGSX]

Okay, well spent the afternoon pulling the carbs apart again and thouroughly cleaning them again. Took plenty of time, carb cleaner and compressed air. Shifted the needle one position on each carb as well.
Put them both back together and mounted them on the bike. Connected everything up double checking everything. Damn thing wouldn't start. It wanted to fire on the right cylinder, but wouldn't fire on the left cylinder. Well got out my spark tester and guess what, no spark on left coil!!!! Got out my multimeter and checked resistance through both coils, it appears that both coils are down on the second windings. Left side is 15ohm and right side is 18-19ohm.
Now looking like I have to replace the coils, what is the suggeston for a replacement? Can I use coils from another GSX ie maybe a 450, or is there an aftermarket coil that I can use?

Steve

ps Hope everyone has a great start to the New Year.

 

[KitKat]

coil relay mod on bikecliffs site

 

[CafeGSX]

Took the coils down to a local auto electrician and both coils are fine, good sharp spark jumping 9mm! I guess the next thing to check is the igniter. Has anyone had any trouble with these? I don't see much can go wrong with them.

 

[kilog55]

the problem with running a inline fuel filter is most arent made for vacuum/gravity type fuel delivery like our bikes are. they also reduce flow being smaller then the ID of the fuel line and the paper is hard to flow through.

 

[landshark]

Where are you?
I know a guy with a lot of gsx250 parts.

Okay, well spent the afternoon pulling the carbs apart again and thouroughly cleaning them again. Took plenty of time, carb cleaner and compressed air. Shifted the needle one position on each carb as well.
Put them both back together and mounted them on the bike. Connected everything up double checking everything. Damn thing wouldn't start. It wanted to fire on the right cylinder, but wouldn't fire on the left cylinder. Well got out my spark tester and guess what, no spark on left coil!!!! Got out my multimeter and checked resistance through both coils, it appears that both coils are down on the second windings. Left side is 15ohm and right side is 18-19ohm.
Now looking like I have to replace the coils, what is the suggeston for a replacement? Can I use coils from another GSX ie maybe a 450, or is there an aftermarket coil that I can use?

Steve

ps Hope everyone has a great start to the New Year.

 

[CafeGSX]

Hi landshark, live in Goulburn NSW.

 

[landshark]

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