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engine missfire 4000-5000 rpms

  • Thread starter Thread starter dana
  • Start date Start date
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dana

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Hi I have a GS550L and between 4000 and 5000 rpms the engine feels like it has a misfire it is ok before 4000 and after 5000. I notice it because that is where the rpms are when crusing. I rebuilt the carbs in order to get the bike running and pulls good when accelerating. Has anyone seen this before? Any insight would be great.
Thanks Dana
 
Those "L" carbs are OEM fitted with smaller jets than the other 550 models, maybe for EPA reasons. I would try raising the jet needles to increase mid-range performance.
 
are you talking about the mixture screw at the back of the carbs? I hve not tryed sicronizing the carbs yet I bought a vacuum sicronizer. Should I try that first?
Thanks Dana
 
First, what are your adjustment screws set at? Even at that RPM range, if you are just "cruising" IE using minimal throttle opening as maintenence throttle, its going to be more on the pilot circuit than the needle circuit. Im not dicounting the above post, he is correct as well, but simply opening up your adjustment screws a bit can help possibly as well. Generally start with them 2 turns out each. When the bike is warm and idling happily, play with them a little, turning each out just a tad untill you hear the RPM rise its highest, and futher adjustment doesnt do anything. Do this for each. Mind you, they may NOT be the same amount of turns out, and that is ok. Sync WILL help your situation some as well i think.
 
Yes, I'm assuming the bike was running essentially problem free - basics good to go...

Just givin' my 2 cents on the 550L carbs since I already tuned & ride a set.

What maintenance has been done, miles, model year & mods are all good info to provide.

Good luck -
 
hikermikem said:
Yes, I'm assuming the bike was running essentially problem free - basics good to go...

Just givin' my 2 cents on the 550L carbs since I already tuned & ride a set.

What maintenance has been done, miles, model year & mods are all good info to provide.

Good luck -
Click to expand...
I certainly agree with you HikerMike. I have found success in shimming the needles as well. Good suggestion :)
 
The bike has 24,000 miles I turned the piloit screws out 31/2 turns out there are no modifications at all. Are you talking about shimming the main needle on the plunger slide?
Thanks Dana
 
One important part missing here ... what year is the bike?

I don't know when the 550L came into production, but if he has VM carbs, the adjustments will be different.

Oh, and this statement:
Are you talking about shimming the main needle on the plunger slide?
Click to expand...
does not make any sense. I realize that is due to your lack of experience, but the main jet is not the needle, and does not have any shims, and the only plunger is for the 'choke' circuit. What I suspect you are referring to is the jet needle that is attached to the diaphragm slide. Those are the needles that HikerMike referred to.

Your mixture screws are out 3 1/2 turns? Have you tweaked them for highest rpm? If not, try that, too.
 
I am talking about the diaphram slide needle I turned the mixture screws out 31/2 turns per factory specs. it is a 80 GS550L it does not have the eariler carb set up. Would one of those colortune tools be worth buying to set the mixture screws before I sycronize the carbs?
thanks Dana
 
I tryed to adjust the carbs tonight with the vacuum sicronizer I bought but at idle the needles flucuate a lot and could not adjust them right. I am going to try to shim the needls to see it that helps this weekend some time. if anyone knows how to set up the carbs with the vacuum sinc could you give me a lesson on how?
Thanks Dana
 
Just wanted to thank everyone for the info I remved the plastic shims on the main needles in put in 2 flat bradss washers the hesitation is gone now bike runs geat. Also wanted to let everyone know that I wnt to Radio Shack and they do not carry the washers now I went to a hardware store and bought the smallest brass washers they had th insie diameter was ok but the outside was too big I had to make them smaller by using a sheet metal hole punch.
Thanks Dana
 
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