I give up!

[drphilgood]

I know i dug my grave on my 80 GS750L when i put fancy chrome pod filters on it.Then dug a little deeper when i cut the rusty exhaust off and made straight pipes.Well i did install a stage 3 jet kit and rebuilt carbs using all new o rings and gaskets.Also set the float height to spec using Bikecliff's website to guide me.#4 cylinder just doesn't sound right ever.The other cylinders have a nice rumble but old #4 doesn't it just kinda sputters.Then i thought maybe the valves arent adjusted so i adjusted them to spec(thanks again Bikecliff)Then i thought maybe i wasn't getting a good spark on #4 not the case.Then i thought i had a dead cylinder there all reading high 90s across all cylinders.
The bike idles like crap,take offs are slow with no exelleration but top end roars!A lot of good it does in big city traffic.Then to top everything off it back fires like crazy on deceleration.So i bought another air box (thanks jedonly)because mine was missing parts when i got the bike.Will this help?What am i missing guys?Ive been fighting my bike all summer!If i cant get this thing running right its outta here!!!

 

[Guest]

With the straight pipe I'd try the needle on the second from bottom notch. I'd also go up one step on the pilot jet.
The #4 sounds like there is still crud in the pilot circuit. If you spray carb cleaner in the pilot air jet it should come out the pilot jet. If not it won't idle on that cylinder.

 

[drphilgood]

With the straight pipe I'd try the needle on the second from bottom notch. I'd also go up one step on the pilot jet.
The #4 sounds like there is still crud in the pilot circuit. If you spray carb cleaner in the pilot air jet it should come out the pilot jet. If not it won't idle on that cylinder.

I will try this.Thanks ,I'm at my wits end here!

 

[almarconi]

More than likely your still running lean. How do the plugs look? The carbs
are still probably clogged. How does it start when the bike is cold? I've been having a hard time getting mine running right. I got so frustrated I ended up taking the bike to a my mechanic. Just got tired of wasting time on it. I figure its worth it just to pay him so I can get it on the road.

 

[drphilgood]

Its starts up easy no choke.The plugs are a dark brown.

 

[Guest]

healthy compression figure is above 130psi
100psi is serviceable limit
high 90s would still work ok in the stock configuration but with your mods you'll have a helluva time getting it to work well at low revs

it your configuration i wouldnt bother trying to jet it correctly before rebuilding the top end

 

[almarconi]

Did you vacuum sync the carbs?

 

[drphilgood]

healthy compression figure is above 130psi
100psi is serviceable limit
high 90s would still work ok in the stock configuration but with your mods you'll have a helluva time getting it to work well at low revs

it your configuration i wouldnt bother trying to jet it correctly before rebuilding the top end

Ah man i didnt want to hear that!

 

[drphilgood]

Did you vacuum sync the carbs?

I havent done that!Will that help?

 

[76FJ55]

when you test compression you need to test it at Wide Open Throttle. if you tested with the throttle closed that could explain the low readings.

 

[Guest]

I haven't done that!Will that help?

Considerably...

 

[drphilgood]

when you test compression you need to test it at Wide Open Throttle. if you tested with the throttle closed that could explain the low readings.

AHA i will test the compression at wide open throttle tomorrow.Ya i tested it at idle.

 

[drphilgood]

Considerably...

Hmm im thinking that may be alittle in depth,Ill check out bikecliffs site and see if he has anything on syncronizing carbs

 

[drphilgood]

Ok do i do a bench sync or the vacuum sync or both?

 

[TheCafeKid]

If you were getting 90psi at idle when warm, you're likely going to be in good shape. Test it anyway at WOT. I think your pilot circuit is still clogged. You have to be meticulous. They are tiny TINY little holes in the pilot system. You may still be lean, but that wouldnt explain one cylinder being bad, and you really cant bother playing with carb sync and tuning untill you have it firing on all four at idle and off idle. Check your compression, do another clean, should be able to keep the orings if you are carefull. Oh, another tip, when you put those orings in again, oil em up a little bit. I have had to pull jets out with new orings only to find they were chewed up from the turning them in. Oil makes things go in nicely. Little tip i learned from Steve...

 

[almarconi]

Nobody mentioned it yet, but where are your mixture screws set? Did you also verify that #4 is getting fuel?

Once you get it running on all four cylinders you should do a vacuum sync.

The compression test needs to be done on a hot engine, all plugs removed, open choke, hold WOT and crank the engine with gauge installed
in the plug hole.

 

[Steve]

Ok do i do a bench sync or the vacuum sync or both?

The main purpose of a bench sync is to get them close after you have had the rack apart, most likely for a thorough cleaning. After you then get it running, to the vacuum sync. If you have not had the rack apart, you only need the vacuum sync.

.

 

[drphilgood]

Hmm i have had the rack apart when i cleaned each carb individually.so i will pull the carbs off,tare apart,clean and rebuild using new orins and oil on rings.Then i will bench sync the carbs.Im getting ahead of my self first ill check the compression.ill let you all know what i find out.

 

[drphilgood]

It lives

It lives

Just an update:I went over to Bikecliff's site and read up on how to sync the carbs.I ordered a Morgans carbtune and a colortune.While i waited on them i tore apart the carbs again cleaned and replaced the orings and bowl gaskets.Also ordered new mixture screws(needles).Last nite i put everything together using all the new hardware.Today i got the carbtune and colortune in the mail.This evening i installed the carbs after i benched synced them.I have to say synchronizing the carbs is really easy with the carbtune.With the syncronizing done my gs sounded alot better but old number 4 was spitting and sputtering still.So using the colortune i adjusted the mixture on number 4 and finally it came to life.After i adjusted all 4.I took my cycle for a cruz and it performed perfect!I still need to take it to a dyno shop but its running good now.I would like to thank everyone for giving me advice and a big thanks to Bikecliff for sharing all his knowledge on a open site!

 

[paco13]

Glad You got it running good, But another thing I didn't see mentioned is to adjust your valve lash. If you have some tight ones it will effect compression, as well as performance.