REbuilding carbs on 77 GS550

[old374]

Hello all,
I have just kitted all of the carbs on my bike. I have a Haynes manual which tells me what the setting is for the pilot screw on the side of the carb , bvut nothing for the one underneath ( in the feul bowl area) I have set them all at 1 turn out as that is where they were before but I don't know if they were right either.

Second question is overflow pipes and breather pipes. When I got this bike he has a pipe coming off every outllet on the carb and running down the back of the engine. So all up there were 7 pipes for overflows. Can anyone piont me in the direction of tidying these up. There is a oveflow off the bottom of each bowl, plus carbs 2,3,4 have pipes coming out of the side. CAn these be routed into each other as a common breather at all?

Thirdly with regard to jetting , I have pod filters and ahort mufflers fitted. The kits installed were a stock item I assume(they came with the bike) and have main jets of 80 and second jet of 50. What will I have to jet up to to get a rich enough mixture. I have lifted all of needles up one notch for mor midrange fuel as per the book. It says that jets really only come into playu from 3/4 - full throttle , which wont be seen much on this bike.

Any advice is appreciated

Cheers
Shaun

 

[Steve]

Hello all,
I have just kitted all of the carbs on my bike. I have a Haynes manual which tells me what the setting is for the pilot screw on the side of the carb , bvut nothing for the one underneath ( in the feul bowl area) I have set them all at 1 turn out as that is where they were before but I don't know if they were right either.

For a STOCK bike, the 'normal' setting is about 3/4 turn. As I read through your post, I see you are not quite 'stock', so 1 turn is probably good.

Second question is overflow pipes and breather pipes. When I got this bike he has a pipe coming off every outllet on the carb and running down the back of the engine. So all up there were 7 pipes for overflows. Can anyone piont me in the direction of tidying these up. There is a oveflow off the bottom of each bowl, plus carbs 2,3,4 have pipes coming out of the side. CAn these be routed into each other as a common breather at all?

Yes, you should have a total of seven hoses, but only the four coming from the bottom are "overflow" tubes. They should definitely be routed behind the engine, and hopefully far enough to the side that they won't dump fuel onto the tyre if things happen to go wrong.

Apparently you are also numbering the carbs correctly. :clap:
The hoses on #2 and #4 are VENT hoses, and used to be routed up, over the airbox to end over the filter area. With your pods, many will remove the hoses from the "T"s and turn the T downward. The whole idea is that the end of the air passage, whether it's the end of the T or the end of a hose, a foot away, needs to be in relatively CALM air. With the stock airbox filling the hole behind the carbs, it was a great place. With pods, there is more airflow and turbulence in that area, so "no hoses" puts the end of the T in a relatively calm area.

The hose on #3 is your vacuum hose that needs to be connected to your petcock to turn on the fuel when the engine is running.

Thirdly with regard to jetting , I have pod filters and ahort mufflers fitted. The kits installed were a stock item I assume(they came with the bike) and have main jets of 80 and second jet of 50. What will I have to jet up to to get a rich enough mixture. I have lifted all of needles up one notch for mor midrange fuel as per the book. It says that jets really only come into playu from 3/4 - full throttle , which wont be seen much on this bike.

The stock main jets were 80, not sure what the 50 was for. With pods and a freer-flowing exhaust, you will likely need something in the 100-110 range, but I can't say for sure.

.

 

[tkent02]

The hoses on #2 and #4 are VENT hoses, and used to be routed up, over the airbox to end over the filter area. With your pods, many will remove the hoses from the "T"s and turn the T downward. The whole idea is that the end of the air passage, whether it's the end of the T or the end of a hose, a foot away, needs to be in relatively CALM air.

There is no T. Just a nipple on #2 and #4 which looks identical to the vacuum nipple on #3.

 

[Big T]

Shaun,

You'll find most of your answers here

http://members.dslextreme.com/users/bikecliff/images/GSR_Greeting.html

One turn out on the pilot fuel screw should be OK, go 2 - 2 1/2 on the air screw to start

The middle hose, on carb 3 is a vacuum that hooks to your fuel tap, don't leave that open. The other 2 are vents, not overflows. The 4 on the bottom are overflows, they should run down the right side of the back of the engine cases, look for a little rectangle there, thread them thru

It will probably run better with the 2 vent hoses removed. Go up to about a 100 main jet. The pilot jet should be about a 15, not a 50. You'll have to tune it from there

With a 550, if you're not going to rev it up, sell it and buy a scooter. The 550 needs to be above 6,ooo prm to make any power

 

[old374]

Thanks everyone, invaluable info there. I have blanked off the Vacuum and will leave the other 2 blank. I am going to do the manual sync tommorrow and have just ordered some 100 jets for it.

Thanks for the link to the welcome page, just what i needed

Cheers
Shaun

 

[Steve]

There is no T. Just a nipple on #2 and #4 which looks identical to the vacuum nipple on #3.

Sorry about that, I do most of my work on the BS-series carbs.

.

 

[old374]

So I have the bike up and running now. It has cheapy pod filters( being replaced for good quality foam filters) and short open flow tapered mufflers. The mufflers are also being replaced with a more restrictive muffler. It has 100 main jets and the rest are factory. The local bike shop synced them up for me and reset all of the needles . When I got it back it was flooding and fouling #2 plug and running really bad. Upon investigation I found the #2 needle was set up with the thick nylon washer under the thin one holding the needle up. I fixed this and it was still rich so I raised the needles one clip. I reset all of the floats to 23mm and test rode. The bike pulls nice and clean to 6000rpm and then starts to miss and fart and carry on and will not accellerate any more. It is flat out at 85kmh.

Any ideas?? I did a plug chop and the plugs seemed a bit rich still but not fouled . I am starting to lean towards coil at themoment because I think I have all of the fuel ok.

All help appreciated

Cheers
Shaun

 

[Guest]

Could be you're entering ignition territory here.

Being a 77 I'd assume it has points, how are they looking? Gapped correctly? Filed if necessary? Also, how are the condensors on the coils? If I recall correctly I have heard they can cause breakdown at higher rev's if they're on the way out... but don't quote me on that!

Also, check to ensure your mechanical advance mechanism is moving freely and springing back as it should, otherwise she won't want to rev real well if the mechanism is not advancing the ignition at the right point.

 

[Guest]

It still sounds like you are too rich on the main jet. I don't know how much 1mm will affect it, but your floats should be set to 24mm, same as the GS1000 according to the stock factory specs. I had the same problem with a set of VM carburetors trying to tune them for pipes and pods. I could push through to higher RPM's but it would be real reluctant to do it in the mid range. I would wait until you settle on your pods and pipes before wasting any more time on it. The foam pods are going to be more restrictive than what you have ora good set of K&N's and who knows what airflow will be consistent until your pipes are on. If you still want to play with it lean it out on the main needles to see if that helps.