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Carb Reassembly

  • Thread starter Thread starter rickt
  • Start date Start date
R

rickt

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I'm finally ready to reassemble the carbs on my '78 GS750. Got the broken tips of pilot fuel screws drilled out by Motorcyclecarbs. Now to the question of installing the new fuel screws. As recommended in the carb rebuild article published on this site, I counted the turns from fully seated when I removed the screws. This bike was parked in 1981 with 2000 miles on the clock and, to my knowledge, the carbs were never altered from stock. All the fuel and air screws were sealed with white paint as from the factory. So, all four fuel screws were approximately 4.5 turns out from fully seated. My concern is that carb rebuild article suggests that the fuel screws are normally 3/4 to 1 1/2 turns out from fully seated. It seems like 1 turn versus 4.5 turns is a huge difference. My question now is - how many turns out should I use when installing the new fuel screws? Do you use a small screwdriver when attempting to gently seat these screws? How does one define "gently?" Could I have actually turned the screws much farther in that I should have when I disassembled the carbs?

Any advice would be appreciated.

rickt
 
careful

careful

You don't have to be too paranoid about seating the screws...just be careful and go slowly. I don't know much about your particular carbs but I'm sure someone with a '78 will write and tell you where to start tuning from. Good luck...it will work out fine.:-D
 
rickt said:
I'm finally ready to reassemble the carbs on my '78 GS750. Got the broken tips of pilot fuel screws drilled out by Motorcyclecarbs. Now to the question of installing the new fuel screws. As recommended in the carb rebuild article published on this site, I counted the turns from fully seated when I removed the screws. This bike was parked in 1981 with 2000 miles on the clock and, to my knowledge, the carbs were never altered from stock. All the fuel and air screws were sealed with white paint as from the factory. So, all four fuel screws were approximately 4.5 turns out from fully seated. My concern is that carb rebuild article suggests that the fuel screws are normally 3/4 to 1 1/2 turns out from fully seated. It seems like 1 turn versus 4.5 turns is a huge difference. My question now is - how many turns out should I use when installing the new fuel screws? Do you use a small screwdriver when attempting to gently seat these screws? How does one define "gently?" Could I have actually turned the screws much farther in that I should have when I disassembled the carbs?

Any advice would be appreciated.

rickt
Click to expand...

Rick
Is the weather here getting you anxious...it is me! If your 78 has the CV carbs, start with the 1.5 out on the air screws and a bench sync, as these adjustments may change, once yu hace the bike up and running well enough to do a final tune. The "gently seated" method, means just that, use a small screw driver and turn the air screws in until you feel the oring start to snug up. At that point, back them out to 1 1/2 turns.

Start the bike and once it has had a chance to warm up, (use a large fan or two, aimed at the block to keep things from getting too hot) readjust the #1 screw to achieve the highest RPM possible, then reset your main idle adjustment back to 1100RPM's and move onto the #2 carb and repeat the process, each time, resetting your main idle adjustment back to 1100RPM's. When you're done, if the carbs are truely clean and have been reset to spec, you'll have it right.
 
Dave,

Are you located near the Twin Cities? Yes, this is the time of the year that I pray for major melting and 50-60 deg. temps!

Your advice is right on for the the pilot air screws. Indeed my air screws were 1.5 turns out from fully seated. My post was in reference to the pilot fuel screws (on the bottom of the carb body). These are the screws that I am most concerned about as I start the reassembly.

Thanks,
rickt
 
rickt said:
Dave,

Are you located near the Twin Cities? Yes, this is the time of the year that I pray for major melting and 50-60 deg. temps!

Your advice is right on for the the pilot air screws. Indeed my air screws were 1.5 turns out from fully seated. My post was in reference to the pilot fuel screws (on the bottom of the carb body). These are the screws that I am most concerned about as I start the reassembly.

Thanks,
rickt
Click to expand...

Yes, 50 miles West on highway 55...Annandale (the playground for the well-to-do peeps from Woodberry! Lakes, lakes, golf courses, lakes, ski resort, lakes) \\:D/ :-D If the specs call for 3/4-1.5 turns out, and you're sure that yours were 4.5 out, then I'd try 2.5 out and adjust in or out from there. Out will richen the mixture, in will lean it out.
 
Gaskets Needed?

Gaskets Needed?

I am in the process of full disassembly and cleaning of the carbs for my GS650GLX, and thought I had all the stuff I needed. I bought new float bowl gaskets, got the o-ring kit from Robert Barr, and ordered new intake boot o-rings (my boots look great and are soft/pliable). However, while reading back through the many posts on the topic, I noticed talk about both float bowl gaskets and top gaskets. Are there gaskets between the top (CV boot/CV Cap) and body of the carb? I also looked at microfische and couldn't see any gasket there, or in the photos in the CV Carb Cleaning Series. If not, what are the post referring to as "top gaskets"? Thanks for any guidance, guys.

Best regards,
Norseman
 
Norseman said:
If not, what are the post referring to as "top gaskets"? Thanks for any guidance, guys.

Best regards,
Norseman
Click to expand...

No, you're reading posts about the VM carbs, which are entirely different animals. Your carbs don't use 'top' gaskets. You're OK, just follow the Carb Cleanup procedure.
 
My bad...

My bad...

Ah, the old MV, uh CM, no, MC, wait, VC, no that's not it, ok, got it, VM con... Thanks, Robert, should have figured that one out considering model year of original post...

Norseman
 
You'll sometimes find mixture screws set to ridiculous settings because a PO was trying to compensate for a lean mixture caused by an air leak (O-rings, intake boots, and/or leaky airbox) or other changes to the intake or exhaust. This does NOT work, in case you were wondering...

I don't assume that anything is correct when disassembling 25 year old machinery.
 
I think you may have seated the pilot screws too far in, thus the broken tips. I would start with 1 turn out. Set your side air screws for highest rpm, do a vacuum synch, and then do some plug chop tests. The pilot screws will only adjust the mixture for idle and just off idle. Read your plugs and fine tune accordingly.
 
Ughhhhh

Ughhhhh

Ok,
I am the very definition of newbie. I can rebuild a truck no problem, but this bike is driving me nuts. I got a 78 gs 550. No idea which carb (how do you know) I rebuilt the carb and set everything to factory specs via clymers. instant start up, perfect idle. my HUGE problem is that when I ride, if I get to 3k rpm's it boggs. 2nd gear....worse. cant get over 15mph. this is a complete project. I bought the bike for a hundred bucks. the 4 into 2 pipes are rusted with holes everywhere. I took out the airbox and installed pods.
now that you have read my story here are my "very stupid questions"
how do i determine what carbs I have
which needles (jets?) are which
any ideas on what I need to do
how do I sync the carbs

thanks.
I am still browsing these posts and I am very sorry if I am a repeater offender.
 
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