Carb fuel and air screw question.....Where to start?

[1978GS750E]

I've finally gotten around to the carbs on my new project, the 1978 GS1000. My question is, since I am replacing the pods with the stock airbox, and leaving the 4-into-1 exhaust on it. What would be a good starting point on the fuel and air screws? When I tore the carbs down, the main jets were #105 and the fuel screws were at 3-1/2 turns and the air screws were at 1-1/2 turns. Anyone running the same set up? Leaving in the #105 jets, I was thinking 2-1/2 on the fuel screws and 1-1/4 on the air screws might be a good starting point???? I really do not have any idea of how it ran before as it was sitting for 13 years before I got it. Any help is greatly appreciated.

[Steve]

What 4-into-1 pipe, and how loud is it?

Seems silly, but a louder pipe tends to flow more air and requires larger jets. But, ... since the main limiting factor on air flow is the airbox, it might not matter all that much.

Stock jetting is 100 on the main and 15 on the pilot. Your 105 main might be a little bit much, maybe not. However, your fuel screw setting is WAY off. Stock, we suggest about 5/8 to 3/4. With pods and a pipe, about 1 full turn, but nowhere near the 3 1/2 turns you had before. I would suggest about 3/4 turn on the fuel screw and 1 to 1 /4 turns on the air screw as a starting point. Adjust the air screw for best idle for each carb. Don't forget to do a vacuum sync. I do a sync before any jetting changes, then double-check after the changes.

Have you CLEANED the carbs and adjusted the valves?

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[1978GS750E]

Thanks Steve. The pipe is a Vance & Hines Pro Sport???? I have no idea how loud it is as the bike has not ran in 13 years. I have adjusted the valves and cleaned the carbs, including new O-rings. Carbs were actually pretty clean as the previous owner told me that he drained the fuel before putting it away, they looked like it! Of course, all the O-rings were very hard and brittle. I thought that the fuel screws were way off when I disassembled the carbs. I'll start with them 3/4 turn and the air screws at 1 turn and see how it goes. Looking forward to hearing this thing run again! Waiting on bowl gaskets, ordered some off of Ebay from hildebrandtgasketcompany and I never received them. Ordered more today, from a dealer, should arrive this week. Live and learn!

[Steve]

Get that thing running. Bring it on up to Bedford in June.

.

[Big T]

Stock main jet is 95, so 105 may be rich.
You may have to raise the needles a notch
On the fuel screws, if you have to open them much more than one turn, you need a bigger pilot jet.

[Steve]

Stock jetting is 100 on the main and 15 on the pilot.

Stock main jet is 95, ...

Had to look that one up. You are correct.

For some reason, I had "750" on my mind.
Still uses a 15 pilot, though.

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[Big T]

It's OL, Steve, if you actually knew every spec I'd be worried about you.

[Steve]

I guess there's no need to worry, I have to look up just about anything that's not for an 850.

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[1978GS750E]

Carb bowl gaskets are due in on Thursday. I'll let you know how it works out. Excited to hear it run and see if my $500 was well spent! LOL

And Steve, I plan on being in Bedford. Trying to decide if I want to ride up there or put the GS1000 and the GS750 on a trailer so I can ride both of them some while I'm there.


Thanks for all the help guys!

[Steve]

You will not be the only one with a trailer, so bring what you want.

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[1978GS750E]

Well this afternoon I got the carbs back on with the stock airbox! If anyone is wondering there are absolutely no profanities left, I used them all! Most of them more than once and sometimes in convoluted multiples! But it is all together now. The fuel screws are set at 1 turn and the air screws are at 3/4 turn. Hooked up my test tank and she started right up without any choke at all. Since it was the first time running since 2006, I wanted to just let it idle a while and sort out the cobwebs! I did not attempt to do any carb adjusting tonight. I did check the battery voltage and it is running a solid 14.7 volts at 2,000rpm. I have a small fuel leak at the rubber connector between #1 and #2 carb. I hope that having fuel in it will make it seal. Going to do more fine tuning on the carbs this weekend if it gets warm enough. Can't wait to actually ride it!

[Big T]

Congrats!
Based on what you posted, I'm guessing you didn't replace the carb boots?

[1978GS750E]

Oh yeah. I replaced the intake O-rings, all the carb O-rings, and got new airbox to carb boots. You really don't want to take these carbs off more than once, so I replaced anything that could be replaced.

[Steve]

Oh yeah. I replaced the intake O-rings, all the carb O-rings, and got new airbox to carb boots. You really don't want to take these carbs off more than once, so I replaced anything that could be replaced.

But, ... as Big T asked: you didn't replace the intake boots?

New boots let the carbs slip in just like your pair of comfortable slippers. With your description that involved a rather complete depletion of the expletive stock, it appears that you still have the old, hard boots.

They're not cheap, but you won't have to change them for another 20-25 years.

.

[Big T]

Oh yeah. I replaced the intake O-rings, all the carb O-rings, and got new airbox to carb boots. You really don't want to take these carbs off more than once, so I replaced anything that could be replaced.

I can take them off or put them on in less than 15 minutes