Trouble with oil and fuel 1978 gs750

[Mocks]

I picked up a 1978 gs750 the other day that supposedly had the rings replaced, head resurfaced, valves cleaned and adjusted along with the carbs gone through... I had to REdo the carbs when I got it, But I think I still need to do a little adjustment to the needles and seats. It runs fine and starts good, but about 1/4 to 1/3 throttle it states to bog down and it picks back up when you throttle through it, am I correct in believing that the needle may need to be adjusted up or down? Also I am not 100% sure the rings were done properly as I am getting a lil smoke on start up and anytime I "blip" the throttle. I don't know if itd be anything to do with the valves as it seems more like a ring issue. Whatcha think? I'm an empty vessel, fill this thing with knowledge! Thanks.

[Big T]

Mocks, did the PO supply you with any receipts for said work? Did he do the work or have a shop do it?

Not enough information given

1. Stock air box or pods?
2. Stock exhaust or 4-1?
3. Fuel screw settings?
4. Air screw settings?


Also, I'd advise going up to GS Owners and introducing yourself (not manditory) and getting your megawelcome. That will fill you with knowledge

The smoke may come from the rings not being seated, ring ends not staggered, bad valve stem seals or other things

[BassCliff]

Greetings and Salutations!!

Hi Mr. Mocks,

With an unknown history, it is "best practice" to perform all of the proper maintenance and tuning so that you can establish a baseline for any further issues. You have a 30 year old motorcycle that probably needs 20 years worth of maintenance. Go through the maintenance lists in your "mega-welcome". Skipping steps or taking shortcuts will lead to frustration and catastrophic failure.

Let me dump a TON of information on you and share some GS lovin'.

I just stopped by to welcome you to the forum in my own, special way.

If there's anything you'd like to know about the Suzuki GS model bikes, and most others actually, you've come to the right place. There's a lot of knowledge and experience here in the community. Come on in and let me say "HOoooowwwDY!"....

Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", "Top 15 Tips For GS Happiness", the Carb Cleanup Series, and the Stator Papers. All of these tasks must be addressed in order to have a safe, reliable machine. This is what NOT to do: Top 10 Newbie Mistakes. Now let me roll out the welcome mat for you...



Please click here for your mega-welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike!

Thanks for joining us. Keep us informed.

Thank you for your indulgence,

BassCliff

[Mocks]

Basically the guy has documented the bike build on the internet on a couple vintage sites, http://caferiders.proboards.com/inde...ead=103&page=1 but I'm pretty sure that after sitting down and thinking about it HE probably put a factory ring set in a not so factory 30 year old cylinder and that may have alot to do with the oil bypass. I feel that the oil passing the ring(s) may be part of the midrange bog.

[Mocks]

And it has pods with a 4 to 1 baffled exhaust. I went ahead and did 1.5 turns out on fuel and 2 full turns out on air. Seemed to make it smooth and didnt see an RPM increase if I went any further out on either.

[Mocks]

Sorry for the multiple replies, I keep remembering stuff... It also came with 120 Main Jets and I stepped them back to 105's.

[Big T]

Sorry for the multiple replies, I keep remembering stuff... It also came with 120 Main Jets and I stepped them back to 105's.

That's a big change in jet size - I'm thinking you should be around 112.5s

Plug chops are your friend when tuning

Do you remember what groove your needles are set on? You may need to open them up one groove

[allojohn]

There are a good few with '77-'79 750's on here running a 4-1 and pods, generally the favored settings are....

15 pilots (stock) mostly. There may be a couple using 17.5.
E-clip on needle in position 4 (1 up from the bottom)
Main jet anywhere between 115 and 125. In one or two cases even larger.

This will get you close to where you need to be.

Oops! BTW welcome to the forum!

[geronimo]

I have 78 GS1000 that does the same thing until it warms up real good ( 20 minutes ) and when my bike was running well it seemed to like the premium gas. Whatever you do don't mess with those carb jets unless its absolutely necessary and you know what you are doing . I changed my jets and now i think i need an aftermarket ignition. Good luck

[Mocks]

One of the plugs is basically getting real wet and I think that may be my main faulty cylinder. I am trying to see if its worth it to do a big bore kit or if I can just have a machine shop that I trust bore and hone the cylinders to a set of rings that I find. and then I'm gonna run through the rest of the top end and make sure the shims are correct and the valves actually seat.

[Mocks]

And the guy who did the carbs before me had the Floats set so high that the bowls never actually held any fuel and then had the 120 jets in there to compensate for the lack of fuel on tap. I'm guessing that was his reason.

[MisterCinders]

One of the plugs is basically getting real wet and I think that may be my main faulty cylinder. I am trying to see if its worth it to do a big bore kit or if I can just have a machine shop that I trust bore and hone the cylinders to a set of rings that I find. and then I'm gonna run through the rest of the top end and make sure the shims are correct and the valves actually seat.

Is that plug wet with gas or oil?

If it's wet with fuel, check the electrical on that cylinder. Swap the spark leads with it's mate (i.e., 2-3 or 1-4), and see if the problem migrates.

If it's oil-fouled, then . . .

[MisterCinders]

There are a good few with '77-'79 750's on here running a 4-1 and pods, generally the favored settings are....

15 pilots (stock) mostly. There may be a couple using 17.5.
E-clip on needle in position 4 (1 up from the bottom)
Main jet anywhere between 115 and 125. In one or two cases even larger.

This will get you close to where you need to be.

Oops! BTW welcome to the forum!

Yep.

My jetting is in the sig below. I have waffled between 15 and 17.5 pilots, but tend to go with 15s. I also shimmed my needle a hair up from the 4th slot.

My mains are 122.5 now, but I haven't really gotten to fully test the WOT plugs.

[MisterCinders]

And it has pods with a 4 to 1 baffled exhaust. I went ahead and did 1.5 turns out on fuel and 2 full turns out on air. Seemed to make it smooth and didnt see an RPM increase if I went any further out on either.

That's pretty far out for the fuel screw. If you're adjusting the fuel screw on an idling motor, you generally want to set those for a minimal amount of fuel, so you have plenty of maneuver room with the air screws for highest idle.

Usually, the pilot screw settings are 1:2 fuel to air. You might carve back the fuel screw to 7/8 to 1 turn out and then start with the air screws at 2. Then highest idle on the air screws.

[Mocks]

It's fuel smell, but the spark is strong on all 4 wires and it my be fouled due to the oil. No? I went ahead and ordered the factory service manual for it. That should help tremendously.