Fuel system check: 77 GS750

[hannibal]

Chuck, thanks for the tip on the springs and description of the slide adjusters and syncing.

I found 110 main jets in the carbs. Stock size is 100 according to this chart I found in another thread. My engine number is 30xxx.


They appear to be aftermarket (no Mikuni marking) so I'm guessing they were added along with the pods. I also found stock 15 pilot jets. I ordered new O rings from Robert Barr and hoping to get those before the weekend. I've been soaking one carb at a time each night then spraying with cleaner and poking through each passageway and jet.

I balked on cleaning the tank last weekend because I couldn't find a rod to fit past the filler opening. I'm going to try bending a hanger to fit. With such a small diameter, I imagine it will be saturated with rust fairly quickly. If I change this out twice a day over the weekend, I'm hoping it'll get the job done. I can always find another hanger to shove in there.

I got 3 of the 4 carb to head boots off but cylinder 1 is pain. Hit it with some PB blaster so I'm hoping for better luck this afternoon. I don't own an impact driver so if this doesn't work, I'll have to cut a big slot with a Dremel and give that method a shot. The boots look decent (still pliable), but the big 32mm O rings behind them are hard and flat so I have those coming from Mr. Barr as well.

Thanks again...

[chuck hahn]

With pods they tend to run lean so the PO went up one on the mains...should be about right. The color of the plugs is whats gonna tell the story here. Whitish grey mean that cylinder is lean. Black and sooty means its rich. You can adjust the side mixture screws to a pointb if the needed adjustment isnt drastic. Turning them in will RICHEN the cylinder and out will LEAN a cylinder.

[hannibal]

The plug were all dry and black originally but I had a leaky petcock. Putting in new plugs when it goes back together.

Just a quick update...
I've reassembled the carbs with new O rings and gaskets. Hoping to get them back on the mounting plate and bench synced this week.

I went in to check valve clearances. I was pretty intimidated by the process, but it turned out to be quite straight forward. Here are my clearances:
Cyl 1 EX .102mm, IN less than .038mm

Cyl 2 EX .076, IN .102

Cyl 3 EX .051, IN .127

Cyl 4 EX .127, IN .051

My feeler gauge sizes are .038, 051, 063, 076, 102, 127, 152. The size listed above is the largest that fits. Is it odd to have so many clearances on the "too big" side? I thought clearances typically decrease over time (still not sure why that is). I'm also concerned about Cyl 1 IN. My smallest feeler (.038mm) didn't fit so this valve is very tight and it already has a 255 shim. All other shims are 265-275.

Two other concerns: On cyl 1 exhaust valve, when I dropped the shim back in the bucket and lightly centered it with my finger, lots of oil came up from below the bucket and there was a bit of a puddle of oil in the cylinder head next to the cam. Any ideas what caused this? Hope it's not a bad valve seal.

On the cyl 4 side of the head, I found this blue gunk behind the cam shaft "cap". I also noticed some blue gunk on the cyl 3 header right where it goes under the bike. Is this just a bad sealing job with some kinda of liquid gasket?

[hannibal]

I've got the carbs bench synced as described by Chuck and the rebuild writeup. After installing on the bike, the writeup says to set idle to 1100 rpm and turn each pilot air screw to achieve the highest idle then reset idle to 1100 and move on to the next screw. Is it correct to set idle with this method before hooking up my Carbtune and adjusting the slide heights to vacuum sync as Chuck described above?

[chuck hahn]

The side screws are generally at about 2 out..the manual states set them at 1 1/4 out..if i recall right. Get the bike running with the screws at about 1 1/2 to 2 out and vacuum sync the carbs. the RPMs will change as you do this as youre moving the slides a little. Be ready to adjust the idle again as you go along. start the initial RPMs at around 2,000 with the big idle knob in the center..gauges set up and start the balancing process and adjust the idle back to 2,000 as it changes.

Once thats done THEN you can fiddle with the side screws...you dont adjust with the bottom pilot screws at all. But to save you the time, I find that all my bike tend to be best at about 1 3/8 out so set them there.

And check the timing also at some point.

[hannibal]

Thanks Chuck!

I've got the cams off now to clean some rust. I'll set timing when I reinstall them using the manual's method of lining up the T mark behind the contact breaker and setting the 1, 2, 3 marks on the cam gears.

Bottom pilot fuel screws: 1 3/8
Side pilot air screws: 1 1/2 to 2
Vacuum sync (use main idle screw to keep idle steady as I adjust each carb)
highest idle method using the side air screws

[chuck hahn]

WAY to FAT on the bottom pilots!!! 3/4 to 7/8 max. 3/4 is about where they came from the factory and 7/8 is just a tad richer...which isnt a bad thing as these bikes came on the lean side for EPA regs back in the day. At 7/8 they are just about right as far as not being overly rich or too lean that youll burn up valves or pistons.

As was mentioned..you set the bottoms and leave them alone. The 1 3/8 I mentioned is the side MIXTURE screws. When tuning the MIXTURE screws are all youre adjusting...follow????

[hannibal]

Gotcha! Thanks!