1981 GS850G, needle jet circuit help? Bike won't rev past 3k or so

[Guest]

Hey everyone! Honestly I've been trying but I can't seem to figure it out. Some background info.

Using an old aftermarket exhaust meant for a gs750 on the gs850

New carb seats
New carb o rings
Adjusted float bowl heights
Installed a rejet kit

I've tried shimming the needle (only one c-clip position) but nothing I've done seems to have changed much. The plugs in the bike currently are BR7ES as it's the closest thing the nearby parts store had. The bike idles and cold starts (with choke) perfectly fine, just no throttle!

The plugs were new (I installed them), but are already gummed up and black. Could it be because they aren't the B8ES that's needed?

[LAB3]

Hey everyone! Honestly I've been trying but I can't seem to figure it out. Some background info.

Using an old aftermarket exhaust meant for a gs750 on the gs850

New carb seats
New carb o rings
Adjusted float bowl heights
Installed a rejet kit

I've tried shimming the needle (only one c-clip position) but nothing I've done seems to have changed much. The plugs in the bike currently are BR7ES as it's the closest thing the nearby parts store had. The bike idles and cold starts (with choke) perfectly fine, just no throttle!

The plugs were new (I installed them), but are already gummed up and black. Could it be because they aren't the B8ES that's needed?

BR7ES is one heat range lower plus it has a resistor in it, B8ES is hotter and doesn't have a resistor. Hard to say if that's the root of the problem but it sure isn't helping!

If you need plugs TODAY I've run Champion N3C with good results, it's a non-resistor plug. Just a couple of days ago I ordered a set of B8ES for my bike off the internet, the local auto parts chain store needed to make a special order to get them and I needed to buy a box of eight minimum.

[rphillips]

I thought with NGK's, the lower the # the higher the heat range. Really doesn't matter, 1 heat range either way won't be the problem. Just wondering, there should be little rubber plugs in the bottom of the tubes, I think, to the main jets. You didn't leave them out did you?

[Zaos]

I'll order some B8ES and see what that does, maybe it doesn't let the fuel burn clean/hot enough.

Yep, they are all there! Could the float level be too high? I did measure and set within spec but maybe that's too high for my bike for some reason

[Big T]

What rejet kit?
Why doesn't it have adjustable needles?

I'm guessing you have pod filters?
What brand?

[LAB3]

I thought with NGK's, the lower the # the higher the heat range. Really doesn't matter, 1 heat range either way won't be the problem. Just wondering, there should be little rubber plugs in the bottom of the tubes, I think, to the main jets. You didn't leave them out did you?

Looks like I was mistaken on the heat ranges, I stand erected!

https://www.ngk.com/learning-center/article/207/what-is-a-spark-plugs-heat-range

[Steve]

Using an old aftermarket exhaust meant for a gs750 on the gs850

Is there a (quiet) muffler on this system or is it pretty much 'open'?

New carb seats
New carb o rings
Adjusted float bowl heights
Installed a rejet kit

Details please.
- What are you calling "carb seats"?
- Which o-rings? Was it a kit from cycleorings.com?
- Hopefully you meant "float height", not "float bowl height". What measurement did you use, where did you measure it?
- What rejet kit? Brand? Jet sizes?

I've tried shimming the needle (only one c-clip position) but nothing I've done seems to have changed much.

Shimming is good, but most do it incorrectly. Where (and how) did you put your shims?

The plugs in the bike currently are BR7ES as it's the closest thing the nearby parts store had. The bike idles and cold starts (with choke) perfectly fine, just no throttle! The plugs were new (I installed them), but are already gummed up and black. Could it be because they aren't the B8ES that's needed?

Don't worry, "no throttle" is the proper way to start when using the "choke".
BR7ES plugs are not correct, and on two counts. If your plugs are fouling with them, it's not the fault of the plugs.

BR7ES is one heat range lower plus it has a resistor in it, B8ES is hotter and doesn't have a resistor. Hard to say if that's the root of the problem but it sure isn't helping!

Actually, it's the other way around, the 7s are hotter than the 8s. Depending on the rest of your ignition system, the resistor in the plug might be too much. You need some resistance, there are three sources: wires, caps, plugs. The stock system has the resistance in the caps. If they have been replaced with non-resistor caps, the resisitor plugs are OK.

Just wondering, there should be little rubber plugs in the bottom of the tubes, I think, to the main jets. You didn't leave them out did you?

The rubber plugs cover the end of the tube to the pilot jet, not the main jet. If they are missing, the bike will start and idle OK, but anything above that will be dreadfully rich.

.

[Zaos]

So the exhaust is an old vance and hynes 4 into 1, i'm guessing it flows more than stock?

Don't remember the exact name for em, but the rubber "seats" that go from the block to the carbs themselves.
O-rings were from cycle o-rings!

Yeah oops hahah. Float height. I used 22.4mm and I measured from where the float bowl gasket sits (without the gasket) to the top bump of the float itself. The top of the black plastic body. Also used a 6sigma kit from ebay. Orignally put 130 mains in there but pulled it back to 120's thinking that may help.

The kit gave a small plastic shim and a small metal one, to put under the C-clip (away from the diaphragm). I thought since the plugs looked fouled that removing the plastic shim may lean out the (im guessing) rich mixture, but it didn't really seem to do much.

As far as I can tell the spark plug cables look original.

I do remember the rubber plugs not being very much rubber anymore. Do they need a tight seal?

[Zaos]

What rejet kit?
Why doesn't it have adjustable needles?

I'm guessing you have pod filters?
What brand?

Unsure on the needles, but it came with shims to adjust. Right now it has no filters on it, put i'll put decent pods on there. The pods that came with the bike looked horrible.

[Steve]

A V&H pipe with a street baffle will flow about the same as stock. Suzuki did something right, their stock exhaust systems actually flowed quite well.

Float height is measured to the bottom of the step, or the top of the round part, NOT to the top of the step where the metal piece is. If you measured to the very top, your height is off by 4-5mm, which will make it rich.

No idea how the 6Sigma jet numbering compares to Mikuni or Dynojet, but the mains don't affect the idle mixture, so it doesn't matter much at this time.

Assembly order on the needles is rather important. On stock needles, starting at the top (away from the point): there is a nylon spacer about 5mm thick, the e-clip, a metal washer about 1mm thick and the spring. Not sure what 6Sigma suggested, but it is normal practice here to remove the plastic spacer and replace it with a stack of washers that is about half as thick. Most 3mm washers are about 1mm thick, so 2 or 3 washers will usually work. The trick is to use the washers (shims) INSTEAD OF the plastic spacer. Anything thinner than the stock plastic spacer will richen the mid-range mixture.

The rubber plugs will make a tighter seal than you think, as they are held in place by some nubs in the float bowls. New ones are great, and are not all that expensive.

.

[Zaos]

So just so I'm on the same page (bottom being the bottom of the needle) is there anything below the c clip? Any washers or spacers? And above it go the adjusted spacers right?

The kit said to put it below the c clip, and made no mention of removing the original spacer. Looking back your way makes way more sense.

[Spyder]

6-Sygma jet sizing matches Mikuni original sizing. They are good kits, and come with very detailed instructions. (At least the kits I have gotten) It sounds like you have your floats set too rich, and your needle, and possibly the main, too lean. Don't try to tune your carbs until you have the filters you are going to be running on the bike. As soon as you put them on, you will have issues all over again. Do you have the original airbox? It would make your tuning efforts SO much easier.

[Zaos]

I wish I had the original airbox. Was a bucket bike for 120$ so I cant really complain I suppose.

Played with the bike a bit more, right at the tipping point of blogging down the cylinder 4 carb backfired (visible flame from carb), is this tuning or valve side?

[Zaos]

So on a whim I took a piece of 2x4 and partially covered all four carbs. Bike revs and sounds awesome. I'm going to try shimming for a richer mix and see what happens, keep ya guys posted!

[rphillips]

I'd be sure to have some type air filter system on there. Prefer orig. but pods beats nothing. The filters not only keeps trash out, also increases vacuum, to make carbs work properly. My opinion, if you get it running without filters, you'll need to start all over again when the filters are installed. Just my opinion.