Perfect Idle and rev up while standing. Stutters and jerks when driving

[Grimly]

The Dreaded Curse of the Previous Owner(s) strikes again!

[Danie.e]

Further Update - according to the Carb specs on BikeCliff website, the emulsion tube should be an X5 with 5D50 needle. I have now found that the carbs are fitted with X6 Emulsion Tubes. Can anyone please inform me what is the difference between these needle tubes
According to the chart the X6 comes out of Gs750 carbs So I must assume I have a bastardised set of Gs750 carbs on the Gs850.

[Danie.e]

Final update: It helps when one go back to basics. Hunt on this site gave the following specs - Main 115, Needle jet X6, Needle 5D57, Pilot 42,5, and Air jet 200 - Carb ID 45170 - took me some serious haggling with a few friiends but eventually got 4 x 45170 carbs and made sure that all passages are properly cleaned. Assembled, started bike and it purrs like a kitten.
Never again struggle with bastardised carbs I get with a project.

[KEITH KRAUSE]

One of the most common, classic symptom of fuel starvation, is the bike will idle and rev up well as long as there's NO LOAD on the engine. Under load, the motor needs more fuel to run well.
As others have said, it's easy to check the electrical system and be sure it's operating correctly. With any problem, you have to be sure the basic maintenance things are done before focusing on the carbs. A basic thing is correct fuel flow to the carbs. I think someone mentioned a fuel filter? Fuel filters are potentially more trouble than they're worth and if the tank is in good condition as it should be, fuel filters are unnecessary. Before taking the carbs apart, fix any tank issues, get rid of the fuel filter, be certain the fuel line is the correct diameter and not kinked. Service the petcock. Clean the gas tank cap venting. Be sure you have fresh, quality fuel. Once you're certain the fuel is flowing correctly and is clean, then any fuel starvation is obviously the carbs. Once in the carbs, check float levels first and float operation. Check the float needle valves and seats. Do NOT mix them up as they wear as a unit. Check that fuel flows through the main passages that feed into the valve seats. Once you're certain the fuel is entering the bowls correctly, you can check/clean the jetting and all carb passages and various o-rings.
If you're not certain about the bikes history, you need to verify all the jets are the correct size while you have things apart.

[KEITH KRAUSE]

I made the mistake of not reading ALL the recent replies. Obviously you were bitten by the previous owner(s) not knowing what they're doing. At least my last sentence of my previous reply might be helpful to someone.
Glad you persevered and got it right. It's all part of the fun of owning old bikes.