Issue with 81 GS650E Fuel Delivery/Idle

[docwatson02]

Any help would be greatly appreciated and thanks to anyone in advance with some advice. I am trying to finish the last part of my restoration of my 1981 GS650E and have found the following two issues to be the last of my concerns so far: 1. There appears to be some sort of issue in the petcock or fuel lines to the carbs, when the petcock is set to pri position or res position while disconnected from the fuel lines, the gas runs freely out of it, while in the on position the fuel does not drain. As I understand from the service manual, the on and pri positions are working correctly, the res position is not. When the fuel lines are connected and the motor is attempting to start there is no fuel being pulled into the carbs from any position on the petcock and therefore the engine is not starting. Anyone know if I need a new petcock or to rebuild mine or is there another possible reason for this? 2. Using a graduated syringe to inject a sufficient amount of fuel into the carb fuel line, the engine will fire but is incredibly loud, to the point of actually making your ears ring for the 10 seconds or so that it runs as well as seeming to be at very high rpms. there is no decline in the volume over the span of time either. Is this a problem in the idle adjustment or some other issue? Pertinent background information: The carbs are the stock mikuni rebuilt and cleaned to factory specs.; airbox and exhaust are both are fully stock with all original parts in place. Petcock is original, fuel lines are new.

[850 Combat]

Sounds like a bad petcock. Unfortunately, all too common. As to the idle speed, are you certain that the carbs are fully closed? Sometimes a needle can hang up in assembly. Also, I once reassembled the throttle barrell incorrectly and the cable was way too tight, so idle was at half throttle. If fuel flows freely on prime, but does not get into the carbs on prime, I would still suspect the float needle valves/floats in some way. How were the carbs cleaned, and what do you mean by "rebuilt and cleaned to factory specs" ? precisely what was done, and how? getting the carbs sufficiently clean can be a tricky business. Note that when on prime, it still takes a while to fill all the float bowls. Also, is there any rust in the fuel tank?

[docwatson02]

The carbs were professionally stripped down and all interior components were replaced inside including the jets, valves, floats, gaskets and so on. Only the throttle bodies themselves were basically left untouched. By factory specs I mean that the parts are all oem parts, no after market or parts that differ from printed specifications found in the service manual. As for rust in the fuel tank, I could not find evidence of any, but seeing as the age of the bike was 30 years, I used POR-15 three step system to seal and clean the tank completely before connecting it to the fuel lines/bike.

[BassCliff]

Greetings and Salutations!!

Hi Mr. docwatson02,

You might want to search the forum a little bit to see what the community thinks about "professional" bike mechanics. In the meantime, let me dump a TON of information on you and share some GS lovin'.

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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

[Nessism]

A new OE petcock seems in order.

As for your carbs, I hope the mechanic knows what they were doing. The typical GS carb rebuild can be performed for less than $50, and that includes buying a bucket of reusable carb dip. I shutter to think what you paid to rebuild yours.

[tom203]

Get rid of 31 year old petcock- it might be made to work, but why not just eliminate it now as a problem. $50 and move on. Very possible that your idle stop screw is holding throttle plates too open-the shots of fuel then have plenty of air,so revs take off.Drop in on Basscliff's site and immerse yourself in his info and be amazed. Many of us have had these types of problems, so take advantage.