Gs850Gl bogging at speed.

[stoy75]

Hey guys and gals. New here and need some help. I just purchased a gs850 a month ago. It is a 1982 with 40000 miles on it. Seemed to run fine the whole way home which was about 70 miles. My boat habits kicked in and I changed the gear oil both primary and final, changed the oil, and put in 4 new plugs. Shortly thereafter I noticed that when cruising at a consistent speed both highway, 55, and local, 35, the bike want to bog in and out sometimes and when the throttle is either rolled on and cracked it bogs and then goes. A few more observations is it has started to backfire on decel a lot more sometimes. Seems to "throttle down backfire" less when it is not bogging. It starts on minimal choke. Had to get a new battery as the last three year old one died. Any ideas?

[hikermikem]

Have you shimmed the needles?

[stoy75]

Ok. I'm admitting newb here... What do you mean?

[hikermikem]

I would start here...

http://www.mtsac.edu/~cliff/storage/...d_Tutorial.pdf

[stoy75]

So it definately sounds carb related?

[Steve]

So it definately sounds carb related?

Yes, it sounds carb related, but I would start with a full, proper "strip and dip" cleaning, so you know what you have as a baseline before making any changes.

.

[stoy75]

Ok. Carbs stripped and dipped. Manifold boots and rings replaced. Problem seems to have worsened a little. Out of curiosity I put the petcock on prime and went for a ride. Problem was still there but bike had substantially more power and the problem did lessen a lot. Rode around on prime a little longer and problem almost disappeared and bike ran much much stronger.

[cowboyup3371]

Sounds like you may have a vacuum issue??? Did you check to ensure your hose is not kinked in any way?

[stoy75]

Which vaccum line and what size is it. I'll just replace it. Should I rebuild the petcock too.

[cowboyup3371]

Instead of replacing parts right away just look at it. It will be the smaller of the two hoses coming off the petcock to the carbs. I think someone said it was 6mm but I'm not positive.

If you KNOW your petcock is bad, then replace don't rebuild it. Most people here have a really hard time getting rebuilt ones to work properly. It's a lot easier and cheaper in the long run to purchase a new one from someone like Z1 Enterprises than it is to fight with that kit.

[stoy75]

I know the line is connected on both sides. Just figured a vaccum line would only be a dollar or two. How would I test it.

[spacepirates]

A good test to do would be to take your tank off (with the fuel lever on "ON") and set it in your garage overnight to see if the petcock leaks.

Then, you can hook up your vacuum line to the petcock (with the tank still off) and apply a vacuum to it (suck on the end of the line) to make sure that fuel flows out of the petcock when a vacuum is applied.

New rubber parts (vacuum hoses, fuel hoses) isn't a bad idea for a 30 year old bike in general, especially when fuel/vacuum hose would only be a few bucks.

[stoy75]

Tank was off all day yesterday when replacing the carb boots and not a drop on the floor when in the on position.

[spacepirates]

Tank was off all day yesterday when replacing the carb boots and not a drop on the floor when in the on position.

the leaking bit without vacuum tests to see that your petcock shuts off when the bike isn't running. More of an issue if you have gas-oil or flooding.

Do check that fuel flows with a vacuum applied though; that test is more to see if your petcock is starving your carbs for fuel when your bike is running.

If that passes, then you have a blockage somewhere else limiting fuel flow. Possible culprits would be kinked fuel line, stuck float valves, dirty carbs, dirty petcock filter.

[cowboyup3371]

Do you also have an external fuel filter on your bike? If so, yank it off. There's no reason for it and most that people use are too restrictive for our gravity fed systems