GS850 is having weird acceleration issues

[ninjadave7]

Hey guys, here's the deal.

RPM's go up smoothly in neutral and in 1st gear. In any other gear, there is a big hole a 4.5kish where the engine bogs down. It pushes through, but takes effort. After 5k, if I keep it at under 3/4 throttle it will accelerate up to redline, not that fast, being 1/2 throttle, but it will go.

If I twist the throttle past 2/3-3/4 the engine bogs completely. Not to the point of dying, but I have to immediately back off to 1/2 to get it to pick up again.

The carbs have been completely rebuilt, new boot O-rings, new air boots, clean/oiled filter, sealed air box, valve clearances checked, air mix screws out 2 1/2, etc. by both me and then my mechanic (whom I went to when I couldn't figure anything else out). He's a bit baffled as well. He said ignition timing is good, and he tried upping the main jet a bit too, to try that.

Seems like 2 different problems, but I don't know.

Help?

[hampshirehog]

Did you completely strip and clean the carbs as per the tutorials? Sounds to me like there's muck in there.

[ninjadave7]

Completely stripped, dipped, sprayed, wire-poked, o-ringed, gasketed, tutorialed! And then the mechanic (who thought there must be dirt too) rechecked all the jets and openings.

[cowboyup3371]

Do you have the stock airbox or pods? Have you done any plug chops when this happens?

[BassCliff]

Hi,

Do you have the stock airbox or pods? Have you done any plug chops when this happens?

Yes, reading the plugs at the point where the engine stumbles will tell you if it's rich or lean. Do the carbs have all stock jets, needles, etc? Did you over-oil the air filter? Check the vacuum hose to the petcock for leaks. Are you using an inline fuel filter?


Thank you for your indulgence,

BassCliff

[ninjadave7]

I haven't done a chop, I can try that. Everything is original/stock except a z1 petcock, and a uni filter, which the mechanic re-oiled because I had over-oiled it. The vacuum hose is new, but could be kinking a little too much because the z1 petcock faces backwards. Carbs seemed to be opening the petcock though, so didn't think about that.

[Mith]

Did you sync them?

Just curious, I didn't see it mentioned......

[ninjadave7]

yeah, sorry, forgot to mention that.

[ninjadave7]

Would changing The jet needle height maybe fix this?

[Big T]

Needle height adjustment wouldn't hurt, but, your needles should have only one position (If you're in the USA)

[ninjadave7]

Ah, didn't know that. Every carb thing I saw talked about moving it up or down. Shoot. Any ideas?

[BassCliff]

Hi,

It still kind of sounds like an air leak somewhere, or the carbs still have some gunk stuck in a nook or cranny. It's not unheard of for a member to clean the carbs two or three times before it's done really well. Check the fuel and vacuum hoses again.

Does the airbox still have the snorkel? Are the "airbox to carb" boots sealed well? If the air intake is completely stock, going up in size on the main jets won't help, might even make it worse. Are the float heights properly set? Are the float valves seating properly?

There's a little article about "shimming the needles" in the carb section of my website. This is what you have to do to raise the needles if you do not have notched needles.

But if everything is completely stock, carbs properly cleaned, bench synched, vacuum synched, idle mixture screws adjusted, etc, it should run like a top. Keep looking. Good luck.


Thank you for your indulgence,

BassCliff

[hampshirehog]

If everything is stock, as Cliff says, the worst thing you could do is play with needle height / jets etc. It's the old check and check again for air leaks or muck.

[ninjadave7]

ok. The air box does have the snorkel and the airbox to carb boots are new and seem to be tight. I'll just keep checking!

[ninjadave7]

Sooo... After we tried a bunch of stuff, the mechanic noticed that the little rubber plugs that should be on pilot jets was gone. It was missing when I took them apart so I never knew they were missing... now it runs like a champ!