Bogging in nuetral

[Swervin]

Hi all!. This is my first time posting here, but been lurking for a while, reading up and searching all I can. Love this place!

1981 GS750L, stock except for V&H 4-1 exhaust and pod filters. Bought the bike in non-running condition, was missing airbox and exhaust had a few rusty holes, hence the new pipes and filters.

Cleaned and rebuilt the carbs to stock specs, replaced the choke cable and petcock and it started right up!

Started with the mixture screws at 1.5 turns out, idle set at 1100 rpm, and idles smoothly once warmed up and the choke off. Carb boots have no leaks and the vacuum/fuel lines are in good shape.

Problem is when I rev it, it hits about 3K rpm and bogs down. If I try to hold it there, the rpm's slowly drop until the engione finally dies. The exhaust doesn't smell rich, and there is some white smoke when I rev it.

To me, that means a lean condition. I adjusted the mixture screws, one at a time, until the highest idle was achieved for each carb, and now it revs to about 5k rpm before bogging. Still idles great off choke. Screws are now between 2.5 and 3 turns out, but still doesn't smell rich, and still has white exhaust.
If I try and hold the rpm's up, again, it keeps bogging and the rpm drops until it dies. If I let off the throttle, it recovers and goes back to a normal idle.

I'm guessing the next step is to order the DynoJet stage 3 kit, but wanted to run it past you guys and make sure I'm not missing something obvious!

Thanks
Brian

[chef1366]

More air (pods and pipe) needs more fuel.
Get a dynojet kit and rejet the carbs.

[Swervin]

Makes sense.

Thanks!

[Swervin]

Started looking stuff over one more time, and found that the petcock was set to the prime position. Would that affect how it runs? Seems to?

In prime (little notch vertical), gas flows all the time, and when in the horizontal "run" postion, gas only flows with engine vacuum applied to petcock. The oil isn't full of gas, so at least I know the floats are working properly!

I let it idle in the "run" setting and it does rev up better, but still hits a wall at about 5K rpm. If I keep the thottle steady, open about 1/4, it revs up and down, inbetween 1500 and 5000 rpm. Only dies if I try going WOT. Carbs make a big suction noise, then the rpm drops very quickly and it stalls.

Now that I've got the petcock in the correct position, I'm gonna retune the carbs and see how it goes. I'll still order up the stage 3 kit, but can't hurt to do a little experimenting in the meantime.

[seuadr]

it won't do any good to do any experementing, though. that wall you are hitting? not enough gas. no amount of fiddling other than larger jets will fix it.

[Swervin]

Ok, I'll be patient until I change the jets.

Would having the petcock on prime effect anything, or was I imagining it running better when i set it to run?

[Thomas Kenny]

Swervin, how does it run with the petcock set to on or reserve???
My GS550ES was bogging on prime and I was getting gas out of the airbox drain tube. I discovered it and turned to on and it runs fine, although the white smoke does seem to indicate you need MORE fuel?????? Regards

[Swervin]

Even though my bikes an 81, it's got an 80 petcock. Those were vacuum operated and don't have a reserve. At first, I thought the lever was missing, but after some searching here, found it's not supposed to have a lever, just a little slot that turns. Kinda wishing I had one with a lever!

[chef1366]

Fuel tank vent or the carbs vents. Take off the carb vent lines.
I wouldn't run the bike with stock jetting because it is very lean and will burn up the motor.