Bike bogs down and dies after reving up to 5k RPM

[Mak]

So I rebuilt the carbs the "right way" per directions on this site. Just started the bike up this morning (about 40*F) and it started fairly easy (to my surprise ). It would only start when choke is fully open but when it warmed up after about a minute, I closed the choke and the RPM stayed about 2500. I know I need to tune it a bit to get it down to ~ 1100 but there is another problem that is more of a concern.

The bike will not start (even after it's warm) with the choke closed. Not sure if it's supposed to do that or something is up with the choke internals. That's not the biggest problem though....

The second thing is, when I give the bike some gas and rev it up to about 5k RPM, it instantly bogs down and dies.. if anyone know what could be causing this, let me know. It's an '82 GS750E.

[Larry D]

After the bike gets warmed up well, you can adjust the idle down with the master idle control knob on the carbs (big brass knob)

How is your air intake system ? Do you have the complete stock airbox and lid ? New intake boots ? Any and all airleaks need to be eliminated.

[mlinder]

So I rebuilt the carbs the "right way" per directions on this site. Just started the bike up this morning (about 40*F) and it started fairly easy (to my surprise ). It would only start when choke is fully open but when it warmed up after about a minute, I closed the choke and the RPM stayed about 2500. I know I need to tune it a bit to get it down to ~ 1100 but there is another problem that is more of a concern.

As Larry said, you can turn down the idler with the idler knob

The bike will not start (even after it's warm) with the choke closed. Not sure if it's supposed to do that or something is up with the choke internals. That's not the biggest problem though....

Let's make sure we have terminology correct. Choke closed means the choke is on. Choke open means the choke is off.
Your bike should have the choke off, or open, after it's warmed up. You turn the choke on, which is closing it, to start it when it's cold.
So which are we talking about?

The second thing is, when I give the bike some gas and rev it up to about 5k RPM, it instantly bogs down and dies.. if anyone know what could be causing this, let me know. It's an '82 GS750E.

This depends on a few things. First, are we using the choke correctly, as outlined above?
Second, is everything stock? i.e. airbox, filter, jetting, exhaust?
Third, hows your fuel delivery looking? Petcock 'on'? Have you tried in the prime position? Fuel flowing?

[chef1366]

If your airbox isn't installed you won't be able to rev up. If it is check for sticky slides.
Is your petcock flowing gas properly?
Is your mechanical advance (if applicable) moving freely?
Good voltage at the coils?
Ignition in good health?

[Mak]

grrrrrr

As Larry said, you can turn down the idler with the idler knob

Let's make sure we have terminology correct. Choke closed means the choke is on. Choke open means the choke is off.

Second, is everything stock? i.e. airbox, filter, jetting, exhaust?
Third, hows your fuel delivery looking? Petcock 'on'? Have you tried in the prime position? Fuel flowing?

I know about the master idle screw. As far as the choke, it only starts with the choke ON (closed) even when it's been running for about a minute or two. Will not start with it OFF (open).

As far as the fuel goes, kinda hard to tell but I think the delivery is adequate since the bike will idle at 2-2.5K RPM no problem. It only dies after I give it some throttle past 5k RPM. Tried the petcock in all positions -- all the same.

The only possibility is the airbox. I did not put it on this time. Just tried to start the bike and see if it would run. I'm guessing that might be the problem???

How is your air intake system ? Do you have the complete stock airbox and lid ? New intake boots ? Any and all airleaks need to be eliminated.

I just popped the carb rack up after cleaning out the carbs so I didn't even bother putting the airbox on. I just wanted to start it up and rev it up a couple times. Do you think this is the problem , no airbox on ?

Also, after I shut her down, I saw some minor smoke coming out of carb #1 from the slit where it sucks air into. Only this carb was doing this.

[Mak]

If your airbox isn't installed you won't be able to rev up. If it is check for sticky slides.
Is your petcock flowing gas properly?
Is your mechanical advance (if applicable) moving freely?
Good voltage at the coils?
Ignition in good health?

Ignition inspection is next on the list. Can I test the ignition by disconnecting the battery and seeing if the bike dies ?

[cowboyup3371]

Ignition inspection is next on the list. Can I test the ignition by disconnecting the battery and seeing if the bike dies ?

I suppose that would work but why do it that way? Why not just verify you have 12v everywhere it is supposed to be using your multimeter?

[Mak]

I suppose that would work but why do it that way? Why not just verify you have 12v everywhere it is supposed to be using your multimeter?

Yes, will definitely do that. Gotta do some research on how to do this though... it might be something with ignition I suppose.

[BassCliff]

Hi,

As Mr. chef1366 alluded to, it will not run right without the airbox installed (too much air in the air/fuel mixture). Make sure the entire air intake system is tightly sealed.

Also check the float height. Did you bench sync the carbs after putting them back together? You'll also need to vacuum sync them in order to dial them in properly. Keep up the good work.

After you are sure the carbs and intake are up to par, see the electrical page on my little website for troubleshooting tips. Disconnecting the battery will not really prove anything, except maybe that your charging system is putting out at least 10 volts. I don't think the '82 has a mechanical advance. It's got electronic ignition.

Thank you for your indulgence,

BassCliff

[chef1366]

Ignition inspection is next on the list. Can I test the ignition by disconnecting the battery and seeing if the bike dies ?

I think you are referring to the charging system. The ignition is what controls spark at the plugs.
Crank trigger
Igniter
Coils including good connections on the leads (spark plug wires)

[Mak]

Did you bench sync the carbs after putting them back together? You'll also need to vacuum sync them in order to dial them in properly. Keep up the good work.

As always BassCliff, your site is my #1 source for good info for me. I did check the float heights and found them to be in the recommended range as well as bench-sync'd them. As far as vacuum sync, I'll hold off for now as the tool is not something I really want to invest in at this time.

The part on testing the voltage/ohms on the electrical parts on your site is confusing though, especially for people like me who like to look at pictures. I will do my best to test all the components.

I will also try to rev it up with the airbox on and see if that makes a difference. To me it kinda seems like after reving it up that high, the carbs are starved of fuel and it dies.

Is there a way to test if there's enough fuel going to the carbs ? I have a see-thru fuel filter installed and there's always fuel in there.

[cowboyup3371]

You will want to get rid of that filter as the one in your petcock does a pretty good job as it is. Plus, the articles I've read on here say those are prone to actually restrict the amount of fuel that gets to the carbs more than they should.

Honestly, although it will get close, it won't run great until you sync them. Yes the tool is expensive ($100) but it's worth it and I'll be buying mine shortly.

[BassCliff]

I will also try to rev it up with the airbox on and see if that makes a difference. To me it kinda seems like after reving it up that high, the carbs are starved of fuel and it dies.

Is there a way to test if there's enough fuel going to the carbs ? I have a see-thru fuel filter installed and there's always fuel in there.

Hi,

Thank you for the kind words.

I'm not a fan of inline fuel filters because they can cause restriction and fuel delivery issues. I know that some people use them but they are unnecessary if your tank is clean and has no rust. If you use an inline fuel filter, make sure it is for a gravity feed system and not a fuel pump system. The recommended filters are those for lawn mowers and other small engines.

Without the airbox installed the engine will draw in too much air. And it won't run its best without a vacuum sync. You can make your own manometer for less than $10. There's plenty of information via the Search feature.

Keep us informed.


Thank you for your indulgence,

BassCliff

[Big T]

Ignition inspection is next on the list. Can I test the ignition by disconnecting the battery and seeing if the bike dies ?

Never, ever do this with any vehicle

[82Shafty]

Mak,

Put a shout out in the Atlanta area for some sync'ing help.