high start up idle then dies

[atrent]

1984 gs400s have replaced the carbs with a pair from ebay. Cleaned as per instructions on Cliff's page. This did not change the way it ran with the original carbs, so now I have a spare pair of carbs. Installed new boots (purchased from dealer) new o rings, using auxillary tank same height as regular tank so no petcock issues. Using a spark monitor there is no sign of spark loss. Starts and runs high rpm (5 to 6 k) slowly drops to 3k, which is where the idle stop is set. Runs for several seconds then dies abruptly. Won't start again until it has sat for a few minutes. Tried flooding the boot area with propane ( I may be living dangerously here) at both airbox and intake manifold areas with no change in speed. Air filter in place and air box cover on. This bike was running ok then started to act up so pulled carbs to replace boot o rings then my troubles started.

 

[BassCliff]

Hi,

Let me grasp at some straws here.

Are you using an inline fuel filter between the petcock and the carbs?

Did you replace the float bowl gaskets? Did you check to make sure the proper punch-outs were removed, if any? Sometimes there are passages that must be open through the gasket on one carb, but not the other.

Did you also replace all of the internal o-rings in the carbs themselves as well as the o-rings on the intake boots?

Did you completely disassemble the carbs and soak all of the metal parts in a good carb dip? Sometimes it takes 24 hours for each carb body.

Did you remove the caps so that the idle mixture screws could be removed and the internal idle passages properly cleaned?

Is the airbox tightly sealed? Is the air filter properly cleaned and oiled?

When using the aux. tank, is the vacuum line from the carbs plugged? Is there a leak in the vacuum line?

That's all I have for now.


Thank you for your indulgence,

BassCliff

 

[tom203]

1984 gs400s have replaced the carbs with a pair from ebay. Cleaned as per instructions on Cliff's page. This did not change the way it ran with the original carbs, so now I have a spare pair of carbs. Installed new boots (purchased from dealer) new o rings, using auxillary tank same height as regular tank so no petcock issues. Using a spark monitor there is no sign of spark loss. Starts and runs high rpm (5 to 6 k) slowly drops to 3k, which is where the idle stop is set. Runs for several seconds then dies abruptly. Won't start again until it has sat for a few minutes. Tried flooding the boot area with propane ( I may be living dangerously here) at both airbox and intake manifold areas with no change in speed. Air filter in place and air box cover on. This bike was running ok then started to act up so pulled carbs to replace boot o rings then my troubles started.

So these are new carbs to you and they give the same exact problem as those carbs you were fighting with a month ago??
"flooding the boot area with propane" - What was this supposed to do?

 

[atrent]

So these are new carbs to you and they give the same exact problem as those carbs you were fighting with a month ago??
"flooding the boot area with propane" - What was this supposed to do?

hipefully if there was an air leak it would sucj in the propane and cause a change in rpm

 

[Larry D]

Did you "bench sync" the carbs before installing them ? Have you synced the carbs at all ?

http://members.dslextreme.com/users/bikecliff/images/carb_sync_notes.html

 

[atrent]

Apparently I have to have a longer reply? Tried to post reply and got message "too short"

Hi,



Let me grasp at some straws here.

Are you using an inline fuel filter between the petcock and the carbs?

No

Did you replace the float bowl gaskets?

NO

Did you check to make sure the proper punch-outs were removed, if any? Sometimes there are passages that must be open through the gasket on one carb, but not the other.

Yes

Did you also replace all of the internal o-rings in the carbs themselves as well as the o-rings on the intake boots?

Yes

Did you completely disassemble the carbs and soak all of the metal parts in a good carb dip? Sometimes it takes 24 hours for each carb body.

Complete dissasemble Not 24 hrs

Did you remove the caps so that the idle mixture screws could be removed and the internal idle passages properly cleaned?

Yes

Is the airbox tightly sealed?

As far as I can tell. The cover is on tight and the boots appear ok;

Is the air filter properly cleaned and oiled?

Cleaned and lightly oiled

When using the aux. tank, is the vacuum line from the carbs plugged?

Yes

Is there a leak in the vacuum line?

Not decernable

Thank you for your interest.


That's all I have for now.


Thank you for your indulgence,

BassCliff

 

[atrent]

bench synced only. Hard to do mush else the way it is running.

Did you "bench sync" the carbs before installing them ? Have you synced the carbs at all ?

http://members.dslextreme.com/users/bikecliff/images/carb_sync_notes.html

 

[tom203]

bench synced only. Hard to do mush else the way it is running.

But are these a different set of carbs from a month ago?

 

[mlinder]

You are having fuel delivery issues, most likely.

 

[atrent]

But are these a different set of carbs from a month ago?

different carbs but same make and model

 

[atrent]

But are these a different set of carbs from a month ago?

different carbs but same make and model very similar results

 

[mlinder]

Right after it dies, turn off your fuel, and check for the amount of fuel in your float bowls.

 

[atrent]

Right after it dies, turn off your fuel, and check for the amount of fuel in your float bowls.

Problem has been solved. Like most problems once you find it the cure is usually fairly simple. I applied air to the cyl. and found it was leaking very badly through the carb. Removed cam cover and checked rocker gap and found there was none. Set the rocker gaps to specs and lo and behold my troubles are over. Runs like a well oiled machine now.
alex