1980 GS450 hanging throttle help needed!

[Guest]

I've had the bike for a couple of year and I recently rebuilt the bottom end of my engine to replace a few leaky seal and since its been back together its had a hanging throttle issue. If you rev it up to about 4 grand it will stay there for a while and slowly come back dow to normal. I have completely cleaned, dipped and re jetted carbs. Ive replaced the stator, voltage regulator, cleaned the petcock thoroughly, replaced the intake boots and rings, and replaced and rerouted throttle cables. The bike is running super strong and idling perfect but the throttle is just not playing nice. My next move was probably to check the valve shims and clearances and maybe replace the exhaust as it has a few holes in it. All was fine before i had it apart and have been racking my brain on this to no avail. Any help would be appreciated!

[mike_of_bbg]

Smells like a vacuum leak. Are the throttles snapping back into position when released?

[JohnESuspekt]

yes, i just reassembled the carbs and everything was fine in there. everyone has been saying its a vacuum leak but there is none

[JohnESuspekt]

i wonder if it could be something with the timing but you cant adjust it on this model

[niclpnut]

My 1100 was hanging. No leaks, jetted properly, etc...

Check your cam timing and valve clearances again.

Nic

[pete]

What about intake? I thought the hanging throttle was partly also caused by leaky carb intake boots, leaky airbox, etc.

Do you know the intake system is sealed well and the air filter is oiled?

What about the carb boots on the cylinder head, have you replaced the O rings on them and are the boots supple?

[Nessism]

A lean idle mixture can make the idle hang too. Where are the mixture screws set?

[pete]

What about intake? I thought the hanging throttle was partly also caused by leaky carb intake boots, leaky airbox, etc.

Do you know the intake system is sealed well and the air filter is oiled?

What about the carb boots on the cylinder head, have you replaced the O rings on them and are the boots supple?

I missed where you said you did the intake boots and O rings...

[JohnESuspekt]

there are no mixture screws on the carbs ive been doing trial and error with different sized jets and i definitely am running rich rather than lean but ive narrowed it down to a good size pilot and main jet... heres a pics

[Nessism]

there are no mixture screws on the carbs ive been doing trial and error with different sized jets and i definitely am running rich rather than lean but ive narrowed it down to a good size pilot and main jet... heres a pics

Your carbs do have mixture screws. Sounds like yours may have EPA caps over the top so that fooled you.
Check this link on how to rebuild your carbs, it shows where the mixture screws are. http://members.dslextreme.com/users/...ning_guide.pdf

[1_v8_merc]

Mixture will definitely do it.

[nejeff]

Trying setting valves and then a carb sync. I have done it all boots, o-rings, carb rebuilt, ect and still hanging...waiting for my valve tool to arrive

[JohnESuspekt]

i have the tool for the valves just need to get some shims to check the sizing

[pete]

Just need to clarify... if you have a 1980 GS450 with the stock carbs as shown in the carb cleaning guide Ed linked to, you absolutely 100% guaranteed do have mixture screws, and if they've never been touched before they will definitely have caps over the top that need to be removed to access them.

I was fortunate that over here in Aus they didn't seal them up like they did in the US.

Trust me when I say you need to get them out and make sure they are spotless and have the O rings on them replaced.

If you don't do this, the 30 years worth of crud in there will make it difficult to tune and probably make it never run right...

[JohnESuspekt]

yeah thanks for that carb link im gonna drill them out this week and resync everything... hopefully between that and doing the valve shims my woes will be cured