GS1000g '81 - won't take throttle

[Guest]

Hi All - 81 GS1000 - new Dyna-S ignition, new coils/wires, new 775 R/R, BIG fat juicy sparks and in time. Carbs cleaned/inspected 3 times. Tank is thoroughly clean, new petcock and screen, clear fuel line so I can see the gas getting to the carbs. Starts and idles great once warm - will not take throttle at all. Only way to get it above 3k RPM is to open the choke. Let off the choke, idles, open the throttle, massive bog and dies - no matter what. Stock jets and airbox, no exhaust mods. History - R/R went bad, was riding it and lost power like you hit the switch ... while coasting to a stop MASSIVE - MASSIVE backfire. R/R was bad, left coil at 1 ohm, and no spark on 2/3 from original igniter after replacing coils - hence the move to Dyna-S, 775, etc. Compression checks at 130 per cylinder, dry, throttle open. Did the big bang blow out some things I cannot see in the carbs? I will be happy, other than the $$$, to put a nice new rack of CR's on it ... but don't want to spend if I am missing something. Been working with the carbs for a month - taking my time - one thing at a time. I am at a loss. Thanks again to all for the ignition help - have to ask again for fuel suggestions !! Getting close to tabling for antique snowmobile season !!!

[Brendan W]

Easy things first.
Still on vacuum petcock ?
How is the vac hose ? Tight both ends no splits any different on prime?.

[455rocketv8]

No different on prime - new vacuum hose and no leaks. New fuel line in clear, can see the fuel in the line, tank is completely clean and verified twice. I can buy a pingel - but the fuel is DEFINITELY flowing from the tank with no issues, so I have held off.

[roeme]

Starts and idles great once warm - will not take throttle at all. Only way to get it above 3k RPM is to open the choke. Let off the choke, idles, open the throttle, massive bog and dies - no matter what.

Replaced intake boot O-Rings yet?

[455rocketv8]

Have not yet replaced the o-rings ... was contemplating them and the boots themselves as they are now 35 years old. Thought they may cause some bad running , but not full failure to take throttle - will try before 1000 $ for CR's !!

[geol]

I would also suggest checking the fuel level; not float level; ensure plugs in pilot passageway and for goodness sake, change the carb boots if they are originals and the orings underneath. There is little reason for a bog if you are getting adequate fuel other than the things I mentioned which amounts to lack of fuel. Only other possible issue is that your mechanical timing advance is in need of removal and cleaning if it isn't advancing due to either rust or crud. It can easily be checked by looking at its function using a strobe timing light. You will see the arms splay out when rpms increase to about 4K.

[Nessism]

Did you do a full carb tear down including removing the pilot jets to verify they are open? Did you follow the carb rebuild tutorial as linked in my signature?

[455rocketv8]

Guilty - I did not !! So I will :-) I DID remove the pilot jets - I did not separate and check all of the gaskets in between nor did I soak the carb bodies - so something may have been missed. Do you (anyone) have a recommended source for all of the o-rings, gaskets, etc? Also will replace o-rings and manifolds ... Thanks again!

Did you do a full carb tear down including removing the pilot jets to verify they are open? Did you follow the carb rebuild tutorial as linked in my signature?

[455rocketv8]

I am going to replace the manifold and o-rings for sure. Also, when I did the ignition I cleaned and triple checked the advance, it looks good. Will re-check one more time. I will hit the carbs once again per Ed above. HAS to run after that !! Thanks again for your time and help

I would also suggest checking the fuel level; not float level; ensure plugs in pilot passageway and for goodness sake, change the carb boots if they are originals and the orings underneath. There is little reason for a bog if you are getting adequate fuel other than the things I mentioned which amounts to lack of fuel. Only other possible issue is that your mechanical timing advance is in need of removal and cleaning if it isn't advancing due to either rust or crud. It can easily be checked by looking at its function using a strobe timing light. You will see the arms splay out when rpms increase to about 4K.

[Nessism]

Guilty - I did not !! So I will :-) I DID remove the pilot jets - I did not separate and check all of the gaskets in between nor did I soak the carb bodies - so something may have been missed. Do you (anyone) have a recommended source for all of the o-rings, gaskets, etc? Also will replace o-rings and manifolds ... Thanks again!

When you pull the carbs be sure to hold the pilot jets up to a light and make sure they are open. Also, squirt carb dip through the choke pickup tubes and make sure the passage up to the choke plunger is open. Also, pull the pilot screws out and squirt fluid though the pilot jet passage and make sure it flows up to the pilot screw and out the three small holes in the carb body.

All these details are described in the rebuild tutorial, including what O-ring sizes you need and where to get them.

[455rocketv8]

Hello All - I just wanted to post an update after all of the help - and say a huge THANK YOU to all who made suggestions. I ordered the full o-ring kit for the carbs and did the complete re-build and soak per the forum presentation. Also, new manifolds, manifold o-rings, and stainless hardware. With an auxiliary tank (still don;t trust my old tank) she starts and winds up as she should! I am still working with the jets as I just can't bear to go back to the air box assembly, and I am waiting on a carb-tune kit to get it just right over the winter. Additionally, I will clean the tank (again!) and have ordered a pingel fuel valve. So I have a completely new Dyna ignition/coils/wires, and completely cleaned the carbs with new o-rings and mani's. I think I should be in good stead! New brake lines and such over the winter - I have already replaced the fork springs and seals and gone with superbike bend bars, and I need to replace the '80's spec air shocks that arrived with the bike. Need a shorter clutch cable and thought I saw that one from an early Kat will fit the bill. Anyway - again, I just wanted to say thank you to all who gave suggestions and to the site in general. Take Care and see you again I'm sure.

[850 Combat]

Guilty - I did not !! So I will :-) I DID remove the pilot jets - I did not separate and check all of the gaskets in between nor did I soak the carb bodies - so something may have been missed. Do you (anyone) have a recommended source for all of the o-rings, gaskets, etc? Also will replace o-rings and manifolds ... Thanks again!

I have personal experience with a hard clogged passage through the bell mouth of the carbs to the pilot jet. No amount of jet and emulsion tube cleaning will fix clogged passages. I've had trouble with soaking, too. There are a number of fuel system passages which you need to prove are clear. The pilot air to the pilot jet / emulsion tube, and then from the pilot jet to the three progression holes in the bottom of the venturi at the butterfly. The air side of the main is worth looking at too, but it is the air side of the pilot that caused my bike some grief. A GS1000G is my personal favorite of the GS family.

Still, with all four giving problems, I'm not certain that a single carb couild make it that bad. A big backfire could well have sneezed the O Rings out of their seats.