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GS450 - Idles but can't give it any gas

  • Thread starter Thread starter tthayer
  • Start date Start date
T

tthayer

Guest
It almost feels like it's starving for fuel. It starts easily enough and will idle around 1200. If I let the choke off it will stumble and die. If I give it any gas it does the same.

I had to dial back the main idle completely and it only seems to run with the throttle bodies as closed as possible.

I went through and cleaned the slides, removed and blew out all the jets and passages, and there is a new air filter, intake boots, and carb boot o-rings. The fuel mixture screws are turned out about 3 1/2 turns. Turning them in or out doesn't seem to have any effect on my ability to rev the engine.

I'm thinking this may be related to float height, but I lack the tool necessary to check it accurately. I'm also going to be replacing the in-line fuel filter in case it is causing starvation.
 
Engine warmed up and choke works properly? Could be getting just a trickle of gas from the petcock, but letting the bowls fill up (prime position) should take care of that. Main jets rattled loose, needle height way off, carbs need synced, etc.
 
Ditch the inline filter

Clean your carbs properly and set your float height

You can get a tool at Harbor Freight for a few $$$
 
Big T said:
Ditch the inline filter

Clean your carbs properly and set your float height

You can get a tool at Harbor Freight for a few $$$
Click to expand...

The filter is the first thing I'm going to try. There are a few German auto parts stores around that will have the correct hose diameter.
 
Hmmm... that sort of sounds similar to when I first fired mine up after the rebuild, but probably not the same reason.

I had rags over the carb inlets as I'm not using the stock airbox, and as it turned out they were far too restrictive and it ran incredibly rich.

It ran so rich that with the idle screw fully out (no idle at all) it was still idling, and the plugs were very black afterwards. I couldn't rev it at all and it would die with any fuel added like the choke etc.

I used a bit of cardboard to set my float height too:



May not be perfectly accurate, but definitely getting it in the right ballpark so it can be fine tuned later.
 
The carb jets are all cleaned out. I just went through and double-checked. The inline filter has been removed and a new fuel line has been installed. I used Pete's awesome float level check and both are dead on at 22.5mm. The choke moves and the passages are clear. I'm at a loss at the moment.
 
Mate I would've used the word "dodgy" as opposed to "awesome" :o

What colour are the plugs? That will tell you if it's too much or not enough fuel...

I'm definitely no guru on this and am probably way off (given my issues when I first started mine) but it sounds more rich than lean to me...

Is there something restricting air flow in or exhaust flow out?
 
Hi,

Not only do the jets have to be clear, the carburetors should be cleaned using this procedure:

[FONT=Verdana, sans-serif]Mikuni BS(CV) Carburetor Rebuild Tutorial [/FONT](9MB PDF file)
(by Mr. Nessism)

There are small passages in the carb bodies that must be cleaned by dipping the carb body in carb cleaner, sometimes for up to 24 hours.

Is the air box installed? These bikes don't like to run without the air box, unless you have re-jetted the carbs to allow for the extra air intake.

If you are using the air box, has it been properly sealed so that there are no leaks in the air intake system? New carb boots and intake O-rings, etc? See:

Air Intake Repair: (PDF file)Airbox removal, intake boots and O-ring replacement


Thank you for your indulgence,

BassCliff


​
 
Seams everybody thinks if you clean out the jets your carbs are clean , they all seam to forget that there is a small passage that , that dirty plugged up jet came out of. Shame ,Shame ,Shame, you have to clean the carbs properly to make them work ,there are no short cuts. Also you need to have your air cleaner and filter assembly on and in place with out any air leaks
 
Last edited:
Hmmm... just re-read your first post...

I went through and cleaned the slides, removed and blew out all the jets and passages, and there is a new air filter, intake boots, and carb boot o-rings. The fuel mixture screws are turned out about 3 1/2 turns. Turning them in or out doesn't seem to have any effect on my ability to rev the engine.
Click to expand...

If all you did was blow through all those passages, then yeah, what the other guys said... need more cleaning! If those carbs have been left to sit for any length of time whatsoever, you will have fuel residue blocking passages, guaranteed.
 
BassCliff said:
Hi,

Not only do the jets have to be clear, the carburetors should be cleaned using this procedure:

[FONT=Verdana, sans-serif]Mikuni BS(CV) Carburetor Rebuild Tutorial [/FONT](9MB PDF file)
(by Mr. Nessism)

There are small passages in the carb bodies that must be cleaned by dipping the carb body in carb cleaner, sometimes for up to 24 hours.

Is the air box installed? These bikes don't like to run without the air box, unless you have re-jetted the carbs to allow for the extra air intake.

If you are using the air box, has it been properly sealed so that there are no leaks in the air intake system? New carb boots and intake O-rings, etc? See:

Air Intake Repair: (PDF file)Airbox removal, intake boots and O-ring replacement


Thank you for your indulgence,

BassCliff


​
Click to expand...

He might have better luck with FC's 450 rebuild guide.
http://members.dslextreme.com/users/cbsaunders/gs/gs450_carb_cleaning_guide.pdf
 
I've found all the guides to be extremely useful.

I found that if I set the petcock to prime, turn off the choke, and finally set my main idle screw in a few turns, the bike actually idles and revs (mostly)!

I suspect the petcock filter is clogged so I'm in the process of draining the tank at the moment. I will go through and purchase new o-rings and will do a proper dip after this.

Thanks for all the input, everyone!
 
Petcock is brand new and free of debris. Guess it's carb dipping time.
 
O-rings ordered and the carbs are mostly disassembled for dipping. I'm having a helluva time with the support bar holding them together along the top. I hit all the screws with heat and it didn't change anything. Next will be some liquid wrench and an impact driver. I was going to do the Pine-Sol method for the dip but someone lent me their Berryman can. It's been used once so it should be good still.

I'll use the downtime to do the valve adjustment and an oil change.
 
O-rings arrived today and a dremel tool assisted in getting the stuck screws removed. The dip proceeds tomorrow and maybe if I'm extra lucky the bike will start the first time.
 
So I dipped the carbs, replaced the o-rings, and replaced the big gasket in the bowls. No change. I did noticed, however, that the right-side cylinder doesn't appear to be firing. I think this is the root of my problem. The coil gets just as warm to the touch as the left side and the spark plug is firing, but that side of the head doesn't heat up and the exhaust is cold. Any ideas?
 
Have you checked your spark plug cap? I know mine were a bit dodgy and I replaced them with NGK plug caps and they're great now. Have you checked the primary and secondary resistance on your coils?

If they both get warm evenly, I'd expect you'll find both primary resistances ok, secondary may measure dodgy which could be the plug cap.
 
not 100% sure if its been asked yet, but have you checked your points gap?
 
94ta said:
not 100% sure if its been asked yet, but have you checked your points gap?
Click to expand...

This bike doesn't have points, but there are some resistance tests I can run. The clymer manual doesn't give much help other than "swap the working coil over to the other side and see if the problem changes sides too," so it's worth a shot.
 
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