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My 85 GS450 runs good ... but lousy idle!

dennco2

dennco2

Forum Mentor
I have been riding my 450 now for almost a year trouble free .... after a lot of restoration during the first year of ownership. I was proud of my carb cleaning and mixture adjustments which produced a smooth 1400 rpm idle and good acceleration. Then about a week ago, I had to use a lot more choke to keep it running when cold ... or the idle would drop to 800 rpms and mostly quit. After several episodes of this, I reluctantly adjusted the main idle screw between the 2 carbs to bump the idle back up to 1300 ... but now the engine has a delayed shut down back to idle from higher rpms. Bike acceleration is still about the same .... good.

Battery voltage read about 12.89 engine off ... but something like 12.45 at idle. I have to try again and use clamp-on connectors so I can get better readings at faster engine speeds.

Can anyone suggest where else I might look .... to get my nice smooth idle back?
 
dennco2 said:
I have been riding my 450 now for almost a year trouble free .... after a lot of restoration during the first year of ownership. I was proud of my carb cleaning and mixture adjustments which produced a smooth 1400 rpm idle and good acceleration. Then about a week ago, I had to use a lot more choke to keep it running when cold ... or the idle would drop to 800 rpms and mostly quit. After several episodes of this, I reluctantly adjusted the main idle screw between the 2 carbs to bump the idle back up to 1300 ... but now the engine has a delayed shut down back to idle from higher rpms. Bike acceleration is still about the same .... good.

Battery voltage read about 12.89 engine off ... but something like 12.45 at idle. I have to try again and use clamp-on connectors so I can get better readings at faster engine speeds.

Can anyone suggest where else I might look .... to get my nice smooth idle back?
Click to expand...
Do you ride it regularly or has it been sitting for a few weeks? Have you take a look at you air filter lately?
 
gsrick said:
Do you ride it regularly or has it been sitting for a few weeks? Have you take a look at you air filter lately?
Click to expand...


I have been riding it about 3 times a week during the summer. I have not checked the stock air filter but will. The idle seemed to degrade suddenly ... while riding and slowing down for a stop light. I pulled the spark plugs out to inspect. They looked a little black but I cleaned them and re-installed.

Previously, I had to keep adjusting the main idles screw because as the engine ran better and better ... the idle got faster. After a 25 mile trip, the engine was running it's best and the idle went up. So I adjusted down and there it stayed for many rides ... until about a week ago.
 
Sounds like something might have plugged a pilot jet. I know it's not that much fun, but I would remove the carbs, drop the float bowls, remove the pilot jets and blow some carb cleaner spray bacward through the passages, followed by compressed air in the same (backward) direction. Make sure the pilot jets are clear, re-install, test.

No need for a full rebuild, if you have done one in the last 10 years or so, and run the bike somewhat regularly since then.

.
 
Steve said:
Sounds like something might have plugged a pilot jet. I know it's not that much fun, but I would remove the carbs, drop the float bowls, remove the pilot jets and blow some carb cleaner spray bacward through the passages, followed by compressed air in the same (backward) direction. Make sure the pilot jets are clear, re-install, test.

No need for a full rebuild, if you have done one in the last 10 years or so, and run the bike somewhat regularly since then.

.
Click to expand...

You are so right ... pulling off carbs is NO fun. Is it possible to pull both float bowls and the rubber caps .... then shoot carb clean through the pilot jets without taking the carbs off???
 
In my opinion, no. The way I do it (usually successfully) is to drop the pilot jet and remove the mixture screw (properly called the "pilot screw" for those who really care). Reach in the throat of the carb (engine side), cover the mixture outlet, spray carb cleaner in the hole where the mixture screw goes. That will force any debris back toward the pilot jet area. If you don't cover the hole with a finger, you will simply spray through the port, into the carb throat. Cover that hole when you blow compressed air through there, too.

You don't have to un-gang the carbs, but you do have to remove the bowls, rubber plugs, pilot jets and mixture screws.

.
 
Steve said:
In my opinion, no. The way I do it (usually successfully) is to drop the pilot jet and remove the mixture screw (properly called the "pilot screw" for those who really care). Reach in the throat of the carb (engine side), cover the mixture outlet, spray carb cleaner in the hole where the mixture screw goes. That will force any debris back toward the pilot jet area. If you don't cover the hole with a finger, you will simply spray through the port, into the carb throat. Cover that hole when you blow compressed air through there, too.

You don't have to un-gang the carbs, but you do have to remove the bowls, rubber plugs, pilot jets and mixture screws.

.
Click to expand...

That sounds like solid advice. When I first had to do a major carb clean on this bike, I had a lot of problems getting the pilot circuit to clear all related passageways. When the job was finally accomplished, I could blow air in one orifice and feel it come out the other 2 ports. It might take me about a week to get to it ... as I have other projects ahead of it.
 
Well ........ problem solved. I am a little embarrassed to admit that this bad idle issue was simply due to the carbs not getting enough gas because it was time to flip the petcock lever to reserve gas. The fuel gauge needle was not quite into the RED zone so I did not suspect that. Lesson learned. Thanks for the suggestions.
 
You can calibrate the gauge system, if you wish. :-k

Some members prefer to have the gauge register "half" when you have half of the tank's capacity filled, but I prefer to calibrate it so the needle is right at the red zone when you need to flip to REServe.

To calibrate the gauge, you will need to determine exactly where the needle points when you need to change to REServe. To do that, make sure the fuel level is above that point. Remove the hoses from the petcock. Install a hose long enough to reach from the petcock to a separate gas can on the floor. Install a vacuum hose long enough to reach to a vacuum pump (Mity-Vac, etc.). With the petcock lever in the RUN position, apply vacuum, let the tank drain. When it stops, turn the key ON, note the needle position. Turn the petcock to PRIme, drain the rest of the tank and remove the float assembly. Bend the arm UP a bit (maybe 1/2"?), that will make the needle read just a little bit lower, maybe putting it at the top of the red zone. Of course, you will need to add gas to check.

Note that this will affect the gauge reading at all fuel levels. If you are used to having the needle at or above the FULL mark for the first 75 miles, that might change to 50 miles. You still have the same amount of fuel, but now you will KNOW when it's about time to switch to REServe. :encouragement:

.
 
I read your explanation twice and then understood the procedure .... but for now I will live with this minor inconsistency .... and re calibrate my brain.

Non related comment ... the GS450 is fun to ride at 30mph around town, whereas my other bike is boring at that speed!
 
Those 450 twins are gas sippers, I have fond memories of my 81 GS450L that I had in High school. It did not have a gas gauge, I wonder what year they added that? I remember one night I was cruising around on it and it started to surge and buck so I reached down to move the petcock to reserve, but it was already on reserve. Another good thing about the gs450 is they push really easy too :)
 
Did you replace the intake boots or at least the boot O-rings? Airbox boots sealed and airbox lid installed?
 
Nessism said:
Did you replace the intake boots or at least the boot O-rings? Airbox boots sealed and airbox lid installed?
Click to expand...

The intake boots were nice and supple and I replaced the 40mm O-ring to the engine side with the hi-temp good quality rubber. Stock air box and filter looked fine and sealed lid on. Bike is running good but doesn't like over 6,000 rpms on gear shifts and I don't even try to get to redline on the tach. Tried a few times several months ago. If the engine revved easily from 7 to 9,000 rpms ... I would say it is running great!
 
fbody_mike said:
Those 450 twins are gas sippers, I have fond memories of my 81 GS450L that I had in High school. It did not have a gas gauge, I wonder what year they added that? I remember one night I was cruising around on it and it started to surge and buck so I reached down to move the petcock to reserve, but it was already on reserve. Another good thing about the gs450 is they push really easy too :)
Click to expand...

My guess is 85 to 88 on the fuel gauge added to the tach gauge. One recycler on Ebay claims 83 to 88, but I don't believe him.
 
dennco2 said:
The intake boots were nice and supple and I replaced the 40mm O-ring to the engine side with the hi-temp good quality rubber. Stock air box and filter looked fine and sealed lid on. Bike is running good but doesn't like over 6,000 rpms on gear shifts and I don't even try to get to redline on the tach. Tried a few times several months ago. If the engine revved easily from 7 to 9,000 rpms ... I would say it is running great!
Click to expand...

Your bike has serious problems. It should pull to redline with ease. Not sure what to even suggest other than going through the Newbie Mistakes thread and making sure all the maintenance is up to date. If the bike is stock it's much easier to diagnose running, particularly carb, problems.
 
I guess I should try to rev this engine up higher next time I ride. Since I mostly just ride the 450 around town at 30 to 40 mph, I have been satisfied with low end smooth power. Previously, on hard accelerations .... the engine pulled pretty good but seemed to starve for fuel past 6,000 - 7,000 and power dropped off. Would like the extra untapped power IF not too problematic to get it.

My attitude has been ..... if I want more acceleration, I just jump on my other bike.
 
Do you have a fuel filter between the petcock and the carbs? I have nothing but bad luck with fuel starvation at freeways speeds or high rpms when there is a filter on the line. Could also be a plugged gas cap, that's easy, just remove cap, take her for 1 - 3 gear blast and see if it runs different.
 
fbody_mike said:
Do you have a fuel filter between the petcock and the carbs? I have nothing but bad luck with fuel starvation at freeways speeds or high rpms when there is a filter on the line. Could also be a plugged gas cap, that's easy, just remove cap, take her for 1 - 3 gear blast and see if it runs different.
Click to expand...


You guys have lots of good ideas. The only filter I am running is the petcock filter in the tank.

Okay, I took the 450 out this evening and got somewhat aggressive with it. It pulled thru the first 3 gears fairly strong and I shifted at 7,000 each time .... then had to shut down for fear of getting the attention of an LEO. I must say, I don't remember it pulling through the gears so strongly. I could have tried to wring 9,000 out of it but was too intimidated. It felt strong at 7,000 with no tendency to fade .... as in many months before. I have done a LOT of work on this vintage bike an possibly not all was attended to with those rpm runs? A few days ago I tried to get rpms .... but that is when I was low on fuel and need to hit the reserve lever.
 
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