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1981 gs450 idle surge

  • Thread starter Thread starter lookoutdriftmike
  • Start date Start date
L

lookoutdriftmike

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what could cause the idle to start out fine then surge up to 2-3K and stick? i was thinking valve clearance but I am waiting to get my manual before getting into all that.

When I blip the throttle, sometimes it will come down but sometimes not. the carbs are cleaned, synched and idle adjusted to 2 turns out from a light seat. I just replaced the plug caps which were a source of some problems. Now it idles great minus the surging occasionally. It has mac 2-1 pipes and stock filter with airbox. I do have a little top end noise but not at idle so much as while tooling around the neighborhood under a light load.

Also, has anyone ever put an oil cooler on this bike? It came with one installed as well as an oil pressure gauge. I made sure nothing was blocked and oil flows through the cooler out the front oil filter cover and back in right under the right side cover.
 
lookoutdriftmike said:
what could cause the idle to start out fine then surge up to 2-3K and stick? i was thinking valve clearance but I am waiting to get my manual before getting into all that.

When I blip the throttle, sometimes it will come down but sometimes not. the carbs are cleaned, synched and idle adjusted to 2 turns out from a light seat. I just replaced the plug caps which were a source of some problems. Now it idles great minus the surging occasionally. It has mac 2-1 pipes and stock filter with airbox. I do have a little top end noise but not at idle so much as while tooling around the neighborhood under a light load.

Also, has anyone ever put an oil cooler on this bike? It came with one installed as well as an oil pressure gauge. I made sure nothing was blocked and oil flows through the cooler out the front oil filter cover and back in right under the right side cover.
Click to expand...

Surging, too lean, either from the 2-1 pipe, or air leaks, or just not being adjusted correctly. Idle mixture screws should be adjusted to the highest idle method, not some random number of turns.

Oil cooler is a leak waiting to happen unless your riding style requires it.
 
I would suspect the intake boot "O" rings of being dried out and not sealing.
They are between the intake boots and cylinder head, so the carbs will have to be removed to access them.

Also, the choke lever on the left side of the #1 carb may have a habit of vibrating upwards a fraction of an inch which is enough to raise the idle rpm considerably.

If you have a Dyna S ignition, retarding the timing 1 or 2 deg may help if you have already done the first two items.

Earl
 
Tkent and Earl have this one covered. Intake boot O-rings would be my first guess unless they have been changed recently. Second guess is the pilot screws.

Regarding the oil cooler, post some photos so we can see how it's hooked up. Never seen one dumping oil back into a side cover.
 
oil return

oil return

this is the oil return.

thanks on the other advice ill pull the carbs again and check the o-rings. so do you think it's possible I don't need to rejet? everything I've read says that the mac pipes aren't really that much better than stock. I just did another plug run after switching the plug caps with new ones and yep, big time lean (at least in the mid range which should be the main jet) all white and crusty. looks like the bad plug caps were balancing out the lean mix with incomplete combustion so I didn't see it after my initial plug readings. thanks again.


mike​
 
ok intake o-rings were BAD. got those from Mr. Barr. thanks. bike is a new animal, consistent idle, good power, and really no warm up. I start it on full choke move it to half after i put my helmet on and zip up and ride off. after i get going i drop the choke and its gravy. I have a little flat spot from 3-4k so i will try moving the needle up one notch (figured out by reading that the needle jet is the mid-range) to see if that gets rid of the flat spot. other than that, no more stuttering and it pulls strong to redline. I love it!!1 thanks to everyone.

mike
 
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Mac exhaust systems are advertised as not requiring rejetting. I doubt raising the needles is necessary. If you have a slight lean condition, that can be solved by raising the float levels 1 mm. I set my 450 to 23mm and the plugs burn perfect.

Earl

lookoutdriftmike said:
ok intake o-rings were BAD. got those from Mr. Barr. thanks. bike is a new animal, consistent idle, good power, and really no warm up. I start it on full choke move it to half after i put my helmet on and zip up and ride off. after i get going i drop the choke and its gravy. I have a little flat spot from 3-4k so i will try moving the needle up one notch (figured out by reading that the needle jet is the mid-range) to see if that gets rid of the flat spot. other than that, no more stuttering and it pulls strong to redline. I love it!!1 thanks to everyone.

mike
Click to expand...
 
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Needle adjustment works great and is easy. Thumbs up from me.:)
 
earlfor said:
Mac exhaust systems are advertised as not requiring rejetting. I doubt raising the needles is necessary. If you have a slight lean condition, that can be solved by raising the float levels 1 mm. I set my 450 to 23mm and the plugs burn perfect.

Earl
Click to expand...

did you leave all the jets stock as well?

My real problem is that I don't know what was ever done to this bike. I am tuning it assuming I can see all the mods. after I get through that I can better diagnose what else might be done.

I will check the float levels and/or needles tomorrow when I have a day to fool around with it but boy am i tired of removing the carbs. haha

I am noticing a ticking sound sometimes. its really weird, almost sounds like its coming from the tank, like something it vibrating against it. it comes and goes not dependent on RPM so i assume it isn't mechanical.
 
Yeah, my jets are stock.

Earl


lookoutdriftmike said:
did you leave all the jets stock as well?

My real problem is that I don't know what was ever done to this bike. I am tuning it assuming I can see all the mods. after I get through that I can better diagnose what else might be done.

I will check the float levels and/or needles tomorrow when I have a day to fool around with it but boy am i tired of removing the carbs. haha

I am noticing a ticking sound sometimes. its really weird, almost sounds like its coming from the tank, like something it vibrating against it. it comes and goes not dependent on RPM so i assume it isn't mechanical.
Click to expand...
 
UPDATE!!1 GS450 tuning process.

UPDATE!!1 GS450 tuning process.

Ok, so i did the float levels first seeing as i didn't check them yet anyway. Good thing. They were set at something like 25 from the lip making them 27ish from where they should be. I pulled them up to 23 as per everyone's advice and WOW!! what a difference. i still get a little hesitation when I twist the throttle quickly but the idle is much better and the power is much better. I am going to try maybe one washer less on the needle but the bike is definitely acting more like it should. I do still have very clean plugs which leads me to believe I need a little more gas in there. I'll see how it acts the next few days and go from there. Thanks for all the advice. This place is awesome.
 
ok, bike runs great but I still have those really white plugs.

Is it possible that its right but I still get that color on the plug? I have a slight idle surge still though sometimes (its random too), i've replaced the boot o-rings, the air screw o-rings and the exhaust is tight and the air box is sealed. I'm going to try a few jets larger on the idle/low speed and the main. I raised the needle one "notch" already. idle is to about 1/4 throttle and needle is about 1/4 to 1/2 and then main is 1/2 to WOT? It pulls really hard at all ranges but I don't know. the idle surging and hanging is what bothers me. valves are good and sync is good. could it be electrical? I looked down in the cyl with a flashlight and it looks like its in good shape too. I did order the cam chain tensioner rebuild parts because it seeps a little but that wouldn't mess with the mix would it?
 
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