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My 1982 GS 450 - journal thread

Today I accomplished my goal of hearing motorcycle noises! She ran! Started right up. I had problems though.

I have a high hanging idle issue. It goes straight to 4000rpm's and won't come down.

I messed with it a little bit but mostly read the forums.

- although the intake boots look ok, the rubber is peeling off of the metal backing plate. I'll get another set of boots. also the clamps seem stretched and bottom out.
- the weather stripping on the airbox lid is severely deteriorated. That's another suspicion I have.
- I also will take the carbs back off and make sure the float heights are set correctly. I didn't do it right.

one odd thing I noticed. The one instance where it seemed to run ok - was when I forgot to reattach the petcock vacuum line to the carb. It was idling at a more normal rpm, and the throttle response was working more as expected. Although a bit slow to come down. Which my understanding is that this would cause a vacuum leak on #1 carb. but it would also be only using fuel from the bowls, which makes me think floats aren't right. but a bit strange that a vacuum leak would cause the idle to come down ... i'll have to investigate this more. maybe the carbs are just severely out of sync, or there's a much larger air leak on carb2 than carb1 and inducing a leak on carb1 lets them both run more evenly.

curious stuff. but I was happy to hear the engine run. it sounded half decent to me, when it wasn't revving to the moon.

advice appreciated!

intake boot on the 'passenger' cylinder :
intakeboot.jpg
 
IF the carbs are way out of sync, things will come to normal-ish as they get closer. You might still have an air leak or other problems, though.
 
IF the carbs are way out of sync, things will come to normal-ish as they get closer. You might still have an air leak or other problems, though.

yea i guess i'll find out. i was gonna mess with the sync a little and see what happened, it being a twin i figured it can't hurt to just twist the knob and see what happens. But I didn't have time today. i stayed up way too late reading and overslept. thru my research last night i learned that someone before me may have put a cheapo carb kit in my bike. That is, if it's true that all mikuni jets are stamped; mine have no markings. so all bets are off in that department. I definitely wasn't fond of the needle jet they used with the rubber tip. it got smashed up into the jet and the tip was deformed.

i have some parts on the way to work on the air leaks, a carb tuner, a fancy caliper to measure the floats, and some other stuff to try. i'll definitely take a second look at the pilot jets and stuff...
 
Jets with no markings???? now that'll got'ta really make you scratch your head don't it?
 
If it ran smoother and didn't run up to 4000 rpm when you took the vacuum line OFF.. I would assume the petcock is shot and it is letting fuel go down the vacuum line.
 
well i'm back working on this project after a few month hiatus. I'm having similar issues to what i had before.

i replaced the intake boots. the airbox looks good and i replaced the stripping around the lid and oiled up the filter. It's still running pretty weird.

I did get a new petcock also but haven't put it in the tank. The original one unseized so I left it on for the time being. I set it to prime to rule out a leaking petcock vacuum port.

So tonight, I went to try starting it up again. It wouldn't start at all unless it was on full choke. it finally did start and revved up to 4-5k. when I remove choke it dies. Could be idle set too low I guess but also, when I give it throttle, it dies. just as before, it runs slightly better with the vacuum line removed from the left carb. the throttle will actually respond then. but if i put my thumb over the vacuum port, it revs high again.

I've got the carbs back off and on the bench, I'm gonna check float height. I don't believe it's set right. I eyeballed it when i added different needle valves.

that's clearly not the move. my measurements:
right carb: 31.6
left carb: 28.5

they are supposed to be at 26.6 if my manual is correct. so they're both super lean.

so those are set correctly now. bending that little tab is nerve wracking. I also discovered that my jets are in fact mikuni originals and that I just didn't look hard enough for the markings. I've got 115 mains and 17.5 pilots.

And, I do believe that fixed it.

It wouldn't start cold without choke. But I slowly inched it up to about half choke, and finally it did! and it didn't run away! I cautiously blipped the throttle and it responded! I inched down the choke and it was still working!! I need to set the idle screw higher because i had to hold a touch of throttle, but it's finally running normally and idling right at ~1k happily!!

so it seems that the old carb boots are probably still good - i'll hang onto those. it's easier to take the carbs out with the new, soft ones anyway. and I've got a spare petcock.

hooray! now all that's left is the electronic stuff! my SH775 needs to go in and I need a new blinker relay, and I want to do the headlight mod, but I think that's all that's left before i can go ride!

https://tenor.com/view/trump-dance-trump-2024-trump-gif-12734161508561409577
 
Needing full choke to (cold) start is normal. Revving high after starting is normal. You then reduce the choke to bring the revs down to 2k or so, where you let it idle for a minute or two to warm up.

Try to reduce the choke slightly to achieve a normal idle (1100 rpm). You can ride away with the choke still partly on, cutting it off totally after a mile or so.

If your bike can hold a 1k idle after it's completely warmed up, fine. Many older bikes just can't do that any more, so 1200 - 1300 rpm is acceptable. If it can't hold an idle below 1400, well, some refreshening, refurbishing or rebuilding might be in order.

I assume you know where the idle set screw is?
 
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Needing full choke to (cold) start is normal. Revving high after starting is normal. You then reduce the choke to bring the revs down to 2k or so, where you let it idle for a minute or two to warm up.

Try to reduce the choke slightly to achieve a normal idle (1100 rpm). You can ride away with the choke still partly on, cutting it off totally after a mile or so.

If your bike can hold a 1k idle after it's completely warmed up, fine. Many older bikes just can't do that any more, so 1200 - 1300 rpm is acceptable. If it can't hold an idle below 1400, well, some refreshening, refurbishing or rebuilding might be in order.

I assume you know where the idle set screw is?

well that's good to know. I'm still new to this machine. The best I could do was to compare my experience to what I could find on youtube, which isn't a whole lot - not many 450's on there. most bikes i've seen on there, they just kick it over and it goes straight to a nice idle. Once I got the floats set right, that's what mine did at about half choke. i was able to reduce it a little at a time after it started getting warm.

Yea I know where the idle screw is. I had it turned all the way out for testing. and yea my bike seemed to like it around 1200 from my limited testing tonight.
 
Congrats, seems like you got it. As long as you get it to idle right when "completely warm", mostly or almost warm don't count.
 
well, it's pretty much done now. Yesterday was insanely productive. I stayed up late and knocked off the rest of the list, mostly electrical stuff. flasher relay replacement and sh775 mod. I even oiled the chain. it's pretty much down to just slapping on the seat and tank...

The flasher relay was easier to fix than i thought. I found a 2 blade relay at oreilly's that matched the existing harness which worked. I just zip tied it onto the rubber mounting thingy and that was that.

I velcroed the r/r to the right side of the airbox. I guess I'll figure out a different place for the tool bag. maybe I'll velcro it to the inside of the plastic. the bracket that was in there for the tool set had to go. I cut and soldered the bullet connectors off the old reg rec and spliced them to the new one. left enough wire hanging off of the old one that it could be set back to stock if someone ever wanted to.

i also removed the glass fuse and replaced it with a mini blade style one.

now I just need to finish getting it running right. It still seems a bit lean, it's slow to come down after a throttle blip. I'm hoping it comes down to pilot screw adjustment. Maybe the floats need to come up a hair more. I do have a carbtune and got the carbs in the ballpark. I'll definitely run some seafoam through the first few tanks.
 
I'm still having running issues. it's hanging like it's lean and taking a long time to go back to idle.
-compression in both cyls is good, 155 (the one i re-shimmed) and 145
-I peeked at the advancer, it's free and the springs seem strong

here's the plugs though. these are the ones that came with the bike and they were both black when I got it. but now the electrode on the right hand cyl has gone white, and the left cyl still looks quite black. this is after running for maybe 15 mins total. these are ngk b8es.

i'm not sure how to determine if this is fuel related, or maybe electrical... I guess I need to get some fresh plugs and do a chop to see what's going on better? I need a hint on what to do next.

20250211_211811sm.jpg
 
recheck for vacuum leaks with carb cleaner, none found.

It's colder today - One cyliner was visibly producing white smoke, or vapor - which I presume is probably unburnt fuel from a misfire (it wasn't doing it every hit). I can hear it periodically stumble/miss. It's in the left cylinder, which has the blackened spark plug. So that would make sense.

I also went to the parts store to pick up some more B8ES plugs. I found out, as probably most of you forum old-heads already know, that plug is discontinued. I'd have to get resistor plugs.

So - I'm gonna order a dyna S and do the ignition mod.

I was hoping to avoid it, as it's expensive on this bike (you have to get the coils) but it seems like a better deal anyway (as compared to tracking down new old stock, used, or knockoff replacements). I'm grateful for brick house builds on youtube for showing the process on a 450 in pretty good detail. I've heard that the dyna coils don't fit so great under the tank, I wish I could see pictures on how people have dealt with this.

Well I guess it's back to the waiting game, waiting on the mail man ........
 
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I wish I could help, or somebody more informed than me would, or could chime in with ideas. Personally, to me, your problems seem way more apt to be fuel than ign.... Hoping you the best.
 
Yea I guess I'll find out. If it's still broken with a new ignition then at least I'll know. and it will have a new ignition ...

it wouldn't be the first time i've thrown parts at it in vain. My intake boots for instance were fine in the end. But at the same time they weren't looking hot either. So I don't feel bad for replacing them even though they didn't solve my issue.

The main reason I'm jumping to ignition is because my symptoms are absolutely identical to a bike that BHB showed on his channel, and the fix ended up being an ignition replacement.
 
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installing the dynatek

i finally got all the parts in the mail and got it put together. I don't know what was wrong with the old ignition. could have been bad plugs or caps for all i know, as easily as a bad ignitor. But when I found out that they don't even make the non resistor plugs anymore that the bike wants, i just went ahead pulled the trigger on the whole shebang. now I don't have to worry about if these 40 year old electronics are gonna go bad randomly. i've been wanting to do this anyway since i got the bike last year and found out about the dyna S mod.

I followed this rough guide from brick house builds, and I'm very thankful for it. it made it really easy. https://www.youtube.com/watch?v=ZqCOEG7uHm0 There's a nice wiring diagram in that video, plus he showed how to cleanly delete the ignitor box without messing with the wiring harness. You just clip off the connector from the ignitor box, solder a few wires together on it to make a little loopback plug, and plug it back in. I also clipped the stock connector from the old signal generator and soldered it to the dyna plate leads, and did the same with the coil leads. it all went together pretty easy and clean.

there was a spacer I had to make to take up the slack in the advancer. it's an m14 bushing/washer with about 1/8" thickness. I found some m14 aluminum crush washers that did the trick. I had to waller out the holes a little with sandpaper to get it to fit on the shaft, then i sanded them flat and took them down until they were just the right thickness. they just so happen to be the same size washers that go in the oil drain plug so that's a plus - i have half a dozen left over.

i also had to bend the mounting brackets a bit for the coils to get them to fit under the tank without the plug wires rubbing too much. i bent those ears inwards maybe like 1/4 to 1/2 inch. it's not perfect but it should be good enough. if the wires ever rub through, i have the stuff to make some more. I need to make more anyway, I got 7mm plug wire and it's too skinny for the boots i have. So I need some thicker spark plug wire.

timing was straighforward once i figured out what the marks meant on the advancer. there's "T| |F R |" on there, the last tick mark is the full advance mark. you just set the crank to that mark, twist the advancer all the way, and line up the plate so the test light just comes on right at that point.

i've also heard you're supposed to cut a notch for that oil pressure sensor screw so it doesn't ground out on the plate. but it didn't seem to be touching. I decided to just put some tape on the back of the plate to insulate it just in case.

I got to crank it up today before work, and it ran tons better. at first, the idle was still revving up and hanging, but it was just badly out of sync. before, I guess because it wasn't firing right, no matter where I set it, it wouldn't sync up right. but this time, i turned the sync screw and the idle came right down and sounded nice and steady.

now the issue is that it's still running a little lean. it's still kinda slow to come down after a throttle blip. It pops in the the exhaust a little, especially revved up to about 2-4k. So I guess I need to pull the carbs back off and make sure they're still clean. And I don't remember if the needles are raised but if not, i'll do that. I've read about that hack where you put the washer underneath the needle to raise it.

Maybe I also need to double check float height and maybe try raising the fuel level a mm or so. and throw some seafoam in the gas just for good measure.

But now, apart from getting the carbs squared away, it's pretty much ready to ride. Just in time, the weather is starting to get nice down here in TX.

20250306_223940sm.jpg
 
i took the carbs back apart tonight. i don't have the right snap ring pliers to get the needles out.

i realized that the needles are significantly different lengths. they are about 1/8" different or a little more. one of them is looser than the other. I think they were worked on and put back together wrong, at least one was. it wouldn't be the first carb part i've found put together wrong. the longer one seems more correct. i'll get the correct snap ring pliers tomorrow and figure it out.
 
i've been thinking about that stupid jet needle all day. I'm starting to question everything. why it wouldn't sync up. why it revs so slow and why the revs come down slow. the fouled plugs. I don't even think it's running lean at this point, i don't think it ever was lean. when I think about it, there always has been a mist of fuel collecting in the intake boots every time i've taken the carbs off after running the bike. and the plugs were black.

I'm starting to accept the more probable truth: there never were air leaks. the ignition system was working fine. the plug was fouled on one side because the needle jet was open too far, and so it was running massively rich! and that was causing it to misfire!​ it wouldn't go into balance because it had two different jets! and they were wildly different. Now that I have the right pliers, I took the plungers apart and looked, nothing was missing, there's even a shim washer under each needle. It's just that whoever put them back together last just didn't put the snap ring all the way down into the groove.

I really should have noticed the height difference in the needles. I saw it when the carbs were apart last. I remember noticing it. But I didn't put 2 and 2 together. I didn't know enough at the time to realize it was a problem. i'm glad no one is trying to pay me to fix this bike... i think i've probably just thrown like 500 in parts at it, chasing my tail.

not that i regret having fresh intake boots and a brand new modern ignition system. but still... the realization! ouch .... x_x Then again, for me, this is as much about learning as it is about eventually riding. but the time lost and the frustration are what's killing me about it.

tomorrow morning i'll find out for sure, when i slam the carbs back on and start it up. if i put it back together and it runs perfect, i'm gonna be so happy and angry at the same time.
 
If I'm not mistaken, you have the carb issue figured out now, correct? I was just reading your troubleshooting thread.....

I know it's not standard procedure here, but the GS450 can use a R/R from a GS500. It bolts in the same spot and uses the same wiring connector. But if your are going with an SH775, do that!

I was reading about your tire issues earlier - the Shinko 705's are really nice (and inexpensive). But also..... too little too late. The good thing about the 450's is that their wheels are exchangable (if my memory is correct). So you could get a 16" rear or an 18" rear from another model.
 
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