Please Help....At wits End!

[Mike_H]

I'm going to apologize right now for another carb post, but I have searched and read hundreds of articles, but still have not had any luck. I have been riding my bike for a couple of months now, and It runs...Ok. But I have some niggling little areas concerning carburation (maybe) that need fixin. The biggest thing is that it is Hard to start when cold.

First of all its a GS650GL, 1982 vintage. I have cleaned the carbs, and replaced the o-rings. I have replaced the intake boot o-rings. I put new plugs in Last season, and have them gapped to 0.025." I have new spark plug boots. Coils measure in spec. Battery is one season old and well charged. Valve clearances are all in spec. The air cleaner and box are original and in place. The exhaust is stock, and in good shape (meaning no leaks). The petcock works properly.

I'm pretty sure the mixture screws are not set right (I think rich), because the bike has a pretty rough idle. Its also pretty doggy until I hit approx 4000 RPM. Once I transition off the pilot circuit, the power picks up and she runs real good up to redline.

Now for the frustrating part. I don't seem to get much of a change in engine Idle speed by adjusting the mixture screws. Starting is a chore. She Needs Choke, and will need to restart 5-6 times before it will catch. Once the engine warms up, it runs fairly well, though it still feels sluggish off idle.

I know the carbs need a vacuum sync. I have only given them a good bench sync. I have been putting the vacuum sync off (cuz I need to pay to have it done) until I get mixture issue sorted out. What I would like to know is if a vaccum sync might solve the problem? I feel like I am really close, but something is just not quite right. One other thing...I did not set the float heights while the carbs were apart. I figured that they were OK, because it ran decent last year, before I rebuilt the carbs, and I have not had problems with flooding. Would this maybe cause some of the symptoms described? Thanks for the help. I wouldn't be this far without the help of the great people on this forum.


Mike

[edit] one last thing, though It seems minor. The air cleaner does not fit well into the box. I have had to "squash" the supporting cage to get the cover to clip on. Is this normal? Just wanted to add this in case it was important. Thanks Again.

[edit 2x] One more thing I forgot to mention. The choke does not raise the idle speed. My bike idles at 1000 RPM, period. Even warm. I think this is wierd, but then again...wierd is why I am posting this thread.

 

[Guest]

Did you do all the work yourself? If you did, a sync will seem really easy. Do carbs being out of sync cause hard starting and pilot circuit issues, yes. First do the highest rpm method with all the idle adjustment screws. Get a mecury stick and do the sync yourself. Check bwringers site, he has very detailed step by step instructions. The mercury sticks are relatively inexpensive and are one of the best purchases I've made for tuning my bike.

 

[KEITH KRAUSE]

Considering the things you say are already checked, I'd have to say the pilot circuit is the problem.
Yes, a vacuum synch is needed but tuning the mixture screws for best idle is always done before the synch. If yours aren't responding to typical adjustments (about 3/4 to 2 turns out) and you have stock jets, I think your pilot circuit is clogged/dirty somewhere. Most common passages that get missed during a cleaning are the tiny bypass ports near the top of the throttle plates. These have to be completely clear so the pilot circuit/mixture screw can operate right.
I'm not sure what you're trying to say is wrong with the air filter fit. Your air box has to be sealed well, if that's what you mean. There shouldn't be any damage to the filter, just to make it fit in.
As for your choke, the first part of your post says the bike needs choke, so it sounds like it's basically working (?) at that point, but the choke should be able to make the bike hit 3,000 plus rpm's when starting cold, though you wouldn't want to choke it that much. Choking a warmed up bike should kill the bike or make it near stalling.
If your choke isn't helping that much, I'd have to suspect the choke starter jet, inside the choke tube, is clogged or partially clogged. The choke cable could have too much play and not allowing the plungers to open enough? That much play should be obvious but it could be that.

 

[Mike_H]

I ran a pipe cleaner through all the passages. Twice. I will have to pull the mixture screws out, and make sure again.

The air cleaner fit issue...Its like the filter support cage is too long for the airbox. the air filter is not damaged, but the cage has a "warp" in it from being pressed into the airbox so tightly.

The choke cable is tight, in that the chokes open all the way (they will almost touch the next carb in line). When you say the "choke starter jet," keith, are you refering to the needle seat in the carb body? Or is there something in the choke needle assembly itself that needs to be addressed?

Thanks for the quick replies

 

[UncleMike]

You used a pipe-cleaner to clean the passages? Wasn't that way too big, or do they make several sizes and I've just never seen them?

 

[GSstiny]

Unless you found some super micro pipe cleaners, I dont think theyd fit into the tiny passages in the pilot jet and choke feeder tube. I used a staple for those when I cleaned mine. If theyre still gunked up that may be contributing to the hard starting.

 

[ghwrenchit]

....a vacuum synch is needed but tuning the mixture screws for best idle is always done before the synch.

Keith,

Just some thoughts on the pilot system. Looking at the cutaway and the relation of the throttle plates, which ever one closes first wins, right? If the others are open or off adjustment, would that not impact proper idle adjustment mixture? I had this problem with number 2 on my 750. The mixture screw did nothing until I sync'd the carbs @ 1700rpm. Then dialed in the idle. Runs great.

Just some thoughts

ghwrenchit

 

[KEITH KRAUSE]

Keith,

Just some thoughts on the pilot system. Looking at the cutaway and the relation of the throttle plates, which ever one closes first wins, right? If the others are open or off adjustment, would that not impact proper idle adjustment mixture? I had this problem with number 2 on my 750. The mixture screw did nothing until I sync'd the carbs @ 1700rpm. Then dialed in the idle. Runs great.

Just some thoughts

ghwrenchit

A slide or throttle plate adjusted wrong can render the mixture screw or air screw useless. Same thing can happen if you try to tune the screws for best idle at anything outside the factory recommended idle speed.
As for the correct procedure when tuning these carbs, most vacuum gauge makers recommend you adjust the air or mixture screws for best idle first and then vacuum synch. You can then fine tune the screws, after the vacuum synch. My first vacuum gauge back in 77?, a "GT", included this info. That's where I first read about it. My current Motion Pro gauge includes this info. I still read the same info/procedure at various websites.
Remember, these instructions assume the BENCH synch has been done previously and done according to exact instructions. If done correctly, the screws will operate/have an effect as designed/expected. If a poor bench synch was done, the screws may not operate as they should.
The recommended order is, bench synch, adjust screws, vacuum gauge synch, fine tune screws.

 

[KEITH KRAUSE]

When you say the "choke starter jet," keith, are you refering to the needle seat in the carb body? Or is there something in the choke needle assembly itself that needs to be addressed?

No. Each carb has a brass choke tube (take off bowls/look inside float chamber). There's a very small jet, the starter jet, located at the tip of this brass tube. It can easily become varnished up/clogged and is easily missed when cleaning. If clogged, your choke is useless. If using a piece of wire, be very careful when cleaning. Don't get too aggressive and cause a burr inside the tube. I use a piece of monofilament line and THEN carb spray, and blow out with high pressure air.
Also, but a much less common cause, is the air passages that allow air to mix with the fuel entering the choke tube/choke circuit. One comes from the float chamber and another air passage is up by the diaphragm area. These have to be clean to allow good fuel atomization before the choke mix enters the main bore.

 

[rkubik]

GS650GL, 1982 vintage... The air cleaner does not fit well into the box. I have had to "squash" the supporting cage to get the cover to clip on. Is this normal?

I have the same bike, and the same fit for the air cleaner element. So here's one vote that it's normal.

 

[Mike_H]

Ok, So judging by the posts, its sounds like I need to check a couple of things. A) Check choke tube for a plugged starter jet. After Keith's description, I believe I know where it is now. B) I'm thinking that I need to do another bench sync. My mixture screws have very little, if any effect on idle speed. I have been limping along with the standard 1.5 - 2.0 turns out, but have gone as far as 3.5-4.0 with no effect. I do know closing them completely will kill that cylinder. Just for a starting point, how much variation can I create with a mixture screw. 500 RPM? or is is more measureable with an electronic tach? Thanks again.

 

[DimitriT]

Perhaps a little more info would help. Do you have any sooty/wet plugs? Cold pipes (meaning they take longer to warm up than the others)? How does the bike respond to the idle adjuster knob? I agree that you can probably do the sync yourself with the mercury sticks (you'll also need a small fuel tank and a fan to cool the motor). This is something you should learn to do as you will have to resync if you reshim the tappets or your compression changes. My view on the tuning process is to get the bike idling (resonably well, like 1500) and do the synch right after. After the sync is done, you can then adjust idle mixture. Adjusting the mixture affects the vacume, so then you go back and do another sync.

Also some of the info your provide worries me: pipe cleaner in the idle bypass port? Yikes. Those holes are very small. You may be able to get a thin wire in there. When you remove the idle screws, you should be able to see some light using a bright light through those holes.

If you replaced/serviced the needle valves, you will probably need to set the float heights. I would measure them and make sure they are within spec. The procedure is pretty simple and you can use a machinist's 6 inch rule (with 64ths) to get a close approximation (just convert from metric). You don't need to remove the floats to adjust the height.

I went through a couple of iterations of the above before I got it close. I was still having trouble with a carb which turned out to have a damaged body and had to be replaced (fortunately found a good one right here for small money).

 

[Mike_H]

Ok, The pipe cleaners were used for the larger passages. I did not force the wire through any holes. For the smallest holes, I removed a piece of wire from my side grinder's wire wheel. That should help resolve anyone's worries about the pipe cleaner. The plugs are not fouled. The pipes heat up reasonably quick (and evenly). Like I said in my first post, the engine runs pretty well. Just cold starts and some hestitation that I would like to take care of.

 

[arveejay]

The passage in the carb bowl, where the brass tube that Keith already told you about goes into, must also be free flowing. If you can't spray cleaner in the big hole and have it come out the little hole in the bowl it can't get gas for the brass tube to pick up.

 

[dalknob]

cold start problems

cold start problems

I had the same issues with my 78 550e. I switched to premium gas & have not had a problem since!

 

[ghwrenchit]

A slide or throttle plate adjusted wrong can render the mixture screw or air screw useless. Same thing can happen if you try to tune the screws for best idle at anything outside the factory recommended idle speed.
As for the correct procedure when tuning these carbs, most vacuum gauge makers recommend you adjust the air or mixture screws for best idle first and then vacuum synch. You can then fine tune the screws, after the vacuum synch. My first vacuum gauge back in 77?, a "GT", included this info. That's where I first read about it. My current Motion Pro gauge includes this info. I still read the same info/procedure at various websites.
Remember, these instructions assume the BENCH synch has been done previously and done according to exact instructions. If done correctly, the screws will operate/have an effect as designed/expected. If a poor bench synch was done, the screws may not operate as they should.
The recommended order is, bench synch, adjust screws, vacuum gauge synch, fine tune screws.

Thanks Keith,

Forgot about the "Bench Sync" aspect of things. I did one first but was limited on instructions. Used a small brass wire. I have a used set of "sticks" with no paperwork. I'll do alittle hunting for a manual.

ghwrenchit

 

[david suzuki]

bloody bikes

bloody bikes

Sounds like some problems i had on a honda cbr 600 once. I'd sync the carbs, adjust the pilot mixture and did pretty much everything else you could do without rebiulding the engine. In the end i was adjusting the shims one day, and while i was in the enigne i thought i'd change the cam chain too. This was when i found the cam timing to be out one tooth on the exhaust cam. I checked the manual and found it very misleading when it came to describing which marks to use for timing the cams. It said to use the "t" mark but in the diagrams it referred to a different mark. So i would check that aswell while checking your valve clearances too. It just goes to show you never know who's been playing with your bike before you......
.

 

[wiredgeorge]

Your float bowls have a check valve that allows fuel to be fed to the brass tube already described that picks up gas for the choke circuit. Take a can of spray carb cleaner with the straw attached and put the straw into each of the bowls; into the holes in the bottom/side of the bowl that connect to the hole up on the edge of the bowl that the choke gas pickup tube fits into. Spray carb cleaner through from the bottom of the bowl and it should come out the bowl edge. If not, use a fine wire to poke into the openings from both sides to clear the passageway and check valve in there and repeat the carb cleaner test until each is free. Next, remove your carburetor choke plungers. If you take your carb cleaner straw and put it in the hole in the center of where the plungers seat and blow carb cleaner, it will come out the end of the brass tube and the two smaller holes on each side. If it doesn't, use a fine wire to clear the holes in each of the brass choke gas pickup tubes. Last, if your mixture screws don't effect the idle significantly, you might want to first clean the pilot circuit. Remove the mixture screw and pilot jet. Blow carb cleaner into the air jet on the intake venturi edge. If gas comes out the MAIN JET, you are blowing into the wrong hole. COVER the holes where the pilot jet and mixture screw were and gas should come out the very small hole on the engine side/bottom of the venturi behind the needle jet (brass thing that sticks out of the bottom of the carb venturi the main jet fits into). If gas doesn't come out in an atomized spray, blow carb cleaner through the pilot jet hole and the float needle hole and poke a wire down into the air jet to ensure this passageway is clear and repeat until you get carb cleaner to spray through the entire pilot system via the air jet and through that small hole on the venturi bottom. If you like, you can also go up ONE size to #40 pilot jets and that will make your bike less cold blooded as well. If you do all these things, I can pretty much guarantee all your cold starting and idle issues will go away... one last point on the idle, replace the orings on your mixture screws regardless of how old they are. These need to seal properly to ensure a good steady idle...

One point on bench sync... it is ONLY for getting a bike running. Don't expect the bike to run smoothly or perform optimally until you sync the carbs with a manometer and if you haven't set the fuel level via the service fuel level measurement technique ALL other carb tuning is very very likely a waste of time.

 

[Mike_H]

Not to whip a dead horse, but I have new information that may be important here. I was stripping my carbs down for paint, and while doing so, checking the installed jets against the service manual. On my air jets, the manual says they should be 160's, but the carbs have 150's in them. Additionally, 1 out of 4 carbs had a 155 in it! Might this be causing some of my starting woes? I hope its this easy.

 

[KEITH KRAUSE]

Not to whip a dead horse, but I have new information that may be important here. I was stripping my carbs down for paint, and while doing so, checking the installed jets against the service manual. On my air jets, the manual says they should be 160's, but the carbs have 150's in them. Additionally, 1 out of 4 carbs had a 155 in it! Might this be causing some of my starting woes? I hope its this easy.

If the bike is stock, then replace those air jets with the correct size.
Since this thread is kinda old, I went back and read it again. By your description of the problem, it sure seems like either a pilot circuit problem and/or choke circuit problem. Correct jets, float levels correct and complete cleaning should work.
Only other thing I need to mention is that you said the choke had NO effect on rpm's?? If the choke is indeed working, on a cold motor, the choke HAS to effect the rpm's. A richer mixture given to a cold motor will increase the rpm's. It's what the motor wants at that time. If there really is no effect, or even barely any effect, then your choke circuit is not operating correctly. With a correctly operating choke, a typical bike can "idle" at least 3K and up if you did choke it too much. First thought would be the very tiny starter jet at the end of the brass tube in the choke chamber is clogged.