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What does it mean when...

Jethro

Jethro

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What does it mean when your engine RPM's don't instantly decrease when you rev the throttle and let off? Mine takes about 12 seconds to finally get down to normal idle speeds. Just rebuilt the carbs- of course I didn't synch. them and I'm sure that is part of the problem. Any ideas?
 
Re: What does it mean when...

Assuming your throttle return spring returns the carb linkages to the stop, and your idle adjustment knob is not turned up so high that the idle cannot decrease, it means your mixtures are too lean. Even if you richen the mixtures, it is very probable that you will not get a smooth idle or throttle progression without synchronizing the carbs.

Earl

Jethro said:
What does it mean when your engine RPM's don't instantly decrease when you rev the throttle and let off? Mine takes about 12 seconds to finally get down to normal idle speeds. Just rebuilt the carbs- of course I didn't synch. them and I'm sure that is part of the problem. Any ideas?
Click to expand...
 
Part of the rebuild was new air screws, do I screw them in or out to richen the mix? Right now they are all 2 1/4 turns out. I know I need to synch, but there is a big ride tomorrow I am leading in New England and I need to make it work for tomorrow temporarialy. Thanks!

P.S. The throttle return springs are strong. Damn strong! Putting the throttle cable back on was a bear!
 
Turning the air screws out allows more air and leans the mixture. Screws in, decreases air and richens.

There is a cable adjuster on the throttle cable at the carb end and another one at the handlebar throttle sleeve. You can turn the screws in to get slack in the cable for an easier re-install.

What year is the 1100? CV or VM carbs?

Earl

Jethro said:
Part of the rebuild was new air screws, do I screw them in or out to richen the mix? Right now they are all 2 1/4 turns out. I know I need to synch, but there is a big ride tomorrow I am leading in New England and I need to make it work for tomorrow temporarialy. Thanks!

P.S. The throttle return springs are strong. Damn strong! Putting the throttle cable back on was a bear!
Click to expand...
 
It's an 81 with CV's. I know it needs a synch, but maybe you can clarify something for me. When synching the carbs, all your really doing is making sure the throttle bodies are spitting the same amount of mix into the engine, correct? So when I do get gauges, all I would do is adjust the screws that attach to each throttle arm. Synching has nothing to do with the mixture or jetting or float hights, correct? Because the bike ran fine before I did the rebuild, so I must be too rich or lean, right? Would I really need a synch? The only reason I rebuilt the carbs is because the air screws were all messed up. One was stripped and siezed, the others were missing the washers and o-rings. Now that I put new screws in, it is running strange.
 
Ok Jethro, for an 81 with CV's I dont believe you have an adjustable fuel pilot and I dont think you have an adjustable air screw either. I believe those functions are rubber plugged on your carbs. You have throttle plates and their initial position is set with the throttle valve adjustment screws for synchronization. Carb #3 will not have an adjustment screw because it is the control carb and all others are to be matched to it. You will have three adjustment screws. The center screw is for carb #2 and the outboard ones are for carbs 1 and 4. Consequently, assuming the float heights are correct, cylinder #3 should be burning the proper color. Its next to impossible to match carb vacuums without a guage, but if youre going to try, opening the throttle plate will increase throughflow area which will decrease velocity (reduce vacuum) and fuel flow will decrease resulting in leaning the mixture. Closing the throttle plate will increase velocity, increase fuel draw and richen mixture.

Synchronizing the carbs means matching vacuums. Jet sizes, needle positions and mixtures are another subject. :-)

Earl


Jethro said:
It's an 81 with CV's. I know it needs a synch, but maybe you can clarify something for me. When synching the carbs, all your really doing is making sure the throttle bodies are spitting the same amount of mix into the engine, correct? So when I do get gauges, all I would do is adjust the screws that attach to each throttle arm. Synching has nothing to do with the mixture or jetting or float hights, correct? Because the bike ran fine before I did the rebuild, so I must be too rich or lean, right? Would I really need a synch? The only reason I rebuilt the carbs is because the air screws were all messed up. One was stripped and siezed, the others were missing the washers and o-rings. Now that I put new screws in, it is running strange.
Click to expand...
 
Ah, thanks Earl. If I don't have air screws, what are the brass screws (accessable with carbs assembeld) that are right on top of the output body, just above the rubber boots on the engine side? I always thought those were air screws to control the mixture. I'll have to dig out the schematic and my manual. Again, I always thought they were the air screws, and when I put it all back together today, it was running pretty rough. They were set at about 2 1/4 turns out, but when I set them at about 5 turns out, the bike ran a lot better (had to decrease the idle screw after I did that). Also, I used to have to choke the bike to get it to start. Now the choke kills it totally, and I have to keep my hand on the throttle a little until she warms up. These carb issues are really complex. Phew!
 
Jethro, do yourself and the bike a favor, synch' the carbs.
Carb tools don't cost much and it's easy to learn how to do.
Dollar for dollar, one of the best tools you can buy.
As for your screws, they are pilot screws. You can adjust the amount of mixture entering the carb throat. Air, coming from the air-jet, and fuel coming up through the main and metered by the pilot-jet, are already mixed when they get to the pilot screw. Some of this mixture goes straight to the carb throat via a bypass port(s). The remainder of the mixture is regulated by the mixture screw. Out to increase mixture amount, in to decrease. So you cannot change just the air or just the fuel. You can change the mixture amount.
IMO, 5 turns out seems too much. If you have to turn them out that far to make it run better, you are just compensating for a lean condition. It's easy to have a lean condition with poorly synch'd carbs.
Before you go on your ride, at least double check your rubber boots and manifold clamps. Make sure they're tight.
 
Yup, no air leaks and all is tight, one of the first things I thought to do. I think it just needs to be synched. The bike actually runs better than it has in a long time, but starting it from cold is a real problem. Time to synch! Hey, what do you guys do for a temporary gas tank while the real tank is off? I tried to rig something out of an empty oil container, but there has to be a better way!
 
I bought a 6 ft length of 5/16" ID vinyl tubing and I sit the gas tank on a stool beside the bike. Run the bike on prime from the petcock and plug off the vacuum fitting.

Earl



Jethro said:
Yup, no air leaks and all is tight, one of the first things I thought to do. I think it just needs to be synched. The bike actually runs better than it has in a long time, but starting it from cold is a real problem. Time to synch! Hey, what do you guys do for a temporary gas tank while the real tank is off? I tried to rig something out of an empty oil container, but there has to be a better way![/qu
ote]
Click to expand...
 
The choke is hooked up correctly, but it does not choke the bike! I can't even start it! Yesterday I had to hook it up to the car battery and just hold the starter for about 10 minutes. What during my rebuild could cause this to happen? The only strange thing I noticed was that the pilot screws looked a little different than what was in there before. The new ones have a little step in the pin about 3 mm from the tip. The old ones were a straight taper. I know the kits I bought were for my 1100E, though.
 
its definitly the sync. a fellow GS friend helped me sync mine this weekend with a good tool, and it has extremely better throttle response now. it revs quick, and falls quick, like it should. another thing to check is make sure your throttle linkage bolts are tight. we found the bolt that holds my throttle arm was loose, which let the slides float a little before falling back down. i'm not sure if your CV carbs have something simliar.

~Adam
 
Jethro said:
The choke is hooked up correctly, but it does not choke the bike! I can't even start it! Yesterday I had to hook it up to the car battery and just hold the starter for about 10 minutes. What during my rebuild could cause this to happen? The only strange thing I noticed was that the pilot screws looked a little different than what was in there before. The new ones have a little step in the pin about 3 mm from the tip. The old ones were a straight taper. I know the kits I bought were for my 1100E, though.
Click to expand...

On my VM carbs, if they are not at least manually synch'd after being taken apart, the bike will have a lot of difficulty starting. Your carbs should be no different in this regard. Do a manual synch and then use a vacuum tool.
 
I think I did do that, as long as what you mean is making sure the throttle bodies (terminology???) are set the same so they open the same amount. I think it means something that I can't use the choke at all, even while the bike is running. Shouldn't I be able to use the choke and my RPM's will raise slightly? I know that full choke might kill the bike, but for the past 5 years I could always apply a little choke and the RPM's would only increase. Now the bike just dies. And it does nothing to help start the engine. However, when it gets going, it runs great- better than it has in years. I don't get it.

???
 
Hi. Just to eliminate back reading and to update things, let's start over.
The bike ran fine, but you did a carb rebuild to replace the mixture screws.
After reassembly, the rpm's are slow to return after opening the throttle.
Also, your choke is not doing anything.
You say you did a manual synch' of the carbs. You also say the choke is hooked up. I'm not familiar with your CV carbs. Regarding the choke, can you see the cable hooked up AND with the proper amount of slack? Can you see the plungers move up and down? Do you have plungers?
Regarding your rebuild, did you take the carbs apart COMPLETELY?
Did you disturb the diaphragms, spring/piston, throttle valves? Did you flush and blow out all passages? How were the o-rings, especially the ones on the mixture screws? Anything else you did to the carbs?
Give us as much info as you can and maybe we can fix this thing.
 
Ok, here goes. Prior to any work, the bike ran ok, certainly the choke worked good and was easy to start. I bought 4 rebuild kits for the carbs because the pilot or air screws (I'm still confused, these and the carb throttle link screws are the only external adjustments possible) were stripped, the o-rings were missing or cracked- it's a wonder it ran well. It did however surge and sputter a little at full throttle as well as going slow or getting on and off the gas quickly. I figured a rebuild and cleaning wouldn't hurt. The rebuild kits did not have the same size jets as what was in the bike, the guy before me may have jetted it for a Vance & Hines 4 to 1 pipe. The mains were 125's and the pilots were 145's (I think??), so I did not replace them. I did replace the float needle valves and pilot or mixture screws. All the springs and washers are brand new in the pilot screws. cleaned it all out good- diaphragms look to be perfect, they should be in place correctly- and slapped it back in the bike. Oh yeah, I made sure the floats were set to factory spec. too. The choke is most definitely hooked up right- no cable slack and actuates the plungers perfectly. Throttle is also hooked up perfectly. I made sure the throttle bodies were set the same using carb number 3 as a guide. Now it doesn't start easily at all. I had to jump off my car battery and hold the starter for about 10 minutes just to get it started. After it did fire up, it the RPM's wouldn't go down quickly when I let off the throttle. In an earlier post, Earl said it may be running lean. I turned what I thought were the air screws out to richen the mixture. This brought my RPM's up, but made the RPM's would decrease quickly when I let off the throttle. So I adjusted the idle set screw down and rode 200 miles on the Sunday GS ride. It runs just fine, but the choke does nothing to start the bike and even 2 mm of pull on the cable (after I finally do get it going) kills the motor. I don't know what to do. Should have left well enough alone, I guess! Thanks for any input you have Keith.
 
Where does one go to get such a carb synch tool for my 450 twin? Sounds useful.

Reply by private message to help keep the thread on subject.

Thanks,
Michael
 
Hi Jethro. The previous owner may have added more possible problems.
You say the bike ran OK but was sputtering/surging at various throttle positions. The choke was good. You have a 4-1 pipe, what style/brand?
Do you have ANY air filter mod's? Does the stock air box still have the top lid or were any holes cut in it? When the bike is warmed up and running OK, just a little choke will kill it? But the choke does nothing to help start it?
Can you find out what the stock jet sizes are?
Is there any chance the old mixture screw o-rings crumbled and may still be inside?
Try to come back with answers to all these questions.
And do the following: Clean/re-gap the plugs.
Warm up the bike and then adjust the mixture screws for the highest possible idle. Turn 2 screws out at a time, in 1/2 turn increments, to achieve the highest idle, then re-set the idle with the idle screw knob.
If at all possible, synch'.
Ride it some, and give us some plug reads.
 
people ask me why i always take cv's off and fit smoothbores the previous couple of dozen replies provide the answer .those smoothies are so easy to care for and tune :D :D :D :D :D :D added bonus more grunt
ozman
 
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