What does it mean when...

[KEITH KRAUSE]

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.

[Jethro]

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.

[Anonymous]

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

[KEITH KRAUSE]

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.

[Anonymous]

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 added bonus more grunt
ozman

[Jethro]

Keith,

Thanks for your dedication here to my problem! Answers as follows:

4 into 1 pipe: It had a Vance & Hines on it until about a year ago. It rotted out and I replaced it with a Mac canister type. When I did, there were no drivability changes- only a different sound.

Filter Mods: The bike has never had a air box cover since I got it. I've been looking for one for about two years- whenever an air box comes on e-bay, it seems the filter box is not included, just the big air box. I have fabricated a cover that is a small frame with wire mesh screen. I've also run the bike with no filter at all (taboo, I know) with no changes in drivability at all. The actual filter is a single UNI foam type filter.

Choke: The choke does nothing to help start the bike, and at any time while running- hot or cold- any choke will kill the bike immediately. Even 2mm of pull on the knob and the bike will cough and die.

Jet sizes: The rebuild kits I bought includes jets to bring it to stock. There are two to chose from, 107 and 112.5.

Mixture Screws: All the old cracked, broken o-rings came out when I cleaned the carbs in the spring. I also made sure these holes were clean when I worked on them last weekend.

The plugs I have in there are about 2 months old. I gapped them and rode for a while and did a plug read. All of them looked pretty good, maybe a little more white than I would like to see, but not super bright white. I still haven't gotten a chance to pull the plugs since this latest problem, I'll do that tonight. With the mixture screws, The highest idle seems to be at about 5-7 turns out- much more than everyone seems to be right. I'll play with it a little more tonight, and let you know what I come up with.

The jets in right now are 125's, I'm sure the last guy jetted for the V & H pipe that was on it. As I understand, the MAC canister is a little more restrictive. Think I should put the stock 107's or 112.5's in and try them? Keep in mind that when I put the MAC on a year ago it ran ok. It wasn't till last weekend when I replaced the mixture screws and needle jets, did I have a problem.

Thanks again!

[Jethro]

Ozman,

What is better about the smoothbores? Are they easier to set up? Why do they make more power?

[nabrams]

You say you replaced the needle jets. It's my understanding that needle jets affect every throttle setting except wide open throttle. It makes sense too - a wider needle will restrict fuel flow and vice versa. If your new needle jets have a different diameter or taper than your old ones, that could explain the difference in behavior.

[Jethro]

By needle jets I don't mean the main jet or main needle, I mean the float jets. Main jets and needles were kept the same.

[shaftzuki]

Jethro - the mystery screws, that you replaced, are the pilot screws - that were once sealed, from the factory, with lead plugs. They mostly affect the idle circuit and can have an impact through to mid throttle. Once you have them correctly set (by ear) and the bike is running, you need to sync the carbs - then and only then will you be able to remove the problems your having. It sounds as though your close - but your going to have to "fiddle" a bit with both sets of screws (pilot and butterfly) ... Take your time, set a fan in front of the engine and do as Earl and Keith suggest. 8)

[KEITH KRAUSE]

It's interesting how the choke will kill the bike when hot (it should) but also kills it when cold? This does'nt make sense to me yet, I have an idea but I'll hold it until you give the plug reads. Drive it around town normally, but when you're ready to turn it off, don't let it sit and idle. Turn it off quickly.
Just be sure to ride it long enough to get it hot.
As for the home made mesh screen filter lid, that's OK, but I believe the stock lid was solid. So your screen lid will allow more air. That effects the jetting.
It's possible the 112.5 mains would be adequate for just the pipe, but with the air box lid mod' I don't think so. Maybe a 117.5? I would try the 112.5 temporarily because I think they're closer to right than the 125's you say you have now. The mains are not giving you the "choke"/starting problem anyways.
You say you changed the needle jets, I think you mean the JET NEEDLES?
If so, why? For re-jetting the pipe? Are they adjustable? Are they the same shape/taper as the stockers? It's much more likely you did something when changing the needles, than the mixture screws.
Any more problems such as, a high idle once warmed up that forces you to lower the idle set knob? Any light "pinging" under hard acceleration from low rpm's? Do you see a heavy black exhaust under acceleration or any black at all? When you are stopped and idling a few moments, is there a black exhaust when you rev' it? This sputtering you mentioned, is it abrupt, like the spark is actually being interrupted, or ? Do you have problems at every speed, or does it get better/worse at certain speeds?
Give us those plug reads.
Regarding the smoothbores, I wanted a set of 29mm for my '79 1000 but finding a set in good shape was not my luck. It was holding up my project so I gave up. I did some research on them and I'm well aware of the performance gain. But I was also given a friendly warning by Vance & Hines and even Sudco (very experienced with smoothbores) that a good set is hard to come by and parts availability is getting worse. Even an employee at Sudco was having trouble finding a good throttle valve for his set. I decided they were'nt for me. Maybe after 6 months of constantly working on my restoration I just got tired of messing with things. Even if someone dropped them in my lap right now, I don't think I'd go through jetting again. I'm happy with my bike's performance. I can always dream.
As for you Jethro, you would need larger smoothbores. It's all up to each person. Do you need more performance, or are you happy with your bike if it was just running right? Do you have the money and time? IMO, the smoothbores work best with K&N pod filters and a better pipe than a Mac.

[Jethro]

Keith,

When I say I changed the needle jets, I am not talking about the mains, I am talking about the float jets or valves- there is a little needle that opens and closes the float valve. I didn't touch the main jets and needles as they looked perfect. Also to be clear, once the bike is running, it runs great, it just takes aout 10 minutes of cranking on the starter to get the thing going! Once it does fire up, it sputters for about 10 seconds, then it runs great- although I do have to keep my hand on the throttle or it will die. After about 2 minutes it even idles perfectly. I don't understand it. The sputtering was only before I cleaned the carbs last spring. No black smoke like you asked about, at any point, hot or cold, fast or slow. No pinging or sputtering. Just the problem with starting it!

[mcycle-nut]

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 added bonus more grunt
ozman

Plus the slides don't slam shut when you land off of a jump. Oh, that's when you're using them on a hillclimb bike.

[Anonymous]

I'm not much of a bike repairman but.....
It sounds to me like it's just a problem with the choke.If I didn't use the choke on my bike it would no doubt take 10 minutes of cranking to get it going.These gs's seem very cold natured.It sounds like your choke could be opening up too much.I don't know how your choke works on your bike but I would make a little more slack in the cable or dissconect the cable at the engine side and do it by hand,(if possible).

[KEITH KRAUSE]

Hi. I thought earlier you mentioned the rpm's being slow to return and other issues such as main jet size, etc. That's why I wanted plug reads.
Maybe I misunderstood.
You say the choke does'nt help start the bike, but it will kill it with just a slight pull when hot. So the choke IS working.
I think your starting problem is a combination of a poor synch' and your mixture (pilot) screws being adjusted too far out and allowing too much mixture into the cylinders for easy combustion.
A poor synch' will make the bike hard to start, even if everything else was perfect.
With the mixture screws out 5 or more turns, you are introducing a very "rich" mixture that may be too much for combustion, especially if you add the choke. You say you have to crank the motor for several minutes to make it start. This makes sense. Even though the motor is not starting,
you are starting to build some heat just by cranking. This heat will help combustion and the bike will finally start.
You also said that once warmed up, just 2mm up on the choke will immediately kill the motor. This too makes sense. Allthough the choke should stall a hot motor, your description makes the motor sound too sensitive to such a small amount of choke. With your mixture screws so far out, you are already running too rich, at least cruising/lower speeds.
IMO, this is what you need to try, manually RE-synch' the carbs.
I have a '80 GS1000E/ST factory manual for BS34mm carbs. If yours are similar, it says to adjust the throttle balance screws in the following order:
#2, #1, then #4. I believe #3 is the master carb and you set the others in that order to match it.
Next, put your mixture/pilot screws back to where they were. (2 1/2 ?)
Then, synch' with a vacuum tool.
My carb-stix was only about $40 and is easy to hook up. It's easy to learn if you've never done it before. Just get some 3' long fuel/vacuum lines and put your tank on a workmate or ? Use a fan or two to keep the motor cool and synch' it. Any questions about synching?
I really believe this will end your problem.