v.m carb problem

[whiterabbitt]

first I would like to say hi to everyone, I ride a '77 GS 750B (95% original) . this is my first post, and I am amazed by the detail and dedication this site shows, there is enough information here to fill a small library! that being said, I dont have the time to search hundreds of threads to solve this problem.

ok so everyone knows about that jet that all the manuals say "factory preset, do not touch" on the bottom of the vm 26ss carbs? well heres my problem, I tore down my carbs, all but that one jet, and took them down to the local bike repair shop to be dipped. when I picked them up the next day I discovered that the mechanic had removed these jets! what do I do? My clymer tells me nothing about them, and I havnt been able to locate the info I need in here or have missed it!
what is this jet? how do I set it? am I panicing for no reason?
I would be grateful for any help here, this is after all my first GS, and first 4cyl. bike.

 

[Adler]

Well Im sure BassCliff will be along shortly to give you the lowdown on finding info but for now, I would read through Paul Musser's VM carb rebuild guide found here... http://members.dslextreme.com/users/bikecliff/images/vm_carb_rebuild.pdf

WARNING: its a PDF file.

 

[Guest]

The jet that you described is your fuel mixture jet. They are not shown on any of the clymer or any other manuals carb diagrams but a good shop manual does describe what they do (along with many internet carb sites). I'm not sure why. Z1 does sell a carb rebuild kit for a 750 that does include the fuel screw for about $20 a carb. To do any type of adjustment or cleaning to the carbs you have to gain access to these screws and remove them to clean the carbs probably. If your mechanic took them out, make sure you get them back along with the spring that was in there. The screws are nutorious for breaking off inside the carbs, hopefully that is not the case with any of your carbs. When putting them back in go slowly to ensure you don't brake any tips off and set them to factory settings. Basscliff's site describes the process very well.

 

[BassCliff]

Greetings and Salutations!!

Greetings and Salutations!!

Hi Mr. whiterabbit,

Since you're in a hurry, just read everything in the links below and you'll be all set!

I just stopped by to welcome you to the forum in my own, special way.

If there's anything you'd like to know about the Suzuki GS model bikes, and most others actually, you've come to the right place. There's a lot of knowledge and experience here in the community. Come on in and let me say "HOoooowwwDY!"....

Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", the Carb Rebuild Series, and the Stator Papers. Now let me roll out the welcome mat for you...

Please click here for your mega-welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike!

Thanks for joining us. Keep us informed.

Thank you for your indulgence,

BassCliff

 

[whiterabbitt]

thanks for the rapid response, the warm welcome and directions to exactly what I needed!

all the needles were given back in a little bag, still dirty, but undamaged, he didnt even have the decency to dip them with the other stuff!!!

a couple of other questions: Is it normal for these screws to sit in drastically different depths (turns in?)?? #3 sits like two turns deeper than the others at one turn out.
what engine speed should I use for the plug chop? 4th gear at 30mph is waay too high with my gears (16-38)
the "mechanic" that caused this post said that I shouldnt need to re sync my carbs (they just got synced about a month ago) since I didnt take my slide assemblies apart, is he an idiot not worth listening to ??



thanks again for the help

 

[tkent02]

thanks for the rapid response, the warm welcome and directions to exactly what I needed!

all the needles were given back in a little bag, still dirty, but undamaged, he didnt even have the decency to dip them with the other stuff!!!

a couple of other questions: Is it normal for these screws to sit in drastically different depths (turns in?)?? #3 sits like two turns deeper than the others at one turn out.
what engine speed should I use for the plug chop? 4th gear at 30mph is waay too high with my gears (16-38)
the "mechanic" that caused this post said that I shouldnt need to re sync my carbs (they just got synced about a month ago) since I didnt take my slide assemblies apart, is he an idiot not worth listening to ??



thanks again for the help

Look at the screws, are they all the same length?
Are some of the tips broken off?
Sometimes the screw tips break off and stick in the tiny port.

What jet did he remove? Hopefully not the needle jet!
Send us a pic of this jet?

 

[Adler]

Is it normal for these screws to sit in drastically different depths (turns in?)?? #3 sits like two turns deeper than the others at one turn out.

NO!!! They should all be roughly the same. Hopefully you havent bent the screws but I suspect the hole is blocked. Take the screw out and ensure the end is sharp and unbent. Then look through the hole with a light shining through the carbs and you should be able to see the light.

 

[BassCliff]

Hi,

Have a look at this thread:

http://www.thegsresources.com/_forum/showthread.php?t=82559&highlight=broken

Then have a look at the VM carb rebuild series:

http://www.thegsresources.com/files/vm_carb_rebuild.pdf

A good running GS starts with clean, well adjusted, properly functioning, mechanically sound carburetors.

You'll find information about the "plug chop" procedure and other carb tuning tips on my website.


Thank you for your indulgence,

BassCliff

 

[whiterabbitt]

ok all the screws/needles are whole and undamaged, same length, springs are all new, the only thing I am not sure of is the hole itself, seeing as how I am at the library and the carbs are at home, I will have to check that later.

I would like to thank everyone, especially basscliff with his awesome site, for the help.

 

[whiterabbitt]

so yesterday I put my carbs on (after checking the holes- all clear) and started the idle adjustment ( using highest idle method ) and discovered that the #3 carb is unresponsive to airscrew adjustments, it actually runs slightly better with the airscrew turned all the way in!! I am lost at this point so ......... HELP PLEASE!!

using highest idle method what kind of variation should I get? #1 rose 500 or so rpms #2 & #4 only changed 100-200 rpms and #3 showed about 100-150 variation at less than a 1/4 out. the other three carbs are set at a 1 +/-1/4, this is my first time doing this so bear with me.

btw: the #3 carb is also the one that the fuel screw turns in farther than the others, by all my inspection of this carb I would have to say that the shoulder that the spring sits on is milled a little deeper.

oh yeah my manometer is on backorder so the carbs are only manually synced.

 

[whiterabbitt]

I am going to try to figure this out this afternoon, so if my theory is bad somebody stop me!!!

I am going to start turning the #3 pilot fuel screw out until my airscrew adjusts to 1 out or so. is this the right way??

if that doesnt work I am going to try swapping the fuel screws around and see if there is a difference there, after all I have no idea which screw goes to what carb ( thanks local mc mechanic!).

on bikecliffs site the instructions for plug chop are vague on one point, Do I take a plug read at idle and make an adjustment ? if so I should start there I suppose.

 

[whiterabbitt]

update

update

ok well i have figured ot one problem only to discover others, typical.

solution for carb #3: I lightly seated all the fuel screws and did a basic feel check (stuck finger in carb throat), then backed off the #3 screw until it matched the others pretty close and used this as my starting point, then set my screws out 1 turn. my #3 airscrew adjusted to just over 1 out, and my plug comes out golden.

if anybody else runs up against this problem, try this.

but now, with all that said, I am having problems getting it to idle smoothly, my exhaust note has changed dramatically (it now has a tinny ping to it), it gags terribly off idle, and has a big midrange deadspot.

it still needs to be sync'd, I have a set of 102 mains (100's in it) #1 is slightly rich (plug black/brown) #2 slightly lean (plug kinda grey) #3+#4 good I think (plugs golden)

any further input from knowledgeable people would be appreciated

 

[Big T]

I don't know what to say about the fuel needle length problem - that's just weird

As far as your main jets go, I wouldn't change them as you have 2 plugs burning perfectly

I'd say #2 may have an air leak and #1 may be symptomatic of a bad petcock

In all this carb cleaning, did you replace the O rings in the carbs and between the carb boots and the head?

It sound like you may have the carbs set too lean now, on the air screw

 

[whiterabbitt]

thanks for the input big t, and yeah they were lean.

yeah new orings in carbs, but not in intake boots, they didnt appear to be deformed or hardened so I just slicked them with grease and reinstalled. they passed the carb cleaner check so....

I had a duh moment when I noticed that the plugs were ngk b7es, and a friend pointed out that they looked like they were overheating. a set of b8es plugs and a little adjustment has given me flat tan electrodes across the board.
Speaking of plugs, is it normal if the bike dies if I pull the #1 or #4 plug wire, but not the #2 or #3? and there is no noticeable change in idle if I pull #3.

does it sound like i am as far as I can go without being sync'd?

 

[Big T]

You should sync the carbs, if necessary, you can fine tune it again later

I'd check how hot the header pipes are at idle

Warm it up for a few minutes, then put your tongue (okay skip that). You can use a HF infrared thermometer, a spray bottle of water, or just holding your hands close to see if all the pipes are equally hot at idle. The amount of sizzle when you mist some water on the pipe is easiest to confirm.

If #3 pipe is cold, it's back to carb cleaning (provided your spark is OK)

Have you done a compression test?

 

[whiterabbitt]

compression and leakdown tests are waiting on a friend to have time/space for me to use his stuff, hopefully i will get them done in the next couple of weeks.

as for the sync I ordered a manometer, an then was told it was on backorder until the end of october!! and i refuse to pay another $58 to the local mc mech, especially after he had the audacity to charge me $46 to dip my carbs and caused this whole ordeal with his vague and misleading statements and now obvious omissions of information. I think he thinks that if he is not very helpful I will give up and bring the bike in so he can charge me $55 an hour to do stuff I am capable of doing myself given the right tools and information. the jerk wont even let me rent his manometer and use it in his parking lot.

oh yeah i had only just found out about this site a few weeks before starting in on my carbs but because of work,gf, and life i get very limited internet time, so i hadn't been able to check out very much stuff. Typical of me to jump in headfirst if no one is looking! AH well chock it up to learning experience! because when I get this all straight I will never be at a loss with my GS again, unless of course its where to ride to next!

p.s. I apologize for the mini rant there, after all it really has no place in this forum.

 

[KEITH KRAUSE]

Basscliff, there's an error in the VM carb rebuild section. I can't remember Paul Musser's username if he even still comes around here. Maybe he could make the change if he was contacted. He asked me to check the whole section out before he printed it and I don't know how it was missed.
In step 37, it mentions vacuum synching. It says to use the IDLE ADJUSTER knob to raise the rpm's to 2,500 to 3,500 rpm's or approximately. That is of course incorrect and would cause major headaches if someone follows that procedure.
You simply begin the synch with the bike idling at 1,000 rpm's or what the factory calls for. Then, I suggest synching at approx' 3,000 rpm's by using the throttle.
Paul used many of my posts when he put the VM carb section together and he must have misunderstood something. When he gets to step 37 it's written as if the vacuum synch is following a complete carb rebuild. One of my posts mentions that after bench synching you should turn up the idle adjuster knob sufficiently so the bike will start. Turn it up a little more than you think it may need because you can always turn it down quickly. If not turned up enough you can easily kill the battery trying to make it start and never know what's wrong. Maybe that's where he thought the idle adjuster should be turned up to begin the vacuum synch?

 

[Big T]

Blow off that manometer order and go to Morgan Carbtune - slightly more expensive and more than worth the cost - mine came in 8 days from England

 

[KEITH KRAUSE]

whiterabbit, not knowing the history of your carbs/motor there can be things wrong that you'd never imagine (damage by a previous owner or parts mixed up/wrong parts installed). So if you get odd vacuum readings or an air screw adjustment appears to have no effect then it could be so many things.
If your pilot fuel screws (underneath) appear in good condition...
First, be sure BOTH tiny pilot circuit holes in the bottom of the carb throat are clear. There's one hole right above the pilot jet itself and then the other hole for the pilot fuel screw to regulate. Be sure both are clear by spraying cleaner or air through them. Look/feel for uniform flow so you know they are 100% clear.
Install them any order you want. Don't worry about how much of the tip sticks out in each carb bore. Simply seat each screw lightly/uniformly and back it out to 3/4 turn. 3/4 is a ballpark figure. If the bike is stock then this is a good starting point. They are set at the factory using emissions equipment and there's no way to set them accurately until you test.
Set the side air screws to 1 1/2 turns initially. On a typical bike this will be good for starting purposes. Once fully warmed up, you can adjust them by using the highest rpm method. They should respond as designed to. Most bikes with VM carbs in good condition will have their air screws between 1 1/4 and 1 3/4 turns out when tuning is finished.
Be sure you have #15 pilot jets.
Also, you should replace the manifold o-rings now. I know you said they look good and maybe they are but you must be sure. They commonly are over torqued and flattened too much and their service life shortened. Replace them and give them a coat of high temp bearing grease to help them last. Replace the stupid Phillips screws (if you still use them) with Allens and torque to about 8 or 9 ft/lb is enough. Inspect the manifolds too. If you have any vacuum leaks you'll never tune it correctly.
Just to mention, before vacuum synching you should be sure the valve clearances and ignition timing are correct.
As for the vacuum synch, I think you mentioned earlier that it was done recently? But you don't know if it was done correctly so it should be done. If for some reason you disturb the jet needles/throttle shaft then you must re-synch each time.
Since the pilot circuit controls mixture at minimal throttle openings and has effect up to 1/4 throttle, the best road testing is to ride around on level or gradual uphill roads at about 1/5 or less throttle. You want the least overlap effect from the cut-away or jet needle. It's all about throttle position and not actually speed/rpm's but just cruising around in 4th/5th gear at lower speeds (40 and under) will be fine for testing. After full warm up, I'd go somewhere that you can hold a steady speed for several minutes and then chop off and check the plugs. The pilot fuel screws are sensitive to adjustment and just a 1/8 turn can matter. Do what the plugs/performance say to. Don't worry too much if the final tuning results in the screws not being perfectly uniform in their adjustment. They are for fine tuning EACH CYLINDER and because of small differences in each cylinder this is normal. Besides plug color, look for a good/steady idle with reasonable warm up time and no obvious signs such as a puff of dark exhaust when you lightly blip the throttle off of idling several seconds.

 

[portdave]

Basscliff, there's an error in the VM carb rebuild section. I can't remember Paul Musser's username if he even still comes around here. Maybe he could make the change if he was contacted. He asked me to check the whole section out before he printed it and I don't know how it was missed.
In step 37, it mentions vacuum synching. It says to use the IDLE ADJUSTER knob to raise the rpm's to 2,500 to 3,500 rpm's or approximately. That is of course incorrect and would cause major headaches if someone follows that procedure.
You simply begin the synch with the bike idling at 1,000 rpm's or what the factory calls for. Then, I suggest synching at approx' 3,000 rpm's by using the throttle.
Paul used many of my posts when he put the VM carb section together and he must have misunderstood something. When he gets to step 37 it's written as if the vacuum synch is following a complete carb rebuild. One of my posts mentions that after bench synching you should turn up the idle adjuster knob sufficiently so the bike will start. Turn it up a little more than you think it may need because you can always turn it down quickly. If not turned up enough you can easily kill the battery trying to make it start and never know what's wrong. Maybe that's where he thought the idle adjuster should be turned up to begin the vacuum synch?

Very interesting. I followed this to a T and I had some issues. I will be doing this again soon when I do my 1000 engine swap into my 750. Thanks for finding this Keith.