Help with Carbs

[79GS1000]

As I am a newbie to the forum I would like to say great forum and the Tech support and help from everyone is top notch.
Good Job

I rebuilt my carbs on my stock 79gs1000 as they were leaking gas.
I used the K&l kit and the bleeder pilot jet was different than the original
so I cleaned up the old one and used it. I installed the orings that I got from http://www.cycleorings.com/. Everything went good on the rebuild. Bench Sync them did the best idle on the pilot air and sync them with the Motion Pro Mercury tool. It idles ok but the problem I have is the is a slight hesitation when taking off under load that wasn't there before at the first low rpm. The other thing is on full open its not like it was before there is just a slight lack of full go if you know what I mean. When taking the carbs apart I noted the screw turns for the pilot air screw and the pilot fuel screw and started with the same settings. The pilot fuel screw was 3/4 to 7/8 out from bottom and I have not adjusted that. Is that where it should be and what is the adjustment for that. This is the first time I have tried to do the carbs myself and it was a learning experience. Mixed up carb 2 and 3 and had to pull them off again and regroup. lol. The fuel t leaked and had to pull off again and fix that. I am getting faster at pulling the carbs and syncing them lol. I used the K&L jets should I have kept my old ones? The old ones have a R and a symbol and 100 on them. Any suggestions from all the people that know a lot more than me it would be help full.

[49er]

I did the same as you and re-kitted. My bike had a 4-1 exhaust system with the standard airbox and had been re-jetted by the PO. He made a pretty good job of re-jetting as it was crisp right through the rev range.
When I re-kittted, I bought the 750 kit. I did this knowing that many of the jets would be leaner than mine, but the price was right and I planned on using only the new needle valve assys, the pilot fuel jets, pilot air jets and associated gaskets and seals.
Out of curiosity, I measured the jet orifaces against a metric standard with known drill sizes. Three of the main jets were slightly undersized and the fourth was oversized. All had the same size number stamped on them. This may be what has happened with your kits.
I suggest that you refit your old jets. The pilot fuel settings should be 3/4 to 1 turn off the seat. The pilot air jets should be 1&1/4 to 2 turns off the seat. Let us know if your performance improves.
Cheers
Ian

[KEITH KRAUSE]

Unless they are somehow damaged, always re-use all the brass jets. They are made to exact measurements and many of the kits are not.
Is the slight hesitation only under load, or does it also do it while revving slowly in neutral? Under load only suggests a lean condition. If you vacuum synched well and the carbs are clean/rebuilt as you say, then I'd try richening the pilot fuel screw (underneath) settings a bit (CCW). There is no exact setting for these, they vary bike to bike. Your present settings sound normal to me for a totally stock bike. These screws are very sensitive. Try a 1/4 turn more out and test. Remember to only seat the screws lightly if you seat them. The sharp tips can break off in the carb body and obviously ceate a lean condition as no fuel will be able to enter through that passage to assist the pilot jet. Hopefully you didn't break them off or a PO(??) Check that the small passage is clear at all 4 carbs if any doubt.
If all are OK, be sure you adjusted the side air screws using the highest rpm method. They will generally end up between 1 1/2 and 2 turns out.
As for your top end small decrease in power, did you adjust the FULLY OPEN slide positions correctly? You do this after the bench synch for the fully closed positions. When the throttle is fully open and held there, the very bottom of the slides must be between .5 and 1 mm above the very top of the carb throat. If the clearance is too little or too much, top speed will suffer a bit. You'll see a screw that contacts the throttle pulley when fully opened. Adjust it accordingly if your measurements are off. I made a very detailed post about bench synching the VM carbs for both closed and open positions, as per factory manual. If interested, a search should find it for you. Sorry, I forget where it is right now.
Also regarding high speed problem, I hope you re-installed the Mikuni mains. Like the pilots, the kit main jets may be incorrect. Always re-use the factory jets. Your mains should be #95.
Also, I assume you checked the float levels? Factory range is .90 to .98" with .94" being a good choice. You should always replace the manifold o-rings too if you didn't. Swap the cheapy Phillips manifold screws for hex heads and torque the new o-rings to 6 ft/lb to avoid squishing them. Apply a coating of bearing grease to help the o-rings last. Of course, the manifolds must be in good shape too.

[KEITH KRAUSE]

One other thing, re-use the pilot fuel screws too if in good shape. Many kits offer replacement screws but they are often not precision made and can cause problems.

[79GS1000]

Update

Took the carbs off once agailn.
Installed the old main jets they were 100's the ones that came with the kit were 95's. used the original pilot jets. benched synced um and reinstalled them. Now I have a high idle and the throttles screw isn't even touching.
The slides are all the way down closed????
help

[tkent02]

If you bench synched it.....

The slides are all the way down closed????
help

There should be just a sliver of light visible under all four slides when you look through them from the intake side. If you have more than that, read the directions again.

[SqDancerLynn1]

You need to go back & redo the mechanical sync starting with the #3 carb make sure it is fully close with the main idle screw backed out, then adjust opening for #3 with the main idle screw until you can just feel a slight drag with a 1/16" drill bit from the intake side Then adjust the others to the same 1/16". this should put you real close for a vacuum sync

[BadBillyB]

Part of doing a carb rebuild is inspecting the intake boots and replacing the "O" rings between them and the cyl head. This is mandatory, before you try to do any tuning at all.....You had already bench synched and vacuum synched the carbs....No need to re-do this when changing main and pilot jets......... The motor has to have an air supply to idle fast. Either the slides are not really all the way down (even though you are not touching on the idle stop screw) OR the motor is pulling air past the boots or the vacuum hose going to the petcock....Make sure the hose to the petcock is connected at both ends......If the slides are not closing all the way, follow the procedure offered by SqDancerLynn1, it will eliminate this issue........BadBillyB

[KEITH KRAUSE]

When first learning to synch these VM carbs, it's very common to adjust them to the point where the "idle" is high but the pulley no longer touches the adjuster tip. Start over.
Bench synch as before. With your 1000 it doesn't have a "master" carb so you can bench synch them in any order you like. Did you read my VM carb synch post or do you have the factory manual?
When ready to vacuum synch, the best way to avoid what happened to you is this.....After complete warm up, hook up the tool and view the initial levels. Now adjust the higher level(s) DOWN to match the lower ones. Don't be concerned about what level they are, just get them as close as possible. If the difference from the lowest level to the highest is 1" or less, you're fine. Closer may be technically better, but you won't really notice significant performance improvement. I try to get them within 1/2" but I've learned how to synch over the years without getting the bike too hot. If you bench synched correctly and the carbs are operating correctly, the initial levels you see should be within an acceptable vacuum range and getting them close/even will be the trick. A lot of times three initial levels will be fairly close together but one will be too high or low. When I first learned to synch the VM carbs, the very same problem happened to me a couple of times. I kept trying to adjust this one, then that one, over and over until the rpm's went higher even though the pulley lost contact. I kept trying to adjust them even, but always thinking I should RAISE them in the attempt. Nothing wrong with the bike, just operator error. I soon learned to just stop and re-bench synch and then adjust the higher levels down to match the lower ones.
You probably saw that over-adjusting one carb can actually change the others levels. That what gets you in trouble. Also, don't over-torque the holder nut that holds the adjuster screw. 3.5 ft/lb is factory torque.
Also, just for your info, #95 is the stock main, not 100.
I doubt your high idle is from an intake leak. It's just the above error in the method you chose to synch the levels. Also, I suggest synching at approx' 3,000 rpm's. If you try to synch at the factory idle of 1,000 rpm's, or very close to, it's very difficult and a waste of time in my opinion. They jump too much. Just be aware that synching at higher rpm's causes heat and if you're still learning, you have to be careful of over-heating. Use two large fans even if you can do it fairly quickly.
One more thing. The valve clearances must be within .03 and .08mm on your 1000. The ignition timing must be spot on. THEN you warm up, adjust the side air screws for best idle, THEN vacuum synch.
Let us know if you still have trouble and we'll try to help.

[byrdman76]

Air filter maybe?

When you performed the rebuild you didnt happen to change the original air filter out with a UNI brand filter or some other form of filter material that was less dense that the original "green filter" did you?

In addition the airbox assembly including the cover is currently installed on the bike.

If so, reinstall the original air filter and start over once the carbs have been synced on the bench.

[79GS1000]

ok Guys thanks for the help.
I pulled the carbs off again and the 4th carb was way outta sync.
Took my time this time and did the bench sync.
I removed my pilot fuel screw on the 3rd carb and somehow the new oring
was cracked and muked up. I installed a new one for now.
I put them back on and am now using the sync tool to set the carbs.
I am really close to being in sync.
Have not put the tank on and rode it yet.
The funny thing I seen is when I adjust the slides to close them the screw is all the in and the nut barely fits on and I had to cheat a little to get the play out of the bar that the 9 mm bolt attaches to. Is something worn or I am doing something wrong?
Now the idle screw is almost all the way in and there is not much to play with for adjustment. I think though that I am in the perfect spot because the slides can close and I can still idle down.
I did set the floats and the intakes are new with new orings.
The bike is old and has 73k on it.
My mistake on the all stock. the PO did cut the air filter box bottom off and cut a slight corner out of one corner to fit an oil cooler in there.
Before the rebuld the full throttle worked perfect. Is that why you think they had the 100's in there. I can put the 95's back in but was going to test the 100's and see whats up.
Still working on it but thanks guys for all the info.
Most of the trouble were my mistakes as this is the first time playing with the carbs.

[KEITH KRAUSE]

I've seen it before. The adjuster screw being too far down is typical of over-adjusting. This just proves what I said in my previous post. I'm not sure about the rest of your description about "cheating a little to get play". I suppose if the carbs are synched and the adjuster screws are in far enough to stay put, you'll be OK. I'd probably re-set every screw and start over but that's just me.
As for your air box mod, it sounds like the cut out hole is similar in size to removing the top lid. A hole that large will greatly effect the mixture. Actually, a full size up (5) to #100 isn't enough in my opinion. I'd go up to at least 105 and test. Maybe more. Take plug reads at full throttle. The plugs will tell you what to do.
The jet needles may need to be raised too. You spend the most time riding on the needles so they need to be right. Test and get plug reads at solid 1/3 throttle to see what the needles are doing. If lean, and I expect them to be, then they must be raised. Adjusting the jet needles is the most work in re-jetting your carbs. You'll need to pull the throttle shaft to set them. This means a new bench and vacuum synch. More work, but running lean is a bad thing.

[79GS1000]

Ok pulled the carbs off again. The jet needle was on the second to the last clip. I moved it to the last clip to raise it.. I bench sync and put it all back to gether. I did a test drive without syncing with the sync tool. I have full power thru the throttle all the way to full open. I am getting closer I think. I looked at the plugs and I need to replace them and do a test drive and check them.
They were really black but I am not sure if that was from before the rebuild.
I did learn to sync better than before as I was trying to sync to far down and didn't raise the lowest slide a little to bring all the rest up a little to give me more throttle screw adjustment and the adjustment screws were a little higher and would give more movement. What I learned from turning the adjustment screw it only will open so far and then when you keep turning the screw the slide stops raising. I picked a happy medium and started from there.
The PO cut the air filter box and it had no cover when I got the bike.
The 100's seem to work ok and I will watch the plugs and see if I have to go up like you said Keith.
Eventually I want to redo the top and bottom end get some pods and a 4 into 1.
Thanks

[79GS1000]

update

The bike runs fine now.
I put everything back together and put in new plugs.
I removed the plugs after 10 miles and they are really black.
I and guessing thats too rich.
Should I lower the jet needle that I raised?

[KEITH KRAUSE]

"Really black", as in wet and glossy/oily, or dry/sooty black?
With 73K and who knows what kind of miles and maintenance, your black plugs could be from a weak spark, low compression, carb related, etc. If oily, I bet the compression is low and that will have to be fixed before going on. If you must ride it like that, then keep lots of plugs around. Sooner or later it won't help to change the plugs.
If the compression is acceptable and the plugs are dry/sooty black, then you need to check some basics before changing the jetting. It may seem like more work but it saves time and frustration in the long run.
If I had the bike and going from what you've told me, I'd do the following. Some you may have done but I'm just going through the basic checks.
Clean all electrical connections including grounds. Check all for tight, including the entire fuse holder, coil terminals, battery and inside plug caps. Check plug leads for any cracking. Charge/fill the battery and be sure it holds an acceptable charge. Measure the volts. Check resistance at the coils. If still points ignition, check points for pitting and clean/replace as necessary. Set points gap/dwell. Set ignition timing after the dwell is set. Use NGK B8ES plugs and gap plugs at close to .027".
Set all valve clearances between .03 and .08mm.
Clean carbs, especially the tiny holes in the needle jet/bleedpipe, air jets at the filter side of carb throat. Be sure all choke plunger rubber is good and the chokes are sealing when you release them. Replace all inner o-rings. Set floats to .94". BE SURE THE TWO PLASTIC SPACERS FOR THE JET NEEDLE ARE INSTALLED IN FACTORY ORDER. Thicker spacer (ring), goes above the jet needle e-clip and the thinner one goes under the e-clip. Reversing these will greatly richen the mixture. Bench synch, then vacuum synch (after initial re-jet.)
Be sure the air filter is clean. Get rid of any in line fuel filters and be sure you have 5/16" fuel line. If you have rust in the tank, fix that with a sealer kit. Be sure the vacuum line is good. Make sure the two float bowl vent lines are clear. Since the box was opened up, it may run better without the vent lines attached.
As for jetting, try the side air screws at 1 3/4 initially and then fine tune when it's warmed up. Try the pilot fuel screws (underneath) at 1 to 1 1/4 turn out from lightly seated. I still think you need at least a 105 main jet but that doesn't seem to be your biggest problem right now. As for the jet needle position, your needles come straight from the factory with the e-clips in the 3rd (middle) position, if you still have the factory needles with 5 grooves. Typically, removing the air box lid requires you to richen the needle circuit by placing the e-clip in the 4th position from the top of the needle. However, sometimes that's a bit rich and you would instead set the needles at position "3 1/2" by placing the e-clip in the 4th position and then placing a .022" jetting spacer directly on top the e-clip. Only 1/3 throttle test/plug chops will tell exactly. Problem is, I know you run with the lid on but I don't know how large the cut out hole is at the bottom of the box you mentioned. I assume it's about the same effect as removing the lid but that's just a guess. I can say that if the box is opened up as I think, an OTHERWISE correctly tuned/good condition 1000 would require at least the 1/2 positon richer adjustment as I detailed. Tell again, what current needle position is. Count FROM THE TOP- DOWN.
Remember, when moving the needles, you must re-bench/vacuum synch to get accurate plug/performance reads.
Give detailed test info please to get the best advice. Say at what throttle positions you got plug reads/performance checks at, etc. The more you include, the better we can help.
Another thought, you can always replace/repair the air box with a used one and go back to jetting that's stock and known to work. A couple layers of duct tape or ? will seal the PO cut out mods at least temporarily and you can then run 95 mains and the needles with the e-clips in the factory 3rd position. All air and pilot fuel screw adjustments would be simple to adjust. With the intake and exhaust now back to stock flow, you know that jetting will work and any richness problems will not be the jetting's fault.