My 1982 GS750E Project

[eil]

If you messed with the sync screws without a sync gauge, you probably did more harm than good, adjustment-wise. Take the carbs back off, do a proper bench sync. Set the pilot screws at 3 turns out from lightly seated. Reinstall.

Fill the float bowls, pull the choke knob and the bike should start and run in this configuration. If it idles too fast, bring down the RPMs with the idle screw knob thingy. It may idle a wee bit rough until you do a vacuum sync and you may need to tweak the pilot mixture some, but it should run without having the mess with the throttle. If it doesn't, there is probably something else wrong.

[Dodik]

have you adjusted or at least checked your valves? and like Eil said do a proper bench sync,

[Anthony]

I already did a valve adjustment, and I made sure it was properly bench sync'd before I installed them. I ran a piece of steel wire between all the butterfly valves, and they were all properly adjusted from that test. I also have been using the Morgan CarbTune, and I only started syncing the carbs with that adjusted. It was showing little to no vacuum in the readings, so I thought that this was because of them being out of sync, but that made no sense since I already did a bench sync. The pilot screws are all at 3 turns out from lightly seated. I don't know what's going on, but the sync is probably worse of now since I tried adjusting them to be able to see any readings on the carbtune.

[eil]

Huh. Well, it sounds like you're doing everything right but something is being overlooked. Unless you have very leaky intake boots, I'm out of ideas, myself. I would say don't give up, keep tinkering, remember the process of elimination.

I don't know who's near you but maybe if you put out a call for help, someone could stop by.

[Dodik]

at this point if you started a bench synced bike that idled at more than 2k rpms there should have been plenty of vacuum.
try this.
bench sync them again.
mixture screws 3 turns out
start the bike. let it warm up, kill the choke.
adjust the idle with the knob/screw on the bottom only do not mess with mixture screws yet. get it as close as possible to 1k rpms or to the lowest setting where bike can run on its own. if it is 2k rpms than let it be.

now stop the engine and connect carb tune.
start the bike
get your idle upto 1500-2000 rpms if it is not there yet. now to get it there use throttle cable adjuster by the grip.
if you still have no reading than you have problem with vacuum (hose not plugged, ripped, bad boots etc) or you may have an issue with cabtune tool itself.
if you do have a reading proceed to sync the carbs. only after the carbs are synced you can start messing with mixture screws

[Anthony]

I will try this. And what should I do about adjusting the throttle cable linkage that attaches were the choke cable goes through on the carbs? There is a nut on both sides of the metal piece, and I think we adjusted it almost close to the top of the threaded tube. Maybe it's something to do with that? How do I go about adjusting the throttle cable properly on the carbs and by the grip?

[Dodik]

throttle cable be treated as a solid link in a way, basically when released it should close all butterfly valves, but as soon as you twist it should start opening them, at this point i would release all the tension you have on it

[mmattockx]

How do I go about adjusting the throttle cable properly on the carbs and by the grip?

I would set the adjuster by the grip to around midway in its travel, then adjust the carb end to have a very slight amount of slack in the cable with the throttle closed. You usually can't set it up tight with no slack because the revs will rise and fall when you move the bars from lock to lock as the cable goes slack and tight from the movement. I like to have the minimum amount of slack that allows full steering lock without the revs changing. Some people seem to like more slack than that but I find having extra slack just makes throttle control less precise for downshifts and the like.


Mark

[Anthony]

So maybe my issue is too much slack right now? I still have to bench sync it, but I might as well get the throttle correct while it's attached. What sucks about all this is that I can't do any testing because it won't stay alive. I can't test for vacuum leaks because I can't get it to be steady, and I can't test for compression because it won't stay on long enough. I haven't done a compression test at all, so I'm not sure what it's sitting at, but I don't think that's the issue. Both me and my dad are stumped at this issue.

[mrbill5491]

You don't do a compression test on a running engine. You just use the starter to spin the engine a few times. The problem here is you'll have to do a cold test since you can't run the engine long enough to warm it up is that right?

[eil]

, and I can't test for compression because it won't stay on long enough. I haven't done a compression test at all, so I'm not sure what it's sitting at,

The compression test is done without starting the bike. Disconnect the coils from the ignitor, remove spark plugs, shut off the gas. Connect compression tester to one cylinder. Remove carbs or hold throttle wide open. Run the electric starter for a few seconds. Record reading, move on to the next cylinder.

[Anthony]

Would running a compression test help in diagnosing this issue? I'm thinking that a proper bench sync may help. But I want to do things correctly, and really want to get all this sorted out. If I can properly bench sync and vacuum sync, and adjust the pilot screws to were it runs good, I would be done. I feel so close, but I'm not at the same time. I'm pretty sure I've already eliminated the issues with the carb internals, I just can't get it to idle/run correctly. Would low compression result in no/little vacuum on the CarbTune tool? The only thing I've changed related to the engine were the spark plugs, oil and oil filter, and breather cover gasket. Everything else engine related I haven't touched. Maybe I have bad plugs? I just am not sure how to start narrowing down things.

[eil]

Would running a compression test help in diagnosing this issue?

Maybe. It's worth a try if you already have the tool. Remember an engine will run if (and only if) all three of these things exist:

- compression
- spark
- correct fuel/air ratio

The process of elimination is methodically checking off every possible thing that can go wrong (starting with the most likely, most obvious, and easiest to check) until you find the thing that's keeping it from running right. Make no assumptions along the way. Test, measure, verify.

I'm thinking that a proper bench sync may help.

I would do that if for no other reason than to get the sync back to a known baseline.

Would low compression result in no/little vacuum on the CarbTune tool?

It could. The biggest tell-tale sign of low compression is hard starting. I honestly don't know if lwo compression would cause the engine to run but not idle.

I just am not sure how to start narrowing down things.

Easy: one at a time. You already have a list of things that you know are right, you have a list of things that you haven't checked, and you have a list of things that you're not sure about. Work through the last two lists and you'll get there.

[Anthony]

Thanks Eil for the responses, they are very helpful. I don't have a compression tool, so I think I may start with a bench sync and trying to run it with no vacuum gauge first. Just a fresh baseline engine warm up. If it doesn't stay on or idle correctly, I can check for compression then and also spark in all 4 plugs. I can also try and mess with the pilot screws to see if the fuel mixture is the main issue I'm having.

[Anthony]

Okay, so I did a proper bench sync, re-installed everything, and it holds a steady idle whatever I set it to. Except it really doesn't like to idle under 2k, it just ends up dying. Also, I hooked up the CarbTune and once again, I saw little/no vacuum readings when the idle is any less than 3k. I can't do a carb sync when the idle is that high. All my boots are either new, or pliable. I checked for air/vacuum leaks using carb cleaner, and the RPM's never raised when I tried it on both sides of the carbs. With that said, what is the issue? Is it too rich? I'm getting some major hanging idle as well. The throttle has a little slack and is not snagged or hung up anywhere. I haven't lubed it. Any pointers on where to go next?