My 1982 GS750E Project

[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

 

[Guest]

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.

 

[Guest]

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?

 

[Anthony]

When I adjust the idle to about 1100-1200 there is huge popping going on coming from the exhaust. Not sure what that means, but I do have a video of it.

 

[Anthony]

Also, cylinder 4 spark plug is very black and carbon fouled. The other three looked fine. Does this help at all?

 

[Anthony]

So with further research, I got my dad to call his mechanic buddy, and he seems to think that my problem may be a valve adjustment issue. We may have improperly set the clearance, as my dad was use to working on car valves which are much different. He also said to try and switch the coil around at 4 and see if that foul plug follows the same coil. Also I need to get a compression gauge and check the compression to make sure that's not the issue, following the valve adjustment. Is this something I can go off of? I just feel like I'm chasing my tail here, and I just want to get this sorted out. Thanks to all that helped so far, I definitely need it.

 

[eil]

If you're not sure about the valve adjustment, then definitely do it again. Make sure to follow the procedure in the service manual precisely. This feeler works perfectly on this engine: http://www.z1enterprises.com/ItemDe...er+Gauges+.004+.005+inch+(1)&item=MP08-0053-1 I use the 0.005 inch blade to set the clearance to 0.127 mm (manual says you want between 0.09mm and 0.13mm).

Is it hard to start? That is the biggest tell-tale sign of low compression.

I used a cheap $20 Harbor Freight compression tester on my 850 and it worked fine. Don't recall off-hand if it comes with an adapter for the 750-sized spark plugs. (It probably does, but don't quote me on it.)

I haven't seen you make any mention of your usage of the choke knob. Do you use choke when starting? Do you have it on when running?

If you think it's idling too lean, there's an easy check for that: with the engine warm, pull the choke knob enough to bring up the idle a bit and then see if you can drop the idle down to something reasonable like 1k RPM by backing out the idle adjust knob. If you can, then it was too lean. If that makes it even worse, then it was too rich.

Also, don't be running the bike for too long without having a couple of big box fans pointed at it, especially at high RPMs. Otherwise, you can overheat things pretty easily.

One of the members on this site (Nessism, I think) has a quote: To measure is to know.

 

[Dodik]

when you said you didnt have enough vacuum my first thought was valve adjustment, check them at least, at this point you have nothing to loose.

 

[Anthony]

My dad did a valve adjustment for me as I've been sick, and he said cylinder 4 exhaust and intake were off, and cylinder 1 exhaust was off. The others were fine. So this may have been part of the issue. Also I made sure not to run it for too long, even with fans. And actually, it has been hard to start. Looks like I need to get a compression gauge and check that once I get it put back together. And no I haven't been using the choke, because it wouldn't start or had an even harder time doing so if I did. How would I fix low compression if that's the case?

 

[Anthony]

Okay so an update, after the valve adjustment i was bolting it up and stripped a thread hole. I repaired it with a heli-coil kit and it's good to go now. So I started it, and now the backfiring and popping is completely gone, but the hanging idle is still severe. What should I do about this huge hanging idle issue?

 

[Dodik]

Did you try to sync them or is there still no vacuum? maybe after your bench sync the butterfly valves are open more than they should be?

 

[Anthony]

Well I bench synced them previously, but they have been slightly changed since the valve adjustment. I don't think it's bad enough to affect the carbtune so drastically as it did before. I haven't tried hooking it up again yet because the idle is just so badly hanging that it will make it difficult to rule out anything.

 

[steve murdoch]

Your check showed no air leaks and the cables are free and clear. Maybe the throttle sleeve itself?
When you say hanging idle do you mean it takes a couple seconds for the revs to drop down to the idle when you blip the throttle?