My 1982 GS750E Project

[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/ItemDet...em=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?

[Anthony]

When I say hanging idle, when I blip the throttle, it stays high around 3-4k for 5-30 seconds. It's the weirdest thing... I do have the PVC pipe throttle mod that makes the throttle 20% less to WOT. Would that be causing an issue? I adjusted the slack properly by the carbs.

[Dodik]

hanging idle is a symptom of lean condition,

i am sure you read this by now but just in case its a good starting point,

http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html

[Anthony]

So I put the pilot screws at 3 turns out, and it has hanging idle bad there. I also tried to hear the upper RPM's and it won't budge above 6k RPM's. Would a lean condition cause that issue too? This is hurting my head :/

[Dodik]

yes if it wont rev to redline your main jet is too small, which positions is the clip on the the needles, and I am guessing you are on DJ124 mains right now? When you are doing all of this is the entire airbox assembled and connected to the filter? Do you have the endcap on the pipe or is it open.

[Anthony]

The needle clips are at the third position I believe, and yes I have the DJ124's installed for the main jets. The airbox is fully assembled and has no intake leaks that I could find from testing. I have a supertrapp exhaust, so the end is capped off but has the fins on the outside to let the exhaust escape in a 360 degree manner. The manual for the DJ kit said to install the 124s if you only have an after market exhaust and stock airbox setup like I do. Is that not the correct thing to do? Or maybe the needle position is off?