1 more issue: Hanging Idle.

[DannyMotor]

Cables are properly routed and lubed, throttle snaps back to closed no issues.

After the bike warms up... meaning, after about 5 miles of riding after choke has been taken off... the RPM's will want to hang out around 4000rpm (the same trouble spot I was having when the bike BOGGED at 4000rpm).

If I pull the clutch... it'll just chill out there. Not moving, then slowly come back down. The throttle is fully closed at this point too... I can blip it and nothing changes until the rpm's just fall on their own.

I even get the little revving between shifts, which is fun.

Now... could this be due to not having ANY oil on the filter? It won't hang up under 3000rpm, only after that (needle circuit) and My boots are in great shape, nice and soft, no cracks or issues, O-rings are brand new, even new gasket washes on the intake port balance holes.

The head gasket is weeping a bit... could it be an issue there? If oil can get out, air can get in, no?

I always thought too much fuel caused high idle (having the choke ON for instance).

If I leave it alone... it idles great at 1100rpm, no issues.

It does need an official balance, fuel screw chops, and 'high-idle' adjustment of the air screws...

I just though since the only change from NOT revving over 4000, to Hanging Idle at 4000, has been completely de-oiling, drying, and re-installing the KnN drop in.

 

[Toasty]

There's an air leak somewhere, probably the carb boots or intake orings.

 

[DannyMotor]

You mean the 2 things that I mentioned were either brand new or fine?

 

[Killer2600]

Hanging idle is a tale-tell lean condition symptom, too much air or not enough fuel.

Foam filters are supposed to be lightly oiled, they work better that way.

Regarding your head gasket weep: if oil can get out, it is possible compression is leaking out too - a compression test may be in order to rule out running troubles from low compression.

 

[DannyMotor]

I thought only, say, tight exhaust valves could cause hanging idle... if 100% everything else was brand-new in-spec and tuned to perfection.

Or are you just saying that it could be a cause for concern down the road?

OH, and it's a cotton/fabric KnN filter... I'm going to try a light coat and see what that does. If it continues.. it's back to the bat-cave and $150 for new boots and clamps.

 

[JimmyR]

FWIW I found tuning my RS36 carbs a LOT easier after I remembered to oil the K+N pods. Dunno if that helps but it was important to me.

 

[DannyMotor]

I just 'lightly' oiled the filter... like, quick little squirts over the whole thing... it's a VERY light pink... not "RED" like it was before... I swear, I used almost 1/8th of the can the first time... this time, no where close.

I'll take it out in the morning and see how she does.

I have a feeling if my boots aren't bad... my hose-clamps may be crap. Two of them kinda bottom out before feeling super tight. I'll get at it tomorrow with some starter fluid and see what it does.

 

[Don-lo]

The bores in the VMs can be very sensitive to a little corrosion in them. I just had a set do this to me (after a full dip). It had pods on it, so it was easy to pull those and watch the slides while I revved it. I could see #3 hanging up, even though it would return great when I put them together. I pulled the slides and found that fine white corrosion in the bores. I used a maroon scuff pad on the bore and the slide, and reassembled. That took care of it.

 

[koolaid_kid]

Those are classic symptoms of an intake air leak. I once rode a 78 850 with the same issue. Once the intake leaks were fixed, it was fine. I would strongly suspect those hose clamps since they bottom out before being fully tight.

 

[Nessism]

Where are the pilot screws set? Both air and fuel?

 

[MisterCinders]

You are lean in the pilot. Either you have an air-leak, or your pilot jetting needs adjustment.

With no oil in the filter you are probably getting too much air, causing the idle to hang.

If re-oiling the filter doesn't work, take the bike out for a bit to warm it up. Then pull over and see if that idle continues to hang at higher rpms. If so, try blocking the airbox with your hand to see if that causes the idle to fall back into place. You can also see if the carb rack/airbox has any play in it (e.g., wiggles up and down at all). If it does, see if tapping or jiggling the rack affects the idle hang.

If blocking the airbox causes the RPM to falll back, you have too much air through the box. Oiling the filter will help, but don't go overboard. Once properly oiled, you may need to reset the air/fuel pilots to lose some of that lean at idle.

If the jiggle affects the RPMs, then you have an air leak in the boots (intake or box). Since you just put in new boots, they are probably not the issue, but you might double check that none of the o-rings slipped out of place. If that's all tight, then your airbox/boots may be at issue.

If your air system is tight but the idle hangs, there are two more things to check.

First, what are your pilot screw settings? Fuel screw should be about 3/4 to 1 turn out, and air screw double that then highest idle.

Second, where is your float level set? If your floats are too high (making the fuel level too low, it will lean out your mixture, especially at idle where the vacuum pull is low. The float specs for the 78 gs750 are all over the f**king place, between Clymer, the Service Manual and Mikuni's guide. I'd try to set them between 23mm and 24.5mm, but double check the float levels with the drain tube tool if you have it. You should also run some fuel through the line into the rack while it's off the bike, to make sure nothing is overflowing, needles aren't sticking, etc. That way, if there is an overflow during the test, it doesn't seep into the engine or airbox.

I wouldn't use starter fluid for anything.

 

[81gs1100]

SO, what changes did you make recently? Did you buy the bike with this issue? Did you change something ( air filters, exhaust). Bike been sitting over a long period of time?

Sounds to be running lean, start the bike, let it warm up to where the idle hangs, and check to see if you can pull the choke and make the idle fall, if so, it is lean. But we need to know what caused this to start.

 

[duaneage]

FWIW try cleaning the slides and bores with carb cleaner spray and make sure they move easily

 

[DannyMotor]

New development:

Started it today and it would hang off idle now... so in the pilot circuit. So the leak got bad wherever it was.

Took the carbs off... checked the boots, orings... two of the boot bolts were loose. So i re torqued them... bent the clamps so they hold tighter... reassembled... ran fine.

Took it for a ride, and all was great. Horsed on it a bit... up to 90, up to 9k rpm... really worked it out. About 5 mins later, I came to a stop and the idle was around 3k... so I turned the screw down... 1100 idle... blipped it... no hang... alls well.

Drove it easy for a mile or so... then came to a stop. CRANKED it off the start up to 9k... shift... cranked it through second and then pulled the clutch in...Boom... hanging up at 4k.

Drove it home and its back to its old ways... hanging idle above 4k all the time.

So.. I definitely jiggled something loose again. The thing is... I pulled into the garage... let it idle and I went to town with wd-40 around the boots and clamps... no change in idle.

So whatever it is...oits very small. Going to take the carbs off again and see if its the boot bolts loosening up again. If not, then I'm stumped.

 

[DannyMotor]

Oh... and this time through I'm setting my fuel screws to 1 full turn out and air to 2 turns out. they were at .75 and 1.25 respectively.

 

[DannyMotor]

Fixed!! Boot bolts were fine. It was the fuel screws too lean!!! Thanks guys!!

 

[TheCafeKid]

Not to pi$$ in your Wheaties, but how lean were they?? If your clamps are bottoming out before they're tight, you may consider replacing them. Also, check your boots again. Soft and pliable doesn't mean good. If they've cracked and or pulled away from the metal flanges they're moulded around, they'll leak there. I made this mistake once on one of my 1000Gs. They felt nice, but within a few days after getting her on the road a couple had completely pulled away from the flange. Needless to say it sucked major air there, and ran like schit limping it home to replace them. It's at least worth a look-see while you're home, vs having a situation away from...

 

[DannyMotor]

The boots are new... The fuel screws were a 1/4 turn lean.

 

[Nessism]

Did you check the fuel screws to make sure there are no broken off tips in the carb bodies? The bike is running lean for some reason, or has an air leak.

 

[DannyMotor]

Needles are brand new from z1. Nothing broken.