Two-faced symptoms

[MisterCinders]

So I pulled and rebuilt my carbs again, as I wanted to make some jetting adjustments anyway. She was running pretty well, but plugs showed rich and it felt a little weak at higher throttle. Not lean-flat or stumbling, just seems to plateau at higher speeds (60-65 mph, 5th gear, 5500 RPM). It's hard to really tell though, as I am still a noobish rider and have very few places to open her up in the city. Could be that I am just a bit chicken to crank up to 6000+ RPM and higher speeds.

I did the carbs last season, but there was some rust in the tank that sludged them up, so off they went.

Dipped them for 24h, like a boss , sprayed, poked through all the tiny bits, etc.

While they soaked, I went ahead an double checked my valves, all gaps were nice and sexy, right on the money.

I also pulled the exhaust to clean it and the engine a bit and to change the oil. One of my filter cover studs is a bit stripped, so I wanted to replace it. That bastard will not move. I'll probably revisit that again with another oil change, once I get a torch for heat to loosen that stud.

Anyway, I reassembled the carbs with the following settings:

Pilot jet = 15 (had a 17.5 awhile back but it ran too rich).
Fuel screw = about 7/8 out
Air = started 2 turns out, did my best to get highest idle. I still struggle to catch those RPM changes though.
Needle = 4th slot down.
Main = 120 (had 125s, so I wanted to bring that down a touch. Stock mains are 102 or 105 IIRC)

My carb boots are good and the intake rings are new from last year. Yes, I have pods and 4-1. Don't hate.

Last night I synched the carbs (bench and carbtune), but they were pretty finnicky. More so than in the past.

This morning, she starts and warms up OK, but once I took it around the block, the engine refuses to drop RPMs. Could be a really bad hanging idle or a sticky throttle cable. I spray checked for air leaks and came up with nothing. As hard as that idle was hanging, even a ghetto spray test should reveal such a large leak. Yes, I replaced the synch screws.

So I am launching this thread to get ideas and track my work.

For starters, here is a weird result. All the operating symptoms shout lean mix and/or air leak. I will pull the carbs again today to root that out. I'll also clean and oil those pods, in case they are too dry. When I checked the plugs after tooling around the block, however, they were black and sooty, showing richness. What the hell?

So here is the battle plan for today:

-- Pull carbs and double check passages and jets. If this starting plan fails, I'll dip them again, but I was hoping to ride this weekend.

-- Pull pods and clean and re-oil them.

-- Lube and hunt down binds in the throttle cables. The throttle snaps back while the engine is off. I cannot tell if the RPMs staying high means the throttle is not closing when the engine is running or if there is just a bad air leak somewhere. The cables are new as of last Fall and resized for my lower bars. They worked fine before, but I'll see if they are binding somehow.

Any other ideas for this lean behavior and rich plugs?

Also, during the synch process, I noticed that my slides give very little room for adjustment. At the bench, it takes a lot more turning of the idle screw to get the slides to the thin drill bit gap (like 1/16"). Individually, however, the slides have almost no room in the screws to go up. Net result is I have less idle screw range and almost no adjustment range per slide.

What can I do to "reset" this so backing out the idle screw will leave me enough room to adjust the slides individually?

As I said before, I have a really hard time hearing, spotting idle changes when adjusting the air screw per the usual process with the idle at 900 RPM or so. A buddy mentioned doing the highest idle setting at higher RPM (like 2,500) to dial in the mixture at the higher end of the pilot circuit.

Has anyone tried this highest idle at 2,500 RPM method?


TIA

 

[BassCliff]

Hi,

OK, I'll start us off.

What pod filters are you using? Many have reported difficulty using the EMGO units.

Are you performing all carb sync and other adjustments after the bike is fully warmed up? (Except for bench sync, of course.)

I don't have VM carbs but I tend to start all of my adjustments with the main idle know as far out (lowest idle settings) as the bike will run, then adjust as necessary as I adjust everything else (highest idle method, etc).

I would think doing a "highest idle method" at 2500 rpm would be practically impossible.


Thank you for your indulgence,

BassCliff

 

[MisterCinders]

Basscliff, you wound me. My pods are K&N as noted in my pro signature block.

Help me with the "practically impossible" at 2,500 RPM? It that because the changes in idle would be even harder to detect?

The low idle knob setting is what I have been doing so far. I just never can detect any idle changes other than at the very extreme ranges (e.g., air screw bottomed out or almost totally backed out at 6-8 turns).

 

[MisterCinders]

Had to do a couple of trial and error runs on this carb re-build. I had the floats set at 25mm instead of 22mm because I misread the chart on the BCliff site.

Still was a bit dicey synching them. Something is out of step between the individual adjustment range and the idle screw range. One of the slides (#2 IIRC) will barely open with the idle screw all the way out. So to bench synch them, I did this:

Back out the idle screw until the #2 slide closed.

Back out the #2 slide all the way.

Back out the idle screw more until it disengaged.

Then adjust the other three until they just close.

Dial in the idle screw to get a decent gap to do the drill bit feeler measure on #2.

Adjust the other three slide to match the gap. Visually this looked ok as a bench synch.

This made vacuum synching a little trickier, because I had almost no room to adjust the #2 slide other than to close it. So I had to fiddle with the other 3 to coax all 4 into step.

It took awhile, but ultimately they leveled out at 2,500 RPM and 1,500 RPM. I think they could be a little more tightly in synch, but it would probably take another tear down to figure out the slide disjoint.

On that issue, what else might affect the initial slide line up to put one so far out of step? All I can think of is a bad spring in the slide assembly -- i.e., the #2 spring is too strong or weak, relative to the other three. I had this problem before, so I made sure to compare the slide components to make sure none of the screws differed in size from the others. They all match.

 

[Steve]

Keep in mind that there are actually THREE adjustments possible on those slides.

The master idle speed knob is an obvious one. The sync screw on each slide is another. There is also a screw that needs to be adjusted for maximum opening. I do not think this has anything to do with your current problem, but feel it should be mentioned, anyway.

Back to your idle problem: Check your sync screws. If they are all set so the slides are at their lowest position (giving highest vacuum readings), the master idle has to be taken up to compensate, possibly not leaving much adjustment room. Try adjusting your sync screws (while the engine is off) to raise the slides. Then, set your master idle to about its lowest position and continue with a bench sync.

By the way, your stock pilots were 15 and your mains were 100.

.

 

[MisterCinders]

Keep in mind that there are actually THREE adjustments possible on those slides.

By the way, your stock pilots were 15 and your mains were 100.

.

I may try to add some room for the master idle at the upper end. Thanks for the tip. The process you describe is essentially what I did at the bench. It just seems odd to me that one slide would be so much lower than the others, such that with the main idle screw out, the one slide will not open more than a hair while the others have far more room to adjust up.

You are correct on the jet sizes. I had increased the pilots to 17.5 to account for pods/pipes, but then went back to 15s when I kept coming up rich. In this last carb build, I swapped the mains for 122.5s.

 

[BassCliff]

Hi Mr. MisterCinders,

Basscliff, you wound me. My pods are K&N as noted in my pro signature block.

Please accept my deepest apologies. I glossed right over your sig file without noticing your upgrades.

Yes, at higher rpms the differences using the "highest idle method" would be harder (for me) to detect. But perhaps you can use Mr. Steve's "reverse" highest idle method. As I understand the idle circuit on VM carbs, the air screw is set approx. twice as many turns out as the fuel screw. Turn the fuel screw in until you hear the idle start to decrease, then back it out a snotch.

Thank you for your indulgence,

BassCliff

 

[MisterCinders]

Hi Mr. MisterCinders,



Please accept my deepest apologies. I glossed right over your sig file without noticing your upgrades.

Yes, at higher rpms the differences using the "highest idle method" would be harder (for me) to detect. But perhaps you can use Mr. Steve's "reverse" highest idle method. As I understand the idle circuit on VM carbs, the air screw is set approx. twice as many turns out as the fuel screw. Turn the fuel screw in until you hear the idle start to decrease, then back it out a snotch.

Thank you for your indulgence,

BassCliff

No problem BCliff, just giving you a hard time. :twistedevil:

I have the fuel screws at one turn out and did my best to highest idle the air screws, starting at 2 turns out. She idles nice and smooth, but plugs will tell for sure. Before this strip and dip, the bike idled and performed well AFAIK. I just kept getting sooty plugs. Between my newbish riding (i.e., I am not the best judge of "running well") and the black plugs, I figured something was out of step. So tearing them down again made sense.

Unless there is a special tool, adjusting for highest idle using the fuel screws seems like a path to madness.

Those are pretty finicky, will break if you go in too far, and are underneath the carbs. Reaching under there with a stubby screwdriver, a prison shank, or whatever, into a tight space, right next to a hot running engine block is not on my to do list. :-\\\

I wonder how Mr. Steve does this exactly? Maybe his method is only for CV carbs. v0v

 

[BassCliff]

Hi,

Ok, see? I told you I'm not that familiar with VM carbs. I forgot the fuel screws are underneath and the air screws are on the sides. Yes, the air screws are much easier to adjust.

I was hoping you could apply Steve's "reverse" highest idle method to the VM carbs. In a nutshell, on the CV carbs you start with the idle mixture screw out too far (3+ turns) and turn it in until you hear the idle decrease. Then back it out 1/8 turn. But I'm not really sure if this same procedure would work with the idle air screw on a VM carb.

So I think I'll shut up now and let someone with more VM carb experience say something much more intelligent.


Thank you for your indulgence,

BassCliff

 

[MisterCinders]

Hi,

Ok, see? I told you I'm not that familiar with VM carbs. I forgot the fuel screws are underneath and the air screws are on the sides. Yes, the air screws are much easier to adjust.

I was hoping you could apply Steve's "reverse" highest idle method to the VM carbs. In a nutshell, on the CV carbs you start with the idle mixture screw out too far (3+ turns) and turn it in until you hear the idle decrease. Then back it out 1/8 turn. But I'm not really sure if this same procedure would work with the idle air screw on a VM carb.

So I think I'll shut up now and let someone with more VM carb experience say something much more intelligent.


Thank you for your indulgence,

BassCliff

It's all good, my man.

I actually tried something like that at the air screw. Basically turned them in until the idle struggled and then backing out until it the struggle ended. That put the air screws totally closed though. Given that I had started with a pilot circuit showing rich plugs, that cannot be the answer.

To recap, with fuel screws out about 1 turn, if I warm up the engine and set the idle at about 900-1000, I hear no idle change with the air screw starting at 2 turns out through almost 5 turns out. I also don't hear any change going in with the air screws until they almost bottom out when the cylinder will sputter and bog (for lack of air).

I'll keep at it, but basically I end up resetting them to 2 turns, stabbing in the dark for idle shifts. Tooling around on the bike for chop, finding rich plugs.

I had similar, if not identical results, with the fuel screws out only 5/8 turn and at 3/4 turn. Having freshened my pods, I started the fuel screws back at the standard 1 turn.

 

[BigD_83]

If you are not hearing ANY change, doesn't that imply an issue with the screw itself?

 

[MisterCinders]

If you are not hearing ANY change, doesn't that imply an issue with the screw itself?

Perhaps, but I have totally cleaned the passages and the screws themselves look fine, have fresh o-rings, etc.

To me the idle thing suggests an air leak or lean condition. In other words, the idle ignores the air screw changes because it's gulping air from another source.

But that doesn't compute when I have no real lean symptoms (hanging idles, etc.), and the plugs come up black and sooty.

I suppose it could be the reverse, where the mix is so rich that the air screw cannot make a dent in it. But I would expect the engine to idle pretty badly in that case, and it doesn't. I'd also expect turning the air screw to kill a rich idle much further out than it does (i.e., at 1 turn out instead of than almost closed).

Basically, I am stumped.

Edit: BTW the hanging idle I ran into in the OP was a bad float setting. She drops RPMs nice and sharp now. But she dropped RPMs well before and still sooted up plugs.

 

[stanger38]

I have a 1977 gs 750 and I am having a problem with the idle hanging. What did you set your float height to? Also 1 of my carb slides has a very limited adjustment. Did you find out if it should be like that and what carb should it be in? Mine is the #4 carb.

 

[MisterCinders]

I have a 1977 gs 750 and I am having a problem with the idle hanging. What did you set your float height to? Also 1 of my carb slides has a very limited adjustment. Did you find out if it should be like that and what carb should it be in? Mine is the #4 carb.

I set the floats between 22mm and 23mm from the gasket surface (without the gasket).

If your idle is hanging, check for air leaks (intake o-rings, air pilot screw settings, tight airbox seals, well-oiled but not heavy air filter, etc.).

Never did sort out the adjustment puzzle, but I was able to bench synch them against the lowest one (mine was No. 2). The bench synch was pretty tight, so the vacuum synch worked out as well. Only had to slightly move one of the outside carbs.

Of course, I still need to do some plug chops to see how the new jetting works out. She idles pretty swell though.

Another hiccup emerges. I seem to have some very slow leaks at the bowl drains. Drops of fuel keep forming at the drain screws. THe screws are fresh and have brand new o-rings. I snugged them in pretty tight, but no gorilla torque, etc.

Any ideas on what else I can do to seal that off?

 

[Big T]

Did you put the new O rings on the drain screws?

 

[MisterCinders]

Yes. Fresh O-rings in there. They dripped like this before, even though the prior o-rings were pretty fresh. Since some other jet o-rings had gotten mangled, I went ahead an grabbed another set from Bwringer and freshened up all the rubber in there.

 

[BigD_83]

Are you sure it is a drip from the drain screws and not gasket leaks working their way down? Is it from ALL drain screws?

 

[MisterCinders]

I'll check. Think it's only some of the drains. I don't see fuel on the bowls.

 

[MisterCinders]

Whiskey
Tango
Foxtrot

This float situation just gets worse and worse.

I pulled the carbs several times this weekend to try and get the float settings right. No matter what I do, the carbs now flood with gas.

Definitely need to change the oil and filter now, as gas may have entered the crank case. Won't start the bike again until I do that.

Meanwhile, I am trying to get the floats sorted, as I cannot change the oil/filter every damn time I test start the bike. After several adjustments, each time I run fuel into the carbs (not running the engine), they spew fuel out of the drain hoses and pods.

The float needles/seats are clean and clear. No gunk, no scoring, etc. I have spares and have tried swapping some out, but the results don't change.

I have tried setting the float heights at different levels. Recall that I had set them too high by caliper (so too low when running) at about 27mm and got lean idling. Then I dropped/raised them to 22-23mm and she idled much better. Now, however, she floods gas.

Specifically, with the carbs installed, vacuum line plugged and remote tank with long fuel line and petcock on PRIME, the bowls fill and within seconds, they overflow into the drain lines and pods. It literally vomits fuel everywhere.

I have changed the float levels to increase them by caliper (so reducing the actual float level) with no changes. They are at about 26mm now. Without even running the engine (because of the oil/gas problem), the bowls fill and start flooding within < 30 seconds on Prime.

BTW - I did check the petcock. It doesn't flow in the ON position unless vacuum is applied. Plus, these results happen with vacuum plugged and petcock on PRIME, so I don't think it is a petcock issue.

I understand that a bad needle and seat will fail to close and allow flooding, but why would most, if not all, of my needles fail at once?

No fuel is coming through the vacuum line (it's not even connected for this). Is there any other potential fuel source/passage that could be overcoming the float system? Maybe the choke circuit is not closing? The seat o-rings are in place and seem to be solid.

My floats/needles are OEM and don't show and crud or ridges. The spares I have for swapping are The springs feel OK, at least not stuck. Is there any particular amount of spring resistance to look for? What else should I check in that inspection?

A few of my spares are those shiny but crappy replacement parts from some rebuild kits. I actually tried a couple of those, only because my OEM spares were jumbled up in the box, so I could not precisely match a needle to its original seat. The kit sets were still in their bags as matched pairs. Yes, those parts are crappy as compared to OEM, but would every one of them fail straight out of the box? Is there any method to matching up seats and needles from the jumble of spares?

I really don't want to drop $125 on four new OEM float needle sets. Any tips on how to test the ones I have to isolate the overflow problem. In other words, how might I check that the float needle valve cuts off fuel flow when closed, which would indicate that something else is causing the flooding?

If the valve is actually closing and there is no other source of fuel into the bowls, the only other culprit I can think of would be the floats. But the floats themselves also look solid. No mangled rubber, and they move easily on the pins. I can drop them into a small bowl of fuel to make sure they actually float, but otherwise I am stumped. Maybe they are catching on some part of the bowl when I close them up? Knocking the bowls with a screw driver does not stop the overflow.

Finally, the caliper measures the float as it rests on the needle. Is there any alternative measurement to account for spring pressure (e.g., measuring the height with spring compressed)? Provided the springs are functioning and not sticking, would that measurement even matter?

 

[MisterCinders]

OK - float height setting recommendations are all over the place, for the same measurement?!?

The specs for the caliper method of setting the float -- i.e., carb upside down, distance from the gasket mating surface (no gasket) to the top of the float bob as it just touches the needle.

Service Manual says 25mm - 27mm

Carb Spec Sheet on BassCliff's site says 23mm +/- 1.0mm (22mm - 24mm)

Clymers says 23mm - 25mm

Mikuni Tuning Guide says 15mm - 17mm

What the hell?