Idle and Synch Puzzle

[MisterCinders]

Hurm, the vacuum ports on my cylinder are jammed in there. Already broke a hex bit trying to remove one.

Will hit them with some penetrating oil and try again later.

Between the bad plug hole, the exhaust leaks and now the vacuum ports, I am beginning to really hate this top end. Guess I will have to pull it apart over the winter and perform an exorcism.

Don't worry, I will be sure to run a "Top End Noob" thread for that odyssey as well. :-)

[MisterCinders]

Status update:

Still cannot discern the idle air screw settings, but have a ColorTune inbound.

Rode around on Sunday in the city with a short hop onto a nearby parkway for some 45-50 mph action.

The bike handles pretty well, but she is not there yet.

The idle circuit is not right, but I struggle to understand which way (rich/lean) she is tilting. Plug checks are hard to read because, although new plugs, they are kind of dirty from previous variations in jetting after I reinstalled the clean carbs.

Question - What is the best way to clean the plugs to get a better reading?

Here are the symptoms now.

Bike starts OK with only a little choke to warm up. Idles at about 1,000 - 1,200.

During warm up, the pods cough and pop a little, as if gasping for air. Perhaps I oiled them too much? I used the K&N spray oil and followed the instructions, but it was hard to gauge the right amount of oil because the directions use a panel filter for an example and refer to "clean side" and "dirty side." This indicated spraying oil on the interior of the pod, which was tricky to control.

Also during warm up, the bike doesn't like any throttle, even running without choke. After a few minutes, this subsides. I suspect the idle circuit is on the rich side. I have fuel screws out 1 turn and air screws out 2-2.25 turns.

Once warmed up, the bike is tad sluggish off the line and occasionally stalls. From the rich/lean tips on the Internets, I cannot tell if this is indicates lean or rich. The exhaust shows no smoke. The exhaust headers are a bit blue, but I am not sure if that is new or old from prior iterations.

Question - What is the best way to clean these pipes to better read them?

With the new pods, I am hesitant to dial in the fuel screws, but the air screws are running out of room to back out. I may turn the fuel screws in about 1/4 turn if I can confirm the richness.

Ultimately, while I get the concept of "rich/lean," reading the mixture from engine performance is a bit lost on me.

I am ready to vacuum synch the carbs, but the vacuum port screws refuse to budge. Already broke a hex bit trying to pull them. The bit came out with a magnet, thank God.

When I have more time to tear her down again, I may have to try an impact driver to get them out. Just to make sure I am not an idiot (I am, of course), those plugs are not reverse threaded, are they?

[Coady]

Status update:

Here are the symptoms now.

Bike starts OK with only a little choke to warm up. Idles at about 1,000 - 1,200.

During warm up, the pods cough and pop a little, as if gasping for air. Perhaps I oiled them too much? I used the K&N spray oil and followed the instructions, but it was hard to gauge the right amount of oil because the directions use a panel filter for an example and refer to "clean side" and "dirty side." This indicated spraying oil on the interior of the pod, which was tricky to control.

Also during warm up, the bike doesn't like any throttle, even running without choke. After a few minutes, this subsides. I suspect the idle circuit is on the rich side. I have fuel screws out 1 turn and air screws out 2-2.25 turns.

Once warmed up, the bike is tad sluggish off the line and occasionally stalls. From the rich/lean tips on the Internets, I cannot tell if this is indicates lean or rich. The exhaust shows no smoke. The exhaust headers are a bit blue, but I am not sure if that is new or old from prior iterations.

I am certainly no expert, but you sound lean to me. I can only go off settings and trial and error on my bike with a 4 in 1 and stock airbox, but with air screws where they are I'd go to 1 1/2 turns on fuel screw - that should help a little with the popping on startup and idle.

However I suspect you have bigger issues with your needle position i.e. you're very lean. I'd search the forums some more, if no-one else chimes in, as there are quite a few posts on 750's with vm carbs and pods and from memory you'd be looking to raise the needle to 4th or 5th position.

And the vacuum port threads are standard - not reverse thread.

[MisterCinders]

When I installed the pods, I adjusted my needle clip to one down (richer) from center - 4th position.

Before I open up the fuel screws, wouldn't I tighten the air screws to reduce a lean condition?

[Coady]

Before I open up the fuel screws, wouldn't I tighten the air screws to reduce a lean condition?

In short yes...

But there is a little more to it than that. I will attempt to give you my understanding, but opinions are a bit divided on this one.

The air screw does affect the air/fuel mixture coming through the pilot fuel hole (at idle if you like), but it also effects the air/fuel mixture through the pilot jet (off idle and small throttle opening). So you're effectively tuning two circuits of the carb and one affects the other, so you're after the optimum balance.

So you can get a good idle (good A/F mixture) by adjusting the air screw in or out to highest idle, but this may not be the best mix for the pilot jet off idle. This is where you may get some rich bogging (hesitates slightly then takes off) or lean slow throttle response.

So you may open up the air screws to eliminate rich bogging off idle, but then your idle will drop or stall, so you have to open the fuel screws to compensate.

To my thinking its best to establish a good pilot jet mixture for off-idle/easy cruising with the air screw and then open or shut the fuel screw to get a good idle. However I’ve read of many people adjusting the pilot circuit with the fuel screw and then doing the highest idle thing – this has never worked for me. I can find/hear highest idle, but this doesn’t make for the best A/F mix for the pilot jet on my bike. As an example, I can get my bike to idle beautifully with fuel screws at ¾ and air screws at 1 ¼ and get perfect colour on my colortune, but the pilot circuit will be rich when just off idle. Whereas I have finally got some grey/tan coloured plugs by opening the air screws to 2 ½ and fuel to 1 ½. This gives me good throttle response and good idle – for my bike and its mods, not yours.

So it’s an imprecise science and a lot of trial and error and/or experience to get the right combination .

That’s why I recommend thoroughly searching the forum for past posts with the same setup as you to get you in the ballpark.

More experienced VM carb tuners might blow my reasoning out of the water but I hope this helps.

[BassCliff]

Hi,

I found this page on some guy's website. Have a look at the VM Carb Tuning link.

Carb Specs:
Float Height/Jetting/Tuning






Thank you for your indulgence,


BassCliff

[MisterCinders]

I have studied that dude's site, but the info there doesn't address re-jetting for pods, etc., and the stock specs show no turns for the fuel pilot screw because of the EPA rules, prohibitions on changing it, etc.

Inferring from the different 77-79 specs, the stock screw settings are

Pilot Fuel Screw - 1.75 (1977) - 2 (1977B) turns out. 78-79 give no setting.

Pilot Air Screw - 1.6 turns out.

Multiple posts here recommend air screws be around 2x the turns of fuel screws.

Right now I have the fuel screws at 1 turn out, and the air screws about 2.25 out. That suggests I am too lean compared to the specs.

With dirty plugs/pipes, I cannot confirm the lean mixture from other symptoms. Moreover, trying to understand the performance symptoms leads to lists like this:

Typical Lean Conditions:

- Poor acceleration; the engine feels flat. [Dunno what this means and have no other bike experience for reference]


- The engine won't respond when the throttle is snapped open, but it picks up speed as the throttle is closed. (A too-large main jet also mimics this symptom.) [Nothing like this]


- The engine runs hot, knocks, pings and overheats. [Had this before and a hanging idle, but I resynched and reset the screws. No more problems with heat, best I can tell.]


- The engine surges or hunts when cruising at part-throttle. [Dunno what this means and have no other bike experience for reference. Not running into surges though.]

- Popping or spitting through the carb occurs when the throttle is opened. Or popping and spitting occurs through the pipe on deceleration with a closed throttle. [No popping in the pipe that I can tell. Some popping in the pod filter. Looks/sounds like a hard "inhale" not a poping out.]


- The engine runs better in warm weather, worse in cool.

- Performance gets worse when the air filter is removed.

Typical Rich Conditions

- Engine acceleration is flat and uneven and loses that "crisp" feel. [Again, the acceleration seems sluggish, but I have little experience with bikes for comparison]


- The engine "eight-strokes" as it loads up and skips combustion cycles. [No idea what this means.]


- The engine's idle is rough or lumpy, and the engine won't return to idle without "blipping" the throttle. [Not sure what this means either. During warm up, the idle is a little lumpy and I sometimes blip the throttle to make sure it stays going.]


- The throttle needs to be open continuously to maintain acceleration.

- Black, sooty plugs, a sooty exhaust pipe and black smoke from the tailpipe that stinks of unburned fuel. [Need to clean the new plugs to get a better reading. They are a bit dark, but not oily.]


- Poor fuel economy.

- The engine works better when cold. Performance falls off as it warms up or the ambient temperature rises. [No real change from warm to cold, other than normal warm-up requirments.]


- Engine performance improves when the air cleaner is removed.

My comments above in red

The symptoms I get are:

• popping from air pods (No. 4) during warm up.
• shaky acceleration off the line and a "dip" (?) in power between idle and >1/8 throttle
• maybe flat acceleration once on the move

But I am not certain of anything. Between vague symptom descriptions, my inexperience with other bikes and/or bikes generally, this is maddening.

Moreover, the symptoms I think I am finding split across the lean/rich spectrum.

I know that plugs are the real indicator, but I need to scrub/clean them to get a better handle on them.

[Coady]

Sounds like you are generally lean.

Have you replaced the main jets yet?

Have you searched the forum for other peoples settings with your mods?

Forget about the stock specs.

[MisterCinders]

I have 110s in the mains, and ordered some 120s and 122.5s to go up further.

Stock mains are 100 - 102.5.

Changed those based on other info on the forums.

[BassCliff]

Hi,

It sounds like you are properly equipping yourself, doing the research, obtaining the parts, etc. I'm sure you'll get it sorted out. Sometimes it takes some educated guesses along with trial and error. Keep us informed.


Thank you for your indulgence,

BassCliff

[KEITH KRAUSE]

You are wasting your time. Get a Dynojet stage three kit that has a needle tapered for your setup. Keep in mind that the Dynojet jets are marked a little higher than a Mikuni jet (DJ 132 jets = Mikuni 130's). Z1 lists this set under your year model, but I would double check that. http://www.z1enterprises.com/detail.aspx?ID=4061

Just for the record, a DJ 138 is approx' the same as a Mikuni 130.

[KEITH KRAUSE]

If you over-oiled the pods you'll know it. Typically, over-oiled pods will allow the bike to start and run "OK" up to approx' 1/4 throttle and then further opening will result in severe bogging. I know the K&N oiling procedure/suggestion is a bit vague and can result in over-oiling. I hold the can approx' 6" away and with each pass I hit 3 pleats. The next pass may have a slight overlap, depending on the color I see. Hitting "each pleat" will result in over-oiling in my opinion. A "pass" is subject to how fast you make it. A pass to me is one second to hit the entire length. Maybe a short second??
Jetting rich or lean? I'll say that assuming your bike is in good tune,...valve clearances, ignition timing, good voltage/spark, clean carbs, etc, then your pilot circuit SHOULD be lean right now. You mention some noise coming from the pods that I take as "spitting". Lean condition for sure. You still have the stock #15 pilot jets and your pilot fuel screws are approx' 1/2 turn richer (based on the factory setting of about 3/4 turns though it does vary some). Side air screws should be set for highest idle but you say you can't hear a difference. Right now you have them adjusted out further than is typical. So I think you're lean at the pilot circuit.
Try setting the side air screws to 1 3/4 turns out. Keep in mind the rpm range they can effect is only a few hundred rpm. On your bike the base idle must be at 1,000 to start. If you try to set at an idle of 1,200 or 1,300 as a base then you'll have problems hearing changes or even be able to effect that higher idle in the first place. But for now, just set them to 1 3/4 and then re-test when ready.
Try 1 1/2 turns at the pilot fuel screws.
REMOVE the two floatbowl vent lines if they're still attached. Pod filters effect the bowl venting and compromise fuel flow under some conditions. Removing the lines eliminates/helps greatly to avoid fuel starvation. In my experience pods and the vent lines stiill attached does not work well. Don't try shortening them either. Remove them.
As for your previously mentioned idle problem, are you positive the throttle cable(s) are adjusted correctly? 2-3 mm is good slack on the pull cable. Lighly zero out the play on return cable. Cable routing/lubing must be correct too.
Be sure the vacuum line to #3 is good and not kinked or cracking anywhere.
When properly bench synched, the VM carbs will allow the idle to be manually turned down to the point of a stall. If yours won't allow that then you've done something wrong.
Test the pilot circuit around town. Keep it under 1/4 throttle position to avoid overlap effect by the cut-away and jet needle. Just putt around (after full warm up) for a few miles on level/uphill road. Pull into your garage and don't let it idle long. Check the plugs. Tell us what you see and any performance issues. Keep in mind the jet needle effects things earlier than some think and any carb sputting could be due to a lean jet needle position too.
Easy to tell if the jet needle is contributing to spitting by cruising steadily in top gear at approx' 50 to 60 mph. You're mostly on the jet needle at that point. Weather/temp can have varying effects too on jetting that's not correct.
Typically, 1 position richer on stock jet needles isn't enough for your pipe and pods. 1 1/2 positions or even two positions is much more likely to be needed (if you can get the stock needles to give good results at all). Was your stock needle settings at position 3, the middle??
I think the 120's aren't enough either. Many owners here have had good results with 125's and 127.5.
I see no obvious reason why you can't check the pilot, jet needle and main jet mixing. As long as the plugs aren't oil fouled or carbon stained then just shoot them with a little spray cleaner and wipe off with a rag. Test the pilot circuit at mimimal throttle as I described. Test the needles at solid 1/2 throttle and chop off/check. Test the mains at full throttle and chop off/check. Tell us what you see.

[MisterCinders]

Thanks, guys.

The jet needles were set at the No. 2 position. I moved the clips down (needles up) by two notches.

My vacuum line is good, no kinks.

I will ditch the vent tubes.

I sorted out the idle screw problem with a better bench synch and now have a much better range on the idle screw.

The pods seem to be over oiled. I bought the full K&N cleaner/oil kit, so I may clean and re-oil the pods to tighten that up.

Valves are good, as I just did those adjustments when I rebuilt the carbs.

Last night I soaked the plugs in a little petrol and brushed/wiped them clean. After I fine tune the things list above (pod oil, etc.), I will reset the screws, up the main jets and try some plug chops.

Thanks again for the coaching and advice.

[KEITH KRAUSE]

Oh. Just remembered something else you said.
There's no need to oil the K&N pods from the inside. (I believe that's what you said you did.) If you oiled from both the outside and inside then I would think you over-oiled for sure. Just clean them and oil as I suggested.
Another thing. When you clean the pods try to keep cleaning solution from excessively entering the inside of the pod. The K&N pods are designed as a one-way filter. Washing them by dunking or like they're a coffeee cup will compromise their flow over time. Just pour about 1/4" deep cleaning solution in a pan and ROLL the pods back and forth until clean. You can then gently (low hose pressure) rinse from the inside-out. Shake off excess water and let air dry only, no blasts of air. Since you have the cleaning kit the instructions should be there.
As for your jet needle adjustments, two positions richer should at least have you in the ballpark. That assumes that position two from the top as you said is actually the factory position?
And if you're not too sure about removing the floatbowl vent lines then keep in mind that Dynojet even tells you to remove them in their stage 3 jet kit info. In my experience it's necessary to do. And I've never had any issue with dirt entering the ports and causing trouble.

[KEITH KRAUSE]

Clean and re-oil the pods, clean the plugs, and follow my screw setting suggestions for the pilot circuit. Test and let us know what the plugs say. Remember that the pilot fuel screws (underneath) can be backed out to approx' 3 turns before they are no longer effective. If you still feel the pilot circuit is lean and the less than 1/4 throttle position plug reads indicate the same then it will be necessary to use 17.5 pilot jets and turn the screws back in to something close to factory (3/4 turn) to start.
Re-reading your post #17 it does indicate you're lean. But with the pods oiled properly will be a better test. Let us know what your tests show. Be careful testing the jet needle and mains as this obviously requires some high speed testing.