Idle and Synch Puzzle

[MisterCinders]

As covered in other threads, I have changed intake o-rings, set the valves, totally rebuilt and bench-synched the carbs, switched to K&N Pods, upped the main jets and am wrestling now with tuning the pilot circuits.

With bike reassembled and a long fuel line to the separated tank, I am struggling with getting the pilot circuit right.

Before I shed that %&^$*ing air box, she was waffling between rich and lean. Now that I have pods in place and the VH 4:1 pipes, I understand the need to compensate for the additional air flow.

Present settings are:

Main Jets - 110s (stock are 100/102.5, and I will likely increase to 120s per earlier suggestions)
Pilot Jets - 15s (stock)
Fuel Screw - 1.25 turns out (a little higher than the basic 1 turn)
Air screw - 1.5 turns out
Needle Clips - one step down (richer) from center slot

Here are the current issues and questions:

Choke

The bike starts with little or no choke. Indeed, it is sensitive to choke. Have I gone too far with my lean worry?

Idle Screw

Screwed all the way in, the bike only idles at about 1,000 RPM. It had a lot more play in the idle screw before. I think I may have bench-synched the throttles too tightly. Will redoing the bench synch bring back more idle screw range? Or do I need to shorten the idle screw spring?

Plugs

With all the back and forth on the carbs, I have not been able to do a real plug chop yet. Three of the plugs are new (recall that the fourth plug works but cannot be changed because of a bad thread expander). Currently, they look pretty dark, but not oily. I think that is from riding it last weekend before these new changes. I am trying to clean the plugs up a bit, so I can get better readings. Can I just use a wire brush and carb cleaner to do this?

Air Screws

I have tried to follow the process on BassCliff's site for setting the air screws, namely, setting the idle low and adjusting the air screw to best idle RPM. I suck at this. The instructions indicate that very slight turns (within 1/4 turn or so) should yield results. I have gone up to about 1 turn and detect no change in RPM. Have I started them too far in perhaps?

Smoke

Previously, I was seeing light wisps of smoke off the cylinder head. They were sporadic but more prevalent when she was running a bit lean. I see them far less now, but the smoke does return occasionally. Inspecting the cylinder head, I found some oil residue, but it was not near any of the seals/gaskets. Not convinced that it is a leak, but I think it is just slop from other work I was doing (e.g., oil splash when a valve shim dropped into place). I have gone over it with a rag to clean off the residue and will look out for any new residue/smoke. What is a good cleanser to use for that?


Tonight, absent other/better ideas ITT, I plan to:

1. Pull carbs and re-synch them to get more idle play;
2. Reconsider putting my air/fuel screw settings back to 1/1.25 (very open to other ideas here);
3. Cleaning the hell out of the plugs to get better readings;
4. Cleaning the cylinder block more to trap any leaks, new residue;
5. Dial in the air screw/idle settings (hopefully);
6. Vacuum synch; and
7. Go get some plug chops.

What did I miss?

 

[almarconi]

Fuel Screw - 1.25 turns out (a little higher than the basic 1 turn)
Air screw - 1.5 turns out

I would think with these setting that you are way too rich. The air screw should be about 2x the fuel screw settings.

If you can't hear the rpm change, consider getting a colortune to set the idle mixture. You'll be able to see the color in the combustion chamber and make adjustment.

Stock pilots should be fine with your setup. Just make sure the pilot circuit is clean and the fuel level in the bowls is within spec.

Carbs need to be vacuum synced.

 

[MisterCinders]

I checked the float levels (dry and wet tests). They check out fine.

I have the vacuum synch tool, but need to get the idle sorted before synching the carbs. Without a helping hand on the throttle, I need to set the idle at 2,500 (with a fan over the engine). Can't do that with the current bench synch.

I thought that might be too rich and will reset those screws to lean out the mixture a bit.

 

[Guest]

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

 

[MisterCinders]

There is no Dynojet kit for my bike.

 

[almarconi]

I have the vacuum synch tool, but need to get the idle sorted before synching the carbs. Without a helping hand on the throttle, I need to set the idle at 2,500 (with a fan over the engine). Can't do that with the current bench synch.

2500 rpm is a bit high, I try to shoot for 1500-1800 rpm. Adjust your baseline idle with the idle adjustment knob, no need to have anyone working the throttle.

Perhaps you could find a more knowledgeable member to help you. I'm sure there are some in the Chicago area that would lend a hand.

 

[rapidray]

His carbs COME with adjustable needles. You need to start by setting the air screws back to stock. Then tune the mixture screws in or out to get the fastest idle. After that, go after the needle & main tuning. That's where I would start. I do the carb sync with the engine at 2000 rpm so you should be able to go ahead with that. If the carbs are WAY out of sync it can make tuning a nightmare. Sync the carbs and then go back to the mixture screws. After you get it to idle good, check the sync one more time & continue on. Ray.

 

[almarconi]

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

The one you referenced is for CV carbs, his are VM. He can get the carbs dialed in with a main jet change it will just take some patience.

 

[MisterCinders]

Ugh. I still cannot detect the RPM changes for these airscrews. Sod it, I am getting a ColorTune.

Also found a small oil leak off the valve cover. That probably explains the wisps of smoke I was seeing - oil drips on the exhaust and cylinder heating up and burning off. Guess I will pull the valve cover and check the seals. I put a new gasket on there, but it may need some grease or sealant. v0v

Re-synched (bench) carbs and reset the fuel/air screws to 1 and 2 turns. Idles OK with more range in the idle screw. Hopefully tightening up that valve cover leak will sort out the smoke wisps.

Also noticed a slight pop from the No. 4 pod filter when the bike was warming up. Looked like the pop was air going into that pod. It seemed to occur only once or twice when I first started the bike. Cause for concern?

 

[Guest]

Do it with two people, one watching the tach at idle, and the one doing the adjustments, having a good ear. You will see some very small changes, just go from one carb to the next until you get them as high as possible, waiting a bit between adjustments. When it's right, your idle should sound really nice without any loping, and the pipe temps. real close. The changes might not be more than a needle width. the person watching the tach can tell you which direction is increasing the idle. When I adjusted mine, a Harley mechanic with an excellent ear was adjusting, and he was actually listening to me when I corrected the direction he was going in, watching the tach. It's that close with some carbs. Drive it for a day, and then see how the low speed manners are. If it is not very smooth at 25 to 30MPH, turn the pilot jets a tad counter clockwise maybe 1/8 of a turn. Drive it for several more days and adjust if necessary. It should not affect the idle. I started with my pilot fuel screws at 1 turn out, and ended up between 1 1/8 and 1 1/4 turns out. I'll refine those by putting around at slow speed and adjusting for color when I have time. The Color Tune will not do as well as the above method, but might get you in the ball park. Sorry about the stage three kit, Z1 listed it for your model year, and I didn't check it further. You will get some lean pops at random from the carbs, especially when starting cold, but it's not a concern unless it's consistent.

 

[MisterCinders]

Cleaned up the valve gasket and sealed it up nice and tight.

Idles well, but I have no ear for the air screws. Will try the ColorTune and OldVet66 method.

Downside is that even with the valve gasket tight, there is still a hint of smoke coming from the head. It trickles out of the No. 2 exhaust head. Not sure what is causing it. Could be the mixture. Could be some other horrific disaster inside?

 

[Guest]

Downside is that even with the valve gasket tight, there is still a hint of smoke coming from the head. It trickles out of the No. 2 exhaust head. Not sure what is causing it. Could be the mixture. Could be some other horrific disaster inside?

Do you mean the exhaust header pipe?

Could be residual oil from the leaking gasket which will stop after a bit of a run? Or maybe leaky exhaust gasket - but then you would also have smoke out the muffler too.

Don't think it's got anything to do with the mixture.

 

[MisterCinders]

Do you mean the exhaust header pipe?

Could be residual oil from the leaking gasket which will stop after a bit of a run? Or maybe leaky exhaust gasket - but then you would also have smoke out the muffler too.

Don't think it's got anything to do with the mixture.

The smoke is from the exhaust header pipe, and there is a tiiny amount of smoke in the exhaust as well. Not steady or heavy though. Too dark out to detect the color, but it is not black.

 

[tkent02]

Idles well, but I have no ear for the air screws.

You don't need an ear, look at the tachometer. You can see tiny changes if you look closely.

 

[Guest]

With my header, I used two gaskets on each pipe, it seems to seal better that way with the stock bolts. I don't know about the 750, but on my 1000, Suzuki put tabs and an extra bolt on the head between 2 and 3 in '79. My '78 leaked there but the '79 motor does not. I expect it is more or less normal.

 

[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?

 

[Guest]

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?

 

[Guest]

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 ? and air screws at 1 ? 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 ? and fuel to 1 ?. 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.