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New Airhead Owner - Needs Help! (Lots of Images)

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Richard W
(@wobbly)
Posts: 2545
Member
 

More detail...

The valves are not adjusted on both cyl at the same time, because they are operating 360 deg different from each other. You adjust one cyl, spin the engine 360 deg and then adjust the other.

On a 4-stroke engine, each complete firing cycle takes 2 revolutions, or 720 crankshaft degrees. Because the engine fires on one side, then the other, there is one combustion every 360 degrees (or 720/2). Because of the alternating firing order, the action of the valves is also 360 degrees out of phase with each other. In fact, it is only by watching the valves that we can really tell what phase the pistons are on. So on a 4-stroke we always watch the valves... not the pistons.

The flywheel marking "OT" means both pistons are at TDC, but that does not tell you anything about which cylinder is ready for valve adjustment. Since the 2 cylinders are 360 degrees out of phase... one is ready for valve adjustment and one isn't. You MUST watch the valve motion to understand when to take action.

A peculiarity of the 4-stroke engine is that while one cylinder is on TDC for the "combustion stroke", both valves are closed. These are the 2 valves that get their clearances adjusted. At the same instant, the opposite cylinder is at TDC on the "exhaust stroke" and both its vales are partially open. That is to say, there is NO VALVE CLEARANCE, and so the valves CANNOT be adjusted at this crankshaft position.

Therefore at the flywheel "OT" position, one set of valves is in the correct cam position to be adjusted, and the other set is absolutely NOT correct. However, the OT mark does not tell you which set of valves to adjust. It is not enough information. The OT mark is then inviting confusion when clarity is required.

Removing both plugs makes this spinning easier. Rotating the engine is best done by placing the bike in top gear and bumping the rear wheel by hand.

1. The best way to adjust the valves is to place the bike on the centerstand, remove both plugs, and place the bike in top gear. Then it's a simple matter to bump the rear wheel (forward or backward) and very accurately control the position of the crankshaft.

2. Using this method, we can so accurately control the crank position that we can completely stop watching the flywheel marks and simply watch the motion of the valves.... and KNOW with absolute certainty when the OT mark will be in the flywheel window.

To Summarize
1. The "OT" mark ("on top") to Germans means the exact same thing as "TDC" (top dead center) does to English speaking mechanics.

2. STOP looking for the flywheel marks as the books suggest, and START watching ONLY the motion of the rocker arms. Watching for the flywheel marks invites mistakes, because they are lying to you exactly 50% of the time. Watching the rocker arms assures absolute certainty, because it is the rocker arm clearance we are trying to adjust. The action of the rocker arms NEVER lies.

3. Simply rotate the engine to a point where you see BOTH rocker arms moving. If you'll find the position half-way through both rocker arm movements (by bumping the rear wheel backwards and forwards), then you can look in the flywheel window and see the OT mark nearby. You may not be exactly on OT, but you'll be close enough to adjust the valves ON THE OPPOSITE CYLINDER. Again, you'll want to adjust the valve clearances on the cylinder where the rocker arms that are NOT moving in the vicinity of the "OT" mark.

4. Once the 2 correct valve clearances are adjusted, then the engine is spun 360 degrees. The roles of the rocker arm movements will then be reversed, the rocker arms you just adjusted will now be without clearance, and the valves on the opposite cylinder can be safely adjusted.

It is only when both sets of valves are correctly adjusted that you will have compression on both cylinders.

Hope this helps.

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 05/27/2019 09:22
Andre Litinsky
(@dretek)
Posts: 24
Eminent Member
Topic starter
 

Okay this makes total sense. I was able to get the valve clearances spot on (within .001" tolerance).

Now the next step is to check timing right? But to do that you need the bike to idle. The weather was warm and I was feeling good, so I decided to fire her up.
After 4-5 tries of different combinations of: having fuel enrichment OFF/ON, backing out idle screws and air mixture I was able to get her to IDLE with enrichment OFF.

I did see some smoke come from the right exhaust nut area.

Also, I was able to hear a bit of "clacking" in the cylinder head. I am not sure if this is okay, or me naturally being concerned?

After turning the bike on again, I noticed the RIGHT EXHAUST is SIGNIFICANTLY Hotter than the left. Almost as if the Left side isn't running.

And same issues as before: when trying to throttle a bit, the bike shuts off.

Am I ready to set timing now that the bike CAN idle? Do fans need to be placed?

Any thoughts or suggestions would be greatly appreciated.

Blue skies,
Andre

 
Posted : 05/27/2019 13:55
Richard W
(@wobbly)
Posts: 2545
Member
 

I agree with Scot. You are very, very close to being "road worthy". It may not run perfectly, but as you start to ride and continue to work out the bugs, the bike will run better and better. These bikes are very simple engines and they respond gratefully to TLC.

However, you must use logic and stop jumping to baseless conclusions. Engine diagnosis and repair is an exercise in pure logic. Some people can do it, and others end up handing over their paycheck to the neighborhood mechanic.

Examples of not-so-logical behavior....
> As was already said, an engine warm enough to idle without "chokes" needs a cooling fan. I don't see a fan.

After 4-5 tries of different combinations of: having fuel enrichment OFF/ON, backing out idle screws and air mixture I was able to get her to IDLE with enrichment OFF.

> Changing these screws will not help starting one bit.
> Once the engine is running, the idle speed and idle mixture screws shouldn't be turned more than 1/8 turn, and when they are a definite change should be heard in the engine. If no change, then STOP and find out why.

Also, I was able to hear a bit of "clacking" in the cylinder head. I am not sure if this is okay, or me naturally being concerned? After turning the bike on again, I noticed the RIGHT EXHAUST is SIGNIFICANTLY Hotter than the left. Almost as if the Left side isn't running.

> The 'clacking' is most likely the sound of the engine running on 1 cyl only. Did you perhaps verify your suspicion by laying a hand on the cyl head or spitting onto the exhaust pipe? So your "concern" was not translated into meaningful testing.
> Did you try pulling gently on the individual throttle cables to see if the corresponding cylinder would speed up ?

With no test results to guide me...
I believe you've fouled a spark plug. Go get 2 new BP7ES plugs. Plug them into the plug caps and lay them on the cylinder heads. Make sure they will both spark by turning the engine with the starter. If they do, place 2 drops on motor oil on the threads of each and install them into the cyl heads.

Put the carb screws back where they were originally. Turn ON the fan. Then try starting the bike again. You might try using only one enrichener lever. This way you can keep one hand on the throttle.

Once started, LISTEN to the engine. The engine is telling you stuff. You must LISTEN. Pull on the individual throttle cables. LISTEN. Do you hear the same increase in engine speed on both carbs?

As was said before, you cannot time the ignition until you can rev the engine to 3000 RPM.

Also read this tread again.... www.airheads.org/forum/technical-discuss...ead-back-on-the-road

Good luck.

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 05/27/2019 19:05
Andre Litinsky
(@dretek)
Posts: 24
Eminent Member
Topic starter
 

@Scot

I will give Bill a call at Rocky Point Cycle. Fortunately, for me, there is a Tech Day for airheads in Culpeper, VA (~50 min away). Perhaps I can lug my beast over there.
Thank you so much for the response.

@Wobbly
One thing is certain, with the carbs at DEFAULT setting, I am able to idle the bike without having the Fuel Enrichment: ON (Lever DOWN). Which confuses me when you write:

"Put the carb screws back where they were originally. Turn ON the fan. Then try starting the bike again. You might try using only one enrichener lever. This way you can keep one hand on the throttle."

I am working on getting some Fans from people in my office.

> Did you try pulling gently on the individual throttle cables to see if the corresponding cylinder would speed up ?

I will need to look at the throttle cables and see how they are set up because as of right now (without being near the bike), I am not 100% sure how to throttle individually.

I am close, I can feel it!

 
Posted : 05/28/2019 17:27
Richard W
(@wobbly)
Posts: 2545
Member
 

I am close, I can feel it!

Friend, that part I am very sure of !! If I had 30 minutes with the bike, you'd be riding it home. With zero malice toward you and/or your capabilities, it's exceedingly hard to diagnose and cure anything via the written format.

However, it is abundantly clear that the Mic carbs are NOT helping the situation and are frustrating both of us. While they might have better performance specs, their cold starting characteristics are miserable. And "starting" seems to be where we are stuck. I'd gamble to say that within the next year, you'll be loosing the Mics and reverting back to the stock carbs and intake setup. That would eliminate 100 problems immediately.

Let me explain the apparent communication deficit between us....
► "Put the carb screws back where they were originally." You stated that you altered those 4 screws to try and get the engine stared. Those 4 screws affect idle. "Idle" is when the engine is running, but the engine was NOT running; it was being started. So you need to put them back to where they were before you changed their setting.

► "Turn ON the fan." Walmart is full of $12 box fans this time of year. Go buy one. Set it up against the front tire on medium speed. You're working on an air-cooled engine. Carb settings change with engine temp. A fan helps minimize the temp changes.

► "Then try starting the bike again. You might try using only one enrichener lever. This way you can keep one hand on the throttle." Stock carbs run lean and sometimes need constant throttle attention to achieve cold engine start. You had previously been using the enrichener valves, but now you are not. This is the first news I've had of this change.

► "I will need to look at the throttle cables and see how they are set up because as of right now, I am not 100% sure how to throttle individually." Well, you simply reach up to the twist grip area and pull on the individual cable housings where they enter the twist grip. Why? Because I can hear the bike running on 1 cylinder in your video. I want to know if both cylinders are capable of running. And pulling on the individual cables is a way to know this. I asked about the cyl head heating, and got no answer. I asked you to test the ignition spark and got no answer. I asked you to installed new plugs and got no answer. I ask for hard metrics, but receive none.

So yes, you're at the point where this particular discussion needs to stop and you need to take the bike to someone, either a local mechanic or a tech day gathering.

I wish you all the best, and would certainly like to hear about the final repair results. I'm sure it's very simple.

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 05/29/2019 09:14
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