Hello airheads. I have a 1978 R80/7 that is running too rich (based on my senses). The plugs look classically rich, my buddy riding behind me says it smells rich and the cylinder top and heads/valves had very thick carbon buildup (I assume a symptom of running too rich).
Yes, valves have been adjusted. Yes, timing is correct. Carbs have had a “sub total” rebuild with cleaning soak and new o-rings. Diaphragms are either new or fully intact. Fuel/air mixture screws are new. The rich condition seems to be true for both cylinders. The “choke” levers close fully.
Main jet, needle jet and needle all are at factory settings for sea level where I ride. I can’t, however, tell if the needle or needle jet are worn enough to alter the air mixture or not.
Without buying new main jets in multiple sizes, new needle jets in multiple sizes and new needles, where should I start in trying to alter the fuel air mixture?
I hope that I have conveyed that I’m aware this is a complex system and there may be other factors at play but I’m specifically asking if renewing or changing main jet size, needle jet size or needle height is something I should consider.
A change in mixture or as I have experienced a drop in MPG was caused by worn main needle and jets. Did you replace these when you rebuilt the carbs? They don't show obvious signs of wear even if they are out of spec. They are not expensive and you only have to oder them off the microfiche at the dealer to get the proper ones for your bike, not much experimentation is needed for what may be a major change in things. LOL, they are not greatly expensive either to replace nor hard to. Good luck St.
Beware! I do not suffer fools gladly! St.
First realize that the actions and results of the carbs are totally dependent upon all other tuning settings. Most home mechanics will usually do about 2 of these and pat themselves on the back as if they've completed the task, when in fact they've only scratched the surface.
1) You mentioned valves being set, that's good. You mentioned timing, but not how? Ignition timing MUST be set with a strobe lamp at high RPM to achieve full ignition advance at the "F" mark. Metallic (steel or copper) core plug wires, absolutely NOT resistor wires from a car.
2) An important part of that "tuning" is the spark plugs. This is mentioned separately because it's an area going through great change right now, and having the wrong spark plug is really easy. The NGK books are wrong, the correct plug are the NGK BP7ES, which are no longer made. The closest new plug is an NGK BPR7ES (#5534) with the internal resistor, which may negate the need for the stock 5K Ohm resistor plug caps. (Research needed on that point.) [As always, lubricate the threads before installing any new or old spark plug.]
3) Steve is correct on the Needle and Needle Jet wear. This is due to physical contact for 50 years. Replace both Needles and both Needle Jets. Additionally if you don't know the age for sure, you need the newer Ethanol-proof float and float needle on both sides. Recheck the float levels, too.
When you replace your Needles it is extremely important that you count the clicks correctly, and then "double check" by comparing the extension of the needle to be exactly the same on both sides, like so...
You will typically not need new Main Jets unless they are clogged by corrosion. Nothing physically abrades the Main Jet orifice like the Needles experience. The truth is... most riders NEVER experience running on the Main Jets anyway. You'd need to be running well over 100 MPH to even begin to be on the Main Jet.
4) A clogged air filter will make the engine run rich, so replace the air filter with a fresh paper element type filter. Air filters get clogged by having mice build winter nests under the starter cover or in the air box which physically blocks the air path and/or having your engine breather system dump oil mist directly onto the air filter. Some disassembly and checking is required.
5) It also makes a difference which fuel you run. You should be using a HIGH octane (93+) fuel rated by "Top Tier".
Read more at https://www.toptiergas.com/
6) After all the above has been done, then you can take the bike out on the road (which is hopefully long and flat) and hold the twist grip at a fixed position for 8+ miles. This will give you a true plug reading on that single, specific jet range. Say 4000 RPM for Needle Jet and wide open for Main Jet. After this ride, hit the kill button while you pull in the clutch, coast to the side of the road, and then remove the plug for a true plug reading.
If you are simply pulling the plug in your shop, then you have no idea what jet you are reading. And you are more than likely simply reading the idle jet setting (since that's the most likely last engine speed)... which will of course be rich.
And that's what it takes to do a proper "plug reading". If you're not doing all of that, then you're wasting your time.
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
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