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'71 R50/5 doesn't accelerate

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Clayton Abshire
Posts: 2
New Member
Topic starter

Hello everyone. New to the forum. 

I had purchased a 1971 R50/5 last year.  I had to shipped here to El Paso, Texas.  I took it out for initial run and it would not go over 50 miles per hour.  

Well covid and my mons passing kept me from doing much.

Now that I have the chance I would like to get it running.


Please any and all suggestions. 

Yes I am going to clean carbs but I was also thinking a jet might be the issue. 


Thanks in advance for an and all help.

Posted : 07/03/2021 18:51
Richard W
Posts: 2549
Posted by: @clayton-abshire

Please any and all suggestions. 

Yes I am going to clean carbs but I was also thinking a jet might be the issue. 

Welcome Aboard !

We are very sorry to hear of your loss.

1. Tune-up. While it may well be the carbs, without a full tune-up it could be anything. And since carb settings totally depend upon ALL other tune-up items, let's first start with the basics of ignition timing, valve adjustments, air filter, spark plug and spark plug wire/cap condition. Then when we know those are prefect, then we can jump into the "deep end".

Taken in the reverse order, any carb ajuststments you might make at this time would need to be completely re-set if (say for instance) the timing was changed. So, first things first.

Now you may well have already done some of this, but there was no mention of it.... so I can only assume it wasn't.


2. Fuel. Fuel is the Number 1 issue facing any engine with a carb. You don't see this with your car because your car uses electronic fuel injection (EFI), which is 1000% different. There are several facets to this issue which you MUST understand....

  • You should be using a high performance, high octane fuel in your Airhead. There is good fuel and there is also junk fuel. You can help yourself by choosing to run a good fuel with "cleaners", like Shell and Chevron. BUT, you should also read and understand all there is to know about Top Tier Fuels....    [Now, everyone gets caught in locations where there is only one brand available. What I'm talking about is what your engine runs 90% of the time.]
  • Modern ethanol fuel will go "bad" starting in about 8 weeks. What is actually happening is that the Ethanol comes out of solution with the gasoline. You get stratification within the stagnant fluid; one layer of gasoline and one layer of Ethanol. So if your bike is to sit or be rarely ridden, you must begin to treat the fuel with a "fuel stabilizer". 
  • This same stratification happens to the fluid inside the float bowl. The ethanol starts to attract water. The combination of water, ethanol and gasoline starts the growth of things that gum-up carbs. Total blockage starts to occur, beginning with the smaller jets. Running the bike may or may not clear the issue, because the fuel is not "pressure washing" the inside of the carb (like it is with EFI). This is what makes fuel brands with an added cleaner advisable. 
  • It is therefore mandatory that infrequently ridden motorcycles use not only a fuel stabilizer, but also a fuel system cleaner. Such a product is StarTron fuel treatment.

Now you have told us that family members have been sick. I suppose this might infer that the fuel in your Airhead tank has been sitting awhile. For all the above reasons.... this is NOT a good thing. If the fuel is over 8 weeks old I urge you to either go on a 400 mile ride and then re-fill with better high-test fuel, OR drain it ALL and dump it into your car. Fuel that will make your Airhead sputter and cough can be run in your car without so much as a hiccup. You car's EFI will quite happily burn it and never know the difference. 

So in this sense, your Airhead now has more in common with your lawn mower and leaf blower, than your car. So if your lawn mower is also not running its best, now you know the reason. The difference is this: your lawn mower runs at a constant engine speed and so it can happily burn "Regular" grade fuel, whereas your Airhead is constantly changing engine speeds.... and needs the ability to accelerate. Which is why your Airhead needs high-octane fuel and your mower does not. 

And that's where we have to start. 


Hope this helps.

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

Posted : 07/04/2021 04:49
David Elkow
Posts: 306
Reputable Member

I concur. There is a “pecking order” to getting things straightened out. Forgive me if you have already done these things. If I were facing this situation, and I knew nothing of the bike’s tune-up status, I would;

1.  Valves - set valve clearances and make sure the valve train seems all ok.

2.  Compression test - best to temporarily remove carbs for this. I don’t know what numbers would be ok for your R50, expect 130-160 psi ?

3.  Ignition timing - A fresh set of points might be good. Set gap and timing. Fresh plugs might be good, too.  To verify the ignition advance, you will need a timing light, and be able to rev the engine to 4000 or so. 

Those items can be checked/set regardless of what the carburetors are doing (as long as the bike will run), and need to be done first.  Then your attention can move to the carb condition, settings and balance. 

And Richard is surely correct, it’s gotta have decent fuel. 

Posted : 07/04/2021 06:07
Richard W
Posts: 2549

In these situations, the 3 words I hate to hear the most are "new to me". Because the new owner is assuming that "if I can just make that one adjustment and spend $15 all will be set right". But that is hardly ever the case. 

If you don't receive an owner's log of all the work done over the last year, then the new owner has to re-trace all the steps along the tune-up trail. A new owner can't assume anything.

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

Posted : 07/05/2021 08:37
Richard W
Posts: 2549

Here's a good list of items to check on a new-to-you Airhead....

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

Posted : 07/28/2021 04:49


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