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Discussion Starter · #1 ·
Okay, let me begin by reminding you guys that I'm new to tuning bikes. So many variables for a new guy. Anyway, I got the bike running pretty good, but it is still backfiring on the right side and idles all over the place and then just dies. It will be idling at 1100rpms and abruptly die.
Also there is a tapping noise in the engine. When I put my stethescope on the right side lower engine, near the oil filter, it is a distinct rapping noise.
So just for fun, I pulled the right side plug wire, which I noticed looked worn. The engine did miss a beat. It runs the same way with the plug wire on as it does with it off. Rpms don't change at all. What is going on? :?:
 

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Sensei
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Chris....Sounds like your "backfires" are when the right side actually/occaisionally fires the plug.... You are running on one cylinder, the left one....
Find out why.... right points, right coil, right HT lead and/or cap....something is BAD!
might even be the feed wire to the points on the right side....
 

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Try a new plug on that side - make sure it's actually firing before you screw it in.

The rapping sound may just be the crankshaft being reluctantly pulled along because the right side isn't firing.

What did you end up setting your air/mixture screws on the carbs??
 

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Discussion Starter · #5 ·
I think I figured it out. The float is not adjusted properly and might be cutting off the fuel. The muffler, header and exhaust are cold on that side. I was feeling the mufflers for pressure when I was trying to adjust the carbs, but I didn't notice it was cold air.
 

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There's a little tab on the float itself which pushes the needle valve closed.
Bend that tab to adjust "float level".
Be sure that the needle valve actually closes - not where the tab just touches the valve.
 

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Discussion Starter · #8 ·
Now that I think about it, maybe that's not the cause. I know I have spark, I know the carb is getting fuel into the bowl.
 

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Discussion Starter · #9 ·
When I took off the bowl, the float is handing down, and the valve is open. So there must be gas getting into the carb. Right?
 

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Sensei
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Not necessarily enough fuel into the bowl......IT will always flow when the float is down (such as when the bowl is off)......You set the float height to keep the supply just high enough to feed the jets, but not so high as to flood into the venturi.....

Spritz some ether at that carb while the engine is running...IF it picks up and both pipes show heat, it's a fuel supply problem....
If it doesn't, something else is wrong...
 

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Discussion Starter · #11 ·
But I don't think there's any gas getting to the chamber. Even if it's not adjusted properly, the cylinder should still fire. Is there another way the fuel could be prevented from reaching the cylinder?
 

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Sensei
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If the fuel does not cover the jets, it does not get drawn into the cylinders .....without fuel, what is there to fire?.... Try the spritz test.....
 

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Or, you could manually fill the bowl about 1/2 way and reinstall it.....
 

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Discussion Starter · #15 ·
Be patient with me. I'm just learning how this works. If there isn't enough fuel in the bowl the jets get no fuel. So the float is cutting the fuel off too soon?

Or the jets are clogged?
 

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Sensei
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If the bowl was full (enough), YES, the jets could be clogged......TRY THE SPRITZ TEST....IT PROVIDES FUEL AND WILL VERIFY IF THE CARB IS THE PROBLEM, or at least that the problem is within the carb.............Let us eliminate that possibility before going anywhere else!
 

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Sensei
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Well, an engine only needs three things to run... Fuel-air mixture, compression, and a spark at the right time.....
The ether provided the fuel-air mixture, ( a spritz behind the carb will gather in enough air as it gets sucked into the carb)
You claim to have spark....(You DO realize that just because a plug will fire in open air does NOT mean it's firing under compression..... Did you try new plugs?)
You either have a lack of compression,(What were your compression readings?) OR the spark is mis-timed ........
 

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66Sprint said:
Well, an engine only needs three things to run... Fuel-air mixture, compression, and a spark at the right time.....
The ether provided the fuel-air mixture, You claim to have spark....
You either have a lack of compression, or the spark is mis-timed ........
(or not actually firing...You DO realize that just because a plug will fire in open air does NOT mean it's firing under compression..... Did you try new plugs?)
What were your compression readings?

Well said, Steve.
The compression on that engine read 172 psi, both sides - this was on the bench, right after rebuild - never run, cold.
I'm hoping it increased a bit now.
The cylinder taper was a little high, but Chris just wanted new rings, not a bore job (economics, something we all understand).
 

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Sensei
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Bill, I thought that was the engine you re-ringed, so I now KNOW three things....
IT HAS COMPRESSION......(and the crank/cam is timed properly, valves adjusted properly...)
A spritz of ether shot behind the carb will provide a fuel mixture adaquate to fire 100% of the time.......(You didn't spray a lot, or directly into the carb did you Chris?)
The ONLY thing left is "Spark at the correct time"....
Either it's not getting spark, Or the spark isn't happening at the right time.....
 
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