Author Topic: 17.5 missing  (Read 4153 times)

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Offline Tim Ladnier

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17.5 missing
« on: June 25, 2014, 10:17:15 pm »
 I have a well built 17.5 and I have noticed that it has a small miss between 5-6k rpm. Any ideas on what this could be?
Tim

Offline Jeff McKelroy

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Re: 17.5 missing
« Reply #1 on: June 25, 2014, 11:02:16 pm »
I have a well built 17.5 and I have noticed that it has a small miss between 5-6k rpm. Any ideas on what this could be?

Is it a gradual loss of power, or sudden loss of power?
Does it clear up past 6,000 RPM?
What do your spark plugs look like?  Drive it into where it messes up on you, kill the motor.  Read your plugs.

Thoughts:

Carb out of adjustment
Weak Valve Springs
Lean Engine (What's your head v.s exhaust temps?)
Fuel pump plugged with debris
Sticking carburetor needle
Plugged fuel bowl vent
Ignition coil breaking down (What's the coil gap?)
Mechanical drag (Iffy)

Offline Tim Ladnier

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Re: 17.5 missing
« Reply #2 on: June 25, 2014, 11:10:16 pm »
Carb is clean as a whistle
new fuel pump
new plug and correct gap.  Also maybe running a little lean looking at the plug
unsure of cht since my lead broke
it doesnt fall on its face at all. Just a momentary hiccup every now and again.
Tim

Offline Jeff McKelroy

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Re: 17.5 missing
« Reply #3 on: June 25, 2014, 11:13:45 pm »
Hmm. At that point I would check the coil gap, if good I would replace the coil with a known good coil.  Any cuts or abrasions on the plug wire?  Dirt under the boot? 

Offline cycloneracer

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Re: 17.5 missing
« Reply #4 on: June 26, 2014, 02:01:55 am »
I've found that EGT us the way to tune and diagnose an engine.  If it is lean it will miss.   Try fattening it up. 
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Offline Tim Ladnier

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Re: 17.5 missing
« Reply #5 on: June 26, 2014, 07:50:11 am »
I'm fairly new at this and there are no adjustments on a Tecumseh carb. How would I deliver more fuel to it. Bigger jet?
Tim

 

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