Chronic Idle Miss

[Anonymous-0]

Have a 50 8N side mount that I recently replaced distributor on because original distributor was worn out. Timing is dead on. Have rebuilt carb and adjusted according to forum, replaced plugs and wires. Dry compression test shows 125 to 127 psi on all cylinders. Doesn't smoke and has plenty of power at half and full throttle. I have a chronic idle miss that I cannot seem to tune out. Any ideas as to how to fix would be appreciated. Thanks.

 

[Ultradog MN]

You replaced the worn out distributer with what?
New one? Used one? Tell us more.
Are you running points or EI? Someone here
recently made the comment that switching to EI eliminated an irksome chronic idle miss.

 

[ZANE]

Try moving the distributor in the direction of the rotation of the rotor and see if that doesn't help???

The mechanical advance system on the Ns can throw you a curve when it comes to timing.

The magnitos on the large radial engines I worked on in the AF (4360 cubic inch) etc were times by using a TDC tool that was inserted into the spark plug hole and calibrated to TDC then the engine was rotated back beyond where the desired timing was to be and then turned in the dirction of rotation to take out all the gear slack etc and then the magnito was moved until the points opened. That was where you locked it down. Then backed it up again and came forward and observed if the points still opened at the desired degrees before TDC.

I always time simple engines like the Ns by ear. Guess how you times a model T or model A???? By moving the timing lever till it sounded right!!! :O)

Did you know if you timed the N engine before TDC and tried to hand crank it you might get a broken arm or hand?????
Zane

 

[JMOR]

(quoted from post at 19:37:05 10/15/10) Have a 50 8N side mount that I recently replaced distributor on because original distributor was worn out. Timing is dead on. Have rebuilt carb and adjusted according to forum, replaced plugs and wires. Dry compression test shows 125 to 127 psi on all cylinders. Doesn't smoke and has plenty of power at half and full throttle. I have a chronic idle miss that I cannot seem to tune out. Any ideas as to how to fix would be appreciated. Thanks.

oes a little choke clear it up?

 

[Den N Ms]

MadMax,I could be a lean idle mixture,At idle below 600-500 RPMs try turning in the side pointing idle mixture screw on the right side of the carb.If the mixture doesn't get richer it could be the idle circuit is plugged or partially plugged up.

 

[Anonymous-0]

I replaced my distributor with a new one purchased from nnalert. It has points.

 

[Dean]

A miss at idle when other performance is OK is usually due to lean idle mixture.

Adjust the idle speed to 400 RPM or less and try turning the idle mixture screw IN a bit.

If you detect no change or can turn the idle mixture screw fully in without stalling the engine, the throttle shaft and/or throttle shaft bore is worn such that excessive idle air is being drawn around the throttle shaft.

Of course, you should ALWAYS verify that the ignition system is spot on BEFORE adjusting the carburetor.

Dean

 

[Anonymous-0]

sometimes a worn throttle plate shaft will cause this also. have a old gas power welder, sounds like it has a pint of water in the dist. till I strike a arc. then just even out sound like a new machine.

 

[Dell (WA)]

MadMax........one of the original founding members of this great N-Board in 1996 used to claim 80% of all carburator problems were found in the electrical system. You doubt?

Go out on DARK NITE and starter up at idle and look fer sparkies dancin' on yer new COPPER CORE sparkie wires. DO NOT USE modern carbon fiber glass string sparkie wires as they will BREAK inside the insulation and cause misses just as you are complaining about.

While yer problem could be lean miss due to worn throttle shaft, I doubt it. To check, spray WD-40 around the shaft and other areas of potential leaks. WD-40 is non-flamable oil but will temporarily seal enny vacuum leaks that might be causing lean-miss. .......Dell, yer self-appointed sparkie-meister

 

[Den N Ms]

Dell you say ,WD-40 is non-flammable oil ?
A engine will run on WD 40 alone.

 

[Dell (WA)]

Den.......look up the definition of "non-flammable" in yer Funk & Waggonal. Diesel is non-flammable; gasoline is flammable. BIG difference. Engine runs on the natural gas pressure charge that WD-40 uses. Yes, the WD-40 oil will burn inside a engine. .......respectfully, Dell

 

[36 Coupe]

since my tractor does Zero work at idle speed i dont care if it misses there,Compression pressure is highest at idle rpm.Open the throttle and do some work...

 

[Den N Ms]

Dell,You need to read more,it might save your arse from burning up. The MSDS for WD 40 is here, and that aint in my Funk and Wagnalls.Flash Point:
122F (49°C) Tag Open Cup.
Wd 40

 

[36 Coupe]

Lets go back to the days when spark plug cleaners were used.After the plug was cleaned with grit air pressure was applied and a high voltage applied at the same time.You could see the spark jumping the gap.Some plugs would stop sparking as air pressure was increased.Since compression pressure is highest at idle speed these plugs would misfire.A wide gap will let the spark voltage increase and make the plug fire every time at idle speed.A miss at idle speed will foul the plug.Prolonged idling will foul the plugs.New plugs with sharp corners on the electrodes always fire better than old plugs with worn rounded electrodes.As long as the engine dosent skip at working rpm under load I dont worry about minor skips at idle.

 

[TheOldHokie]

(quoted from post at 23:57:57 10/18/10) Dell,You need to read more,it might save your arse from burning up. The MSDS for WD 40 is here, and that aint in my Funk and Wagnalls.Flash Point:
122F (49°C) Tag Open Cup.
Wd 40

It's pretty much semantics unless you are a DOT or NFPA safety inspector. Combustible liquids are defined as any liquid that will ignite if it reaches its flash point in the presence of an ignition source. Flamable liquids are Class I combustible liquids with a flash point below 100C. WD 40 is a Class II (flash point of 100C-140C) combustible liquid - and will go POOF in a heartbeat if vaporized in the presence of a spark.

TOH

 

[Den N Ms]

Oh and by the way,WD 40 spray cans use Co2 for propellant NOT natural gas or propane.
Co2 is a fire extinguisher.