8n side mount question

[boler76]

trying to tune engine with vacuum gauge, needle stays at 18 for a few instants and then fluctuates slightly (1 or 2 ) then back to steady over and over no matter what carb setting , 3 cylinders have 105 comp and the third has 110, valve gaps checked and rechecked , oil pressure is 55, points set at 25 thou, and bushings in dist are not loose, spark plugs changed more than once and solid core plug wires installed, what are the opinions as to what should be checked and fixed thanks

 

[R Geiger]

How does it sound when under a load? Myself, I would throw the vacuum gage away and not worry about it.

 

[Jim in LA]

Googled vacuum gauage readings and got this:https://www.onallcylinders.com/2016/03/31/vac-visual-quick-guide-vacuum-gauge-readings/

 

[wore out]

" Myself, I would throw the vacuum gage away and not worry about it.''

X2

 

[boler76]

eliminating the vacuum gauge sounds like a simple fix!!

 

[Duner Wi]

Do you know how long in years/hours since new valves and guides?
Is tractor in storage for months at a time? Do you use gas with alcohol.

 

[Indiana Ken]

The gauge is suggesting sticky valves. Has the tractor been sitting....? I would run it for an afternoon and re-check. See if the gauge still thinks the valves are sticking.

 

[Eman85]

Does the tractor perform well? If so you're done call it a day and enjoy it.
Just for the heck of it where are you connecting the vacum gauge? No vacum ports on an N to easily connect to.

 

[HFJ]

(quoted from post at 11:26:14 07/13/23) Does the tractor perform well? If so you're done call it a day and enjoy it.
Just for the heck of it where are you connecting the vacum gauge? No vacum ports on an N to easily connect to.

i'm curious too. there was a (rare, i think) manifold variant with a vacuum port, but i guess it wouldn't be too hard to drill and tap your own. i do not speak from personal experience here

 

[Duner Wi]

My 9N has a factory vacuum port. when electricity went out 70 years ago you ran a hose from tractor to
vacuum line., We ran 2 buckets that way milking cows.

 

[Bruce(OR)]

Vac gauge is a fun toy. Your supposed to tweak the screws for the highest vac reading. I prefer the GM Lean Drop adjustment which is about the closest to Stoichiometric as you might achieve. The problem with the vac gauge is if you have a well running engine with a decent carb on it you can go a bit too far and need to back off the final setting to have an engine that will start easily enough.
Timing is another way to increase vacuum reading but then once you tweak the dist for a great vac reading it will not restart worth a spit. Timing being a bit too far advanced, if memory serves.

 

[used red MN]

For one you do not tell us if the engine is at an idle or full throttle. No diagnosis can be given without that info. I would guess an idle. If you were a knowledgeable mechanic working on multiple engines a day an placing your vacuum gauge on everyone to gather data to assess what the gauge is telling you, to me this sounds like the only way to truly diagnose problems with that instrument. Do not get me wrong a vacuum gauge can give you a fair amount of info about an engine. I also think back in the day it was an impressive tool for the mechanic to help him sell his diagnoses. Hummm, mechanic opened my hood and put his fancy tester on the engine. He now says his test concluded I need x y s done to my engine.. bingo another believer. When in all likelihood the actual knowledge and experience of the mechanic did the diagnosis.
I agree with the others who have said if it runs relatively good stop trying to split hairs.

 

[lastcowboy32]

This reply sounds like how variability is handled in many disciplines. At work, I've done electromagnetic compliance testing... measuring the frequency and strength of radio waves coming off of a piece of equipment.

You can imagine, this is extremely variable.

For someone to make a differential determination between one design and another, you literally have to put them on the same test bench at the same facility, the same day. Even then, the test reports have all sorts of disclaimers about "confidence intervals" etc.

On a running engine, to be looking at a little jitter in a vacuum gauge... especially on a 75 year old running engine... is all working within the tolerance of the measurement itself. Especially if you haven't put that same gauge on... maybe 10 different samples of 8N engines in the same port... showing different running conditions...

Intelligence is what the gauge says, wisdom is what you infer from it.

 

[lastcowboy32]

Critic of my own comment... these forums are non-tonal. I can sound judgy... and saying that you're wasting your time...

Even in the work example that I mentioned, we would make changes to a design based on measurements, especially if taking the measurement and reviewing the design brought up things that could be tweaked with minimum sweat and provide some insurance... and the changes that we would make would be based on old school basics of what affect the measurement... for instance, in this case... if the tractor runs fine; maybe consider not undergoing any heroic measures... but, people experienced in this sort of thing say that maybe a valve is a little sticky. There are a few things that you can do do help that that were mentioned.

And, if you did, there is a chance that they would help the engine without even changing the reading.