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Ford 9N, 2N & 8N Discussion Forum
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update on vent, sparks, carb etc

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Hey Dell, other

10-30-2006 17:47:31




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Ron,ar here,again: I finally got the new autolite plugs installed today. I also installed a new, better quality plug wire set. I had already installed a new set but they were the cheapest I found. Remember, back when I first brought this tractor home it did not run and I just wanted to get it started to see what I had before I spent too much initially. Anyway, I put the new wires and new autolite plugs in. Our Napa store could only provide Autolite 216 plugs for some reason. It seems to run better and I checked the spark at dark so I could really distinguish the color. It is definatly blue and will jump about 1/2 inch gap so I am pleased with that. Now about the stumble at WOT. I have not tried it with a load so that is still a question unresolved except I am still learning a few things about the "hole" I drilled in the top half of the carb. If, after I let it warm up first, I go from idle to WOT, the hole has to be uncovered or it stumbles a lot. No amount of adjusting solves it either. Now, if I set the lever at idle, cover the hole,it runs fine, but at low idle it always did. However, with the hole covered, if I slowly move the throttle lever to WOT it does not stumble at all. It is only if I go from low idle to WOT quickly that it runs rough. I checked fuel flo again, thinking it was too little fuel flo and could not "catch up". I has plenty of flo. I rigged my timing light up on a set of temporary reference marks and it appears to be advancing tho I do not know for sure how much it should advance. More as I learn.....thanks.

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Klatch

10-31-2006 08:05:14




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 Re: update on vent, sparks, carb etc in reply to Hey Dell, others, 10-30-2006 17:47:31  
I guess I'm confused, if your engine now runs satisfactroy at WOT and you only have issues with quickly opening the throttle, whats the problem. This isnt a drag racer, dont you set the throttle and leave it there?



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ron,ar

10-31-2006 10:56:42




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 Re: update on vent, sparks, carb etc in reply to Klatch, 10-31-2006 08:05:14  
The real issue is that under load while mowing it tends to mis-behave. I can't load it up here in the yard like I do in the field. It's close, probably closer than most but I still know it ain't "rite".



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Jerry/MT

10-30-2006 22:07:24




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 Re: update on vent, sparks, carb etc in reply to Hey Dell, others, 10-30-2006 17:47:31  
When you snap the throttle forward, you open thethrottle plate up and the airflow to the cylinders increases causing a minimum pressure to occur at the venturi throat. This sucks in fuel from the main jet as well as from the accelration well. (That's the volume around the main nozzle and this additional fuel is supplied through the holes in the nozzle.) It semms to me that when the hole is uncovered, you have atmospheric pressure on the bowl vent so that when you accelerate, you have some additional enrichment, over and above the fuel that in the acceleration well especially at the higher rpms. This is due to the fact that the normal bowl vent is not pressurizing the fuel bowl, the atmospheric vent is, since p atm>p carb inlet. When you slowly move the throttle, with the atmospheric vent covered, you have adequate fuel supply from the accelerating well because you're changing the rpm so slowly you are in effect not running a accel transient but a series of near steady state operating points so whatever enrichment is available from the acceleration well is adequate.

You state that your advance is 8-12 degrees and so you think your centrifugal advance is OK. What should the advance be? My TO-30 advances 26 degrees from idle to max rpm. 8-12 degrees sounds like it's too little but I don't much about these Fords. If the advance is too small this could explain your problem at high rpms and it's independent of the carburetor issue. If I were you, I'd find out what the advance should be and check your advance as a function of rpm.Check the distributor for bushing/shaft wear also.

Just my thoughts on this matter....

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Dell (WA)

10-30-2006 19:28:56




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 Re: update on vent, sparks, carb etc in reply to Hey Dell, others, 10-30-2006 17:47:31  
Ron..... ...yer stumbleing from yer TOO RICH mixture caused by yer experimental vent that has unbalanced your down-pointing mainjet control needle. By gently creaping up on it, you manage to keep yer sparkies from flooding out and quitting.

Yer carb has 2-jets that are 8-32 thread. Convince me that you have not miss-installed and swapped them. One is in the bottom of the bowl under yer slanted emulsifier nozzle. One is in the carb top.

My hand written notes say the 9N-9533 mainjet at the bottom of the bowl under slanted emulsifer nozzle is 0.074 hole (slightly bigger than 1/16" drillbit) and is #8-32 thread. The other #8-32 thread is the 9N-9914 economizer jet with 0.041 hole and is in the carb top. (n.b. 1/16 will NOT fit hole)

The other carb top-jet is the 9N-9596 idlebleed jet with 10-32 thread and 0.024 hole.

Remember: ALL CARB DRAWINGS LIE but the threads don't..... ...Dell

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ron,ar

10-30-2006 20:29:56




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 Re: update on vent, sparks, carb etc in reply to Dell (WA), 10-30-2006 19:28:56  
While those two jets are the same size thread, they are not interchangable. The one in the top has a sort of shoulder and will not fit physically in the main jet position in the bottom of the carb under the main nozzle. I know this because I tried to switch them early on in this deal. The mainjet while having the same outside thread is smaller overall than the low speed jet because of the low sped jet's "shoulder".How-ever the main jet has the bigger inside hole. The low speed jet while being bigger because of it's "shoulder" has a smaller inside hole. I think I just said the same thing you said,except that I am convinced the two are not interchangable in position. Besides all that, about a month ago, after reading your first post on this subect, I removed them and using a drill index, made sure the biger hole jet is in the bottom. My eyes may decieve me but you can't fool that drill bit:^)

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ron,ar

10-30-2006 20:41:17




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 oh, I forgot... in reply to ron,ar, 10-30-2006 20:29:56  
you said:
"yer stumbleing from yer TOO RICH mixture caused by yer experimental vent that has unbalanced your down-pointing mainjet control needle. By gently creaping up on it, you manage to keep yer sparkies from flooding out and quitting"
>
>
Dell, I don't think I made it plain in my intial post; if I cover the hole and go to WOT it stumbles. If I cover the hole and ease into it up to WOT it does not stumble. If I uncover the hole it does not stumble in either case. If I go to WOT with the hole uncovered, then reach down and cover the hole, then it starts to stumble and will eventually stall out. Also I put my timing light back on it again and I would guess it advances about 8-12 degrees at full throttle. That is just a guess without using a degree wheel. It is enough to convince me I am not having centrifigal advance problems. I can live with it like this, I would just like to know WHY it has to have that hole to operate right. Not to mention, I know what will happen if that litle hole plugs up while I am mowing:^)

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Dell (WA)

10-31-2006 07:31:23




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 Re: oh, I forgot...thats ok in reply to ron,ar, 10-30-2006 20:41:17  
Ron..... ..my I&T FO-4 sez the frontmount centrifical advance is 25deg. Iff'n yer only gittin' about 8-12deg, I can see a MAJOR high-rpms ignition problem. I suggested earlier yer frontmount distributor drive might need replacing because of wobbles. You discounted that claiming the bushings are good. Might be time to take it into a good HOT-ROD ignition shop for a distributor machine test?..... ..Dell

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ron,ar

10-31-2006 10:54:31




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 i'm guessin at it in reply to Dell (WA), 10-31-2006 07:31:23  
I will put a degree wheel on it later this week if I get in earlier. Hard to work 12 hrs and get much done at home. Wobbles is not the problem. I do know how to read the Sterret dial indicator, eyes ain"t that bad yet. Brain maybe, but not eyes:^)
You got lots of snow there yet?



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ZANE

10-30-2006 18:58:19




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 Re: update on vent, sparks, carb etc in reply to Hey Dell, others, 10-30-2006 17:47:31  
Check the fit of the Venturi at top and bottom to be sure it is sealing off. If it isn't that can cause the symptoms you are experinacing. I explained how the leaking venturi can cause this a couple of pages back on the "vent" thread.

Zane



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ron,ar

10-30-2006 20:15:48




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 Re: update on vent, sparks, carb etc in reply to ZANE, 10-30-2006 18:58:19  
I read that post on a couple of occasions. The venturi fits tight. You may remember, I smoothed both surfaces of the carb halves on a sheet of sandpaper on a sheet of flat glass. The venturi fits tight between sandwiched between them and is not bent nor distorted in any way. I also made sure it is in right, will not fit down right if in backwards. Thanks for the tip tho, I can see where a loose fitting venturi tube would cause these problems.

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CENTAUR

10-30-2006 18:15:05




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 Re: update on vent, sparks, carb etc in reply to Hey Dell, others, 10-30-2006 17:47:31  
I am confused.Did you drill a hole in the top of the carburetor or are talking about where the idle adjustment screw should go.CENTAUR



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ron,ar

10-30-2006 18:26:49




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 Re: update on vent, sparks, carb etc in reply to CENTAUR, 10-30-2006 18:15:05  
Centaur, this is a long drawn out tale but the short version is that after many other things we tried here, I was advised to either cut a "nick" in the bowl gasket or drill a very small hole in the top carb half as it was believed the bowl vent was plugged. More of a diagnostic step than a "fix". The symptom BTW, was a high speed needle that had to be screwed out WAAAy to far to get the rough running out of it at high speed. It has gone downhill (or up depending on your view) since then. :^)

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