The Fordson Tractor Pages Forum

My dexta hasn't ever reved over 1550rpm since I've had it, despite tweaking the throttle linkage etc. Today I had the air filter out to clean, soaking in parafin. After reassembly I'd achieved about 1650rpm...

So, I did as I was advised by a guy that used to work with dextas etc in days gone by, and set light to the gause filters. Keeping an eye on the heat, they burnt slowly for quite some time and practicaly sparkled when done. Now I have a no load speed of about 1750rpm...

I understand that the air cleaner parts all add a load to the engine, but for information I should point out that with the filter parts disconected at the manifold, I can easily achieve 2200rpm+

Would the oil grade within the filter make a difference? I replaced that today after cleaning all the old gunge out.

My only other suspicion is in the direction of the vacuum governor, but it's not something I'm familiar with so haven't a clue what to look for or how to diagnose a fault...

Any help here will be much appreciated. I'd like to be able to do some PTO work in the near future, hence the investigation...

Thanks

i have a similar problem with my standard dexta. i just assumed it was something to do with a worn engine? or if the fuel lift pump wasnt working well enough to get enough fuel to the injection pump.

Take the whole filter assembly off, remove the bottom cup and all the non steel parts.. Get a big pot from the kitchen, drop the filter housing with all the wire guaze in the pot, add enough water to cover, about a teaspoon of low sudsing detergent (ie laundry type)
and boil it on the stove for while... This will
get out all the dirt that won't dissolve in the parrafin.
If the water gets real mucked up, repeat with clean water and more detergent.

Will also remove the paint, so you'll have to repaint it.

Did wonders for mine.

When I first got my Dexta she wouldn't rev past 1450 rpm. Opened up the pneumatic governor and found that the spring had rusted through at one point and thus failed. Had a new spring made as replacement ones were not available then, and has revved fine since.

This might be worth checking.

Regards
John

Commander, were you suffering from similar problems before carrying out your cleaning?

Yes, not quite as bad as yours though...Mine would rev to about 1800
rpm before, to 2200 after cleaning.

I had previously rebuilt / replaced pretty much everything...a complete
teardown and engine rebuild, rebuilt injectors, new diaphram in the
governor.......it was in my case the last 'missing' piece to getting it running like it should.

I had soaked my cleaner in mineral spirits ( I have a parts washer that uses it).......read on here that boiling it in hot soapy water would clean it out thoroughly.

makes sense and I should have thought of it anyway.....(I have worked at a drycleaner). chemical solvents (kero, parrafin, paint thinner, perc) tend to be good degreasers, but not so good at plain old dirt.

Boiling mine loosened up dirt, grass seeds and so forth that the degreaser left behind.

That is if the rev counter is correct then

BTW which models revved at 3000rpm ?

The ones with external pistons and rods

In general, none of the tractors went over 2100/2200rpm.

BTW which models revved at 3000rpm ?

Did the 3000 number come from the information page on this site?
(A little high but keeps the 135 boys awake! )

Our '62 Super Dexta runs up to 2400 but was fueled to match the New Performance Super Dexta when the pump was in the shop some years back.
And in the June/63 Nebraska test for the Super Dexta it was high idling at 2417 but it posts the rated rpm at 2250 and rated Hp at 39.5 so the test must have been for the standard Super Dexta.

Some versions of the Perkins 152 engine were made to run at 3000rpm (maybe the turbo version on a compressor.)

Les

landowner wrote:That is if the rev counter is correct then

I can't say this is a scientific measure, but I have reved another 3 cylinder ford/fordson tractor alongside the dexta and it sounds as though the two match.

i once had a problem with one of my dextas that wouldn't rev above 1800 , i found out that the pre cleaner was to blame i opened up the fins with a screw driver a little and it now revs at 2250

dexta4 wrote:i once had a problem with one of my dextas that wouldn't rev above 1800 , i found out that the pre cleaner was to blame i opened up the fins with a screw driver a little and it now revs at 2250

How wide did you open the fins? My dad took a shine to the tractor a few days ago and he tweaked the fins, it made a marginal difference...

So, today I spent a little time searching for clues. I removed both ends of the vacume pipe and blow through with an air line. All was clear. I then took a deep breath and removed the pneumatic governor cover... Again all seemed well. There was a very little moisture in here, could it be fuel? would that indicate any problems?

I also found the gauze filter on the side of the injector pump. It was solid with muck! I rinsed with parafin, set light to it, and blasted with the air line.

All went back together fine. I have a few questions...

Can the diaphagm perish? There were no noticable holes etc but that might not mean it's airtight...

Should there be a gasket between the two surfaces when you refit the governor cover? Without one, I very much doubt that the governor can be airtight...?

Although I pleased that I cleaned out the filter and checked other areas over today, I've still not achieved any more revs!!!

Hi, I am speaking from experience on a fe***son here, but yes the diaphragm can and does perish, and should NOT have holes in it!
If it does however have holes, it would make it rev higher.

Regards,

I can think of a fairly long list of problems that will keep one from reaching full power/revs. Your statement in the first post that it revs fine with the air cleaner hose disconnected leads me to believe that there is excessive restriction in the air cleaner or possibly in the hose.

I have found wasp nests, mouse nests, acorns etc in the oddest places in old cars , tractors and so forth over the years. People sometimes leave equipment sitting around partially assembled and the critters get in.

Is the air cleaner really clean? Pull the hose off at the cleaner and see if you see any thing clogging up the works.
Is the hose clear? Collapsing under vaccuum?

There are throttle stops (screws) on the manifold, for idle and WOT. The WOT stop may be screwed in to far and holding throttle plate back.
Problem with the throttle linkage? Does the throttle plate go to (near) wide open when you pull the throttle lever back?

Pull the side cover off the injector pump housing. Do not attempt to adjust anything inside this cover or you'll have worse problems With engine off, the spring in the governor should push the rack to full stop (max fuel delivery).
Pulling the stop cable should move the works in the opposite direction.

Poor fuel flow......clogged strainer in the tank , clogged main filter, worn delivery pump, kinked or clogged up fuel line.

Problems with one or more injectors, or with the injector pump. These tend to cause clouds of black smoke and/ or very rough running. Does it start up smoothly on all 3 cylinders?

No , or very low, compression in one cylinder. Again ,would tend to run very rough. ( a hole in a piston, or badly burnt valve).

Thanks fo such an exhaustive reply commander!

commander wrote:Is the air cleaner really clean? Pull the hose off at the cleaner and see if you see any thing clogging up the works.
Is the hose clear? Collapsing under vaccuum?

The air cleaner certainly has no small mammals residing inside. I've not taken notic of the hose, will watch for collapse. It certainly isn't original...

commander wrote:There are throttle stops (screws) on the manifold, for idle and WOT. The WOT stop may be screwed in to far and holding throttle plate back.
Problem with the throttle linkage? Does the throttle plate go to (near) wide open when you pull the throttle lever back?

All is well in this area. I understand the throttle stops. Throttle plate is wide open, no problems with the linkage...

commander wrote:Pull the side cover off the injector pump housing. Do not attempt to adjust anything inside this cover or you'll have worse problems With engine off, the spring in the governor should push the rack to full stop (max fuel delivery).
Pulling the stop cable should move the works in the opposite direction.

I'll take look, thanks for this.

commander wrote:Poor fuel flow......clogged strainer in the tank , clogged main filter, worn delivery pump, kinked or clogged up fuel line.

I suspect I have a rather dirty tank, and maybe the strainer is a bit clogged. It's on my to-do list when my new primer tap and filter arrive.

commander wrote:Problems with one or more injectors, or with the injector pump. These tend to cause clouds of black smoke and/ or very rough running. Does it start up smoothly on all 3 cylinders?

Generally the tractor runs very smoothly. However, not so easy to start now that we're past the best of the summer.

commander wrote:No , or very low, compression in one cylinder. Again ,would tend to run very rough. ( a hole in a piston, or badly burnt valve).

As above, runs very well in general.

Again, thanks for your help, I've got a few more clues now...[/quote]

My Super Dexta was hard to start and would not rev. Addicted to ether.

When I pulled the engine apart I expected the piston rings to fall out but all was ok.

The culprit was the injector pump. Three broken springs and the bearings had collapsed. Cost me a fortune.

I have rebuilt the engine anyway but all along it was only the injector pump. The ether also cooked the injector tips.

Steven

So...

Cleaned fuel tank. Installed new tank strainer. Renewed fuel filter.

No change.

Tomorrow I was going to check injector pump timing.

Can anybody tell me how to check for wear in the fuel lift pump? From memory, the plunger can be depressed approx. half way through it's movement before any resistance is felt. Does this indicate wear? It looks to have a relatively new diapragm.

Thanks again in advance on any further comments.

Sam

Try it without the air cleaner pipe to manifold on before you spend too much money. Go easy on the throttle though.

ello

when i've cleaned oil bath filters i've used my hot washer set high - hot 80 - 90 *c
run it through both ways un till it comes clean , best to jam the houseing against something or ull be chasing it around the jard lol
u WILL get filthy doing it , and wet , but its worked for me .

the heat brings of the paint too .

i bet the boil method will work better, but i'd be shot if i did that in the kitchen