Delta won’t Rev: air filter issue?

[fredthedog]

Hi all

My Dexta wouldn’t Rev, I checked the pump and diaghpragm and all looked ok.

I removed the cover from the injector pump and moved the rack sideways which does increase the revs.

Next looked at the air filter, if I removed the pre-cleaner/mushroom the revs do increase.
I’d checked oil level in the bowl (wasn’t far out or dirty), but with the mushroom removed, when looking down the vertical tube you can see displaced oil and feel the rush of air.

I have removed and cleaned the overall air cleaner assembly in and out (currently painting it) before I refit.

Note I have no second air filter mesh and the original 4.5” deep oil bowl are missing, the latter being replaced by an aftermarket blue bowl around 2.75” deep that also has an inner bowl.

I propose to methodically test when replacing, first with no bowl/oil, then add bowl (dry), then adding oil, also with/without the mushroom.

I welcome any comments or advice on what the issue may be! Am I missing something obvious? Thanks

[Daves rusty bits]

You say you`ve repainted the air cleaner, I would say check you havn`t coated the fins of the mushroom top with too much paint, presuming it ran well before. I bought a repro mushroom top for my power major and it cut the revs by 600rpm. Cleaned off a thick coat of paint from the underside of the top and the revs returned. Air needs a good slick surface to move over. Dave

[Billy26F5]

Be careful uncovering the pump as then there's nothing to keep the dirt out, also remember that controlling the rack directly needs to be done in the way the governor would do it to avoid an overspeed and damage.
Next check you can actually open the butterfly valve fully in order to check this, while you check that ensure the air hose is ok. Ensure the air filter is fully clean and also that all its parts are there and matching, sounds like the bowl is not the correct one for this filter. Also be careful with repro pre cleaners as they don't often follow the original design and can cause these issues and also fail to do their job (dirt can cause similar issues in original ones too). The short answer is that you need to find original parts where you don't currently have them. You must be able to reach 2200 rpm unloaded with the air filter in good condition and the pre cleaner in place and no leaks between there and the manifold. This should enable full fuelling at 2000rpm giving you the full 32 hp the Dexta has. You should never run without the air filter and pre cleaner unless you can be sure no dirt is in the air you're in, and then only to do tests of this nature if needed.
Sandy

[fredthedog]

Super advice, many thanks, the rack cover is on, i have cleaned the permanently installed mesh. I’ll te-assemble and test at different stages. Thanks for the 2200 revs info; most useful! More to follow!!!

[fredthedog]

Hi all, a brief update (and thanks for previous advice)....

So the history: this was a tractor ressurected so previous condition/working status is unknown!

Following the cleaning and refurb of the air cleaner (following the poor max revs issue), I've checked and the butterfly valve and hoses are OK. I obtained the following readings from the rev counter with the motor unloaded:
- With now oil bowl or precleaner fitted: Max revs 2400 rpm
- With bowl installed dry: no oil: Max revs 2300 rpm
- With bowl installed with oil: Max revs 2250 rpm
- With bowl (with oil) and precleaner fitted: Max revs 1650 RPM

So sounds like this may be the pre-cleaner (I have a long one and a short one, both give similar readings and feel like they are restricting the engine)

Welcome thoughts? Can anyone recommend a pre-cleaner/supplier that they know are ok?? Thanks

I'll get the Topper fitted and give it a try, tbh before fitting the precleaner it did rev and pull ok so i feel I have a diagnosis!

[Billy26F5]

Sounds like your pre cleaner is in trouble, the 50 rpm extra you have above the maximum speed without it gives you a reasonable idea of what it should be. The precleaner needs to be clean and in good condition, loose paint can also cause issues. Don't get a new one, they're known to cause such issues, and some are so poor they don't even clean.
Sandy