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HELP serious rich running problem

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HELP serious rich running problem

Postby Pops » Wed Jul 04, 2018 5:43 pm

Had to divert into Rochester Sunday due to major power loss which looks like serious rich running - ignition and compressions have been eliminated and its pouring out black smoke and miss-firing and won't rev past 2100 with things being worse on large throttle openings.

All the basic mixture stuff ruled out ie air filter, collapsed scat hoses,, main jet or needle dropped out, cold start jammed on, Carb heat stuck in etc.

My engineer stripped the carb with me today and apart from a little bit of debris in the cold start chamber it appears to be fine.

We refitted the carb, ( new inlet rubber as well because I had one) and its just the same.startes straight up,ran rough at all revs and really bad at higher revs and throttle settings

Any ideas? Mine is an early 2200 SK with the 32 mm carb. I've had it for 11 years and its up to 1200 hours and has never missed a beat before. currently unflyable and stuck at Rochester.

not been on the forum a for a few years - sorry folks
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Re: HELP serious rich running problem

Postby Steevo » Wed Jul 04, 2018 8:09 pm

Was this something that happened all of a sudden or something that got worse over time?

A carby doesn’t usually just go bang all of a sudden. In-fact, other than a blockage, there isn’t really that much to go wrong especially all of a sudden.

When you say compressions and ignition are fine, what were the compression figures. I assume it was a leak down test and not a normal compression test.

If the timing was out, this could cause this kind of behaviour but that would show up in a compression test and other symptoms, but that would be something serious to put the timing out such as broken flywheel bolts.

The carby could be flooding. I have recently had a few issues with my carby. This turned out to be a float issue. It was not immediately obvious but due to the issue, the float was floating low so raising the fuel level in the bowl causing a rich mixture. But even with that, all I got was lumpy running and black spark plugs.
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Re: HELP serious rich running problem

Postby Pops » Fri Jul 06, 2018 2:14 pm

Looking back I would say it’s been starting to run richer over past 4 or 5 hours but
Then got a lot worse. It’s definitely rich running not timing / flywheel etc
Had a message from Gary Cotterell who is now in NZ with a few pointers. Apparently engine
Breather problem or blow by pressurisation of crankcase a can cause the fuel pump to over pressurise. He says carb / engine very sensitive to this and can even stop the engin. Also he has advised that there
Is an airway that leads to the atomisation jet that blocks easily especially if carb heat is open

So things to look at

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Re: HELP serious rich running problem

Postby Steevo » Fri Jul 06, 2018 3:27 pm

Well Gary knows what he is talking about.

If the fuel pump was to over pressurize, then it would force the float needle valve to stay open creating a very rich mixture and flooding.
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Re: HELP serious rich running problem

Postby Matt » Mon Jul 09, 2018 11:28 am

what were the compression reading? If the compressions are good like you say then you don't have to worry about blow-by over pressurizing the crankcase. A blocked breather wont take five minuets to sort out. Have you checked the carb floats for sinking? You should perhaps check the output of your fuel pump. It will require a pressure gauge plumbing into the system. Could be over pressure as mentioned.
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Re: HELP serious rich running problem

Postby Pops » Thu Jul 26, 2018 8:52 pm

Carb ultrasonic cleaned and completely rebuilt with new float needle, floats weighed and heights re-set
Crankcase over pressure checked and eliminated as problem
Air filter, hoses etc checked
Fuel pressure eliminated as problem
Flywheel still attached !!

Any further ideas
Nb it's a solid lifer engine

Sadly it looks like I'm going to have to de-rig and trailer home so we can dig deeper although can't figure out what we might even be looking for.

Is there any way valve timing could slip? I can't see how.
What's chance of both ignition coils failing in same way simulataneously ? I will do a swap next just in case

As a reminder symptoms are:

Id.es and starts ok
Starts missfiring on part throttle openings at about 1400 rpm
On wider throttle opening will Rev up to about 2200 rpm with loads of misfire and black smoke
Then revs fall back to 1800 - more throttle is opened worse it is


At a bit of a loss to be honest

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Re: HELP serious rich running problem

Postby hobson » Thu Jul 26, 2018 10:14 pm

Have you tried running it without the airbox connected? Just briefly to ensure it is breathing correctly.
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Re: HELP serious rich running problem

Postby Steevo » Fri Jul 27, 2018 8:12 am

When you get to issues like this, anything is possible.

It's a bit down to educated guesses now until you discover the issue. A double coil failure is possible although unlikely that both behave the same way. Have you checked the coil gap?

Regarding the carb, you seemed to have overhauled it all but one of the things I didn't see mentioned was valve seat. If they fail, they can seal ok when you push the float up with your finger but when there is just a bit of fuel pressure they can leak causing a rich mixture.

Restricted airflow (as mentioned in previous post) you can check by removing the hose entirely.

Almost impossible the timing has slipped. It's not a belt or a chain like most engines, the timing is set in place by the flywheel bolts so even if 5 of the 6 bolts had failed, the timing would be held in place (not for very long but this would be obvious).

Other electrical items are dizzy caps, rotors and leads.

Fuel pump is also a source of problems that is not always easily detected. What fuel pressure are you getting (how was fuel pressure checked). The spring in the fuel pump can rust and when they do, they change the pressure within the fuel pump which can cause intermittent high pressure spikes (I have had this on mine causing very rich running or fuel starvation).

Failing that, you are then starting to look at the engine itself. Leaks around the induction system (try spraying some easy start around the induction system while the engine is running).

Then we go to sticking valves or leaky valves or sticking piston rings. But a proper leak down check should identify these unless it's intermittent or only happening when they are working hard.
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Re: HELP serious rich running problem

Postby diablo » Fri Jul 27, 2018 6:08 pm

Pops

dont de-rig yet ...

I would do a check on exciter magnets on flywheel.

Your bird is one of the first. Exciter magnets are known to go weak, the symptoms would be what you describe as it would be running on two cylinders. exciter magnets are known to lose they strength which would lead to misfiring and all sorts of other strange probs. Let me know if you need some, I have some spare ones in my goodies box.

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Re: HELP serious rich running problem

Postby Steevo » Fri Jul 27, 2018 7:05 pm

There is a pull test you can do on the magnets. I cannot remember the values, they are in the manual somewhere. They should hold a certain amount of weight. But probably easier just to replace them.

Now Dean has mentioned this, I remember having issues with the SPL-450 when I first purchased it and they came up on the inspection report. Mine didn’t give the issues you have but made it difficult to start. But they do affect the coils so since you mentioned the unlikely double coil failure, these magnets could easily give the impression there is something wrong with both coils.

Great suggestion Dino.

EDIT: Just found it. You should be able to pull 1.5kg-2.5kg against the magnet. If you use a metal suitcase weighing scale you should be able to test the magnet. Put the metal hook on the magnets and pull. If the scale gets to over 1.5kg before it detaches then the magnet is ok. Anything less than that then it needs replacing.
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