Author Topic: Air cooled design flaw on the 350?  (Read 929 times)

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LowEnd

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on: February 06, 2022, 10:00:19 am
I've posted this in the meteor threads but I wonder if any of the galaxy brains over here can chime in.

So I have this problem of the engine not instantly going into overrun/engine braking when riding in a "spirited" manner. The engine goes to idle instead of full overrun for periods between 3 and 20 (twenty!) seconds. The idle can be interrupted by pulling the clutch (without changing gears) or rear braking. It isn't predictable and is a dangerous design fault.

So all of you engineers and mechanics out there here's a possible explanation from a mechanical engineer who completed their masters on air cooled engines.

"The issue occurs after periods of high engine load suggesting that the engine temperature is higher than optimal. Air cooled engines only have one feedback mechanism which can control temperature and that’s to trim the fuel mixture rich. In a situation where the engine is above ideal temperature and suddenly has no load/closed throttle, it’s reasonable to expect that the ecu will take advantage of this to cool the engine as much as possible. The ecu is likely adjusting the idle speed to maximum and adding as much fuel as possible to achieve the maximum cooling effect in the minimum amount of time, therefore meaning the thermal headroom of the engine is raised again and engine wear is minimised. Liquid cooled engines, on the other hand, also have this mechanism however it's very rare that it would actually trigger. The oil/crank case temp of an air cooled engine will vary from like 80-140, but a liquid cooled one will be like 90-110, so you'd have to be absolutely slamming a liquid cooled engine to get it to do that."

Feedback wanted lads and ladies. What say you?  If this is just a part of the normal operating system of the meteor then its going to get cleaned up and traded in pronto.


Adrian II

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Reply #1 on: February 06, 2022, 02:41:46 pm
An ECU on a lean-burn Bullet? This is too fancy for us, I think we can just about get our heads around TCI ignition.  ;)

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AzCal Retred

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Reply #2 on: February 06, 2022, 05:59:50 pm
Here's a good start!  :o ;D  ( https://accessories.hitchcocksmotorcycles.com/accessory-shop/carburettor-kits/38529 )

Voodoo problems like this are why us old luddites like things we can see & understand. Didn't find an actual EFI conversion kit, so it would certainly be a voyage of discovery. The new 350 makes about the same HP as the old Bullet, so the 32mm Mikuni should be workable.

OR - mebbe the resident EFI champion Viczena would chime in, this is in his wheelhouse, he'd likely have some insights. He really likes EFI, maybe PM him?

A trifecta of Pre-Unit Bullets: a Red Deluxe 500, a Green Standard 500, and a Black ES 350.


richard211

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Reply #3 on: February 07, 2022, 09:21:11 am
It is an interesting observation, something that is really bugging me is that when engine braking, the engine goes to idle. That part does not make sense, as far as I know the Meteor 350 does not have a slipper clutch. Under engine braking was the throttle shut? If that is the case that could explain the engine going to idle, but that would highlight another issue, which could be the  gearbox. I suspect the gearbox is somehow going into a false neutral.


axman88

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Reply #4 on: February 07, 2022, 08:48:25 pm
I'm not sure what you mean by engine "idle", vs. "full overrun"?  I understand idle, but I'm not familiar with the other term.

I've experienced motorcycle engines failing to reduce revs with a closed throttle when they had air leaks in the intake after the point where fuel is introduced.  The extra air would allow the engine to over-rev. uncontrollably. 


Bilgemaster

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Reply #5 on: February 08, 2022, 12:29:51 am
I'm locking this redundant thread from further posts. It really shouldn't have been posted here anyhow, but rather only in the "350 Meteor/Classic" section.

Discussion of the matter at hand continues over there at https://forum.classicmotorworks.com/index.php?topic=32496.0

Merging the two threads would only cause disarray at this point, so say goodbye to this one!
« Last Edit: February 08, 2022, 12:34:37 am by Bilgemaster »
So badass my Enfield's actually illegal  in India. Yet it squeaks by here in Virginia.