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Author Topic:   Throttle and/or rev. limiter
jokor3 posted 10-20-2003 04:57 PM ET (US)   Profile for jokor3   Send Email to jokor3  
Is there a throttle limiter on the 70 hp Yamaha? Also is the rev. limiter (if thereis one) adjustable?
Sal DiMercurio posted 10-20-2003 11:25 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
No, the rev limiter is not adjustable, it's there to prevent you from over reving the engine.
jimh posted 10-21-2003 08:18 AM ET (US)     Profile for jimh  Send Email to jimh     
On my 70-HP Yamaha engine, I don't recall reading anything in the owner's manual about an automatic "rev" limiter, nor do I see anything in the electrical schematic that would suggest there is one. I also don't see anything in the mechanical linkages that would suggest a speed limiter.

Perhaps my engine is too old (1987) to have this refinement. Pleaes describe in more detail how this works, is it electrical or mechanical, and where on the power head this device is located.

Moe posted 10-21-2003 09:30 AM ET (US)     Profile for Moe  Send Email to Moe     
Rev limiters on carbed engines are usually part of the electronic ignition module. On those where ignition module determines the amount of ignition advance, it's possible just to retard timing to TDC or later. Others do things like not charging/firing the coil every other power stroke, which can result in some backfiring of unburned air/fuel in the exhaust.

Those on EFI models simply quit firing the fuel injectors.

jimh posted 10-21-2003 09:07 PM ET (US)     Profile for jimh  Send Email to jimh     
If there is an automatic electronic speed ("rev") limiter on the Yamaha 70-HP outboard, I wonder why they make no mention of this in the operating manual?
Sal DiMercurio posted 10-21-2003 09:25 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
They make no mention of it because it's most likely in the power pack & theres nothing you can do to over ride it.
It's put in the engine so you wont blow it up by over reving & theres absolutly nothing you can do to change it, so why mention it.
It simply shuts your engine off when it reaches maximum redline.
Theres all kind of little goodies inside the dfi engines that we can't do anything about & theres no reson to even tell you about it because is something that can't & shouldn't be screwed around with, like a governor on a diesel engine, same thing except the diesel continues to run at max rpms where the outboard simply shuts itself off.
Moe posted 10-21-2003 10:22 PM ET (US)     Profile for Moe  Send Email to Moe     
It's usually 200-300 rpm past the redline on the tach, so most people don't ever know about it. Those who do experience it for the first time, usually look at the tach past the redline, and think, "OS, I've blown the engine!"

Then all becomes well again once rpms drop. Note that on cars, bikes, etc, these WON'T stop someone from downshifting to too low of a gear, letting the clutch out, and overreving the engine that way. Modern automatics have "stupid driver ignore" circuits and won't downshift until road speed is appropriate for it.

jimh posted 10-22-2003 11:19 PM ET (US)     Profile for jimh  Send Email to jimh     
I have a simpler theory: they make no mention of it because it is not there to mention.

Any other interpretation is much more complicated and makes huge assumptions. It is beyond comprehension that they'd have such a feature and not ever mention it anywhere. Please give a pointer to some place where this is mentioned by Yamaha.

Perry posted 10-23-2003 02:39 AM ET (US)     Profile for Perry  Send Email to Perry     
My motor is not a Yamaha but there is mention of the overrev limiter under engine features in the users manual. They do not mention how it works though.
mtbadfish posted 10-23-2003 03:38 AM ET (US)     Profile for mtbadfish  Send Email to mtbadfish     
Here is a page that shows Yamaha 60 - 90's as having an "Electronic over-rev Limiter" as a standard feature.

triblet posted 10-23-2003 10:34 AM ET (US)     Profile for triblet  Send Email to triblet     
With a modern electronically controlled engine, it's just
a little bit of firmware in the engine management computer
to provide a rev limter function. Since it will cut down on
warantee repairs from the hotrodders, it makes a lot of sense
to do it.


hauptjm posted 10-23-2003 03:35 PM ET (US)     Profile for hauptjm    
I was under the impression that all modern electronic ignition outboards had rev-limiters: DFI and carbureted.
Sal DiMercurio posted 10-24-2003 12:33 AM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
As far as I know, they all have them.
jimh posted 10-24-2003 02:57 PM ET (US)     Profile for jimh  Send Email to jimh     
The current manual for the Yamaha 70 HP engine (2004) does not appear to exlicitly mention over-rev protection, however the Yamaha website implies that this is part of the 2004 engine's features.


In as much as I don't have any written evidence from Yamaha about my 70-HP engine (1987), I don't really think it reasonable to just assume it has over-rev protection. Perhaps this feature was added to their product line more recently. I still think that if they have this feature it ought to at least deserve a mention in the owner's manual.

As for original author's engine, he failed to mention the model year and appears to have not contributed to this thread since his initial question. It is therefore hard to conclude that he has this feature, too.

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