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 Compression braking?

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daniel_pww
Squinternotto
Squinternotto
daniel_pww

Posts : 4
Join date : 2021-06-07

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PostSubject: Compression braking?   Compression braking? Icon_minitime1Fri Jun 25, 2021 12:16 am

Compression braking?
Took my new-to-me (first Guzzi) 1100 GRiSO out for a good thrash tonight. It pulls well on acceleration, but surprised that when I let off on the throttle, the motor takes a while to wind down.

*When I let off on my FJR 1300, compression braking is instant & very significant.

Is weak compression braking a Guzzi thing (heavy flywheel) or is my throttle hanging up?

Out of gear, the engine seems to wind up & down fine.

Thanks in advance.
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Oz1200Guzzi
Don Abbondio
Don Abbondio
Oz1200Guzzi

Posts : 5167
Join date : 2014-03-13
Age : 66

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PostSubject: Re: Compression braking?   Compression braking? Icon_minitime1Fri Jun 25, 2021 1:35 am

Daniel, really depends on what your map is set up for. Some like it, others don't. Personally I like it, a lot. So much so, that I cut fuel completely below the lower TPS settings - I throttle off, engine braking, that is until you hit around 2600 rpm, where the idle circuit comes into play.

What map do you have? Perhaps Mark (Beetle) can steer you in the right direction?

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daniel_pww
Squinternotto
Squinternotto
daniel_pww

Posts : 4
Join date : 2021-06-07

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PostSubject: Re: Compression braking?   Compression braking? Icon_minitime1Fri Jun 25, 2021 7:07 am

Thank you,
New to Guzzi, never had to contend with map/ECU issues on my Japanese fours.

I did a first oil change yesterday & pulled the gas tank to investigate a vent line that had shaken loose.

After reinstalling the vent line (it's capped, left rear of tank) bike ran much better, but I def want to resolve this throttle / compression braking issue.

In gear or not, I believe any motor should immediately rev down when the throttle is closed.

I am brand new to Guzzi world, but it sounds like the ECU is not behaving as I'd like. Will have to chase this down.

Cheers
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Pete Roper
GRiSO Capo
GRiSO Capo
Pete Roper

Posts : 8111
Join date : 2013-05-29
Age : 64

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PostSubject: Re: Compression braking?   Compression braking? Icon_minitime1Fri Jun 25, 2021 1:09 pm

Something is definitely not right. What is the idle speed? If you blip the throttle at idle does it take an excessive time for the engine speed to drop? What speed does it idle at?

Has the throttle stop screw on the LH throttle body been moved? It should be plugged with yellow paint.

With the W5AM ECU as used on all the CARC series bikes the target idle speed is coded into the mapping and is controlled by an air over idle valve known as a stepper motor. The early steppers had an alloy body and were prone to jamming issues with the stepper valve in the body. This is most likely to occur if the owner insists on running the engine oil level at the 'Full' mark on the dipstick as oil will expelled into the airbox and from there through the stepper until the oil finds its own level, usually somewhere about mid way between the 'Add' and 'Full' marks on the stick. Treat that point as your 'Full' mark. Don't keep topping it up.

A gummy stepper can produce a host of problems but a high or hanging idle is the most common but the first thing to do would be to give the bike a full tune. The process has been well documented here so I won't repeat it but you will need a manometer of some sort, (The Morgan Carbtune is a decent and inexpensive option.) and the Guzzidiag suite of tools and cables or equivalent.

To me it does sound like something is amiss and given the age of the bike I would think it likely that someone who doesn't know what they were doing may of messed with the throttle bodies in an unhelpful way. Also if a previous owner has fitted an aftermarket air filter of the K&N type that will of been a disaster so check and if it has one piss it off quick and put the original paper type back in. It's a big twin. It should spool down quickly and 'Engine Brake' well on the overrun. Methinks you have some reading and work to do.

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Steak
L'Innominato
L'Innominato
Steak

Posts : 2909
Join date : 2013-05-28
Age : 56

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PostSubject: Re: Compression braking?   Compression braking? Icon_minitime1Fri Jun 25, 2021 2:27 pm

+1 on the Morgan Carbtune.

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2012 MOTO GUZZI GRiSO 1200SE

2013 MOTO GUZZI STELVIO 1200NTX - Orange Blossom Special

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lcjohnny
GRiSO Capo
GRiSO Capo
lcjohnny

Posts : 409
Join date : 2016-01-25
Age : 66

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PostSubject: Re: Compression braking?   Compression braking? Icon_minitime1Fri Jun 25, 2021 3:47 pm

All cheap vacuum gauges will vary slightly in absolute reading and response time.
I know that if you are careful this does not really matter
BUT
in my experience it does make the job of synchronising choke opening slower and more painfiul

so whether you use Carbtune or dial vacuum gauges I recommend buying a set of 4 and finding two that are pretty much the same response.

Jon

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daniel_pww
Squinternotto
Squinternotto
daniel_pww

Posts : 4
Join date : 2021-06-07

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PostSubject: Re: Compression braking?   Compression braking? Icon_minitime1Fri Jun 25, 2021 5:54 pm

Thanks for the feedback, appreciated!

Plugs, socket for inner, air filter.... all ordered & enroute.

*Always a line to walk, tool up (more) or get a quote on a 1x job Laughing

**Out again for a good run tonight. More I ride the bike, better it behaves (or is it me? Smile, bike had barely been run the year prior to my purchase). On the road bike seems to like idling (at stops) around 12-1500. Throttle off, slowing or down a grade, bike seems to still 'hang' on rpm drop.... HOWEVER at 2500 rpm the bike aggressively (as it should) compression brakes.

Made a video...
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