Having Idle Problems on the newly running 1938 S

[guzz...@gmail.com]

  Now it's time to address the idle problem I'm having with the S. When I started it the first time a shot of ether, full choke and it fired right up and ran great. After warming up for a while and removing the choke it became apparent that I needed to adjust the idle mixture. Well I've been doing that for a few days now with no resolve. Here's what I know, it runs fine, I can set the idle speed screw up to keep it running but it's too fast. As I lower it it backfires through the carburetor a little and then eventually quits firing and dies. When I screwed the idle mixture screw from 1 1/2 in or out it became apparent that it liked it in. The farther in I took it the faster the engine ran at a set throttle until it was bottomed. This tells me I believe that I need a different size idle jet. I'm not 100% sure if I should go larger or smaller. I replaced the existing idle jet, a 50, with a new idle jet of the same size just to make sure it wasn't clogged with the same outcome.

I found a 55 Pilot jet for a Falcone Sport in Italy but not sure that is the way to go. The metering screw is on the engine side of the slide, see picture, which means as you screw it in it leans the mixture, but it likes to idle with the choke on telling me it needs a richer mixture.

I have gone through passages twice and found a piece of fiber in the center hole at the bottom throat of the carb. See picture I 

[John O Regan]

There are very small passages that bring the tickover miixture up on the engine side of the throttle slide or under the leading edge of the throttle slide, check that these are clear

Check the fit of the slide in the carb body, needing choke could mean that theres a lot of air leaking around the slide

John

--
You received this message because you are subscribed to the Google Groups "Guzzi Singles" group.
To unsubscribe from this group and stop receiving emails from it, send an email to guzzi-single...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/guzzi-singles/ec24fcd1-b429-4654-a279-e674d522adeen%40googlegroups.com.

[Dave Knaack]

The backfire indicates it’s not getting enough fuel …. Float level, idle circuit or too much air leaking in ????

Sent from my iPhone

On Aug 3, 2022, at 4:24 PM, John O Regan <chate...@gmail.com> wrote:



To view this discussion on the web visit https://groups.google.com/d/msgid/guzzi-singles/CAGLq%2Bg%3DzazBUL6antVoz24faS6-1%3DPi9%2BrV%2BaPQqLLwwfHqAWA%40mail.gmail.com.

[Patrick Hayes]

On 8/3/2022 1:52 PM, guzz...@gmail.com wrote:
> The metering screw is on the engine side of the slide, see picture,
> which means as you screw it in it leans the mixture, but it likes to
> idle with the choke on telling me it needs a richer mixture.

I am not certain, but I believe this old carb will have an AIR metering
screw. Turning it in does not reduce fuel flow but rather idle air
flow. So, in becomes more rich and out becomes more lean. Your
performance with the choke on hints at this. Experiment and report back.

Patrick Hayes
Fremont CA

[Guzzi SVT]

Thanks Pat for affirming what I thought I was seeing but going with how normal carburetors work.

I have checked the tiny holes on either side of the slide and clean them out with tiny wires, a frayed bicycle brake cable, they get pretty tiny.

I looked at the slide slot and it seems to be clean enough.

I will use the smoke test, if I can get my brother to breath his cigar smoke into my carburetor mouth, and  the WD-40 test my father taught me when looking for a leaky cranky seal on my 120 Suzuki when I was a kid.  I know my machinest  did not replace the intake valve guide, saying it was in good shape. If it was too loose it would allow air to suck by it.

My brother has a set of jet files he used when he was tuning the carburetor on his 1979 turbocharged BMW. I may use these to open up the spare 50 pilot jet I have after making sure there's no intake leaks.

My brain is working overtime until I get this latest problem figured out.

--
You received this message because you are subscribed to a topic in the Google Groups "Guzzi Singles" group.
To unsubscribe from this topic, visit https://groups.google.com/d/topic/guzzi-singles/pk9vYMy4i7o/unsubscribe.
To unsubscribe from this group and all its topics, send an email to guzzi-single...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/guzzi-singles/b9ef221c-22ea-68fe-43de-a41ad40da736%40comcast.net.

[Roger Rowland]

Hi assume you have a manual advance/ retard when ticking over this should be 6 to 8 Degrees crank, when you close the advance is anything happening? Air leak manifold? Float level ? As for jets did it run well on these ? If so why’s it changed 

        Regards Rog England 

Sent from my iPhone

On 3 Aug 2022, at 22:31, Dave Knaack <fastgu...@gmail.com> wrote:

The backfire indicates it’s not getting enough fuel …. Float level, idle circuit or too much air leaking in ????

Sent from my iPhone

On Aug 3, 2022, at 4:24 PM, John O Regan <chate...@gmail.com> wrote:



There are very small passages that bring the tickover miixture up on the engine side of the throttle slide or under the leading edge of the throttle slide, check that these are clear

Check the fit of the slide in the carb body, needing choke could mean that theres a lot of air leaking around the slide

John

On Wed, Aug 3, 2022 at 9:52 PM guzz...@gmail.com <guzz...@gmail.com> wrote:

  Now it's time to address the idle problem I'm having with the S. When I started it the first time a shot of ether, full choke and it fired right up and ran great. After warming up for a while and removing the choke it became apparent that I needed to adjust the idle mixture. Well I've been doing that for a few days now with no resolve. Here's what I know, it runs fine, I can set the idle speed screw up to keep it running but it's too fast. As I lower it it backfires through the carburetor a little and then eventually quits firing and dies. When I screwed the idle mixture screw from 1 1/2 in or out it became apparent that it liked it in. The farther in I took it the faster the engine ran at a set throttle until it was bottomed. This tells me I believe that I need a different size idle jet. I'm not 100% sure if I should go larger or smaller. I replaced the existing idle jet, a 50, with a new idle jet of the same size just to make sure it wasn't clogged with the same outcome.

I found a 55 Pilot jet for a Falcone Sport in Italy but not sure that is the way to go. The metering screw is on the engine side of the slide, see picture, which means as you screw it in it leans the mixture, but it likes to idle with the choke on telling me it needs a richer mixture.

I have gone through passages twice and found a piece of fiber in the center hole at the bottom throat of the carb. See picture

<IMG_20220803_151815984.jpg>

<IMG_20220801_082326233_2.jpg>

I 

--
You received this message because you are subscribed to the Google Groups "Guzzi Singles" group.
To unsubscribe from this group and stop receiving emails from it, send an email to guzzi-single...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/guzzi-singles/ec24fcd1-b429-4654-a279-e674d522adeen%40googlegroups.com.

--
You received this message because you are subscribed to the Google Groups "Guzzi Singles" group.
To unsubscribe from this group and stop receiving emails from it, send an email to guzzi-single...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/guzzi-singles/CAGLq%2Bg%3DzazBUL6antVoz24faS6-1%3DPi9%2BrV%2BaPQqLLwwfHqAWA%40mail.gmail.com.

--
You received this message because you are subscribed to the Google Groups "Guzzi Singles" group.
To unsubscribe from this group and stop receiving emails from it, send an email to guzzi-single...@googlegroups.com.

To view this discussion on the web visit https://groups.google.com/d/msgid/guzzi-singles/45A622CC-C429-4291-A1B1-215302072954%40gmail.com.

[Don West]

My little Stornello will only run on a Champion N12 spark plug, this has a particularly long projection nose style of plug.  It will start on the recommended N5, but won't rev. 

It might be worth trying a few different plug styes if, like me, you have a selection in a drawer.  

Don

--

You received this message because you are subscribed to the Google Groups "Guzzi Singles" group.

To unsubscribe from this group and stop receiving emails from it, send an email to guzzi-single...@googlegroups.com.

To view this discussion on the web visit

https://groups.google.com/d/msgid/guzzi-singles/CAJs29jgYj-jvQNskZ%3Dz-AxruXJzRZHoHk_0gnkCsWBNho6eM8Q%40mail.gmail.com

.

[Richard Wood]

Carbs do wear over a long period of time but given the mileages these old bikes do now I doubt that wear is the issue if they were running fine within recent memory.

Correct float level is a good starting point otherwise you are robbing Peter to pay Paul adjusting idle mixture by other means. Having said that I haven't found float settings documented. I would try therefore, assuming the idle mixture adjustment is an air screw,  the 55 jet as it's an easy swap and your symptoms all point to weak idle mixture. All things being equal you should be then able to back out the airscrew from fully in for best/better idle speed.

In the case of my Airone the air screw adjustment is still not very well defined but it does idle and now starts first kick with a tickled carb and quarter throttle, with choke set according to ambient until after a minute or two of running to ensure pick up. At very low idle speeds retarding a little from full advance helps otherwise that remains on full. I put this down to the highest octane fuel I use to avoid ethanol.

What cured the blocked idle circuit previously inhibiting starting and idling was cleaning out the fine idle air bypass drilling on carb mouth with narrow plastic wire.

Richard

[Guzzi SVT]

I picked up the bike last October at barbers and it hadn't run in over 30 years since dropping an exhaust valve. I spent the winner cleaning everything up and just got the magneto back before I started it. Timing is from 0 to 30°. I'll be looking for any kind of vacuum leak with a smoke test or some other form of air leakage. Who knows maybe bubbles. I started at zero timing and advance it for idle. I push it to full advance while driving. I found out the difference while driving and seeing that the advance said retarded some so I pulled it back and felt the definite power shift in the engine. So I tightened up the advanced screw to keep it from self-adjusting while I rode. It does seem funny that the stock 50 jet isn't correct for this engine so I'll be looking for other problems before messing with it.

You received this message because you are subscribed to a topic in the Google Groups "Guzzi Singles" group.
To unsubscribe from this topic, visit https://groups.google.com/d/topic/guzzi-singles/pk9vYMy4i7o/unsubscribe.
To unsubscribe from this group and all its topics, send an email to guzzi-single...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/guzzi-singles/033BE46C-7C7C-4985-A547-108CCA64BF17%40btinternet.com.

[Rick Yamane]

This is similar behavior to my GTV. I have other things to tackle but I was writing it off to a worn slide. This is a problem quite common in old Amal concentrics, seems less so in the old Dellortos but not unheard of.

There are companies sleeving the Amals and also changing to a brass Mikuni slide.  
The worn valve guide is a new one to me but makes sense. I guess on more modern engines with enclosed valve trains this would become less pronounced because it would be pulling in crankcase vapors and oil, not air alone.

The Jikov conversions talked about earlier were interesting but having dealt with lots of Jikovs on CZ and Jawas I think parts for those would be even tougher than Dellorto parts to find.

 

Rick

 

[Alan Comfort]

Brand new "Made in India" 26 mm Jikov carburetors can be bought on eBay for around $75, but if you are going the non-original route I think that a Mikuni will be a better choice. It will cost more than a Jikov and you will need to buy a range of jets to get it dialed in, but the end result is worth it.

Alan in Roberts Creek

--

You received this message because you are subscribed to the Google Groups "Guzzi Singles" group.
To unsubscribe from this group and stop receiving emails from it, send an email to guzzi-single...@googlegroups.com.

To view this discussion on the web visit https://groups.google.com/d/msgid/guzzi-singles/BYAPR18MB2821F8749B7C79C90704C458D59F9%40BYAPR18MB2821.namprd18.prod.outlook.com.

[jerry atric]

Valenti in italy bores the dellortos and fits over-size slides. Look on the bottom of the slide, the over size ones are marked with a +10 (1mm over I think) I bet that solves the problem. Or, as mentioned, the Jikov🤮

[Richard Wood]

Reminds me of an Italian company Cassa del Carburratori in Modena I believe. The name says it all but they provided me with a pair of 40mm pumper Dellorto's bored out to 41mn for an 1105cc V twin special I built up back in the day. Not sure if they are still trading.

Richard 

You received this message because you are subscribed to a topic in the Google Groups "Guzzi Singles" group.
To unsubscribe from this topic, visit https://groups.google.com/d/topic/guzzi-singles/pk9vYMy4i7o/unsubscribe.
To unsubscribe from this group and all its topics, send an email to guzzi-single...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/guzzi-singles/185deead-8ad9-4f62-b82d-07bf4aeacde3n%40googlegroups.com.