LM3 jetting

[fossilrider]

Hey Guys, Fossil (Steve) here. Back in September, I bought a very nice "83 LeMans III and am very proud to own such a nice example of such a great model Guzzi. I have only had the opportunity to get it out maybe 6 or 7 times and never for more than 40 miles or so at a time. I love most everything about this bike (realizing, as a fellow told me about a LM 1000 I bought from him a few years ago, "it's a MANS bike". Of course he was referring to the throttle pull, reach to the levers, muscle needed to maneuver with the short bars etc.). The only issue right now that I would possibly like to address is the fine tuning/jetting. Cold blooded seems to be standard fare here, which I can live with, but even after fully warmed up there are a couple hesitation/stumble spots in the rev range. The worst seems to be in the 2000-3000 range. The question I have is: am I asking this bike to do something it won't do, or should it pull through this range cleanly, with some authority? I don't remember the LM1000 having this issue. Maybe it is me, since I also have a Griso1100 and am possibly trying to compare the two. I haven't synced the carbs or opened the carbs to see what is in there for jetting. I'm just fishing before I dive in. Any help would be appreciated. Foss

 

[Stevex]

Although I have the LM2, not the 3, I've read a lot about the 3 on another Guzzi website.
The 3 is fitted with the lean burn carbs but some (previous) owners for whatever reason seem to think that jetting them as per the LM or LM2 is the way to go, performance wise. Apparently not...it turns the 3 into a dog.
First thing I'd do is check that all your carb internals / settings are as Guzzi intended for the 3.
You describe the same symptoms I've read about when incorrect jetting is installed in your bike's carbs.
Although the 850 Guzzi really needs to be kept above 4,000 rpm, it should still pull cleanly from lower rpm in the low gears.

 

[john zibell]

In addition to what Stevex has said, another thing top remember with Carb bikes unlike FI bikes, the slower you twist your wrist, the better she will pull.

 

[Tony F]

Hi Steve

You may well have the lean burn carbs. Do you have a copy of Guzziology? There is a section on un-Americanizing your carburettors.

Check the timing and carb balance ffirst.

Is the stumble related to revs or throttle opening ? Put some masking tape on the twist grip and switch block and mark the fractions of throttle openings so you can see when/what is actually happening.

What ignition system are you running? If it is using the standard mechanical advance is this advancing correctly?

Set up properly it will pull like a train from idle but it may require some work.

Regards
Tony

 

[Bigbear]

I agree with Tony,
My 1100 carby Sports is ex USA & came with the small outlet Lacrafoni's, a mistral crossover and needles & jets that meant at least 2 minutes warm up before she would even pull away from standstill, & was still lean with the needles raised.
The Guzziology book is invaluable, and after reading it saw the problems they had with the pressurised airboxes.
The author mentioned a jet/ needle combination that a UK reader had suggested, & it just so happened the bike came with a box of needles/ jets that had exactly what was mentioned.
Changed them & presto 70% better but still needed warm up with steady throttle or it would stall.
Then got a pair of vacuum gauges & synced the carbs after a good clean & added iridium spark plugs - 80% better.
Raised the needles after a long run that suggested still running a bit lean - 90% with a clean ( not lean) burn which would have being fine, but I couldn't see how the mistral crossover (with its opposing pulses )was better than the "can" Dr John designed & said gave more Hp gain than any engine mod.
Bought one on eBay & hey presto instant start up without any stalling on throttle & runs 100%.
The bike is so turbine smooth now so much you would consider it injected; on long trips riding in 4th at just over the speed limit it will return 48mpg.
Get the book, have a read & a play - you can do it!

 

[Tony F]

Hi

The following table of Euro and US jetting spec for the LM3. Ive also added the specs I copied many years ago from the owners manual of my friend's LM3 which, curiously, differs from both specs in the needle jet size.



Some differences there!

Tony

 

[not-fishing]

I'm in the process of "sorting out" an '82 V50-III jetting where the only mod was worthless cheap pod air cleaners and here's what I found.

First check your intake manifold gaskets and just replace them. At a buck apiece they're pretty cheap. One side of the V50 had a 1/2 thickness full ring then a 1/4 thickness half ring.

I next got rid of the torn cheap Chinese pods and got a set of K& N's.

Stock jetting on the V50 phbh 28 carbs was 48 (pilot) or Idle jet with 118 main and needle at 2nd position (from the top) needle.

A V50 Monza owner in Europe told me he used 55 (pilot) idle jet, 130 mains and 1st position needle which work great for him (K & N's and Monza exhaust).

I like to do things in increments so I first ran 50 pilot, 122 mains and left the needle alone. Still a lot of boggieness off the line so my next big jump was needle in the last position (4 or 5?). Big difference!

My revision last Sunday was 54 pilot, 125 mains and needle in the 2nd position. On a "Salmon Falls" run yesterday the little goose was really starting to sing.

I dusted off my old ('70's) Heathkit exhaust analyzer and tonight I'll see what it says. Then I'll decide which pilots and mains to buy.

Of course without a dyno I'm still guessing but at least I can get her close.

I know the mains & pilots do affect the 1/4 - 3/4 throttle but just moving the needle made a big difference.

 

[fireflyr]

I asked a similar question on another website and Pete Roper had this advice for an '84 LMIII:

"As for jetting? Whip the bell crank off the top of a carb and lok at the atomiser orifice. If it has a horse-shoe shaped shroud around the atmospheric side of the atomiser about 5-8mm tall it's got the 'Lean Burn' carbs, (It should do.). If this is the case try AB 268 atomiser with a K18 needle on the second or third notch, 120 main, 50-53 pilot and a /5 slide. Don't worry too much about the pumps. I usually turn 'em off. With a 50 slide it's a bit richer off idle than with a 60 and less prone to stumbles."

I haven't had mine apart yet but there is a slight hesitation, or rather a bit of a lag at 5000 to 5300 then the freight train is back on. At 6000 it's hold on to your hat. I really don't think I will change anything but it will be interesting to see what's in the 32 year old DelOrto's.

Pat

PS I still not sure what that all means.......

 

[Jim Pavlidis]

Hi Guys
I have a mark 3 with staintune exhausts and air pods I have 120 mains 60 pilot (does not idle with 50s )K18 needle on 3rd notch and 265 atomisers.My problem is it takes 2 to 3 kilometes to warm up and idle once warm it flies.Funny enough when i park it in the garage and i let it idle the generator light goes on but still idles.The left hand plug is running slightly rich and the right plug slightly lean.I havent been able to go for a long run due to covid.Any suggestions eg carbs or timing it still has points the air filters are no name brand.
Cheers

Jim

 

[john zibell]

Hi Guys
I have a mark 3 with staintune exhausts and air pods I have 120 mains 60 pilot (does not idle with 50s )K18 needle on 3rd notch and 265 atomisers.My problem is it takes 2 to 3 kilometes to warm up and idle once warm it flies.Funny enough when i park it in the garage and i let it idle the generator light goes on but still idles.The left hand plug is running slightly rich and the right plug slightly lean.I havent been able to go for a long run due to covid.Any suggestions eg carbs or timing it still has points the air filters are no name brand.
Cheers

Jim

Are the carbs synchronized? Are valves set to Spec? Not uncommon for the charging light to go on at idle if it is low. Idle should be 1000 to 1100 RPM.

 

[Jim Pavlidis]

Are the carbs synchronized? Are valves set to Spec? Not uncommon for the charging light to go on at idle if it is low. Idle should be 1000 to 1100 RPM.

Thanks John,
Did the valves about 1000 ks ago carbys are synced but need syncing regularly but I feel its the routing of the accelerator cables.In regards the charging light it is ok when I ride and stop on the road its only when i go into the garage and let it idle before turning it off the light will go on most times .In regards the plug colours would it be valves the synchro of the carbies or a combination of both.Any proven method you know of for routing the cables

Thanks
Jim

 

[john zibell]

Just route the cables so they are not stressed, no sharp curves, and avoid tie wraps. They need to have some movement. I haven't seen a MK III in some time. Does it use a plastic cable splitter on the throttle cable?

 

[Jim Pavlidis]

Just route the cables so they are not stressed, no sharp curves, and avoid tie wraps. They need to have some movement. I haven't seen a MK III in some time. Does it use a plastic cable splitter on the throttle cable?

Hi John
The mark 3 dosen't use a cable splitter . I have the cables routed straight from the throttle to each side of the tank on top of the quarter fairings.the left side cable seems longer than the right one. Do the cables need to be routed under the tank through the top parts of the frame as suggested by some owners.
Regards
Jim

 

[john zibell]

Do the cables need to be routed under the tank through the top parts of the frame as suggested by some owners.
Regards
Jim

Yes it helps. Route toward the center then out to each side. Are the cable new? New cables experience stretch until they settle in.

 

[Jim Pavlidis]

Hi guys

john thanks for your help and sorted the issue however on another note I fully recharged the battery as it went dead.Bike started fine however backfired on acceleration.When idling in neutral and rev a bit over 2000 rpms and more the left exhaust was backfiring loud with flames coming out the rear of exhaust.I rechecked all battery terminals the leads and spark of both plugs is good.Sounds like I may upset some wiring when removing and installing the battery. Any ideas? it would seem to be electrical what about the valves would it cause this.
Cheers
Jim

 

[john zibell]

You are burning un-burnt fuel in your exhaust. Check ignition wiring. You are not getting consistent firing of your spark plugs.

 

[Jim Pavlidis]

You are burning un-burnt fuel in your exhaust. Check ignition wiring. You are not getting consistent firing of your spark plugs.

Thans john
How do i check the ignition wiring does it go from the positive terminal to somewhere behind the connectors near the fusebox

 

[john zibell]

Thans john
How do i check the ignition wiring does it go from the positive terminal to somewhere behind the connectors near the fusebox

Asking that question tells me you need to take it to someone that understands ignition systems. Could be a bad connection or a failing part. Spark plug lead arching to ground. most anything could be your issue. If still running points a condenser may be going bad.

 

[Jim Pavlidis]

Asking that question tells me you need to take it to someone that understands ignition systems. Could be a bad connection or a failing part. Spark plug lead arching to ground. most anything could be your issue. If still running points a condenser may be going bad.

Thanks John will check the wires and connections