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1983 Le Mans III

Sounds like a visit from the slap fairy is in order. I still don't think compression's related to your overfuelling though. If it runs fine over 3k it's not ignition. My bet's still on float level or needle and seat especially if you've been moving the tank around, you could have stirred up some crud that's stopping the needle from seating.
 
Series4 said:
Sounds like a visit from the slap fairy is in order. I still don't think compression's related to your overfuelling though. If it runs fine over 3k it's not ignition. My bet's still on float level or needle and seat especially if you've been moving the tank around, you could have stirred up some crud that's stopping the needle from seating.

I went at it again.
My big problem is that I tend to think that left jug is exactly the same as the right jug therefore the carb adjustments should be identical. (Right?)

Ya well this is what happened today.
Started everything off by backing 1.5 turns (on all 4 screws) on both carbs.
Brought it up to temperature and adjusted the throttle (slide) screw on the right.
My right cylinder definitely needed more air so I screwed it in giving a nice popping heard and felt with my hand on the R exhaust.
RPM increased a bit ….. balance it out by unscrewing the L throttle and got it to idle at +/-1100 rpm.

The plug’s colors are more/less the same. (Mine you I still had a noticeable heat difference between jug)

Readjusting the carbs caused my rpm to stay up there longer when giving full throttle.
The idle adjustment screws were left at 1.5 turns.

Later during the day I started it up again. (Didn’t touch any adjustments)
The right exhaust was popping more that the left side. (Reversed situation)
I was running out of fuel, turned off the engine, backed 1.5 turns on the 2 throttle screws on both carbs ….. restarted the engine, both were balanced.
(Kept the idle screws the same)

Your right
Gonna have to clean the fuel tank …. suspect the residue, crud is making the carbs do this!!!
 

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Good work, these problems can be frustrating to solve. I think the engine will also be happier on BP6ES plugs rather than the BP7ESs it has at the moment. Both my LM3 and T3 have BPR6ES and they're perfect.

BTW I've sold my LM3 (Rosanante) to a friend. I love the bike to bits and had a great Euro tour on it but I've decided I really want a LM1. I think the LM3 is probably the best of the LM series but I prefer the styling of the earlier bikes.
 
I’m still having difficulty tuning the LM3 on idle and hoping someone can point out what I maybe missing ….. actually only my right carburetor doesn’t seem to be responding on the idle (Mixture) adjustment. (The throttle stop screw reacts OK)
The Dellorto 36mm were rebuilt recently and I purchased identical 50 idle jets on both carbs. I thought that some crud may have gone into the carbs and clogged a jet or something but …..
I removed the bowl to check if the float was sticking, made sure the float’s needle valve was closing properly this was good. (Both have the same weight floats)
I checked the idle jet to see if there was any debris.
I blew some air between the inlet orifice, tapered mixing screw tip and the jet going to the bowl to make sure air pass-thru was good.
All seemed good!

Engine has no problem starting and when needed I can put the choke lever on and will idle at 2k. (Hearing both cylinders more or less balanced)
Once the engine is warm I try to balance the carbs on idle position by adjusting the throttle stop and mixing screw.

On my left cylinder both adjustment makes the engine vary in rpm and I can feel / hear the popping of the exhaust.
On my right cylinder I can adjust the throttle screw to hear the exhaust popping so to balance with the left …… but the idle adjustment does nothing at all.

Other words I can screw the mixture adjustment right in or take it completely out and it does nothing to the right side.

Another indication that I’m not balanced properly is the plugs ….. the left side is a little hotter that the right. (When I take them out)
I rev the engine to 6000-7000 without it missing a beat ….. so can’t be electrical.(Timing)

Any thoughts?

Thanks
 
Dan,

It is not uncommon for one side to be less reactive to the mix adjustment screw, but you should still get reaction. At this point, the only thing that comes to mind is a bad carb body (the one that doesn't react). It is rare, but I've seen it with Del' Orto and Bing carbs. If these are the original carbs at their age I'd look into replacing the one that won't adjust. Also if you have the correct pilot jet, the idle mix screw should be close to 2.5 turns out from fully seated. I'd consider 50s slightly on the small side as I prefer to use 52s or 53s in the LeMans series machines.
 
Whilst it is possible the carb body is the fault I think you are being a bit hasty John, considering Dan´s level of expertise.

I´ve read your process previously Dan and I´m not surprised at the result.

The mixture is probably not having any effect as it is being over ruled by something.

A few things to try:
1. Spray WD 40 over the inlet rubber and all joins. If the engine note changes then it is an air leak.
2. Make sure the throttle cable has slack and the slide hits the throttle screw when released.
3. Back off the throttle screws so it idles at well under 1000rpm. You can bump it up later.
4. Whilst idling pull one plug at a time. Make sure they run about the same each side and one side isn´t carrying the other. Adjust the throttle screws and again make sure the slide hits the bottom.
5. Starting the mixture screw at 1.5 turns out make bold 1/2 turn adjustments and wait and listen. In is leaner, out is richer. Go for the best idle. Once you have it to the closest 1/2 turn do 1/4 turn either way and go for the best.
6. At the same time hold your hand near the end of the exhaust. Hot is lean, cool is rich. You are feeling for a nice definite pulse in the change from warm to cold.
7. Once both sides are running as well as they can then re-do 4 and ensure both slides contact simultaneously. Adjust the cables until they do.

I´ve typed enough. I´m out of here.
 
Dan, I had a similar problem that was fixed by putting a tankful of spirited kms to good use. The poor thing's been wasting away in a garage, a decent gallop will work wonders.
 
I'll just add some thing to ponder. On my phf equiped t3 I removed the two tiny 'emulsion' tubes which if I remember correct are up under the idle jet in order to get the carbs to transition better up off idle. These tubes are pretty small and even hard to see.( Noted in guzziology for removal I believe)I wonder if you have only one or a blocked one.
I checked the idle jet to see if there was any debris.
I blew some air between the inlet orifice, tapered mixing screw tip and the jet going to the bowl to make sure air pass-thru was good.
All seemed good!
Something is stopping the right idle circuit from operating correctly. if the right is always(mostly)richer/cooler then its obviously getting more(Too much) fuel at idle so could you have a damaged idle screw seat ie oval, out of round, off centre, cracked or nicked or or or? Check by passing air down as you did before, with the screw turned home; do both and compare

I wonder if you removed both carbs and sucked on them in turn to see if one felt different from the other ....even blocking various openings etc

Can you do a temporary swap to the opposite sides? :whistle:

Oh! the BP7ES's are cold, I'd only bother with em if you are constantly blistering the BP6ES ones. I ran 5's for ages and they lasted well .with out too much blistering
 
Thanks
Spray WD40 gonna check for any vacuum leaks ...thats one thing I didn't think about.

To synchronize the throttle cables I unscrewed the throttle screw completely, gave a 2mm slack and listened to when both slides hit bottom at the same time (hearing the tock while swinging the grip) then after adjusted the throttle screws.

The state its in now the left side is carrying the other when the plug is pulled.
I definitely know the right is rich cause the head is cooler than the left and the right puffs out smoke.

I get the feeling I will have to take the right carb apart again.
Something tells me that there is an air restriction somewhere.
On a previous post I took the compression without full throttle and got 140psi on the left and 125 on the right. (full throttle 150 to 170psi each) .... the 125 right tells me it ain't sucking right.
And then I can check if I have a damaged idle screw seat ie oval, out of round, off centre, cracked or nicked or or or lke Kym suggested.
 
After 9 months or so of leisure work on the 83 LeMans3 I finally can say it’s finished.
I tried to keep the replacement parts as original as possible, ….. restoring this baby with the help of members here and MG cycle I like to thank you’s all.

I downloaded some pics of the final results ….. Cheers





Starts, Sounds and Rides beautifully.
 

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Man that is one sweet ride. I would love to get it on and scrape some knee pads. :evil:
 
I solved a running rich on right cylinder problem on my Mk1 lemans...I had tried every possible fix...6 months work.
The fix was replacing the 2 x slide needles!!!! they looked Ok but when I put in a new set the problem was solved..
It's a cheap fix and worth trying...Note they were k5 needles...steve
 
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