Pinging

[zach]

Hi
You have similar issues to those I had with my high compression LM engined SP.
What did you set the squish to and what is the compression ratio set at?
What ignition system are you using? If you are using the standard mechanical advance, is it working correctly? New springs may be worthwhile as they are probably >30 years old.
If you have 36mm carbs to fit it may not be worth putting much effort into setting up the 30mm carbs.

Tony

Tony, how did you resolve the issues with your bike?

 

[guzzigray]

Really??? Yeah I'm using the stock heads... Are you sure about that? I know they have larger valves but larger chambers???

Can you concur John?

Larger valves = larger chamber. A Lemans chamber is approx 60cc.

 

[zach]

Larger valves = larger chamber. A Lemans chamber is approx 60cc.

I believe you but I would not assume that... It's not like the mid size valves are much bigger. It's possible there would be enough room without enlarging the chamber for the larger valves. I bought a compression gauge today to see what I am running.

 

[guzzigray]

Sorry to be persistent but Guzzi enlarged the mid valve head combustion chamber for a reason. 44/37 vs 41/36. There's a big enough difference there to need a bigger chamber. Not only piston to valve but valve to valve.

 

[zach]

No need to apologize! i really appreciate your input. I couldn't find and information on that when I began the project.

I took it to work today after lowering the idle a bit and it shut down fine twice.

I was talking to one of my buddies today about my dieseling problem he said "oh that's what that sound is? Mine(1100 sport) does that occasionally and I just though it was some sound of endearment like it was telling me "we made it!" And he said he would respond by saying something like "good Guzzi!"

Lol

I need to know what I would be looking for with my compression test. I have heard an 850 LeMans was around 210...

 

[john zibell]

Compression pressure depends on compression ration, the condition of the engine, and the gauge. Standard Guzzi engines run about 150 to 170 psi on my gauge. An atmosphere at sea level is about 14.5 psi. Take the pressure you read and divide it by that number and you will get your approximate compression ratio. 210 psi is diesel compression range (14 to 1 up to 25 to 1) at 203 to 362.5 psi.

 

[zach]

Went out today to run the compression test and found the right side was putting out an easy 150 and the left went to 125 after more cranks... The spark plugs have changed a bit as well. Not sure if I uploaded right but the one with the dark threads is the left one

 

[john zibell]

Hopefully you had the throttle wide open. There should be no more than 10 psi difference between cylinders. You have a problem on the low cylinder. A leak down test can tell you if it is valves or rings. To get a good indication on the plugs, you should be shooting against a white background, and we need a better view of the center insulator, that is angle the end up.

 

[zach]

Ugh Actually I forgot to hold the throddle open... I just wanted to show the threads which show that the left side got hoter than the right recently... I will have to charge the battery before I run the test again...

 

[zach]

Ok! Sorry it took so long. I did the compression test properly and found both sides were putting out about 190psi. So that would mean I have a 13 to 1 compression ratio? After talking with a friend of mine who owns a cool moped/motorcycle shop(who is actually familiar with old bikes) he advised me to try turn my idle down a little. It was not really set high but I though I would give it a try. After that I have not had any dieseling.

I am going to go back and make sure that my carbs are properly balanced as I haven't don't for a little while.

I am thinking about buying a wide band oxygen sensor from Innovate. The Lm-2 has obd-ii capabilities so it would be useful for my car as well. I think it would be handy to have if I want to set up different carbs in the future.

 

[john zibell]

13 to 1 is pretty high. That is higher than any stock Guzzi, and nearly enough to make your engine a diesel. I'd be concerned on what the combustion pressures would do to your engine. I'm sure it can take it, but it might accelerate wear. Be sure to put in only the highest octane fuel you can find. With that compression ratio, 100 octane aviation fuel wouldn't be out of order. In the old days, Sunoco stations had a 99 octane that my old T and T-3 ran really well on.

 

[guzzigray]

I believe you but I would not assume that... It's not like the mid size valves are much bigger. It's possible there would be enough room without enlarging the chamber for the larger valves. I bought a compression gauge today to see what I am running.

According to Guzziology and measuring heads I have kicking around, Lemans 1 combustion chamber is 1mm deeper and 2mm wider…..

 

[zach]

According to Guzziology and measuring heads I have kicking around, Lemans 1 combustion chamber is 1mm deeper and 2mm wider…..

Defin

According to Guzziology and measuring heads I have kicking around, Lemans 1 combustion chamber is 1mm deeper and 2mm wider…..

Thank you, you have been very helpful. It makes sence that they would be larger.
You mentioned that you have been kicking around some heads???

 

[guzzigray]

Defin


Thank you, you have been very helpful. It makes sence that they would be larger.
You mentioned that you have been kicking around some heads???

Sorry, UK Englishism : kicking around = lying around.

 

[zach]

Haha I know. My curiosity is sparked because I might be interested in some "kicked around" not being used heads lol

 

[guzzigray]

Haha I know. My curiosity is sparked because I might be interested in some "kicked around" not being used heads lol

I only have mid valve square fin heads kicking around…..

 

[zach]

According to Guzziology and measuring heads I have kicking around, Lemans 1 combustion chamber is 1mm deeper and 2mm wider…..

Hey so would you say its and even 1mm bigger all the way around? I am thinking about opening up up my chambers and eventually fitting larger valves. Possibly this winter

 

[Chris R]

What heads are you using ?? If they are SP they have a smaller combustion chamber than a Lemans which the new pistons are designed for…..SP heads and Lemans pistons will be very high compression. Timing for the Lemans is 8/34. Something to consider

The SP heads use the same casting as the lemans heads but the combustion chamber is set about 2mm deeper i.e. the static compression ratio will be slightly lower with the SP heads. The intake valves on the lemans are slightly larger but in fact the flow is worse than the small valve heads. The lemans performance comes mainly from its higher compression, carbs and cam. What John said: set the squish tight - like 30-40 thou. The improved squish is the one advantages of the large bore kit from gilardoni - the standard heads don't really breathe well enough to take full advantage of the extra capacity.

You will need to recurve the timing to a maximum 36 degrees of advance.

Do fit 36mm carbs if you can. Do get the dellorto tuning guide and sort out each circuit one at a time -BTW the accelerator pump is the last and least important circuit to deal with.

Given todays fuel I would strongly recommend twin plugging the heads. You can run even less advance which is good. I would run the coldest plug possible.

Other than that start your jetting rich and move one number at a time towards lean. Change one thing at a time.

 

[Stevex]

You will need to recurve the timing to a maximum 36 degrees of advance.

36?, a Le Mans 850 is only 34.

 

[Chris R]

36?, a Le Mans 850 is only 34.

You might be right - that is the number I remember but I also remember that the haynes manual had a different number from the factory at least for the Lemans.

The advance curve is not really gospel - the number was created by the factory on the dyno using whatever fuel was standard at the time and place- in this case 70's high octane leaded at Mandello's altitude. Fuel definitely changes and by going to the Gilardoni's so has the required curve i.e. you have to set the advance according to your engine configuration. You retard it and/or enriched it until it stops detonating - of course this means you may end up with an engine that doesn't run very well. Now that alcohol is being added in amounts greater than 10% to most NA fuel to prevent detonation going up on jet sizes is likely required.

The curve itself is pretty crude as it doesn't take into account load or any other factor (temperature, barometric pressure, humidity). Basically the curve follows the Brake Mean Effective Pressure of your engine - which is a 3d curve. This is the advantage of a proper programmable ignition.

If you twin plug - which I recommend as it means you can probably make the engine work without reducing quench (which helps suppress detonation) - from experience you can knock the ultimate advance back about 6 degrees but optimally you will have to recurve the ignition as you still need 6-8 degrees static advance at idle.

As John says If it still pings on the gas you have available and local environmental conditions then you have to either fit thicker base gaskets and/or drop the compression by machining (if there is sufficient meat for safety) or fitting lower compression pistons