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Pinging

I've skim read most of this and I think we're looking at three possible causes, fueling mixture, ignition or a cylinder head problem. I'll offer my thoughts on the mixture.

The picture of the spark plugs doesn't show what you should be looking for, you need to look inside them. You also want both plugs to look the same and have a coffee colour (not black coffee!), in theory you have two separate engines connected at the crank. They need to be doing equal amounts of work and if the carbs are set the same and one side is leaner than the other then the jets may be dirty. Needles and jets need to be in good condition, if a previous owner has mixed and matched used carb parts it'll never run right.

Tick over should be set in the usual way and use the lolly stick method to check both slides start to lift at exactly the same time.

To do a proper plug check you need to check the mixture at 4 different throttle openings. 1/4, 1/2, 3/4 and full. If you just go out for a ride and then pull the plugs the mixture you'll be looking at is from the throttle opening from last 30 secs or so of the ride, which is not a true picture of how it's running.

Mark your twist grip with a thin bit of white tape and put another piece on the switch gear next to it. Open the throttle to the stop and put another bit on the switchgear where it is now. With this full range being visible on the switch gear put 3 more markers at 1/4 1/2 and 3/4 throttle.

Get a long straight road, preferably on a slight rise, have the engine fully warmed up and run from a slowish speed in 4th gear for 30 seconds or so at the 1/4 throttle mark. Pull the clutch and kill the engine and bring it to a stop so that the engine hasn't run at any other throttle position. Pull the plugs and check their colour. Write notes from what you see.

Do the same again for 1/2, 3/4 and full throttle and you'll know whether the needles will need to be raised or dropped, if they end up on the bottom notch, fully raised and it's still lean, go up a size on the jets. Take care on the full throttle run, it can be a bit scarey, you may need to use top gear.
It's an awful lot of trial and error but the results are worthwhile and you'll know a lot more about your carbs.

All of this is of little cost but takes time and once your satisfied that the carbs are doing their job correctly then start looking to the other areas for a solution. BTW the plug condition can also indicate pre-ignition.
 
Thanks chris!

I don't really understand the first paragraph in the previous message... you are saying that the sp heads have a larger combustion chamber in the heads? That's opposite of what I was told in one of the last messages... I think it was guzzigray that was saying the guzziology stated the Lm heads are about 1mm deeper in order to make enough room for the larger valves...

You mentioned about setting the squish but I did before(another previous post) and found I could go without the base gasket. I don't know if you read this but I am using the high compression pistons and coming out at 13:1 compression after I added the base gasket... I don't see how setting the squish tighter would help.

It has been running well with no audible detonation or pinging but until I drop the compression a bit I am limiting my use of the bike. I was saying that if I opened up the combustion chamber 1mms I might get closer to the size of the lemans combustion chamber and thus lower the compression and potentially be able to fit larger valves in the future. Does that sound about right?
 
Thanks chris!

I don't really understand the first paragraph in the previous message... you are saying that the sp heads have a larger combustion chamber in the heads? That's opposite of what I was told in one of the last messages... I think it was guzzigray that was saying the guzziology stated the Lm heads are about 1mm deeper in order to make enough room for the larger valves...

You mentioned about setting the squish but I did before(another previous post) and found I could go without the base gasket. I don't know if you read this but I am using the high compression pistons and coming out at 13:1 compression after I added the base gasket... I don't see how setting the squish tighter would help.

It has been running well with no audible detonation or pinging but until I drop the compression a bit I am limiting my use of the bike. I was saying that if I opened up the combustion chamber 1mms I might get closer to the size of the lemans combustion chamber and thus lower the compression and potentially be able to fit larger valves in the future. Does that sound about right?

No the SP heads are slightly smaller volume wise - they sink the hemisphere on the lemans to fit the taller lemans piston.

How squish works exactly is up for debate: I have heard two theories. One is that having a tight space forces the end gases vigourously into the combustion chamber causing a lot of swirl which improves combustion. The other is that the sudden change in volume on the downstroke causes cooling leading to less detonation. It may be a bit of both. All I know is that reducing the amount of squish really helps prevent detonation.

You have to be careful because of pistons touching the head - check really carefully with plasticine.

This is why fitting a thick base gasket is a somewhat bad compromise - but one you may have to make depending on funds.

Static compression only really gives you an idea of where you are - compression is a dynamic thing affected by a number of things ie. Cam profile used, volumetric efficiency etc. For example If you have an engine that has poor volumetric efficiency you can run more compression without detonation.

I would say that 13 to 1 is really on the edge for modern fuels - I would be looking at different pistons or machining them. I wouldn't fit the lemans valves - they don't actually flow better in my experience having measured both on a proper flow bench. I would instead invest in someone qualified like Mike Rich to do proper scientific porting work i.e. validated with a flow bench. I have never met Mike- am only going from others experience and his website.
 
Ok great thanks for clarifying. I know I have enough clearance because when I was setting up the engine I found that I had something like 60 thousands which is more than enough to run without the base gasket... Since I was having the pining and detonation(when I shut off the bike) I went to a colder plug(actually the correct plug)and put in the base gasket(as advised by a participant in in this forum) but i was still having pining and detoantio so i was told to try raise the needle(temporary "fix") i think after that it improved but not enough. Then i talked to one of my buddies that owns a moped dealer/motorcycle shop who knows a lot about guzzis said try lowing the idle i didnt think it was high but i tryed it and after that I had no more pining or detonation! I would be curious if I was to set the squish tighter now if it would help prevent detonation like you described apart from the very high compression.

I am still thinking if I was to remove a bit of the chamber and lower the compression taking care to keep the volume of the chambers even if I could adiquatly lower the compression enough while having the " better flow" of the smaller valves... Maybe?

Im absolutely not apposed to having mike or someone that can also bench test and do it right... It's a Guzzi I want to give if the best! But I am also thinking it wouldn't be that hard to increase the chambers myself... Thoughts?
 
Ok great thanks for clarifying. I know I have enough clearance because when I was setting up the engine I found that I had something like 60 thousands which is more than enough to run without the base gasket... Since I was having the pining and detonation(when I shut off the bike) I went to a colder plug(actually the correct plug)and put in the base gasket(as advised by a participant in in this forum) but i was still having pining and detoantio so i was told to try raise the needle(temporary "fix") i think after that it improved but not enough. Then i talked to one of my buddies that owns a moped dealer/motorcycle shop who knows a lot about guzzis said try lowing the idle i didnt think it was high but i tryed it and after that I had no more pining or detonation! I would be curious if I was to set the squish tighter now if it would help prevent detonation like you described apart from the very high compression.

I am still thinking if I was to remove a bit of the chamber and lower the compression taking care to keep the volume of the chambers even if I could adiquatly lower the compression enough while having the " better flow" of the smaller valves... Maybe?

Im absolutely not apposed to having mike or someone that can also bench test and do it right... It's a Guzzi I want to give if the best! But I am also thinking it wouldn't be that hard to increase the chambers myself... Thoughts?

Grinding the combustion chamber is not the way to go - you have to really grind out a lot of material to make an appreciable change and unless you know what you are doing you are likely to decrease flow and/or combustion. The larger lemans chamber is about mechanical clearance only. Are you sure you are really at 13 to 1? How did you measure it?

The simpler route is to find the right pistons (if they are really produce that high a static) if you can't stop detonation.

My first stop would be twin plugging after getting everything else sorted (i.e. timing, fuel mixture, plug heat, squish height).
 
I would add that although the hemispherical design is now thought of as dated some of the most powerful engines on the planet are hemispherical i.e. dragsters. The advantage are largely unshrouded flow around the intake valve and minimal surface combustion surface area to overall combustion chamber volume. The main area for improvement with the guzzi is the intake port breathing - the short turn radius is where improvement is mainly to be had.
 
While that is a valid point about Hemi combustion chambers, those super powerful Hemi's all use forced induction.
Hemi's do have advantages, but they also have disadvantages. In order to have a good compression ratio with a non-forced induction hemi the combustion chamber ends up with a horrible shape.
 
Yeah I am sure about the compression I tested it multiple times with a new tester..

Huh.. what if I have a shop shave a bit of the top of the piston? Then I can set the squish tighter and lower the compression a bit

What do you mean by "short turn radius"?
 
Yeah I am sure about the compression I tested it multiple times with a new tester..

Huh.. what if I have a shop shave a bit of the top of the piston? Then I can set the squish tighter and lower the compression a bit

What do you mean by "short turn radius"?

Calculating the CR using a compression tester is not really the correct way to do it - to get the proper number you have to calculate in adiabatic heating and air pressure which is difficult to do accurately. To properly calculate the compression you need to measure the combustion chamber by putting the piston on TDC and filling the combustion chamber via the spark plug hole with a calibrated burette. It helps to seal the piston with plasticine and to use heavy oil. You then divide the CC volume by the swept volume minus the CC.

Yes you can machine the top of the piston which is good because it maintains squish BUT you have to be careful that there is a safe amount of meat on the piston.

The short turn radius is the lower part of the intake tract - as opposed to the 'roof'' where the tract turns down to the valve seat.
 
I measured an SP/Convert/T3 head today. Combustion chamber is 55cc. Lemans 83mm piston is approx 22cc. Based on a 1.2mm thick compressed head gasket and piston deck flush with the cylinder you have in the region of 11.5:1 compression.
 
Really!!! That makes me feel a lot better... The lemons is supposed to be around 10:1 right? So 11.5:1 does not sound like a dangerous level in my mind. I should probably run the test on my own I suppose...

Thanks
 
While that is a valid point about Hemi combustion chambers, those super powerful Hemi's all use forced induction.
Hemi's do have advantages, but they also have disadvantages. In order to have a good compression ratio with a non-forced induction hemi the combustion chamber ends up with a horrible shape.

That's true but you have to put it in context of the engine's evolution - the guzzi started out as a low compression plodder with a flat piston and an ideal hemi (i.e. minimum surface area to volume) and then got increasingly ugly with lumpy piston tops as Guzzi upped the performance. Of course they didn't change the head geometry to suit the increased compression with a flat top piston - which was doable but probably not economic.

To me 11.5 is even still a bit high for today's fuels - at a minimum I would twin plug and set the squish tight.

It really depends on your particular local conditions - i.e.. fuel available, temperature, barometric, humidity - so any of us are just guessing. .
 
With a well designed combustion chamber over 12:1 with todays fuels is easily do-able. But the Guzzi does not have that luxury.
When Guzzi upped the compression ratio the easy way, with domed pistons, it made for a crappy combustion chamber shape. It is what it is. Can you still get good power out of a Guzzi motor? Sure. It is a lot like getting good power out of an older 2 valve Ducati motor. It can be done, but it is not as easy as it could be. You want to, as you said, add a second plug and set you squish tight. It is the same with the 2 valve Ducati's.
On the wife's V11 I actually milled the heads to add a larger squish area (stock it has a beveled edge) and then set the deck height.
On our Ducati race bikes we would run the squish so tight the piston would almost hit the head in the squish area. If carbon builds up in your squish area you don't really have a squish area.
 
I agree with everything you said!

Modern hemis like the amazing SRT8 (Take a look at http://www.allpar.com/mopar/new-mopar-hemi.html) has a hybrid combustion chamber that is something between a traditional hemi and a Westlake 2-valve combustion chamber. Interesting Dodge uses rim flow anti-reversion valves - which work well with the Guzzi head.
 
Hey guys it's been a while... now that it is winter and holidays are almost over I am starting to thing about what I can begin doing to my guzzi...

I have an extra set of heads(t3) that I might send to Mike Rich to get twin plugged and ported. these heads were on an engine that had an oil issue and torched crank so I am not sure what condition the valves are in but since it's apart I am interested in getting lighter, high flow valves for this bike... any information or direction on this is appreciated.

I was wondering, I have heard that having a hotter cam can help lower the compression...

Should I do all this stuff at the same time? I just don't really want to have to take it apart ever again lol

Merry Christmas
 
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