Crazy jetting not so crazy afterall

[bluesman Guzzi]

Hi, I`m not sure I`ll get a response here after my (regrettable) disagreements with some of the stalwart members here, but here goes in the hope that we all advance our knowledge.

My bike, a Nevada Club, LAPD, call it what you will, suddenly ran very lean and hot, dangerously lean in fact, plug chops revealed white plugs in all throttle ranges.

I`d previously had the carbs off to clean and free off the chokes pistons, messed one up by trying to push the choke piston through from underneath, so replaced the carb body on that side. Naturally I assumed that human error was responsible for the sudden poor running of the bike so stripped the carbs again 4 more times hoping to see where I`d gone wrong, but nothing there. I checked thoroughly for vacuum leaks, nothing there either.

Looking online to find out the jetting for the Nevada 750 I could only find this for the listing, 102 main, 36 idle 266T atomiser, X8 needle 3rd notch and slide 40, and began to wonder why my carbs were jetted so lean. If I compared my carbs set up of 105 main, 32 idle, 264T aromiser, X88 needle 4th notch, and a 50 slide. I`d changed the mains to 135`s to account for straight through "safety" pipes and the air filter system for a couple of foam pods.

I was questioning this set up here at guzzi tech and fell out with a couple of people because I disagreed with their diagnosis of my situation. I was a pain in the ass with it too, admittedly, but I was saying that I felt it must be the manufacturer`s spec as surely nobody would make such changes for any modifications, making it leaner, why would someone do that I exclaimed.

I was told I had it set up far too lean and in danger of damaging the engine. I knew this just couldn`t be the fault as the bike had been running exceptionally well over the past 18months with 2 European trips undertaken. Something had to have changed. I`m not a complete idiot though and I know a good running engine from a bad one, and something had changed considerably.

Despite this, I bit the bullet and bought the richer stock set up mentioned above. This took the white appearance off the plugs, but the bike still runs horribly and is very uneven through the throttle range.

However yesterday I found this in a manual online, its the carb specs for the Nevada 750 club and now know for sure that the set up was correct for my bike after all.


Carburetor data
Venturi (Ø 30 mm)
Throttle valve 50
Atomizer 264 T1
Main jet 105
Idle jet 32
Starter jet 60
Needle X 88 (4th notch)
Float 9,5 g
Idle screw adjustment: open 1 and 1/2 turns approx

So I`m back to where I started, though I have considerably less cash than when I started.

So now I`m looking at the ignition side of things.

I cant see it being the coils as I doubt they`d both go and would expect that to affect one side only if one coil goes bad.

The only thing left I feel is the digiplex electronic timing unit. I`m thinking it must be significantly over advancing the timing and thus running the engine very hot, does that make any sense to those experienced with the digiplex?

I always thought if they failed the bike simply wouldn`t run, but I just cant put it down to anything else.

Anyway I`m off to my mate`s workshop this afternoon to check the timing and take it from there.

I`m wondering if a points conversion is possible on this bike, would anyone happen to know?

Thanks, Martin

 

[bluesman Guzzi]

Mmm. . . just been speaking to Corsa Italiana, Moto Guzzi dealer`s in the Uk, and they tell me that Guzzi no longer supply the digiplex ignition unit and they`re simply not available anymore, and said my best bet would be to look around for a second hand unit. The last time they stocked them they were a whopping 300+ English pounds!

Not so good news then, to say the least.

I`m now wondering if its possible to retro fit a points system to this engine, would anyone be able to tell me if this is so?

Cheers, Martin

 

[Moto Fugazzi]

A while back that my mechanic told me how to test the digiplex. It was very easy, and I don't remember how to do it for the life of me.
You may want to post on Wild Guzzi, as I'm sure there are a couple of dealers on that sight that should know how to test them. Keep the post simple and to the point-"how do I test the Digiplex"

 

[bluesman Guzzi]

Thanks for that, I`ll give that a try. I like how you list your Rickenbacker with your bike. I`m a Gibson man myself

I`ve just bought a second hand digiplex 2s for £42 inc postage, from a 97 Nevada. Just hope it works ok.

|`d still be very interested in a conversion to points if its possible, I know the performance/economy may suffer slightly, but not so much to affect my riding enjoyment I wouldn`t have thought. I think on the le mans the dizzy black box fitted where the ECU sensor fits to the flywheel housing on my Nevada. To have the parts for a conversion in advance of something going wrong with any future ECU that I use would be a handy back up to carry on trips.

Cheers, Martin

 

[chris a]

I don't think points will do...the small blocs only used them for a short period and they seemed to be a pita to set.They were superseded by the motoplatt and then the digiplex.The drive on the camshft changes from ignition type to type and the whole points system will cost you loads anyway.
Best move as far as i'm concerned is either to use the other digi you have, get the other one checked over and fixed ( someone out there does overhaul them )or change the ignition to a ZGD from Volker Saches in germany.I've used one of his units for a few years now and it is really faultless so far.he has an uprated version specifically for the smallblocs now.
http://www.elektronik-sachse.de/index_en.htm
The old adage " if you think it's a carburation problem then it's probebly an ignition one " stikes again !!

 

[bluesman Guzzi]

Best move as far as i'm concerned is either to use the other digi you have, get the other one checked over and fixed ( someone out there does overhaul them )

Yes you`re right, I agree. Assuming the one I`ve bought turns up in good working order :unsure: . Hopefully I can use the s/h one I`ve bought whilst I find someone in the UK that can overhaul the one that`s gone down. Then fit the repaired one and have the other as a spare.

or change the ignition to a ZGD from Volker Saches in germany.I've used one of his units for a few years now and it is really faultless so far.he has an uprated version specifically for the smallblocs now.
http://www.elektronik-sachse.de/index_en.htm

Thanks, that may be useful, and if not for me, maybe for someone else searching this issue in the future.

The old adage " if you think it's a carburation problem then it's probebly an ignition one " stikes again !!

Lol, doesn`t it just!

Cheers, Martin