Guzzi Lemans Plug Fouling

**Voltaire** · 16th January 2017, 19:44

My Guzzi Lemans 2 has been WIP for a year.
LH plug fouls after about 30 KMS.
I've checked the ignition, valve clearances, stripped and cleans the carbs ( multiple times)
Tonight I printed off the specs and stripped and wrote down all the jets and needle numbers, all as per spec.
Then I thought i'd swap the carbs over and see if the problem was the engine or the carb.
Ran ok for about 20 kms then started to bog down.
The problem had moved to the other side so its the carb.
I've played with Dellortos on my BMW and this is first time I've stuck this.
Wise words welcome

**AllanB** · 16th January 2017, 19:50

Stock air filters or pods? If the later is one a dirty bitch and the other a clean nun?

**Voltaire** · 16th January 2017, 20:00

Originally Posted by AllanB

Stock air filters or pods? If the later is one a dirty bitch and the other a clean nun?

It came with cone shaped K and N pods. I have just cleaned and oiled them.

**jim.cox** · 16th January 2017, 20:11

Worn needle and/or seat

**Grumph** · 17th January 2017, 05:33

Standard PHF36's ?

Possibilities are:
blocked air correction jets/passages
Worn needle/needle jet combo
Crack in the carb body - below fuel level on the central tower carrying the jets.
If the problem only shows up hot, this could be it...
Do the floats carry the same numbers ?
Float needle jet fitted correctly into the body ? Any crack around that ?

**Voltaire** · 17th January 2017, 06:05

Originally Posted by Grumph

Standard PHF36's ?

Possibilities are:
blocked air correction jets/passages
Worn needle/needle jet combo
Crack in the carb body - below fuel level on the central tower carrying the jets.
If the problem only shows up hot, this could be it...
Do the floats carry the same numbers ?
Float needle jet fitted correctly into the body ? Any crack around that ?

List for tonights investigation.
floats are both the same, 10 grams
next on list is checking for worn parts and cracks.
This is why we love old bikes...isn't it....keeps the brain active....

**Kickaha** · 17th January 2017, 07:30

Check the accelerator pumps as well

**Grumph** · 17th January 2017, 09:05

Originally Posted by Kickaha

Check the accelerator pumps as well

Thought about that - Dellorto take the fuel up and over the top to the nozzles in the bore. I don't see how there can be a bleed of fuel through the system while running. I'd check the pump ramps in the slides in case one side is a very long ramp...
Mikunis, Yes, with their system there can be a fuel bleed if something sticks. Bloody Dellorto pumps are hard enough to get to work in the first place...

**Paul in NZ** · 17th January 2017, 14:35

Also check the choke mechanism - they are VERY prone to sticking....

**Voltaire** · 17th January 2017, 18:45

So got home and stripped the LH carb again.....
Checked out the main suspects, needle, needle jet and idle jet.
Found in my BMW racer bits box another PHF 36 and it looked less munted.
As they are not the same mounting took out the bits needed and compared them.
Visually no real difference.
Found a drill bit that was a sliding fit into the needle jet and it was a bit sloppier on the old one.
What the hell I thought fit them and go for a ride.
I did the same 30 kms as last night, bit of mean streets of Onehunga and Mangere plus a few strops up and down the motorway.
Initial impression was smoother, no popping from exhaust, seemed to pull better and happier to run a higher gear at lower revs.
Pulled out plug on the actual spot I did it last night and not sooty.
Rode back thru urban area and it would feather along at 60 KMPH/2000 rpm without issue in 5th ( try that on your Ducati )

Conclusion: when you buy an old bike fit new jets.
Gong to order all new ones.
Thanks for all your advice and tips, always appreciated

Photo from a while back.
Its a lardy thing compared to the R90s but its got lots of ommph and old blokes come up and talk to you...

Click image for larger version.

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**Grumph** · 17th January 2017, 19:10

Guy who lives around the corner from me has a Laverda 3C. Carbs needed a refresh.
He got someone else to supply and fit the new brass and slides - not cheap..
He came round to me with them in his hand asking why they wouldn't synchronise - and what the hole in one new slide was.
They wouldn't sync because it had the short cables in the gantry of 2 different lengths...
The hole in the slide was at the bottom of the ramp and is supposed to have a plug in it with a spring to stop the needle fluttering.

He found cables of the same length and fitted them. I made up a brass plug for the slide and pressed it in. Never heard of that missing in a new slide...

The guy who did the job apparently lives in Rolleston and i'm told is a truck mechanic. He knows how to charge....

**Hobbyhorse** · 17th January 2017, 19:58

A good result John.

Do you think that new jets would sort the Vespa front end?

**AllanB** · 17th January 2017, 21:35

Originally Posted by Voltaire

Rode back thru urban area and it would feather along at 60 KMPH/2000 rpm without issue in 5th ( try that on your Ducati )

Not a chance in hell - it would buck me off - I've recently gone from a 15 to 14 tooth front sprocket - it would still pack a paddy. At last I can run all 6 gears at sub walk home speed on the open road (but still get a ticket speed...).

Carbs. I have one somewhere in the garage. Oh my Lawnmower still has one.

**OddDuck** · 17th January 2017, 21:47

Originally Posted by Voltaire

Rode back thru urban area and it would feather along at 60 KMPH/2000 rpm without issue in 5th ( try that on your Ducati )

Since fitting the Keihin FCR41's I can tootle around at 2,500 - 3000 RPMs quite happily. Simply wouldn't have happened with the stock Mikuni's. Not sure about 5th gear at 60 though... massive driveline backlash, high gearing and all...

Nice looking Guzzi btw, love the classic styles.