850 lemans tune up questions

[1down5up]

All,

Currently trying to tune my 850 lemans (950cc gilardonis) and have come across a few things I Havnt encountered before.

Bike has a fairly recent rebuild, refurbished carbs, new dizzy springs and points etc. Have also confirmed the markings in the flywheel are true.

1. I have timed both cylinders statically but they are way off on full advance, probably 4 or 5deg by eye, it has new advance springs.

2. Using a timing light the right cylinder is very stable, but the firing on the left seems very erratic. It bounces all over the place especially when revving for the advance.

3. Carbs - syncing the carbs as well using a tune pro mercury guage. I've got them balanced (same reading on guage) and activating at the same time (throttle cables) but when I blip the throttle the left cylinder does the "normal" drop and then raise, but the right cylinder just holds steady and then raises (kinda hard to explain in words). It's like the right cylinder doesn't pull the same (any) vacuum when blipping which obviously isn't the case - if I swap the vacuum leads from one to the other it stays with the right cylinder.

Any help appreciated

[moto-uno]

The erratic timing on one cylinder leads me to believe it may be a substandard ignition points .Being as they are both driven
by the same advance cam . Assuming you have tried adjusting the low speed and no real improvement , try spraying some
WD 40 all around the carb to cylinder head and see if there's a temporary increase in engine speed , if yes , an intake leak .
Refurbished carbs , by whom , someone with lots of Dellorto experience ( choke seals , etc ) . Also , maybe try taking the
points cap off and watch the ignition points , you may actually see some irregularity . Good luck and keep us aware . Peter
ps: if you notice a much brighter spark on one set of points , it may be a failing condenser .

[chuck peterson]

“New advance springs…”

Just a WAG from 2000 miles away…Try the old ones…lots of opportunities to get the wrong springs. Are the new ones identical by measuring thickness length strength

Pumper inside carb? Little tiny white ball in place?good luck

[80CX100]

“New advance springs…”

Just a WAG from 2000 miles away…Try the old ones…

^^^^^This^^^^^

With known issues involving substandard new replacement parts, ie points, condensers etc, I'd throw the old springs in for shits & giggles and see what happens.

[guzzisteve]

Only on the left would be points, try the old ones on this. Make sure you clean the cam and put new point lube on it. I've seen it fling off onto points too.

[huub]

quite possible it got a new advance unit somewhere in the past , you can modify yours to give enough total advance.
springs are unlikely to cause the error , after 4000 rpm is is on max  advance anyway.
the erratic spark on one side soun ds like typical fos a bad condensor, i've had quite a ew fail out of the box

for the cync issue , make sure anything is up to specs before trying to sync , with erratic sparks on one side , getting it synched through the whole rev range is pretty impossible

[1down5up]

All, a follow up and conclusion for those interested.

It ended up being the choke rubber plungers......

I had actually dug them out and flipped them as I had been caught out by these little b@$+@rds before.... But they had gone hard and had no "give" in them at all. I thought they would still seal ok but evidently not.

Got some 6mm oring chord from a local bearing supplier and hey presto great idle.

Timing on the other cylinder has sorted itself out, thinking the clip may not have been on the spark plug lead.

Will wait for the rain to pass and take it for a run but I can already tell the idle is much better and alot easier to start.

[Dave Swanson]

Good result and good on you for sticking with it.  Report back when you've had a chance to ride it proper.