le mans mk11 cant get idle set on left carb

festive greetings to all, been trying to get her running for christmas after a rebuild,idle on the right carb set by removing left plug cap and tweaking mixture screw  till sweet spot was found, this is where the festive fun stopped,  i replaced left plug cap and removed right cap to set left carb, no matter where i set the mixture screw i cant get any joy.  i could do with some things to look for.

recap on work done/ barrels honed new rings/comp identical 150psi both sides/new guides new exhaust valves/ carbs sent off for sonic cleaning (phf 26 high top dellorto) seals and gaskets renewed in both carbs/ float height 18.5./ slides synced  fuel tank cleaned ans sealed inside/ new spark plugs new points and condensers.  i have good blue spark on right pot and also on left which is where the problem is/ i have fuel to float bowl/seals on mixture screw and idle adjuster so i have spark and fuel but  cant get anywhere with the left side  thoughts gents please not sure what my next move is

kind regards russ

Could your left side choke piston be failing to seal?
All the best,

Agreed…and b careful doin it that way cos you can blow leccy ignition…

It’s OK he’s got points, but yes nobody with electronic ignition pull off a plug cap!

When you say ‘no joy’ what exactly happens, does it fail to run at all or idles but can’t change the speed?

thanks to all of you for a reply i know its tough this time of year, will try to isolate choke tonight (remove cable leave plunger and spring and cap/seal of tube) see if that helps.Bike runs strong on the right but misfires on left and wont tick over on any setting, i am getting some fuel mist whisping out he back of carb. When i gave it a test ride she pulls and heistates pulls  hesitates, shes close to good but no cigar just yet, thiught gents please  kind regards russ

Ahh yes Miko…mea culpa…wasn’t paying attention…x

Maybe re-check your LHS valve clearances? Try plug swap to see if the problem changes side=dud new plug. Ignition timing on LHS?

evening gents, so far  i have isolated the choke on left side( removed cable left spring and plunger in place with cap and rubber bung in pipe) no joy still misfiring and the odd blue flame out the exhaust. i tried  a ngk plug that was in the bike when i bought it no change. The valves on left sound interesting, if i set it too tight maybe thats letting fuel  air mix into pipe cusing the odd flame?  The timing? i didnt touch the timing as such iput new points  and condensers,  can the timing slip somehow onleft only?  i have a strobe i used on my old bonnie is it any use this old girl?  i really appreciate the help.  I will do valves tommorow, how can i tell if the timing has sliped on left side?   very kind rgards russl

Hi Russ, I noticed you said in your first comment that you have sealed your tank!, my tank was sealed with petseal by a moto guzzi dealer about 1 week before I bought the bike as a non runner after a £1200 rebuild bone by the moto guzzi agent, the bloke I bought it off couldn’t understans why it wouldn’t run!, when I got it home I found that the  petseal used to seal the tank had started to leach into the fuel and this ended up like a thick sticky jell in the carb and like concrete on the valves and Pistons,
this is what started the whole rebuild for me! So if you have used petseal then maybe it’s worth a check, cheers Chris.

Coils ok…swap em over maybe…

hey chris,  used a product called TAPOX seems to have done a good job.  Right side running good so i guess the fuel is ok but thanks for input.  Will also swapout coils see if thats the issue   regards russ

Ah now we may be getting somewhere.

If you change the points you MUST retime the ignition, and each side is done separately ~ right side first by rotating the timing unit body, then the left cyl. points by moving their own special sub-mounting plate. Often this doesn’t offer enough leeway to do it so have to cheat a bit by altering the points gap as well.

You can set it static by turning the flywheel to align the retarded timing mark in the bell housing ‘window’, RH first then LH, and getting the points to open at those 2 positions (respectively). For LM’s the retarded mark is 8 degrees BTDC, I think. Roughly 2 teeth of the starter ring gear. For other Tonti’s it’s 2 degrees.


Or you can cheat by filing the screw slots a little to give the required adjustment. I had to file the ones on the Convert quite a bit. I think this is because the tolerances on the construction of the actual points can vary widely. I love fiddling with points, quite rewarding when you get it right…

Regarding the valves, always set them very loose after a rebuild, say an extra 3 or 4 thou. Then reset to the book after 100 miles or so when you re-torque the heads.

hi mke, thought the timing might be a good place to start given what you said  if im making a mistake here tell me, get right pot on comp stroke wait for mark with (D) next to it/ i continue clockwise untill i see a line with no mark (as per lemon) ive slacked housing bolts and with test light i have rotated housing till light comes on and line is smack bang in the middle of hole/ pinched up housing bolts and move on to left pot/ get it on compression stroke wait for  mark with (S) next to it ,continue to rotate until next line rolls up and  adjust back plate to get test light on ( this line seems a long way from (S) much longer than from the (D) so far away to my eye it looks  too much to adust with just the plate.( the previous owner said this bike has a lightened flywheel fitted, so not standard, am i using the wrong marks?)  im using the method in the haynes manual to time this  thoughts mike please   regards russ

Hi Russ, this from Guzziology.


^ yes, for static timing use the retarded line which is the one nearest to ‘D’ or ‘S’. And you have to look for it BEFORE the letter appears, or, rotate it backwards from the letter.

Also you have to make sure it is actually at TDC of the compression stroke, not 180 degrees out of phase instead.

Tried the old condensors again? I had all kinds of ‘issues’ earlier this year were that were masked by the fact that the new condensors I fitted were duff.

happy new year gents, sorry I haven’t updated-been in the festive buzz, bike had to wait… So far checked valve clearance all good/exhaust clamps all good no leaks/ timing underway ,right side second line up from (D) test light on just as second line is in the center of hole. Left side not so straight forward got the second line up from (S) but test light is way of as I said before so im buzy modifying left plate to shift the points anticlockwise to allow me to set the fireing point spot on(how come these thing are not right from factory? very strange) If she runs I can strobe it to the third mark up from ( D S) should I rev to 4500rpm ?(guzziology) . if im still having trouble ill change back the condensers/ ht leads/ caps and plugs after that there is only the coils and the carb which is the last resort( I had the phf36 high tops pro cleaned even though the bike ran well the only thing I changed apart from seals and gaskets was float height, they were both at 21mm and 22mm which I reset to 18.5mm ? FINGERS CROSSED THE TIMING SORTS IT :wink: KIND REGARDS RUSS

Not second line up, that’s full advance, you want first line up, which is almost on top of the letter ‘D’ or ‘S’.

If in doubt, as LM’s are 8 degrees BTDC, then for the retarded position, get the letter centre in the hole, then turn the flywheel anticlockwise by two teeth on the ring gear.