750 SF1 36mm Dellorto carbs

hooksey said:
[quote
40? BTDC equates to around 11mm (iIrc, check the manual) BTDC for a quick 'n easy check

piet

Hey Piet what?s this 11mm measurement ?
Is that taken from piston top ?
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YES.

If you guys would RTFM, it is described within...  :D

It is actually a quite accurate method of ascertaining the 40? BTDC position and requires no faffing around with looking for TDC, which is totally irrelevant for the setting up of the DMC.  The slightly oblique position of the depth guage when sticking your probe down the plug hole has only very, very little effect on the measurement, not enough to cause any concern.  This ain't rocket surgery...

piet
 
CLEMTOG said:
have you fitted 36mm carbs (PHF) where previously there were 29 or30mm type (VHB)
and not changed anything else?
that could be the root of all of this.
CLEM
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No the bike came with the 36mm Dellorto's, the old bodies where worn out, despite fitting all new internal bits the old castings where just finished, Wolfgang supplied new Deollorto 36mm bodies and I then swapped over all the new internals, the only difference is the design of the intake castings, they are not the same as the originals, I first fit the original plastic manifold spacer against the head followed by a shortened down original aluminum manifold and then the new rubber boot which slides over the original manifold an into which the Dellorto intake manifold fits. A typical clamp ring then tightens around the rubber manifold and clamps the Dellorto body tight into position.

Carb float height now set to 18mm as per the carb position in the Dellorto manual. Going to recheck the TDC, 10 degree and 40 degree with a degree wheel. Using the piston plunger gauge it looks to be spot on but the degree wheel will tell for certain.

I checked the float gauge with a caliper





Original green Dellorto floats



Adapting the manifolds for the new style intake boot





I will disassemble the three part intakes; plastic spacer / aluminum manifold / rubber boot and apply some RVT Silicone around the mating surfaces, the O rings are new



Now back down to the shop
 
I removed the intake manifold studs, modified four M8 stainless bolts, turned down the heads of the bolts and made up some nylon spacers to not over compress the rubber boots. The reason for the plastic spacer, the aluminum manifold and the rubber boot other than the crab needs the boot, is without the plastic spacer the distance from the back of the carb to the air box is too great and the rubber boot from air box to carb would be too short.



I ran a bead of black RVT silicone between the rubber boot and aluminum manifold,



I am pretty confident there are no leaks from the intake bootrs



Fitted some narrow clamps to not foul the clamp on the bolts



So I think I can say the crabs are properly mounted

I use the base magnet form a parts tray, glued to a degree wheel, it just happens to be the diameter of the crank shaft flange





A piston stop made from an old spark plug and then I confirmed TDC



Marked 10 and 40 degrees BTDC



Checked the DMC is on position 1



Fired it up, bike will run off choke but it wants to run at 3000 rpm, if I turn down the idle screws it will drop to around 2000 then it just sputters and dies.

It takes choke on to restart it, can quickly turn the choke off and the same scenario repeats itself.

As it gets down to 2000 rpm the strobe light is reading very close to the 10 degrees BTDC mark. At 5000 rpm the 40 degree BTDC is aligned. I did not alter the position of the DMC plate from where it was set previously.

So the issue remains pretty much the same.

Fiddling with it all afternoon the generator light remained ON and at the end of the day the battery was out of life, I have a new gel battery, a rebuilt generator, new generator belt, the voltage regulator is new and the wire harness is new. So it appears the damn battery is not charging or all the starting and stopping just killed it but I suspect a charging problem as well.......

This Laverda hates me! Maybe it just doesn't like being parked between Guzzi's and Morini's >:(

I will keep trying,.... if I can't get it sorted it will be in the back of the truck and off for a visit to Wolfgang Haerter in B.C. for the professional attention of a real mechanic!

 
sfcpiet said:
YES.

If you guys would RTFM, it is described within...  :D

It is actually a quite accurate method of ascertaining the 40? BTDC position and requires no faffing around with looking for TDC, which is totally irrelevant for the setting up of the DMC.  The slightly oblique position of the depth guage when sticking your probe down the plug hole has only very, very little effect on the measurement, not enough to cause any concern.  This ain't rocket surgery...

piet
Click to expand...

Righto Righto .... be buggered if I?ve ever seen that in a manual  :-[ Maybe if they had a big set of fun bags drawn over the top of all the important stuff, I would see it  :D
 
Piranha Brother 2 said:
Just to clarify what i mentioned earlier - head has definitely not been off since it last ran OK? Cam timing is definitely correct?
Click to expand...

No the head has not been off since the rebuild, The valves and valve seats were professionally ground, I believe the cam timing is correct. I could pull the covers and check the marks But again I think they are correct. I am getting the same symptoms with the new Dellortos that I did with the old set so I really wonder if its the carbs? Symptoms seem to point to an intake manifold leak but I think that has been now ruled out.

Its just weird that it will not idle below 3000 rpm with choke off BUT it will idle at around 2000 rpm with the choke on. The idle jest are not blocked, the jets are new and the carb bodies are new.
 
So it was rebuilt and the problem you have now was present with the old carbies after that rebuild? Has it run properly at all since that rebuild?

If you could get hold of a camera thingy to check the cam timing marks you wouldn't have to do anything more than remove a tappet cover or two.

I'm just trying to eliminate other issues in my head ...

If it is carbies, it sounds like the entire idle mixture system is being bypassed. Not sure how, but pretty major symptoms.
 
Piranha Brother 2 said:
So it was rebuilt and the problem you have now was present with the old carbies after that rebuild? Has it run properly at all since that rebuild?

If you could get hold of a camera thingy to check the cam timing marks you wouldn't have to do anything more than remove a tappet cover or two.

I'm just trying to eliminate other issues in my head ...

If it is carbies, it sounds like the entire idle mixture system is being bypassed. Not sure how, but pretty major symptoms.
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I have a bore scope is it possible to read the cam / head alignment marks without dropping the motor down and pulling the top cover off?
 
Canuck750 said:
I have a bore scope is it possible to read the cam / head alignment marks without dropping the motor down and pulling the top cover off?
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Don't think so - others might know better.
I recall, it was mentioned that, timing marks on the chain wheel can be off by quite a bit.
If you know what cams are in, why not use a long nose/probe dial indicator on an exhaust valve, to find the true cam timing with the degree wheel ?


 
A fairly good indication of whether you are a tooth out is to check if it pulls a vacuum AFTER top dead centre compression. If you cover the plug hole with your finger and turn the motor forwards, you should get a lot of pressure, too much to restrain with your finger as it approaches TDC, then the very good indication, it should create enough vacuum on the way down just after TDC that if you whip your finger off it will pretty well pop (sort of like the trick you do with little kids when you whip your finger out of your mouth if you know what I mean). Motors I have found with a tooth out - several -  have had virtually no vacuum on the down stroke.
Those o-rings and the sealing of your inlet insulators look absolutely pox to my eyes. The head and all the other mating surfaces should be spotless, there is a shitload of vacuum they have to seal at idle and you should not need to use sealant. Besides which RTV silicone does not seal petrol.
 
Canuck750 said:
Fiddling with it all afternoon the generator light remained ON and at the end of the day the battery was out of life, I have a new gel battery, a rebuilt generator, new generator belt, the voltage regulator is new and the wire harness is new. So it appears the damn battery is not charging or all the starting and stopping just killed it but I suspect a charging problem as well.......
Click to expand...

Was the generator "charged/flashed" after the rebuild?  If the generator was completely disassembled (field windings out, etc), the remaining magnetism will be lost.  Without this magnetism, no current will be produced.  IIrc, DF(?) should be connected to a 12v + source, the housing flashed with 12V -.  This creates enough magnetism to allow the generator to start working.  If all is well with the generator, it should motor in the correct rotation (no belt fitted!!) when D+ is connected to +12V, DF and housing to 12V-.

piet
 
A fellow on the Wild Guzzi motorcycle forum tells me that the new Dellorto 36mm pumper carbs have an inlet for a carb balance tube and that the inlet is on the opposite (back) side of the carb body from the air and idle screws. He replaced the 36mm carbs on his Le Mans MKIII with the same carbs and found the inlet holes did not come with plugs and he had the same symptoms until he looked into the casting to see there was no plug.  I am betting when I get back to my shop this afternoon I am going to find the same thing. If that has been the cause of my troubles I am sure going to be embarrassed but also relieved!

With respect to the generator rebuild it was done by Wolfgang and I am pretty confident it came back ready to run but I will check as per your advice Piet and also trace all the wiring from the generator to the regulator and instrument.
 
Spent a couple hours going through the bike, first remove the carbs and manifolds, clean, recheck O rings, torque down manifolds, refit carbs, slight improvement, bike idled at a lower speed but will not hold idle without stalling once idle falls under 2000 rpm.



I flat sanded the aluminum surfaces on a glass plate with a sheet of 250 grit wet / dry



The carbs do not have the take off port for the sync tubes, the holes on the back of the carbs are not drilled through, too bad, thought it was going to be the cure



So bit the bullet, pulled three of the four engine mount bolts and tipped the motor down and pulled the top head cover



and it looks like I indeed have the cam chain off a tooth



Thanks to all of you who diagnosed the timing, the cover gasket needs replacement so I ran over to a gasket supply company and they scanned the old gasket and CNC cut me two new ones in less than 15 minutes, amazing!! This is the machine making my gaskets.

https://www.youtube.com/watch?v=hY-YE9LDd3Y&feature=youtu.be


 
Wow! That gasket machine is just the bees knees! isn't digi tech incredible (except that my kids are glued to their phone screens  >:( )!

Fantastic that it looks like you may have found the problemo. If it does indeed sort it, I'll take 1st prize in the guessing game  :D :-* :D

By the way, a very nice looking SF you have. You'll love it once it's running sweetly.
 
Piranha Brother 2 said:
Fantastic that it looks like you may have found the problemo. If it does indeed sort it, I'll take 1st prize in the guessing game  :D :-* :D
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Yep, I think you nailed it, great diagnosis!, what led you to think it was the timing?

And why would bring off one tooth allow it run over 3000 rpm but not under 2200 rpm?
 
When my bike was 1 tooth out it was ok down low but had no top end, maybe it depends on 1 tooth forward or back.
 
Vince said:
When my bike was 1 tooth out it was ok down low but had no top end, maybe it depends on 1 tooth forward or back.
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Yes, retarded or advanced will make a big diff. You have to remember that the degrees out at the cam wheel is double the degrees at the crank. I'll hold back on taking any credit until you have it back together and confirm that it idles (after carb adjustments!!) beautifully.

It's just something you learn to look for. Troubleshooting is what mechanics is really all about. I was keen to learn WHEN this 'carby' issue arose - which is why I asked about the chronological relativity (you like that piece of fukken awesome magniloquence!  :LOL:  ) of rebuilds, new carb fitting etc. Sequence of events is all important. keep us posted.
 
Well I think I have it sorted, got the timing chain and cam in the correct position then reset the DMC to spark at 40 degree advance on position '0', After switching to position '1' I found I had to slightly rotate the timing clockwise  a few degrees and fiddle with the idle screws until I could hold around 1500 rpm. Perhaps a bit fast of an idle but it struggles to run slower. I had to fit the old slides into the carbs and they are worn, the new ones lack the ramp on the underside to engage the idle screws. At idle I am strobbing the 10 degree advance mark and at 3000 rpm it jumps up to full advance / 40 degree mark.

The generator light staying on was a poor ground of the voltage regulator, fixed that and the generator light goes off around 1700 rpm.

Thanks again for all the help, now if it would just stop raining I could go for a ride!

 
No ramps for the idle screws?! You really have got some extra unwanted stuff getting in the way of a sweet running SF. Can you file the ramps in? Usually the castings are the same.
 
Piranha Brother 2 said:
No ramps for the idle screws?! You really have got some extra unwanted stuff getting in the way of a sweet running SF. Can you file the ramps in? Usually the castings are the same.
Click to expand...

I dug out the new slides that did not have the proper ramps for the old Dellorto's having forgotten that the 'new' style Dellorto's will take these slides, and sure enough the new style idle screws with their two part assembly work just perfectly, glad you tweeked my memory of those parts. So I now have the right slides for the new carbs, hopefully they make that little bit of difference.

I have to figure out a clutch issue, the cable is too long for a decent range, probably missing a ball bearing in the stack of rods / balls in the clutch, will strip the parts out and check the parts diagram today.
 
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