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General Category => General Discussion => Topic started by: canuck750 on July 30, 2019, 10:16:15 AM
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Looking for some advice to diagnose an ignition or perhaps a carburetor problem on my Laverda SF1 750 twin.
I have a new programmable electronic ignition and have installed a new pair of Dellorto 36mm pumper carbs (stock spec jets and needle) with float set to 18.5mm as per spec.. Valve gap is correct cold, timing is strobed to check full advance at 40 degrees BTDC. Spark appears to be strong on both plugs. Coils are original Bosch units, high tension leads and are new with a pair of new NGK plug caps.
Having difficulty getting the left hand cylinder to idle smoothly, while running I can remove the left hand plug lead and bike will continue to idle, if I then remove the right hand plug the bike will not idle unless I give it more throttle.
Problem with left hand cylinder maintaining an idle.
Any ideas what to check next, could it be a coil issue?
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I have no experience with Laverda but have you synchronized the carbs?
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While you have it idling, place three or four fingers loosely over the carb and see if idle increases or no. Possible internal vacuum leak or further adjustment of that carb needed. My $.02
Paul B :boozing:
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I think you've got a bad coil. They can gradually fail. Try swapping the coils and see if the problem migrates to the other side.
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I think you've got a bad coil. They can gradually fail. Try swapping the coils and see if the problem migrates to the other side.
Thanks, is there anything 'special' about these old Bosch coils, circa 1972?
I am wondering if the coils MG Cycle sells for Moto Guzzi Tonti frame bikes will do the job.
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Jim, check the choke plunger, make sure it's sealing properly. With the bike idling, shine a light on the choke port in the throat of the carb. If it's not sealing, you'll see fuel vapors being drawn into the motor.
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I like to use an inductive timing light to see if the ignition is firing. Easy to just watch the light. Good way to find misses at any RPM. Quick and clean if you can get to high tension wire. Mike
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Carb problems are ignition and vice versa. You should swap the coils before spending money on them (Guzzi content). Choking the offending left carb is also good advice from RinkRat. Also, does lefty have the correct idle screw?
Hunter
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Thanks, is there anything 'special' about these old Bosch coils, circa 1972?
Have you syncronised the carbs?
Just a tip, if your coils are from 1972 you should change them anyway.
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blue bosch coils used to be the hot ticket. 3 ohms but standard auto size so mounting is troublesome.
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It caught an infection from my diseased Eldo Jim :boozing:
Nick
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Thanks guys! I will swap the coil leads and check the choke plungers.
I don't think I can blame your Eldo for this one Nick, the Laverda just prefers to stay in the garage!
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Having difficulty getting the left hand cylinder to idle smoothly, while running I can remove the left hand plug lead and bike will continue to idle, if I then remove the right hand plug the bike will not idle unless I give it more throttle.
Problem with left hand cylinder maintaining an idle.
Wait, you are saying that if you pull the plug lead, it continues to idle. If you remove the spark plug, it will not idle.
??
Did anyone disturb the valves or valve timing?
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Wait, you are saying that if you pull the plug lead, it continues to idle. If you remove the spark plug, it will not idle.
No. just removing the plug lead, It won't idle on the left cylinder (right plug lead off).
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No. just removing the plug lead, It won't idle on the left cylinder (right plug lead off).
Duh, I was missing the left/right bit there.
Ignore that.