Help Needed With Some Info Please

Gandolf

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Hi guys, my mate has a t120 Bonneville, he has dyslexia which is why i am here on his behalf, the right hand side exhaust is hot and the left hand side is tepid, he has a 1960 120. things i have done, compression test one kick 25ppf, 4 kicks 75ppf on both cylinders, ive swapped the carbs over, and the coils nothing makes any difference, ive set the tappets cold to 2tho inlet and 4thou exhaust, has any one heard of a this ,or know any reason why this would be happening. cheers steve
 

Greyfell

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Initially, I might have said the two cylinders are burning unequally, but you don't mention a loss of power or straining to maintain speed. Therefore, the thought comes to mind that the left-hand side exhaust has a partial blockage, forcing most of the exhaust out the right-hand side.

I might be wrong; I don't have many years of experience, but this does explain the difference, logically.
 

Gandolf

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Initially, I might have said the two cylinders are burning unequally, but you don't mention a loss of power or straining to maintain speed. Therefore, the thought comes to mind that the left-hand side exhaust has a partial blockage, forcing most of the exhaust out the right-hand side.

I might be wrong; I don't have many years of experience, but this does explain the difference, logically.
its one exhaust per cylinder, no connecting pipe, i stood at the rear with a hand in front of each pipe, and the rhs has warm gasses and the lhs cool, the lhs one does get hot eventually but no where near the rhs one, which was the reason for swapping the carbs over and then the coils, when i adjust the air screw on the lhs all though it makes it run a little rough it still keeps going, but if i do it on the rhs it stalls, both the air screw are set to one and a half turns out, and i only adjust very slightly, the same thing occurs when the carbs are swapped over, it has electronic ignition fitted, when testing for a spark manually both are strong, ive tried the plugs in both sides and that makes no difference, i have personally not ridden it, but my friend said he noticed no loss of power the factor to check was the colour of the pipes. rhs clear blue for around 6 inches down from port, left hand side is still chrome colour. it has me puzeled.
 

Gandolf

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its one exhaust per cylinder, no connecting pipe, i stood at the rear with a hand in front of each pipe, and the rhs has warm gasses and the lhs cool, the lhs one does get hot eventually but no where near the rhs one, which was the reason for swapping the carbs over and then the coils, when i adjust the air screw on the lhs all though it makes it run a little rough it still keeps going, but if i do it on the rhs it stalls, both the air screw are set to one and a half turns out, and i only adjust very slightly, the same thing occurs when the carbs are swapped over, it has electronic ignition fitted, when testing for a spark manually both are strong, ive tried the plugs in both sides and that makes no difference, i have personally not ridden it, but my friend said he noticed no loss of power the factor to check was the colour of the pipes. rhs clear blue for around 6 inches down from port, left hand side is still chrome colour. it has me puzeled.
i will swap ht leads over today as i forgot to do that yesterday, i am also going to check fuel flow from each tap, and drop a timing light on the ht leads while it is running, other than that i am at a loss.
 

Qship

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This forum is for the newer T120s. May get viewed by someone with more experience on the older T120s posting in the classics section.
 

Rocky

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There are a couple of very knowledgeable members monitoring the classics section.
That's where you should direct your questions about the Meriden T120's.
 

Gandolf

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Think ive sussed it any way, timig light not flashing on lhs, pointing towards electronic ignition box, but yeh will look for the classic section.
 

Greyfell

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Sounds like you're well on your way to finding the source of the problem. Posting your question in the recommended section will get you verification.
 

Gandolf

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I have found the problem, First question i asked my friend was are the plugs new, his reply was yes. i should have tested them under load, i replaced the lhs plug and got an improvement, so that led me to raise the slide on the lhs, slowly i could hear the engine pick up , so i removed the carb and stripped it down, both side plug where wet, so i removed all the jets and internals and cleaned with carb cleaner, i also lowered the needle both sides by one notch, This improved its running , after i adjusted the mixture screws on both carbs its like new again, both pipes getting hot equally. Initially i thought that the mk3 box was at fault, but because it ran on one that could not have been the case as it contains a switching diode so moral of the story is check the basics first, despite what your told. Thanks for all your help.
 

Rocky

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Greyfell

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Good work. Sehr Schön, Gandalf.
 

triumph david

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Glad you found the problem, alot of times its something simple.
 
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