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Hello all, first tech question on the forum. Working on a 79 standard, generally stock save for Harley muffs to replace the rotted stockers.
Symptoms:
Bike starts, idles, syncs beautifully. Could probably suck the mercury outta the sticks if I crank the throttle hard enough. Get it on the road for a shakedown and it will fall flat on its face (eventually dying) at anything over 1/4 throttle. I managed to clock about 1.5 miles around the neighborhood checking all the other functions of the bike but have yet to conquer the fuel. I've found that half choke seems to help but I can not break the 3000 rpm wall.
Carbs have been pulled and cleaned twice (currently disassembled again for another round) and each time I've verified fit and function. These are unproven carbs. 137.5 mains, 42.5 pilots, 180 air jets, floats at 1" from the gasket seating surface. Each time the carbs have been broken down to their bits save for pulling the butterflies. Emulsion tubes are clear, and the two centers match as do 1&4. Diaphragms pass the drop test (placing thumb over air horn) and fuel supply is good. Every time I drop the carbs the bowls seem equally full but I havent tried to measure what comes out. No bubbles in the fuel lines and petcocks run full blast.
After the second iteration of cleaning didn't produce any change I started looking into electrical. The pick up wires did need repair (no change in performance) one coil had a broken plug wire and all 4 had poor connections to the boots (replaced coil and trimmed all 4 wires and made tight connection to boots) and again no change in performance. I think it was just happy luck that I found these failures in the hunt.
Tested the ignition box and it meets all criteria from Yamaha in regards to voltage and ground. Plugs are brand new ngk bp6es.
I'm nowhere near throwing in the towel but I would be glad to hear some outside Input. I do have a couple parts bikes I can pilfer and oseaghda (a seasoned member here that just so happens to have dumped this pile of parts on me) is local and generally willing to help out (but he's getting stumped himself).
The only thing I haven't checked is compression, it's on my list but I keep forgetting to get the plug adapter I need.
Long long post. Sorry, but I think having all the info I have is the best way to try and remote diagnose.
TLDR: carbs are clean and set to factory, ignition Checks out, bike falls flat on the road above 3k rpm but syncs and runs great in neutral.
Carb sync:
Symptoms:
Bike starts, idles, syncs beautifully. Could probably suck the mercury outta the sticks if I crank the throttle hard enough. Get it on the road for a shakedown and it will fall flat on its face (eventually dying) at anything over 1/4 throttle. I managed to clock about 1.5 miles around the neighborhood checking all the other functions of the bike but have yet to conquer the fuel. I've found that half choke seems to help but I can not break the 3000 rpm wall.
Carbs have been pulled and cleaned twice (currently disassembled again for another round) and each time I've verified fit and function. These are unproven carbs. 137.5 mains, 42.5 pilots, 180 air jets, floats at 1" from the gasket seating surface. Each time the carbs have been broken down to their bits save for pulling the butterflies. Emulsion tubes are clear, and the two centers match as do 1&4. Diaphragms pass the drop test (placing thumb over air horn) and fuel supply is good. Every time I drop the carbs the bowls seem equally full but I havent tried to measure what comes out. No bubbles in the fuel lines and petcocks run full blast.
After the second iteration of cleaning didn't produce any change I started looking into electrical. The pick up wires did need repair (no change in performance) one coil had a broken plug wire and all 4 had poor connections to the boots (replaced coil and trimmed all 4 wires and made tight connection to boots) and again no change in performance. I think it was just happy luck that I found these failures in the hunt.
Tested the ignition box and it meets all criteria from Yamaha in regards to voltage and ground. Plugs are brand new ngk bp6es.
I'm nowhere near throwing in the towel but I would be glad to hear some outside Input. I do have a couple parts bikes I can pilfer and oseaghda (a seasoned member here that just so happens to have dumped this pile of parts on me) is local and generally willing to help out (but he's getting stumped himself).
The only thing I haven't checked is compression, it's on my list but I keep forgetting to get the plug adapter I need.
Long long post. Sorry, but I think having all the info I have is the best way to try and remote diagnose.
TLDR: carbs are clean and set to factory, ignition Checks out, bike falls flat on the road above 3k rpm but syncs and runs great in neutral.
Carb sync:
.
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