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Discussion Starter · #1 ·
Alright I'm at my ropes end. Helping a friend with his freshly bought 85 yammy fz 750. Originally the fuel pump wasn't priming correctly, we replaced that with another inline pump; also replaced the fuel filter. Well the bike would run, having to choke the hell out of it and revving it when at an idle to keep it from dying. The bike had been sitting a long time and so I recommended a good carb cleaning.

Surely enough two pilot jets were blocked completely, the other two were definitely sclerosed as well with fuel jelly. Everything within the carb was replaced and screwed down well, only the main and pilot jets were removed and cleaned. We replaced the carb and throttle/choke cables. Everything was reinstalled and torqued down correctly, I've cleaned tons of carbs. The throttle closes completely, the choke isn't sticking.

Now the fuckin thing wont fire up, the fuel pump isn't priming the line as far as I can tell as the fuel filter is staying nearly empty. We can get the bike to run by pouring fuel into the carb and also by pulling the line off the gas tank and filling the line/fuel filter to the pump. When we do this the bike will rev/idle at 8k rpm. The bowls are getting fuel as I can drain them off and get plenty of gas out of each bowl.

What the hell, I feel bad for the guy; he drove it home today after pouring some in the carbs and just sat on the ground with his head in his arms in front of it. He's been dying to have a bike, help me help this dude; this bike means a lot to him, it's his first.

Anything at all, because I got nothing.
 

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Is the tank vapor locking? Sounds like it isn't the carbs, sounds like you aren't getting any fuel to them. Did you try leaving the top to the gas tank open when priming? It may be different with bike without fuel pumps so everything I said may be irrelevant
 

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well just from what you have said if the fuel pump isnt priming there a problem there if the fuel isnt getting to the carbs there is no way its going to run is the pump running and just not pushing fuel to the carbs cause if you[ can run the bike by priming the carbs manually then your inline fuel pump isnt working right
 

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Discussion Starter · #5 ·
Is the tank vapor locking? Sounds like it isn't the carbs, sounds like you aren't getting any fuel to them. Did you try leaving the top to the gas tank open when priming? It may be different with bike without fuel pumps so everything I said may be irrelevant
We tried it with the gas cap open, no change. I'm having to learn a lot about it myself, I do not do much with carbs; I can clean them with my eyes closed but I haven't much a clue on troubleshooting/tuning.

well just from what you have said if the fuel pump isnt priming there a problem there if the fuel isnt getting to the carbs there is no way its going to run is the pump running and just not pushing fuel to the carbs cause if you[ can run the bike by priming the carbs manually then your inline fuel pump isnt working right
We'll try a new fuel pump. The pump he's got is just some random inline pump but the shop uses them on a lot of bikes with no issues but no telling what kind of condition it's in.

As suggested above plus if your pump is running but no fuel then it could be a blockage in the line feeding the pump from the tank. Make sure you got plenty of gas in the tank too( I've done that a couple of times where I didn't have enough gas in the tank)

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No blockages in the lines, we disassembled the lines completely and replaced the petcock even. And yeah there's a half tank in there poured fresh.


Thanks dudes, I'll throw a new inline pump in after clinicals today and report back. Keep your fingers crossed!
 

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Did you check the plugs? It sounds like its running really lean and the only way you can get it to run is flood the carbs. It could be the fuel pump is to small and not pumping enough fuel or your float height is set way to low and the gas isn't reaching the crabs till you flood the bowls.


Check the plugs they'll tell you a lot.
 

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Discussion Starter · #7 ·
Did you check the plugs? It sounds like its running really lean and the only way you can get it to run is flood the carbs. It could be the fuel pump is to small and not pumping enough fuel or your float height is set way to low and the gas isn't reaching the crabs till you flood the bowls.


Check the plugs they'll tell you a lot.
Plugs look good, no signs of lean or rich running. I ordered him an OEM fuel pump so we'll see on that one. The pump is smaller than the one stock to the bike so not enough pressure is definitely possible but the bike would at least start before the cleaning with the same pump; although it took heavy choking and wouldn't idle without revving it.
 

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Discussion Starter · #8 ·
As it turned out one of the coil wires was unplugged and a fuel line was kinking in a not so obvious place. Plugged it in and rerouted the lines and bingo bango; this 1985 runs like a hoss. It's not faster than my 05 600 gsx but it can definitely run with it. Really surprising, I was expecting it to be marginally slower being such an older bike that's been ran through with exempt mileage on the title but she screams like a champ all the way up to 165.
 
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