650 maxim no go

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honda750
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650 maxim no go

#1 Unread post by honda750 »

i got this bike a week ago, had to clean the carbs, ran BEAUTIFULLY the first time i tried it. sat for 3 days and it wouldn't run nicely for anything. have to keep the choke on, the throttle races on its own sometimes. recleaned the carbs, ran slightly better, not much. it was louder after the second time i cleaned the carbs. plugs are coated with a ton of carbon every time i try it. i know that means rich mixture, but it would also mean weak spark im told. any suggestions?
im stumped
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Last edited by honda750 on Mon Feb 23, 2009 4:51 pm, edited 1 time in total.

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flynrider
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#2 Unread post by flynrider »

Did you clean out the tank as well? Chances are that if the bike sat around long enough to gunk up the carbs, you've probably got some of the same gunk in the tank. Right after you clean the carbs, it'll run great until the gunk from the tank gets into them.

Whenever I'm resurrecting a bike that has been sitting long enough to gunk up the carbs, I put an inline fuel filter between the tank and the carbs before starting it (even if I gave the tank a good cleaning).

This may not be your particular problem, but the fact that it ran good right after you first cleaned the carbs seems to be pointing in that direction.
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BuzZz
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#3 Unread post by BuzZz »

You might have an air leak, either from a cracked intake boot or from an improperly sealed carb.

+1 on checking the tank and fuel lines, too....
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honda750
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#4 Unread post by honda750 »

as for the tank cleanliness, I've flushed it several times with 89 octane unleaded, and it has an internal filter on the petcock, but i guess its a possibility. The lines should all be good because I've run it quite a bit and haven't spotted any leakage...When I first got this one I didn't know about the prime setting, and therefore flooded everything trying to start it until there was gas pouring out of the exhaust, in case that could have any effect, and I was definitely thinking about the intake boots and filter assembly. The oboots show slight signs of age/wear, but I was hoping to hold out until I saw a good deal on Ebay for them. I could see an intake leak being the cause of the major carbon buildup on the plugs, and it sounds like the best idea so far, but I still have a couple questions.

Why the racing throttle at seemingly random times?

I read somewhere that weak spark would cause carbon buildup, could this be it? are these the right symptoms?

When I took apart the carburetors, the needle like pin in the float valve was stuck solid on two of the carburetors. I freed these up, but would that have something to do with adjustments.Tomorrow I'm going to try to get time to take them off again and look at the float valves to make sure they are sealing well. Today I took a clear hose and connected it to the drain screw at the bottom of the carbs and the fuel level went up 1/2 in. over the bowl seals....this seems bad to me, like that could be the prob. Is that possible?
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