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Discussion Starter #1
I have a 1982 Honda cb650 that I cant get to run correctly. So far I have put new rings in, checked the timing, took the carbs apart and cleaned them and replaced the needles and gaskets, and then bench synced them. I also moved the air/fuel adjustment back to factory setting. I have read about how to adjust them, but they say you have to have the bike in idle, which I can't do. I have everything together now and it wont run under 3,000 rpm. It runs very good above that and it very responsive on the throttle. It seems that I have ran out of ideas and could use some help.
 

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You've turned the idle RPM adjustment down? Does it just die below about 3k? Will it idle with choke? What does it sound like when it dies?

Check and recheck the carb boots for leaks, could be a good vacuum leak.

Did you replace the tiny o-rings around your idle mixture adjustments? If they're dried and shrunk they can leak and allow air into your idle circuit.

Idle circuit blockage still?
 

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Discussion Starter #4
Where should the idle adjustment be set at. When I had the carbs off I screwed it all the when in till it touched the arm and then about 4 turns.

I checked the carb boots for leaks again, and they seem to be OK.

I didn't change the idle adjustment o-rings, can that be done with out taking the carbs off. Someone has already filed off the knobs so they can turn all the way around.

As far as what it sounds Luke when it dies, if it drops below 3,000 it just instantly quits. It doesn't backfire or sputter, just dies. When I choke it, it will idle at 1,000 rpm for about 15 seconds then slowly die.

Thanks for the help.
 

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I have everything together now and it wont run under 3,000 rpm
What do you mean? Engine shuts off below 3000 or you just can't get idle below 3000.

High idle is typically a vacuum leak.

There is a vacuum line from the petcock to one of the carbs..it serves 2 purposes:

1. When in the prime position, a small amount of gas is sucked directly into the engine.

2. Shutting off the flow of gas when the engine is off.

If the petcock is malfunctioning, you'll be sucking in gas and it will idle high. Typically, it will idle fine when cold, but high once warm.
 

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Discussion Starter #6
I have to hold the throttle open to keep it at 3,000 or above, if I move the throttle back and the rpms go below 3,000, no matter what I do, it will die. Not sure if that makes sense.

A previous owner has removed the vacuum lines. The fuel line comes straight out of the petcock to the carbs.
 

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For me, for now, two areas.

1. Charging
Honda's of that era had charging problems. I bought an 82 CB550 brand new and within a year it had a similar problem.
>Below ~1800rpm, it would discharge the battery.
>If the battery voltage dropped too low, the bike would die below 1800.
>I would have to pop the clutch to get it running and keep the idle above 1800 until the battery recharged..it was a total pain.

So, when the RPM drops below 3000, does the headlight dim rapidly? What's the battery voltage with the bike off vs. running at 3000+ and less than 3000? An alternator output test may be in order.

2. Vacuum leak.
If you're sucking air, that leans up the fuel mixture; suck enough air and she will stop running.

>Check the boots between the engine and the carbs for cracks or holes; are they attached securely with no gasket leaks?
>Did the the previous owners do a good job of plugging the vacuum lines?

Here's a trick..you'll need a helper.
Let the helper run the throttle while you spray tiny bursts of starting fluid directly into the air intake and see if you can keep it running below 3000.

If so, you have a vacuum leak or some problem with air/fuel ratio being delivered by the carbs.

PS> Go very easy with the starting fluid...stuff is very volitale and emptying a can into your engine would do really bad things....just tiny 1/4 second bursts is all that's needed to goose it and keep it running..if it will stay running.
 

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Discussion Starter #9
The charging system seems to be fine, I have a new battery and it is always charged up before I start cranking away.

I believe it has to be a vacuum leak. I decided to take the carbs off, and break them down to the very last piece. I have never done this before, but it sounds like a good tune up is in order. If anyone knows of a good step by step instructions would be great.
 

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I don't know of anything specific to your model outside of a repair manual - those are helpful.

Generally speaking, take photos of complicated bits to remember how they go together, keep parts organized and clean. I like to use an old muffin pan for that. Be OCD about cleanliness when doing carbs. Replace old rubber parts (o-rings, etc). Compressed air is a wonderful thing! I like to spray aerosol carb cleaner through the passages and then shoot 125psi shop air through - especially in the tiny idle and low speed passages.

I also like to use larger clamps on the carb boots. When boots get old and a bit stiff I think more clamping pressure is helpful.

Some people boil carbs with or without pine-sol.
 

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Discussion Starter #11
OK. Thanks for the info. I definitely should get some better clamps for the carb boots, the factory ones tightened all the way. ( I still didn't notice any leaks around this area.)
 

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Discussion Starter #12
Well after breaking the carbs apart I believe a found out what the problem is. First the O-rings around the air/ fuel adjustment screw were completly shot, and a couple of them missing. And second, all the slow speed jets are plugged. I have the air/ fuel screws ordered with new rings, and got 3 of the 4 slow speed jets unplugged. I am still having trouble with the last one. I have soaked them in a bucket of carb cleaner, air compressor several times, boiled them in water and lemon juice and have tried several other chemicals soaking on top of the jet, but it is still plugged. It is one of the pressed in kind, and I don't want to remove it. Any ideas of what to try next?
 

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I hate to say it, but if you can pull them it makes cleaning them easier. I use a drywall screw - screw it in until it resists firmly, then clamp some vice grips to it at a 90 degree angle, and hammer (tap gently!!!) them upward, pulling the jet out of the carb body. The actual orifice is far enough inside that it doesn't get damaged by the screw. It is risky, but I've done it many times.. good old Honda!

Just make sure the bore is really clean before you try pulling, and lube helps.

Aside from pulling, if you have a set of stiff wire jet cleaners that's probably your next best bet, or you might get a micro drill bit down there far enough, just don't break it off inside.

And do try 450zuki's suggestion, try attacking it from the other direction or sucking it out. It might be that type of blockage.
 

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Discussion Starter #15
Well I was getting ready to do the vacuum idea and ended up boiling them again and soaked the stuck one over night. It is now unplugged thankfully. So now the fun part of assembly. Thanks for the help everyone! Hopefully I'll get this thing going before the snow flys.
 

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Carbs...

These ain't get the kind of carbs you get when you eat too much vegetables.
these motorcycle carbs are delicate pieces of machinery. You must be careful, take as much time as youi need, and follow every manual, install everything right, that hardest part about carbs is that it takes a while to do it all right. Now that we are through the salad....
when you bench sync, use a flash light, and shine it through from behind of the carbs with the butterflys/throttle closed. If the light shines through, your butterflys are not closing. They are machined to close completely. no light will shine through. If light shines through, your butterflys are in backwards. if you don't have a set of carb jet cleaners, and you are an avid welder cutter, you can sometimes use the torch tip cleaners to clean out the jets. The tip cleaners are made to cut copper, so be very careful not to open the jets up when you clean them..
sounds like you are a good mechanic. motorcycles are delicate precision toys that girls should never touch, even when they are just sitting there...
 

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Discussion Starter #18
So I have cleaned the carbs very carefully and had to unclog the slow jets on all 4 of the carbs. Then the accelerator pump was clogged as well. I installed new needles, o-rings, and other seals. Followed the manual every step on sync'ing the carbs and mounted them to the bike. It is still not running any different then when I started.

So far I have- checked the timing, installed new piston rings, spark plugs,and rebuilt the carbs.

I am running out of ideas of what to check, it seem to run strong at high rpm, but seems to be running rich, then at slow rpm it wont run, or struggles to run on choke. I have also adjusted the idle screw, and the idle mixture screws (which have new o-rings and hardware) and tried them at various settings.
 

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Did you try to keep it running at slow RPM with starting fluid?

You'll need a helper. Remove the air filter, start the bike, slowly drop the rpm's, when it's close to dying, give a burst of starting fluid, release the throttle and try to keep it running with bursts of starting fluid.

If you can keep it running at slow RPM with starting fluid, then your fuel air mixture is too lean; vacuum leak or carb problem.

If you can't keep it running with starting fluid, then at idle it's probably too rich. Once it dies, remove a plug and see if it's wet.

There is a fine line between Rich/Perfect/Lean...either side of perfect and your idle will suffer first.

This could also be an electrical problem. Your coils could be producing a weak spark at idle due to a drop in input voltage. Hook a volt meter to the battery and watch the voltage as you drop the RPM; there should not be much of a change.

If you have a spare spark plug, you can remove one of the plug wires, plug in that spare plug, touch the threads to the frame, run the bike on three cylinders, and watch the spark at various RPMS; it should not vary in intensity...wait until the sun goes down and do this in low light...test all of the coils...weak, flaky coils can drive you insane with starting, running, idle issues.

Great info on coil operation and testing:
http://www.aa1car.com/library/ignition_coils.htm
 

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Discussion Starter #20
Using starting fluid I could hardly keep it running at 1,500 rpm, if it fell below that it would die.

Ater that test I pulled all the spark plugs. They were all dry and black. They are new spark plugs and have correct gap.

At 1,500 rpm while struggling to run it was at 13 volts, and anything above 2,200 rpm was at a constant 15 volts.

I then pulled a plug wire and tested it on a spare and it seemed to have the same brightness of spark. Not sure how to describe this but I will try - While running at high rpm it sparked in 2 different spots on the bottom of the plug, alternating between the 2 each time it fired, then when it droped down to 1,500 rpm I was only getting 1 spark and ocassionaly the other would jump in. I tried other plugs and they did the same thing.
 
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