Topic: RE: My $100 dollar CB500 - Thanks to everyone

[Greggo]

Rubber.  That will be your solution.  Air leaks from the worn out rubber o-rings that seals the motor at the intake spigots, the carb to spigot boots,  and the carb to air box boots should all be checked for leaks.

[wowbagger]

Rubber.  That will be your solution.  Air leaks from the worn out rubber o-rings that seals the motor at the intake spigots, the carb to spigot boots,  and the carb to air box boots should all be checked for leaks.

What's the best way to check for leaks? I've seen some videos of people using unlit MAP gas around the boots and waiting for the engine to race but that seems a bit on the sketchy side to me.

[mrbreeze]

You didn't mention if you did a carb sync. The engine will usually run on just a bench sync but will display the high idle and chain slap noise. Make sure the timing and points are set properly. Valves and timing chain tension are set. Then do a vacuum sync and you should be good to go.

[chewbacca5000]

You didn't mention if you did a carb sync. The engine will usually run on just a bench sync but will display the high idle and chain slap noise. Make sure the timing and points are set properly. Valves and timing chain tension are set. Then do a vacuum sync and you should be good to go.

I have not done a vaccume sync yet as my guage is broken.  Going to make a home made unit over the next day or so.  As far as ignition goes I found 2 bad advancers one had springs so weak it went straight to full advance with little effort.  The other had 1 bad spring.

So far I have done the following and each thing is bringing progess.
1. Put stock pilot jets back in.
2. Taken out junky air screws from kit and replaced with solid ones from cb750
3. New Orings on manifold.
4. New advacer, Pamco ignition, 2OHM resistor pack for the 3OHM coils

All this is helping, but am not sold.

Last night and this morning I got it to idle, but I have not tired it fully warmed up.

Fuel level in the tank is very low, and the seal on the cap is broken.  Not sure if that matters.  Weather is better with humidty at 67% vs 100%.

Might go for a test drive and see what happens.  If it goes well I will fill the tank up and see if the problems return.

I am considering removing after market needle valve and seat as well. 

I have been able to completely rule out vaccume leak, cable ajustment, or bad advancer.  Everything points back to fuel delviery / level.

I'd be intereted in any other theory on this.

[Stev-o]

No theory here, but do put a gallon of gas in the tank to be sure fuel is available. Confirm petcock is clean and working.
Seal on the cap should not be an issue, you need a vent there as fuel is gravity fed.

Ride that sukka!

[wowbagger]

I just vacuum synced my carbs last night and it fixed the high rpm issue. My #4 carb was pretty far off. Now, it rides great and the tons drop down as they should once I let off the throttle.

[chewbacca5000]

I just vacuum synced my carbs last night and it fixed the high rpm issue. My #4 carb was pretty far off. Now, it rides great and the tons drop down as they should once I let off the throttle.

Thanks for the post I might just have to give this a shot.  Thanks!  And to you Steve-0 won't worry about the cap just yet.

[Greggo]

WD40 works just as well.  Only way to check the o-rings between the motor and the spigots is to pull them...they get flattened from the constant heat cycles, and it's a good idea to just replace 'em.

[chewbacca5000]

WD40 works just as well.  Only way to check the o-rings between the motor and the spigots is to pull them...they get flattened from the constant heat cycles, and it's a good idea to just replace 'em.

Thanks Greggo.  Pulled and they were flat as a pancake and once was completely cracked.  Replaced with new orings and no leaks at all.  Idle is improving getting it to stay around 2K after a warm up.  It slowly comes back down, but will eventually die.

I am thinking a carb sync might be the ticket worked for wowbagger.  Got a manometer setup today.  I will give this a shot hopefully one carb is way off.

If not then I will go back to floats hanging up, needle / seat etc..

[chewbacca5000]

I just vacuum synced my carbs last night and it fixed the high rpm issue. My #4 carb was pretty far off. Now, it rides great and the tons drop down as they should once I let off the throttle.

I am trying to do a sync today and from what I can see everything appears to be way off.  Number 4 wants to suck up all the fluid before I can do anything.

Any tips would be appreciated.  Thanks!

[Greggo]

Did you ever bench synch them? 

[chewbacca5000]

Did you ever bench synch them?

No I looked at them and they all appeared to close so I left it at that.  I did not change any of the linkage from the original so I thought I would be good.

Just did a sync with my dial gauges and good it close idles at 1,200 on center stand going to go for another test run wish me luck.

Edit: It must of done something as now it stalls out.  Will try it again I guess.

[chewbacca5000]

They should be so synced so why I am I stalling at every stop sign.  No more racing that seems to be fixed, but now it stalls.  Plugs are black and sooty.  Using pamco, dyna 3 ohm coils, hm resister with Iridium plugs this setup screams on my cb750. 

[Stev-o]

Rich rich rich

[Tews19]

Is the last pic of it sync'd? If so, that's way off.  You need them closer... I was told to sync off the  carb with the highest reading and go from there....

[chewbacca5000]

Is the last pic of it sync'd? If so, that's way off.  You need them closer... I was told to sync off the  carb with the highest reading and go from there....

No last pic is just my setup.  Got them all pretty close, but it is hard to tell this gauge is not the greatest.  Bike no longer has the racing idle.  I think the sync must be good enough if it was terrible would it not affect other throttle positions as well.  It runs awesome in all other throttle positions other than idle 1/4 to full.


Steve O might be right it's just too rich of a mixture to idle properly.  1,2,4 were all black with suit.  Only 3 was tan.

I will double check float height tomorrow.  I have heard these particular carbs are very sensitive to float height.

Strange thing is that some times it does idle just fine.  It is usually best when it's cold.

[Stev-o]

What size jets?   What exhaust??

[Greggo]

It runs awesome in all other throttle positions other than idle 1/4 to full.

That's just how they are.  Can't crack to WOT too quick from 1/4, especially if the revs are low. 

[Tews19]

Greggo is correct.You cant gun it from idle. For the air mixture screw. I screwed in all the way. Then let out 1.25 turns

[chewbacca5000]

Greggo is correct.You cant gun it from idle. For the air mixture screw. I screwed in all the way. Then let out 1.25 turns

It is fine at all throttle positions.  Does not stall when I give it gas just at stop signs, intersections and my driveway.  Even if I gently ease of the throttle it still stalls.

It behaves better cold.  Tonight I took the tank off to put the "correct NGK D7EA plugs did some messing around and it idled rough, but did not die.  It only dies when after it's warmed up. 

[chewbacca5000]

What size jets?   What exhaust??

Good question not sure what the main jet size is got it in what I am calling the "carb kit from hell".  Not sure if I used the after market needle or not?

Exhaust is a 4 into 2 MAC style with no baffles, they were punched out or rusted out.

[Tews19]

Maybe the floats are stuck but in close position.? Then when you go to restart some fuel is forced??? Into the bowls?


Or possible you have a loose connection from the coils?

[Stev-o]

What size jets?   What exhaust??

Good question not sure what the main jet size is got it in what I am calling the "carb kit from hell".  Not sure if I used the after market needle or not?

Exhaust is a 4 into 2 MAC style with no baffles, they were punched out or rusted out.

These motors generally run better with back pressure, can you fab up some? (Cans can be made to work when on a tight budget). 
And thinking jets are big....

[chewbacca5000]

What size jets?   What exhaust??

Good question not sure what the main jet size is got it in what I am calling the "carb kit from hell".  Not sure if I used the after market needle or not?

Exhaust is a 4 into 2 MAC style with no baffles, they were punched out or rusted out.

These motors generally run better with back pressure, can you fab up some? (Cans can be made to work when on a tight budget). 
And thinking jets are big....

I'll try to make something up.  You think after market main jet is too big?

[seanbarney41]

Did you set the idle speed with the bike fully warmed up?