Topic: 77 carb sync walk through

[BobbyR]

Well done!!!!!!!!!!  I would not get too anal about the bike at this point. Most of these bikes idle at an indicated 1200, I am sure that is plus or minus depending on your tach. As you run the bike you will probably find it will run better. They also run rich, but, if you are not blackening plugs, I would not sweat it. You made it through the carb synch, so go find something else to improve. If you keep taking the carbs off taking them apart you will likely break something. Enjoy your bike, life is short, ride rather than wrench!

[TwoTired]

The backfiring was coming out of the exhaust.  How would it come from the carbs?

Back fire in exhaust could be a build up of fuel.  Carb back fire can be from early ignition timing, lean mixtures, poor valve seat closure etc.

  Or, in severe lean cases, no pick up at all. This sounds more like what happens when i hit the gas from idle very quickly

Still sounds like accel pump issues, to me.

I'm guessing you didn't properly clean the two check valves in he accelerator pump circuit. or verify they function properly. I cleaned everything, not sure about how to make sure they were functioning properly though

You can test the pump by pulling off the #2 float bowl with the acel pump attached, filling it with gas and actuating the pump rod.  If it's working, you'll need safety glasses for continued good vision.

Did you check the holes in the periphery seal were open? I have no clue how to perform this step

See attached pic.  I had to drill mine open again, as they were swelled nearly shut.  Be carful not to tear the rubber while drilling, or you'll have a leak.

Did you verify that all the squirters in each carb shot a nice even burst of fuel when the throttle was applied? yes i checked everything by using carb cleaner and shooting some into the holes and got nice pretty mists out the other holes and ends, the jets were clean for sure!

I put the carb bank in a bench vise. Reinstalled the #2 bowl filled with gas, and worked the throttle a few times.  You can then see if all nozzles are squirting and with the same intensity.

Electronic tachs (test equipment) can be purchased that use the timing pulses from the ignition to calculate accurate RPM.

Even without the accurate tach you should find the proper IMS setting to correspond to the mods made to your bike.  I doesn't seem likely the stock book values will be relevant.

[dgilling]

Still sounds like accel pump issues, to me.

I forgot i had pictures of the accel pump its not the best angle though.  this is what it looked like before i cleaned it really good with carb cleaner.

You can test the pump by pulling off the #2 float bowl with the acel pump attached, filling it with gas and actuating the pump rod.  If it's working, you'll need safety glasses for continued good vision.

How do you fill it with gas when the float bowl is off?  and to actuated it do you just push on the rod that sticks out where it pokes through the top of the bowl?

[TwoTired]

How do you fill it with gas when the float bowl is off?  and to actuated it do you just push on the rod that sticks out where it pokes through the top of the bowl?

You're kidding right?
Imagine there is beer instead of gas in the tank and your only mug is the carb bowl you just removed.  Now can you get beer into your mug?

I used a spare gas can with a pour spout usually employed on my lawn mower.  But, if you remove the hose from the petcock and set it to "ON" or "reserve", holding the carb bowl under it should fill it with gas.

Cheers,

[dgilling]

Actually no i wasn't kidding.  Based off your description it didn't make any since.  If you removed the float bowl like you said then when the gas is turned on gas would just run out making a mess with no bowl to catch it which is like what you described.

This doesn't explain how to test the accel pump.

so you remove the bowl, hold it there and fill it up, push on the rod that pumps the accel pump and watch gas squirt out from where the float bowl should seal??? is this correct?

[TwoTired]

so you remove the bowl, hold it there and fill it up, push on the rod that pumps the accel pump and watch gas squirt out from where the float bowl should seal??? is this correct?

Yep.  I can feel in the rod if it is pushing air or fuel.  Should be all fuel, and none should go back into bowl from the pump at the bottom.

Cheers,

[eurban]

I'm sure there are many ways to test the pump, but you can certainly check for basic operation with the carbs on the bike and the air box removed.  Fuel up the carbs and whack open the throttle.  Is fuel squirting towards the engine from each brass nozzle? Oh, and I would agree with TT's assessment that it still sounds like you still have an acell pump issue . . . .

[mustangcar]

did you find the feed hole coming out of the float bowl?,it brass with a little square plug in it,gas will squirt out of it when the plunger is pumped,try cleaning any little grit around that square plug with a fine wire or needle,,

[TwoTired]

did you find the feed hole coming out of the float bowl?,it brass with a little square plug in it,gas will squirt out of it when the plunger is pumped,try cleaning any little grit around that square plug with a fine wire or needle,,

Be careful poking sharp implements in there, for behind that square plug is a check valve, a round ball, I think.  If that gets surface imperfections, it won't seal and then forever behaves as if it were dirty and ineffectual.

Cheers,

[winnipeg550guy]

I purchased one of these off Ebay and I gotta say it is super easy to use and is pretty accurate, cured my carb problems.
 Inexpensive and easy to use can't ask for more than that
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&viewitem=&item=230242569500#ebayphotohosting

 

[mturner1286]

in regards to that carb balancer from the UK. How much did it cost in American dollars? including shipping.  do you think it would work well on my 73cb 500 four? Was it as easy to use as the advertisement says? 

[Johnie]

I think you are talking about the Morgan Carbtune.  I paid $80 for mine in 1999 so I bet it is over $100 now.  You can check them out at www.morgancarbtune.com  I would not be without it.  Mine came with brass nipples and I heard they are now coming with plastic ones that can break.  So some guys are finding the brass to replace those.  Maybe you can buy the brass from Morgan instead???  Yes, it is as easy to use as it says and will work on your 500.  The first bike I used mine on was a 77 CB750K after I had done my first carb rebuild in my life.  That bike never ran that good even when I had it new.  Carbs were spot on when I finished.

[winnipeg550guy]

in regards to that carb balancer from the UK. How much did it cost in American dollars? including shipping.  do you think it would work well on my 73cb 500 four? Was it as easy to use as the advertisement says? 

 I use mine on a 74' Honda CB550k carb which isn't much different from the 500's, in fact I actually use the 550 carbs on a 73' Honda CB500 motor.
In the end after shipping costs(very reasonable and fast for overseas) I think between $35. - $40. CDN./ US. at todays exchange rates.

 And yes, it is very easy to use. It took me longer to go to the fridge, grab a beer, remove fuel lines then tank for best access for tuning,bike needs to be running though so you need to pick up longer fuel lines(cheap at most hardware stores) and place the tank up and out of the way. I also bench tuned mine a while later when doing some jet adjusting and it was spot on.
 Instructions are straight forward even for a guy like me who's never done it before.
 It might not be as precise as the expensive tuners but it fit my budget.