Topic: dies after carb rebuild

[Ernest]

74 cb 750 with stock air box and 4 to 2 exhaust.  The engine is actually a k6.  I bought the bike running but in bad shape, took it around the block a couple times and then started to tear down the carbs for cleaning.  Following a Clymers manual I have adjusted valve clearance, cleaned the points, adjusted cam chain, changed oil and filter, new plugs, new battery and then took apart the carbs to clean and adjust float height.  I only removed the jets for inspection and quickly screwed them back in.  The inside of the carbs were in good shape so I put it all back together and focused on cleaning the outside.

I have not checked the timing or compression because I dont have the tools yet to check those two things.

I got the murcury manometer hooked up to the vacuum holes,  I turned the mixture screws out one full turn according to Clymers and set the sync nuts down about 1/4" from the lock nuts to start the sync.  I did not bench sync the carbs first, and only read that later from a post here.  I have gotten the bike to kick start about a half dozen times but it idles above 2000 and eventually dies before I can start adjusting the sync nuts. 

The oil light will go off when I do get it to start for that short time but then will come on when it dies.

I'm not sure what to be focusing on first, I don't know how to see if the oil pump is working unless the engine is running and to look into the valve openings.  Or should I open the carbs back up and bench sync it first?  Do the jets need to be adjusted or do they just screw in until they are tight?

One other question, I'm new to bikes so this may sound stupid but...I quickly drain the battery to 8 volts when trying to get the bike running.  Does it matter if the battery is not fully charged when only kick starting it?

[KB02]

Okay, This probably won't answer every question you have, but it will answer a few.

Asd for the battery, that's not uncomon to drain it down using the electric starter. If you're just using the kick starter alone, then you might want to look into your electrical.

As for the carbs, it almost sound like your not getting gas for some reason. Either that or your timing is off. Time to get that timing light (or you could try static timing to see if you;re in the ball park.)

As for the oil light, that sound perfectly normal.
Hope this was at least a little bit of help.

[scondon]

    I'd do a bench synch on the carbs. If your just lining things up "visually" then line up the throttle slide openings rather than the adjuster nuts up top.

   Depending on how you cleaned the points(file/emory board, brake cleaner on paper) your timing may have been thrown off a little or a lot. Static timing with a test light should get you running at idle. You can static time without tools by removing a plug lead, inserting a spare plug in it, then rest the tip of the plug against the steel exhaust clamp. remove poionts cover and slowly rotate the engine until you see a spark.Note where you are on the timing mark at this point and make adjustments until spark is happening on the "F" mark(either 1-4 or 2-3) depending on which plug lead your testing). This method can drain a weak battery quick so best to have a full charge.

  Oil light goes off when oil is circulating(engine running) and comes back on when oil stops circulating(engine dies-stops running). Sounds like yours is working properly.

   Jets screw in until tight. Do not overtighten or you risk splitting the aluminum carb body.

    OK to kick start at any battery level, but best to have a fully charged battery when doing diagnostics.

[Ernest]

great help, now I just need some patience.  I'm anxious to get out and ride!

thanks

[TwoTired]

I only removed the jets for inspection and quickly screwed them back in.  The inside of the carbs were in good shape so I put it all back together and focused on cleaning the outside.

The smallest jets are the slows or idle jets and are more likely to be clogged than the mains.  Did you check both in each carb?

I have not checked the timing or compression because I dont have the tools yet to check those two things.

A simple instrument lamp with two wires and alligator clips will make a handy timing light for static timing.  Just clip it across the points you are timing and turn on the ignition. The lamp should change state at the time marks as to turn the crank manually.

I have gotten the bike to kick start about a half dozen times but it idles above 2000 and eventually dies before I can start adjusting the sync nuts. 

 You don't HAVE to bench sync carbs before using the manometers.  But, if it won't idle below 2000 you may have blocked slow jets in the carbs.

The oil light will go off when I do get it to start for that short time but then will come on when it dies.

This is a good thing. 

Or should I open the carbs back up and bench sync it first?  Do the jets need to be adjusted or do they just screw in until they are tight?

Screw in tight after cleaning.  Carb removal at your option.

One other question, I'm new to bikes so this may sound stupid but...I quickly drain the battery to 8 volts when trying to get the bike running.  Does it matter if the battery is not fully charged when only kick starting it?

A brand new, fully charged, 14 Amp Hour battery will electric start (150 amps) for about 90 seconds, where it will be drained and have low voltage.  You'll have to run the bike above 3000 RPM for 15 minutes to recharge the battery.

The coils need more than 8 volts to make good spark at the plugs.  Kick starting is iffy at this voltage.  You can get a good leg burn going and still not get the engine to light off.
Use an external charger to recharge your battery.  Turn off your headlight and just use the kick start until you get the bike running properly.

Cheers,

[my78k]

I agree that it is most likely blocked slow jets...I would be very surprised if it is so far out of time or so out of synch that it wouldn't even idle (albeit very roughly)...

Pull your slow jets and soak them in carb cleaner...then do the copper wire trick and be SURE that they are clean. They are ridiculously small and plug very easily. Also may want to throw on a fuel filter once you get them good and clean so as to not have them plug back up again.

Will it run with full choke?
 
Dennis

[Ernest]

Will it run with full choke?

I've found It starts with lever up chokes closed and then I have to start inching the lever down opening the chokes.  The longest I've gotten it to run was maybe 1-2 min before it quits.  If thats what you were asking?

I've got lots of good info here to go on.  thanks a bunch.

[my78k]

yeah that sounds like clogged slow jets to me...

The idle jets are responsible for fuel up to about 1/8 or so of throttle...First thing I would do (and have had to do twice now myself) is pull the carbs back off and ensure they are totally clear! Make sure you can pass a thread of copperwire through them...It really is amazing how little it takes to plug them. Also, if you get them clean but feed them from a dirty source (i.e. rusty tank) it's only a matter of time before you have to pull them off again...found that one out the hard way...

Dennis