Topic: cb500 starting issues: Solved. I'm a moron, there I said it

[Danno]

I am sure you are right Dave and agree whole heartedly I was just trying to alert him to the fact that if  he was trying to run it with stock jets even after he got the passages clear it probably still would not run right

and I could not remember if I had the stock jet sizes right for that motor and knew you would know better

And I agree that with that amount of oxidation in those carbs the only way to get them cleaned other than with a three dip system and air is the way Dave is telling you

[davis96]

I am sure you are right Dave and agree whole heartedly I was just trying to alert him to the fact that if  he was trying to run it with stock jets even after he got the passages clear it probably still would not run right

and I could not remember if I had the stock jet sizes right for that motor and knew you would know better

And I agree that with that amount of oxidation in those carbs the only way to get them cleaned other than with a three dip system and air is the way Dave is telling you

Well as I said in my first post, I upgraded to #115 mains so I don't think that'll be a problem with velocity stacks and 4-1 exhaust.

[luap]

a heads up on the harbor frieght compression tester (least the one I got) didnt come with the thread pitch needed to screw into the head, if you get around a air compressor you could also check the valves, on my buddys build everything new or rebuild except the checking the valves put it all together kick kick push push nothing leak down test valves hanging open 3 bent valves replaced reassembled fired first kick
also if your second guess gas getting to the carbs put some clean line on

[davis96]

Yes that loo between middle carbs should be two long vent lines open and ending under the bike with the drains. Cut on long angle at end so they dont clog easy.

I think that might be the case with other years, maybe 72, but the '71 carbs loop the vent hose around the spring like I've done. Either way that surely isn't my main problem here.

a heads up on the harbor frieght compression tester (least the one I got) didnt come with the thread pitch needed to screw into the head, if you get around a air compressor you could also check the valves, on my buddys build everything new or rebuild except the checking the valves put it all together kick kick push push nothing leak down test valves hanging open 3 bent valves replaced reassembled fired first kick
also if your second guess gas getting to the carbs put some clean line on

Good to know. I'll search on how to check the valves

[ben.cb500]

Mines a 71, vents/breathers.

Drop small amount of oil in cylinders to temp boost compresion, use a starter spray, i have used brake cleaner.... maybe little extra compression might help. If it runs initially, u can rule out spark but mayeb not to some degree compression

[Scott S]

Mines a 71, vents/breathers.

 Same here. They should be vented to the atmosphere.

 I also agree that a high E guitar string mat be too small. Use a small drill bit...something about the size of the lead in a #2 pencil. You may just have the slide closed too much.
 There ARE lots of tiny internal passages that could still be clogged. Did you spray carb cleaner in both directions through all the tiny little holes and orifices? I do it with the jets out AND installed until I get a good stream of carb cleaner.

[davis96]

Mines a 71, vents/breathers.

 Same here. They should be vented to the atmosphere.

 I also agree that a high E guitar string mat be too small. Use a small drill bit...something about the size of the lead in a #2 pencil. You may just have the slide closed too much.
 There ARE lots of tiny internal passages that could still be clogged. Did you spray carb cleaner in both directions through all the tiny little holes and orifices? I do it with the jets out AND installed until I get a good stream of carb cleaner.

Well I've seen the vent tubes set up both ways, but I'd be glad to pull off the U-shaped tube and see what happens. I re-synced with a 1/8 drill bit, should add some air.

I was able to form an airtight connection between a compressed air can and a slow jet. I screwed that setup into to each carb and sprayed air through the idle circuit, and everything seems to be free and clear now. I will attempt to start again today if possible.

[andrewk]

Have you tried it without the vents connected to each other?

[davis96]

Have you tried it without the vents connected to each other?

I tried to start it again today after
(a) re-setting the floats
(b) re-routing the fuel lines to stock position
(c) using a dinky air can to spray orifices, and
(d) converting the center vents from connected to free hanging open to atmosphere....
Nothing. Same backfires which points to the motor not getting any fuel.

Now the plan is:
-Buy new can of carb cleaner, get after the orifices again, maybe try some pipe cleaners
-Rig tubes from drains to double check the level of fuel in the bowls
-Try again!

I'll keep you guys posted,
Davis

[Danno]

this has happened before on rebuilds just for giggles if your plugs show at least some fuel try switching the leads green and yellow on the points the other thing I have heard of is the wrong wire on the coil is grounded just grasping at straws with you but after all that you have checked that would be the next thing I would try if you are absolutely certain that the passages in the carbs are not plugged up

ps if those are not the exact right colors on the points trigger wires I apologize I am color blind

[davis96]

Ok so I did a few things, the biggest being blowing out all the passages (especially the idle circuit) like everyone suggested. My method of choice is pictured here:

The red is the straw from regular spray carb cleaner, the pink is a bit of adhesive heat shrink tubing, then that is stuck into a clear piece of tube which in turn overlaps one of the idle jets.
I just screwed it into each spot and it actually sealed quite well. After a bit of spraying, it appears there is no blockages.

The other thing I did was a twist on the method I found here of checking the float height via the drain holes. In the factory drain plug holes i installed brass hose barbs, and mounted clear tubing in such a way that it could be semi-permanent. The main reason is i was missing drain plugs and had a hodge-podge of bolts and screws plugging the bowls, which could not be easily removed for the purposes of draining the bowls.

I went through it a bunch of times in my head and I can't see why this won't work. Everything is fuel-tight and the tubes are vented to equalize pressure, but angled such that they shouldnt be prone to rain... worse comes to worse, I can remove the tube and put a plug on the end of the barbs.

I'll report back with results as soon as possible
Davis

[dave500]

did you blow where that slow jet screws into?in the actual carb body?both ways?if you havent this might be your problem,,if these discharge ports in the carb body are blocked itll be impossible to start,im only going by that first pic of the grotty carbs you posted,,and i imagine white gummy crud packed into those discharge ports,,even though youve done a thorough clean of the removable brass,those still tiny discharge ports must be clear,it only takes a half a grain of nothing to block them.

[Dimitri13]

Double-check that the manifold screws are in (where you would screw in the brass tubes for a carb sync).

Ask me how I know

[davis96]

did you blow where that slow jet screws into?in the actual carb body?both ways?if you havent this might be your problem,,if these discharge ports in the carb body are blocked itll be impossible to start,im only going by that first pic of the grotty carbs you posted,,and i imagine white gummy crud packed into those discharge ports,,even though youve done a thorough clean of the removable brass,those still tiny discharge ports must be clear,it only takes a half a grain of nothing to block them.

Yes all the passageways in the carb body were blown out, both ways

[verslagen1]

Does it start with starting fluid?
if it does then it's the carbs
if not then electrical

[Kurt V]

I'm sure no expert on SOHC4's, but have worked on lots of old engines. Two things I do know:

1. If you have fuel, air and spark you get ignition.
2. 95% of fuel problems are really electrical problems.

Get some starting spray and spray a bit in the intakes while trying to start and see if you get anything.

The fact you are getting some backfiring makes me think you have a problem with points or with timing. If that was not the problem, and some gas was getting to the cylinders I would think you would get the engine to turn over slightly, not backfiring.

[davis96]

I'm sure no expert on SOHC4's, but have worked on lots of old engines. Two things I do know:

1. If you have fuel, air and spark you get ignition.
2. 95% of fuel problems are really electrical problems.

Get some starting spray and spray a bit in the intakes while trying to start and see if you get anything.

The fact you are getting some backfiring makes me think you have a problem with points or with timing. If that was not the problem, and some gas was getting to the cylinders I would think you would get the engine to turn over slightly, not backfiring.

Well the main problem is I don't think ANY gas is getting into the cylinders because I can't see or smell anything on the plugs. I'll confirm that its a fuel issue next time I try to start by spraying some gas into the cylinders.

[davis96]

Double-check that the manifold screws are in (where you would screw in the brass tubes for a carb sync).

Ask me how I know

Ran out and made double-sure that, in fact, the manifold screws are still in place

[andrewk]

Did you happen to disassemble the advance mechanism to clean it?  If you have the points cam installed 180 out, the bike will backfire, similar to a super lean condition (like no fuel), at least before you get the cylinders loaded with fuel, then it makes bigger booms. 

Definitely try priming it with some gas or carb cleaner to see if it will fire off.  If it won't, you're looking at timing/ignition issues, which you will have to address first before you can perfect the carbs.

[andrewk]

Also, try hand choking the bike on one side while you crank it over.  That can help the carb force fuel through the first time- you'll probably flood it out a bit, but if you get it running that way, it will clear up quickly.

[spot45]

I am following this thread closely, as I have had similiar problems myself with my CB500K1.  Just out of curiousity what do the plugs look like?  Are they gapped correctly?   Have you checked your timing? I.e. points.

[davis96]

I am following this thread closely, as I have had similiar problems myself with my CB500K1.  Just out of curiousity what do the plugs look like?  Are they gapped correctly?   Have you checked your timing? I.e. points.

Yeah all the plugs are new and are gapped correctly. They look brand new, it is obvious no fire has taken place in the combustion chamber. Regarding timing, I have a light but since the motor isn't running I had to do a static timing set. I did so per the manual instructions using a 12v light bulb, so theoretically the timing should be correct.

[davis96]

Update:    1/27/12 The bike still will not crank, it won't even act like it wants to turn over.

- As far as I can tell, the idle circuit is cleared and functional. When I sprayed carb cleaner in the idle jet hole and looked into the throat, I could see the fluid forcefully spraying out of the inner hole.
- Air screws: 1 turn out
- Re-synched the slides (bench), using 1/8 drill bit
- When I got the carbs back on, it acted pretty much the same as before. So per the advice here, (with the throttle open) I sprayed gas into the throats of the carbs, then tried to start again. The motor did not behave any differently, except: the backfires ceased, and at one point the #1 carb kinda caught on fire.
- To make things more complicated I messed with the float valves like an idiot and now all 4 overflow no matter what I do.
   I've read your minds; let me address your concerns:
   1. Float height - I have done trial/error with the carbs on the stand, connected to the tank; I've tried it with floats set at 22mm (factory spec), as well as higher and lower. The leaks persist.
   2. Float movement - Floats are in good shape and move freely/do not bind on the hinge pins, which are straight and have been polished smooth.
   3. O-ring - The seats have new o-rings.
   3. Cracked overflow tubes - I am sure that this is not the case, because I can see the level rise all the way to the top before beginning to overflow using the sight tubes I installed in the drain holes.
   4. Seating surfaces - Both the seats and the needles have been pulled, cleaned, polished with abrasive paste (toothpaste), and spun against one another with polish so as to match the seating surface.

Regardless of the leaky valves, as long as the float bowls have fuel aren't too low, the motor should run...right? 
So my tentative plan is to re-do the timing and tappet adjustment tomorrow, and get some actual starter fluid instead of just gas. At the moment I'm more concerned with the bigger problem of getting the damn thing started than the overflow problem.
All ideas appreciated, thanks
-Davis

[Spanner 1]

Is the Blue point wire connected to the left-hand 1+4 points and the Yellow to the r/h 2+3 ?
Is the l/h Blue point set firing the 1+4 spark plugs ?..... Check that, por favor.

Did we time the bike with the correct point gaps too ? and are the points shiny clean ?

[davis96]

Is the Blue point wire connected to the left-hand 1+4 points and the Yellow to the r/h 2+3 ?
Is the l/h Blue point set firing the 1+4 spark plugs ?..... Check that, por favor.

Did we time the bike with the correct point gaps too ? and are the points shiny clean ?

Wow, I am embarrassed. You called it; the wires were backward. 
In my own defense, I'm not colorblind; it's just that I replaced my old 2+3 coil, and despite my specific request, the guy sent me another 1+4 coil... sooooo both have blue wires.
I REALLY hope this is the problem! Now I'm trying to figure out if 9pm is too late to go try to start her up again
Thanks! I will report back as soon as possible.
-Davis