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

[davis96]

*edit*
Problem solved!, see page 3.
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Hey guys,
First, let me say that I'm not a huge noob when it comes to SOHCs... I had a cb350f a while ago which I worked on plenty. Posting a question is always my last resort, but I have searched the forums extensively and I'm at my wits end. I bought this '71 cb500 for $300 bucks not running and cannot get it running for some reason.

Symptoms:
I turn on the fuel and ignition (handlebar switch set to "run"), I push the starter button and the starter turns, but the engine doesn't start or attempt to start. Have tried every combination of throttle/choke while attempting to start. The choke mechanism functions properly. I've pulled the float bowls afterward, and they do have fuel; no fuel leaks from the overflow tubes. Putting my hand up to the exhaust, I can feel puffs of air coming out. Occasionally it will backfire. Grounded plug to engine block and confirmed I am getting park from both coils. After attempting to start, I pulled plugs and they are not wet and do not smell like gas at all.







What's on the bike:
-New battery, fully charged
-MAC 4-into-1 Exhaust (baffle is still installed)
-Velocity stacks with screens to keep out larger debris (spare me the lecture on how I should have kept the stock air box please)
-Larger main jets (#115, up from #100)

What I have done:
-Oil change, new filter
-New plugs, gapped correctly
-Tappet adjustment
-Static timing set
-De-rusted tank
-Carb clean/rebuild (Pulled them all apart, cleaned everything including emulsifier tubes, boiled the bodies in lemon juice. Float height set to 22mm. All floats move freely.)
-Bench sync using a high E guitar string
-Air screws are set to 1 ¹/₈ turns out

It seems under the circumstances (namely the lack of gas on the plugs) that I am having a fuel issue... I have the carbs out again and am going back through all the holes ensuring that I haven't missed something. I find it strange that none of the cylinders would be pulling in fuel/air mixture, especially since the carbs don't seem to have any air restriction whatsoever (with the velocity stacks). Perhaps the idle circuit isn't getting air through the air jet?

Let me know what you guys think
Thanks!
Davis

[BAchvytrk]

are you postive all the passages in the carbs are clean and clear? pilot jets clean and clear?

[davis96]

are you postive all the passages in the carbs are clean and clear? pilot jets clean and clear?

I know for a fact that all the brass pieces (pilot jet, main jet, and emulsifier tubes) are free and clear of any and all debris. I don't have access to a compressor here, so I cant really be sure about, say, the passages leading to the pilot jets. But I have the carbs open on my new rotisserie carb stand:
and I'm attempting to go back through them again and ensure all passages are clear.

[BAchvytrk]

use an old eye dropper or something similar to drop gas or carb cleaner down any passages you might be unsure of, say the pilots. should run out the other side. nice rotisserie by the way. you could use brake clean as it dries up fairly quickly if your going to check all the passages like this.

[luap]

have you tried rag with some gas on the intke side of the carbs to see if it will pop, what happens when you kick it over
  did you increase to idle jet, Id say the stock 38 are to small, 
anything change if you jump the starter silenoid relay, 

[davis96]

have you tried rag with some gas on the intke side of the carbs to see if it will pop, what happens when you kick it over
  did you increase to idle jet, Id say the stock 38 are to small, 
anything change if you jump the starter silenoid relay, 

I'll give the rag trick a try tomorrow. As for kicking it the result (or lack of result) is the same, just tires me out more.
What do you mean when you say "jump" the starter solenoid relay?
If it helps I have tried starting it while connected to a charger, to eliminate the battery as a possible issue (even though its brand new).

[davis96]

Floats set right?

Yea, 22mm. I don't know if I should adjust the float height somehow since I increased the jet size. Makes sense to me, but I have never heard anyone allude that it is necessary or even beneficial.

[JustinC.]

Are you sure fuel is making it into the bowl? 
You can check the fuel level in the bowl with clear tubing on the drains, hold the tubing up and open the drain.
I've found this very helpful to eliminate the guess work.

Lemon juice huh? Carbs look great!

Best of luck

[seanbarney41]

I noticed you used a tiny little guitar string to do your bench sync, I think guys generally use something more the size of a .125 drill bit.  The string should work ok for syncing but you may need to hold the throttle open to start...

[Randy]

did you make sure the carbs are getting fuel at all?.... I like to open the drains making sure fuel is flowing threw all the carbs... What is the slide set at... I had to but mine at the last notch.. Also did you try to run it on squrting gas into each carb, starting it up and seeing if it will run that way... I used gas in a spray bottle on the stream setting..

[luap]

just take a screwdriver an touch both terminals same time on the strart silenoid relay, with the stacks Id say some 42 idles  while you have the carbs apart , also with the stacks id say best bet is butterflies closed sucking ALOT of air, cant totaly remeber but think i had the same problem with the start spinning but nothing else, I had the starter cable on the same side as battery positive on the relay

[luap]

take the tubing off that is looped around the return spring those are breathers

[dave500]

youve done a good job getting those carbs looking clean,,but you must really blast compressed through the tiny passages that are throughout the carbs,some of these have bent/angled designs that can only really be cleaned properly with compressed air,,i mostly cast doubt on ignitions,but after i read the carbs werent air blast cleaned i wouldnt be satisfied they are truly cleaned within those tiny passages.

[davis96]

did you make sure the carbs are getting fuel at all?.... I like to open the drains making sure fuel is flowing threw all the carbs... What is the slide set at... I had to but mine at the last notch.. Also did you try to run it on squrting gas into each carb, starting it up and seeing if it will run that way... I used gas in a spray bottle on the stream setting..

I'm about 95% sure they're getting fuel, because every time I take the carbs off after trying to start a bunch of gas pours out of the bowls when I open em up. When you say "the slide" are you talking about moving the clip on the needle? As far as I know they're at the stock position, but I'll check it out right now.

[dave500]

fuel might be getting into the bowls,,and staying there?the tiny slow jet paasages arent letting the fuel up into the airflow maybe?if those are blocked the bowls can fill and thats it.,your before pics show some very clogged carbs,,id be inclined to blast at least a pressure pack of carb cleaner through them again,the slow speed jets are truly tiny and it sometimes takes a good full pressure air blast to get these clear,like 120 psi blast that a pressure can cant do.

[davis96]

youve done a good job getting those carbs looking clean,,but you must really blast compressed through the tiny passages that are throughout the carbs,some of these have bent/angled designs that can only really be cleaned properly with compressed air,,i mostly cast doubt on ignitions,but after i read the carbs werent air blast cleaned i wouldnt be satisfied they are truly cleaned within those tiny passages.

Is there any way to do this properly without a compressor?
The closest analogue I can think of is a can of electronics duster...

But the main problem I see with that is sealing on the orifice. If the air source isn't totally sealed on the orifice, air will just shoot out the sides around the little straw that comes with it, so there would still be no guarantee that the passage is cleared.

[dave500]

please read my just edited previous post.

[scottly]

Try spraying a short burst of starting fluid into the carbs; if it fires and runs for a couple of seconds, you are not getting fuel through the carbs.

[seanbarney41]

I'd try those spray cans of carb cleaner that you can get at an auto parts store for cleaning those tiny passages...they blast pretty good pressure (although certainly not 120psi) and you can watch for it to come out the other end of the passage.  Also the solvents in the carb cleaner are much more powerful cleaners than lemon juice...

[ben.cb500]

Use a bicycle pump with the water toy attachmen not ideal but might  reveal a clog if not able to blow clear through

Even a poorly timed ignition should hint at starting.

No compression?

Spray a starter fluid while cranking it.

[davis96]

Ok guys it looks like the consensus is that since I don't have a compressor at school, I should shoot the orifices with carb cleaner, which I'll do tomorrow (my can of cleaner is completely empty from the first cleaning).

Oh and I double checked my float height and it seems the floats might have been a little low, which might have been a big source of my trouble (I hope). I have re-set them to 21.5mm (just in case). I wish it wasn't dark/freezing cold outside so I could try again 

[davis96]

Use a bicycle pump with the water toy attachmen not ideal but might  reveal a clog if not able to blow clear through

Even a poorly timed ignition should hint at starting.

No compression?

Spray a starter fluid while cranking it.

One of the thoughts in the back of my mind was maybe it didn't have good compression (ignorance is bliss). I may call autozone/advance and see if either one loans compression testers (I know their reasonably cheap as tools go, but I really just don't want to invest in MORE tools if I can get it running without it. Time will tell, I may end up having to buy one from harbor freight.

[ben.cb500]

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.

[Danno]

just a case in point if you are trying to run the bike with out any airbox your jets are not big enough  the stock jets on that bike were 40  slows and 100 mains if I remember right is that right Dave? that being the case you need some restriction to the air circuit like the stock air box or you probably need at least 110 mains you might get away with the 40 slows but 42 may be better 

am I right Dave

[dave500]

looking again at your first pictures of the cruddy carbs,,that white rubbish is hard ingrained deep within the discharge ports of the carbs,even though the removeable brass is fine those may still be blocked,,they must be blown through every which way over and again a few times to be sure to get them clear,you would surely at least get a fart out of the engine if it had a hint of fuel with a good spark even if its wrongly timed,im sure youve got the timing correct and i as i said before i mostly blame ignition for these problems,,but just going by your before photo and the fact that compressed air hasnt been available to you id be blowing the carbs through again,it should fire and run even with the "wrong" jets danno,even with low compression it should fire or at least fart,,im still guessing the slow discharge ports are still blocked.