Topic: Fault finding or head melting?

[Johnny Salt]

Hello
Hopefully somebody can help me out. I bought a CB500 (F1) a while ago which had been sitting up for 4 years, it had trouble idling. I stripped and cleaned the carbs and tank as there was a bit of rust about. I rebuilt the carbs using a keyster carb kit (which reading some of the posts makes me believe that might have been a mistake!). Now the bike is even more difficult to start, in fact I dont think that two of the cylinders are firing, which would leave me to think that there is a problem with one of the coils. Also after kicking it over a few times and taking a look at the plugs some seem quite wet and some seem bone dry, so now I was thinking there is defiantly a fuel delivery problem. I’m a bit concerned that this hole I’m digging is getting bigger and bigger in fact I’m not sure I can any longer see the wood for the trees so to speak. Would one of you guys (or gals) be able to supply me with a to - do list start to finish, of things that I should sort out in a logical order. I have a Clymer and a copy of the manufactures manual but I’m a little unsure about the best fault finding route to take. Also just for pig iron there is no way I want to bring it to a shop, I want to do this myself.
Thanks and take care.

[Bob Wessner]

You can do this yourself, trust me, if I can anyone can. 

I guess if I were you, after sitting for four years, I would go through all the recommended tune-ups first, get everything to the recommended specs.

You say you clean the carbs, but you didn't describe how you went about it. Did you completely disassemble and then blow out all the passages? Are the floats set to the correct height? You found rust in the tank, how did you clean and did you install any in-line filters?

You also say two plugs are not firing? Which two? The cylinders are paired to the coils. I don't think my first thought in this case would be a faulty coil, though not impossible, just not the first thing I would chase. When you kicked it over, were the wet plugs the same ones not firing? I guess we need more detail, but start with the recommended tune-up steps, all of them and go from there.

[Gordon]

First of all, glad to hear you're committed to doing this yourself!   Not only will you actually learn something, but you'll be better able to diagnose and fix problems as they come up in the future.  And like Bob said, if he can do it, anybody can.

Do what he said, and go through a complete tune-up so you have a good foundation to start out on.  Then look through the FAQ's and search the tech forum for topics about cleaning out the carbs.  Clogged carb jets and passages is probably the single most common problem these bikes have after sitting for a while, so there's no shortage of posts on this subject. 

Now, to check for a fuel delivery problem, open up the drain screws on the float bowls to see if anything comes out.  If yes, then that's not your problem, if no, tap the offending float bowls with the handle of a screwdriver to see if it's just a stuck float or valve.  If still no fuel, pull the fuel lines off the petcock to see if you're getting fuel out of both nipples from the petcock.  (Does the 500 have two fuel lines?)  If you don't get fuel from both, then the petcock needs to be cleaned or rebuilt.  You should also replace all the fuel lines while you're at it, and consider adding in-line filters.  The lines could be full of rust and other crud from the tank. 

If you go through all these procedures, starting with the tune-up and thorough carb cleaning, you're pretty much guaranteed to find and fix the problem.  Just don't skip anything along the way, or you'll regret it.  Good luck!

[Bodi]

The keyster kits are OK, I've had some strangeness using the kit jets and needle though. Generally it takes a LOT of miles to cause any wear a jet or needle however... the carbs usually just need the float valves and rubber bits plus the mixture screw (as it seems to be abused rather often). So personally I don't use the kit jets or needles unless there's an obvious problem from corrosion or damage. The Keyster complete kit costs about what the OEM float valve kit would, and you get the rest of the parts too.
Do a quick tune-up, setting the valve lash and ignition timing (static timing is sufficient for a decent start). As mentioned, the cylinders spark in pairs (1-4 and 2-3) so if a pair is missing you might have an ignition problem, but look for fuel issues first.
After replacing the float valves you need to set the float height to spec, the procedure is described in these forums and elsewhere.
Make sure the choke system is working correctly.
 Definitely the inline fuel line filter(s) are important and will help prevent future problems if installed.
After disassembly/ressembly your carbs could be way out of sync, that would make starting dubious and explain wet/dry plug differences. You can set them "by eye" on a bench and do a proper vacuum sync later, check that all 4 slides are about the same amount open (different for CV carbs, but I think you have slide throttle carbs).
A can of "quick start" ether fluid is nice for finding carb issues, a shot in each carb mouth before immediately kicking and any motor with spark will almost always start and roar for a second. Dangerous (super easy to burn down your bike and/or garage with the stuff) too, use it outside and be careful. If it goes with ether then dies, well then you have a fuel problem.
At some point you should do a wet/dry compression check to see how tired the motor is. If you're satisfied that the carbs are cleaned out completely and set up to a decent condition, the valves are adjusted right, timing set and ignition giving you good sparks... if you still have trouble a compression test is a good next step.

[cadler]

When you cleaned the carbs make sure you get the idle jet.
That is the jet that is mostly clogged

[Johnny Salt]

Thanks Guys,
I'm gonna hit the road from work now and get cracking on this tonight, ( best tell the wife to get the kettle on). But first off I will try answer some of your questions then let you know how I get on tomorrow.

I completly stripped and cleaned out all passage ways using carb cleaner and compressed air. I set the float heights as per the spec.
Last night I drained the bowls (actually because I was about to throw in the hat and so I didn't want fuel lying about for an extended time)   and there was fuel in all of them HOWEVER I'm not too happy with the way the fuel flows from the petcock. It is the type of tap with two nipples Bob but there is a far stronger flow from one of them, in fact you only seem to get any flow from the bad one when you block off the good one, and even then its not great flow, is this normal?.
I actually did strip and re build the petcock however to tell the truth I was never 100% happy with the way I had put it back together as I should have but I couldn't see any other way for it to go. I also replaced the fuel lines and installed two inline fuel filters. I cleaned out the tank using a good handful of nuts and bolts and shaking the SH1t out of it for as long as I could bear the sound. This appears to have done the job, no more bits of rust coming through.
 
Tonight I will start by checking which plugs are not sparking, and which cylinders are not staying dry or getting wet, take a deep breath and run through the tune up steps. 

One last questions when you say Tune up steps, do you mean the likes of the servising lists at the start of the Haynes Manual?

Thanks again,

Johnny

[cadler]

did you put your plug wires in the correct sequence?

[Bob Wessner]

One last questions when you say Tune up steps, do you mean the likes of the servising lists at the start of the Haynes Manual?

Don't have the  Haynes handy, but meant set point gap, plug gap, chain tension, adjust valves, etc.

[jtb]

Johnny, My 750F2 only has one nipple on the petcock, but it seems to me that if you have 2 (as a lot of the K models do) that fuel should flow equally from each.  Is that right, Bob?  If Bob agrees, I would check the petcock for blockage.

John

[Bob Wessner]

It flows equally from both on mine, each feeds one set of two carbs. Didn't the thread say earlier that two were dry..hmm.

[TwoTired]

The very early petcocks fed two carbs from the bottom of the tank and the other two were fed from the stand pipe (higher fuel level).  This starved only two cylinders until reserve was selected and all carbs were fed from fuel tank bottom.

This arrangement persited until 1975 US models on the CB500/550 where all carbs were fed from the stand pipe or bottom of tank dependent upon the petcock selector position.  Even later, the petcock was changed to a one outlet type.

Anyway, try running your bike from reserve petcock position to avoid fuel tank level issues.

I'm confused about the CB500 F1 designation as there is no such thing for US models.  CB500s were K0, K1,K2 (71,72,73).  CB550's had k models 74 through 78, and F models 75-77  (F0, F1, F2).

I can't imagine a correct Keyster kit for a CB500 F1 designation.  On each carb body mount flange top right is a stamping that idicates what bike configuration the carbs were originally tuned to operate.  627B, 022A, 069A are the stampings I've recognized, so far.

Please clarify bike model and carb type.

Also, tell us which cylinders are wet or not firing and which head pipes get hot (flash finger touch).  1-4 fire with one point set ands 2-3 the other.  Ignition isues fall into these boundaries.

The fuel feed issue is along 1-2, 3-4 boundary.  If we knew which two cylinders weren't firing, we could better guide your efforts.

Tuneups are at 3000 mile intervals.  Gotta establish that regimen some time, no?

Cheers,

[Bob Wessner]

The very early petcocks fed two carbs from the bottom of the tank and the other two were fed from the stand pipe (higher fuel level).  This starved only two cylinders until reserve was selected and all carbs were fed from fuel tank bottom.

Never knew that. Just keep learning something new all the time.

[Jonesy]

The very early petcocks fed two carbs from the bottom of the tank and the other two were fed from the stand pipe (higher fuel level). This starved only two cylinders until reserve was selected and all carbs were fed from fuel tank bottom.

Never knew that. Just keep learning something new all the time.

Same here. I always thought I didn't have the fuel lines routed correctly or something, and that when the tank was low it did not have enough head pressure to move the fuel to the carbs. Now it makes sense...

TwoTired, you're very deserving of the title "Expert"!

[TwoTired]

My 74 Cb550 taught me the petcock details.  My commute path had several gas stations along the route, so I routinely ran the thing 'til reserve was required.

At cruise there was a very subtle change in engine sound as only the slow jets of two carbs starved first.  If you didn't pay attention, you would eventually lose two cylinders completely.  Which, of course, got your full attention as you would lose 10 then 20-30 MPH until the fuel bowls finally filled enough to get all the cylinders working again.    But, at least there was some power from the engine if you feathered the throttle properly.

Later with the 76 and 77 Cb550F the old habits bit me.  Again at cruise the engine changes pitch and the throttle gets kinda non-descript.  But, then NOTHING.  The engine outright dies.  If you are really quick on the petcock switch, you only lose 40 mph.  Imagine these events in traffic at 70 and 80 MPH.  Stress.   On bikes with the newer petcocks, any change in engine behavior gets a fuel reserve response to take that variable out of the equation.

I think I like the earlier scheme better.  I wonder why Honda changed it?
Cheers,

[Jonesy]

With the early 750's it's almost the same. I'll roll on the throttle and get a lot more lugging noise from the engine rather than power! Flip over to reserve, and we're all better...

[Johnny Salt]

good morning,
thanks for the further help LAds, I'll give just a very quick update on where I'm at.

While rotating the engine to get tdc on the first cylinder, with the points cover off I noticed that the points gap didn't look right (by right I mean that the gap, by eye, looked different for both) however before checking this I said that I would attend to the tappets, I removed the tappet covers, took guage in hand, bent it so that I could hook it 'down and under' and went to take to first reading. The first tappet I did check required adjustment but I wasn't happy with the way I was doing the job, primarly because the confined space and angle meant that I didn't think I could get a good feel as to which ones were catching / moving too freely etc. basically I dont have the experience just yet. Also the guage split half way along where I made the bend so I was worried that it could fall apart completly. So with this in mind I have decided to remove the rocker cover completly and do the job then.

I cant say which two cylinders were running dry as the tank is empty and I wanted to adjust tappets and points before I moved onto this part.  But tonight I will get some new fuel, check the tap operation in bath settings , hook it up and kick over the engine a few times, then check the plugs. I'll let you know how I get on.

When reading back on this looks like I didn't do much atall last night even thought I was in teh shed for almost two hours, but I'm happy to know that I have already recognised two problems which will need fixing.
Also regards the petcock, thanks for the heads up on this TwoTired, I will get those carb identifiers and double check the bike model too, it was born in 1976, actually the bike came from Italy originally. One last thing I got the Keyster kit from Dave Silver Spares, I gave them the engin number year etc and this was the set that they sent out, it all appeared to fit right.
Cheers

Johnny

[cadler]

Whats a keyster kit?

[bistromath]

Er I don't think you can set the valve clearances with the head off. Normally you set it again after the head goes back on.

[dusterdude]

bistro,he said rocker cover off.at least i hope thats what he`s goin to do.

[bistromath]

Nurrrrrrrrrrrrrrrrrrrrrrrrrr 

Carry on.

[Bob Wessner]

The very early petcocks fed two carbs from the bottom of the tank and the other two were fed from the stand pipe (higher fuel level).  This starved only two cylinders until reserve was selected and all carbs were fed from fuel tank bottom.

I have to admit that this was so contrary to my earlier belief about the fuel flow between "on" and "reserve" it gave me pause, plus I think my descendants were from Missouri  . I happened to have a K4 tank sitting around so I thought I would conduct a little experiment and its internals, including the valve, are the same as my K0.

I pulled the petcock and taped off the standpipe and reinserted it and filled the tank with water. Based on the above, in the "on" position, one of the outlets should have still passed some fuel, correct? No fuel passed from either outlet until I moved the petcock to the "reserve" position then both outlets passed fuel. It appears to function as I had originally thought.  Have I missed something.

[TwoTired]

The very early petcocks fed two carbs from the bottom of the tank and the other two were fed from the stand pipe (higher fuel level).  This starved only two cylinders until reserve was selected and all carbs were fed from fuel tank bottom.

It appears to function as I had originally thought.  Have I missed something.

No, I think I did.  You're correct.  I'm wrong on this one, I think.
I set out to affirm my assertion this morning by dismantling an old CB500 fuel petcock.  To my surprise.  Both outlets are clearly fed from the same source.  Either stand pipe or base of tank.



Concerned about early signs of dementia,    I tried to recreate my earlier summary judgement.  I then realized it was based on empirical testing and was flawed in concept but not necessarily in effect.  Here's why.

Each of the two outlets on the petcock is fed from a common bore with the supply at one end.  If you rolled a small BB in one end and let gravity have its way, it will fall out the first and nearest down tube it encounters.

When the fuel level gets low enough to approach the top of the stand pipe the head pressure of the fuel in the system falls.  This effect is more pronounced while the bike is running stationary without the fuel sloshing around from changing inertial forces.    Anyway, if fuel is being used by the carbs, the common bore feeding the fuel outlets deplete and if the head pressure is low enough, only the first outlet encountered is filled.
This is what I saw.

I was syncing carbs in the shop and two cylinders starved for fuel.  The tank was on a stand nearby and two clear hoses were being used to extend the two fuel lines over to the carbs.  It was clearly seen that only one of the hoses was dry and the other filled.  Switching to reserve immediately filled the other fuel line and all carbs worked again.  A "discovery" was born.  Flawed, yes, but still relevant, I think.

Consider people troubleshooting run problems on bike with low fuel levels.  They can encounter exactly the same effects I saw (starvation of two carbs) that can be simply overcome by switching to reserve.

I still maintain that not everything I know is wrong.  It's up to you guys to figure out which things aren't.  Sorry, I'm not 100%   

Nice catch, Bob!   

[Bob Wessner]

I still maintain that not everything I know is wrong.

Never would have thought that. Still enjoy the detail, foundation and background you often provide beyond the simple "yes," "no," or "maybe" answer.

[Johnny Salt]

thanks for all your suggestions on this lads. its givin me a lot to do, especially since I discovered that the rockers are mounted to the rocker cover so its obviously impossible to check tappet gaps without this in place. Now I can wait for a new gasket, no matter I can polish the cover and test twotired and bobs theorys on double nipple petcock operation while I'm waiting.

talk soon.

[dusterdude]

tt wrong?...nooooooooooooo it cant be.hide the women and children the barbaric horde is coming to get us.