Topic: Post Rebuild Carb Tuning

[aglick87]

did you say you bead blasted the carbs?  better be certain that none remains in the small openings in the carbs.  something else to consider is that plugs 1 and 4 are black.  ironic how plugs 1 and 4 fire off the same coil.  I'm not familiar with your bike.  but most fours have 2 coils.  I would look into timing/ignition if it was me.  I don't know if this would work or not.  but you could try giving a shot of starting fluid in each carb and firing the bike up.  if it revs up smoothly then dies down, you know your timing is out the door and you can focus your attention on fuel delivery.  I'm a newb myself, but I'm just throwing out ideas that mechanically make sense to me. 

[Bob Wessner]

Zeke,

I it helps, and misery loves company, I can identify with your frustration. I've probably had my carbs off four times including a good cleaning and rebuild kits. I'm currently looking for a T-shirt of something with a picture of carbs on it with the big red circle with the bar through it so I can share my feeling with the world.  Now I know why everyone has gone to fuel injection.

[Zeke]

did you say you bead blasted the carbs?  better be certain that none remains in the small openings in the carbs.  something else to consider is that plugs 1 and 4 are black.  ironic how plugs 1 and 4 fire off the same coil.  I'm not familiar with your bike.  but most fours have 2 coils.  I would look into timing/ignition if it was me.  I don't know if this would work or not.  but you could try giving a shot of starting fluid in each carb and firing the bike up.  if it revs up smoothly then dies down, you know your timing is out the door and you can focus your attention on fuel delivery.  I'm a newb myself, but I'm just throwing out ideas that mechanically make sense to me. 

Yeah, I did bead blast them -- I had all the external parts assembled with seals and covered the big openings with rubber and used dowels to plug the fuel/vac/accelerator pump holes.  There was a small tiny bit of media in there though.  Hit it with the hose, bucket, carb clean, and  compressed air.  I'm pretty sure they are clean, but while they are off I will clean them once more.  If I can see that I've bunged up the float height enough that it causes lean condition, I'm going to focus there.

On a side note, I swapped my coils left to right to see if #2 and #3 run rich -- if so, that coil might be weak.

Yep, Bob, I'm right with you.  I've spent over 40 hours tinkering and resetting stuff just to be sure since she first fired up and it still runs the same.

Thanks for all the help,

Zeke

[Dragman836]

just thought I would ask. is this your first rebuild? I'm curious if you got the cam chain off by one link when putting the top end back together . Ijust did my eng. and almost did the same thing. You said you could'nt see the timing mark. you should have lined up that mark with #1 @ TDC. (1-4) perhaps this is why you cant see your timming mark and this situatin would also effect vacume which would affect trying to set your carb. So take out #1 spark plug and find physicaly Top Dead Center then take off your timing plate and see how close your timing mark is to the timming mark then tell me

[Zeke]

just thought I would ask. is this your first rebuild? I'm curious if you got the cam chain off by one link when putting the top end back together . Ijust did my eng. and almost did the same thing. You said you could'nt see the timing mark. you should have lined up that mark with #1 @ TDC. (1-4) perhaps this is why you cant see your timming mark and this situatin would also effect vacume which would affect trying to set your carb. So take out #1 spark plug and find physicaly Top Dead Center then take off your timing plate and see how close your timing mark is to the timming mark then tell me

Hey Dragman:

It is my first SOHC honda rebuild.  I spent about an hour farting around with the CAM chain when reassembling, making damn sure that it was right on.  Don't know if the engine would even run off a tooth, would it?  At least it surely wouldn't idle as well as mine.  True, it won't idle without the choke, but I'm working on it.

I have to say though, you got the best of me with that one and I had to go out and check it.  Thankfully, the long socket extension I used to probe the piston hit its high mark when the timing mark was on "T".  So the gods have spoken.

Couldn't say about the vacuum thing, but it's got to be relate to my choke issue -- of course, then the choke door is closed you are letting less air into the engine, thus less vacuum?  I'm sure they don't intend you to sync with the choke on, though it doesn't really say you can't.

As far as the timing light -- I think the reason that I can't see the mark with the strobe is position of the inductive clip.  There are instructions in the box that say if you aren't getting a consistent strobe or it's not working properly you should slide the clip up and down the wire -- with my new wires the heat protection tube in it goes all the way to the ends, so the only place I can clip is right next to the coil -- and it's cramped there for the clip.

So, when I get it running I'm going to remove that tube for the time being and slide the clip to see if I get a more reliable reading.

On a stupid side note:

I love setting the timing on boats.  Take 'em out, floor 'em, twist distributor until you get max speed. 
Did the same thing with my brother's old Chevy Van too -- but driving down the freeway at 100 was kinda scary!!

I'll update when carbs are back in.

Zeke

[kghost]

Choke on = more suction

"T" mark is on the crank and has not a whole lot of relation to Cam timing if its off.

[Zeke]

OK, so I've known for a few days now that my #3 float was upside down.  I'm such a moron 

KG, yeah you are correct about the choke -- I don't know why it's not pulling vacuum -- but then again I never used the carbtune before now.

Anyway, regarding the cam timing -- yeah you are right about that too.  But, I'm telling you I mindf---ed that part of assy to death with my manuals and pictures spread around me and I was off a tooth in both directions several times and finally got it right.  I'm pretty certain, of that, then again I put one of my floats in upside down so what the hell do I know?  I don't wanna listen to you guys about that -- I wanna believe that I did that right.

OK, bike is running again -- but dammit my choke arm that is wired together cracked again -- it's hanging on for dear life.  I'm still trying to find someone that can make me a new one from my CAD design.....

I disassembled and cleaned all carbs again -- that's when I discovered my folly.  As I thought, the carbs are cleaner than a newborn baby's ass.  Every passage is as clean and clear as it was before.  I set pilots at 2 turns out -- manual calls for 2-1/8 for my model year, but it's not easy to keep track of that 1/8 turn.  Throught the idle drop procedure, it'll end up where it needs to be anyway.
Also did a bench sync.

Bike seems to idle better (I wonder why, with the float in rightside up) and I can take it off choke a bit more.  I wasn't able to fully warm it up or ride it as it got dark on me.

When I revved it I got sputtering from both #3 and #4 exhause pipes.  I hope to god this is because I haven't done a pilot adjustment, as my patience is thin.  If it doesn't work for me this time I'm going to take it to a local motorcycle mechanic who services all the local police bikes -- a friend told me he's really good.  I just need the bike on the road.  I'm starting a new job next week and until I move I have a 49 mile commute each way to work. 

I'm gone this weekend so I might get back to it sunday night.

Zeke

[Zeke]

Back at it.....

OK, so I fired it up today for a few minutes, determined to find something wrong that I hadn't found before.....

Some of you might remember me mentioning in this thread that my 2-3 plugs have good color, and 1-4 do not.

Today, I had her running for about 2 minutes and felt the pipes -- 1 and 4 were cold -- I guess that means they ain't firing.  # 2 and 3 were too hot to handle after two minutes.

I was actually happy, because at least that gives me something to look at, right?  Well, when I pulled all plugs and spark tested, all the plugs are sparking.  I wouldn't say it's the best spark ever, but it's blue.  Battery's at 12 volts.

What the hell?  How can they not fire?  All the float bowls have gas, and I've cleaned the carbies like 3 times now, THEY ARE SPOTLESS?

So I checked further the ignition system -- I had already swapped the coils and I suspect this has been going on the whole time.  I don't have a spark tester so through a search here I tested the coils -- 2.2 ohms in the primary coils, and around 12.2K ohms in the secondarys.

I tested the pulsers and they both measured OK -- one was 530 ohms and the other 542 ohms -- they can be 530 +/- 50 ohms.

I'm probably going to just take it in this week -- I don't have time to play with it -- new job wants about 60 hours/week for the next 3 weeks, and the commute is an hour each way.

But, if anyone has an idea I'd like to hear it.

Thanks,

Zeke

[SteveD CB500F]

I haven't read all 31 posts so maybe you've tried this:
Are the plugs damp with gas when you remove them?
Have you swapped/replaced the plugs?

I have seen plugs spark perfectly onto the cylinder head, but not when under compression - new plugs fixed it.

[ckkles650]

Hey Zeke,  Sometimes if you step back and relax a bit things will work out. First, You need to remember that the crank turns twice for every turn of the cam. Becuase of this you can not just look at the timing mark and put it on the 1-4 T. The cam must be aligned with the notch on the right side of the cam facing foward and exacly centerd with the top of the head. You won't be able to see the notch with the rocker cover on. Another way, is to look at the cam lobes, when the lobes are both down (both valves closed) you will be in the correct position, TDC #1. Secondly, in regaurds to the engine not idling except with choke on, I'm guessing that you probably have a vacuum leak. If you had the carbs completely off the bike you must make sure when you installed them that the carbs were pushed all the way into the boots on the engine side. This usally takes a bit of muscle to do as there is a groove in the boot(s) that the carb neck has to seat in. If the carbs are not seated in properly they will leak vacuum. One way to check is to spray WD40 around the boot to see if any is drawn into the engine. The engine will change RPM when you do this if there is a leak, the WD40 will not hurt the engine. Another possible leak is the test plugs for doing a carb sync. If these are open or are not sealed the engine will require more choke to run. (from experience) I just completed a rebuild on a 79 cb650 and went through some of the same problems as you.
Keep with it and good luck.

[Zeke]

Hey All:

For those who are still watching this thread.....

I'm running on all 4 cyls now -- turns out that the PO must have had an electrical fire or something, as the wires that go to the points had been spliced in by the main harness above the airbox -- using only crimp connectors.  Must have been loose -- so I pulled the harness out the side and soldered, heatshrinked, and connectorized -- now I've got 4 cylinders!!  Yeah!!

Thanks for all the suggestions -- now to tune!!

Zeke

[rcflyer91]

e-mail me thad CAD file for the choke arm, I'll see if I can make you one.
I work in a machine shop.

Jim