Topic: CB500 power issues

[camelman]

I'm having a few issues with a CB500, and am looking for advice.  I recently rebuilt the engine with new seals, #1 piston, #1 piston rings, and honed the #1 piston.  I cleaned the carbs up, set the float heights, and put her back together.  I adjusted the valve lash, set the timing (after replacing the points and condensers), rebuilt the coils with new leads, verified the spark plug boots had the correct resistance (5k ohm if I remember correctly), and put in fresh gasoline.

The issues I'm having are poor upper RPM performance, burbling throughout the rpm range, and no apparent charging.  I checked timing with a timing gun, and I can't adjust the timing plate enough to set the "F" line at the mark.  I trimmed out the timing plate slots, but I still can't get all the way through to the "F".  Because of this, full advance is never reached.  Can anyone give any advice on either of these subjects?

Thanks,
Camelman

By the way, I did verify that the slows and mains are stock (40 and 100).  I set the air screws to 1.5 turns out, and the entire motorcycle is set up with the stock intake and the stock 4-1.

[TwoTired]

Whoops.  The CB500 never came from the factory with a 4 into 1 exhaust.  They all had 4 into 4.  So, your 4 into 1 is NOT stock.

Did you check the FAQ for info on the timing plate adjustment?  Are you using Diachi points?

What clip position is the slide needle clipped in?  Are they Honda slide needles or aftermarket?

Can you describe the spark plug deposits when the engine is killed while the engine is "burbling"?  And what throttle positions does this occur?

When you cleaned the carbs, did you clean the emulsion tube's air bleed holes (they are behind the main jets)?

[camelman]

TT,

Thanks for the fast response.  I typed incorrectly the first time.  It is a factory 4-4.  The burbling comes at all rpms and throttle positions.  The more throttle I give it, the more it burbles, although the burbling decreases as the rpm climb.

The needle position was set correctly (according to whatever "stock" information my roommate found), and the entire carb bank were cleaned out in the most environmentally ethical manner possible (I think the local hippies would have killed us if they saw it).  I paid special attention to the emulsifier tubes and all of the passages.  The slide needles are stock as far as I can tell.

I just read your adjustment post for the timing plate, and will try that next.  I can't remember which points I'm running, but will get a look in the morning.  I'll do a plug chop too to find out how it is burning.

Does this sound like clogged carbs to you?  That's the feeling I'm getting.  I wonder if I should pull them apart again for another cleaning.  I rinsed the tank out, but I'm sure there is some crud left in there.  I didn't get a fuel filter in there before starting it, so there is a chance some debris got into the carbs from the tank.

Camelman

[dave500]

umm,err,?have the carbs been syncronized?

[CB500_k2]

If you have stock coils it is rather hard to put new wires in them.  I tried with mine by pulling out the old ones and pushing in new wires in the holes.  I got some discharge to ground around the the new wire grafts and had to get new coils before I could get a strong spark at the plugs.  How did your put new wires on??

[camelman]

The carbs have not been synced by gauges, but they are bench synced.  The power issues occur at full throttle too, so I don't think it is specific to syncing the carbs.

I've done a few of these coils now, and I've had good results.  I cut out the old wires, install new ones, and fill with a high temp epoxy.  I then wrap the entire coil.  It works well and is documented in the FAQ.

Camelman

[TwoTired]

Does this sound like clogged carbs to you?  That's the feeling I'm getting. 

Without a spark plug read on clean plugs, it is hard to predict.  If too rich, it is either adjustment or blocked air passages.  The air passages premix air with the fuel before entering the carb throat  That's why I asked about emulsion tubes given your claim of "burbling".

You should also compare all the spark plugs with each other, looking for equal deposits.

I wonder if I should pull them apart again for another cleaning.  I rinsed the tank out, but I'm sure there is some crud left in there.  I didn't get a fuel filter in there before starting it, so there is a chance some debris got into the carbs from the tank.

If you don't know what the internal settings are or what parts are inside, I don't see how you can avoid getting in there to find out. (assuming the problem is mixture related.)

I don't think you should be avoiding a proper vacuum sync.  A mechanical sync does not allow for individual cylinder differences in volumetric efficiency.


Cheers,

[camelman]

I'm pulling the carbs back apart.  We did a plug chop, and the cylinders vary from rich to lean, so I believe the carbs are dirty again.  I'll finish up with a vacuum sync when everything is up and running correctly.  I just don't want to put that effort in until the rest of it is correct.

By the way, does anyone know if a CB550 alternator will fit a CB500 engine?  I looked up the cover part numbers and they match, but the actual windings were not listed as interchangeable.

Thanks,
Camelman

[dave500]

ive got a couple of both engines and the alternators look the same,ive got a few stators and fields on the bench and are identical.

[spitcrazy]

Camelman, I would like to add here that as far as the air screw, 1.5 turns didn't work for me, too lean. about 1 turn is money, try that. I had the same burbling. I have found two different specs   on the air screws for these, one being 1 turn +/- 1/8 that works. Try that.
 Doesn't work: http://www.motorcycleproject.com/motorcycle/text/specs.html (is this for a pilot screw on the engine side - newer carbs??)
 Works: http://forums.sohc4.net/index.php?action=dlattach;topic=5410.0;attach=3002;image (intake side - old carbs?? guessing here!)
Plugs are tan after a warmup run and idle chop.

 I know that this shouldn't affect upper RPM but once I did these things and got the fuel levels in the bowls right. it smoothed right out across the range.

One of my floats was off. I pulled it again and it would seem that the spring in one of the needle valves is weaker than the others so the angle I had the carb bank on was compressing that valve as I set it.... float ended up too low so that cylinder was starved for fuel... be careful that each float is just contacting the valve when setting it.

FILTER!

Timing. I had the same problem as you, setting my timing, I ran out of room. After playing with it for an hour, back to the laptop. After reading this: http://www.motorcycleproject.com/motorcycle/text/sohcign.html
I noticed the part about eliminating the free play (slop) in the plate by "peening" (see the drawing at the top of the article)  the mounting bosses gently so they grip the plate and there is resistance to turn it. I first rotated the plate counter clock until at a quarter of the adjustment range, then gently tapped the bosses with a drift and mallet until it was snug.
Proceeded with gapping and timing and the timing was pretty much dead center of the slots. Advance is perfect as well. Took about 5 minutes to time it! That free play in the plate is a nightmare and now it is permanently gone. Other tips on this forum suggest using a bent feeler gauge held under one of the screws to fill the gap at one of the bosses to prevent the slop. if you are hesitant to bang on the bosses, this will accomplish the same thing.

Here's a pic of an alternative peening of the bosses that someone did with a punch.... the little dimples on the bosses:
http://forums.sohc4.net/index.php?action=dlattach;topic=71538.0;attach=118118;image

Use OEM "TEC" points only, I have no experience with Diachi, but there is enough info and analysis here that they suck! Listen to HondaMan and TT........ run away!!

I am a noob and reading what these two gentlemen have to say has ended up with my 500 running like a top! I have no vac gauges but the bench sync seems so close that I can ride with no issues. Not optimized but still very good.

[Deltarider]

I have no vac gauges but the bench sync seems so close that I can ride with no issues.

I share your experience. I have a set of Boehm vacuum gauges. Made in Germany, but I suspect they're out of calibration. The last three times, over a period of twenty years, I simply benchsynced my carbs and always managed to adjust them within 2 cm Hg and that's well within manufacturers specs. Four dials or tubes may look impressive, but you don't need them. When you benchsync carefully, for a final check afterwards just one vacuum meter will do. When you suspect mechanical problems in a cilinder, needle behaviour will tell you.
There's so much talk in this forum about syncing. Unless you strongly suspect a PO messed up the sync, I'd advise you to check valves and ignition and find the timing your engine purs nicely.