Topic: 71 CB500 carburation problem

[mdstrat]

Can anyone help me with this problem? I have a 71 Honda CB 500 I'm trying to restore. I don't know alot about bikes. This bike belonged to my wife's deceased husband and sat for years before I got it. I am an automotive technician and I have cleaned and coated the fuel tank, removed and cleaned carburators, replaced jets and needs with the same sizes. Bike seems to run rich, very rich, number 4 pops out exhaust and has very high HC on exhaust anylizer, 2000 ppm, others are at 500 to 650 ppm, Float settings are at 23mm, air bleed screws are out 3 to 3 1/4 turns, Bike cruises fairly well but will pop out exhaust, Idle is unstable and have to rev to keep from stalling out at times. Ignition timing is ok, and points and condensors are ok (46-49 degrees dwell). Cylinder compression is good and equal on all cylinders. I have been playing with this bike for 4 years but just can't seem to get it right. Any suggestions?

[lucky]

So these are the facts.

1971 CB500.
Exhaust type?
Intake type?
Main jet size?
Idle jet size?
Slide needle clip position from the top?
Mixture screw turns out?
Float setting 23mm. Stock was 22mm.
Dwell 40-49º??? wide range Is the point gap correct?


Also if the condensers have never been changed they need to be.

All of the question marks need to be answered in case the previous changed and stock parts or settings. Then I could help you.

[mdstrat]

Exhaust is straight pipe had two into one mufflers but mufflers are gone, intake is stock, main jet #100, slow jet #40, needle clip position is 4th from top, air bleed screws 3 - 3 1/4 out. piont gap is correct however dwell fluctuates, 46 to 49 degrees.

[mdstrat]

To all on the forum; There seems to be a communication problem on my part, (I'm new at this). My bike is running excessivly rich, bike had sat for years, I've removed cleaned and replaced jets and needles in carburators with the same sizes and clip positions. The intake is stock, the exhaust was two into one muffler, but the mufflers are gone, now it is staight pies. Started with factory float setting at 22mm, way too rich!! leaned out to 23mm still rich but not as bad as before. Point gap is correct and ignition timing is correct.

[mdstrat]

OOPS forgot to mention, Main jet #100, Slow jet #40, and needle clip position is 4th from top.

[iron_worker]

I thought the 500's stock jetting was 38/98?

Sounds like you might need a smaller idle jet. You shouldn't have to have the air bleeds turned out that far. I have heard that if they aren't in their 1 to 2 turns out range that they can cause eratic mixtures.

Hopefully someone will chime in with what stock for a 500 is.

IW

[LesterPiglet]

Float heights do not adjust mixture, they should be set to factory settings.

[Deltarider]

I thought the 500's stock jetting was 38/98?

Better not to communicate 'thoughts' and help to avoid this forum fills with incorrect data. It's 40/100 for the 500. In Europe a few countries had the 500K3 that had 42/90 in PDcarbs.

[lucky]

I thought the 500's stock jetting was 38/98?

Sounds like you might need a smaller idle jet. You shouldn't have to have the air bleeds turned out that far. I have heard that if they aren't in their 1 to 2 turns out range that they can cause eratic mixtures.

Hopefully someone will chime in with what stock for a 500 is.

IW

Stock jetting for the 1971 CB500 was #100 main jet,#40 idle jet,needle clip fourth down from the top. Mixture screw 1.5-2 turns out.

[lucky]

Float heights do not adjust mixture, they should be set to factory settings.

I agree.

[lucky]

Mdstrat keeps saying"straight pipes" and two mufflers etc."Two into one muffler" etc.,.

He has a 4 into 2 system with no mufflers. Is that right???
But does it mean you now have 4 straight pipes or 2 straight pipes?
Otherwise how many open pipes are there ? Two or Four???

This is what I know so far.
FACTS:
1971 CB500.
Exhaust type 4 into 2 (no mufflers).
Intake type stock air box and stock filter.
Main jet size #100mm(stock)
Idle jet size  #40mm (stock)
Slide needle clip position fourth from the top. (stock)
Mixture screw turns out?
Float setting 23mm. Stock was 22mm.

He keeps saying it is running rich but does not say what evidence there is.
I am wondering if the choke is on, or if it is not a 1971 since nothing makes any sense.

MDSTRAT...Could you check your choke operation and look at your spark plugs?
If you already did that let us know, also look on the frame on the steering head and tell us if the tag on the right side is there and what year it says just to cover all the bases.  Thanks. LUCKY

Float levels should be reset to stock setting.

We may have to go back to the beginning and check the compression for broken rings or just heavy oil consumption.

How many miles are on this motorcycle?  I guess I should have asked that FIRST.  My own fault. QUOTE from MDSTRAT "bike had sat for years,"

Piston rings could be stuck in the pistons.

OK Compression check is NEXT.

[mdstrat]

Ok lucky, as I mentioned earlier I could not send you a picture of my exhaust, but this is wwhat I'll do I'll change my avitar pic. Compression is good in all cylinders. I've been thinking about what you had said earlier about my exhaust not having mufflers which will reduce back pressure and increase flow through the engine, so maybe I need to reduce my jets?

[mdstrat]

Now if you can see the picture the pipes are two to one on each side and are separated on the ends.

[mdstrat]

I hope this helps everyone to see the exhaust, the bikes throttle respones is sluggish and RPM's are slow to rise, exhaust gases on my anylizer indicate high HC and high CO and low O2 indicating a rich fuel mixure

[lucky]

Now I understand.

Thanks for the work you did to get photos for us MDstrat.