Topic: cb500 - rich condition possibly not due to carbs ? (partially fixed)

[paul_D]

Hi,

Took my bike out for a quick and cold(+1celsius) jaunt around the neighbourhood to see if my carefully set and checked floats,  and new needle valve and seat corrected my issues from last summer. They didnt.

The bike starts up very nicely, idles well when warmed up and when I start riding its fine. about 2-3 minutes in through the neighbour hood it begins to backfire and sputter above 3-4000rpm before dieing. The bike refuses to restart. The plugs are all four fouled up. The same scenario played out identically last summer (above 20 celsius)

My carbs are 649A
100 main
40 slow
3 clip
1 1/8 air screw
all passages well and nice and clear
every part are free and clear (even the each emulsion tube)
Carbs are all balanced with manometer

My filter is a uni 4055 with very light k&N filter oil sprayed on
My exhaust is a 4-1 jardine set
My plug caps are all new 5kohm caps
My ignition is a Dyna-s kit
My fuel lines are new and no kinks


I understand a needle clip being off by one or something causing it too run rough or a bit rich. But the bike dies after 2-3 minutes of riding on brand new d7ea plugs gaped at 0.065.


Are there any thoughts to what may cause this ? What else should I check ?

Edited: title (19/04/2014)

[Trad]

To foul that badly after a few minutes is pretty severe. Are you sure they are gas fouled and not oil fouled? How's compression?

[paul_D]

All 4 are dry and flaky black. My exhaust and rear swing are are the same. The rear wheel adjustment mechanism that's usually chrome is a flat black now.

[dave500]

youve got the choke operation correct?try it without the air filter.

[paul_D]

Choke is open. Lever down.

[grcamna2]

I'm thinking possibly the floats are "heavy"(ethanol/fuel soaked & weighed down if they're plastic) or if you have brass floats they could be fuel filled.

[paul_D]

They are black plastic floats.

They sat dry with no fuel for a few years before I got the bike, the bike was sitting and had no fuel.

I would think they "lightened" up over time. I could weigh them and see though. But i dont think there is an excepted value on those.

Mind you I checked each float set at 22mm and the fuel bubble in the clear tube was 2-3mm below fuel bowl lip.

[paul_D]

I'm pretty much stumped here. I might be selling it. I'm not sure yet.

[TwoTired]

I'm pretty much stumped here. I might be selling it. I'm not sure yet.

You probably should sell it. As it is beyond your capacity to sort it out.

I believe I told you before, that those 649 carbs need specific induction components (inlet restrictor to go with #78 mains) to behave properly, and that unless you have full and total understanding of those carbs, you won't get them to operate correctly or behave as the 627b, or 022A carbs.

If you still want it to run properly without the inlet restrictor, then get yourself some 627B carbs to put on.  Those are pretty straight forward to sort out here on the North American continent.  Otherwise, sell the problem to someone else to solve.

I don't have any 649 carbs, or I would be able to do a detailed comparison and determine why your carbs can't behave properly.

imo

[seanbarney41]

have you done anything with the ignition system at all?...other than assuming the currently suspect dyna s works fine.

[paul_D]

I'm pretty much stumped here. I might be selling it. I'm not sure yet.

You probably should sell it. As it is beyond your capacity to sort it out.

I believe I told you before, that those 649 carbs need specific induction components (inlet restrictor to go with #78 mains) to behave properly, and that unless you have full and total understanding of those carbs, you won't get them to operate correctly or behave as the 627b, or 022A carbs.

If you still want it to run properly without the inlet restrictor, then get yourself some 627B carbs to put on.  Those are pretty straight forward to sort out here on the North American continent.  Otherwise, sell the problem to someone else to solve.

I don't have any 649 carbs, or I would be able to do a detailed comparison and determine why your carbs can't behave properly.

imo

I don't want to sell, just in over my head on this issue. It's been wearing on me and I'd really like to be able to ride it.

I know you've mentioned the restrictor and 78's before. I have 4 filthy 78 mains I'll clean up from a second set of 649A's, but no inlet restrictor. I have this type of inlet (pictured) and the North American tray with metal mesh. I'm not sure what the pictured one is from, I received it with a bunch of parts from the previous owner.

How else could I try to restrict it ?

I also have some 022A carbs. (needs to be completely cleaned and rebuilt though.)

have you done anything with the ignition system at all?...other than assuming the currently suspect dyna s works fine.

I've checked each for spark, and considering each pipe gets hot that seems ok. I've timed it with a strobe, idles well and advences properly according to the strobe.
I've changed all the spark plug caps to new ones as well.

What else comes to mind ? I am more than willing to check it out.

[TwoTired]

I know you've mentioned the restrictor and 78's before. I have 4 filthy 78 mains I'll clean up from a second set of 649A's, but no inlet restrictor. I have this type of inlet (pictured) and the North American tray with metal mesh. I'm not sure what the pictured one is from, I received it with a bunch of parts from the previous owner.

How else could I try to restrict it ?

I also have some 022A carbs. (needs to be completely cleaned and rebuilt though.)

Without a pretty thorough exam of the 649's, I would abandon them in favor of the 022a models, as it is well known what makes the latter work without the inlet restrictor.

The Air horn you pictured is either from a Cb550 F model or a Cb550 K3 model which has PD style carbs.  The difference between these is the inlet screen, which is more open on the F model and shrouded/reduced on the K3's type.  It's just a different insert into the formed horn inlet.  Neither of these reduces the inlet area to the extent that the 649 set up requires.

If you can get precise opening dimensions from Deltarider, you can mimic the inlet area size with a custom insert, either in the horn type you've shown, or the tray type you have now.  Then use the stock internal set up for the 649a, which I'm sure Delta with be happy to provide you.

I still think you would have a more direct route to success with well sorted 022a carbs, jetted to 627b specs., as I feel the 649's have something inside them different besides the normal jetting features of the 022a's.   

[paul_D]

Thanks TT, I know  the restrictor you pictured, I think Ill likely tape off part of the opening to make a restriction and stick with the 649a;s with the 78's im cleaning. At least then I think I can finally say the carbs were or werent the culprit.

I'm also looking at getting this http://www.canadiantire.ca/en/pdp/equus-compression-tester-kit-0251016p.html to test the compression on the bike.

Any suggestiongs for salvaging carbon fouled plugs ? They dont sell d7ea's around here and I have to keep ordering them.

[LesterPiglet]

Burn the plugs on a gas cooker or with a torch, then wire brush them.

[paul_D]

Should I replace the dyna with points to be sure ?

[seanbarney41]

have you checked the voltage at the coils?

[paul_D]

have you checked the voltage at the coils?

No I havent checked the voltage.

I am considering swapping the coils out for new dyna dc8-1's and the dyna-s for a points set up.

[TwoTired]

If all the head pipes are getting hot, you don't have a spark problem.

Contrary to popular belief, you simply don't need big spark for the engine to run well.

High compression engines, yes.  Driving worn, used plugs for extended periods, yes.

But, spark is NOT going to fix a mixture problem.

[dave500]

dont switch back to points if the dyna is running fine.

[paul_D]

How can I be sure it is running properly. Make sure it isn't failing under load or heat or something.

[dave500]

it would be miss firing and farting or similar,tried it with the filter out yet?you dont want to start frigging around setting up dual points right now.

[paul_D]

It does start miss firing and back firing after its been risen a little.

I have tried it with out the filter.

[dave500]

try new fresh plugs the instant it starts to foul up and miss,you only get a few minutes before it fouls up though?

[paul_D]

Yes. I start it up. Let it warm up and then ride it. 3 quick blocks and i accelerate up  a bit before sputtering out (aroubd 3-4000 and above) and dying until I put new plugs in back at home.

[dave500]

have you got any smaller slow jets?try 38s,ive always found any 500/550 goes best with 38/100