Author Topic: 1 rich cylinder - is it the carbs? PD46C  (Read 280 times)

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Offline cwchan

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1 rich cylinder - is it the carbs? PD46C
« on: September 16, 2019, 09:43:09 am »
Hi All,

Everytime i tune up the bike i learn more about it and slowly get it running better and better.

I feel like i'm close to a bike that runs perfectly.... when pulling the plugs, cylinder #2 is rich and the other cylinders look slightly rich but good. 

I have a uni foam air filter on the stock airbox, stock exhaust.  The cylinders were honed last winter (stock bore).  A number of years ago i got the valves re-seated and the valve guides done (drilled out and bronze lined?? - the mechanic said it would be easier, cheaper and better than replacing the valve guides).  Valve spacing is set.  Rechecked (the next day to let it cool) after running it as i found that sometimes the nut would loosen a little.  I got dyna coils and dyna s ignition.  One thing that made a big difference in ignition timing is making sure that the 23mm nut is centered on the 10mm bolt that goes into the crankshaft.  There was a wobble when un-centered that was throwing off the dyna s magnet.

That leaves me with the carbs.  Cylinder #2 has been rich (carbon fouled) as far as i can remember and i've never personally dived deep into the carbs until recently.  I dropped it off at Sirius Consolidated years ago for their carb service and it was crap.  They put 88 main jets in there, the floats were set all over the place, and the pilot screw spring in carb #4 was too short.  Fixing the floats and screw spring gave me a huge improvement in how the bike idles.

My current carb settings are:
Main jet: 95 (the 88s i had were too lean and the only other ones i have are 110s at the moment). 2,110 ft elevation
Slow jet: unknown.  i don't recall ever seeing an etching indicating the size on these.  It doesn't look like they've ever been removed
Needle position: unknown.  This is my main suspect.  i'm wondering if they are set differently
Air screw: 2 turns out
Carbs are synced.  The no-name sync tool has 4 gauges and i found they all read slightly differently.  I made sure to check the vacuum reading on the same gauge for all cylinders by constantly switching out the tubes.  This was essentially like syncing with one gauge.

I have the bike at a stage where i can live with it but i'd really like to get it dialed in.  Driving around in stop and go traffic it idles between 1000-1300 (digital tach wired into harness).  It doesn't surge wildly like it used to.  If i rev it, it jumps up and falls back down to idle quickly.

So i plan to dive into the carbs this winter but i'm wondering if there is a key spot i should look at and focus my efforts.
I've had this bike for almost 10 years now.  I've gone through my old posts and i really feel good about the how much i've learned.  Sometimes i thought i solved a problem only to find out later that the true problem was elsewhere.  I really inherited a basket case.  Its in a really good state now, comparatively.  I want to get it just that much better

Thanks in advance
« Last Edit: September 16, 2019, 12:20:23 pm by cwchan »

Offline pjlogue

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Re: 1 rich cylinder - is it the carbs? PD46C
« Reply #1 on: September 16, 2019, 11:00:49 am »
Easiest thing to do is check for an air leak at the carb-cylinder intake boot.  Use a can of carb cleaner and spray each boot to carb seal and head to boot seal with the bike idling and warmed up.  If the RPM changes you know you have a leak.  An air leak will cause a rich condition on these pulse induction carbs. 

-P.

Offline Deltarider

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Re: 1 rich cylinder - is it the carbs? PD46C
« Reply #2 on: September 17, 2019, 03:36:00 am »
... An air leak will cause a rich condition on these pulse induction carbs. 
-P.
Forgive me my ignorance, but can you enlighten me on this?
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Offline maxheadflow

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Re: 1 rich cylinder - is it the carbs? PD46C
« Reply #3 on: September 17, 2019, 07:21:01 am »
I don't see when the carbs were last synchronized.

I'll agree on the manifold leak.  Seems to me that it would make the cylinder run lean.

Offline pjlogue

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Re: 1 rich cylinder - is it the carbs? PD46C
« Reply #4 on: September 17, 2019, 12:29:27 pm »
I read this in Mark's book under the carb section and I have also experienced this on my K6.  I can't remember the specifics as to why this happens but I'll review it tonight and see if I can find it. 

My outboard cylinders were running rich and I could not figure out why.  I read Mark's book and then checked for air leaks at the boots and sure enough both had an air leak.  Fixing the air leak (clamps were stretched so I fit a band of gasket material under each band) solved the air leaks on #'s 1 and 4 and with no other adjustments my plugs were no longer black all the time.

-P.

Offline cwchan

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Re: 1 rich cylinder - is it the carbs? PD46C
« Reply #5 on: September 17, 2019, 06:12:54 pm »
Ok. I check again... the issue I had with spraying the carb cleaner is that it evaporated quickly after spraying

I synced last week. Maybe I recheck it tomorrow


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Offline Deltarider

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Re: 1 rich cylinder - is it the carbs? PD46C
« Reply #6 on: September 17, 2019, 10:36:50 pm »
Ok. I check again... the issue I had with spraying the carb cleaner is that it evaporated quickly after spraying
I'm afraid I don't understand. Spraying is done whilst engine is idling. It should work.
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Offline cwchan

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Re: 1 rich cylinder - is it the carbs? PD46C
« Reply #7 on: September 17, 2019, 10:56:40 pm »
I'm afraid I don't understand. Spraying is done whilst engine is idling. It should work.

The engine was warm and the carb cleaner evaporates soon after it is sprayed on the warm engine



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Offline Deltarider

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Re: 1 rich cylinder - is it the carbs? PD46C
« Reply #8 on: September 18, 2019, 12:22:35 am »
Have a look at this picture if you like. Forget about the arrows. They are there to point out something else. You are supposed to spray to the front and rear of the rubber boot where it is fastened to the manifold (front) and the carb (rear) and also where the manifold meets the head. In that spot there's an O-ring that may have become old, hard and brittle. Spraying a mist of either brake cleaner or carb cleaner will immediately change the rpm indicating a leak. When not, there's no leak.
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Offline dave500

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Re: 1 rich cylinder - is it the carbs? PD46C
« Reply #9 on: September 18, 2019, 12:52:43 am »
use soapy water.

Offline pjlogue

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Re: 1 rich cylinder - is it the carbs? PD46C
« Reply #10 on: September 18, 2019, 08:44:19 am »
In checking, the reference to boot leak and running rich is on page IV-12 or IV-13.  He did not give the physics of why a leak causes a rich condition in the 1500-3500 RPM range.  It may be because these are pulse induction carbs as opposed to constant vacuum. 

-P.

Offline maxheadflow

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Re: 1 rich cylinder - is it the carbs? PD46C
« Reply #11 on: September 18, 2019, 06:23:06 pm »
Quote
Air screw: 2 turns out

Couple things.  It's not an air screw, it's fuel.   On the cylinder that is rich, try turning in the mixture screw 1/2 turn.

Its possible that someone opened up the pilot jet when cleaning it out. 

Offline cwchan

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1 rich cylinder - is it the carbs? PD46C
« Reply #12 on: September 18, 2019, 08:45:07 pm »
In checking, the reference to boot leak and running rich is on page IV-12 or IV-13.  He did not give the physics of why a leak causes a rich condition in the 1500-3500 RPM range.  It may be because these are pulse induction carbs as opposed to constant vacuum. 

-P.

Confirmed. There is a leak on #2 and to a lesser extent #4.  Both between the intake manifold and the cylinder head.



1-4 left to right. You can see 4 is the next richest

Thanks. I’ll see how the spark plugs read after sorting out the leaks

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« Last Edit: September 18, 2019, 10:22:58 pm by cwchan »

Offline Deltarider

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Re: 1 rich cylinder - is it the carbs? PD46C
« Reply #13 on: September 18, 2019, 10:41:19 pm »
How did you come to the conclusion there are leaks?
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Offline pjlogue

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Re: 1 rich cylinder - is it the carbs? PD46C
« Reply #14 on: September 19, 2019, 05:07:20 am »
In checking, the reference to boot leak and running rich is on page IV-12 or IV-13.  He did not give the physics of why a leak causes a rich condition in the 1500-3500 RPM range.  It may be because these are pulse induction carbs as opposed to constant vacuum. 

-P.

Confirmed. There is a leak on #2 and to a lesser extent #4.  Both between the intake manifold and the cylinder head.



1-4 left to right. You can see 4 is the next richest

Thanks. I’ll see how the spark plugs read after sorting out the leaks

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As Deltarider asked; how did you determine the leak?  If it was from spraying carb cleaner on the boots while the engine was idling read on. 

If your boots are cracked I would replace them.  If it is a matter of the rubber being very stiff you can heat them with a hairdryer and tighten down on the clamps.  If the clamps are stretched like mine were so there was no more thread to tighten you can glue a 1/16" thick strip of gasket material to the inside of the clamp to give more compression to the boot. 

I tried softening the boots with wintergreen oil and a carrier.  They softened all right and also swelled.  I would consider this if I was desperate and in a bind.  Not a long term solution in my mind.

-P.

Offline cwchan

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Re: 1 rich cylinder - is it the carbs? PD46C
« Reply #15 on: September 19, 2019, 09:18:59 am »
I used the carb cleaner method.  I used the straw thing to spray in specific spots this time.

Its not the boots that are leaking though.  Its where the intake manifold meets the cylinder head.  I know there are some o-rings that are in there.  I remember replacing them but maybe i didn't tighten it enough.  I have some spare o-rings if tightening the intake manifolds doesn't work.

Thanks again

Offline RAF122S

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Re: 1 rich cylinder - is it the carbs? PD46C
« Reply #16 on: September 19, 2019, 03:50:55 pm »
I have replaced these orings on another bike I have and when I pulled the carbs and motor for some other work I discovered the orient had slipped and was partially cut but still sealing.  When they get old they grow hard and are almost like plastic, they can get that hard and brittle.  Change out the orings and see if your plug fouling lessens or goes away.
Looks like you have it running pretty rich.
When did you last clean your air filter or replace it?
Have you checked the ohms of your spark plug caps? They should be around 5k ohms each.
Weak spark can contribute to rich running too...
David stuck in the curvy back roads of "Upper East" TN

 

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