Topic: Cold #3 Cyl, stumped the PO and me. Searched, tried the usual - next logical?

[Spanner 1]

Thanks, 750, us old fogies get run-over sometimes and dismissed as loonies...until someone takes the bait and actually realizes we might be right ( even if were wrong! ).

[eldar]

Well considering that I suggested swapping the wires, caps and plugs in my first post.....
I stand by what I said.

[Spanner 1]

The scary as **** thing for me is all my rantings can be proved/dis-proved by a jumper wire installed by the poster..poster?, shoot, who was the poster,again ?.

[bradweingartner]

Easy...when a load causes a voltage-drop ( due to crap wiring etc) there is a TIME FACTOR in the voltage rising back to it's previous level.....it does not happen instantly.
Now if you hit that rising voltage AGAIN before it reaches it's peak ( same load repeated )..it now causes a bigger voltage drop , do it again and even lower . In this case you reach too low voltage to make a spark ( 1 TIME ONLY , ANY CYLINDER ). THEN , no spark=no further voltage-drop caused, so voltage is ' free' to rise and has TWO cycle -times ( 'cos it missed a spark ) to get back up to initial level... I have said this ten different ways..!!

One thing your theory lacks, and yes I do agree with you on how this could potentially remotely happen in a system not necessarily related to the motorcycle in question.

A dud firing gives a longer period for the voltage to rise. Gotcha.

However, what are the chances that each and every time this guy fires up his motorcycle it starts on the same exact cylinder to cause it to ALWAYS be #3 that's cold? And also what are the chances that the voltage deficiency, which seems to go away at RPM, would always reset on the same cylinder?

Pretty slim to never in a million years I'd say.


On a separate idea, what about a rounded cam lobe? Not that I've ever seen it or heard about it, but the previous post about a valve stem divot piqued the idea.

[PJ]

Eldar is right... Plugged idle jet in affected carb or it has no compression on #3 cylinder therefore no heat.
peace
PJ

[754]

One squirt of gas, will tell the tale...









if it doesnt catch fire..

[Spanner 1]

Brad have very good questions!!
Noticed all replies are down to 1 liners...very zen !!!
Seriously, Brad, I'm working on your Q...I know the answer if I can articulate it !! There is a reason for everything !!! It is to do with the specific resistance in the supply path...

JUST B.T.W. do you agree that one cyl. of a pair can fire ( same coil ) but not the next one ?

[shoemanII]

i spent a little more time on the bike last night, here goes:
-- cleaned all passages in the idle circuit using braided brass wire with a diameter just under each passageway diameter followed with carb clean and compressed air.  did this poking and flushing multiple times.  also checked/cleaned the 90 degree bend at the beginning of the circuit.  re-checked the idle/main jets and float height at 15mm.  no improvement

-- installed a set of new ngk dr8ea plugs at .025.  no improvement

-- measured v at the points as described somewhere.  11.13v on both sets, when one set was open the other held apart by buisiness card.  measured batt v at 12.22v static, 12.57 +/-running

-- after 15minutes or so of revving/running, #3 does get hot but i think that's because i'm on the mains at some point.  idles at 1200 "ok" but not that smooth.  when i open the throttle quickly at 1200 hesitates a bit.  when i open the throttle quickly at 2000 it takes off nicely.   

talked w/an old honda guy i know about the throttle valve on #3 that has some scrapes/scuffing i mentioned in a previous post and he said it probably wasn't the problem, but i'm gonna swap it out w/#4 anyway.

have swapped plug leads between #2 and #3 w/no change

all plugs have the little round adapter, are tight

too snowy for a road test, will do and report back

still need to check fuel level by clear lines   

will try a coil swap just to get it off my "list of possibilities"

will reset air screws to 1.75t

when conditions are better, will bring the bike in for a carb sync

thanks for the replies.  this is a real challange but plenty of time for solving this prob before spring.  i do think i'll get it and will keep checking.
bobp

   

[eldar]

It was #2 and #3 that need to be swapped not #4. If you meant #2 though, that proves ignition is not the issue.
Have you checked to make sure your accel pump is shooting gas into all 4 carbs? you should get a small squirt from each of the brass tubes at the throat of the carbs.

From there, clean your plugs and run at idle for a few minutes. Open your garage of course
After a few minutes of running, pull #3 and see what color it is then. With the 78 bikes, you want a very light tan, almost a dusting really as these carbs are lean runners.

Also what plugs are you running?

[shoemanII]

yes, swapped plug leads between #2 and #3.  (brain fart - too much gas and carb clean fumes?)  plugs are ngk dr8e.
will run the bike tomorrow - supposed to be 45!

thanks, i think we'll get this someday.
bobp

ps: your thoughts on the worn throttle valve inside #3? 

[PJ]

I think your probably at the point where you will have to actually start tuning the engine, timing, point gap, valve adj, sync the carbs, etc. You will have to do it again later after you have gotten it running better but that's how it goes when an engine is that far out of tune. Don't get lost in the details, If you grab a plug wire and crank the engine and it hurts you have enough spark to ignite the fuel, simple. It either sparks or it doesn't, these ignition systems have been serviced roadside for years. Go back and check the accelerator pump jets for a small squirt when you turn the throttle, with the airox removed you can see it with a small flashlight. You are doing your testing with the airbox and vent hoses in place, right? It makes a difference in how the engine responds.
PJ

[eldar]

plugs are ngk dr8e.

THAT is part of the issue. DR plugs should NOT be used. Standard plug is D8EA. I suppose if you do not have resistor wire or caps, THEN you could do the DR plugs but I would still go with D8 plugs. Get the D8 plugs and see what happens.

[shoemanII]

ah, just checked - the previous plugs were d8ea but i bought dr8ea in error yesterday.  no chnge when running the dr8ea plugs. 

neither wires nor caps look like anything special and are not labeled "resistor".  i'll get new d8ea and stick 'em in. 
bobp

[eldar]

Well if you had old d8 plugs, the dr plugs would not have been a change. the R denotes Resistor and that cuts down on spark.

[TwoTired]

-- measured v at the points as described somewhere.  11.13v on both sets, when one set was open the other held apart by buisiness card.  measured batt v at 12.22v static, 12.57 +/-running

That's a pretty low voltage.  While it is unlikely to cause single cylinder firing issues, it is a warning that your battery is depleted.  Don't expect the bike to charge the battery at idle, it needs RPM to do that and for a good long while, as it doesn't recharge the battery very quickly even when the engine is revved up.  Lights and starter use energy faster than the alternator can provide it, especially at idle.

-- after 15minutes or so of revving/running, #3 does get hot but i think that's because i'm on the mains at some point.  idles at 1200 "ok" but not that smooth.  when i open the throttle quickly at 1200 hesitates a bit.  when i open the throttle quickly at 2000 it takes off nicely.   

You don't get "on the Mains" till 3/4 throttle position.  You will switch to slide needle dominance (Throttle valve) at about 1/8 to 1/4 throttle position, with these mechanical slide carbs.

still need to check fuel level by clear lines     

Yes, do that.  A low fuel level in the float bowl mimics problems of the slow/idle/pilot circuit.  Its siphon tube is higher in the chamber than the mains/throttle valve fuel pickup.

when conditions are better, will bring the bike in for a carb sync

For certain carb sync is most sensitive at idle setting, and could well be the sole cause of you cold head pipe(s).  Consider if one slide is more closed than others, How could the cylinder receive the an equal A/F charge at idle setting?

You'll get it.  You are addressing the proper steps.

Cheers,

[bradweingartner]

Brad have very good questions!!
Noticed all replies are down to 1 liners...very zen !!!
Seriously, Brad, I'm working on your Q...I know the answer if I can articulate it !! There is a reason for everything !!! It is to do with the specific resistance in the supply path...

JUST B.T.W. do you agree that one cyl. of a pair can fire ( same coil ) but not the next one ?

Yes, but I think your theory is loony and you are off your rocker! Just to be clear. 

I can see your train of thought however and I have seen/heard of similar occurrences as you are describing but NOT in motorcycles. Except in systems in which a sequence is guaranteed to start at the same point every time the results would never be repeatable.

Besides, if this cylinder is cooler than the rest but not dead cold, it MUST be sparking. If it's sparking, but weaker, it would still use up all the available juice in the system which ultimately would cause the bike to die. No replenishment of the charge.

[sangyo soichiro]

I think this thread is very good.  I encourage everyone to keep cool and keep the discussion flowing.  I am learning a lot, and I'd bet you all involved in the discussion are honing your thought processes, whether you end up being correct or not. 

A few words on troubleshooting and the scientific method...
1. Formulate a hypothesis (or better yet, a few hypotheses).
2. Dream up a way to test the hypothesis.

Without #2, #1 is just mental masturbation.  Every scientific theory must be testable. 

Spanner says it perfectly:

The scary as **** thing for me is all my rantings can be proved/dis-proved by a jumper wire....

With that tidbit of info out of the way, I hate to inform you that you are ALL WRONG! 

My hypothesis:
M-theory predicts that there are 11 dimensions of space-time (not just the 3 spatial and 1 time dimensions).  The electrons (which we all know are NOT inanimate little sub-atomic particles, but rather are really living, conscious little critters that sometimes choose to make our lives miserable) are sliding between these 11 dimensions.  It just so happens that the wire to this poor soul's #3 cylinder is the gateway between these dimensions.  These evil little electrons could complete the circuit through the spark plugs if they wanted to, but they choose to go through the porthole just to piss us off.  But they are not acting alone... they are in cahoots with the little gasoline molecule-monsters that reside in the #3 carburetor and have convinced these little bastards to wait for the economic bailout.

[Markcb750]

I think this thread is very good.  I encourage everyone to keep cool and keep the discussion flowing.  I am learning a lot, and I'd bet you all involved in the discussion are honing your thought processes, whether you end up being correct or not. 

A few words on troubleshooting and the scientific method...
1. Formulate a hypothesis (or better yet, a few hypotheses).
2. Dream up a way to test the hypothesis.

Without #2, #1 is just mental masturbation.  Every scientific theory must be testable. 

Spanner says it perfectly:

The scary as **** thing for me is all my rantings can be proved/dis-proved by a jumper wire....

With that tidbit of info out of the way, I hate to inform you that you are ALL WRONG! 

My hypothesis:
M-theory predicts that there are 11 dimensions of space-time (not just the 3 spatial and 1 time dimensions).  The electrons (which we all know are NOT inanimate little sub-atomic particles, but rather are really living, conscious little critters that sometimes choose to make our lives miserable) are sliding between these 11 dimensions.  It just so happens that the wire to this poor soul's #3 cylinder is the gateway between these dimensions.  These evil little electrons could complete the circuit through the spark plugs if they wanted to, but they choose to go through the porthole just to piss us off.  But they are not acting alone... they are in cahoots with the little gasoline molecule-monsters that reside in the #3 carburetor and have convinced these little bastards to wait for the economic bailout.

quantum sarcasm...

[754]

I would be giving it a squirt.., to positively elminate 1 out 3 causes, before I would switch fresh plugs.....

 So far, it seems you have eliminated one thing, a bad wire out of a pair.

Toubleshooting, simply put.. process of elimination..

[shoemanII]

i found some small dia clear tubing and checked fuel levels in the bowls; all are very close (+/-1/8inch) to the bowl/body seam.

just for grins, i swapped over the scraped/scuffed throttle valve on #3 over to #4.  no change

set pilot screws to 1.5T and idled the bike for 5 minutes last night with the new dr8ea plugs and noted all pipes were now hot, but bike still stumbly.  an improvement i think.  i'll pick up new non-resistor plugs and repeat.   

the only step in a usual tune-up i haven't completed is a carb synch, and will let my local bike shop do that.  no synch tool in my "shop".  at the same time we'll do the "squirt test".  temps are 50 today but roads are terrible - mud.     

think i'm gonna take a break from trouble-shooting on my bike, is taking all my spare time.

i do want to openly and clearly offer my sincere thanks to all who have offered suggestions and maybe a little support.  this is a great site and am sure my struggle with tuning a 30 year-old bike has helped someone, somewhere.

there has been some success:  i yanked the engine, did a "puck job" including new gaskets here and there, and can report no leaks.  the carbs now at least look gorgeous - spotless/buffed.  and i can now disass and re-rack a set of carbs without causing any harm.

thanks guys - will report back in a few weeks. 
bobp

ps:  am nearly approaching a zen state (or something).  maybe "it is what it is".  stay tuned - ha sorry for the pun!                

[eurban]

Glad to hear that things have somewhat improved.  Did you bench synchronize (using some convenient object like a 1/16th inch drill bit to gauge the gap between the bottom of the slide and the carb bore, you first adjust the idle speed knob to get the gap between the #2 non adjustable slide and the carb bore the exact size of your measuring tool and then adjust all the other slides to be exactly the same) the carbs when you had them off?  Perhaps your slides are so far off that she can't run right?

[shoemanII]

haven't done that, but will. PO said he did it, but i'll check anyway. 

was gonna give myslf a break on the F/Kmongrel for a few days.  painted/installed the exhaust on my DT2, checked the charging circuit v, final check before inspection - all is well.  blasted around the muddy roads for a bit tonight:  no reg/ins/plate, felt like a real hooligan, and is running fine.  did a full refurb over the winter: wheel, head and swingarm bearings; tidied up the electrical; polishing covers/rims/hubs; chain/sprockets; truing wheels, etc.  much fun.  later, and thanks!
bobp         

[shoemanII]

can now report a huge improvement, after a little recent tweaking.
-- did not send the accel pump to carb dipper guy, so i cleaned it's ports with wire/carb clean/compressed air.  then put a little puddle of carb clean in the bottom and pumped the rod until a nice stream came out of the four ports.  (square plug in a round hole leaves 4 ports).  then left to sit overnight soaking full of cleaner and repeated flushing the next day
-- held accel pump onto float bowl and pumped carb clean a few times, now better
-- took off #1 carb from rack and held all carbs vertically.  dribbled carb clean into pump circuits and blew out with compressed air until all jets had a fine mist coming out into each carb
-- made sure mickey's ears on the diaphram were oriented right, were off little before
-- put carb rack back on a tested - nice shot of fuel into each throat - never had that before.  a success!
-- removed the #3 pilot jet then shot some carb clean/compressed air backwards, from the carb throat side.  noted a nice stream, ok
-- i had previously cleaned/reassembled the pilot jets as i found them, but were not right.  PO had:  jet, then spring, then "o"ring then washer.  reassembled with "o" ring last
-- did a "bench sync" according to a someone's post in this thread, needed a lttle tweak on #3.
-- found out that "F"s have 110 mains due to the OEM 4/1 exhaust.  installed a set of new 110's.

started up and #3 cold for about 20 seconds, then all 4 get hot evenly.  after 5 minutes of running bike will idle at 1250 and revs well.  no minor stumbling when revving, no backfire popping at high rpm.

some minor adjustment of the pilot jets per plug condition, and a real carb synch at the shop will finish the job.  will probably put in a new set of points i've got laying around, even tho the ones in the bike are clean.  thanks guys, i'm outta here!

let's ride!!           


   

[Hush]

Well done Shoeman, from frustraited owner to happy rider, that's some graduation.

[eurban]

-- i had previously cleaned/reassembled the pilot jets as i found them, but were not right.  PO had:  jet, then spring, then "o"ring then washer.  reassembled with "o" ring last

Sounds like you have her running well but but I have to tell you that what you are calling a pilot jet is actually your idle mixture screw.  The pilot jet is a brass part pressed into the carb body next to the main jet holder.  It must be wiggled out gently with plyers (padded or using something like leather as a padding) soaked, cleared with a single strand of copper wire and the passages below sprayed clear.  I would suggest that you perform this step if you haven't . . . .