Topic: I'M AT THE END OF MY ROPE WITH A DEAD CYLINDER ISSUE

[ChortlingSandcaster]

If the valves were not seating, I wouldn't have the compression that I do, before all this started with # 3. I was having trouble with the float sticking on #4, that's when I pulled off the carbs and and cleaned them and adjusted the floats, put the carbs back on, the #4 float problem  was taken care of, but the #3 no fire problem started, I'm going to pull the carbs tonight and recheck all the passages and orifices clean and reinstall tomorrow...

My idea was the 'too large' valve clearance is a secondary issue, not the primary issue.
Still, you can get 140+psi per hole if everything's dandy.
Let me say that the valves issue doesn't sound like the #3-not-firing cause,  but I would assess it.  120psi is getting a bit low there.  At some point after the #3 issue is solved,
you might consider doing a leakdown test.

On some Mikuni carbs it is possible to install the throttle slide BACKWARD.  That could cause this problem, potentially.  Easy to check, too -- just pull the air cleaner stuff off and look at the #3 carb's throat from the air cleaner side.  Verify that you can see the arched cutaway in the throttle slide, that it is facing *towards the air cleaner.*

If the carb slide is in backward, you will only see metal, and not the arched cutout that is supposed to face backward towards the air cleaner.   Despite the fact that I know about this simple issue, I have still gotten it wrong and installed throttle slides backward.  You know it right away when you start it, the affected cylinders dont run very well if at all.

By the way:  can you start the bike, rev it for a bit, then pull the #3 plug and tell us what you see?  IS THAT PLUG WET?  Or is it 100% dry?
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[scottly]

He has roughly the SAME compression across all four cylinders; nothing that points to #3. BTW, the tappet clearances on these bikes tends to open up with time, due to the concentrated wear on the adjusting screw where it meets the valve-stem. 

[ChortlingSandcaster]

He has roughly the SAME compression across all four cylinders; nothing that points to #3. BTW, the tappet clearances on these bikes tends to open up with time, due to the concentrated wear on the adjusting screw where it meets the valve-stem. 

Ahh...the point of difference.  Tappets and their adjustment screws.  I remember them from doing valve adjustments on my cb400f.  The point about the valves rising upward into the head is valid though, Scottly -- as the valve seat wears, the tip of the valve stem moves UPWARD.  No getting around it.

Your 'tappet screw wears out' point is well-taken.   

On DOHC bikes that don't have tappet arms and adjustment screws,  I'm talking about the buckets-and-cam-lobes situation, there is no tappet adjustment screw to wear out, and the valve clearances get smaller over time, not larger. 


I suspect (unless you're suffering from burning valve seats due to poor adjustment) I suspect that the adjustment screw on the tappet would wear out *faster* than the valve seats wearing?   Is that your contention?

[scottly]

I suspect (unless you're suffering from burning valve seats due to poor adjustment) I suspect that the adjustment screw on the tappet would wear out *faster* than the valve seats wearing?   Is that your contention?

Yes, exactly!

[Spanner 1]

Any tappet operated valve would increase its tappet to valve clearance with ware IMO.... unless it's cam lobes wore at the ( exact ) same rate!
Re-read the whole dang post and I don't see anywhere you said you tried another plug in #3. All I saw was ' all new plugs', 'swapped wires' etc. but not the plug, could you please do that, could be bad under compression/ fuel even if 'free air' spark is O.K..... even a messed-up carb on 1 cyl. will get warm/ hot if you run and rev. the bike for a few mins. with gas entering the cyl. from main/slow/pump somewhere. The engine vacuum will draw fuel from the carb and make it fire even if it's 1 time in 50 compared to other cyls. unless the fuel level in the bowl is below the level of the jets ( don't think so )....

[750goes]

Spanner - I thought I already said that   

simple test

put another plug onto the end of the lead for #3 cylinder and ground it out - leaving the one in the head still there.

kick it over and watch for spark on the #3 plug

if you have spark - put in a new plug .......

[Spanner 1]

Agreed!.. yes you did..... but the poster ' at the end of his rope ' didn't seem to think it was a possibility, I guess

[tlbranth]

swap #3 & #4 plugs & see if the problem changes cylinders.

[ChortlingSandcaster]

Paddy Paul, it is *really* important to know what the #3 spark plug looks like when you start the bike, rev it for a little while, then remove spark plug #3 and check.

IF THE SPARK PLUG IS WET --  you know you're getting gas into #3 and the problem is flooding and/or spark issues (electronic ignition prob, marginal connection inside the #3 spark plug wire, float level is set wrong so that too much fuel is flowing into the carb bowl, stuck float in #3, ...)

IF THE SPARK PLUG IS DRY -- presto you know you're probably not getting any fuel into #3.

This one simple check, take all of 3-5 minutes, will tell A LOT.

I had a dead cylinder on my Kaw triple recently and when I pulled the plug it was wet.  Then I *knew* it was getting gas (maybe too much).

[Spanner 1]

Everyone hates taking-out #2 or #3 plug in a 750 !!! and will try everything else first ! ( I've done that )....

[Hannibal Smith]

I can't take it any more.

We all know what is wrong with it.

[Jerry Rxman Griffin aka MuthaF'er]

I didn't look at all the replies but has anyone mentioned to check the tip of the valve stem for dimpling? If it is worn inward then you're not getting the lift your feeler gauge indicates you will.

[ChortlingSandcaster]

I can't take it any more.

We all know what is wrong with it.

Hannibal Im shrouded in a dark cloud of ignorance (that may be standard for me btw), what do you think we all think is the problem?  I have only been able to throw out guesses and would love to know what the entrails have indicated in the message stream here in case I or someone else on the board here runs into this problem....thx

[Hush]

Tell us now before I have to hang myself from the nearest beam......did you find the problem PP?

[Hannibal Smith]

It's the one thing that wasn't checked, but was assumed to be in working order.

[Ogri]

Ferchristsakes... it's the spark plug. Just because it's new - don't mean anything. Just because it sparks when laid on the cylinderhead - don't mean anything. A faulty 'plug under compression will not fire.


Swap the plug from no. 3  with any of the others - the problem will move to whichever cylinder you put it in. 

A timing light would've solved this immediately.

[paddy paul]

 The problem was that when ever i checked for fuel delivery i would either drop the float bowl, check for fuel, or pull the drain plug to make sure there was gas in the bowl, after pulling the carbs and cleaning/ blowing everthing out I noticed that the #3 main jet was screwed in farther than the rest  so the float level was correct but the main jet for #3 was not getting any fuel because it was sitting up higher.. adjusted the float bowl, put the carbs back on and it fired on the first kick. All are firing and it runs like a beast.. thanks for all the input ....

[zzpete]

  I love happy endings!!

[scottly]

Me too!!! Thanks for the update, paddy.

I love happy endings!!

[Spanner 1]

Great... but I don't believe you !!!.... main jets 'screw-in' and stop. If one is 'loose' then it's lower into fuel bowl !! = more fuel to cyl.
Actual prob. was bad plug.... IMVHO.

[Hush]

Well he's right in some respects, if the main jet was pushed too far "up" into the carb body then the needle would definitely block the main closed, therefore no gas gets to #3.
But the question still is.....was it a "push in" main jet or a "screw in" main jet?
I'm assuming the carbs have been synched.

I'm really happy that PP has got his bike going and he is happy but........

I'm wondering if all the other 3 jets are not screwed in properly and unscrewing the only jet that was correctly fitted lined up the needles and cured the problem?

Only taking the carbs out and doing a check would prove/disprove this theory so next time you need to yank your carb rack off PP, let us know what they look like will ya.

[ChortlingSandcaster]

Man, you guys just need to stop being so frigging provoking, stop playing 'GOTCHA' with
the posters on the board.

I *know* you dudes have done silly stuff and desperately kept it to yourself.
I sure the heck have!  We all do dumb stuff and we usually don't like getting
all public with it.

Let people come on this board and FEEL COMFORTABLE about what they
disclose.  If you 'read between the lines' maybe the guy's embarrassed.  Let that go,
don't make him feel foolish by challenging his veracity.

I've heard you guys say 'its all in fun' well, to me its 'fun' to let posters decide what they want to disclose, and to look at it and say 'he found something silly and is embarrassed.  Heck I've been there.'

Because the board here is EDUCATIONAL, it's reasonable to want to make it clear to others on the board what you think is a likely cause, and you are all adult enough to DO IT DIPLOMATICALLY such as:

"Congratulations, most of the time the real problem is X."

Because the way some of the posters pounce on people ITS 100% UNDERSTANDABLE why
a poster, who might find a silly mistake, will be concerned he's gonna get laughed at --
and then not even post.

We need to have a comfortable place here where we don't challenge folks who may be
concerned that they're going to get pounced on.

How would you feel if you *really* didn't want to disclose you made a silly mistake?
And then someone calls you out for the entire world to see as maybe being a liar.
Let people make mistakes without the fear of getting POUNCED on.  Grow up about that.

This is a great resourceful place but we cannot make people feel intimidated and jump
all over them.   Otherwise people aint gonna post dudes!

READ BETWEEN THE LINES of someones post and realize:

"Oh I get it, he found something that he feels would be embarrassing, heck I've done that too, I remember when I..."
and not come back and get all accusatory and have multiple people ganging up on a guy
and saying "I don't believe you" and "I second that"  - THAT AINT 'FUN' dudes and it
aint adult behavior either.

Read between the lines.   Use your adult courteousness.   If posters come on here and
you shut them down by accusing them in that kind of 'fun' they aint gonna come back dudes.

Ive seen good boards die, recently one in England, because of one or two instigators
started jumping down people's throats, and then others, their 'lemmings', seeing
the two instigators not being reigned in, lemmings kick in and then normal, adult
courteous people GO ELSEWHERE.  In a few months the new postings fell to nothing.
 The courteousness DIES throughout the board  when it happens.

THAT AINT FUN DUDES.  Give people the room to not be perfect.  Give people the room
to not broadcast if they think they'll get embarrassed by admitting it.

If you have an honest concern that other readers need to know the TYPICAL story,
then put your DIPLOMACY hat on and say something like  "Congratulations, most of the time the real
problem is X."

[scottly]

CS, you underestimate the folks on this forum: we tend to congratulate the folks that admit to their mistakes, and celebrate their successes!!!!   

[Hush]

Don't take it all so personally CS, these guys help each other all the time, sometimes we give each other a serve too .
In this case I think the forum members are pleased the poster got his bike going but if we don't understand how he got to that happy result we didn't learn eanything and neither did he.
Also sometimes when a poster asks for help and we need clarification on his problem, many new members have difficulty explaining or supply errors in their information.
Spanner and Dave were asking for clarification on the main jet point.
My suggestion would be to delete your post and watch how this works out. 

[750goes]

hey Sandcaster - you come on pretty heavy for a guy who maybe wants some assistance and information from the learned group called "the forum members", so giving everybody or anybody a serve about how to respond is a bit harsh in my eyes.... if you don't like the comments then that's fair enough...if you think this forum isn't fair thats fair enough as well.... if you think there are many opinions about the subject posted ... I think there might be......put up with it.............don't get narky and bag out members who like to state their opinion or comment, just because you percieve or don't like the inferred or non inferred tone is irrespective..............

be happy