Topic: Almost ruined the engine by adjusting the valves

[cb650guy]

Ok,
So I have still been unable to get my Honda 1980 CB650C to idle.  I am confident the issue is no in the carburetors because I have cleaned them now multiple times.  I wanted to do an all around thorough tune-up so I decided to adjust the valves.

After I adjusted the engine would idle above 2K rpm, however, it would not idle below that and I noticed my exhaust pipes were blackening.  I immediately shut off the engine and checked one of the spark plugs and it was WHITE!!  I think I need to redo the valve clearances and I wanted advice.

Here is the steps that I took.  Maybe someone can tell me if this sounds correct.

1) I took off the cover on the right side in front of the clutch to get to the crank shat bolt.
2) I turned the bolt with a socket wrench until the index marker was on "1.4T"
3) I adjusted the intake and exhaust on cylinder 1
4) I adjusted the exhaust on cylinder 2
5) I adjusted the intake on cylinder 3
6) I then turned the crankshaft 360 degrees and adjusted everything else.

By "adjust" I mean I checked/fixed the clearance between the rockerarms and camshaft lobes.

Does this sound correct?


Here is another question:  Why do I have to turn the crankshaft 360 degrees before adjusting some of the cylinders?


Thanks,
Adam

[DavePhipps]

Sorry I don't have the manual handy to confirm the vavle adjustment. However it sounds like you're running lean in the low end of the carberation(air screw/float level). Do you have aftermarket pipes, and is the airfilter stock?

[cb650guy]

I followed the manual exactly.  Can you explain how to verify that a cylinder is in TDC position.  My understanding is that whatever cylinder I am working on must be in TDC.  Is this correct?  To get Cylinder 1 in TDC I believe I need to align in the index marker with "1.4T" on the crankshaft. 

If cylinder 1 is in TDC are any of the other cylinders in TDC?


Adam

[cb650guy]

No I have OEM pipes and the stock airfilter.  If I am too lean should I move the air screw in or out?

Is it possible I am running too hot (white spark plugs) because of the carburation and not because of the valve clearance.  The spark plugs were black before the valve job.

[Hondawggie]

No I have OEM pipes.  If I am too lean should I move the air screw in or out?

Question, do you know where the idle adjuster screw is and have you
- let the bike warm up, 10 minutes or so
- then turn that idle adjuster screw to get the idle to 1000rpm
You can find the idle adjusting process on page 50 of the Owner's Manual (click the link that Markcb750 gave).  Looks like the idle setting screw is at the rightmost carb and faces frontward.


It sounds like you *might* have an air leak if you've already found and adjusted the idle knob and you have
- white plugs
- pipes getting too hot

If you have an air leak, a symptom is the bike will not return to a good idle level (1000rpm +/-) even when you try to use the idle adjuster knob.

You can check for loose clamps on your intake rubber boots between the engine and the carbs, and check the clamps between the back of the carbs and the airbox.

The next page in the Owner's Manual, page 51, shows you what the stock airbox looks like.
Is your airbox stock?

The shop manual lists the following possible causes for running lean, which leads to white plugs, overheating and discolored exhaust pipes:
- clogged fuel jets in the carbs
- float level too low
- fuel cap vent clogged
- intake air leak

among others.  When you cleaned the carbs did you check and set the float height as per the manual, which says it should be 12.5mm or 0.50in ?

[cb650guy]

Yes I am aware of the idle adjuster screw.

With full choke the motorcycle idles nicely but even with a full throttle it wont get above 4000 rpm. 
With no choke the motorcycle can idle around 2K rpm, but if it goes below this it dies.

The airbox is stock and the carburetor was tuned correctly, this includes the float height. 

Can wrong valve clearances affect the operating temperature?

I do not believe I have any vacuum leaks.  I checked by spraying WD40 over the boots and watching the tachometer needle.  Tomorrow I will go out and get some starter fluid, let the bike run and spray the starting fluid around the boots to see if the need jumps.


Thanks,
Adam

[Hondawggie]

Yes I am aware of the idle adjuster screw.

With full choke the motorcycle idles nicely but even with a full throttle it wont get above 4000 rpm. 
With no choke the motorcycle can idle around 2K rpm, but if it goes below this it dies.

The airbox is stock and the carburetor was tuned correctly, this includes the float height. 

Can wrong valve clearances affect the operating temperature?

I do not believe I have any vacuum leaks.  I checked by spraying WD40 over the boots and watching the tachometer needle.  Tomorrow I will go out and get some starter fluid, let the bike run and spray the starting fluid around the boots to see if the need jumps.


Thanks,
Adam

"Won't rev above 4000rpm" -- that is dramatic.
To clear your mind that you did the valve adjustment correctly:

1) I use a black permanent ink marker when I check valve adjustment to make sure I get the 360 degree rotation.

2) TDC is easy enough to check -- you already have the spark plugs out -- so rotate the crankshaft to the "1,4T" timing mark as per the manual; then....

3) now, with the crank aligned at the "1,4T" mark, using the permanent ink marker, mark the nut you used to turn the crankshaft, just a small tick with the permanent ink marker near the timing mark or something......then.......

4) with the crank still sitting aligned at that "1,4T" position, use a flashlight and look in the plug hole of the #1 cylinder and make a mental note of where the top of the piston seems to be in the cylinder........

5) now, watching the mark you put on the crankshaft nut with the permanent ink marker, slowly rotate the crankshaft for a full 360 degrees, ie. the tick mark from the permanent ink marker goes all the way around in one circular motion and comes to a stop at "1,4T" again  -- at this point you have certainty that you truly have done one rotation and only one rotation

6) now check the #1 spark plug hole again with the flashlight and make a mental note of where the top of the piston seems to be in the #1 cylinder.

While this isn't the ONLY way to do this (watching the lifters rise and fall is another way), using the above steps will get you pretty comfortable with your ability to (1) know when the #1 piston is at TDC; and (2) know you have rotated the crank 360 degrees and ONLY 360 degrees, so you can adjust the other valve clearances with confidence you've got the crank in the correct position



Just as a sanity check?  If it's me, with "won't rev above 4000rpm", I'm checking the valve clearances again -- use the above steps to eliminate doubts about crank and piston position.  Won't take long, and after you do it, you can eliminate the valve adjustment as causing the problem.

Something has happened if you've gone from sooty plugs to white hot plugs and "won't rev over 4k rpm."
 
Since you apparently have a concern about the valve adjustment you've done, re-check and eliminate that as a possible issue then go on from there.

[bollingball]

Don't have a 650 but there is TDC and another TDC four stroke! don't you need to be on compression stroke Both valves closed. I use a pencil in plug hole watch it come up and mark it with a sharpie

[Trevor from Warragul]

Rotate the crank while looking at the inlet valve for No #1.  When it dips, then comes back, line up the 1.4 mark...  easy

[Hondawggie]

Don't have a 650 but there is TDC and another TDC four stroke! don't you need to be on compression stroke Both valves closed. I use a pencil in plug hole watch it come up and mark it with a sharpie

Right on about that, the manual says 'TDC of the compression stroke' which as Morini said can be known by watching the #1 intake valve.

If you look at the manual, it *could* have been more clear about the distinction btwn TDC for compression vs. exhaust strokes -- the fsm for the valve adjustment section is pretty terse about that issue. 

The rising/falling intake valve on #1 is mentioned in the fsm for the cb750, don't know why Honda didn't do that in the 1980 cb650 manual at http://cosky0.tripod.com/imagelib/sitebuilder/misc/show_image.html?linkedwidth=actual&linkpath=http://cosky0.tripod.com/sitebuildercontent/sitebuilderpictures/page03-06-valve-clearance.jpg&target=tlx_new.

[dave500]

i always do each cylinder individualy.

[cb650guy]

Why must we rotate the crankshaft 360 degrees?  Does this mean the camshaft is rotating 180 degrees and since each camshaft lobe is 180 degree off?

[Bob Wessner]

Didn't see this mentioned, but when you are adjusting the valves, to verify that a particular cylinder is at TDC, both rockers should be loose, no tension on them as the valves are closed at TDC.

[MCRider]

Didn't see this mentioned, but when you are adjusting the valves, to verify that a particular cylinder is at TDC, both rockers should be loose, no tension on them as the valves are closed at TDC.

That is correct, except to remember as stated above, you want TDC on the compression stroke, not the exhaust stroke. TDC Comp will have both rockers loose, assuming that neither has tight clearances (usually not) But if one valve is tight you won't be able to use the "both rockers are loose test.

Following the intake down then back up is the fool proof way to know you are on compression.

The OP asks why turn it 360deg? If you start with 1 on TDC Comp, then 4 will be TDC Ex. Turn the crank 360deg to get 4 on TDC comp.

[Bob Wessner]

Good point of clarification, thanks for adding it.

[cb650guy]

So to be clear.  I should start with cylinder 1 at TDC and to do this I can just stick a screw driver in the spark plug hole, rotate the crankshaft and wait for the screw driver to get to its highest point?  After I am done with BOTH intake and exhaust on cylinder 1 I rotate the crankshaft 360 degrees and do the same thing to cylinder 4?

[MCRider]

So to be clear.  I should start with cylinder 1 at TDC and to do this I can just stick a screw driver in the spark plug hole, rotate the crankshaft and wait for the screw driver to get to its highest point?  After I am done with BOTH intake and exhaust on cylinder 1 I rotate the crankshaft 360 degrees and do the same thing to cylinder 4?

Check your PMs. Morini's post above has the best way. I wouldn't stick a screwdriver in as you may foul the valves if you aren't where you need to be.

[Spanner 1]

Stick yer thumb/finger in the spark plug hole, turn the motor when you feel compression your on the comp. stroke for that cyl., bring up to TDC mark adjust. Repeat for each cyl....don't have to remember how many turns or whatever and get confused, like us more 'mature' owners  
P.S. I would NOT run that bike until valve clearances are set for sure on the compression stroke TDC for each cyl.... IMO  

[cb650guy]

Thanks for all of the advice I have gotten in this thread.  I rechecked the valve clearances and fixed my mistakes from the first go round.  I am fairly confident that the valves are now within spec.  The bike is still having an issue of not idling below 2k rpm with no choke and not revving above 4k rpm with or without choke.  I have gone through the valves and carbs now twice for each.  I am thinking both of those issues are okay and I do not believe that I have a vacuum leak but I will check for sure tomorrow.  My plan is to get some starting fluid and spray it around the intake boots with the bike running and watching the tachometer.

Assuming I have no leak I think the next step is to check the timing.  Does this sound reasonable?  I do not have a timing light so I was going to just do the static timing.  If I set the static timing would it be enough for the bike to atleast idle properly without a choke?


Thanks,
Adam

[scottly]

By trying to run the bike up to 4000 RPM with the choke on, you may have fouled your spark plugs.
By all means, do check your static timing, and while you're at it, check that the advance mechanism moves freely.

[cb650guy]

Thats a great thought.  I will try that when I get home.  Why would fouled spark plugs allow the engine to choke but not idle though?

[MasterChief750]

i always ask this question because i did it. have you changed your oil recently? did yo put the correct amount in, this will have nothing to do with the plugs being white but not being able to rev over 4k on my bike was a sign of too much oil in the crankcase. i drained some oil off and revved just fine.

[Duanob]

With full choke the motorcycle idles nicely but even with a full throttle it wont get above 4000 rpm. 
With no choke the motorcycle can idle around 2K rpm, but if it goes below this it dies.

I do not believe I have any vacuum leaks.  I checked by spraying WD40 over the boots and watching the tachometer needle. 

I think you have a classic sign of a vacuum leak. I'm not familiar with the 650 but the 550 has O-ring gaskets between the intakes and the head. Mine were brittle shrank and had pieces missing. Heat will do that to rubber. After replacing them with new ones my bike ran great (Of course after the 3000 mile tune up and carb clean). And carb cleaner sprayed on the boots didn't seem to affect the rpms at all. Luckily my boots were in good shape inside and out. It takes a few mintues to pull off your intake rack to check. Good luck.

[tlbranth]

Take off all the covers so you can see all the rockers. When #1 intake is all the way open, #4 intake is all the way closed. Adjust #4 intake. The same applies to the exhaust valves. #2 & #3 are paired in the same way. Just turn the engine and watch for a valve to open. When it is, adjust its mate. In this way you can adjust all the valves with a total of 2 turns of the engine. Keep notes on which ones you've adjusted.