Topic: New plugs go black, runs bad, after about 2 hours use

[2timer]

Hello,

I have a K2 CB750, with a K4 engine and F2 carbies, stock airbox and good stock filter, and points ignition, with 4 into 1 pipes.

I bought this as a near finished project bike, still is a project 6 months later. For someone who is pretty much a useless drongo with mechanical things, this has been a good learning experience. I have had some satisfying moments with it. I have fixed some indicator problems, got the instrument lights and kill switch working,  and repaired the damaged starter button that only let it crank the starter intermittently. I have got it registered and fixed an overcharging problem, but one problem persists, so I haven't got to ride it much. It runs really well, with new plugs, but after about 2 hours at most, the plugs blacken up and it breaks down badly. Clean the plugs as well as I can, and it still runs bad on number 3 cylinder. Needs new plugs to run well.

When it runs well it pulls like a steam locomotive, unfortunately it also smokes like one.    I can't work out what colour the smoke is, perhaps whitish to greyish at idle and revving a bit. When riding, there is a cloud of whitish, bluish smoke on acceleration.

This was further complcated three days ago by the number 3 carby overflowing from the overflow hose. Hadn't done that before. Tap on it and it stops eventually, then starts again moments later. I just put new plugs, D8ES-L, into it and took it for a ride, ran great again, idles well, about 1100, goes like a beauty, and the carb isn't leaking at the moment.

When I was playing around with it I discovered that when the number 3 plug lead is off it doesn't smoke, so some of the problem revolves around cylinder 3,  in the head or rings I am assuming. However I could live with the smoke for a while, at least until some copper (policeman) gives me a tap on the shoulder. I'd just like to ride it for a while before I have to work on the motor.
I've been trying to sort the probems out first so that when I do the motor, I can put it back in with a reasonable expectation that everything will be ok. 

The riding I have done is just around local suburban streets, so not fast, can't think of any where offhand to do WOT plug chops yet.

The spark plugs all look much the same, pretty black, although when I pulled the plugs just before, to put the new ones in, 3 was as clean as when I put it in, had't been firing well. The spark on 2 and 3 seems the same as 1 and 4, but when you pull the plug leads off 2 or 3, it didn't seem to affect the motor as much as pulling 1 or 4. Haven't tried this with the new plugs yet.

When I was trying to get it to run on all four, I noticed that pipes 1,2, and 4 were hot as soon as I started it, while 3 wasn't firing. Is that normal that they heat up so fast, within seconds.

SO THIS IS ALL LEADING UP TO MY QUESTION, finally.
When I bought it the PO told me he had changed jets in it, from I believe 130 to 120, but wasn't sure if it was right yet, and he hadn't synched the carbs. I think it must still be running rich pretty badly, considering how quickly it happens, and at low speeds. Do you think that is likely?

If I have to change the main jets, can I get them out readily, safely, without removing the carbs, can you remove the float bowls even? How do you do it? Does anyone have pics of what I am looking for? Is this going to be one of those  carbs off rite of passage things.   

If you have lasted to here, look forward to hearing from you, thanks for taking interest in my sad tale.

Later,
Nev
 

[750goes]

I think you are running way too rich on all cylinders by the sound of it

If #3 carb was overflowing and the whitish sort of smoke does not appear when plug lead is pulled off #3 and it does not make a great deal of difference to engine running if #3 is off, and the plug is clean on #3 it sounds way like

TOO MUCH FUEL getting in there..................YES it is running RICH.....

the fuel metering on the F2 carbs is after the carb throat - wind it in to get it lean....wind it out to get richer......

if you have not synched the carbs, then I think you may need to do so - I would also check the jets to make sure they are at least the same size ones in all four carbs...

and check the float levels - I bet you have also got some problems with #3 carb float needle and or jet.....

120 main jet is also quite big for that motor...........do you have 4-1 exhaust or all 4 pipes....baffle or no baffles ??

let us know

carbs are not hard to pull off - putting back on is the reverse effort multiplied by two.....

YES do the carb sync.....YES.........

[750goes]

Hi,

you need to get the bike running, then do the following after it has warmed up

starting from carb number 2 (the one with the accelerator pump)...have a portable tacho attached to the bike so you can see it clearly.........every 1/4 turn in on the air mixture screw watch for the rise of rpm...ithis may take a few seconds to have an effect, if a rise in rpm happens, continue to adjust the mixture screw until the rise in rpm stops (just wait a few seconds each time for the carby to adjust to the setting)...when the rpm rise stops wind it back 1/4 turn...and leave it alone...

now do each carby the same way........1 3 & 4.....do not adjust 2 again...

now do it again

repeat.................get to the highest idle on each carby then back it off 1/4 turn.........

you also may need to adjust your main idle screw down as you do this process....do everything slowly...........

it will probably clear up your rich problem.......

if it stumbles and carries on a bit doing this you may need to clean your idle jets...

I would also still clean or check the float needle on #3....

you can roughly also measure the volume of fuel from each float bowl by undoing the drain screw and catching the contents, and if they are close to the same volume, at least the float heights may be the same....whether they are right or not will leave for next time....


let us know how you go

is the smoke starting to get a bit thinner - also have you adjusted your valves
when was the last oil change ??

[kaysystems]

When you have the carbs off, look at the intake end of them. There is a small brass (probably dirty) jet, on the opposite side to the idle screw. Make sure that you can pass a #100 carb wire through it. This jet feeds air to the main jet. Cleaned mine & the plugs are fantastic

David

[mlinder]

Why are you running d8ea-L's?

L denotes half heat range. Not the right plug. You want straight D8EA's.

Hondaman says blocked emulsifier passages can cause the behavior you've got as well. (same thing kaysystems said, actually.)
First get the right plugs and see if it's still happening.

[TwoTired]

Yes it certainly seems as though it would be rich, but I just don't understand why it runs so well while it has new plugs, then it seems suddenly to break down and run poorly after about 2 hours.

An engine running too rich, doesn't have enough oxygen to burn all the in the chamber.  This leaves behind unburned hydrocarbons (Carbon soot) deposited on the surfaces of the combustion chamber.
The spark plugs are supposed to jump the spark gap between center electrode to the tang reaching over it.  If there is a carbon trail coating the center electrode insulator, the spark voltage follows the carbon trail instead of jumping the gap.  The carbon fouled plugs can be recovered by abrasive blast material, or a blow torch to remove the carbon deposits.  ... Or replacement.

Since you've had overflow issues, I would check the fuel tank for rust or other contaminants.  And, the carbs for crud inside.  Remove a bowl and look for sediment.  Any bits larger than 0.016 inch can muck up the idle system.

The carbs you have call for 115 or 110 as a main jet if you are going to use the stock air filter.  The mainjet becomes more dominant for the fuel mix as you position the slides nearer to WOT.

If you are determined to use the 120s then you will likely need to change the air filter to a less restrictive one, such as a K&N.  However, since your carb are no longer adjusted for proper mix across the throttle range, a change in filter may help the high throttle positions but not the low or midrange.  Meaning, you may need to address the Idle Mixture Screws and the slide needle adjustments.

To determine how much effect the air filter has on your high range throttle settings, temporarily take out the air filter, and go for a ride.  If your high speed issues improve, then you have confirmed a rich mixture problem and must decide if you will address the final fix with properly sized main jets or air filter changes.

Cheers,

[turtle]

Hi Nev
Its great to hear the bike is up and running.
One thing that hasn't been mentioned here is the quality of the petrol. We have found that it tends to go off if it sits around in a vented system for any length of time. (I have been told that some of the additives evaporate.) If the bike has been sitting for while with the same petrol, it pays to drain the tank and start again with fresh.
We look forward to seeing you and the bike at the VJMC meetings.
Jane

[mlinder]

The d8ea-l is a colder plug, far as I can tell. If you are running rich, better sort out your carb issues before running colder plugs.
I'm sure hondamans suggestion is a good one, were all the other issues sorted.

[BobbyR]

I would also be certain that the choke butterflys are opening completely. Unburned fuel smoke will disappate quickly, while oil smoke will linger a while. I am running 120 mains with no problem. You can step D7ea plugs are hotter and will stay cleaner in a rich environment. If the bike had been laid up for some years it has to break in again, the rings free up and things get. You did not mention the Oil you are using. Sounds like you are well on your way to having a runner.

[BobbyR]

BobbyR,
your comments about the choke butterflies may have some merit. It has the F2 choke cable up to the handlebars, but no mount or knob on the end to adjust it with. On the rare occasions I have had to use it I have pulled it out with pliers, then pushed it back in as well as I could, seemed to go right back in. I actually went looking for one yesterday as well as the new plugs, but couldn't get a new cable. I was wondering myself if that may be causing problems.  I did run D7EA plugs, didn't seem to make much difference.

If you do not have to use the choke when starting cold, you are running rich. These suckers are cold blooded. The cable sheath is captured at the top of the carb asebmbly, this can be overlooked easily, and the sheath will move and the center cable not, don;t ask how I know. I had a hard time at first, but she is running really well now. It is a game of inches with these things.

[BobbyR]

BobbyR,
your comments about the choke butterflies may have some merit. It has the F2 choke cable up to the handlebars, but no mount or knob on the end to adjust it with. On the rare occasions I have had to use it I have pulled it out with pliers, then pushed it back in as well as I could, seemed to go right back in. I actually went looking for one yesterday as well as the new plugs, but couldn't get a new cable. I was wondering myself if that may be causing problems.  I did run D7EA plugs, didn't seem to make much difference.

Yes it would be nice to have a reliable runner that I could enjoy whenever I want. I have to laugh to myself sometimes, I see blokes here who drag some derelict bike home and it seems a week or so later they have stripped it down to a bare frame and rebuilt it into some stunner and they seem a bit hohum well I did this and that, it was a piece of cake, and I'm thinking good grief, look at these blokes, I can't even get this old bus running right.

Well the World is full of BS artists, I think you call it high noting. I have a jerk down the street with a Shadow that is pimped out to look like a Harley. As I was struggling like you are with getting my bike running he would rev it up and take off. 3 months later we happened to meet at a stop light. I asked him later how my new rear tire looked. Your bike looks perfect. Get past this small problem and you will ride with pride. Check out Terry in OZ, he may have some wisdom. Nice chap and knows his stuff.   

[Bob Wessner]

BTW, does anybody know anything about the right angle ratchet screwdriver I referred to for adjusting the mixture screws on the F2 carbs? I read it in a post recently, but lost track of it.

Would this be the type of tool you are looking for?

http://www.sjdiscounttools.com/lis64250.html

[BobbyR]

BTW, does anybody know anything about the right angle ratchet screwdriver I referred to for adjusting the mixture screws on the F2 carbs? I read it in a post recently, but lost track of it.

Would this be the type of tool you are looking for?

http://www.sjdiscounttools.com/lis64250.html

As a true Aussie, you don't need no stinkin rachet. Just rinse the burns with some Fosters and tough it out. 

[jtb]

2timer,
I had a similar problem, #4 would foul so badly it would only hit on 3 cylinders after 25 miles or so.  My problem was the infamous F2 valve guides.  Sounds like yours is mainly carbs, and you will get it sorted out.  After 4 years, it is only since last fall that I have been able to ride mine whenever I want to without a lot of prep (new plugs, etc).  Keep after it, it'll come.
John

[turtle]

Hi Nev
We are looking forward to seeing that gorgeous bike at the meetings.
Jane

[jay72chevy1]

Here ill help clarify the NGK hot cold issue. The plug with a  9 in it is the coldest 8 little warmer than 9, 7 little warmer than 8, and so on. So the lowest number is your hot plug and your high number is your cold plug. GL