Topic: The smoke continues... Now with videos...

[Reganator]

Ok, I started a thread about this previously, but it didn't quite yield results and I was operating under an oil burning assumption.  I'm not anymore, this smells like gas.  The data:

White / grey smoke, smells like gas
The bike: 71 CB750 frame, 72 K2 CB750 engine, 75 F0 CB750 carbs, Kerker 4 into 1

Carbs are stock setup, 40 pilots, 105 mains, air screws 1 turn out.

Smoke smells like gas...

Video of bike starting and idling slow and cold:
CB750 low idle

Video of bike warmed up and idling at about 2750 with smoke after warmed up:
CB750 warm high idle

I'd say it runs pretty well off idle and feels pretty good. It does rumble a bit on decel.

While cold it also occasionally backfired and has some nice popping in the exhaust. 

I'm guessing this means lean?  Perhaps I need a larger pilot?  Maybe I don't know what I'm feeling for and need larger mains?

Whatcha think?

I'm going to pull a plug in a few minutes here and post a picture.  I just have to run an errand and give the bike a minute to cool down.

[iron_worker]

Why is it idling so high? Can you not adjust the idle down any? It should idle nicely around 1200.

Do you need choke to start it when cold? Didn't look like it. If not, then you're probably way rich at idle. Smokin after warming up would confirm this also I think. Cold engines need more fuel to run properly (hence the choke) so the mixture is probably close to right when cold and then as everything warms up and the fuel atomizes better, the engine needs less fuel ... and it starts to smoke.

Your main jet has really nothing to do with your A/F ratio at idle.

I'm betting the plugs are bllllaccckkkk.

IW

[Reganator]

It wasn't completely cold, I had run it for a few minutes earlier in the day, but it does seem to need the choke to start.  If I try to take it off choke to soon the idle seems to surge a little for a second.  Good question on that though, and I'll be sure to keep an eye on the behavior at idle when cold tomorrow and let you know.

I have issues adjusting the idle, if I try to turn it down to a normal speed when warm using the idle adjustment screw it tends to not want to start and stay running unless I stay on the throttle.  There is no rolling it back to idle until its warm.

Now for the bad business...

Here's plug from cyclinder 4.  Couldn't get the camera to focus up close very well here.  For those that are wondering, it looks like bloody hell.  It's black and has a wet appearance to it.  Could be oil, could be gas and carbon mixed, I don't know.

[img width= height= alt=" title="Hosted by imgur.com]http://i.imgur.com/yg8amcc.jpg[/img]

In case you are wondering, that pipe is still getting hot so that he'll seems to be firing at least part of the time.

Now, here is the plug from cylinder 1, it's black but nice and dry.  Kinda pretty actually.

[img width= height= alt=" title="Hosted by imgur.com]http://i.imgur.com/hYZf8Jc.jpg[/img]

Completely dry, but still somewhat black.

So... Seems rich then... Or... Opinions?  I think I'm heading to Autozone for a new plug for #4 right now. 

[Edit] Game plan:  going to go replace that plug at Autozone, then I'm going to back air screws out to something like 1.25 turns.  Test ride and plug pull to commence afterwards.  I'll report back with results.

[Reganator]

Ok, I replaced that plug and went to 1.25 turns out.  Seems to be better.  A little less smoke, but much more noticeable pop in the exhaust.  I've got a video for ya, trying to show the exhaust and more importantly the popping exhaust audio.


Getting better?

Anyway, there it is.  Hopefully I'm on the right track.  I'll have to pull a couple plugs when it cools.  I'll be really interested to see what that #4 I replaced looks like.

[Tews19]

On my 71 750, the stock main jet size is 120. I have a Mac on my 74 and it sounds kinda like you but not as consistent as yours. I also am running 120s with that one.

[Reganator]

I'm running 105 mains at the moment.  Stock for the F0 carbs that are on the bike.  I think one of the previous owners decided to slap on some F0 carbs when they did the 4 into 1 instead of changing jets or otherwise tuning the original carbs.  Seems like a reasonable guess since the F0 had a stock 4 into 1, but it doesn't seem to want to idle correctly / idles rich.  Feels good on the throttle though, so far as I can tell not having ridden one before.

That's my theory anyway.

[Reganator]

Ok, new information.  Something is set up maybe wrong on my bike.  According to this image I scalped from another post about a custom oil tank:

[img width= height= alt=" title="Hosted by imgur.com]http://i.imgur.com/D81xp7p.jpg[/img]

my setup might be wrong.  Can anyone confirm this?

When I picked up the bike the breather hose from the oil tank was running to that top nubbin labeled "to atmosphere" and my bottom nubbin, well I'm not sure what if anything is on there.  Can anyone confirm 100% which routing is correct?  I had noticed that the valve train seems to build up a little pressure which seemed odd to me.  Caught that when I was waiting on a new tappet cover when one of mine cracked it's threads off.

For bonus points, what effect might this incorrect routing have?  Could the extra pressure help to force oil down into my cylinders possibly contributing to my smoke situation?

[Harsh]

The "to atmosphere" is correct.  It does not hook up to the oil tank.  The "from oil tank" goes to/from the bottom spigot on the oil tank.  The top spigot on the oil tank vents to the atmosphere as well.

I can't remember your other thread, but have you you synced the carbs?  I agree with IW..that is a high idle.

[Reganator]

Carbs have been synced, like I was saying I kinda have the idle adjustment screw turned a little high to make cold starts easier.  Once I get this thing dialed in a little better and the weather warms up a bit I'll be turning it down so it idles at a normal speed.  I'm also waiting on a battery since mine is pretty well shot and that seems to push the idle a little higher as well, not to mention that I'm a little more tolerant of it for the sake of keeping the battery a little more charged up.

[iron_worker]

I believe the popping is from being over rich still. It's excess fuel in the exhaust that is burning.

You need to get that idle down. You're probably actually idling partially on the idle jet and partially on the needle jet it's so high. So adjusting your idle screw won't have the affect it should.

Your idle should be adjusted at full operating temperature. The bike *should* require choke to start when cold will also require you to maintain a little bit of throttle to keep it running for the first minute until it starts to warm up.

Just because the carbs were tuned and set up to run on an F bike does not mean they will run properly on yours. You are going to need to do some experimenting and figure out what jets you need for your setup.

IW

[Reganator]

Experimenting?  You're telling me!  Seriously though, slapping F0 carbs on there was PO's idea, not mine, I'm just stuck picking up the pieces.  I'm going to be toying with it more today.  On the agenda:

1:  Going a little leaner on the air mixture seemed to help, so I think I'm going to try 1.5 turns out to see what that does.

2:  I'm going to adjust that idle back down when the bike is warm and after I do item 3.

3:  replace battery

4:  reroute breather hoses as they are routed incorrectly.

5:  Test ride and pull plugs.

As far as the rich / lean debate is concerned I keep hearing that exhaust popping may have to do more with a lean condition than rich, however I think I have plugs fouling and they are certainly black, so I think keeping the pressure under the valve cover down by rerouting that breather hose to its correct connections may help keep oil out?  Don't know, but I'm going to try it and hopefully I can get my plugs to stop fouling and firing regularly and maybe eliminate some of that popping in the exhaust.  We shall see.

[lucky]

It does not matter which carbs are on it. The carbs don't care.
It does matter what the jetting is for that engine.

The smoke??? How many miles on it? Has it ever been rebuilt?
IF not it probably needs valve guide seals and maybe it needs rings too if it was sittin for a long time. Valve guide seals are over 30 years old.
The cam chain tensioner rubber rollers could be degraded and spitting chinks of rubber all through the engine oil system including the crankshaft oil galleries.
Check your oil pump screen as soon as you can.

CARB set up with stock INTAKE system.
Stock.
#120 main jet.
#40 idle jet.
Slide needle clip position middle.

Probably about 1.5 turns on the mixture screws, since it has that exhaust.
Sync the carbs.

[iron_worker]

A lean condition usually creates excessive popping when you're decelerating and engine braking. Your bike is popping under no load at idle ...which is a totally different scenario.

IW

[lucky]

A lean condition usually creates excessive popping when you're decelerating and engine braking. Your bike is popping under no load at idle ...which is a totally different scenario.

IW

I agree. Open up those mixture screws.

[Reganator]

I kept hearing that I should use stock setup for the carbs rather than the engine, but maybe that doesn't carry over for F0 carbs on a K model engine.  For what it's worth, it seems to run great when I'm on the throttle and rich at idle, so I'd be hesitant about putting 120 mains on it and removing the 105 jets since it is already on the rich side. 

Just to be clear, the carbs are all at stock settings and jets for the F0 model at the moment. 

As for the mileage... kinda dicey there.  It has 30 something k on the clock, but it's a 71 K1 frame with a 72 K2 engine, so the best I can say on mileage is that it's pretty much unknown since it seems the engine was swapped at some point.  Compression seems pretty good; I'm going to measure it if I still have issues after my tweaks for today. 

The valve seals are exactly what I'm worried about.  I guess we'll see in a few more miles and after some more tweaks if more drastic measures need to be taken.

[Reganator]

Sorry, you guys posted again while I was replying.

I'm at 1.25 now, going 1.5 today is the plan.  I'll report back if it helps things.  It actually doesn't seem to pop much on decel since I went to 1.25 out yesterday, but the popping at idle increased pretty significantly, smoke seemed to improve / decrease, I'll see if that holds today.

[lucky]

Sorry, you guys posted again while I was replying.

I'm at 1.25 now, going 1.5 today is the plan.  I'll report back if it helps things.  It actually doesn't seem to pop much on decel since I went to 1.25 out yesterday, but the popping at idle increased pretty significantly, smoke seemed to improve / decrease, I'll see if that holds today.

Need to be clear.

Get the popping on decel at IDLE to cease... THEN treat any popping on acceleration while being driven as a separate problem.

But it is hard to help you properly with out all of the information.

[lucky]

I kept hearing that I should use stock setup for the carbs rather than the engine, but maybe that doesn't carry over for F0 carbs on a K model engine.  For what it's worth, it seems to run great when I'm on the throttle and rich at idle, so I'd be hesitant about putting 120 mains on it and removing the 105 jets since it is already on the rich side. 

Just to be clear, the carbs are all at stock settings and jets for the F0 model at the moment. 

As for the mileage... kinda dicey there.  It has 30 something k on the clock, but it's a 71 K1 frame with a 72 K2 engine, so the best I can say on mileage is that it's pretty much unknown since it seems the engine was swapped at some point.  Compression seems pretty good; I'm going to measure it if I still have issues after my tweaks for today. 

The valve seals are exactly what I'm worried about.  I guess we'll see in a few more miles and after some more tweaks if more drastic measures need to be taken.

The F model had the stingiest emission requirements of all CB750's.
Small jets and everything really restricted.
The main jet only comes into play at WOT. There is just a little cross over from 3/4 to WOT but not much.

IF the compression is good then you could just replace the valve guide seals without taking the cylinder head off. I can show you how that is done with photos.

[Reganator]

Thanks lucky, may be interested in the instructions on replacing those valve seals.  I'll let you know very soon.

I'm kind of a slow poke, so you may be correct that I need a larger jet for WOT, I notice when revving past about 6k things get a little... warbly is how I'd describe it.  For the moment it's perfectly rideable though and I'm just trying to kill my issues at idle before moving through the other adjustments.

Stupid question here, almost 100% that the answer is no, but can those valve seals be replaced with the engine in the frame?  Second question, I'm running 10w40 at the moment, do you think switching to 20w50 might improve the situation if there is oil getting past the valves?

[iron_worker]

Going to 20w50 is a bandaid, at best, for trying to reduce your oil consumption.

You have to pull the engine to get the valve cover off of a 750 unfortunately... unless you have a frame splice kit.

Btw, what the hell does "warbly" mean? 

IW

[Reganator]

Drats on the valve cover removal.  Seemed like there would be enough room in there, but I knew it was a crap shot.

Not sure how to describe it, just... warbly... ever messed with a wah pedal on a guitar?  So imagine you're revving my engine up, moving from 1k to 6k everything is nice and smooth, just that smooth increasing pitch.  Past 6k you start to get this oscillating tone, higher then lower then higher then lower, like someone is messing with a wah pedal.  That's the best explanation I can give.  I'm mostly worried about the smoke and idle issues right now, but I'll see if I can get a recording of that later on so you can hear better what I'm talking about.

Again though, my main focus for the moment is the smoking and popping at idle since the bike performs pretty well and is perfectly rideable.  Just trying to get that sorted.

I know 20w50 would be a band aid of sorts, but from what I understand I should be running it anyway and if it helps this issue all the better.  I'd rather wait as long as possible to replace those valve seals.

Thing that still bothers me is that it... #$%*... Lucky is about to be pissed at me but I swear this is just a coincidence, I know how to adjust valves and I guarantee mine are 100% adjusted properly... Anyway, we rode it for a couple real short rides and it wasn't smoking, after those couple rides I finished putting a couple things back together and adjusted my valves and about the second ride after that is when it started smoking.  It was a longer ride too.

I suppose if you have questions about how I did it, ask away.  Used .002 for intake and .003 for exhaust, adjusted one cylinder at a time, did intake while exhaust was fully opened and then exhaust while intake was fully opened.  Double checked after after I tightened lock nuts, Tripple checked after turning engine over...

But now I'm tempted to check cylinder 4 again just to be sure since it's fouling so bad.

[Reganator]

As a side note and a thank you for all the help I just wanted to drop this offer:  I know of a pretty good salvage shop here in Saint Louis, so if any of you guys are looking for something a bit rare or difficult to find let me know and I can check into it for you.  If I can find it I'll get it to you for the cost of the part and shipping.  The guy's prices are a bit all over the place though, some low, some about right, some high, but I suppose that's the case just about anywhere.

[Reganator]

Well... I'm not quite there yet, but I think the smoke is mostly done.  Seems like a poorly routed breather hose may have been causing my issue.  Instead of going to atmosphere it was routed to the oil tank.  I think the extra pressure may have been helping push oil past the valves somehow.

[chewbacca5000]

Since no one else has mentioned it as far as i can tell those older engines do not have any no seals on the exhaust side.  You will always have some white smoke.  I'd give the bike a good 3,000 mile tune up ride it and go from there.  It will always smoke a little.  I have an early 72 which also smokes with no exhaust guide seals.

The popping sounds like fuel igniting in the pipe. 

[Reganator]

That's interesting.  I didn't know they did not have seals on the exhaust side.  It has almost completely stopped smoking now though, I think that breather hose was the source of my issues.  The popping continues along with a new symptom, some hesitation coming off idle.  It does, however, run quite well and strong now.  I think I'm going to pull and clean all the plugs and leave it as is for the time being.  It isn't misbehaving much now, so I think I'll take a break from it while I'm ahead and enjoy simply riding it for awhile.

Next on the agenda when I come back to it is a switch to 20W50.  I'll of course be changing the filter as well and while I'm at it I seem to have a slight leak around the oil pan.  I think I'll be taking care of that with a new gasket.  Since I'll have the exhaust off I'm going to be redoing the wrap on the lower portion (scraped on a speed bump, damnit) and putting some new exhaust gaskets in.  If I really have some extra dough, possibly a new petcock and new coils.  I'd rather not wait until mine fail completely and the wires have been trimmed as many times as they're going to be.