Topic: Getting extremely frustrated with idle mixture...anybody here in Austin, TX???

[hevykevy420]

HELP!!!  i am thowing tantrums in my garage 

I am having a difficult time setting the idle mixture on my '78 cb750.  i am having a rich running condition that i can't seem to get rid of.  when i start the bike, i'm getting white smoke out of the exhaust until the bike is fully warmed up.  if i give it a bit of throttle when warming up, the smoke billows out of the exhaust.

the bike runs great at speed at all stages of throttle, its just rich when at idle.  i've checked the spark gap, timing is spot on, point gap is good, and i've synchronized the carbs with vacuum gauges.  i'm running ngk D8ea or something plugs.  the plugs are kind of tan at the tip, but black around the insulator, no white is showing at all.  i have the stock airbox with stock element, and 4-1 exhaust with the correct muffler packing material, stock coils and plugs.  i'm using 110 mains, but not sure what pilots, i assume stock.  i used an 836 piston kit and also a high lift cam with the HD springs in the head. 

i bought the digital tachometer, and when trying to set the fuel screws, i really can't tell much fluctuation one way or the other on the digital meter when going in or out with the screws, it kind of bounces up and down on the meter, so setting the screws has been an absolute nightmare.  if i go all the way in on the screws, the bike won't start, but any amount of turns out, it seems it is rich.  wtf?

1)  Is my cam throwing the idle off?
2)  Could it be my float bowls levels are off?  i checked these and thought i had them right.
3)  Is anybody in Austin that could help me out?  I'm so close to having this thing dialed in, and getting frustrated.

[Lumbee]

...hey heavy...my rule is this, if the plugs look good, then the mixuture is OK.  I've had 3 77/78 models, and I've always set the air/idle screws to the standard 1 3/4 turns out, and left it alone.  From there I used jet and needles settings to achieve the proper air/fuel ratio.  As far as the smoke at start up, I think this is common.  What happens is as the bike sits, oil from the top end tends to leak down through the valve guides.  This leaves oil sitting on top of the pistons.  When the bike is first started the oil burns off, hence the smoke the first minute or so after being started.  Sounds to me like your plugs look OK.  What is your gas milage like?  If that is 40mpg or better, then I'd say u'r OK.  You may want to look at the Accel. Pump also, there should be a gap between the lever arm, and the pump acctuator (not sure all my terms are right here).  Like 0.08" or something like that.  If its set to close you could be throwing to much gas on acceleration...

[eldar]

Dont know how your weather is. I get no white smoke on startup, ever. I get some lite black carbonish smoke. My plugs are pretty white but I have d7ea for now. If I had d8, they would be a little darker. I smell unburnt gas on start up and for a bit while warming up. I am pretty sure I still run lean. When you set your idle mix, You should be around about 1200 - 1400 rpm or so, below that and idle can get a bit lumpy. It is possible your accel pump is set wrong. Cant really set it with carbs off and it is hard to set it with them on! But set it with the carbs on.

[Lumbee]

...I guess I should backpedal a little     The smoke I get on startup is more black/dark smoke than white...either way I think the key is that if it goes away after the bike is warm then your OK...

[BobbyR]

I had a problem like yours and i caused it. When cleaning the slow jet with a Guitar string, I picked up the wrong string and opened up the orifice. She sure started quick, but I could have had 4 flame throwers going if I put a match to the mufflers. The PO may have punched them out by accident. I replaced them with a set from some busted carbs I picked up somewhere.

[ShiftyAl]

I live in Austin and have JUST started to try to get it running after sitting up for a time. What part of town do you live in? We should meet up regardless and perhaps share experience and knowledge. 'Maybe' together we might make one decent mechanic?! 

[Patrick]

I live in Pflugerville (people in Austin know where that is). If you two together make a good mechanic, between the three of us we would be pushing 1.25 good mechanics. But sometimes I get lucky.....

We ought to take a ride in the Hill Country or on Lime Creek Road sometime.

Patrick

[hevykevy420]

Patrick and shifty al, see the IM's i sent.  sometimes these bikes need 1.25 mechanics : )

Lumbee- I am doubtful that what is burning and making the smoke is oil, the head was completely rebuilt 'cause i needed heavy duty springs, and i assume the seals are good.  Could i have a clogged return oil line or something at the top end??  I am getting a very slight oil leak out of the valve cover...maybe the oil is not returning to the bottom end???  I will check accel pump clearance of .08, and also MPG when i burn through the tankful, thanks for the tip...

eldar-  you are right, that accel pump is a beotch to get to, i will also try to set with rpm gauge at a higher rpm (1,200-1,400)  should i try the D7 plug? 

bobbyr- I was very carefull when cleaning the jets not to make the orifices (I love saying that word  ) any bigger b/c i had heard of people doing this accidentally.  i didn't use any type of poker, just carb cleaner and make sure the holes in the jets were clear and i could see through them.  unless the PO damaged them, i don't think there's a problem here.

i will keep wrenching and post results, hopefully successful!!!!!  thanks everyone!!

[Noel]

White smoke that goes away when hot... black insulators...

I know you just did the top end, but... have you checked compression?

[Heirborn]

I have a '70 and have my idle screws out 3.5 turns, float bowls set at 30mm and try not to let the revs drop below 4 large when riding....helps keep the plugs clean. Still get to use my plug cleaner and keep a clean set avail. My bike is pretty tired and could use a rebuild but I ride it as-is for now.

By the way I am in Georgetown. I think the Saturday Night car show is now meeting at the old HEB on 79 and Main. I will most likely head over there on Saturday evening around 7:00 and hang out with my wife and some "car" friends. 

[hevykevy420]

Noel- I haven't checked the compression, do i have to buy another tool    do you think oil is getting past the rings or something?

heirborn- i will have to check out that car show...

UPDATE:  I now have the fuel screws set at just a quarter turn out.  trying to set them using the digtal tach was abandoned as i couldn't really tell at what point the max rpm was.  i turned them all the way in until i could hear the engine start to protest (which was all the way closed), then just backed out a little bit, enough to keep the engine at idle.  i also adjusted the accell pump arm and gave it a little clearance.

the bike fires right up with full choke BUT i'm still getting a little smoke when cold that goes away when warm.  the bike is running great on the highway, at this point i am thinking just ride the bike and quit worrying about it.  i'll check the MPG and oil levels to see if i'm still rich for some reason i can't figure out, or if i'm burning oil somehow.

[Noel]

Noel- I haven't checked the compression, do i have to buy another tool

They're cheap enough. Personally, I really like having compression numbers; it's kind of the cornerstone of engine performance. YMMV.   

do you think oil is getting past the rings or something?

Oh, maybe. When I hear of smoking that goes away when warm, especially in combination with fouled plugs, I tend to think of rings. The fact that you're on a recent rebuild would seem to make it unlikely, though.

But hey, I think you're on the right track: the bike starts and runs w/o problem, so you probably shouldn't worry too much. Just keep an eye on things and see if they get worse or not. Maybe switch to D7EA to avoid fouling out.

BTW, I know that the 500/550 are rich at idle as stock. Perhaps that's the case with the 750 as well?

More BTW: are these new plugs? Even with correct fueling, high mileage plugs will look like yours do. Were it my bike, I'd check compression, toss in some new plugs, and do some throttle chops.

[hevykevy420]

Noel-  i will buy a compression tester and post results, i should have one anyway.

i will also try new plugs, mine are not new, but not high mileage either. can you tell me what the difference is between D7EA/D8EA and their effects on the engine?  I know one is colder one is hotter, which one though???  I searched for this a few days ago, and couldn't find a clear answer.  at idle it seems like i have a slight rattle in the engine, not sure if it is predetonation or pinging, or just my cam, but either way i don't want to blow up my engine using the wrong plug.

Reason i ask is that i'm in Texas, every day is 100 degrees.  plus, i am in stop and go traffic on the way home, so add heat from everyone's exhaust (cough, cough), plus sole scorching heat reflecting off of pavement, and the ambient temp is much hotter than 100.  I've been impressed by the 750's resiliency, it doesn't seem to mind at all (my sweat glands are another story though...)

now is when someone posts "you need terry's oil cooler" and i reply "i am too poor right now, all $$$ is in the engine".

[Noel]

Be interesting to hear the compression results. We'll be praying for you.

The heat range thingy can be a mite confusing. Essentially, for a given engine temperature, a hotter plug will run, well, hotter. This means that it will burn off more carbon and such, but also that it will cause detonation sooner/earlier. Generally speaking, it's best to run the coolest plug that won't foul. Don't fall into the trap of thinking that plug range affects engine temperature: the engine is making the heat. The plug is just reacting to it.

Numbering system are different. With NGK, lower numbers are hotter. D7EA is the hottest plug you should use in your bike, and being as you live in a very warm area, I think my suggestion to try it was bad advice. I wouldn't go lower than the 8, and would be happier with an even higher number, myself.

At the very least, rich isn't dangerous the way lean is, and if you do have a problem with rings it doesn't sound like a severe problem. I wouldn't worry too much. But some compression numbers would be nice, eh?

[Noel]

Oh, and the rattle is probably normal. If it goes away with the clutch pulled in and/or at off-idle, you don't have a problem. Just an antique engine with loose (air-cooled) clearances and no water jacket to muffle the music!

[GroovieGhoulie]

Oh, and the rattle is probably normal. If it goes away with the clutch pulled in and/or at off-idle, you don't have a problem. Just an antique engine with loose (air-cooled) clearances and no water jacket to muffle the music!

Those symptoms sounds like a textbook case of clutch rattle which is usually caused by carbs that are out of sync.  Re-syncing the carbs should take care of the problem.

[eldar]

yeah in that heat, d7s would be bad. Stick with the 8s you can try d9 but start with d8.

The trick with setting idle is to start at operating temp and make sure your idle is fairly smooth. That is usually going to be between 1200 to 1500 rpm. Your cam is going to cause some lump too so you may be a bit higher on 1400 side.

[Noel]

Those symptoms sounds like a textbook case of clutch rattle which is usually caused by carbs that are out of sync.  Re-syncing the carbs should take care of the problem.

Could well be, but note that his other bike is a late model RC51. If he's comparing his SOHC sounds to his (glorious) RC51 sounds, you can understand why he might be alarmed.

Hopefully he can hook up with a fellow SOHCer in his neck of the woods and get an "in person" second opinion.

[hevykevy420]

The SOHC is a world of difference compared to the RC.  Funny thing is, I find myself riding the SOHC all the time now, the RC is just built for the track, very uncomfortable, and Walker Texas Ranger is just not fond of the first gear breaking the speedlimit capabilities.  6 months in TX and already multiple "violations".  Plus, that rear facing cylinder is making roasted peanuts out of my posterity in the 100+ rush hour temps combined with stop and go traffic in Austin.  Thank God the seat is some protection on the CB750, I want to have little mini me's too 'ya know?  Not to mention how hot the RC gas tank gets, I worry sometimes, at what temperature can gasoline ignite from ambient heat?  The frame gets so hot I cannot touch it or I will get burned    Good thing they put the frame right by where your legs contact the bike...

Anyways...I just checked the rattle on the SOHC, it DOES go away when I pull the clutch in.  I'm guessing this is normal, the bike shifts OK, a little clunky on down shifts, but upshifts are nice and smooth.  It doesn't miss gears, and I can find neutral most of the time.  I don't think the carbs need to be synched, i just used the vacuum tool a few days ago when trying to set the idle mixture, and got them all pretty close to the #2.

As far as the SOHC second opinion, I hope to get that very soon, it is always nice to hear another garage or better mechaneck tell you it sounds OK.

I will stick with the D8's for now, and will continue to check plug readings.

I am checking sears Noel for compression tester right now...

Thanks everyone for the advice and help!  I am almost there!!!!

[hcritz]

Hey Heavy...
Living in the SOUTH in the summer is such fun! I'm in MS so I understand the heat issues.
I have 77 750K...although completely stock. I park in the shop and even when it's quite warm outside I get some vapor out the pipes when it's first started...mine is just water condensation burning out of the pipes. With the Humidity we have it's not uncommon and goes away as soon as the pipes heat up...usually a whitish color...
When the temps drop I will sometimes even get water dripping out of the pipe connections...leaves a lovely black spot on the shop floor. I do get some darker smoke even warmed up if you rev the engine quickly...this is just the temporary rich condition with the accelerator pumps on the late model bikes and avoids the stumble that the earlier bikes seem to experience.
I suspect that if there's no blue oil smoke...and the center electrodes are clean...all is well. Just ride and enjoy.
H.C.

[Noel]

I'm inclined to agree. And even if there is a problem, it's unlikely to be serious.

FWIW, kevy, you'll need to get a compression tester with a 12 mm adapter, or buy one after market. Learned that one the hard way...

[hevykevy420]

hcritz- I never considered the smoke to be condensation.  That would make sense, because the smoke is a whitish color, not blue, and only a bit of the smoke comes out upon cold start up.  thanks for the info!!!

Noel- I called Sears for the compression tester, but the only one they had with the 12mm was like $60, Autozone had one for like $40.  I'd like to find one a bit cheaper than that online hopefully, but i definitely want to check the compression!!!  if anyone has found a cheap tester with the 12mm adapter, send me the link!!!

[tsflstb]

Go look at Harbor Freight on S. Lamar.  They may have some new locations in town since I've lived there.  Not the best quality, but how often do you check compression?

This one is $10, and comes with a 14 and 18 mm adapter.  Looks like the 14 mm adapter is bigger than the actual tool, so it may be 12 mm without having to use an adapter.  Might want to give them a call or take a spare spark plug in to check the threads.  If you had to, you could probably find the adapter at NAPA or Autozone for a few bucks.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=92697

Freakin' heat is miserable this time of year.  Especially in traffic on a motorcycle.

[Jerry Rxman Griffin aka MuthaF'er]

Do you have the stock screws in it? Reason I ask is I once used Keyster kits. Thought it wouldn't hurt to put in new kits. The replacement screws had holes in the bottoms. The stock did not. Couldn't keep plugs from seroiusly fouling around town. Put the old stock screws back in and no more problems. I need to mention I'm riding a 75 750F. Our carbs are different and I don't have a clue about yours.

[Noel]

That Harbor Freight tester is the cheapest I've seen by far. If it turns out you'll need a 14 to 12 adapter for it, you can try these folks:

http://www.etoolcart.com/index.asp?PageAction=VIEWPROD&ProdID=5053

The cheapest specialty M/C compression tester I'm aware of is around 30 bucks.

http://www.tooldiscounter.com/ItemDisplay.cfm?lookup=STATU-310P

[hevykevy420]

Do you have the stock screws in it? Reason I ask is I once used Keyster kits. Thought it wouldn't hurt to put in new kits. The replacement screws had holes in the bottoms. The stock did not. Couldn't keep plugs from seroiusly fouling around town. Put the old stock screws back in and no more problems. I need to mention I'm riding a 75 750F. Our carbs are different and I don't have a clue about yours.

I haven't changed the fuel screws, if thats what you're referring to, but maybe PO did.  I don't see any holes in the screws.  I think your carbs have air screws, mine directly control the amount of fuel in the idle mixture, so i don't think there should be any holes in them.

[hevykevy420]

That Harbor Freight tester is the cheapest I've seen by far. If it turns out you'll need a 14 to 12 adapter for it, you can try these folks:

http://www.etoolcart.com/index.asp?PageAction=VIEWPROD&ProdID=5053

The cheapest specialty M/C compression tester I'm aware of is around 30 bucks.

http://www.tooldiscounter.com/ItemDisplay.cfm?lookup=STATU-310P

yeah, i called the place and they said they have them in stock here in Austin for 4.99!!!  I can't quite tell if the thing has a 12mm thread before the fittings though.  I called napa, autozone, advanced autoparts, a bearing place, a hydraulic place, and nobody had a 14mm to 12mm adapter.  THANK YOU FOR THAT LINK, I PROBABLY WILL HAVE TO ORDER THAT ADAPTER.

[Noel]

If the Snap-On truck visits your area you can buy one from them. At Snap-On prices, of course.