Author Topic: idle not right (Read 5148 times)

cd811 · « **on:** June 22, 2006, 09:05:02 PM »

the bikes running very good...actually, never better...the problem is irregular idle...in the morning when cold(starts first kick)I have to idle screw up to take my hand off throttle...if I leave screw alone ,after it warms up it's too fast...so I try to set idle screw after motor is warm(ya know compromise)...but sometimes when motor is hot,when I try to idle ,it goes dead(fun in traffic) or idles too fast...carbs are clean clean clean...runs like a rat on cheap speed...tune -up has been done over and over...valves,timing.carb sync...plugs are just the right color with jets at 38/105,clip in the middle...compression great...new float valves with float height checked several times...mix screws set at 1/2 turn(runs best there)...if ya don't know, this is my 73 811 with 4-2(open) with breadbox...I have NOT replaced slide needles...think they could be problem?

...some may say it's a lean condition, but my plugs say NO...any ideas...elder, I hope I'm not whining...

scondon · « **Reply #1 on:** June 22, 2006, 10:20:40 PM »

A couple things I've learned while trying to put a perfect tune on my 836. It's also in the manual for stock 750.

1) idle screw should be set for ideal idle while engine is HOT. Set it, leave it, deal with having to hold the throttle while the bike warms up on cold mornings or get some 77-78 carbs with accel. pump and choke cable. Wish these carbs didn't have to be nuclear hot to work well, but that's the way they are $:-\$

2) setting all the mixture screws at the same setting is just a starting point for getting them set properly. Mine are set at 1, 3/4, 1/2, and 3/4 and the bike runs at it's best with the least amount of hesitation getting on the throttle. I start with them all at 1 turn then adjust each one by turning it out to 1 1/4 and slooowly turn it in until I hear the idle rise then a little bit more until it starts to bog down, then back out to the "sweet spot". Do all four this way and then go back and double check.

Having trouble at idle can also be caused by leaking intake rubbers, dirty pilot jets, etc... sounds like you've got the float height well taken care of

Slide needles shouldn't be affecting idle as they don't come into play until you get on the throttle.

You've been on the boards for a while and I'm probably not telling ya anything new, but hope this helps.

Gordon · « **Reply #2 on:** June 22, 2006, 10:33:00 PM »

Quote from: scondon on June 22, 2006, 10:20:40 PM

1) idle screw should be set for ideal idle while engine is HOT. Set it, leave it, deal with having to hold the throttle while the bike warms up on cold mornings or get some 77-78 carbs with accel. pump and choke cable. Wish these carbs didn't have to be nuclear hot to work well, but that's the way they are $:-\$

Never understood why some folks are so against turning up the idle stop screw to hold the idle while the bike is warming up. I've done this on all four sohc4's I've had and have been doing it every day for over two years on my 750 and never had a single problem with it. I turn it in to hold the idle while it's cold, and then turn it back down once it's warm.

This produces the exact same result as holding the throttle open with my right hand, but without the need to hold the throttle open with my right hand, and has no adverse effect on the carbs.

scondon · « **Reply #3 on:** June 23, 2006, 08:33:09 AM »

You're right, turning the idle screw is the same as twisting the throttle and has no adverse effect on the carbs or engine. Not "against it", just like to get ignition and carb tune at best settings so I don't have to fiddle with the idle everyday. I used to turn it in and let the bike warm, then set it at 1100rpm and head to work. By the time I'm off the freeway it's at 2000rpm and I'm adjusting at the stoplight. Repeat for the ride home.Also, petcock on my F tank is same side as adjustment screw which makes adjustments on the fly a finger burning experience.

Fast forward, my bike will actually run at 500rpm now. Takes about 30 seconds to get near 1000 and idles hot at 1200. No more reaching down at the stoplight. Granted it is a rebuilt motor, probably couldn't get a 30 year old engine to run at 500 but you get the idea.

byidesign · « **Reply #4 on:** June 23, 2006, 10:59:37 AM »

If you don't want to hold the throttle, you can
get a throttle {lock /clamp} J..C.Whitney still
sells them ....crank RPM.up it to where you want it
and flip the lever, it will stay until released,
they are mostly used as a cruise control, but
will work just as well for that......then you can leave the
carbs adjusted for warmed up running...
Hope it helps
Bruce

TwoTired · « **Reply #5 on:** June 23, 2006, 12:04:45 PM »

Quote from: cd811 on June 22, 2006, 09:05:02 PM

I hope I'm not whining...

Oh well....

I remember as a child getting in the Chevy (1946 model, I think) with mom and watching her get it started. The Starter button was on the floor above the gas pedal. On the dash was a pull knob marked "C" and one next to it marked "T". These were choke and throttle, where the throttle would raise the engine idle (a lot, if you so chose). Since your foot couldn't easily be on both the brake and the gas pedal, the pull throttle kept the cold engine from dying while you drove it with the cold engine.

Later, carburetted cars had an automatic choke with a bi metallic spring that closed the choke and activated a fast idle cam while the engine was cold. That spring was a "cold motor sensor".
Today, cars have temp sensors, exhaust sensors, throttle position sensors, RPM sensors, etc., that relieve the enormous burden of keeping a cold engine running from the operator, whew.

The only cold motor sensor on the SOHC4s, occupies the driver seat. In 77, the SOHC4 550&750 made a technological leap forward, getting a choke knob and a coupled fast idle cam to raise the idle during cold warm up. I'm guessing that the patent on this device common to cars in the early 50s finally expired.

You may ask why is throttle required? (Immediately dreading a long winded answer).

Gas doesn't burn in a liquid state. It must be vaporised so that the molecules of fuel can get up close and personal with each oxygen molecule in the air. Vaporization occurs more readily as the temperature increases, and the cold metal walls of the engine cylinder actually act to condense (turn the fuel back into liquid) the vaporized mixture fed to the cylinders. The result is a very inefficient and barely stable combustion process, until the engine is at operating temperature. Not only is more fuel needed (choke) during warm up, but due to the inefficiency of the cold engine, more air, or throttle, is needed to make the engine operate at the same crankshaft rotational speed, compared to when the engine is warmer and more efficient at combusting the chemicals fed to it.

To sum up, the SOHC4 needs extra throttle during the warm up period, which must be provided by the operator; choke knob, idle knob, or twist grip.
If you want your old technology bike to run cold like a new technology vehicle... Well, you're just whining. And, stamping your feet isn't going to change things either.

Learn to work the machine or get something made in this decade. But, where's the sport in that?

Cheers and humor implied...

Gordon · « **Reply #6 on:** June 23, 2006, 12:19:38 PM »

Never had one of them fancy '77 or newer sohc's with the fast idle cam, guess I've just always prefered the "vintage" macines!

ProTeal55 · « **Reply #7 on:** June 23, 2006, 12:29:14 PM »

My scoot has ALWAYS had a funky idle issue.
I am sure I am past due on a complete carb. cleaning/rebuild, but I am having too much fun actually RIDING the bike to tear it apart.

I always adjust the idle screw so the bike will idle on it's own after startup.
As I ride, and the motor begins to build heat, I will just lower the idle to keep it where I wanna be.
My bike likes to be just below 1000rpm as far as idling goes..I do this a few times and then all is well.
Before parking the bike for the night, I ususally give the idle screw a little turn (increase) to help the next days starting procedure.

My bike has been like this from day one, and I have just become acustomed to it.
It is what it is...

tramp · « **Reply #8 on:** June 23, 2006, 01:57:54 PM »

i just play with the choke when it's cold

cd811 · « **Reply #9 on:** June 23, 2006, 08:14:49 PM »

thanks for all the replies...sounds like just a common character of the early carbs...actually ,that's good to hear because I thought something was wrong...I can live with it...thanks for the pilot screw tip Scondon...I'll try that

TwoTired · « **Reply #10 on:** June 23, 2006, 09:27:53 PM »

Quote from: scondon on June 22, 2006, 10:20:40 PM

2) setting all the mixture screws at the same setting is just a starting point for getting them set properly. Mine are set at 1, 3/4, 1/2, and 3/4 and the bike runs at it's best with the least amount of hesitation getting on the throttle. I start with them all at 1 turn then adjust each one by turning it out to 1 1/4 and slooowly turn it in until I hear the idle rise then a little bit more until it starts to bog down, then back out to the "sweet spot". Do all four this way and then go back and double check.

Sean,
This looks like a reasonable proceedure for carbs that have idle mixture screws like the 77-78 carbs. Are you saying this is good for the earlier carbs with Idle Air bleed screws?

Cheers,

8 Track · « **Reply #11 on:** June 23, 2006, 09:52:16 PM »

I've done the same thing with my '76 750. Started with 1 turn and look for the sweet spot. I've done this countless times and I always end up at 3/4, 1/2, 1/2, 3/4. I have a throttle lock and I've given up with trying to keep it running when cold. I turn my screw to keep it going. As I approach a stop, I pull the clutch. If it's too high, I lower it while I'm coasting. If it stalls, I give the engine a bump with the clutch. Just don't rear end the stopped traffic! I've been through the bike with a fine tooth comb and nothing has changed this characteristic of the idle dilemma.

Where's the sport of just pushing the start button and going all day, no worries mate?

scondon · « **Reply #12 on:** June 24, 2006, 09:18:44 AM »

Quote from: TwoTired on June 23, 2006, 09:27:53 PM

Quote from: scondon on June 22, 2006, 10:20:40 PM
2) setting all the mixture screws at the same setting is just a starting point for getting them set properly. Mine are set at 1, 3/4, 1/2, and 3/4 and the bike runs at it's best with the least amount of hesitation getting on the throttle. I start with them all at 1 turn then adjust each one by turning it out to 1 1/4 and slooowly turn it in until I hear the idle rise then a little bit more until it starts to bog down, then back out to the "sweet spot". Do all four this way and then go back and double check.

Sean,
This looks like a reasonable proceedure for carbs that have idle mixture screws like the 77-78 carbs. Are you saying this is good for the earlier carbs with Idle Air bleed screws?

Cheers,

Hey TT, Here's what the shop manual says. This is after setting all screws to one turn out, vaccum synching the carbs, and apparantly to be done with vaccum gauge still hooked up(?):

Turn the air screw slightly at a time within 1/8 turn in both directions from original setting, pausing for about 5 seconds to locate a point of highest engine speed by the tachometer. Perform this adjustment to all carburetors.
If it takes over a full turn more or 1/2 turn less than the original setting to change the engine speed check the following possible cause

Air screw requires over 2 turns: Air screw adjustment requires less than 1/2 turn:

Clogged air passage Clogged slow jet

Worn air screw valve Clogged slow jet passage

Float level too high Float level too low

loosened slow jet Excessively worn air screw seat

It goes on to describe adjustment to "Each throttle cable" so this procedure should cover all the early 750 carbs. Additions to the K3-5 carb sections gloss over this same procedure in periodical maintenance section while describing the vacuum synch. "If adjustment is necessary, it is performed with the pilot air screw and the throttle stop screw".

Rushoid · « **Reply #13 on:** July 21, 2006, 06:41:03 AM »

Sorry to bring up an old thread but...
How long should it take for these things to warm up? My '78 750 F3 seems to take forever. Haven't timed it yet but I would guess 7-10 minutes. I pull the choke all the way and it always starts right up and idles fairly smoothly. No smoke until it gets close to warm then it's black (with choke on. No smoke with it off.). When it's warm it runs great - good throttle response, good power, smooth idle, etc. I'm getting 40-42 mpg with my big butt on it. I never have to mess with the idle screw, just pull the choke when cold. So is this warm-up time normal? Or am I missing something.

Gordon · « **Reply #14 on:** July 21, 2006, 06:56:43 AM »

It depends on what you mean by "warm-up". Are you talking about getting all the way to normal operating temperature, or just warm enough to start riding?

What kind of plugs are you using? I was having a similar problem with my K1 taking too long to get warm enough to ride, and I believe it was TwoTired who suggested switching to the hotter D7EA plugs. I did, and it made a significant difference, also made it a little easier to start in sub-freezing temperatures.

eldar · « **Reply #15 on:** July 21, 2006, 07:15:07 AM »

Well, I dont know how big your butt is but mine is about 220 pounds. I get 40mpg and my warm up time of course varies with outside temp. My 78 750K only needs choke to run at lower rpm and idle. Once started, it will run higher rpm with no choke at all and have loads of power but is a little rough. Not good for the engine to rev high though when cold. I know I can get better mileage and warm up times though.

I need to adjust the low speed mix on my bike yet. I have done everything else but have jsut not played with the tach settings on my dwell enough to get around to doing my bike. It is suprising how lean these bikes actually run! Those spark plug charts that sometimes pop up have NO relevance to our bikes. What is called too hot or bad is about what our bikes run at, at least with a d7 plug. A d8 wont show much either.

I dont know if you have done it but do a idle tune with an tach/dwell or a sensitive shop tach. That will probably help.

StevieMac · « **Reply #16 on:** July 21, 2006, 08:05:23 AM »

I'm a big fan of those throttle locks. I put them on all my bikes. They work great when warming up these old bikes and I like being able to temporarily lock the throttle while I'm riding so I can give my right hand a bit of a rest now and then.

I've also done the old set the idle for startup and then adjust it down as you ride and it warms up too. That works just fine but I do find that the throttle lock makes it just a bit easier.

Rushoid · « **Reply #17 on:** July 21, 2006, 11:59:32 AM »

Eldar, I WISH I was as light as you! Remember the pic of the "World's Largest Twins" riding those little bikes? That's about what I look like on my 750! (OK, not really). Haven't used the dwell tach but I'll see if I can round one up to borrow.

Gordon, I guess I'm talking "warm enough to open the choke" warm. I know my plugs are D7xx, I just can't remember the xx.

Pretty sure the first was an "E" and the second was close, but not the ones listed in the book. I guess I'll invest in the D7EA plugs too.

Thanks guys!

Lumbee · « **Reply #18 on:** July 21, 2006, 12:17:20 PM »

...hey Carl, if you have crappy idle, might I suggest Electronic Ignition, and matching coils. I'm running Accel Coils on my chop, and I noticed a difference when starting and nice stead, low idle...

eldar · « **Reply #19 on:** July 21, 2006, 12:55:13 PM »

Coils and dyna would be nice for sure.
You should get something out of tuning with a dwell/tach. It allows you to fine tune the low speed mix.

Gordon · « **Reply #20 on:** July 21, 2006, 12:56:32 PM »

As long as you can ride it fairly quickly after starting, I don't think there's a problem. 7-10 minutes to get to normal operating temp seems about right to me. My K1 doesn't have the fast idle cam on the choke like the later models, so I have to turn up the throttle stop screw when I first start it, and it usually takes about that long until I can turn it back down all the way and still have it idle normally.

Check the number on your plugs. You probably have the D7EA, but make sure there's not an R in there. If so, then you have resistor plugs, which these bikes don't need, because they already have resistor caps.

eldar · « **Reply #21 on:** July 21, 2006, 01:19:15 PM »

Well with the earlier Ks, that might be right but our bikes are made to run leaner which of course causes the engine to heat faster. He may not warm much faster than that but he should still tune the low end to get his full economy and power.

cd811 · « **Reply #22 on:** July 21, 2006, 09:47:06 PM »

latest update...jets are at 38/115...I installed new slide needles(Honda)(clip in the middle)...mixture screws are at 1 full turn all the way across...I installed Dyna coils when I built the bike ,but I had points...about 1 month ago I installed Dyna s ignition...I went from d8ea to d7ea spark plugs...the overall idle circut is much improved and, I feel ,is about as good as it's going to get...I set the idle screw when the engine is hot and try to leave it alone...I also have no more low rpm or "off the bottom" stumble or hesitation...I believe the small amount of idle irregularity and sometimes slow slide drop is (like eldar and tt pointed out) is a design of the times...I can live with it or spend a lot of money and update with replacement...thanks for all the help

Lumbee · « **Reply #23 on:** July 22, 2006, 02:47:59 PM »

...hey Carl, you riding up to Mammoth Springs with us in October?

cd811 · « **Reply #24 on:** July 25, 2006, 05:13:29 PM »

I don't know...way to early for me to tell...sure sounds like fun

News:

Author Topic: idle not right (Read 5148 times)

cd811

cd811

eldar

eldar

eldar

cd811

cd811