Topic: Inconsistent Idle - Over a year later - ALMOST THERE!!! 9/24/11

[BobbyR]

Polish them with what? 0000 steel wool?

No, unless they have corroded why would you polish shiny chrome with steel wool? You remove all the crap with chemicals and then if they have some fine scratches you use ATF and 800 sandpaper like a shoeshine rag. Then a finer grit and then some chrome polish. They were chromed so they would slide smoothly. Mine were literally locked in solidly with varnish. I had to soak the for a week to get them out. They came out mirror smooth.

When people talk about sticky throttles they only think about cables and springs, they forget about what inside the carb body is actually being moved by the cables and the springs. If you think about everything as a system you get a better result.

[KB02]

Sticky slides and bad cables are one thing, but if that was the issue I would never be able to get the idle to come down - which I can. If the Idle is racing while I am at a stop, for instance, I can let the clutch out into the friction zone just to where the engine starts to pull and that will pull the idle down as it tries to transfer power to the rear wheel - which is not moving. Basically, I can use the rear wheel like a brake on the engine. Once I do this, the engine stays at the lower RPM until I accelerate again.

[Spanner 1]

Same answer as ScottS and his 'idle hover'.... I think the engine vacuum is pulling fuel from those big 'ol 130 mains @ idle and causing a runaway rpm, fix would be to drop the needles a notch to better close the main jet when the slides are at idle... cause?, oversize mains, pods, 4-into-4 not stock exhaust and their effect on engine vacuum vs. fuel induction.... IMO.

[BobbyR]

I have a 78 and there are no clips on the slides. It is hard to imagine the 130 mains causing it since the mains come in later. Did some one to that washer trick to raise the needles sometime in the past? 

[MoMo]

When I said sand, I used as fine wet/dry as I could, 1000 grit.  Also, 0000 steel wool shouldn't harm the slides.   The important thing is to get the gummy stuff off, the super fine hone/sand just helps the  slides move freely.  Good luck,

[Spanner 1]

Whoops, it's a '78 = no slide clips, still may be 'shimmed' ?..... main jets do not add fuel to the mix at idle under normal circumstances.... but it's not stock restriction at either end of the combustion cycle.....( pods and different 4 into 4's )...... one other thing, 1 carb with a high float level will make fuel much more available in that main jet to be inducted into the motor by idle vacuum and were off to the races ( rpm ), the one cylinder carrying the other 3 until the slides lift all by themselves ( I've seen it, but you dont have to believe me ) with the increased induction air thru' the carbs holding the rpms at 3 or 4 K......

[KB02]

Whoops, it's a '78 = no slide clips, still may be 'shimmed' ?..... main jets do not add fuel to the mix at idle under normal circumstances.... but it's not stock restriction at either end of the combustion cycle.....( pods and different 4 into 4's )...... one other thing, 1 carb with a high float level will make fuel much more available in that main jet to be inducted into the motor by idle vacuum and were off to the races ( rpm ), the one cylinder carrying the other 3 until the slides lift all by themselves ( I've seen it, but you dont have to believe me ) with the increased induction air thru' the carbs holding the rpms at 3 or 4 K......

Okay. This has become the next thing I need to check. I have shimmed the needles on these carbs. They are basically raised "one clip" in height. I will pull them and see if removing the shims fixed the issue. I had never thought of that. - BUT - I shimmed the needles to smooth out the transition from slow to main jet. It was very choppy. Would turning out the mixture screws help this issue as well? Floats all seem to be set evenly. The pics below are taken while using the clear tubing trick. The pics are taken at different angles, but by eye they look nice and even.

Same answer as ScottS and his 'idle hover'.... I think the engine vacuum is pulling fuel from those big 'ol 130 mains @ idle and causing a runaway rpm, fix would be to drop the needles a notch to better close the main jet when the slides are at idle... cause?, oversize mains, pods, 4-into-4 not stock exhaust and their effect on engine vacuum vs. fuel induction.... IMO.

I just re-read Scott's thread start to finish again to see if anything else rings a bell.

[BobbyR]

 This may be a long shot, but you have methodically gone through most everything else:

The 78 carbs use true idle mixture screws, not air screws like the earlier models.  If for whatever reason there was some damage to the tip of the screw or the seat, vacuum could draw enough fuel through one or more of them to cause the engine to rev.   

[KB02]

Okay. Here is my plan of attack, let me know what you all think:


I have pulled the carbs off the bike.
I checked the float heights and they were all WAY off. They were set to around 11mm vs. the Cylmers manual says 14-15mm. They have now all been set right at 14mm.
The idle mixture screws were set to 1 1/4 turns out. I have now set them all at 2 turns out.
I now am setting my sights on the needles. I have them shimmed to about the point of one clip up. I am going to drop them down to 1/2 clip up.
Then I am going to re-test (which will probably not be until Wednesday next week).

Not that I have been doing any proper plug chops, but here is what Cyl's 1&4 look like at the plug (looks whiter in real life than it does in the pic):


It has been popping on decel as I have been road testing it which indicates lean, correct? The reason I put in two shims (each shim is a 1/2 step) was to smooth out the transition from slow to main jet. By enriching the idle circuit, that will give more gas to the mid range and I can drop down the needle. Or should I un-shim the bugger completely?

[Spanner 1]

A float 'height' of only 11mm would support my theory with a too high fuel level in the main jets.....hope this latest work is the fix....

[BobbyR]

Okay. Here is my plan of attack, let me know what you all think:


I have pulled the carbs off the bike.
I checked the float heights and they were all WAY off. They were set to around 11mm vs. the Cylmers manual says 14-15mm. They have now all been set right at 14mm.
The idle mixture screws were set to 1 1/4 turns out. I have now set them all at 2 turns out.
I now am setting my sights on the needles. I have them shimmed to about the point of one clip up. I am going to drop them down to 1/2 clip up.
Then I am going to re-test (which will probably not be until Wednesday next week).

Not that I have been doing any proper plug chops, but here is what Cyl's 1&4 look like at the plug (looks whiter in real life than it does in the pic):


It has been popping on decel as I have been road testing it which indicates lean, correct? The reason I put in two shims (each shim is a 1/2 step) was to smooth out the transition from slow to main jet. By enriching the idle circuit, that will give more gas to the mid range and I can drop down the needle. Or should I un-shim the bugger completely?

That plug is carbon fouled, you can find the NGK guide here: http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp

Interesting that you found the floats out of spec since the fuel level in the tubing looks fine, I would like to see what they look like now that you have them in spec.

[KB02]

That plug is carbon fouled...

No way. I know the difference. The center is white. Clear carbon around the outside, yes, but the center is not even close to fouled. Like I said, it's much whiter than it came through in the pic.

It's much closer to this in color:


Picture taken from here:
http://www.4secondsflat.com/plug_chart.html

[KB02]

So with the floats set at the factory setting of 14mm, the idles screws at 1 3/4 turns out and one shim under each needle the bike STILL has the idle issue and runs like sh!t. I'm about ready to f*cking give up on this damned thing.

[rangelov]

Let's go back to basics.

Your bike is bored to 850.  Is the cam stock or not?  The exhaust shouldn't make any difference for jetting, if it is relatively quiet.

Why raise the needles? because?  Do you really need a richer mixture at part throttle? The needles should be all  the way the down, especially with larger mains.  All they do is improve driveability at part throttle.

Why the increase to 130 mains?  A larger engine will pull more fuel through given carburetion.  The 850 will pull more fuel than the 750 using the same carbs and jet sizes.  Did you check the mixture with stock jetting?  Was it really running lean at max throttle and max power?

And you should know that the carb circuits are NOT independant.  A richer idle will richen the mains, etc and conversely, etc.  One change will effect everything else.

What is your compression ratio?  What heat range plug are you using?

My bike has a big bore kit.  It been there for decades.  I don't know what the jetting is.  I think, it might be stock.  My manifolds are hard, so I'm not pulling the carbs to check my settings.  (It takes a mallet to reinstall the carbs)...

[Cuts Crooked]

Perhaps an old ammo reloaders rule might be in order........CHANGE ONE THING AT A TIME! Try it, if no change in performance, change one more thing......ad infinitum........till you find the thing that makes a difference.

[MoMo]

an aside but something that may be helpful to rangelov-use a heat gun on low to warm up the rubber manifolds. Makes them flexible so the carbs slide right in, Larry

[a700guy]

do the fuel screws have the correct spring, washer. oring orientation?

[KB02]

Your bike is bored to 850.  Is the cam stock or not?

no. Webcam 63a

The exhaust shouldn't make any difference for jetting, if it is relatively quiet.

Glass packed 4 into 4. Fairly free flowing.

Why raise the needles? because?  Do you really need a richer mixture at part throttle? The needles should be all  the way the down, especially with larger mains.  All they do is improve driveability at part throttle.

The transition between the two jet was horrible. raising the needle smoothed it out.

Why the increase to 130 mains?  A larger engine will pull more fuel through given carburetion.  The 850 will pull more fuel than the 750 using the same carbs and jet sizes.  Did you check the mixture with stock jetting?  Was it really running lean at max throttle and max power?

Plugs showed that it was way lean with smaller jets. I wanted something smaller than 130's but the local shop did not have any.

What is your compression ratio?

10.5 : 1

What heat range plug are you using?

Stock plugs

do the fuel screws have the correct spring, washer. oring orientation?

Yes.



On my test ride yesterday, it took FOREVER for it to come off of choke. It was only in the low 60's, but it shouldn't take 10 minutes to come off choke. Another indication that it is WAY LEAN.

[rangelov]

Why the increase to 130 mains?  A larger engine will pull more fuel through given carburetion.  The 850 will pull more fuel than the 750 using the same carbs and jet sizes.  Did you check the mixture with stock jetting?  Was it really running lean at max throttle and max power?

Plugs showed that it was way lean with smaller jets. I wanted something smaller than 130's but the local shop did not have any.

What heat range plug are you using?

Stock plugs

Since we are at the basics;

Believe it or not, the spark plug heat range is determined primarily by compression ratio.

Your compression ratio is 10.5:1, stock is 9:1.  You should be running one heat range colder plug, with increased compression ratio.  When reading the spark plugs for mixture, you will get inaccurate readings, if you are running the incorrect heat range. 

Yes, your bike may be more streetable w/ NGK D8EA, but at max power (when you're doing plug chops) you should be running NGK D7EA.  At max power (main jet), you are running a much richer mixture than you think. 

[the-chauffeur]

No help to you, but I've suffered with exactly the same problem ever sine I've had mine (coupla years). 

The idle has always been all over the place - and there seems to be no 'stable' setting where once warmed up, the bike ticks over at a constant (low) rate.  Unless the idle is set at the point where the bike cuts out, it just seems to want to climb.   Using the idle adjust seems to be an unnecessarily precise science, too.  If you're not absolutely mm perfect, it's too far one way or the other.  One other thing - I found that I could get the engine to calm itself down for short periods by holding the throttle closed - essentially pushing the handle to its limiter the wrong way.  Like you, cleaning and rebuilding using new bits still didn't help me find out what the problem was.

It's in bits for its second rebuild right now (don't ask) so I've sent the carb bodies - along with the engine cases - off for vapour blasting.  I very much doubt that'll make any difference, but I guess it's worth a go.

[KB02]

One other thing - I found that I could get the engine to calm itself down for short periods by holding the throttle closed - essentially pushing the handle to its limiter the wrong way. 

I've tried that, but it did not work for me. Sounds like you might have a cable bind somewhere.

Since we are at the basics;

Believe it or not, the spark plug heat range is determined primarily by compression ratio.

Your compression ratio is 10.5:1, stock is 9:1.  You should be running one heat range colder plug, with increased compression ratio.  When reading the spark plugs for mixture, you will get inaccurate readings, if you are running the incorrect heat range. 

Yes, your bike may be more streetable w/ NGK D8EA, but at max power (when you're doing plug chops) you should be running NGK D7EA.  At max power (main jet), you are running a much richer mixture than you think. 

Okay. I stopped by the bike shop (the ones who dropped my Ducati while changing tires  ) and bought 4 new D7ea plugs. I was hoping to get out in the garage yesterday and change them out, but things just didn't work out that way. Oh well. I'll drop them in and give it a shot at some point this week.

[KB02]

Okay. I swapped out the plugs and did not make any other changes. Here is what the old plugs looked like when I took them out:



NO matter what I did for lighting, my cell phone just could not make them look as white as they do in real life. They really look on the lean side of normal. And they are pretty even across the board, too.


Then I put in the new D7EA plugs and went for about a 10 minute ride. The bike would not run for beans off choke. I had to run at least partial choke the whole time. Here is what #4 looked like:



Again, horrible cell phone pic. The plugs is super light and looks super lean. And that is WITH running the choke for most of the ride.

Mixture screws are set at 1 3/4 turns out. Should I give them another full turn out since it is this lean?

Floats are at 14mm. Books says they should be 14.5. I almost think I should raise them up to about 13 or 12. Maybe a jet is not getting enough fuel?

[rangelov]

I gave you wrong information.  D7EA is hotter than D8EA.  With higher compression ratio, the plug needs to be colder.  In this case, you should have been using D9EA.

That is why the new plugs look so lean.  I'm really sorry that I gave you the wrong part number.  I got things backwards because Champion numbers ago the other way, lower for colder.  NGK is higher for colder.

I get confused in my old age.  I must be getting senile.  The heat range does need be adjusted for higher compression ratio.  A higher compresion ratio provides more energy.  The plugs may look to be more normal with the colder plug.

The colder spark range should be used to tune the main circuit, that is full throttle, full power chops.  Start there and then work your way down to the idle circuit.  You may have to go through several iterations, since all of the circuits are inter-related.

This chart from NGK
http://www.ngksparkplugs.com/docs/tech/partnumberkey.pdf  may help more than I did.

You can use any brand you like, be sure to use the correct heat range, one range colder for tuning.

Remember that you can use the standard spark plug after tuning, for general driving around.  That will generally keep it from fouling at low speeds.  But it will look lean.

[KB02]

As I have the day off I will be making the rounds and running errands and will most likely pick up some new D9ea plugs and try those - or I might just clean up the 8's I have and go with that.

 - BUT -

running the 7's has given me an idea. It appears as though that I am running WAY lean. This would account for the idle trying to hang high. a far greater amount of air is entering the combustion chamber vs. the amount of gas that is going in. Essentially this mimics the effect of opening up the throttle at lower speeds as the jets are relatively unaffected and it is just the slow jet that is being utilized. The engine thinks that I have the right sized jet but the slide is further open thus increasing engine speed (greater Air to fuel mixture). When I get it to calm down, the engine is realizing that there is only so much fuel.

Do this make sense, or am I way off base?

I'm going to open up the mixture screws one full turn each and test with new or cleaned plugs. I should have time to work on it today. Hopefully the rain that is forecast will hold off.

[bollingball]

If the slides are clean what about the hole they are sliding in? Also if they work so good with cables disconnected but hang up when reconnected it seemes like it has to be cable issue.