Topic: Won't cold start w/o extreme idle adjustment.

[D-Ral]

I posted this in another thread, but I am starting a new one as per advice given.

Is this normal?

Currently, I have to jack my idle and full choke to start. It's super annoying because I have a tank with the petcock on the left, so I have to lift the seat and tank to get to it. I'll start the bike, it'll blubber along at 1400, and then after about 15 seconds I will have to start opening the choke or she will die. As I open the choke, the revs will sky rocket and I'll have to quickly lower the idle before I wake all of my neighbours. It doesn't seem to work in a linear fashion, however. I'll turn it down a bit, and it will idle a little lower, and then turn it down a little bit more and it will dip down from let's say... 3000 to 1200. It's odd. Anyway, once I get the choke off, it will idle steadily at 1400-1500. I'll blip the throttle a bit, and if its not warm enough, the idle will hang around 2500-3000. Just a little turn of the idle screw will bring it back down. When blipping the throttle results in a normal rise and then fall of rpms, I know I'm good to go. After about 20 minutes, it wants to idle around 2100 at red lights, and because my petcock is in the way I have to pull over to lower the idle again. I'll drop it down to 1200 - 1300.

Is this normal? Once the bike is warm, it rides like a dream. Throttle is super responsive. Haven't checked the plugs yet.

750K4, 105 mains, 40 idle, needle in the middle, 1 turn air mix, stock airbox, and 4-1 kerker.

If I shut the bike off and start it 10 - 15 minutes later, it will fire right up, no problem. But if it sits long enough to get cold, I'll need to play with the idle screw again. I don't turn the throttle when/right after I hit the starter because I'm afraid to flood the engine. Again. Ha ha.

[iron_worker]

Kind of sounds like how my bike used to run before I cleaned the carbs. The culprit in particular is the idle jets, I believe. I had 2 fully blocked and 1 partially blocked ... a real nightmare to get to idle when cold.

A hanging idle is usually due to a lean condition so check that you don't have any vacuum leaks. Your Kerker 4-1 is probably making you run a bit lean (since I notice you have stock jetting ... I also have a K4) as well but I would think that it would have a more predominant effect closer to WOT.

IW

[LesterPiglet]

Idle speed should be set when the engine is fully warmed up. Set it there and you should never have to touch it again.
I control my cold idle with the throttle.

[iron_worker]

Agreed with Lester. If the bike is in proper tune then even starting from dead cold on a chilly day should only require 30s - 1 min or so of hand throttle application before the engine warms up enough to idle on it's own (without adjusting the idle).

IW

[D-Ral]

Kind of sounds like how my bike used to run before I cleaned the carbs. The culprit in particular is the idle jets, I believe. I had 2 fully blocked and 1 partially blocked ... a real nightmare to get to idle when cold.

A hanging idle is usually due to a lean condition so check that you don't have any vacuum leaks. Your Kerker 4-1 is probably making you run a bit lean (since I notice you have stock jetting ... I also have a K4) as well but I would think that it would have a more predominant effect closer to WOT.

IW

I cleaned the carbs immediately after getting the  bike instead of riding it to check the tuning. Now I know that was a little foolish, I was just horny to clean it all up. However, I did have the engine running.

Anyway, the carbs were gross, so I cleared em all up with a wire brush, solvent, guitar strings in the passages, and compressed air. The PO had 110 mains installed and the needle height was one setting from the middle, I can't remember whether it was up or down. The kits I ordered only came with 105s, which I believe were stock for at least part of the k4 production run. But I don't have a stock exhaust, so it doesn't matter anyway. I installed the 105 mains and moved the needle clips to the middle position. I just ordered new band clamps for my carb and airbox boots, but I haven't found any leaks by spraying WD-40.

As to running lean, I am getting a little bluing on my header pipes. It only occurs on the bend right after they exit the head. My pipes aren't chrome, and I cleaned them up with a lot of spray lune and green scrubbies. A friend of mine told me that a little blue is normal, but I don't know.

The OTHER issue I have get to reveal could also be affecting my startup. On each choke slide there is a spring loaded brass flap. On one of my carbs, the spring is weak and won't hold the flap closed very well. But my idle only races when I start to open the choke, so... I dunno.

[D-Ral]

Idle speed should be set when the engine is fully warmed up. Set it there and you should never have to touch it again.
I control my cold idle with the throttle.

Agreed with Lester. If the bike is in proper tune then even starting from dead cold on a chilly day should only require 30s - 1 min or so of hand throttle application before the engine warms up enough to idle on it's own (without adjusting the idle).

IW

Ok, so let me get this straight: close choke, hit the starter, when the engine turns, turn the throttle to idle engine, release choke as needed, and then everything is gold? You'll have to forgive me, as I don't have anyone around me with an old bike and I am usually a watch and learn sort of person. I flooded the engine a little while ago so I stopped blipping the throttle until I was sure it would hold idle without it.

[TwoTired]

imo, it is kinda normal.
This machine employs a choke that only changes the mixture ratios via inlet butterflies and not the slide openings.  Cold engines have poor atomization properties, so the engine needs a bit of throttle as well as enrichment (choke), during cold start operation.  As the engine warms and atomization improves, the engine gets more efficient, and prior settings result in increased RPM.  Variable choke application during warm up is quite normal.

I believe the K4 had a throttle friction adjust knob under the twist grip, which can hold the throttle a bit open to keep the engine running with partial choke.  Using this would circumvent the need to adjust the idle knob during cold operation and choke application.

To address the idle hang, I recommend searching for inlet runner vacuum leaks, and/or do an accurate vacuum sync of the carbs.

BTW, the stock carbs have no accelerator pump.  The twist grip cannot add fuel to start by twisting action.  Only the choke can do that when the engine's pistons are moving.  You won't flood the engine by twist grip action alone.

You know, it is fine to operate/drive the bike as it warms up.  Your hand is on the throttle while driving, so you can hold whatever RPM is necessary to keep the engine running, and you can easily reach down to incrementally nudge the choke off as the engine warms.  At the end of the warm up process, the idle stop hold the engine at the warm engine idle RPM setting.

Unless you are ridding in very hot weather or in conditions that allow the the engine to retain high heat, using hotter heat range spark plugs (D7), will improve cold engine operation and responsiveness.

[LesterPiglet]

I usually put my choke on and hit the starter and twist the throttle to start. Once the engine is running, I can take the choke off completely and keep the engine running with the throttle. (Your bike may need longer choke time.) This is a series of light blips of throttle. I ride away almost immediately. And if it still hasn't warmed up enough to idle before I need to put my feet down then I keep it alive with the throttle.
It doesn't take long to get full operational temperature with this method.

[D-Ral]

Usually I do drive away with it not completely warm, but choke is open and I adjust the throttle screw in a parking lot after about ten mins of riding.

I will definitely try using the throttle grip instead of the idle screw later when I ride. I suppose holding the throttle open and turning the screw are basically the same thing. One wouldn't cause flooding if the other didn't. Hopefully my band clamps I have on order will solve my hidden vacuum leak. I have synced my carbs already and had no issues. Would this mean I don't have a leak?

Thanks for your help guys, I really do appreciate it.

So, one more question concerning mixture. Would my slightly blue-on-the-bend header issues indicate a lean mixture or is this normal? I'm not getting any bogging or smoking. Rpms rise normally when engine breaking. I ordered some 110 mains just in case, but I figure a needle clip adjustment would be more necessary as I am usually mid throttle. I know that running lean is more destructive than rich, so I'm a little paranoid about destroying the only vintage vehicle I can afford!

[D-Ral]

I usually put my choke on and hit the starter and twist the throttle to start. Once the engine is running, I can take the choke off completely and keep the engine running with the throttle. (Your bike may need longer choke time.) This is a series of light blips of throttle. I ride away almost immediately. And if it still hasn't warmed up enough to idle before I need to put my feet down then I keep it alive with the throttle.
It doesn't take long to get full operational temperature with this method.

Ha ha. Usually I am pushing my throttle forward to get my idle down at red lights so that the driver beside me doesn't think I want to race!

[LesterPiglet]

Some blueing on aftermarket pipes is normal as they are usually single skinned or not great chrome.

[TwoTired]

So, one more question concerning mixture. Would my slightly blue-on-the-bend header issues indicate a lean mixture or is this normal? I'm not getting any bogging or smoking. Rpms rise normally when engine breaking. I ordered some 110 mains just in case, but I figure a needle clip adjustment would be more necessary as I am usually mid throttle. I know that running lean is more destructive than rich, so I'm a little paranoid about destroying the only vintage vehicle I can afford!

Bluing is not normal per se.  However it can be an indication of lean mixture at certain throttle positions.  A better way is read the spark plug deposits.
Also, be aware that there is a pilot circuit to feed fuel, as well as two limiter devices for fuel in the main path, that being; the main jet for 3/4 and above throttle position, and the mid-range slide needle (taper, thickness, and position within the slide needle jet).

There is opportunity for one throttle position to be lean while others are not, and vice versa.  That is the beauty of the stock settings along with the stock engine components, induction and exhaust.  Honda made those settings for you.  With mods, you have to attempt to replicate what Honda engineers did in finding those settings.
It's not all about style and looks.

[D-Ral]

So, one more question concerning mixture. Would my slightly blue-on-the-bend header issues indicate a lean mixture or is this normal? I'm not getting any bogging or smoking. Rpms rise normally when engine breaking. I ordered some 110 mains just in case, but I figure a needle clip adjustment would be more necessary as I am usually mid throttle. I know that running lean is more destructive than rich, so I'm a little paranoid about destroying the only vintage vehicle I can afford!

Bluing is not normal per se.  However it can be an indication of lean mixture at certain throttle positions.  A better way is read the spark plug deposits.
Also, be aware that there is a pilot circuit to feed fuel, as well as two limiter devices for fuel in the main path, that being; the main jet for 3/4 and above throttle position, and the mid-range slide needle (taper, thickness, and position within the slide needle jet).

There is opportunity for one throttle position to be lean while others are not, and vice versa.  That is the beauty of the stock settings along with the stock engine components, induction and exhaust.  Honda made those settings for you.  With mods, you have to attempt to replicate what Honda engineers did in finding those settings.
It's not all about style and looks.

Already raised my right hand and promised to all authorities of sohc to let my stock airbox be. I'd have the stock pipes if they didn't cost an arm and a leg. I don't have oem needles and jets, but I was thinking I had better get them, just to eliminate possible problems. They are clean and new, but the needles may be of different shape.

[D-Ral]

To properly read plugs for idle, I suppose I should start with clean plugs and only let it idle for a bit before I pull em.

[TwoTired]

To properly read plugs for idle, I suppose I should start with clean plugs and only let it idle for a bit before I pull em.

Since the K4 has no accelerator pump, the idle mixture is purposely set rich, to offset the inrush of air and loss of vacuum pull on the metering jets when the throttle is twisted.  This, plus the fact that heat availability is limited during idle operation, means that the plugs will have a very difficult task of self cleaning during idle.

Carb tuning usually starts with the main jet selection.  Full power, wide open throttle makes the proper heat to show mixture deposit color on the plugs, assuming the plugs have ONLY experienced that operating regime and no others.  Pretty much need a test track or dyno for this.

After the main is selected, mid throttle tests under load optimize the deposits to show where slide needles should be positioned or the taper changed.

Lastly, the pilot circuit is adjusted, so that under load and in any gear, the throttle can be twisted up to one half of remaining range (mark the throttle) and still produce smooth power advancement, (if not neck snapping).  More than half twist can often be achieved.   However, the plugs will tend to foul after prolonged idling.

[D-Ral]

And that's why my plugs fouled. Too much idling.

Anyway, when I left work earlier, I started her up and only used the throttle grip to warm up.  Works fine. I get it now. Ha ha. Thanks for the input today, guys.

[01Thomas]

I don't think your K4 qualifies, but my K1 has a throttle tension adjustment screw, between where the throttle cables go into the throttle housing. I use one hand on the throttle and with the other I just screw up the tension screw a bit to keep the idling to about 1200 rpm. Then I put on helmet and gloves, release the tension screw and ride off, reasonably gently at first. The bike definitely benefits from having a smooth idle at 1200 compared to trying to sustain combustion at about 850 or some such rpm. And the plugs burn cleaner too.

If your K4 doesn't have that throttle tension screw, it can be retrofitted quite easily, which I've done to my Seeley. Honda just blanked the boss between the throttle cables where the screw used to be. Drill and tap to M5 and find the screw and springs etc at your local junkyard. Or get a machinist friend to make you up such a screw.

[D-Ral]

I don't think your K4 qualifies, but my K1 has a throttle tension adjustment screw, between where the throttle cables go into the throttle housing. I use one hand on the throttle and with the other I just screw up the tension screw a bit to keep the idling to about 1200 rpm. Then I put on helmet and gloves, release the tension screw and ride off, reasonably gently at first. The bike definitely benefits from having a smooth idle at 1200 compared to trying to sustain combustion at about 850 or some such rpm. And the plugs burn cleaner too.

If your K4 doesn't have that throttle tension screw, it can be retrofitted quite easily, which I've done to my Seeley. Honda just blanked the boss between the throttle cables where the screw used to be. Drill and tap to M5 and find the screw and springs etc at your local junkyard. Or get a machinist friend to make you up such a screw.

Yes, I have heard mention of this tension screw. Not really sure where it is. Ha ha. I have an aftermarket switch that looks completely oem so I'm not sure if it will have one. I do have some broken old switches however, so I could rob them for parts. I will look at a parts fiche later and figure out what you mean.

[LesterPiglet]

(My)Starting Procedure for Honda CB550
Normally I would have ridden away before the end of the video.

[HondanutRider]

There are two types of choke/throttle arrangements that Honda bikes employed on various models.  Most of the early models had a choke that was not connected to the throttle, and its application simply restricted the air intake.  The second/later type of design also advanced the throttle slightly as more of the choke was applied.

In the first design, with a cold engine the choke is applied and the throttle opened about 1/8 to 1/4 turn and HELD (not twisted or pumped) while the starter is engaged or the kick starter applied.  Holding the throttle steady at this setting, the choke can slowly be disengaged in stages while the engine warms up.  When the choke is disengaged a bit, the engine speed will likely increase and some of the initial throttle setting can be relaxed.  Also as the engine warms up, some gentle blipping of the throttle can be performed to see if the motor is ready for less choke.  If really cold, after starting the throttle can be raised while running to promote a higher idle and faster warm-up.  Eventually the motor should warm up sufficiently to have the choke and throttle completely off, a smooth idle speed present, and an even response to gentle blipping of the throttle up to 1/2 open.  Experienced riders can speed the warm-up process by riding off with the choke still on, carefully riding the throttle while minding the choke, and thereby loading-up the motor.

The second/later design of choke advances the throttle with its application.  How much advancement and when it is fully released are usually parameters that can be tuned or adjusted at set-up.  When starting with this design of choke, the throttle does NOT need to be touched (or held open) when starting.  If it does, then it is either very cold or more likely the throttle advancement mechanism needs adjusting.  With a cold motor, once started and running with full choke, the choke can be relaxed in stages and the engine speed should decrease.  A sign that the choke is ready to be released some is when the engine speed climbs to a higher level (e.g. 4,000rpm).  Again, the warm-up period can be reduced if gentle riding is performed while some of the choke is still on.

Either design works properly only when everything is correctly adjusted - e.g. idle speed, mixture, timing.  Using the choke for starting-up is usually needed for a cold engine, but sometimes also briefly needed when still warm.  Get to know your motor, how it responds, and what it needs to start.

[lucky]

D-ral, what kind of bike?

What kind of intake system?

EDIT:
750K4, 105 mains, 40 idle, needle in the middle, 1 turn air mix, stock airbox, and 4-1 kerker.

With a stock airbox and stock filter and Kerker exhaust, all you would need is a mixture screw adjustment about 1/4 richer.

[D-Ral]

Firstly, thanks for posting that video. Would have really helped to have found it beforehand. This is my first motorcycle, my first experience riding a 40 year old motorcycle, and my first experience messing with ANY engine, so I eat up all of the visual learning I can get.

Secondly, my switch does have a threaded hole between the two throttle cables. I remember seeing a screw and spring in the stock switch that I have lying around and not knowing what it did. Now I know. I will rob it for my own.

Thirdly, thanks for the info on chokes. Again, I'm a sponge. Gimme the info and I'll soak it up. So why does it take an experienced rider to take off with the choke on? This morning I started my bike and drove to work. I still have no throttle lock screw, so I held the throttle open with my hand and adjusted my choke with my other. I feel like I want to open the choke further as the engine starts to gurgle and spit a bit. The rpms rise, I adjust my throttle hand, and repeat until choke is off. This took a minute or two, and then I rode off, engine still cold and unable to idle steadily without a little throttle. Now, the engine didn't perform normally at all. It lagged when accelerating. Plus, I stalled once when maneuvering in first gear. Other then that, I was fine, and my ride to work is only 10 or 12 minutes.

I feel like I will take about 20 minutes before the engine will idle at 1200-1300 steadily. This is where I have set my idle screw when at operating temp.

I guess my question concerns the life and care of my engine. When I ride away with a cold engine, should I keep rpms low or high? I know this is a high revving engine, but it seems counter intuitive to ride around at 5000rpm instead of shifting when the engine is cold.

[D-Ral]

D-ral, what kind of bike?

What kind of intake system?

EDIT:
750K4, 105 mains, 40 idle, needle in the middle, 1 turn air mix, stock airbox, and 4-1 kerker.

With a stock airbox and stock filter and Kerker exhaust, all you would need is a mixture screw adjustment about 1/4 richer.

This is because the exhaust has less back pressure, thus causing the intake to suck more air and therefore increasing the carbs' requirement for fuel, correct? Will turning the screws in make a more rich mixture?

[TwoTired]

I guess my question concerns the life and care of my engine. When I ride away with a cold engine, should I keep rpms low or high? I know this is a high revving engine, but it seems counter intuitive to ride around at 5000rpm instead of shifting when the engine is cold.

You do want to limit engine bearing loads while the engine/oil is cold.  So, no drag racing during warm up, or pulling trailers, etc.  It's a horsepower thing.  You only need about 5HP or less to sustain the bike's forward motion (this increases with air resistance).  It can take all the HP the engine can make to attain speed rapidly, climb steep grades, or to drive at 100MPH pushing all that air aside.   So, the goal is to not make the engine work hard during the warm up period, and it will be fine.

About RPM:  The cylinder walls where the piston's rub are lubed with oil squirted on them from the crankshaft. This is effected by both oil viscosity and oil pump pressure which increases, to a point, with RPM.  In all my years of riding the 550, I've kept the engine between 1500-5000 during riding warm up. (Note the 550 has a red line ~1000 RPM higher than the 750.)  I've also decided that 10W40 oil will squirt the cylinder walls better during the warm up period than 20W50.

So, perhaps with thicker viscosity oil, you may want to consider less internal engine loads during warm up.  I would want that thicker oil in my engine during long high power rides though the hot air, though.

[D-Ral]

I guess my question concerns the life and care of my engine. When I ride away with a cold engine, should I keep rpms low or high? I know this is a high revving engine, but it seems counter intuitive to ride around at 5000rpm instead of shifting when the engine is cold.

You do want to limit engine bearing loads while the engine/oil is cold.  So, no drag racing during warm up, or pulling trailers, etc.  It's a horsepower thing.  You only need about 5HP or less to sustain the bike's forward motion (this increases with air resistance).  It can take all the HP the engine can make to attain speed rapidly, climb steep grades, or to drive at 100MPH pushing all that air aside.   So, the goal is to not make the engine work hard during the warm up period, and it will be fine.

About RPM:  The cylinder walls where the piston's rub are lubed with oil squirted on them from the crankshaft. This is effected by both oil viscosity and oil pump pressure which increases, to a point, with RPM.  In all my years of riding the 550, I've kept the engine between 1500-5000 during riding warm up. (Note the 550 has a red line ~1000 RPM higher than the 750.)  I've also decided that 10W40 oil will squirt the cylinder walls better during the warm up period than 20W50.

So, perhaps with thicker viscosity oil, you may want to consider less internal engine loads during warm up.  I would want that thicker oil in my engine during long high power rides though the hot air, though.

Perfect, I've been using 10w40, as there is not much hot air up here. Thanks again for the information.