Topic: Solved: Warming up the 750K, throttle stop screw tending

[Kaze]

I start my CB750K cold with a little choke and tend the throttle for a second until I get my throttle stop screw where it needs to be in order to hold it at about 2 grand. I idle at 2 grand until it's warm. When the engine warms up and the idle climbs (as it does) I back off the throttle stop screw and idle more like 1000 to 1100rpm.

Is babysitting the throttle stop screw just a fact of SOHC4 CB750K riding? I think so. But then, I don't sit there holding the throttle until it's warm. As soon as the bike is started and my gear is on, we go.

Guys who rode the bike when it was still new in 197x, same deal or not?

EDIT: This topic was apparently covered in "Warm up and idle speed what's normal?"

[Don R]

 Yup, there is no fast idle system on the early 750 choke, my 78 GL1000 has it, which seems odd after being used to 750's forever.

[PeWe]

My Mikuni carbs on the K6 has fast idle with choke. 2500 rpm and more.
A little bit irritating. Race carbs.

My K2 CB 750 carbs better in that manner.
Idle adjusted when really warm, 1200 rpm wich make rides easier.
Choke on when starting, off after 10sec. It can idle now.

This is the 064A carbs. Shipped with CB750 F 1975 according to Shop manual.

The stock K6 086A need a little choke on for a little longer. Different needle, leaner than 064A.

The older Mikuni VM29 have variable choke with increased idle.

[carnivorous chicken]

There was a conversation that included this recently, elsewhere on the forum. Either the screw or the grip are the two ways to feather the idle until it gets warm. I prefer the grip so I don't have to reach down and tweak the screw, just seems easier to me, and then I know with the screw in the same place it'll find its idle. But six of one, half a dozen of the other.

[newday777]

I start my CB750K cold with a little choke and tend the throttle for a second until I get my throttle stop screw where it needs to be in order to hold it at about 2 grand. I idle at 2 grand until it's warm. When the engine warms up and the idle climbs (as it does) I back off the throttle stop screw and idle more like 1000 to 1100rpm.

Is babysitting the throttle stop screw just a fact of SOHC4 CB750K riding? I think so. But then, I don't sit there holding the throttle until it's warm. As soon as the bike is started and my gear is on, we go.

Guys who rode the bike when it was still new in 197x, same deal or not?

"throttle stop screw"
Is this the screw under the grip(pre K5 1975) or the idle adjustment on the carbs?
You chose to leave off the actual year of which you want to know about. (197x) you have left too much out of the equation.

[BenelliSEI]

I keep the idle screw/stop on the carbs clean and well coated threads (anti-seize). It’s so easy to reach in and adjust it that I usually turn it up a bit (once the choke is off) and then drop it down before setting off. Part of owning a SOHC Honda.

[jonda500]

Don't know why Honda discontinued the screw in the switchblock under the grip that the older models have - I use that screw to hold the throttle open a little for a few minutes while I put on my helmet and gloves, after which it will just barely idle without stalling at around 1000rpm and I release the screw before taking off. Maybe Honda was worried about folks using it as a cruise control?
John

[Tracksnblades1]

My Mikuni carbs on the K6 has fast idle with choke. 2500 rpm and more.
A little bit irritating. Race carbs.

My K2 CB 750 carbs better in that manner.
Idle adjusted when really warm, 1200 rpm wich make rides easier.
Choke on when starting, off after 10sec. It can idle now.

This is the 064A carbs. Shipped with CB750 F 1975 according to Shop manual.

The stock K6 086A need a little choke on for a little longer. Different needle, leaner than 064A.

The older Mikuni VM29 have variable choke with increased idle.

Do you know what pressure the oil filter bypasses cold oil..

Man, 2500 seems high on a cold morning with 20w-50.. that would peg a gauge on an old unmolested  F1….

[Kaze]

Vocabulary...
I say "Throttle Stop Screw" for the large, ridged screw on the end of the carburetor that controls how low your idle can go. Left side until K4, right side from K5-8. I used to call it the "Idle screw" but people kept thinking I was talking about the idle mixture / air screws. Is there an official term for this screw? "Gear preparation time screw"

"Feathering" the throttle is new to me. I get it by context of course. Fun term.

DonR and Pewe: Is your fast idle system electronic?

Carnivorous Chicken: I saw that thread but couldn't track it down. That's the one where Benelli said "Part of owning a SOHC Honda."

NewDay: In this case, I didn't think the year mattered, since all years from K2 to K7 were the same deal for me. I set the throttle stop screw on the end of the carbs and put my gear on, turned it down when the bike was warm.

K2... my switches weren't stock so I didn't have that. I also didn't have the winker-beeper kill switch on the bottom of the left grip.

K4... Now that you mention it? I never used that screw by the handlegrip on my K4. I remember seeing it and thinking something like, "That's a goofy little knob" and went on my merry way. I was too young and too busy to care about things like that. Good times.

[Don R]

 The fast idle on a gl1000 is linkage operated.
  If a guy was inclined to use a set of 77-78 PD carbs, he could adapt a fast idle solenoid from a 750 Hondamatic. Don't ask me how. I've never done it, I've only heard of the F carbs being put on an A and retaining the A's solenoid. 

[Tracksnblades1]

The fast idle on a gl1000 is linkage operated.
  If a guy was inclined to use a set of 77-78 PD carbs, he could adapt a fast idle solenoid from a 750 Hondamatic. Don't ask me how. I've never done it, I've only heard of the F carbs being put on an A and retaining the A's solenoid.

I thought the Auto’s solenoid ran a vacuum slave to actually do the work..?

In the autos case to increase the idle when it was in gear idling against the torque converter. Then once back in neutral dropping the idle speed back to the same rpm as in gear. If properly adjusted it would idle near the same rpm in gear against the converter or in neutral..?

[Kaze]

The cool thing is, if I ever get one of the earlier year CB750s, I will know what the "funny little screw" is.

Don: Your 69-70 750s have the idle / throttle stop screw on the carbs too, correct? (I would assume, but better not...)
If they weren't so expensive, I'd like to get a 70 just to explore it. But, too late.

Hondamatics...alien tech.

[flybackwards]

This is the previous thread that I started:

http://forums.sohc4.net/index.php/topic,193574.0.html

[Don R]

The cool thing is, if I ever get one of the earlier year CB750s, I will know what the "funny little screw" is.

Don: Your 69-70 750s have the idle / throttle stop screw on the carbs too, correct? (I would assume, but better not...)

 Nope, no screw on a set of 4 cable carbs, at times I adjust the single throttle housing cable near the right control. The K1 Hot Rod's 29 Mikunis have an idle screw but it's way up in there and difficult to reach. K2 has the screw, as does my brothers K4.

 

[Kaze]

(EDITED)
Don: Wow. This is exactly why I almost always might say "K2-K8" when talking about this bike, (as opposed to 69-K8) because those first ones are like unicorns compared to horses. "But... it's a horse?" "Well yes, but it has a horn and grants wishes." "Wishes?!" "Okay I lied about the wishes."

Flybackwards: There it is! Thanks. That's the "scary" thread that talks about bent spark advancer shafts... That's probably why I couldn't find the thread. I was hiding under my bed after reading it.

[HondaMan]

American Honda was threatened with a lawsuit (by the US DOT, again) in 1973 about the "cruise control screw" on the right (throttle) grip.
As it turned out (after Honda removed the screw) it was a former HD employee who had obtained a job within the DOT who sent the letter to Honda on the DOT letterhead: in other words, it wasn't "official".

Rumor had it that he 'left his position' (fired?) at DOT after this story got out in 1976 (it may be been 1977...). I only remember it because of how many of the 750 riders who had 'traded up' to a newer one were trying to find ways to add it back because we ALL used it for 55 MPH riding: this was when the gigantic Cruise Control mechanisms appeared in the marketplace to fill in the void. We've seen a few of them on 'barn find' bikes here in the forums.

[PeWe]

My Mikuni carbs on the K6 has fast idle with choke. 2500 rpm and more.
A little bit irritating. Race carbs.

My K2 CB 750 carbs better in that manner.
Idle adjusted when really warm, 1200 rpm wich make rides easier.
Choke on when starting, off after 10sec. It can idle now.

This is the 064A carbs. Shipped with CB750 F 1975 according to Shop manual.

The stock K6 086A need a little choke on for a little longer. Different needle, leaner than 064A.

The older Mikuni VM29 have variable choke with increased idle.

Do you know what pressure the oil filter bypasses cold oil..

Man, 2500 seems high on a cold morning with 20w-50.. that would peg a gauge on an old unmolested  F1….

That is something to have in mind. Oil filter spring and when it will let filter move and bypass oil. Oil pressure gauge show +60PSI at idle.
I think I have seen closer to  80PSI.

My bike is parked in the warmest part of the house, the garage.
Never lower than +21C.

I let it idle for 30 sec before take off, use clutch to glide away. The mechanical choke off a few minutes later.
Engine need to be fully warmed up before initiated use of throttle. I feel when clutch lever get more play when warm.

[Don R]

 I was looking at a bypass today, I have an aftermarket filter housing and matching big head bolt that currently has no bypass in it. I found an old stock bolt that's mostly rounded off to swap the bypass valve from. It was surprising to me how easy the valve moved when pushed with a small screwdriver.
 Caution: oil related car engine story,
A couple years ago our big block chevy lost a rocker arm needle bearing, the tiny needles went into the oil pump and some material made it into the rear two main bearings, yet when I cut the oil filter open it was clean inside. I could only conclude that the stock type K&N oil filter media, high flow billet pump and heavy oil was keeping the bypass open a lot.

[HondaMan]

I was looking at a bypass today, I have an aftermarket filter housing and matching big head bolt that currently has no bypass in it. I found an old stock bolt that's mostly rounded off to swap the bypass valve from. It was surprising to me how easy the valve moved when pushed with a small screwdriver.
 Caution: oil related car engine story,
A couple years ago our big block chevy lost a rocker arm needle bearing, the tiny needles went into the oil pump and some material made it into the rear two main bearings, yet when I cut the oil filter open it was clean inside. I could only conclude that the stock type K&N oil filter media, high flow billet pump and heavy oil was keeping the bypass open a lot.

Interesting, indeed!
Honda says the oil filter bolt is supposed to bypass at 21 PSI. But...aftermarket oil filter bolts fit several other bikes (like Kawi KZ1000) that have much, much lower pressure bypass numbers (I think the KZ1000 MAIN oil PSI is only 30?), so you might have to take the Honda spring out of the old bolt and use that instead?

[Don R]

I was looking at a bypass today, I have an aftermarket filter housing and matching big head bolt that currently has no bypass in it. I found an old stock bolt that's mostly rounded off to swap the bypass valve from. It was surprising to me how easy the valve moved when pushed with a small screwdriver.
 
Interesting, indeed!
Honda says the oil filter bolt is supposed to bypass at 21 PSI. But...aftermarket oil filter bolts fit several other bikes (like Kawi KZ1000) that have much, much lower pressure bypass numbers (I think the KZ1000 MAIN oil PSI is only 30?), so you might have to take the Honda spring out of the old bolt and use that instead?

 Actually, the aftermarket bolt currently has nothing inside except the roll pin that holds the bypass valve in, so I was going to use all of the Honda bolts internal parts. I'm a little wary of it but it's all chrome and I have a project K2 that I was planning to bolt all of the chrome to that I removed from other bikes.

[newday777]

Don: Wow. This is exactly why I almost always say "K2-K8" when talking about this bike, because those first ones are like unicorns compared to horses. "But... it's a horse?" "Well yes, but it has a horn and grants wishes." "Wishes?!" "Okay I lied about the wishes."

Flybackwards: There it is! Thanks. That's the "scary" thread that talks about bent spark advancer shafts... That's probably why I couldn't find the thread. I was hiding under my bed after reading it.

Be careful on bunching years together like your 'K2-K8' together statement as there are so many changes in those years, on many aspects of the SOHC 750s, especially concerning the carbs and choke concerns of this thread of yours, roundtop carbs of K2-K6 changed out on K7 to PD carbs(totally different animal!).

The throttle stop screw on the hand control was only on K2-K4.

I so wanted the throttle stop screw on my new K5 and K6  back in 75 and 76 that while I was parts manager, I spent some time trying to figure out how to change the controls to the K4, but I hadn't learned enough about the wiring differences between the years(I was only 20 years old at that time....), so I just opted to put on one of the 'big aftermarket throttle lock' cruise controls that I had ordered in to sell over the counter. I wish I knew then what I know now.......

[rotortiller]

After 1973 the throttle friction was removed from the Kawasaki H2 Triple however there were no stories about a Fergy guy being at the heart of it. I liked that throttle feature on long trips, especially so for a CB750 with its stiff return spring.

[Tracksnblades1]

I was looking at a bypass today, I have an aftermarket filter housing and matching big head bolt that currently has no bypass in it. I found an old stock bolt that's mostly rounded off to swap the bypass valve from. It was surprising to me how easy the valve moved when pushed with a small screwdriver.
 Caution: oil related car engine story,
A couple years ago our big block chevy lost a rocker arm needle bearing, the tiny needles went into the oil pump and some material made it into the rear two main bearings, yet when I cut the oil filter open it was clean inside. I could only conclude that the stock type K&N oil filter media, high flow billet pump and heavy oil was keeping the bypass open a lot.

Stock sbc and bbc start by-passing  @ 17 psig and are fully open @18psig..
Both their bypasses would bypass with a 17 psig or greater differential from the outside of the filter to the inside…so if you had 60psig of oil pressure but your main bearing oil galley had 40psig because of a partially plugged oil filter or cold oil, your bypass was bypassing a percentage of oil around the filter media going straight to the oil galleys…

Most racers would pipe plug the factory bypass and would run two quart ACDelco tandem truck 427 tall deck oil filters.
A high volume big block oil pump mounted on a tight clearance SBC would still kick the big oil filter’s oring out on a cold morning with a premature throttle jazz even using 10w30 oil..

But when following the 10psig of oil pressure per 1000 rpm gospel back then, you didn’t worry about idle and cold oil..
You just needed 70psig for 7000rpm and 80psig for 8000rpm..at the rods and mains..

[Kaze]

Be careful on bunching years together like your 'K2-K8' together statement as there are so many changes in those years.

Figures somebody would bust me on that wording...

My comment was more about pointing out that I rarely add 69-71 to my discussions. I've edited the text.

[PeWe]

Interesting discussion.
So the oil filter bolt will bypass oil during normal use?
Normal cruising when warm, pressure around 40PSI.

I thought that bolt bypass valve should let oil outside filter when filter was so clogged that oil will not pass, or at least not enough to lubricate.

Oil with particles better than no oil.

[rotortiller]

PeWe, The bypass situation is possible when the cold oil is too thick to  pass easily through the filter or for when the filter gets clogged.

[Tracksnblades1]

Interesting discussion.
So the oil filter bolt will bypass oil during normal use?
Normal cruising when warm, pressure around 40PSI.

I thought that bolt bypass valve should let oil outside filter when filter was so clogged that oil will not pass, or at least not enough to lubricate.

Oil with particles better than no oil.

Honda designed it as a full flow filtered system. Normal use with a clean filter at operating temperature would filter 100% of the oil.
 
There has to be a pressure differential within the filter itself. With a 21# pressure differential, as Hondaman wrote, the by pass would open allowing unfiltered oil to be added to the filtered oil to prevent catastrophic failure. Especially for those that never change oil or filters.

I’ve attached a service manual picture. It’s similar to the automotive bypass, just a different means..

Also Don R,
The picture show the oil pressure differential within the oil filter housing will increase the effectiveness of the oil filter spring you were posting about not having enough room for with the wix filter on the GL.

[Don R]

 So, if your oil pressure is 60 psi then the filter would bypass if pressure after the filter dropped to around 39 psi. Makes sense.
 

[Tracksnblades1]

So, if your oil pressure is 60 psi then the filter would bypass if pressure after the filter dropped to around 39 psi. Makes sense.

Yes.  And I If you wrote that with 60# of pressure on the outside of the filter element, the bypass would open when the pressure on the inside dropped to 39#, it would mean the same..

That’s the question that’s swimming in my mind because the oil pump regulator it set to that same 60# pressure at operating temp. Actually the main regulator is set at 56.9 psig @ 4000 rpm @ 176*F operating temperature according to the manual. But, Mine reads 60# also when hot..

But where we screw the oil pressure gauge into is the oil galley (filtered) oil…

[rotortiller]

Here are typical psid (differential pressure) bypass valve values for various filters used in bikes and cars.  About 4/5th the way down and it is interesting data for what it's worth.

https://motorcycleinfo.calsci.com/FilterXRef.html#BMW 

My feeling on the different bypass settings is that finer media may 'traffic jam' at a different point or more or less media surface area is present. Most engines run in a similar or general PSI range for oil pressure and that is why most bikers choose a superior automotive oil filter over the overpriced or underpriced OEM. Just because a filter has a slightly different bypass value does not make it unacceptable.

There has been in the past  spin on bike filters without a bypass employed in engines with no engine bypass feature and unlike what the sohc4 has. Because the sohc oil filter is a fixed paper media design the bypass oil filter bolt spring pressure was set with that specific media in mind by size and construction. With spin-on bike filters I choose the longest one that will fit, some peoples' SOHCs actually employ a spin on with an integrated bypass oil filter using a threaded adapter. I have never experienced a problem with (my fav) Mobil-1 substitute spin-on oil filters or alternate SOHC clone paper filters on several bikes I have and many more I have owned.

Sometimes a caution can be found in the power-sport manual about reving the engine right after cold start up causing critical damage. These full flow non-bypass filters were also used in tractors lol.  Kawasaki stopped selling a no-bypass spin-on OEM motorcycle oil filter about 8 years ago thank goodness.

Even if your filter bypasses on cold start up or at other normal operating transient situations it is simply bypassing previously cleaned oil so really it is no big deal. The thing to remember about a bypass situation is that it does not dump the crap accumulated in the filter media into the oil flow, that's why its called bypass-oil flow route around the filter media traffic jam.

[PeWe]

Thanks guys! That explained it all!

Not rev a cold engine has got another reason for me. Never had any thoughts about oil filter, only the lubrication and clearances.

Oil with particles in the oil pan that filters thru the pumps strainer. Small stuff from clutch fibers etc.

[dave500]

so back to the cold idle "throttle hold"thumb screw,i use mine on my 500 when i fire it up cold,gear up as it fast idles,then wind it off,ride away but not hard power for a few minutes,no way any old carburetted car or bike will idle straight up cold with no sort of fast cold idle arrangement or manual throttle actuation!i think anyone born since fuel injection and never used carbs much wouldnt have that feel you need for such an occurrence?in the old days it was part of learning to drive?

[Kelly E]

Back in 06' I was in school for automotive technology. I was the old guy there at 46yo and one of the teams of hot #$%* young guys were working on a Datsun 260Z. They had pretty much murdered the battery trying to start it with no success, it's a carburetted motor. I was teamed up with a sharp young gear head and he said are you going to go help them? I said no but watch this.
After it had been on the jump box for a while I snuck over there when they weren't looking. I got in the car, pulled the choke and it fired right up. Immediately I shut it off, pushed in the choke lever and jumped out of the car. They were all asking how did you do that? I told them to try reading the books instead of trying to get the internet to tell you how the car works.
They were clueless about the choke. On a Datsun 260Z the choke lever is on the side of the console by the parking brake. They never saw it.

[RAFster122s]

For many a manual transmission is an anti theft device…most kids and young adults cannot drive them.

[newday777]

Back in 06' I was in school for automotive technology. I was the old guy there at 46yo and one of the teams of hot #$%* young guys were working on a Datsun 260Z. They had pretty much murdered the battery trying to start it with no success, it's a carburetted motor. I was teamed up with a sharp young gear head and he said are you going to go help them? I said no but watch this.
After it had been on the jump box for a while I snuck over there when they weren't looking. I got in the car, pulled the choke and it fired right up. Immediately I shut it off, pushed in the choke lever and jumped out of the car. They were all asking how did you do that? I told them to try reading the books instead of trying to get the internet to tell you how the car works.
They were clueless about the choke. On a Datsun 260Z the choke lever is on the side of the console by the parking brake. They never saw it.

 Good one

[Kelly E]

For many a manual transmission is an anti theft device…most kids and young adults cannot drive them.

That's the truth. My hotrod 85' GMC S-15 is a 5sp plus a secret parking brake release and it's carburetted. The thieves don't stand a chance.

[Kaze]

First stick I ever drove was a 3 speed dump truck. I was a seasonal for the parks department. Killed it on a hill. Then restarted, put it into gear, and shook the whole goddamn truck like it was an iron earthquake. After that, it was awesome.

Motorcycles are the BEST though. Each hand and each foot has its own job. None of that moving my foot around like I'm playing a #$%*ing pipe organ.

As for carburetors, you guys ever have a car that didn't start, so you took off the air cleaner and put a screwdriver in there to hold the butterfly open? That was like... Dad car lesson 2 in my house. Lesson one was give it a bit of gas before you turn the key, but don't pump the bastard or you'll flood the som#$%*.