Author Topic: Engine idle when cold question for you all (Read 2639 times)

stueveone · « **on:** March 29, 2007, 09:30:35 PM »

Hey guys.
How well do your 750's idle when cold?

My bike won't really start unless it's choked, but then I have to IMMEDIATELY un-choke for the bike to run. Then, once it's started, I'm not out of the woods yet, but have to toggle the throttle until it can idle on it's own. I also notice that the idle slightly increases with engine temperature. Is this normal?

Do you have to immediately un-choke your engine so it won't die?
When the engine is cold, you have to toggle the throttle so it won't die?

750goes · « **Reply #1 on:** March 29, 2007, 11:12:42 PM »

full choke for about 2 seconds after starting then back it off to 3/4 for another 10 seconds then at 1/4-1/2 until warm...bit of a lumpy idle until fully warmed up....

hopterfixer · « **Reply #2 on:** March 30, 2007, 05:37:30 AM »

I hit the starter with full choke on, and immediately as lights off I simultaneously drop the choke and feather the throttle. I hold it open just enough to keep about 1400 RPM allowing the oil to warm and circulate. I let it sit for a minute or so and then off I go. I have been wondering the same thing having never ridden another CB750. I keep hearing how cold blooded they are, but the KZ650 I had is what I would call cold blooded. You had to have the choke on full to start it, and when it light, it jumped to 4000 RPM and stayed there until you lowered the choke a little. You could not even blip the throttle with out killing it until it was good and ready to go.

gerhed · « **Reply #3 on:** March 30, 2007, 07:12:35 AM »

On the Cycle-X setup that I have:--2 carbs
First--flood it bigtime!
For starting--Fully choke one carb--open the other one up all the way
After a minute or two at 2000 rpm--open the other one up-idle drops down-- and ready to go.
Runs better after 5-10 minutes at speed.

c_kyle · « **Reply #4 on:** March 30, 2007, 07:32:23 AM »

My 650 does not like the choke at all. In WV, it required a small amount of choke, but down here in FL, it's no choke at all.

Jonesy · « **Reply #5 on:** March 30, 2007, 07:45:46 AM »

To start mine I have to give it full choke and crack the throttle. Ones it starts I have to open the choke a tiny bit and keep the engine revving around 3,000 RPM. After a few moments I can take the choke off and let the smoke clear, but I have to "tickle" the choke to keep the bike from stalling. After a few minutes the bike will idle OK without the choke, but until it fully warms up if I give it a handful of throttle it just falls on it's face. Once it warms up fully it takes off like a rocket.

It is normal for the idle to go up a bit as it warms up.

GammaFlat · « **Reply #6 on:** March 30, 2007, 11:26:50 AM »

Full choke for start, immediately back down to 1/2 to 1/4 (my hand is on the choke while turning over). I usually turn the idle up at the thumbscrew and futz around with other stuff for 2 mins or so. The idle wants to run up (probably when all cylinders start firing

) ) so I gradually back down the idle a little and choke a little. Mine really runs like crap when it's cold out seemingly forever.... I've recently changed to a Dyna-S and a stock airbox so that may help- formerly cones and very fresh points. (my experiences are with the older setup) I am also about ready to re-jet. I'm thinking my jets are too big for my setup... probably need to get closer to stock (right now, my only deviations from stock are MAC 4-1 and Dyna-S). (76 CB750)

JTB

dusterdude · « **Reply #7 on:** March 30, 2007, 01:50:15 PM »

idle speed will increase as the bike warms up

feliz · « **Reply #8 on:** March 30, 2007, 01:56:34 PM »

I read in an early seventies Brit bike magazine (the review is on a CD I recently purchased) that happened to be reviewing the CB750 that the reviewer cranked the idle up several turns before starting the bike, full choke, start, choke off then he let it run for about five minutes at fast idle before turning the idle down. I do that now and it works for me rather than having to feather the throttle for 2-3 minutes. I avoid using the choke any more than I have to to avoid plug fowling.

hopterfixer · « **Reply #9 on:** March 30, 2007, 02:25:38 PM »

I personally would rather feather the throttle than fiddle with the idle all of the time. I tried that at first, but it got annoying always adjusting the idle back down when it was warm, it seemed like I was always making adjustments.

fmulharin · « **Reply #10 on:** March 30, 2007, 02:43:11 PM »

Quote from: GammaFlat on March 30, 2007, 11:26:50 AM

Full choke for start, immediately back down to 1/2 to 1/4 (my hand is on the choke while turning over). I usually turn the idle up at the thumbscrew and futz around with other stuff for 2 mins or so. The idle wants to run up (probably when all cylinders start firing ) ) so I gradually back down the idle a little and choke a little. Mine really runs like crap when it's cold out seemingly forever.... I've recently changed to a Dyna-S and a stock airbox so that may help- formerly cones and very fresh points. (my experiences are with the older setup) I am also about ready to re-jet. I'm thinking my jets are too big for my setup... probably need to get closer to stock (right now, my only deviations from stock are MAC 4-1 and Dyna-S). (76 CB750)

JTB

Quote from: GammaFlat on March 30, 2007, 11:26:50 AM

Full choke for start, immediately back down to 1/2 to 1/4 (my hand is on the choke while turning over). I usually turn the idle up at the thumbscrew and futz around with other stuff for 2 mins or so. The idle wants to run up (probably when all cylinders start firing ) ) so I gradually back down the idle a little and choke a little. Mine really runs like crap when it's cold out seemingly forever.... I've recently changed to a Dyna-S and a stock airbox so that may help- formerly cones and very fresh points. (my experiences are with the older setup) I am also about ready to re-jet. I'm thinking my jets are too big for my setup... probably need to get closer to stock (right now, my only deviations from stock are MAC 4-1 and Dyna-S). (76 CB750)

JTB

I do about the Same (CB750 K6) Start it with the choke full for a few seconds drop it down to about 3/4 and turn up the Idle screw.

As I'm futzing around, Bungie cording my Laptop bag to the Sissy bar, getting my gloves and Hemlmet on, I Drop the Chock down to fully closed. I figure 4 or five minutes goes by, and the bike is ready to go. I drop the Idle back down and and Head off to work. Temps in the Morning have been around 35 degrees this week.

OCNYCB750

TwoTired · « **Reply #11 on:** March 30, 2007, 04:03:20 PM »

Don't the early 750s have one of these to hold the throttle open during warmup?

feliz · « **Reply #12 on:** March 30, 2007, 04:11:30 PM »

Quote from: TwoTired on March 30, 2007, 04:03:20 PM

Don't the early 750s have one of these to hold the throttle open during warmup?

Actually my K3 does but for some reason which I haven't been able to figure out yet you can screw it all the way in and it never tightens up the throttle control.

Jonesy · « **Reply #13 on:** March 30, 2007, 04:16:18 PM »

Quote from: TwoTired on March 30, 2007, 04:03:20 PM

Don't the early 750s have one of these to hold the throttle open during warmup?

Yep. They dropped it in '75.

Quote from: feliz on March 30, 2007, 04:11:30 PM

Actually my K3 does but for some reason which I haven't been able to figure out yet you can screw it all the way in and it never tightens up the throttle control.

You might be missing the little steel "brake shoe" (#5):

slarty-bart-farst · « **Reply #14 on:** March 30, 2007, 04:26:39 PM »

From cold Full choke,hold the revs up a bit,blip throttle a couple of seconds until it starts puffing on all cylinders then 3/4 choke, blipping throttle then ride off slowly. Making the engine do some small work puts heat in quicker than standing still. Knock choke of with my knee as I ride. I have my tickover set real low 500 rpm as I prefer the sharp throttle response so the bike wont tickover until very warm.

super pasty white guy · « **Reply #15 on:** March 30, 2007, 05:08:41 PM »

Damn, you can idle at 500?

Mine dies if I let it drop below 1000 on the tach. Maybe the tach is off- it's certainly not the stock one.
What's a normal idle speed on these?

dave

clarkjh · « **Reply #16 on:** March 30, 2007, 06:55:29 PM »

Quote from: Jonesy on March 30, 2007, 04:16:18 PM

Quote from: TwoTired on March 30, 2007, 04:03:20 PM
Don't the early 750s have one of these to hold the throttle open during warmup?

Yep. They dropped it in '75.

Quote from: feliz on March 30, 2007, 04:11:30 PM
Actually my K3 does but for some reason which I haven't been able to figure out yet you can screw it all the way in and it never tightens up the throttle control.

You might be missing the little steel "brake shoe" (#5):

My 74 has it and I lost #5, so........ I just took a small piece of sugar maple and mad a new one, should work like a charm when put back together.

James

Jonesy · « **Reply #17 on:** March 30, 2007, 07:54:58 PM »

You can still get them from a Honda dealer as well.

Gordon · « **Reply #18 on:** March 31, 2007, 06:55:29 AM »

Quote from: TwoTired on March 30, 2007, 04:03:20 PM

Don't the early 750s have one of these to hold the throttle open during warmup?

Yes, but the idle speed screw is easier to use.

TwoTired · « **Reply #19 on:** March 31, 2007, 11:37:07 AM »

Quote from: Gordon on March 31, 2007, 06:55:29 AM

Quote from: TwoTired on March 30, 2007, 04:03:20 PM
Don't the early 750s have one of these to hold the throttle open during warmup?

Yes, but the idle speed screw is easier to use.

You say potaytoe I say potahtoe.

Gentlemen, choose your thumbscrews and stand back to back. Pace off at the count, turn and...turn and...turn and...
idle?

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Author Topic: Engine idle when cold question for you all (Read 2639 times)

fmulharin

slarty-bart-farst