Topic: Cold Blooded

[Vintageguy]

My 1978 CB750F is cold blooded as Hell. Even in warm (or hot) conditions this bike is rough off idle, and takes forever to warm up. Run like a mail train through the gears and in higher ranges, but bad at low RPM and from a stop. Eventually it will smooth out to one degree or another, but I'd like better idle and acceleration from low RPM's. Stock jets I'm sure, as this is a 9,000 mile totally original motorcycle. Any ideas? Thanks in advance. 

[jgger]

Check that your timing advancer isn't stuck. Also compare the 1,4 timing to the 2,3 timing. Chuck the plugs, if they are not a "coffee stain" brown, check for intake air leaks.

At least that's where I would start.

[Vintageguy]

If an air leak, where would be good to check. I assume around air box, correct? Thank you.

[bryanj]

Those are, a good 5-10 minutes before they will even try to run with no choke

[seanbarney41]

I do not know what you mean by wishy washy.  But I do know about the set of 712's I had, unexpected and unpredictable loss of grip, slow to warm, would not ever warm up at ambient temps as high as 65 F.  They are a very hard compound, either that or they age harden rapidly.  That is why they last so long.  Others have not had such problems.  Maybe mine sat on the shelf too long, I dunno.  All I know is I will never buy Shinkos again, despite the attractive price tag.  I ran mine at similar pressures to you.  I would try much lower pressures, especially in the cold.

[Erny]

I do not know what you mean by wishy washy.  But I do know about the set of 712's I had, unexpected and unpredictable loss of grip, slow to warm, would not ever warm up at ambient temps as high as 65 F.  They are a very hard compound, either that or they age harden rapidly.  That is why they last so long.  Others have not had such problems.  Maybe mine sat on the shelf too long, I dunno.  All I know is I will never buy Shinkos again, despite the attractive price tag.  I ran mine at similar pressures to you.  I would try much lower pressures, especially in the cold.

I think you answered here to another thread  : http://forums.sohc4.net/index.php/topic,180026.0.html

[seanbarney41]

I do not know what you mean by wishy washy.  But I do know about the set of 712's I had, unexpected and unpredictable loss of grip, slow to warm, would not ever warm up at ambient temps as high as 65 F.  They are a very hard compound, either that or they age harden rapidly.  That is why they last so long.  Others have not had such problems.  Maybe mine sat on the shelf too long, I dunno.  All I know is I will never buy Shinkos again, despite the attractive price tag.  I ran mine at similar pressures to you.  I would try much lower pressures, especially in the cold.

I think you answered here to another thread  : http://forums.sohc4.net/index.php/topic,180026.0.html

well...where the hell is my head?  Way to be on top of my thoughts more than myself, Erny! 

Maybe the mods will move my post?  ...er, I will just delete it...{skulks away back under rock}

[jgger]

If an air leak, where would be good to check. I assume around air box, correct? Thank you.

Did you check the plug color? An air leak would be from the carbs to the motor.

[Airborne 82nd]

I do not know what you mean by wishy washy.  But I do know about the set of 712's I had, unexpected and unpredictable loss of grip, slow to warm, would not ever warm up at ambient temps as high as 65 F.  They are a very hard compound, either that or they age harden rapidly.  That is why they last so long.  Others have not had such problems.  Maybe mine sat on the shelf too long, I dunno.  All I know is I will never buy Shinkos again, despite the attractive price tag.  I ran mine at similar pressures to you.  I would try much lower pressures, especially in the cold.

I think you answered here to another thread  : http://forums.sohc4.net/index.php/topic,180026.0.html

well...where the hell is my head?  Way to be on top of my thoughts more than myself, Erny! 

Maybe the mods will move my post?  ...er, I will just delete it...{skulks away back under rock}

Just copy then paste where you meant for it to go then delete from here

[Airborne 82nd]

Wait a minute will I need to delete mine now lol

[Airborne 82nd]

To OP Have you setup or adjusted your choke to your fast idle cam? That really helps a lot with cold start idles on our PD carbs.

[kerryb]

My '78k is cold blooded, but not bad when above 70 degrees and it does warm up pretty quick. 
You can check for air leaks by spraying a little starter fluid near areas that typically develope an air leak such as; near the carb boots (carbs to engine) and near the choke shaft where it enters the carb bodies.
Questions;  has it always had this condition or did it show up after winter storage?
                     Has it had a "tune up" since you got it?  Maybe the carbs need cleaning, if so be prepared to replace all the rubber parts, but keep all the brass parts.  Maybe running some seafoam through the tank is enough to clean it up some, and avoid pulling the carbs just yet.
                    As mentioned earlier, check timing, advancer, plugs, and maybe do a carb synch to be sure they are all playing well together.
If you do end up pulling the carbs to clean them, its just tedious, not hard.

Its all part of the adventure.

[Vintageguy]

I did check to see if my carb boots were secure and found most to have loose to very loose screws. Where is the timing advancer located, please?

[Vintageguy]

Forgot to mention, I live in Florida so this old girl gets no winter down time. I ride this bike (and all my bikes) at least 1 time per 2 weeks. Thanks.

[Tracksnblades1]

I did check to see if my carb boots were secure and found most to have loose to very loose screws. Where is the timing advancer located, please?

Behind the point plate.....😇

Hondaman has a mod to eliminate ignition timing scatter and proper advance rpm while your there...

[1976cb750f836]

A larger pilot, and raise needle 1 clip, will improve throttle response! And shorten choke time.

[Maraakate]

Those are, a good 5-10 minutes before they will even try to run with no choke

Really?  Mine does seem to take about 5-10 minutes to get warmed up to idle nicely with no choke.  I still have a few tiny air leaks from the felt washers on the airbox side of the carbs.  I'm also missing the brass press-in on the 4th carb at the end.  I put some tape over that to stop that leak but don't think it really made any discernible difference.

In any case, for me, when I start my 77 CB550K I have to start it with choke fully closed (second detent).  As soon as it starts you let it sit at this until it's about ready to die.  Takes about 20-30 seconds.  When I get to the first detent it will not idle very well, it almost dies in this range unless you adjust the throttle stop screw, which I DO NOT do.  Instead, I hold the throttle in very slightly to rev it around 2000RPM for about another 20-30 seconds.  From here, with the choke around the first detent I can finally ride it around and hold idle.  I slowly move the choke lever down here and there at the next few stops over the next 5-10 minutes until the idle is stabilized.  Keep in mind I am riding in 30-40F weather right now.  Not sure how it will perform if it's nicer out.  Never replaced the air filter.  I have aftermarket unknown 4-into-2 pipes from the 80s or 90s on them and may or may not have something to do with my issue.  However, I hear this possibly normal.  I am not used to this though, as my 79 CM400A can hold idle consistently after a minute or so.

I've done the usual, clean the carb and new plugs, new battery, etc.  Have not adjusted valves, cam chain, or points yet.  Also have not synced the carbs.  I don't have any air leaks at the boots.

[Erny]

I think topic here is about 750 not 550.
My 750 K7 is cold blooded too, it also taked long time running on choke to keep it idling. My friend has exactly the same with his K7.
I plan this winter to put bigger pilots (40) and full cleaning of carbs, incl ultrasonic.
Did not plan raising needles, but will consider too
Hope there will be improvement

[PeWe]

My CB750 K2 will not start without full choke. When started possible to reduce to half. It must continue on choke 5 minutes or more.

If bike has no need of choke might be rich running carbs. My CB750 K6 have had that issue.

[1976cb750f836]

When these bikes were new, Gas was different than now!  Carbs need slightly richer settings than they did when they were originally engenered !

[maxheadflow]

When I got my K8, it would only run with the choke on until real hot.  If I didn't run with the choke on, it had a real issue running at any speed below about 3500 rpm.  Did all the checks.  Timing, valves, carb bowls. Once the bike was, hot each idle mixture screw could change the idle but all like the setting at about somewhere over 3 turns. 

When I took the motor down to fix the cases I, rebuilt the air cleaner, installed a 4 into 1 and rejetted the carbs.

The mods were:

1. Remove pilot jets, drill by hand with a pin vise and a #78 wire drill. If you simply twist the drill through the jet by hand, it pulls itself through at a constant rate. Once through, you can pull it out. It will come out snug. Drill all the jets and then go back and try to get the same force on the drill drag on all jets. This will get you close to all the same size.    #78 gets you a 0.4064 jet nominally. 

2. I looked in to the slide cutaway and it seem pretty small and IMO most of the lean spot is right at the slide cutaway as far as tuning goes. It makes sense.  Light cruise sees a lot of the slide cutaway.  IMO if you raise the needle you are getting more fuel in the mid range.  I ended up filling the for holes on the emulsion tube,
 with solder.  You can see the arrows pointing to the one side of the tube. This mod helps the carb pull fuel at lower demands (kinda like slide cutaway).

3. Went from 110 to 120 mains. (Probably not needed.)

Last weekend, I went from San Diego to the desert through a 4000 foot pass and the motor did not miss a beat.  I used 89 octane as recommended here and it ran well. Cali gas has Ethanol . Based on the fill from reserve and the fact that I've yet hit reserve I suspect it's getting over 40 MPG (if the odometer is accurate).

Bike is not cold blooded if the temps are around 90 or above. (Was warm here on Sunday).

[1976cb750f836]

If bike has no need of choke might be rich running carbs. My CB750 K6 have had that issue.
[/quote]

That's exactly correct!
All my bikes are rich, plugs burn dark, but they don't foul, and no fuel smoke out the exhaust,mpg not important to me.  On a 50 degree day, I full choke, start bike, then go to half choke, then rev engine to 3k , 20 seconds, choke off then bike will idle, slow but idle.
It can be ridden then. No stumbling or jerking. Much more present to ride than a lean burn engine. And slightly rich engines run cooler.

[Maraakate]

I think topic here is about 750 not 550.
My 750 K7 is cold blooded too, it also taked long time running on choke to keep it idling. My friend has exactly the same with his K7.
I plan this winter to put bigger pilots (40) and full cleaning of carbs, incl ultrasonic.
Did not plan raising needles, but will consider too
Hope there will be improvement

Whoops, sorry thought we were talking about 550.

[BenelliSEI]

Both my K7 and K8 can be “cold blooded” they run best after 5-10 minute warm up. Of all my K’s, they benefit MOST from a really accurate carb sync, every few seasons. That seems to bring them back in line.