Topic: Hard to start when cold... CB750K4

[sbparks]

Hi Folks,

 I thought I'd ask this question after my weekend rides...

 My bike is typically difficult to start when cold.  When I say cold, I mean the first start of the day, out of the garage.  Once warmed up all seems to be well.

 So to start it I'll typically close the choke and attempt to start.  I'll get a few hits and possibly, the engine will run for a short period (10-20 seconds).  I'll try again and the second time, the engine usually wants the choke opened.  Once started, it seems to run best with the choke open or at least part way open.  After a few minutes of running, I'll open the choke completely and after warming up things settle out.

 I know this is a pretty general question, but is there something I should look at to improve my cold starts?  Its a bit of a pain to sit there and continue to crank the engine while everyone else is up and running so effortlessly.

 I should also mention that my carbs have been completely cleaned/rebuilt prior to this riding season.

 Thanks for any ideas.

Scott

[andy750]

I have the same bike - CB750K4 and its the easiest bike to start from cold. It takes one kick or one push of the button with choke lever up and then I close choke immediately once it fores up. Wait 15 secs then ride off. No problems. I have stock jetting (40/110), stock exhaust, stock airbox. Its always been like this. You have something not quite right -carbs balanced?

Dont believe the "they are all like this" line.

good luck in sorting it out.
cheers
Andy

[sbparks]

Andy,

 Thanks for the reply.  So your typical start up is to have the choke closed for the initial startup and then immediately open the choke once it fires up?  I'll give that a try for sake of argument and I'll report back.

 My setup is very close to stock... 40 idle jets and 110 main jets.  Stock airbox .  The carbs were just recently synched (as close as I could get them).  My exhaust is aftermarket... a four into two.  I don't know what brand, but someone once thought they might be a Jardine (sp?) or something like that.  I have the jet needle set at position #4, but that doesn't affect start up (or does it?).

 I appreciate any ideas.

Scott

[andy750]

Thanks for the reply.  So your typical start up is to have the choke closed for the initial startup and then immediately open the choke once it fires up?  I'll give that a try for sake of argument and I'll report back.

Correct. My bike runs on the rich side so this works for me. I get 40+ mpg (and thats not riding slow). My needle is in the middle position.   

good luck
Andy

[Duke McDukiedook]

You might want to adjust your valves if you have hard starts.

[Gordon]

Do a full tune-up.  If that doesn't significantly improve things, then start checking things like strength/color of spark when trying to cold start, cylinder compression, voltage at coils.  Check the ends of your spark plug wires to make sure they're making a good connection inside the plug caps.  Does the K4 have a fast idle cam on the choke?  If so make sure it's set correctly.

[Johnie]

I have the same bike and had the same issue when I brought it home from the previous owner. I did the full tune and still had an issue. Turned out the choke valves were not in sync. I think 1&4 were even, but 2 & 3 were way off compared to 1&4. I re-adjusted them all even so when the choke handle was up, all choke valves were evenly down. There is great improvement on start-up now.

[sbparks]

Andy,

 I cold started the bike this evening using your proceedure to see if there was a difference... Possiblly, yes.  Seems that I do get a quick start with the choke on, then, better running idling with the choke off.  I did get a few stalls, but it was more quickly overcome this time.  Seems like I do need to set the idle screw higher during the cold start to get things moving.  After it starts to warm, then I drop the idle RPMs to a more comfortable level

 I decided to ask this question after two episodes of lengthy start sequences just last Saturday.

Johnnie,

 I did spend quite a bit of time trying to sychronize the opening closing of the choke plates when I reassembled the carb assembly.  I do remember thinking to myself, "Gee... this could be just a little better than what I have it... Ah, it'll be ok...".  The choke plates are good, but not perfect.  Possibly something I could look at...

Thanks guys.

[grumpy]

Do a full tune-up.

Yep.
Check it all. Plugs, points, timing, valves, etc.

My K3 is (essentially) all stock starts the same as Andy's.

[Old75_ratafe]

I know on my 75 the #3 (I think) carb has the linkage that goes to the #2 & #4 goes both ways... It doesn't the one is actually slightly longer than the other found that out the hard way after I rebuilt mine.

[Whaleman]

This problem with my K2 ended with the replacement of the rubber carb manifolds. Dan

[jkot55]

I had the same problem with my CB750K5.  I adjusted everything as you did and it was still cold-blooded.  The idle speed adjustment is a good quick-fix but there might be another option for you.  I solved the problem on mine with a Hondaman Ignition.  This thing was literally plug-and-play.  Starts right up, stays running and is good to go after just a little warm up.  Hondaman is always on here so you can just start another thread and he'll give you the info.  I don't remember the cost but it was a bargain.

[sbparks]

 Thanks for the continued suggestions!

 Jkot55... I am running one of Hondaman's electronice ignitions.  I did see an improvement... especially when I have the throttle more open (when I am on the road for instance).  But cold startup could still stand to be improved.

 Whaleman... I have new rubber manifolds on my list up upgrades for this bike.  New clamps as well as mine are as tight as I can get them.  I did soak the rubber manifolds in the wintergreen oil and hot water in an attempt to soften them.  They are still pretty tough.  So, this winter, I'll probably throw another load of cash on the bike in new parts.  Oh well!

 Thanks again for the suggestions.

Scott