Hard starting when cold - '83 cb750

C

chickenStripCharlie

Coast to Coast
83 CB750 DOHC .... starts really hard when cold. Usually I crank it for a while on full choke. Then eventually starts to catch on on half choke with just a tiny bit of gas. Takes like 5 minutes to get it going. Wouldnt mind speeding that up a bit.

Never starts on full choke. Disclaimer: I think when i installed the carbs the choke plates would not close 100% so my full choke is more like 7/8 choke.

Short of pulling the carbs, what else can I do?

- The bike runs fine when it is running so I dont think it is a fuel delivery issue.
- stock airbox & new filter
- new plugs
- float seat height not touched when carbs were cleaned
- when warmed up starts instantly! Just a quick starter press and fires up.
- new battery at 12.7V or so.
- no fuel leaks.

I recently learned that you can get hotter/cooler plugs. Would a slightly hotter plug be an option to try?

Thanks for the advice!!

P.S. I'm gonna get a video of the hard start tomorrow just so ya'll can see :)
 
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Could be unrelated, but what engine oil are you using? Also, does your starter motor need cleaning (mine did)? And what jetting have you got in your carbs and how many turns out are your mixture screws?
 
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Old Hondas are notoriously cold blooded so anything slightly off will make it worse. That being said it should fire quick on full choke but need the choke for a while and you should be able to slowly remove the choke as it warms, or start riding and turn it of completely. I wonder if your pilot circuit has crud in it still'?
 
Engine oil is rotella 10w40 I think? Maybe 15w40. I will have to look.

Starter motor: I dunno. It looked clean on the outside. It cranks fine. I gave it a new thick cable to the solenoid, but never thought I needed to open it up.

Heres a video. Excuse my neighbor and the ticking (small exhaust leak I think)

You can see on full choke it didnt do anything. Then I go to half choke and try to.give it some gas - doesnt work.

Eventually you can see it fires on half choke but takes a while

Toward the end you can see I'm able to start pretty much instantly even though it only warmed up for a minute.

Thoughts? :)

 
Have you checked the valve clearances? If they are tight it will be harder to start when cold but typically runs better when it warms up.
 
HerrDeacon said:
Have you checked the valve clearances? If they are tight it will be harder to start when cold but typically runs better when it warms up.
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Yes. Who ever owned it before had done some work on it. The valves were all within spec and compression was 170 across the board.

I dont remember if the valves were on the tight end when I checked. I have it written down somewhere in the garage. I will look for it later tonight. Good call!
 
I had a CB900F when I lived in cold Edmonton. It was a slow cold-starter and it needed the choke on until it was completely warmed up. I put 33mm smooth bore carbs on it and it was like night and day, started easily and ran well before being completely warm. You probably don't want to go to the expense of changing carbs but I think this indicates that there is a good chance that the problem is with the carbs, the choke specifically.
 
Did you check for intake leaks? That would lean the bike out and sometimes these leaks are only a problem around idle.
 
What about priming the cylinders with 5-10 blips of the throttle before hitting the starter button to dump some gas in there first?
 
As I understand the thread, it will not start on full choke but starts on half choke and after that it will start without chock even if the motor is still cold.

So that suggests that the pilot jets are too large or the mixture screws are way too far out.

You could also try just starting it on half choke from dead cold. And don't be afraid to let it churn over a bit longer. It's quite normal for a cold motor to have to crank for 5-10 seconds to get it to fire up. 10 lots of one second pushing the start button are not as effcetive as a rule as one single ten second churn.
 
+1. Another test for too big of a pilot or too far on the mixture screw is if you get it running and go full choke it will die or want to die.
 
teazer said:
As I understand the thread, it will not start on full choke but starts on half choke and after that it will start without chock even if the motor is still cold.

So that suggests that the pilot jets are too large or the mixture screws are way too far out.

You could also try just starting it on half choke from dead cold. And don't be afraid to let it churn over a bit longer. It's quite normal for a cold motor to have to crank for 5-10 seconds to get it to fire up. 10 lots of one second pushing the start button are not as effcetive as a rule as one single ten second churn.
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Somehow, I missed misunderstood that the choke had to be set at half.
 
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Jimbonaut said:
What about priming the cylinders with 5-10 blips of the throttle before hitting the starter button to dump some gas in there first?
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I feel like a moron ... for not trying this.
I just went out, gave it 5 twists and got the bike running from cold in about 10-15 seconds.

I honestly dont have an answer for why I didnt try this. I guess just too long since I've last owned a carburated bike *shrug*

Thanks!!!
 
teazer said:
As I understand the thread, it will not start on full choke but starts on half choke and after that it will start without chock even if the motor is still cold.

So that suggests that the pilot jets are too large or the mixture screws are way too far out.

You could also try just starting it on half choke from dead cold. And don't be afraid to let it churn over a bit longer. It's quite normal for a cold motor to have to crank for 5-10 seconds to get it to fire up. 10 lots of one second pushing the start button are not as effcetive as a rule as one single ten second churn.
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I believe the mixture screws were turned out 2.5 turns. Or maybe 2.75

I wasnt sure what so I just did what I googled from the net and I think it was 2.5
 
Without choke on the accelerator pump test or with choke?

Asking for a friend as they say..
 
teazer said:
Without choke on the accelerator pump test or with choke?

Asking for a friend as they say..
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With choke! Ran right away (struggling) for 3-4 seconds and died. Then I did half choke and a tiny bit of throttle and it fired right up and continued to run.

I am OK with this as the starting procedure. It was pretty quick.
 
chickenStripCharlie said:
I feel like a moron ... for not trying this.
I just went out, gave it 5 twists and got the bike running from cold in about 10-15 seconds.

I honestly dont have an answer for why I didnt try this. I guess just too long since I've last owned a carburated bike *shrug*

Thanks!!!
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Alright alright alright :cool:

Back in business
 
chickenStripCharlie said:
Thanks!!

Hey what's your "winterizing" procedure for the cold Montreal? Or do you just run it every so often?

To be honest I let my Honda ATV sit for months and never really take good care of it and it always fires up just fine. Lol.
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Pretty standard I think - I fill the tank, add Stabil, run the engine for 5 minutes or so to make sure the stabilized fuel has entered the carbs, drain the carb bowls, remove the battery and stick it on a trickle charger at home. I cover the end of the exhaust so no moisture gets in, and fling a cover over the bike. My garage is colder than witch's tit (unless I'm in there with the heat on) - so I also put some cardboard between the tires and the garage floor. Ever month or so I'll push the bike forward a couple of inches too so as to rotate the contact patch with the floor. Think that's it - anything else I've forgotten I'll edit this post
 
Jimbonaut said:
Pretty standard I think - I fill the tank, add Stabil, run the engine for 5 minutes or so to make sure the stabilized fuel has entered the carbs, drain the carb bowls, remove the battery and stick it on a trickle charger at home. I cover the end of the exhaust so no moisture gets in, and fling a cover over the bike. My garage is colder than witch's tit (unless I'm in there with the heat on) - so I also put some cardboard between the tires and the garage floor. Ever month or so I'll push the bike forward a couple of inches too so as to rotate the contact patch with the floor. Think that's it - anything else I've forgotten I'll edit this post
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Cool. Do you make sure it is ethanol free gas? I heard Chevron 91-94 is supposed to be 100% ethanol free?

I have some stabil that's like 3 years old. Wonder if stabil itself can go bad? Lol

Thanks man!!
 
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