Topic: bike runs terrible after heating up

[dday]

Hello, I'm new to this forum and New to the Hondamatic.
I have a 1978 cb750a. I just had it in the shop. they changed the oil and filter,cleaned the carbs and syncd them. starts and runs great til it gets hot. Then it stalls at every stop and is a mother to get started again.I looked thru this whole site looking for any previous post .sorry if i posted a repeat.Could my problem be coils, spark plug caps,wires etc help .....I really enjoy the bike but only for 30 minutes at a time Please give your two cents. I welcome any ideas thanks DDAY

[dday]

Here's a pic of her....only 8,000 miles...

[TwoTired]

Remove the spark plugs and describe the deposits or post clear pictures of the electrodes with light shining into them.

Most interesting would be from the moment in time when the bike was hard to start and give a clue to combustion conditions at the time of the problem.

[raymond10078]

I have never experienced the problem myself, but I have read many posts about condensers failing after the bike gets hot.

Do you own a timing light?  If so, use it to see if you have sparks when the symptoms appear.

Is your choke closing, or releasing completely?

Are your valves set correctly - or have they been checked?  I wouldn't think that would be the problem unless they are adjusted with essentially zero lash.

Is the air filter, and its passages clean/clear?  I've read about a number of bikes with nests and stuff in the airboxes.  I've also read about cheap air filters being too restrictive.

Lots of possibilities - but they are all related to fuel, air, and spark.

[dday]

The bike has just been looked over at the local shop. Carbs cleaned and synced. air filter replaced, new plugs, (pulled them Clean as a whistle). all wires like new. rode it today for about an hour had to feather the throttle to keep in running at stops.Only died once.choke opens and closes as it should. I dont own a timing light. I payed over 400 bucks to have it tuned up gonna take it back Monday and see what's up. I will get results or i'll get my money back

[raymond10078]

Does it idle for long periods in Neutral?

If the problem is only in gear, you may have a problem with the idle control circuit.  There is a solenoid that is energized when in gear, that applies vacuum to a dashpot, and slightly lifts the carbs slides - to increase the amount of air/fuel - to keep the idle speed up when in gear.  If the dashpot is not "pulling up", then its either the dashpot, the vacuum hoses, the solenoid, or the circuit that controls the solenoid.  If the dashpot is "pulling up", then it may not be adjusted quite right.  I recall that there is a screw on the right side of the carb set (in between carbs 3 and 4) that you can try adjusting.

Good luck.

[tomsweb1]

Hey Dave! It's Tom. Glad you came over here, you will never find better advice given than from these guys here! kandrtech is right about the condensors. If you do get new points and condensors, always buy Honda. The cheap stuff is far more trouble than they're worth! If you have an ohm meter, you can check your spark plug caps. Measure the resistance in them, it should be around 5,000 ohms. You can also measure the coils. with the caps off, the resistance between the high voltage cables on a coil should be around 20,000 ohms. I know it's not easy, but you should try to make these measurements when you are having problems. The primary (low voltage) side of the coil should have around 3 ohms. Unfortunately, there is no simple way to measure the capacitance of the condensor, however, you can see if it's doing something by connecting an ohm meter to it, and ground. If the resistance goes down, it is taking a charge.
 None of the procedures will rule anything out completely, however, they will sniff out any major problem in the ignition system.

 Hope this helps!

[raymond10078]

Just a thought - when you say it runs terrible - it first sounded like it runs bad at all speeds.  Later posts made it sound like the bike wouldn't stay running at stop lights.

It would help us all (to better help you) to better clarify "how it runs bad", and exactly when (idle, off-idle, slow speeds, high speeds, etc).

[dday]

You all have been very helpful. Thankyou. I will take notes of  this page an give them to the mechanic on monday. for I have no way to work on this bike myself.

[dday]

 All is great with the bike .Took it out and ran the hell out of it. got her up to 75 mph and held her there for for a 30 min ride. She runs great now just needed her pipes clean. Now i have to fix the fork seals and she'll be perfect...

[gaskog]

Hi everyone
I think i have the same kind of problem with my -76.
It runs great in neutral. It seems to loose a bit to much idle when put into Drive. When driving, it starts to run very poor after passing 50-60 km/h (live in Europe...), like it looses all effect in hi speed.
And it keeps floating over in carb no.1.
HAve tried about everything i can think about my self( and my brother-in-law that is a self-decleared 750 expert...)..;o)

frustrating summer greatings from NOrway
Geir ARne
(I own one the four running hondamatics in Norway)

[Danno]

two things it could be either the fast idle selonoid is not working or as another member said i would bet on condensers