Help with '78 Honda Starting Problems

[supersport78]

Hi,

I am hoping someone out there may be able to help me with a problem I am having with my Honda. It is a 1978 Honda CB750F Supersport.

It was running fine, up until about a month ago. Here is the basic background:

I live in El Paso, Texas. Usually, we have a very dry summer, but since August, we have had a lot of rain. The bike is set up for our elevation and weather. Anyway, as it has gotten cooler in the mornings, the bike doesn't want to start. It will turn over and over, but not start. Last week, it took me an hour to start it. Now, if I let it sit all day and go out in the afternoon, it starts up just fine on the first try.

The mornings are not cold here. Maybe upper 50's to low 60's. It has a K&N air filter and the points are new. The plugs look fine and the gap is good. The battery has a full charge to it, unless I try and keep starting it in the am. Then I have to hook it up to the charger. The battery is also new.

I am wondering if the coil and wires have anything to do with this. Also, I am thinking it is time for another valve adjustment. It has been a while since the last one, maybe a year....

Any thoughts?

Thanks,

Darci

[CB750F]

I think that maybe you aren't getting enough fuel. Make sure the choke is working right,those old Hondas kind of need the choke to get fired in the morning.

If the choke is ok then check out the carbs. If the pilot jet is plugged up or has dirt in it they are hard to start. If someone changed them to leaner ones then they are real hard to start,especially in the cooler weather. Being you have a K&N filter (or do you have the indivdual filters,one per carb) you are flowing a lot more air than stock. You may need to jet it up some by getting larger jets in the carbs. Pull your plugs out and if they look real white after you have been using them for a good while you may need to re jet the carb to get enough fuel. They should be an even tan color on the tip.

Mine will actually kick start easier when cold than when using the electric start. The reason for that is it takes so many amps to use the electric start it kind of takes away some juice from the ignition and lessens the spark.

As long as you have a nice fat blue spark you should be ok in that department unless the coils or plug wires have a small crack in them and the spark is jumping to ground because of the damp.Sometimes spraying them with silicone spray will seal them up for some time. Take a plug wire and bend it some and if you see cracks they might be leaking spark to ground when the air is damp in the morning. I've even wrapped them with electrical tape to get by for awhile when they are like that.I'm fairly sure that the plug wires are non-replaceable on yours as they are mine however here is a site that sells coils and what not for yours if you should find that you need them.

https://www.partsnmore.com/cat_index.php?model=cb750_sohc&category=x

[supersport78]

I think that maybe you aren't getting enough fuel. Make sure the choke is working right,those old Hondas kind of need the choke to get fired in the morning.

If the choke is ok then check out the carbs. If the pilot jet is plugged up or has dirt in it they are hard to start. If someone changed them to leaner ones then they are real hard to start,especially in the cooler weather. Being you have a K&N filter (or do you have the indivdual filters,one per carb) you are flowing a lot more air than stock. You may need to jet it up some by getting larger jets in the carbs. Pull your plugs out and if they look real white after you have been using them for a good while you may need to re jet the carb to get enough fuel. They should be an even tan color on the tip.

Mine will actually kick start easier when cold than when using the electric start. The reason for that is it takes so many amps to use the electric start it kind of takes away some juice from the ignition and lessens the spark.

As long as you have a nice fat blue spark you should be ok in that department unless the coils or plug wires have a small crack in them and the spark is jumping to ground because of the damp.Sometimes spraying them with silicone spray will seal them up for some time. Take a plug wire and bend it some and if you see cracks they might be leaking spark to ground when the air is damp in the morning. I've even wrapped them with electrical tape to get by for awhile when they are like that.I'm fairly sure that the plug wires are non-replaceable on yours as they are mine however here is a site that sells coils and what not for yours if you should find that you need them.


Thanks! I was thinking about the coil and wires yesterday. I have had the bike since June of last year and it looks like the coil and wires are the original. I have recently replaced the regulator/rectifier, points and battery.

I am not running the individual pods. Just the regular K&N that fits in the stock air box.

Thanks again for your help. This is really perplexing me as it starts up great in the afternoon without a problem!

[kz1000g]

The only thing I can think of is that the dew is getting on something. When it has had a chance to dry out all day it starts?

Paul Sr.
kz1000g