help: weak spark, poor cranking

[Al 91]

Hello All,
I have been viewing a lot of post on katriders.com. This site definitely seems to be a "powerhouse" of knowledge on Katana's.
I sincerely need help on a cranking issue that has been going on with my 1991 GSXF750 for YEARS. I have owned the bike since 2000 and have put up with this cranking problem the entire time.(If you can believe that.)
The bike runs great but it is a pain to start up. I am hoping someone will hope me troubleshoot the problem. All my local mechanic did was to install a new battery and starter to make the engine "spin over" faster. This helped a little at first. The local mechanic says it cranks fine for him. Not so. He just wants for my bike to be "out of there." I even left the bike with him for two weeks.The new starter and battery was just a "band-aid" fix.
Here are the symptoms. I usually put it on full choke and leave it there till it cranks.(I never smell gas or see any signs of flooding) A small shot of starting fluid sometimes helps. Here's the strange part. It usually cranks the SPLIT SECOND you let off the starter button ! More fire going to plugs in that split second I guess. It will start EASILY every time you push it and pop the clutch. Must be a spark issue.
I have tried spinning it over on "prime" to see if this would help. Nope ! The chokes are working.
If you turn the engine off and wait about 15 minutes it will usually start right up every time. Cold starting is really bad. I guess it helps when the fuel is vaporizing properly. Weak spark is able to ignite vapor.
I have a Clymer manual which I think is pretty good. I also have a nice Fluke brand multi-meter. I am a semi-fair amateur mechanic that can follow directions pretty well. I sure could use some help on this issue.
Like I said, It's been haunting me for years !

Many thanks in advance.

Albert

[ctandc]

First off...

Do you have any modifications to the carbs or exhaust?

And why "FULL" Choke?

I've commute on my Kat, and ride well into the 30's and I never use FULL choke.. Just engage it a bit, and crank it.

[Al 91]

Thanks for your input. Over the eight plus years I've had this problem I've tried every choke position possible.

I forgot to answer question about modifications to exhaust and carbs.

I do have headers and Yoshimura exhaust. I don't know about carbs.

Bike came to me like it is. Had it since 2000.

[Trackerrrr]

Have you checked your choke cable to make sure it actually works at the carbs correctly? I would check ALL your electrical connections under the seat and clean them up especially at the battery and CDI connections. Some folks have tried using a relay to keep the headlight off till the bike fires which will help with voltage drop while cranking.

[Kfreak]

The new battery ans alt. helped in the beginning. After awhile, no. I'm going to say look at the output of the alt. Check all electrical connections.

[Al 91]

I have been communicating with "Arsenic" about the starting problem.

His suggestion is that the On/Off and starting switch is most likely the culprit.

I plan to replace this switch as soon as I receive it.

I will post the outcome after replacing the switch.

Many thanks for all the help and suggestions.

[GregS]

Sounds like your weak spark, if indeed you have weak spark, is caused by the same thing as your slow cranking. That would be low voltage.
Check your battery voltage while cranking, is it above 9.5 volts? If not let's check the charging system and battery.
If it is then check the voltage, while cranking, at the coil primary positive terminal. Is it at least 9 volts?

[pilotdada1]

Sounds like your weak spark, if indeed you have weak spark, is caused by the same thing as your slow cranking. That would be low voltage.
Check your battery voltage while cranking, is it above 9.5 volts? If not let's check the charging system and battery.
If it is then check the voltage, while cranking, at the coil primary positive terminal. Is it at least 9 volts?

This sounds like good advise. I would also consider doing a voltage drop test on the various Batt and starter cables. Set a volt meter on volts, put one lead on the batt+ terminal and the other on the starter sol on the batt wire side. While cranking the starter your meter should read less than .3 volt. If it reads more you have a cable or connection problem. Do the same between the starter sol and the starter and again between the ground cable attachment point and the ground terminal on the batt. Also do this on the 2 starter sol terminals (big ones-batt/starter)
James

[Al 91]

Cranking problem solved; finally !

After many years the slow cranking problem is finally solved !
It was bad spark plug wires right where the spark plug boot screws in to the stranded copper spark plug wire. (1991 750 katana GSXF)
I found the suggestion some where on this site. The suggestion mentioned that older motorcycles' spark plug wires insulation may have become old and brittle close to the engine. The post said to trim off about the last half inch of wire after unscrewing the boot. This would give a fresh connection. (my boots practically fell off the wire. Very poor connection !)
My local Suzuki shop had replaced the starter and battery twice. That helped a little for a short time but was only a "band aid fix."
I replaced the starter switch myself and this did not help either. The coils checked out perfect.

I then did the spark plug wire "trim."

My Katana now cranks perfectly every time !!!!! Hot or cold , doesn't matter.

All I can say is thank God for the guy that made that post about bad spark plug wires !

If anyone knows who made that post , please let me know.
I want to personally thank him.

Albert Florence, SC

[ImakeTV]

how did the spark look? how did you know it was weak? Mine is a sky blue color.

[Wild-Bill]

Blue is a nice, hot spark.