Author Topic: 73 honda cb 750 wont start (Read 5815 times)

njf33 · « **on:** April 13, 2015, 02:16:22 PM »

I have a 73 honda 750 cb. It sat through the winter . I replaced battery. Tank has over quarter tank oil levels good bike shows no signs of leaking any fluids. I tested the silonoid it has power rectifier has power everthings grounded properly. Bike when starter button is engaged starts up like it wants to start but just doesnt get there. Spark plugs are getting spark. Somethings ive noticed are the gauges oil nuetral etc dont light up only lights that work on bike are tail lights. A similar story said signs point to ignition switch. So next im going to test that make sure its getting power and also make sure engine is getting gas. Anyone with similar issues all and any advice would be appreciated.

Chachi · « **Reply #1 on:** April 13, 2015, 02:18:09 PM »

To rule it out... try on reserve. Might be surprised. Visual tank level can be deceiving.

njf33 · « **Reply #2 on:** April 13, 2015, 02:26:07 PM »

Good call I will try that. Its those little things sometimes that slip the mind. Thanks.

Stev-o · « **Reply #3 on:** April 13, 2015, 02:29:12 PM »

Check the voltage on your battery, should be 13+V if fully charged.

flybox1 · « **Reply #4 on:** April 13, 2015, 02:53:43 PM »

Quote from: Stev-o on April 13, 2015, 02:29:12 PM

Check the voltage on your battery, should be 13+V if fully charged.

yuup! +1

njf33 · « **Reply #5 on:** April 13, 2015, 03:38:21 PM »

Battery is fully charged.

Allen Statu · « **Reply #6 on:** April 13, 2015, 03:48:30 PM »

Quote from: flybox1 on April 13, 2015, 02:53:43 PM

Quote from: Stev-o on April 13, 2015, 02:29:12 PM
Check the voltage on your battery, should be 13+V if fully charged.
yuup! +1

Same thing happened to me. I had a new battery and checked a number of electric parts. Grounds, solenoid (replaced), and rectifier/regulator, flash relay (for some lights). But I jumped my bike with a portable charger, and it started right up. I then started charging my battery with a tender, until I got a better quality battery.

Also similar thing with my lights. Only the brake light would go on, but when I had the ignition in park.

Stev-o · « **Reply #7 on:** April 13, 2015, 03:50:19 PM »

Quote from: njf33 on April 13, 2015, 03:38:21 PM

Battery is fully charged.

Checked with voltmeter?

njf33 · « **Reply #8 on:** April 13, 2015, 05:37:59 PM »

DH · « **Reply #9 on:** April 13, 2015, 09:22:24 PM »

+1 on a charged battery, but is this a NO CRANK issue or a CRANKS but WON'T START issue?..just for verification

calj737 · « **Reply #10 on:** April 14, 2015, 05:22:26 AM »

I'm betting KILL switch is not allowing 12v to coils

check the BLK/WHT wire at the coils for 12v with key ON and stop switch set to RUN.

njf33 · « **Reply #11 on:** April 14, 2015, 07:22:49 AM »

Cranks but wont start.

MoMo · « **Reply #12 on:** April 14, 2015, 07:28:02 AM »

so you have spark, good compression and fuel in the correct ratio? You've eliminated spark, probably has good compression because it ran before, so that leaves fuel. Turn petcock off, drain fuel from carbs and let "fresh" fuel flow in. Should start...Larry

Stev-o · « **Reply #13 on:** April 14, 2015, 07:29:58 AM »

+1 fuel. Have you checked your petcock for possible clog?

njf33 · « **Reply #14 on:** April 14, 2015, 07:38:29 AM »

Thats on list for tommorow that and checking contact on starter and ignition switch off next 2 days gonna try and git r done. Keep you guys posted.

iron_worker · « **Reply #15 on:** April 14, 2015, 08:06:35 AM »

Quote from: Stev-o on April 13, 2015, 02:29:12 PM

Check the voltage on your battery, should be 13+V if fully charged.

It will be 13+ immediately after charging. Let it sit for a few hours and then test the voltage to see if it maintains at least 12.6V. f it drops below this then it's probably bad.

However, sounds like by the amount of cranking you are able to do that the battery is not the issue. Are you sure there is spark on all 4 cylinders?

IW

Vinhead1957 · « **Reply #16 on:** April 14, 2015, 08:22:05 AM »

+1 on changing the fuel, remember the bowls. Bad fuel even smells different. More like varnish. The biggest problem with these bikes is fuel, old fuel and the effects of old fuel

njf33 · « **Reply #17 on:** April 14, 2015, 12:50:52 PM »

Yes spark on all 4 cyl. The more I read about the fuel the more im betting on that would make scense sat all winter. Im going to start with that so at least I can rule it out.

mystic_1 · « **Reply #18 on:** April 14, 2015, 04:15:10 PM »

Yeah if the bike sat all winter with only 1/4 tank of gas, it's likely absorbed a bunch of water from condensation during temperature changes, plus it oxidizes "faster" due to the smaller ratio between the exposed surface area and the total volume.

If you top off the tank with good gas that should dilute the bad enough for the bike to run and ride, then you can burn it off. Or, tap it out and dump it into your car's tank where it'll dilute even more. Or run it in your lawn mower, etc.

mystic_1

MoMo · « **Reply #19 on:** April 14, 2015, 09:31:27 PM »

Quote from: njf33 on April 14, 2015, 12:50:52 PM

Yes spark on all 4 cyl. The more I read about the fuel the more im betting on that would make scense sat all winter. Im going to start with that so at least I can rule it out.

Quote from: MoMo on April 14, 2015, 07:28:02 AM

so you have spark, good compression and fuel in the correct ratio? You've eliminated spark, probably has good compression because it ran before, so that leaves fuel. Turn petcock off, drain fuel from carbs and let "fresh" fuel flow in. Should start...Larry

njf33 · « **Reply #20 on:** April 15, 2015, 12:41:35 PM »

Fuel filter clogged drained old gas out of carb changed oil babys purring now. Thanks for all the advice and helped very much appreciated now time for a cruise.