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Author Topic: CB750 Project Chopper (First Build)  (Read 8108 times)

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Offline captaincrash80

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Re: CB750 Project Chopper (First Build)
« Reply #25 on: February 04, 2009, 09:50:31 AM »
Had checked it previously but will re-check
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Offline mystic_1

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Re: CB750 Project Chopper (First Build)
« Reply #26 on: February 04, 2009, 03:36:34 PM »
Observing arcing at the points, and running multimeter tests on components, is all well and good, but personally I'd verify spark at each plug as Alan suggests, by pulling each in turn, re-attaching it's lead, and grounding it to the engine while cranking.  If you have good spark on all four this can save you a lot of chasing around, if not then as they say... "well THERE's your problem" :)


Remember, Fuel, Compression, Spark.  You must have all three.  Compression sounds like it's ok, verify the other two.

mystic_1
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"A ship in harbor is safe, but that is not what ships are built for."
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Offline captaincrash80

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Re: CB750 Project Chopper (First Build)
« Reply #27 on: February 04, 2009, 09:31:46 PM »
Compression: good
Spark: yessir
Fuel: getting to the carbs fine, not draining out of the overflows

My battery is dead right now and a friend is borrowing the charger  :(. As far as I know I'm following the proper procedure for kickstarting (kill switch on, in neutral, etc). What else could I be missing? Wait, that list could be really long......
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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: CB750 Project Chopper (First Build)
« Reply #28 on: February 05, 2009, 12:54:03 AM »
If your battery is dead DEAD vs just temporarily electron challenged then that very well could be part of your problem. A truly dead battery won't allow continuity in the electrical system. I will now yield the floor to TT for his unparalleled electrical expertise  ::)
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As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline captaincrash80

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Re: CB750 Project Chopper (First Build)
« Reply #29 on: February 05, 2009, 05:27:09 AM »
Thankfully the battery is new and not toast  :)
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Offline mystic_1

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Re: CB750 Project Chopper (First Build)
« Reply #30 on: February 05, 2009, 05:31:51 AM »
If it's run down pretty far, it'd still cause problems.  750's have excited-field alternators, no permanent magnets, so they need a half way decent charge in the battery in order to run.

Charge it up and see where that gets you.  If you have a spare car battery lying around, jump it off of that.  Don't use a running car to jump the bike though, may be too much charging current.

mystic_1
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"A ship in harbor is safe, but that is not what ships are built for."
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My build thread:  http://forums.sohc4.net/index.php?topic=68952.0

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Re: CB750 Project Chopper (First Build)
« Reply #31 on: February 05, 2009, 05:47:19 PM »
I had a similar problem with mine. Struggled with it for weeks. Thought it was electrical. Turned out the petcock while turned on was not allowing any fuel through. Even though the my inline filter showed gas in it (so I thought it was getting gas), it wasn't pumping enough into the carbs. Fixed the petcock and it ran like a champ.
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Offline captaincrash80

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Re: CB750 Project Chopper (First Build)
« Reply #32 on: February 07, 2009, 10:48:54 PM »
Quick update:

Checked valve clearances and timing, tried to jump it off my truck battery (truck wasn't running) and still no go. I have spark on all 4 cylinders, there's gas in the carb bowls (just rebuilt the carbs) and even with a shot of ether it still won't go  :(. I'm running out of ideas at this point. Any thoughts would be greatly appreciated. We've had 3 good riding days lately and I'm getting desperate  ::)
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Offline Tim in Ohio

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Re: CB750 Project Chopper (First Build)
« Reply #33 on: February 08, 2009, 06:22:24 AM »
Quote from: captaincrash80 on February 03, 2009, 06:33:59 PM
So I've been trying for the past couple of days to get my engine to fire with no luck. The starter isn't engaging so I decided to just kick it over. That hasn't worked either...

Things I've done so far:
Changed oil
Ran new wires (just the minimum needed to run, will be making a new wiring harness for the final build)
Rebuilt carbs
Cleaned spark plugs

... I also have the points cover off and can see it sparking...

I'm no expert, but here are some of my thoughts:

You have the points cover off and "can see it sparking"??  That doesn't sound good.  Hey smart electrical guys...  should you see sparking under the points cover?  Some sort of short?

Also: You "cleaned the plugs..." If it was me, I would spend a few bucks for some brand new plugs, just to be sure you aren't working with freshly cleaned, bad plugs.

Your carbs looked like total dung to start with.  I have had carbs that to the eye looked clean as a whistle, but needed one more cleaning before they would give it up...  carbs are freakin' finicky.

You said there was a possibility that there had been standing water in the engine.  If I came across a bike as described, I wouldn't expect it to start until I opened up that engine and surveyed the innards for necessary rehab.

Just some thoughts.  I could be full of crap.   :-\
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Offline captaincrash80

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Re: CB750 Project Chopper (First Build)
« Reply #34 on: February 08, 2009, 08:32:40 AM »
Ordered new plugs last night/this morning. Not thrilled about the thought but will prob pull the carbs again tonight and give them another cleaning  :'(. As for the water that could have been in the engine that was kinda a guess b/c of the creamy color the engine had when I drained the old oil. But it looks like I'll be tearing it apart sooner than I thought  :P. At least I've got the vast, unlimited knowledge of this forum to help me out  ;D. Wish me luck!   
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Offline captaincrash80

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Re: CB750 Project Chopper (First Build)
« Reply #35 on: February 11, 2009, 09:13:26 PM »
MAJOR UPDATE:

Finally got my charger back from my buddy, charged the battery up, sprayed some ether in. Didn't get much outta it. Then I swapped the condensors for another set I had lying around, tried again and got a sputter. Then was able to get it to run for about 10 sec (burning off the ether) and then it died. Could this be from the plugs not being up to par? I have a new set ordered that should be arriving any day now. Does the ether have a lower flash point and is therefore easier to ignite? I'm sooooooo excited now that I heard it fire that I can't wait to move forward!!!!
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Offline Tim in Ohio

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Re: CB750 Project Chopper (First Build)
« Reply #36 on: February 11, 2009, 09:21:20 PM »
Somebody smarter than me may have other ideas, but when I have had bad plugs in the past, they wouldn't make the engine "run for 10 seconds"...  I think your carbs are suspect.  Sounds to me like a fuel starvation issue.
Curious... what is this business about "ordering plugs"?  No bike shops in your area?  Usually any motorcyle dealer with a parts counter should be able to hook you up right on the spot out of their inventory.
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1973 Honda CB350  Four

Check out my CB350F resto project...  watch a complete moron build a bike in front of your very eyes!: http://forums.sohc4.net/index.php?topic=38903.0

Offline captaincrash80

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Re: CB750 Project Chopper (First Build)
« Reply #37 on: February 11, 2009, 09:49:39 PM »
Tim:
I ordered them b/c all the money I had available at the time was in paypal  :P. I thought it might be fuel starvation as well, but there seems to be good flow. I can cover the intakes of the carbs with my hand (one at a time) while cranking and it is pulling fuel up through the jets (the fuel come sup onto my hand). Any good ways to test that you know of?
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Offline captaincrash80

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Re: CB750 Project Chopper (First Build)
« Reply #38 on: February 13, 2009, 09:38:24 PM »
Well, after all the problems I had getting the bike to run I finally figured it out. Contaminated fuel. Apparently the gas that was inside my gas can was no longer good. Drained all the fuel, put in fresh and it fired up on the first kick!!!! Going to pick my frame up tomorrow so that I can finish cleaning it up and then the real fun begins  ;D
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Offline mcuozzo

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Re: CB750 Project Chopper (First Build)
« Reply #39 on: February 15, 2009, 05:26:34 AM »
Congrats Captain.  And take comfort in the fact that you probably saved someone (ie me) from going through the same torture.  I'll remember this when (if) I finally get my bike back together.

Now go ride!
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Offline captaincrash80

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Re: CB750 Project Chopper (First Build)
« Reply #40 on: February 15, 2009, 06:19:48 AM »
mcwozzo:

Don't worry man, you'll get it back together  ;D
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Offline captaincrash80

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Re: CB750 Project Chopper (First Build)
« Reply #41 on: March 08, 2009, 01:26:09 PM »
Quick update, finally got the frame repainted, put the motor back in it and made it a roller. Here's a couple of mock-up pics, what do you guys think?



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