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At withs end with this bike

5K views 33 replies 7 participants last post by  One1 
#1 ·
Hey guys as most of you no i had a starting problem after the engine rebuild. It turns out the timing was off. So timing has been adjusted to a T. Carbs cleaned, plenty of fuel. Plenty of spark. Battery fully charged even tried jumping it off a freshly charged car battery and still wont start. All connections checked and rechecked. All grounds sand shiney and tightened. Still nothing. It wont even fire with starter fluid. Its cranks and cranks but just wont catch. Anyone on here got any ideas on what could cause this. Everything is working as it should. Im at breaking point with this and im close to parting it out.
 
#4 ·
Was it the cam timing?

Maybe a compression check? Seems that with everything there, you should get at least a nice ka-boom once in a while.

No rats nest, or air filter foam, blocking the air intake?
i havo no way of checking ignition timing at all. There is only 19000 original miles on the bike and from what i can gather without a guage there is compression there. The timing is spot on 305* degrees on the rear as instructed by the service manual. How would i go about checking the ignition timing. And if all else fails i think a rebore is the last option on this.
 
#3 ·
Was it the cam timing?

Agree about the spark and pressure. What color is the spark?

Maybe a compression check? Seems that with everything there, you should get at least a nice ka-boom once in a while.

No rats nest, or air filter foam, blocking the air intake?
 
#10 ·
I know it sounds crazy but, I have a 19hp B&S engine on my wood splitter it was running fine. I welded something on it and when I tried to start it, I got nothing. I changed everything I could think of. I remembered I didn't change the spark plugs. put new plugs in and bingo!!! You might try a set of plugs.
 
#11 ·
Sound advice however the plugs i have are brand new. They were the first thing i could rule out. There is only 4 things left i can try. Starter rebuild, new carb rebuild kit, switch pickup coils like spokster said and a rebore. After that i am out of options as everything else checks out..
 
#13 · (Edited)
Yes, they look reversed. A bit hard to see the colors in the pic, but I can tell the black/yellow wire is in the wrong place.

According to the repair manual: VN750_Vulcan_Service_Manual_Parts_Catalogue

Rear cylinder wire colors: black/white and black/red at the top position (rear cyl)

Front cylinder wire colors: black/yellow and black at the bottom position (front cyl)

Swap them around and it's gonna start right up! :)
 
#18 ·
Do you have a voltmeter to read the battery voltage? It could be weak by now if hasn't been charged at all.

Is there any chance the cam timing is still off?

How long did it run while holding the start button? Would it rev up, or just fired a bit more? How well was it running? The start button has a wire connected to the CDI box, consensus here is that it alters the ignition timing during starts. (could be the reason for backfire on low voltage starts)
 
#19 ·
No i dont have a voltmeter. However the battery was not fully charged but i did connect to a car battery. As for cam timing, i set it exactly to the instructions in the downloadable manual. It only ran for a few seconds as i didnt want to keep the start button pressed to long and damage the motor. It would not rev at all. Do you think it could be to do with the cdi box?. I will fully charge the battery today and see was that the problem. So plan today is clean plugs, drain carbs (just incase), fully charge battery, recheck all connections and im also trying to locate a gauge to measure compression. Fingers crossed.
 
#20 ·
Can't rule out the cdi yet. Not sure what tests there are for it, check the manual.

You have decent spark, but is it at the correct time.

Something about the start button, it means something, but on this system I'm not sure what. That symptom has been mentioned here before, but I'm not sure if anyone ever posted their fix. Never hurts to try the forum search.

Sometimes on old points ign systems, running only in the start position, meant a defective ballast resistor. But the ballast resistor on those old systems was there to keep the points from getting more than 9v, to reduce burning of the contacts. Could be something similar happening in the CDI, because there is that white/red wire between the start button and the CDI. The ignition timing could be going numb when you release the start button.
 
#21 ·
i will definatly check out the start button. Im sure i seen a few posts on that somewhere here. I tried it again today. Fully charged the battery, cleand the plugs, and drained the carbs. Got some backfire again. Then after several tries she finaly fired up. However it would not fire with the choke on. I had to keep twisting the trottle to keep her alive. As soon as i stopped reving it cut out. I played around with the mixture screw which led to it firing in the first place then when i played with mixture screw again it would not fire. Im thinking now more on a fuel issue than mechanical. It started and thats a huge step in the right direction.
 
#30 ·
I've found that soaking in white vinegar does wonders for jets.

I left a couple of wrenches soaking two weeks, forgot about them. The rust was gone, but so was the chrome. /forum/images/smilies/icon_biggrin.gif
lol sounds about right. Done the same thing myself 😂. Right the only thing i can think of that i didnt clean was the jet on the bottom right in the picture. I was unable to get it out. Which jet is this and is it suppose to come out?
 

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#33 ·
Have you managed to get it started yet? Did you move the stator when you had the motor open? I ran into a similar issue when I reinstalled the stator with the wrong orientation which meant the ignition timing was completely off
 
#34 ·
These bikes will test you. Lol. If i knew then what i know now after building VN750’s for 10 years I probably wouldn’t have bought it. Lol. The good news is that you’ll eventually learn what each things makes it act like and you’ll Be able to fix it by ear. :) at this point i usually don’t have to touch it to know what’s wrong, but even now I still get surprised by the bike with quirky things it does.
 
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