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Hello guys and gals. Im will from the wet misserable windy island of ireland. Iv Been riding for years but this bike is braking my heart. I have finaly took the plunge and registered on this fourm as i have been a ghost it the back ground for some time now. So please this is my first post so go easy on me.馃榿.
Right first off i need some help from all ye wonderful people. I got this 1986 vn750 as a project with a blown crankcase. This has been replaced along with clutch plates, gear dampers an the likes. Valves have been reseated, timing is spot on. All marks line up correctly. Ear shave completed on the bike as she was a us import. Carbs cleaned and recieving fuel. The problem im having is when i try to start it. She turns over and over but wont catch. Carbs give a bit of a blow but thats as far as she will go. The concern i have is that when i am turning it over the starter motor stops all of a sudden and theres a clunk when it stops. As if it locks up and stops dead. When i try again it does the same thing. Turns over for a bit and then stops with the clunk. Is this the sign of a bad starter motor and is that why it wont start. Any help very much appreciated.
 

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Welcome aboard!
I've spent a lot of time holding in the start button, and I've never had it 'clunk'. or do anything that I'd describe as a sudden stop. I don't think the starter motor is to blame. Sounds more likely that a valve is interfering with a piston or something. Are you able to turn the crankshaft manually without interference?
 

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Discussion Starter #4
Hi and thanks for the welcome. Sorry for the late reply im still trying to figure out how to work the site. Yes i can turn the crank shaft manualy no problem at all. Im currently as i type this, cleaning the carbs again. So i think the best thing i can do is post a video so you know what i mean. Sorry for the noob stuff but as soon as i have the carbs done i will start it and show you. As for the electrics. From what i can tell everything seems to check out. All lights work where there suppose to all earths have been checked and rechecked. I am at withs end at this point.
 

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Welcome, what shape is the electrical system? Good battery? Sparks? Etc?
Also the battery is brand new. And theres a nice blue spark from all 4 plugs.
all electrics seem to be in good shape. New battery aswell.
Gotcha, if you feel the starter is the issue, Maybe try to push start it? That鈥檚 easier in 2nd gear but the bike needs to be rolling a bit to get it in a higher gear than 1st

Just a thought
 

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First thought was one of the carbs filling the cylinder with gas - hydro lock. Any plugs that are really wet? Oil smells like gas?

Any chance the camshafts got mixed up? Valve timing would be off.
 

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Discussion Starter #9
First thought was one of the carbs filling the cylinder with gas - hydro lock. Any plugs that are really wet? Oil smells like gas?

Any chance the camshafts got mixed up? Valve timing would be off.
the plugs were wet but not drenched. All cams and chains set according to the haynes bible. Its like as if it stops drawing power and just stops dead. Then when i hit the start button again she cranks few a few seconds and stops again. I will be installing the carbs again today after cleaning for the second time. Battery is fully charged also. Could an intermittened starter relay cause this ? I will post a video as soon as i try it
 

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the plugs were wet but not drenched. All cams and chains set according to the haynes bible. Its like as if it stops drawing power and just stops dead. Then when i hit the start button again she cranks few a few seconds and stops again. I will be installing the carbs again today after cleaning for the second time. Battery is fully charged also. Could an intermittened starter relay cause this ? I will post a video as soon as i try it
Wet plugs can point to a flooding carb with a sticking float. If it was the front cylinder, could also be leaking gas though the petcock vacuum line. So check that hose, it should be dry at all times. Gas can leak through there constantly, even on the 'off' setting, this fills the cylinder and crankcase with gas.

Could be a dead spot in the starter armature, but, do you notice the any of the lights brightening as if the current draw dropped? Same applies to bad starter relay. If the light stay slightly dimmer, the starter is still trying.

You can test for a bad starter relay, jump across the two largest terminals, see if the starter cranks normally.

There's another starter relay inside the junction box, those do fail occasionally.

If you keep hitting dead-ends, the battery should be load tested, regardless of age. Is this a wet cell or AGM type?

About the cams - I mean could the cams have been swapped front to rear? The marks can be set, but if the rear cam is in the front, it would never work.
 

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Discussion Starter #11
the plugs were wet but not drenched. All cams and chains set according to the haynes bible. Its like as if it stops drawing power and just stops dead. Then when i hit the start button again she cranks few a few seconds and stops again. I will be installing the carbs again today after cleaning for the second time. Battery is fully charged also. Could an intermittened starter relay cause this ? I will post a video as soon as i try it
Wet plugs can point to a flooding carb with a sticking float. If it was the front cylinder, could also be leaking gas though the petcock vacuum line. So check that hose, it should be dry at all times. Gas can leak through there constantly, even on the 'off' setting, this fills the cylinder and crankcase with gas.

Could be a dead spot in the starter armature, but, do you notice the any of the lights brightening as if the current draw dropped? Same applies to bad starter relay. If the light stay slightly dimmer, the starter is still trying.

You can test for a bad starter relay, jump across the two largest terminals, see if the starter cranks normally.

There's another starter relay inside the junction box, those do fail occasionally.

If you keep hitting dead-ends, the battery should be load tested, regardless of age. Is this a wet cell or AGM type?

About the cams - I mean could the cams have been swapped front to rear? The marks can be set, but if the rear cam is in the front, it would never work.
cams are in the correct places as the rear cams have a grove in them so i no they are fine. I just have the carbs done so i will put them in now and check for all the things you just said. Its a yuasa wet cell battery. Brand new only used to try and start the bike which dies very fast upon trying.
 

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cams are in the correct places as the rear cams have a grove in them so i no they are fine. I just have the carbs done so i will put them in now and check for all the things you just said. Its a yuasa wet cell battery. Brand new only used to try and start the bike which dies very fast upon trying.
If all else fails ... A video of it cranking? Voltage reading before/during cranking?
 

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Discussion Starter #13
cams are in the correct places as the rear cams have a grove in them so i no they are fine. I just have the carbs done so i will put them in now and check for all the things you just said. Its a yuasa wet cell battery. Brand new only used to try and start the bike which dies very fast upon trying.
If all else fails ... A video of it cranking? Voltage reading before/during cranking?
ok just tried it and its the same story. Here is a video of what im on about.
 

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Those starter noises sound pretty weak. Have you tried jumping it from a larger vehicle's battery? (don't turn on the other vehicle if you do)
 

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Does it ever bang loud? Like a backfire? That sounds basically identical to when my battery was starting to die last year.
 

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It sounds ok, but a bit weak rolling over.

Like he said, jump it off a car (not running), just make sure you're getting a good connection. A running car alternator could possibly fry the R/R, but you can hook a 1000 amp bulldozer battery to it and it won't hurt a thing.

It didn't fire once.

Plugs wet or dry after that?

Also as said, backfire is usually a sign of low voltage on this bike. Don't recall any other machine being like that, but this one is for sure.
 

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Discussion Starter #19
It sounds ok, but a bit weak rolling over.

Like he said, jump it off a car (not running), just make sure you're getting a good connection. A running car alternator could possibly fry the R/R, but you can hook a 1000 amp bulldozer battery to it and it won't hurt a thing.

It didn't fire once.

Plugs wet or dry after that?

Also as said, backfire is usually a sign of low voltage on this bike. Don't recall any other machine being like that, but this one is for sure.
it never backfired. Im second guessing myself now as in the timing. I think i might be 180 out which would make the starter be under a lot of strain. I thing instead of going the 305 degrees like the manual said i just rolled back to the marks on the rear cylinder. Big mistake. I dont no why i didnt think of this earlier. Is there an easy way to re ajust the cams on the rear cylinder while the engine is on the bike. I have a bit of space as the bike had the ear shave done so theres no crap in the way..
 

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I thought someone here posted about slipping the chain somehow.
 
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