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post #11 of 40 (permalink) Old 05-26-2019, 12:37 PM Thread Starter
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Also when I turn the key the only light that comes on is the neutral light (green). Is this correct? I thought the red oil light should also come on?
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post #12 of 40 (permalink) Old 05-26-2019, 05:48 PM
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Is there petrol in the carbs loosen the screw on bottom of float bowl see if petrol comes out is the vacuum pipe connected
It could run on one cylinder but it would take some cranking to get it going the rear coil is bolted to the battery carrier a bit fiddly to change but easy
I have sent you a pm with my mobile if you need to chat look in your message's
I live in Leeds Yorkshire
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post #13 of 40 (permalink) Old 05-27-2019, 04:05 AM Thread Starter
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Quote:
Originally Posted by trev uk View Post
Is there petrol in the carbs loosen the screw on bottom of float bowl see if petrol comes out is the vacuum pipe connected
It could run on one cylinder but it would take some cranking to get it going the rear coil is bolted to the battery carrier a bit fiddly to change but easy
I have sent you a pm with my mobile if you need to chat look in your message's
I live in Leeds Yorkshire
Hi,

I've checked the float bowls and both are getting fuel. The amount of hoses on the carbs confuses me a bit, I have 4 in total, 2 are fuel hoses and I think the other 2 are vent hoses. One of the vent hoses was connected to the fuel petcock and the other hose has a bolt in the end of it?? Im trying to start the bike using a auxiliary fuel tank and I've connected the 2 fuel hoses together with a 'Y' piece connector.

I have just read your PM, I really appreciate the offer.

Thanks,

Pete
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post #14 of 40 (permalink) Old 05-27-2019, 04:33 AM
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Each carb has its own inlet the two inner ones that are connected together are the overflow the petrol tap has two outlets one to each carb then on the left carb there is a a short pipe that connects to the petrol tap and on the right carb if that one is blanked of that one is to to do with the US emissions law which you don't really need
I would make sure the engine is turning freely first take a plug out from each cylinder take the little left cover off held on with three crosshead screws and then use a 17mm socket and see if you can turn it anti clockwise freely DO NOT TURN IT Clockwise sorry forgot to say you need to drop the oil to take cover off

Last edited by trev uk; 05-27-2019 at 04:48 AM. Reason: Add text
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post #15 of 40 (permalink) Old 05-27-2019, 03:28 PM Thread Starter
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Originally Posted by trev uk View Post
Each carb has its own inlet the two inner ones that are connected together are the overflow the petrol tap has two outlets one to each carb then on the left carb there is a a short pipe that connects to the petrol tap and on the right carb if that one is blanked of that one is to to do with the US emissions law which you don't really need
I would make sure the engine is turning freely first take a plug out from each cylinder take the little left cover off held on with three crosshead screws and then use a 17mm socket and see if you can turn it anti clockwise freely DO NOT TURN IT Clockwise sorry forgot to say you need to drop the oil to take cover off

Hi,

Tonight I drained the oil and took out each spark plugs individually and manually turned the engine anticlockwise. The good news is I was able to turn the engine. The engine was hard to turn, then a bit easier to turn, then hard to turn ... etc etc. Im presuming this is normal and relates to the pistons moving up and down?

Not sure what the next step should be? Ive ordered another coil to get the rear 2 spark plugs sparking, from there I guess I will need to buy a new battery? I read somewhere the vn750 needs at show atleast 10V when the start button is pushed - is this correct? I get just under 10v at the moment.

Also, im now getting fuel showing on the spark plugs

Thanks,

Pete
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post #16 of 40 (permalink) Old 05-28-2019, 12:49 AM
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Quote:
Originally Posted by calebj View Post
It's okay, you gave Jerry his needed excuse to copy paste his massive experience that his inexplicably led to a complete inability to work on many things.
Just because you can work on some things doesn't mean you can work on everything. I really have no doubts I could disassemble and reassemble a VN750 engine. But like I said, there are a lot of things in it that can't be checked, like in a car engine, and a lot of parts that if they are found to be worn beyond spec, would cost a fortune to replace. If anybody plans to rebuild a VN750 engine, I suggest watching ALL of Andrew Roth's videos (he was known as Roach on here. Don't know what ever happened to him. I located his videos on YouTube.

https://www.youtube.com/results?sear...h+vn750+videos.

He never checked the crank or con rod bearings in those videos, he just assumed (or maybe hoped would be a better term) that they were ok. Simply taking an engine apart and putting it back together is not rebuilding it. EVERY single thing must be checked and either found to be within tolerances or replaced, and the design of the Vulcan 750 engine makes that extremely cost prohibitive (which is the case with all Japanese motorcycle engines, it's just that the VN750 has about twice as many parts as the average Japanese v-twin. Way back in 1969, the first CB750 was the first motorcycle engine that was cheaper to replace than rebuild. Before that most motorcycle engines were designed to be rebuilt.

First make sure you are getting fuel to the carbs. Open the drain screw on each one and see if there is gas in the float bowls. The VN750 carbs do not have an accelerator pump, so you may not be getting enough liquid gas into the cylinders to wet the plugs if it doesn't turn over for very long.

All Vulcan 750s turn over slowly, it's just the way they are, but they should continue to turn over. And yes, you should be able to get it to fire on only one cylinder. Another quirk the Vulcan 750 has is after sitting for some time with gas left in the carbs, it will sometimes start up on the front cylinder, and it can take some time for the rear cylinder to kick in. I have no idea why it does this. But if you have spark, compression, and a close to correct air/fuel mixture, then the front cylinder should at least fire. The rear coil is not difficult to replace. A car battery, fully charged, has way more than enough power to start a Vulcan 750. It sounds like you may have some electrical issues. The oil light should also come on. I could have sworn on my 2002 the headlight did not come on until the engine started, but on my newly purchased 1997, the headlight, tail light, and all the instrument lights come on with the key in the on position. It still starts up ok.

There are 2 large hoses that go from the petcock to the carbs. These are fuel lines. The Vulcan has a vacuum operated petcock. The small hose that goes from the front carb is just to supply vacuum to the petcock. The small hose on the rear carb is part of the PAIR (emissions system) which has probably been removed, and it should be plugged up. Oh, there is one more hose that connects to the carbs. That is the float bowl vent. The two carbs share a common float bowl (somewhat unusual) and on a stock bike that vent is plugged into a hole in the right air filter housing.

With the plugs out, there will be no compression, so there should be no change in resistance when turning the engine over by hand. It should turn easily all the way around. I wonder is something is binding inside the engine, making it harder than it should be to turn over. That could overload the starter, make it turn slower, and pull more power than it is supposed to from the battery. It would also make the starter motor get really hot, and I would think it should eventually blow a fuse. The starter is not connected to the engine, so it would have nothing to do with how it feels when turning it over by hand. It sounds like, for some reason, a problem is causing your engine to be harder than normal to turn over.

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike
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post #17 of 40 (permalink) Old 05-28-2019, 02:45 AM Thread Starter
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Quote:
Originally Posted by VN750Rider/Jerry View Post
Just because you can work on some things doesn't mean you can work on everything. I really have no doubts I could disassemble and reassemble a VN750 engine. But like I said, there are a lot of things in it that can't be checked, like in a car engine, and a lot of parts that if they are found to be worn beyond spec, would cost a fortune to replace. If anybody plans to rebuild a VN750 engine, I suggest watching ALL of Andrew Roth's videos (he was known as Roach on here. Don't know what ever happened to him. I located his videos on YouTube.

https://www.youtube.com/results?sear...h+vn750+videos.

He never checked the crank or con rod bearings in those videos, he just assumed (or maybe hoped would be a better term) that they were ok. Simply taking an engine apart and putting it back together is not rebuilding it. EVERY single thing must be checked and either found to be within tolerances or replaced, and the design of the Vulcan 750 engine makes that extremely cost prohibitive (which is the case with all Japanese motorcycle engines, it's just that the VN750 has about twice as many parts as the average Japanese v-twin. Way back in 1969, the first CB750 was the first motorcycle engine that was cheaper to replace than rebuild. Before that most motorcycle engines were designed to be rebuilt.

First make sure you are getting fuel to the carbs. Open the drain screw on each one and see if there is gas in the float bowls. The VN750 carbs do not have an accelerator pump, so you may not be getting enough liquid gas into the cylinders to wet the plugs if it doesn't turn over for very long.

All Vulcan 750s turn over slowly, it's just the way they are, but they should continue to turn over. And yes, you should be able to get it to fire on only one cylinder. Another quirk the Vulcan 750 has is after sitting for some time with gas left in the carbs, it will sometimes start up on the front cylinder, and it can take some time for the rear cylinder to kick in. I have no idea why it does this. But if you have spark, compression, and a close to correct air/fuel mixture, then the front cylinder should at least fire. The rear coil is not difficult to replace. A car battery, fully charged, has way more than enough power to start a Vulcan 750. It sounds like you may have some electrical issues. The oil light should also come on. I could have sworn on my 2002 the headlight did not come on until the engine started, but on my newly purchased 1997, the headlight, tail light, and all the instrument lights come on with the key in the on position. It still starts up ok.

There are 2 large hoses that go from the petcock to the carbs. These are fuel lines. The Vulcan has a vacuum operated petcock. The small hose that goes from the front carb is just to supply vacuum to the petcock. The small hose on the rear carb is part of the PAIR (emissions system) which has probably been removed, and it should be plugged up. Oh, there is one more hose that connects to the carbs. That is the float bowl vent. The two carbs share a common float bowl (somewhat unusual) and on a stock bike that vent is plugged into a hole in the right air filter housing.

With the plugs out, there will be no compression, so there should be no change in resistance when turning the engine over by hand. It should turn easily all the way around. I wonder is something is binding inside the engine, making it harder than it should be to turn over. That could overload the starter, make it turn slower, and pull more power than it is supposed to from the battery. It would also make the starter motor get really hot, and I would think it should eventually blow a fuse. The starter is not connected to the engine, so it would have nothing to do with how it feels when turning it over by hand. It sounds like, for some reason, a problem is causing your engine to be harder than normal to turn over.
Thanks for all this info, it is much appreciated.

I'm definitely getting fuel to the float bowls and the plug ends are now 'wet' so that issue is resolved. The hoses that should be on the float bowl vents have been removed for some reason.

It sounds like my findings aren't as good as I'd hoped. What is the most likely cause of the binding (I still suspect the bike overheated as the coolant is a brownish colour)? Or is it a case of it could be anything? Any advice on where to look next would be much appreciated. I am by no means a mechanic but I can carry out maintenance works and have rebuild top ends on 2 stroke dirt bikes - I appreciate this engine will be a completely different kettle of fish but I'm happy to try and learn

Also, I will take a closer look at the oil light - hopefully its as simple as a blown bulb!

Thanks,

Pete
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post #18 of 40 (permalink) Old 05-28-2019, 10:37 AM
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Pete with the plugs out and in neutral you should feel very little resistance if it goes tight in places I think there is something a miss in the engine if you try and start it with a decent battery you could do more damage if you are not going to do anything with it if its goosed fine give it a go but if you are I would take the engine out and start investigating
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post #19 of 40 (permalink) Old 05-28-2019, 11:01 AM Thread Starter
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Originally Posted by trev uk View Post
Pete with the plugs out and in neutral you should feel very little resistance if it goes tight in places I think there is something a miss in the engine if you try and start it with a decent battery you could do more damage if you are not going to do anything with it if its goosed fine give it a go but if you are I would take the engine out and start investigating
Hi Trev,

Just checking, I took each plug out individually (I.e I had 3 plugs in each time I manually turned it). Was I supposed to take all 4 out at the same time and then try and manually turn it?

Thanks,

Pete
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post #20 of 40 (permalink) Old 05-28-2019, 11:23 AM
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Phew that's good news take them all out and try it again let me know
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