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To the original poster. Since the carbs are an unknown, I would go ahead and pull them, disassemble them, and clean them out good. Yes it's a real PITA, definitely not an easy job unless you've done it many times, but if you clean them right, it is a one time thing. From then on, use Seafoam every once in a while to keep them clean, and if the bike is going to sit for more than a couple of weeks, use the drain screws to drain all the gas out of the float bowls. If you have a choice, use real gas, rather than the gas/moonshine mix most places are selling.

While you have the carbs off, you can check them and the manifolds (the rubber parts between the carbs and heads) for damage. Sometimes after many years, the manifolds can deteriorate and develop cracks. Look everything over, and put it all back together carefully. The best way I have found to check for air leaks, and the least messy, is to use a propane torch (unlit), open the valve, and hold it around the carbs and manifolds. If there is even a slight leak, the engine will suck in the propane, and idle speed will go way up. Be aware that to affect running to any noticeable degree, the air leak would have to be in the carbs themselves, the manifolds, or manifold connections. An air leak on the air filter side of the carbs will not affect running, though it can let dirt into the engine. In fact, the engine will run just fine without the filters, though it might be a little on the lean side. Check the carb vents, and make sure you are getting gas to the carbs.


I would definitely check the splines, like, right now. That is the biggest weak point of the VN750, and it seems to affect ALL VN750s. The factory never lubed them right in the first place, and if they are damaged, you have a very big (expensive) problem.

Are you sure the pipes were red? The Vulcan 750 has double wall pipes, and for the outside pipes to get red would be almost impossible. I would almost think the aluminum engine would melt first. My pipes never even yellowed, even after 80,000 miles. And it is definitely NOT a good idea to run the engine at high rpm without a load on it, that is, actually riding it. Revving it really high in neutral for more than a second or so can do some serious damage.
 

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Discussion Starter #22
Well I took my carb apart to make sure it wasnt that and let me tell you that sea foam works great! That baby was absolutely pristine! So it wasnt a dirty carb which leads me to believe it's a air problem. So my question is what should I replace and where can I find it, having trouble finding parts!
 

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Discussion Starter #23
yes, didn't seem to help very much. however, since i took off the carb and saw how it actually works, i have a better idea of how to adjust it and will try that when i put the carb back on, which i might do later today if I'm feeling up to it =)
 

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Discussion Starter #24
well it was at night....but yeah they were cherry lol guesse I'm lucky i didn't damage anything...guesse thats another kudos to the engine maker huh? that v twin is something else
 

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Discussion Starter #26
well he seems to know what he's talking about. I've known people like your describing, which is why i got on here to pick peoples brain. Its especially nice that everyone here has the same bike! Gotta love technology. Anyways, he's said the same things everyone on here has said so far, I just wanted to check his opinion against some other peoples before I started working on my first vehicle with no previous bike mechanical experience =)
 

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Backlash, if you will use the quote function/button, we can more easily understand whose post you are replying to.
 

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$550 ... damn ...
Sounds like you have good mechanic skills. Since it is winter (I am assuming you are in the northern hemisphere) I think I would take the time to remove the carbs and go through them. Clean the jets and all the other little holes, check the air cutoff diaphrams, and other rubberized stuff, including the mounting boots. After back together, I would set sync with a cheap length of clear tubing and some transmission fluid. If you don't already have a service manual, I think there is one here on the site somewhere. I suppose it's a 'rule everything out at once' approach. I know if I did it, you can ... Good luck, that was a great deal !!!
 

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Discussion Starter #30
$550 ... damn ...
Sounds like you have good mechanic skills. Since it is winter (I am assuming you are in the northern hemisphere) I think I would take the time to remove the carbs and go through them. Clean the jets and all the other little holes, check the air cutoff diaphrams, and other rubberized stuff, including the mounting boots. After back together, I would set sync with a cheap length of clear tubing and some transmission fluid. If you don't already have a service manual, I think there is one here on the site somewhere. I suppose it's a 'rule everything out at once' approach. I know if I did it, you can ... Good luck, that was a great deal !!!

yeah, i'm not bad with a wrench....only thing is, i'm having trouble putting the darn carb back in....i'm not sure which side goes where. I know they're labeled front and rear, but when i put them in that way it looks like my acceleration and deceleration cables aren't going to reach the carb the right way..if you or anyone else has a picture of their carbs from both sides, relatively close up, that would be a tremendous help. I'm in Florida btw, all year riding down here, whooo! Once I get her running properly anyway.
 

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I believe member Crobins365 has (had?) a bunch of carb pics in her gallery. I just tried to access them and couldn't find them. Maybe you will have better luck!
 

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I added a photo album that has a pictures of the left and right views of the carburators when they are mounted on the bike. Hope that helps.
 

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Discussion Starter #33 (Edited)
To the original poster. Since the carbs are an unknown, I would go ahead and pull them, disassemble them, and clean them out good. Yes it's a real PITA, definitely not an easy job unless you've done it many times, but if you clean them right, it is a one time thing. From then on, use Seafoam every once in a while to keep them clean, and if the bike is going to sit for more than a couple of weeks, use the drain screws to drain all the gas out of the float bowls. If you have a choice, use real gas, rather than the gas/moonshine mix most places are selling.

While you have the carbs off, you can check them and the manifolds (the rubber parts between the carbs and heads) for damage. Sometimes after many years, the manifolds can deteriorate and develop cracks. Look everything over, and put it all back together carefully. The best way I have found to check for air leaks, and the least messy, is to use a propane torch (unlit), open the valve, and hold it around the carbs and manifolds. If there is even a slight leak, the engine will suck in the propane, and idle speed will go way up. Be aware that to affect running to any noticeable degree, the air leak would have to be in the carbs themselves, the manifolds, or manifold connections. An air leak on the air filter side of the carbs will not affect running, though it can let dirt into the engine. In fact, the engine will run just fine without the filters, though it might be a little on the lean side. Check the carb vents, and make sure you are getting gas to the carbs.


I would definitely check the splines, like, right now. That is the biggest weak point of the VN750, and it seems to affect ALL VN750s. The factory never lubed them right in the first place, and if they are damaged, you have a very big (expensive) problem.

Are you sure the pipes were red? The Vulcan 750 has double wall pipes, and for the outside pipes to get red would be almost impossible. I would almost think the aluminum engine would melt first. My pipes never even yellowed, even after 80,000 miles. And it is definitely NOT a good idea to run the engine at high rpm without a load on it, that is, actually riding it. Revving it really high in neutral for more than a second or so can do some serious damage.
Well, let me correct myself, and use the quote button so people know what I'm replying to =). The outside chrome part was not red, just the actual inside pipe. Not the cover. On the right hand side of the bike that exhaust pipe looks like oil does on water, if that makes any sense. And it didn't look like that before. I guess thats me bluing the pipes or some such? I'm planning on getting a different exhaust anyway, thinking of going with this one http://www.amazon.com/Cobra-Boulevard-Slashcut-Motorcycle-KAWASAKI/dp/B000I592V0 but yeah, when I was revving the engine to try and get the carb cleaner through it ( bad idea i know that now) it was also backfiring some, since it was at night i could actually see small flames coming out. So I have a short series of questions that if someone could answer i think i might be a little closer to figuring this out. Also, i checked on all my boots and hoses, not just for air, but on the entire bike, and every hose is still very flexible, no corrosion or cracking or any wear at all really so I'm kinda doubting it would be a vacuum leak.

1. What causes your pipes to blue or get that strange look on them?
2. Would improperly adjusted air mix screws cause backfiring and poor low rpm/idle running?
3. Would a carb sync fix backfiring or poor idle?
4. Could it possibly be a burnt valve or valve seal? It doesn't even think of dieing at high rpms with the choke off btw. Just wondering (and praying its not)
5. And just out of curiosity, how do i get to the splines and where are they exactly o_O? Once I get there, what do i use to lube them properly? Oil, grease, gear oil like on a manual transmission (still have some from the one i just overhauled) and if its any kind of oil or fluid, is there a particular viscosity?

Anyone got an answer feel free to enlighten me, I'm very eager to figure this out and get my baby running. Then I can move on to the fun part. Cosmetics =)
 

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1. I've heard too lean a fuel mixture leads to blue pipes. Others may know more.

2. Backfiring on decelleration is normal for these bikes. If you ease off the throttle, it doesn't backfire as much. You can "marble" or "coaster" the engine to eliminate or greatly reduce the backfiring. Do a search for these procedures here and it should explain what is needed.

3. If the carbs are clean (many aren't) and it runs rough, it might need to have the carbs synched, but unless someting was done to the carbs, they should be synched already.

4. More than likely, the carbs need cleaning. Here's a good place to have it done at a good price if you don't want to tackle it yourself: http://www.carbworx.com/

5. Click on the Search button on the tool bar toward the top of this page. Type in Fergy under Member Search. Go to one of his posts and click on the spline lube procedure in his signature. Use a grease/paste with at least 60% moly content, such as Honda Moly 60 or Guard Dog Moly.
 

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Excessive heat is what 'blues' the pipes. There's combustion in the pipe. If the bike has not been 'marbled/coastered', by design, there is fresh air being delivered to the exhaust through the stock emission equipment. This fresh air can mix with the unspent fuel and burn in the pipe. As FliteControl said, coastering, and setting the fuel mix slightly richer will mostly eliminate this occurrence. Secondly, I would definitely check compression for a valve timing or closure problem. Excessive heat is one thing, but glowing red is an entirely different level.

Any time you remove the carbs, you should sync them as soon as the bike is running again. My 2 cents.
 

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Discussion Starter #36
1. I've heard too lean a fuel mixture leads to blue pipes. Others may know more.

2. Backfiring on decelleration is normal for these bikes. If you ease off the throttle, it doesn't backfire as much. You can "marble" or "coaster" the engine to eliminate or greatly reduce the backfiring. Do a search for these procedures here and it should explain what is needed.

3. If the carbs are clean (many aren't) and it runs rough, it might need to have the carbs synched, but unless someting was done to the carbs, they should be synched already.

4. More than likely, the carbs need cleaning. Here's a good place to have it done at a good price if you don't want to tackle it yourself: http://www.carbworx.com/

5. Click on the Search button on the tool bar toward the top of this page. Type in Fergy under Member Search. Go to one of his posts and click on the spline lube procedure in his signature. Use a grease/paste with at least 60% moly content, such as Honda Moly 60 or Guard Dog Moly.
I already cleaned the carb I'm in the process of putting it back in but it was pristine whew I took it apart so I'm not sure if the problem was fixed guesse I'll find out soon lol
 

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If you still have problems, try starting a new thread in the applicable section of the forum. You'll probably get more responses there.
 

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Here is the link to Crobins external carb pics from the stickey thread at the top of the *Carbs and Fuel* forum.
http://www.vn750.com/photopost/showgallery.php?cat=548

"Marbleing" or "coastering" the exhaust header cuts off fresh air which causes unspent fuel to burn in the pipes. This is the source of the popping upon deceleration. You probably still need to richen the air/fuel mixture to eliminate/reduce further the popping, as the factory setting is only 1 5/8 turns of the screw out from the seat. See picture above for location. The a/f mixture screw is covered by a metal cap or plug, which needs to be removed in order to adjust the screw out further. Usual a/f adjustment fix seems to be from 2 1/2- 3 1/2 turns out maximum. Only 5 turns until screw falls out, so seal screw in place with dab of silicone sealant to retain setting and avoid loss of screw.

Link to fergy`s spline lube write-up and pics.
http://pages.tstar.net/~fergy/writeups/final_drive1.html
 

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Discussion Starter #39
If you still have problems, try starting a new thread in the ok applicable section of the forum. You'll probably get more responses there.
Ok will do thank your advice and sharing your knowledge and experience, along with everyone else, its given me a much better idea of what to do.I'll move this to the appropriate section and list everything I've fine so far may even be able to include a sound clip of what its doing
 
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