Originally Posted by VN750Rider/Jerry
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-Boulevar.../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 =)