Hello again folks, having a bad day today. Have a 82 VF750C that was given to me. As we all know there is no such thing as a free bike! Have been fighting this issue for quite a while now. Bike will start but acts like it is dumping raw fuel into the front two cylinders. Needless to say I have checked compression, which checked fine and also have had the carbs off and cleaned 3 times. Found some carb diaphragms with help from your previous responses and made no difference even tho I know 2 were bad. This thing blows so much rich smoke that I could farm it out as a mosquito fogger. I guess my question is, what are the differences in parts between the downdraft and sidedraft carbs? The reason I ask is that the previous owner had the carbs apart before I got it and it wouldn't shock me if parts have been switched between carbs. Also, is it possible the fuel pump is forcing fuel past the float needles? There is nothing found in the manual about how the fuel pump should actually work, much less a fuel pressure check. I do know that even with the new diaphragms the front two cylinders carb slides do not appear to move with throttle input when looking down the velocity stacks with the engine running. The rest of the bike is in pretty good shape considering the years, but if I can't get this sorted out I am reluctantly considering parting her out. I hate to do that with a vintage bike! Anybody run into anything like this before?
Well we will do our best to help are you trying to run her with out the airbox in place because these bikes just will not run very good with out it in place :-? and I would think the pump would not force fuel past the needles because it would fill your bowl first and that would cause fuel to come out other places not good either but could fill the bowl and come out the vent passage causing it too flood down the cylinders and cause that problem I would say that you could find another set of carbs on Ebay easy enough. How did the float needles look did you have them out were the rubber tips soft or pliable did they have a circle worn in them thats where I would start !!!
Needle and seats appeared good with no wear pattern in evidence. I may try to find a set of carbs on Bay or does anyone have any experience with rebuilders? I've been working on bikes since I was a kid and am also a licensed aircraft mechanic and this is the first time I have ever been stumped on something this long. Frustration does not even begin to describe it right now. Thanks a lot for your posts and help!
Oh yeah,I was running without the airbox lid in place today but previously everything has been bolted up and still having issues.
What you describe is exactly what I had going on with an '88 Super Magna I was rebuilding. Had the carbs off more than once. The problem was not corrected until I replaced the floats, needle valves and valve seats. The needle valves themselves looked absolutely fine, but the bike had been sitting for years, & I suspect that the seats had developed pits, etc that the fuel was leaking by. This occurred on the Front left cylinder which would have been the last carburetor to have gone dry during its long storage. Just my experience. Hope you can diagnose your problem. Please let us know what you find.
I'm with Trapper on this one, floats, needle valves and valve seats should get you back in the saddle. The worst thing that can happen to a bike is it sit and not be ridden; it's a long hard road back to running right after the carbs gum up. Don't give up on her though, with a little TLC and a shop service manual it will be up and running in no time.
That is what I tell people garage dust is the number one killer of a bike. :lol:
Quote from: Magnum Magna on April 28, 2008, 10:39:02 PM
That is what I tell people garage dust is the number one killer of a bike. :lol:
Without a doubt. I've saved 2 now from possible extinction
Okay guys, I will not give up. I will save up my pennies and go for the new needles/seats. It makes perfect sense to me but the darned things looked in great shape. However your experience sure outshines mine with the Magnas and your advise is taken to heart. Will update with results as soon as I get her back together. Thanks so much for your input and support!