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Discussion Starter #1
Hello! So lately my bike has been getting maybe 25-35 miles to the gallon, usually making me stop to refill at about 65 or 80 miles. I don't see any noticeable leaks, and the bike has smoke on startup that goes away pretty quickly. Also, when hot, if I turn her off she'll refuse to start up again until a very loud backfire occurs, then she'll start up a few turns after. Any ideas gentlemen?
 

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Check the petcock vacuum line after running a bit. If it's wet, that's a problem. Oil smells like gas?

If I open the throttle on a hot start, it will backfire every time. Sometimes it needs choked just stopping long enough for gas.
 

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Discussion Starter #3
Vacuum lines are dry, oil smells like regular oil, but I may have messed up with choking on hot starts. Friend of mine said it may be the valve stem seals but I'm really trying to avoid having to try to get the engine off as I'm a parking lot mechanic lol.
 

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Valve seals? For which problem?

If it's not running rich for some reason, see if the front brakes are dragging after being applied. Rear brake too for that matter.

Is it down on power? Running on both cylinders? 65 miles to reserve, that's about half the mpg as normal.
 

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Discussion Starter #5
From what I can tell, she's running on both cylinders. Both pipes are hot, and no loss of power is noticed, as I used to have to deal with single-cylinder running quite often (wrong petcock issue there, fixed now haha). I haven't checked the brakes though, but you're right, it isn't running rich or smoking while running so the gas usage shouldn't be so dramatic. I've seen this bike get at least 125 miles before a fillup before, and that was at a 1/4 of a tank, so I'm not sure what's up. I'll take a look at the brakes later tonight and fill it up to keep track of it again.
 

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Let's check simple stuff first:

Air Filters ok?
Run a healthy dose of SeaFoam in the tank.
Is it good gas and not from a mom-n-pop store?
Drain the carbs.
Brakes not dragging?
All plugs firing?
Air pressure in tires good?
Oil good and at correct level?
 

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All plugs firing?
I second this!
I had a bad plug wire that was grounding on the cylinder head. It was only firing one plug. I was new to the bike and didn't know what it should have felt like. It sounded almost normal, and both pipes were hot.

This bike runs 5-25 degrees of timing advance. My truck (1 plug per cylinder) runs 14-45 degrees. Losing a plug is like retarding the timing by 10-15 degrees!
 

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There are only so many possibilities here. Did this happen all at once? Has anything else changed? The gas has to be going somewhere. It is either running really rich (check the plugs) it is leaking, either outside or inside the engine (check and see if thee oil level has gone up) or something is putting a huge load on it. It is not likely the brakes. They would have overheated and failed fairly quickly, though you can put the bike on the centerstand and spin the wheels and see if they turn easily. Since you have smoke on startup, hard starting, and backfiring, I'd say it is probably running too rich. Mine has hit 35 mpg at 80 mph on the freeway many times, but goes back up to around 50 mpg when I slow down to around 65 mph. How fast are you riding?
 

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We did have a poster recently with a collapsed front brake hose holding pressure. When this happens, the brake can stay applied for a varying period of time after the lever/pedal is released. One application of of the brake starts the process over.
 

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That can certainly happen, but I have never seen a collapsed hose. I have seen the return hole in the master cylinder get plugged up and not release pressure. This is fairly common on bikes where the brake fluid never gets changed.
 

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That can certainly happen, but I have never seen a collapsed hose. I have seen the return hole in the master cylinder get plugged up and not release pressure. This is fairly common on bikes where the brake fluid never gets changed.
I've seen so may collapsed hoses, I've lost count. More common on autos, probably because the hoses are lesser quality. But you'll never actually see one, since they collapse internally, unless you want to strip the hose apart. .... then you still may not 'see' it, it takes pressure to produce the collapse.

We had a poster last month with a plugged return hole in the MC holding the brakes on. Way back, we had someone with the rear brake dragging. https://www.vn750.com/forum/gtsearch.php?q=rear brake dragging
 
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