Author Topic: Terrible gas mileage ... like 40 miles to the TANK ... (Read 5667 times)

larryblevinson · « **on:** July 17, 2010, 05:10:28 PM »

So, I replaced the stock muffler on my '76 CB750A with a resonator exhaust tip, which makes it a bit louder and throaty. I went out today to ride up through New Hope, Pa., and back through Frenchtown, NJ, filling up once along the way. On the way home, it actually ran dry and I coasted into a gas station. Since I am very new to this type of maintenance, where do I go for instructions on tuning it to the new exhaust system. It runs with power when it has fuel. What to check first, second, and third? Thanks.

Raef · « **Reply #1 on:** July 17, 2010, 06:50:32 PM »

I would be keeping a close look out for leaks watching the over flow tubes, it seems the bike would be running poorly if all that gas was running through the motor

scrapvalue · « **Reply #2 on:** July 17, 2010, 07:16:09 PM »

When you open up the exhaust the way you did, it will make the bike run leaner, not richer.
I second the idea of checking for leaks.

vern401 · « **Reply #3 on:** July 17, 2010, 09:25:41 PM »

turn the petcock on and give it a few minutes to fill the bowls.
Look all around the engine and under the bike for gas leaking out someplace.
If the overflow tubes are connected you may have gas comming out near the rear tire.

MCRider · « **Reply #4 on:** July 17, 2010, 10:13:51 PM »

Did it really run dry or is there still gas in the tank and the petcock filter stand is clogged?

If really empty, gotta go with the leak theory and not your pipe.

larryblevinson · « **Reply #5 on:** July 17, 2010, 10:14:56 PM »

Quote from: scrapvalue on July 17, 2010, 07:16:09 PM

When you open up the exhaust the way you did, it will make the bike run leaner, not richer.
I second the idea of checking for leaks.

Really? I would have thought that reducing the back pressure would make it suck up more ... but, obviously, I have no idea what I am talking about, so I really appreciate the assistance. I love the Internet. Video to come.

larryblevinson · « **Reply #6 on:** July 17, 2010, 10:16:15 PM »

Quote from: MCRider on July 17, 2010, 10:13:51 PM

Did it really run dry or is there still gas in the tank and the petcock filter stand is clogged?

If really empty, gotta go with the leak theory and not your pipe.

I must have put in 8 gallons to go about 80 miles today.

w1sa · « **Reply #7 on:** July 17, 2010, 11:03:46 PM »

I think the resonator fitment is largely/mostly coincidental to your consumption problem.

If you dont find significant leakage, which would seem unavoidable since you seem to be using more than 4 times the normal usage rate, I would do a tune-up procedure including filter, valve adjustment, cam chain adjust., timing and ignition (spark) performance.

MCRider · « **Reply #8 on:** July 17, 2010, 11:15:17 PM »

Quote from: larryblevinson on July 17, 2010, 10:16:15 PM

Quote from: MCRider on July 17, 2010, 10:13:51 PM
Did it really run dry or is there still gas in the tank and the petcock filter stand is clogged?

If really empty, gotta go with the leak theory and not your pipe.

I must have put in 8 gallons to go about 80 miles today.

Dang! You got me...

larryblevinson · « **Reply #9 on:** July 18, 2010, 06:07:45 PM »

Here is the video that shows leaking gasoline falling on the No. 3 header tube -- assuming the first cylinder is on the left side. Look for the black spot to show up on the driveway in the first 10 seconds of the video. If you look closely, you can see the smoke from the gasoline dripping on the pipes. I can't tell if it is the valve cover gasket or the head gasket, but either way, I think it is beyond my limited skills. Unless you know someone in the neighborhood who wants to tutor.

Raef · « **Reply #10 on:** July 18, 2010, 06:35:32 PM »

i don't have a 750 but is it possable it is leaking from a fuel line or the carbs and running around the fins

vern401 · « **Reply #11 on:** July 18, 2010, 07:05:01 PM »

Wow that is an odd place for gas to be dripping.... and quite dangerious.
Running down cooling fins mabe.
Hole in gas tank mabe.pull and look for any wet area under it or around the tank seals.
Check your oil and see if it has thinned out allot. if it is real thin and seems to be making oil then you have a bigger problem....

Raef · « **Reply #12 on:** July 18, 2010, 07:23:33 PM »

I never thought about the tank dripping on the motor.

larryblevinson · « **Reply #13 on:** July 18, 2010, 08:24:08 PM »

If the gas tank was dripping, wouldn't it be dripping all the time and not just when the engine is running? Shouldn't there be a big puddle of gas under the bike and none in the tank? That is not the case, actually, just asking.

Raef · « **Reply #14 on:** July 19, 2010, 02:18:11 AM »

sit the bike in the sun and see if it drips, If I leave my gas turned on the only time the carbs drip is when the tank is heated by the sun.

maybe the heat from the engine is making it swell?

if that much gas were comming out of the gasket, it seems you would have a dead miss and I think it would be more of a spray than a drip

Mark

KB02 · « **Reply #15 on:** July 19, 2010, 04:09:23 AM »

Quote from: larryblevinson on July 18, 2010, 08:24:08 PM

If the gas tank was dripping, wouldn't it be dripping all the time and not just when the engine is running? Shouldn't there be a big puddle of gas under the bike and none in the tank? That is not the case, actually, just asking.

Logic says that a constant leak would be the case, but lets be honest, when has logic ever really come into play?

One possibility would be a lot of rust flakes in your tank covering up the hole. the vibration of the engine disturbs the rust flakes enough that they open up the hole, allowing fuel to pass. When the bike is shut off, the rust flakes re-settle and plug the leak.

Just a random guess, but I can see how it could work. Whats the condition of your tank?

flybox1 · « **Reply #16 on:** July 19, 2010, 08:32:13 AM »

can you dip your tank in flour and look for a wet spot?

fletcha221 · « **Reply #17 on:** July 19, 2010, 08:36:53 AM »

Thats what she said.

Simon · « **Reply #18 on:** July 19, 2010, 08:59:03 AM »

Is the engine running on all 4 cylinders? Maybe one cylinder is pumping way to much gas (stuck float + clogged overflow tube) and it's leaking through the exhaust header gasket? Just a thought...

S.

TwoTired · « **Reply #19 on:** July 19, 2010, 09:45:15 AM »

You can see rust at the bottom of the tank in the video. Yes it can only leak when vibration is present. Or, change it's rate of leakage with vibration.

larryblevinson · « **Reply #20 on:** July 21, 2010, 10:18:13 PM »

ok, thanks. Off with the tank ... anyone know where I can get a new one if this one is toast?

Gordon · « **Reply #21 on:** July 21, 2010, 10:29:06 PM »

Quote from: larryblevinson on July 21, 2010, 10:18:13 PM

ok, thanks. Off with the tank ... anyone know where I can get a new one if this one is toast?

ebay or the classifieds section of this forum.

MickeyX · « **Reply #22 on:** July 22, 2010, 01:13:08 AM »

BARRY'S CYCLE AND SALVAGE - 120 Walnut Street - Montclair, NJ 07042
Phone: 1-800-822-7797 or 201 746-3622 Fax: 201 746-1424

MOTORCYCLE JUNK SHOP - Highway 83 - Clermont, NJ 08210
Phone: 609 624-3057

NICK'S MOTORCYCLE AND SALVAGE CENTER - 159 Lebanon Avenue - Williamstown, NJ 08094
Phone: 609 728-9607 Fax: 609 875-7148

RCW SPORT MOTORCYCLE SALVAGE - 279 River Road (P.O. Box 535) - Bellemeade, NJ 08520
Phone: 908 874-0701 Fax: 908 874-7124

KB02 · « **Reply #23 on:** July 22, 2010, 05:12:37 AM »

okay, I'm moving to New Jersey...

You could also try to clean out and seal your tank. POR 15, Red Coat, or Kreem tank sealer are all products for fixing just what you have (depending on the severity of the leak).

xenoscr · « **Reply #24 on:** July 22, 2010, 09:37:32 AM »

Quote from: KB02 on July 22, 2010, 05:12:37 AM

okay, I'm moving to New Jersey...

You could also try to clean out and seal your tank. POR 15, Red Coat, or Kreem tank sealer are all products for fixing just what you have (depending on the severity of the leak).

Don't forget radiator shops as an option. I recall seeing this post a while back about a shop in Brooklyn, NY... looks like it's a bit over an hour from Hamilton, NJ. Probably something closer but here's the thread:

http://forums.sohc4.net/index.php?topic=69414.0

last post from vames has the address.

XeNoSCR

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Author Topic: Terrible gas mileage ... like 40 miles to the TANK ... (Read 5667 times)

larryblevinson

scrapvalue

larryblevinson

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