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Alright all i have a question. normal mpg for my 77 is about 20-24mpg. and all i read this is about 10 mpg lower than average. It came with 1100 carbs and i bought the correct 77 carb and had Pete Boody overhaul them so I know the carbs are dead on. it runs good to me. I can open it up and quick acceleration, Starts easy even in 30 deg weather I have in Tennessee right now and have been riding it to work when over 30 deg F. Any who. I bought a compression tester to check compression. I wondered because when i got the bike off craigs list it has 1100 side covers and but correct 77 engine number. it also had spare headers with it so i have wondered if the previous owner had a problem.
I checked the compression with all the plugs out and the throttle open.
cylinder compression
1: 140
2: 90 to start. then tried couple more times and it got up to 130.
3: 145
4: 150

not sure about the readings. if this has something to do with the mileage or not. ok lets have some input if you could help me out.
would testing it after it has run to operating temp work better to check?
 

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An operating temperature reading would be better.

How far are you going to work and at what speeds?

When riding my 1200 at near freezing temperatures around town I only get about two thirds the fuel millage I get in summer on the highway.
 

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Work is about 5-6 miles from me. half the distance is on back roads and go about 30-40mph. then hit the 2 lane highway and get to 55 or 65 the rest of the way.
 

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Compression should be tested with the motor warmed up and throttle wide open. All plugs removed.

Your compression numbers may be a little low, but the mileage, as you say, isvery low. I would expect 35mpg or more from that bike. Do you have any evidence of fuel leaks? Float problems?
 

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Not that i know of...i am not seeing any fuel leaks. and i would think the floats are ok...I have been getting the same fuel millage last year right after getting carbs rebuilt. I had them professionally done by pistol pete or pete boody who is about 5 mile from me. he is one of randakks approved carb experts and several people locally say wonders about him. He did the 77 carb fix for me also. I would say the floats are good do to that. i use the recommended 2 oz of miracle motor oil in every tank.
 

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First off, trying a couple more times skews the test. To get the most accurate reading, let the bike set overnight so it is dead cold when you run the test. Next, lock the throttle in a wide open position. Pull all spark plugs, then crank the engine the same for each cylinder. If it cranks five revolutions to get the highest reading on cylinder one, crank exactly five revolutions on all the other cylinders. You have now completed a dry test.
When I worked for Jaguar, they told us that a variation of 8% between the highest and lowest cylinder was normal. More than that is a problem. I've always used the same range for bikes.
Now, squirt two or three squirts of automatic transmission fluid in cylinder one, put your finger lightly over the hole and crank two revs, then check that cylinder again. Now do the same on cylinder two, then three, etc. Holding your finger over it while it pops, spreads the oil uniformly over the cylinder walls. You have now completed a wet test.
Again, 8% is about the limit. If you find your compression higher wet than dry, it means you have weak or broken rings. No change between the two tests but a low reading, indicates a valve or head gasket is probably at fault.
 

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WingForChrist wrote:
Work is about 5-6 miles from me. half the distance is on back roads and go about 30-40mph. then hit the 2 lane highway and get to 55 or 65 the rest of the way.
Egg sack lee.:ROFL:
Wait tell you get it on the highway in summer for a long ride and see how it does.
 

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Ken. I did a boyscout benefit group ride last year and road about 60 mile on a loop and the police let us through all the stop signs and lights. it was cool. so a non stop ride i got the best mpg and it was right at 30 mpg.
 

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SidecarMike wrote:
First off, trying a couple more times skews the test. To get the most accurate reading, let the bike set overnight so it is dead cold when you run the test. Next, lock the throttle in a wide open position. Pull all spark plugs, then crank the engine the same for each cylinder. If it cranks five revolutions to get the highest reading on cylinder one, crank exactly five revolutions on all the other cylinders. You have now completed a dry test.
When I worked for Jaguar, they told us that a variation of 8% between the highest and lowest cylinder was normal. More than that is a problem. I've always used the same range for bikes.
Now, squirt two or three squirts of automatic transmission fluid in cylinder one, put your finger lightly over the hole and crank two revs, then check that cylinder again. Now do the same on cylinder two, then three, etc. Holding your finger over it while it pops, spreads the oil uniformly over the cylinder walls. You have now completed a wet test.
Again, 8% is about the limit. If you find your compression higher wet than dry, it means you have weak or broken rings. No change between the two tests but a low reading, indicates a valve or head gasket is probably at fault.

Agreed. Compression testing should be done to a cold engine. Testing a warmed-up engine is essentially cheating yourself out of accurate results.

The manual says what Mike states above -test at room temperature with 5 or 6 revolutions per cylinder. Manual also states if below 142psi or a difference of 15psi between any two cylinders, then a tear-down is in order (your callon that :cool:). Good tips for wet/dry testing. A leak-down test afterwards can confirm wet/dry compressiontesting.

Cylinder testinghas a "first come, first served" type of approach with no averaging in attempts. The first time don't lie, but the second time just might. Third time is a guaranteed "truth" or "lie", depending on what you're wanting to hear your self tell your self.

171 PSI is as new (assuming no carbonization/coking).


Edit:

In the Real World, both Hot and Cold routes used together have their merits. Cold testing and Hot testing. With the cold test, you get the base figure facts for referencing tolerences/conditions withing the combustion chamber against a hot tests operating conditions. Compared, there is insight to be gained just as with wet/dry testing. Relying on only one of the two routes should be with the cold test though, ...IMO, as heat-expanded components that are out of spec in a "cold" state are likely in a pre-failure/failure statethough still operational.
 

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Ok...well i bought a 76 parts bike that showed a cold 90 on th #1 and 2.



did not test the rest. so i am wondering. if i do a overhaul? what kind of price am I looking at putting into it. Does not have to be accurate but would think about $800 if not more, but if around that i would be willing to put into it because i love these bike better than the fancier new ones. my love has always been for the old wings.
 

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Ok...well i bought a 76 parts bike that showed a cold 90 on th #1 and 2.



did not test the rest. so i am wondering. if i do a overhaul? what kind of price am I looking at putting into it. Does not have to be accurate but would think about $800 if not more, but if around that i would be willing to put into it because i love these bike better than the fancier new ones. my love has always been for the old wings.
 

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...just buy a used engine. $2/3/400.00 all-day-long most days on eBay/elsewhere's.

You could always go the tear-down route, but most opt-out for the simple-plan of replacing the engine with known spec'd compression figures. Most all on eBay list the figures, as they know it's a make or break deal. Plenty of good engines there.

Example = $200 to buy and $120-$200 to ship (+/-, locale and terms-n-such) puts you way under your budget for other "maybe needed" stuff. Lotsa good life left in a 30K wrecker-motor (as I like to call them).
 

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Andy is corect, the old saying is you need 100 psi to run. With your readings your compression is fine.
 

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The compression check should be done with the engine warmed up.
Check the ignition timing but I suspect the float levels are a little too high.
 

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Dave. I not sure if it would be the float. I had 1100 carbs on it when i bought the bike and got the same gas milage. I bought some 77 ebay carbs to match the engine and had pete poody, pistol pete that randakk recommends over haul them. they are still getting the same milage but runs a lot better with the clean carbs. since having them cleaned, every tank i put in the recommended 2oz marvel mystry oil and fuel stabilizer.
 

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Gas mileage on a good tank, one up of easy riding can hit 42 or so. Your compression numbers are OK but the spread between cylinders shouldn't be more than 10 and better if only 5. That 130 to 150 spread is not good, makes it hard for the engine to run smoothly. Re do as stated above warm engine, throttle wide open. If you can't get all above 140 and close together you have some issues but not a big deal. If one is lower add a little oil to the cylinder if it comes up ring issues if not valves issues.

170 is perfect, 160's very good, 150's good, 140's OK, 130's marginal and over haul needed according to the manual..but yep she'll run OK down into the low 100's even 90's.

Have you looked at your plugs they may tell the story one of more may be fouled or a gas leak from your carbs, petcock, fuel pump???
 

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I have to disagree with CaptainMidnight85. Why take a chance on a used engine if you can rebuild and know what you have when you are done? Just because a seller says he got 150 pounds across the board, doesn't mean he really did or that his gauge is accurate. What happens if you go through all the work and expense of swapping, only to discover he exaggerated? If you can buy a used engine cheaply, by all means do so. Do it with the intention of rebuilding it before you install. Then you can continue to ride until you are ready to install, and you will know you have a good machine when you are done.
When I worked as a mechanic, people always wanted me to install used parts to save money, but then expected me to warranty the part as if it was new.
 

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Well when i put the rebuilt carbs on last spring I had to try it and got it to 105 :action:quickly and scarred the piss out of me so I had to back off back down to 55. Only time i was that stupid;)



when I pulled the plugs last night they looked light grey. I will try to get back out tonight and check them again. I will get picks of them and post them.


I do have a spare 76 bike(reg not LTD)i picked up for $200. Had all but the plastic on it false tank and speedomete. It is very rough. I have even thought of rebuilding the engine and if i can get it titled will be a project naked rebuild.so if rebuild is needed i would rebuild that off the bike and then swap. but always have the old cb360 back up.
 

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doh. double post...:?
 
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