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Old 02-26-2012, 10:26 PM
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Vacuum Gauge craziness??

I loaned my vacuum gauge to my son as he is growing frustrated attempting to get his build tuned. He begged me to please drop by and help him figure out WTF was going on because the gauge needle was all over the map.

I installed the gauge, started the motor & he was correct. The needle flips back & forth from vacuum to pressure... almost spanning half of the dial.

Weird stuff! I also noted that one of the exhausts never gets hot, well, not like the other side. The air mixture screw has no effect either.

It is a twin cylinder Honda. (I know this is a car forum guys, but he did install a race cam & custom made forged pistons... besides, lotsa hotrodders have hot-bike experience too!)

I was thinking that perhaps one of the el-cheapo exhausts he is running may be clogged because of sloppy manufacturing (Chinese). That is my best guess, anyone want to weigh-in on this?

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Old 02-26-2012, 10:42 PM
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Quote:
Originally Posted by DENCOUCH
I loaned my vacuum gauge to my son as he is growing frustrated attempting to get his build tuned. He begged me to please drop by and help him figure out WTF was going on because the gauge needle was all over the map.

I installed the gauge, started the motor & he was correct. The needle flips back & forth from vacuum to pressure... almost spanning half of the dial.

Weird stuff! I also noted that one of the exhausts never gets hot, well, not like the other side. The air mixture screw has no effect either.

It is a twin cylinder Honda. (I know this is a car forum guys, but he did install a race cam & custom made forged pistons... besides, lotsa hotrodders have hot-bike experience too!)

I was thinking that perhaps one of the el-cheapo exhausts he is running may be clogged because of sloppy manufacturing (Chinese). That is my best guess, anyone want to weigh-in on this?
Do a leak down or compression test- it could have a bad head gasket.
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Old 02-27-2012, 08:26 AM
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Quote:
Originally Posted by cobalt327
Do a leak down or compression test- it could have a bad head gasket.
Thanks, I will try this. A leak down tester is on of those tools I haven't added to my collection yet.

He is running a copper head gasket with copper head gasket sealant. I inquired as to whether or not he spec'ed the flatness of the head or barrels before he assembled them. He cleaned up the heads with some wet 800 grit & a pane of glass.
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Old 02-27-2012, 10:35 AM
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Just click on this link and then on "scenario" on each number.
If the gauge is going that far back and forth it sounds like the intake is getting pressurized which to me sounds like a intake valve is either burned or stuck open.
http://www.secondchancegarage.com/public/186.cfm
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Old 02-27-2012, 10:39 AM
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Quote:
Originally Posted by DENCOUCH
Thanks, I will try this. A leak down tester is on of those tools I haven't added to my collection yet.

He is running a copper head gasket with copper head gasket sealant. I inquired as to whether or not he spec'ed the flatness of the head or barrels before he assembled them. He cleaned up the heads with some wet 800 grit & a pane of glass.
You wouldn't think the head gasket would be leaking after all that, might want to get a closer look at the valve train while you're at it. Was anything done in the way of adjusting the valves, new cam or followers, ran extra hard? Could have broke a spring, etc.
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Old 02-27-2012, 07:00 PM
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[QUOTE=cobalt327]You wouldn't think the head gasket would be leaking after all that, might want to get a closer look at the valve train while you're at it. Was anything done in the way of adjusting the valves, new cam or followers, ran extra hard? Could have broke a spring, etc.[/QUOTEI

New cam installed. This is his first big go-it-alone project & I was not in any position to assist him with it. It seems that whn he broke down the motor to go big bore, he completely disassembled everything completely for cleaning. The valves in a box, the rockers in another, the rocker shafts... well, you get the idea. I inquired about if he had a valve job while things were apart, and he answered that after reassembling the head, he poured acetone in the ports & did not note any leakage.

One thing out of the ordinary, the rocker arm shaft seems to be loosening up, that is, the nut that holds the shaft in the head & bolts through from the outside. My Son said it keeps leaking & when he puts a wrench to it, it is "loose again"!

Perhaps the rockers on the intake are attempting to seize to the shaft during operation? The valves are being held open?
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Old 02-27-2012, 10:12 PM
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[QUOTE=DENCOUCH]
Quote:
Originally Posted by cobalt327
You wouldn't think the head gasket would be leaking after all that, might want to get a closer look at the valve train while you're at it. Was anything done in the way of adjusting the valves, new cam or followers, ran extra hard? Could have broke a spring, etc.[/QUOTEI

New cam installed. This is his first big go-it-alone project & I was not in any position to assist him with it. It seems that whn he broke down the motor to go big bore, he completely disassembled everything completely for cleaning. The valves in a box, the rockers in another, the rocker shafts... well, you get the idea. I inquired about if he had a valve job while things were apart, and he answered that after reassembling the head, he poured acetone in the ports & did not note any leakage.

One thing out of the ordinary, the rocker arm shaft seems to be loosening up, that is, the nut that holds the shaft in the head & bolts through from the outside. My Son said it keeps leaking & when he puts a wrench to it, it is "loose again"!

Perhaps the rockers on the intake are attempting to seize to the shaft during operation? The valves are being held open?
Could be... what size, make, etc. is this bad boy?
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Old 02-27-2012, 11:32 PM
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[QUOTE=cobalt327]
Quote:
Originally Posted by DENCOUCH
Could be... what size, make, etc. is this bad boy?
CJ360 w/ 2MM larger bore. Long duration cam w/more lift 109 lc. He spent years in England & grew addicted to how they build bikes over there.




Last edited by DENCOUCH; 02-27-2012 at 11:38 PM.
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Old 02-27-2012, 11:44 PM
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Quote:
Originally Posted by DoubleVision
Just click on this link and then on "scenario" on each number.
If the gauge is going that far back and forth it sounds like the intake is getting pressurized which to me sounds like a intake valve is either burned or stuck open.
http://www.secondchancegarage.com/public/186.cfm
Thanks. I have this site bookmarked & have used it in the past as I have never faced any of the issues they exhibit, but would want the added info. I went to this page & believe me... what this gauge is showing is not even close to the scenarios they show. This is a "New one" for the list!
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Old 02-28-2012, 02:16 PM
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No Wonder

its not an American made Harley
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Old 02-28-2012, 09:21 PM
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Quote:
Originally Posted by rsfyj
its not an American made Harley
Actually it is, but a very secret prototype.

I wish I was in a position to remove some of the covers to illustrate a few of the exotic parts enclosed therein; the patented self-generating nitrous-oxide power adder, the crank bearings utilizing super-cooled friction-less bearings, and the nano-technology employed in the construction of the transmission... it has a 9-speed gearbox the size of a walnut! The complete motorcycle as it sits weights only 39.3 pounds constructed from carbon fiber. It sports no alternator, but takes advantage of the wheels being magnetized and what at first glance appears to be brakes, are actually the rotors supplying 3-phase power stored in the spokes, using the space between, as a natural insulator.

Now go away & let us men get back to work on this issue.
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Old 02-28-2012, 11:41 PM
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Cafe racer styling always appealed to me. Reminiscent of a bike featured in Cycle or Cycle World many years ago (mid/late-'70's), called the "Gentleman's Express". It was built around a 500 4 cylinder Honda, I believe it was.
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