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Offline KRONUS0100

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quick question
« on: October 19, 2011, 08:31:13 AM »
1976 CB750F
carbs are adjusted and synched pretty darn near perfect.
#3 pipe is hotter by about 100 degrees than other 3 pipes which are 240 degrees after 10 minutes.
I am thinking #3 air screw (idle air) is slightly out of adjustment.  am I correct? 
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MATT
current bikes:  1976 CB750F, 1981 GS1100E
bikes owned:1981 GL1100I, 1990 GS500E, 1981 GS850, 1977 and 1979 GS750, 1974 CB750, 1975 CB750, and a 1982 GS750E

Offline flybox1

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Re: quick question
« Reply #1 on: October 19, 2011, 08:37:57 AM »
10 minutes of what?  idle? highway speeds?
what do your plugs look like?
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'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

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Offline KRONUS0100

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Re: quick question
« Reply #2 on: October 19, 2011, 09:03:05 AM »
my bad.  bike was on center stand idling in barn with floor fan in front of it.  used a digital heat sensor themometer to take the readings while checking to see if all 4 were indeed firing.  plugs are a tiny bit rich at idle, but are good at hiway speed plug chop.

I was just curious as i just obtained this lil thermometer to test the function of the cat converter on our truck....and got to thinking it would work great to test the pipes on the bikes.......no more burned fingers kinda thinking.
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MATT
current bikes:  1976 CB750F, 1981 GS1100E
bikes owned:1981 GL1100I, 1990 GS500E, 1981 GS850, 1977 and 1979 GS750, 1974 CB750, 1975 CB750, and a 1982 GS750E

Offline shizzomynizzo

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Re: quick question
« Reply #3 on: October 19, 2011, 01:39:22 PM »

I would think the plug to that cylinder would be reading too rich or too lean of the screw is outta wack...u can always check it...screw it in and see how far out it was.

I am unsure why that pipe would read 100 deg hotter... Are the pipes coted at all?

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Offline tlbranth

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Re: quick question
« Reply #4 on: October 19, 2011, 05:20:47 PM »
Shizzo: Don't want that li'l green guy to overdo. If he needs any help.........
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Offline shizzomynizzo

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Re: quick question
« Reply #5 on: October 19, 2011, 07:08:12 PM »
Yeah ::), he has his hands full  :P
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2001 Street Glide

Offline Don R

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Re: quick question
« Reply #6 on: October 20, 2011, 05:14:11 PM »
I'm sure you were careful but mine is very sensitive to aim.
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Offline phil71

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Re: quick question
« Reply #7 on: October 20, 2011, 06:19:40 PM »
100 degree difference ?? Really?
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Offline TwoTired

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Re: quick question
« Reply #8 on: October 20, 2011, 06:36:39 PM »
Any difference in volumetric efficiency can contribute to exhaust temp differences. (As well as mixture ratio)
Are the tappet clearances exactly the same?
Are the cam lobes of equal profile/timing?
Compression identical among cylinders?

If yes to all above, then lean the idle mix on the colder cylinder and check for effect.
Of course, if it is already leaner the the others (exhaust gas analyzer), then maybe go richer.

For the instrument, check out the spot size being measured. (It is NOT the laser dot, that's just an aim pointing device.)  Also, distance changes the spot size.

(I'm guessing about the instrument details, since you didn't specify.)  A "Wrench", could be made of iron, steel, plastic, brass, or silly putty.  They would have different capabilities/functional considerations.

Cheers,
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Lloyd... (SOHC4 #11 Original Mail List)
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