« previous next »
Pages: [1]   Go Down

Author Topic: #2 & #4 pipes turned blue  (Read 1968 times)

0 Members and 1 Guest are viewing this topic.

Offline Jiminy Indy

  • Enthusiast
  • **
  • Posts: 131
#2 & #4 pipes turned blue
« on: October 18, 2012, 05:38:51 AM »
Just got a '77F and did all the usual new bike tune-up things (points, timing, valves and so on). But also replaced the idle jets with the stock size 35s (they were all boogered up and clogged) and upped the main jets to 120s as I had to replace the trashed stock pipe with a MAC 4-1. Otherwise all stock set up. Had a friend come over and did the carb vacumn sych and all was good. Went for a long (20 mile) shake down and when got home noticed that the #2 & 4 pipes turned blue. It did run OK when I first bought it except obviously in dire need of a tune up so it must be somthing I hosed up.

Any ideas on why just these two might turn blue?
Logged
Of all the things I've lost, I miss my mind the most.

"Shot up the alley and then cut across the street" - now that's some violence you can appreciate!

Offline bjatwood

  • I never claimed to be an
  • Expert
  • ****
  • Posts: 976
  • 1973 CB750-K3
    • Minbikers Proboards
Re: #2 & #4 pipes turned blue
« Reply #1 on: October 18, 2012, 05:41:45 AM »
Do you have a infared heat gun to check the pipe temps after you run it. That would tell you if the #2 & #4 pipes were hotter/leaner than the other two.
Logged
Brian
#24193

I believe that the Finest things are the most thoughtfully made, not the most expensive!
http://minibikers.proboards.com/

Offline Jiminy Indy

  • Enthusiast
  • **
  • Posts: 131
Re: #2 & #4 pipes turned blue
« Reply #2 on: October 18, 2012, 06:29:41 AM »
No, never needed one before.

So if these two are running hotter, then that means leaner? Just adjust the screws to make it run richer? quarter turn or so? It really does seems to run OK as-is.
Logged
Of all the things I've lost, I miss my mind the most.

"Shot up the alley and then cut across the street" - now that's some violence you can appreciate!

Offline 750resurrection

  • Hot Shot
  • ***
  • Posts: 288
Re: #2 & #4 pipes turned blue
« Reply #3 on: October 18, 2012, 06:53:01 AM »
 
 Yep, that's the way to do it. Not sure how you're going to tell once they are already blue - the harbor freight has a temp gun for 34.99

 If you hand touch quickly on the bottom of the pipes ( near where they meet) shortly after starting and revving you can tell, not sure how easy that is on your 4 to 1.
Logged

Offline Jiminy Indy

  • Enthusiast
  • **
  • Posts: 131
Re: #2 & #4 pipes turned blue
« Reply #4 on: October 18, 2012, 07:13:19 AM »
OK, thanks. I'll give that a try.

Just seems kind of weird as I set them all the same (1-3/4 turns if I remember - whatever the manual said anyway)
Logged
Of all the things I've lost, I miss my mind the most.

"Shot up the alley and then cut across the street" - now that's some violence you can appreciate!

Offline iron_worker

  • Master
  • *****
  • Posts: 2,081
Re: #2 & #4 pipes turned blue
« Reply #5 on: October 18, 2012, 07:14:54 AM »
If your pipes suddenly started turning blue after changing the jets I would definitely suspect your own work.

What size pilots and mains were in there that you replaced?

Turning the mixture screws richer will only adjust your idle-1/4 throttle mixture which I highly doubt is causing your blue-ing. I would suspect your mains.

IW
Logged

Offline Old Scrambler

  • My CB750K3 has been in 39 States & 5 Provinces
  • Old Timer
  • ******
  • Posts: 3,810
Re: #2 & #4 pipes turned blue
« Reply #6 on: October 18, 2012, 08:05:07 AM »
+1 on the IDLE air-screws....Did you install new exhaust gaskets?  Are the pipes properly fitted to the head?
Logged
Dennis in Wisconsin
'64 Triumph Cub & '74 Honda CB750 Bonneville Salt Flats AMA Record Holder (6)
CB750 Classic Bonneville Racer thread - http://forums.sohc4.net/index.php/topic,135473.0.html
'63 CL72 Project(s)
'66 CL77 Red
'67 Triumph T100C
'73 750K3 Owned since New
'77 750F2 Cafe Project
2020 ROYAL ENFIELD Himalayan

Offline Jiminy Indy

  • Enthusiast
  • **
  • Posts: 131
Re: #2 & #4 pipes turned blue
« Reply #7 on: October 18, 2012, 10:02:25 AM »
I replaced the 105 main jets with 120s based upon what I've read here when going to the different pipe. I can't tell the size of the old idle jets but replaced with new 35s. The side going into the carb body has what looks to be lots of cross holes drilled so it looks like swiss cheese so I don't know what the PO was thinking.

Did replace the copper crush gaskets and the pipes are tight against the head so everything appears to be mounted correctly. Didn't want to over torque them down and risk pulling a stud so snugged them up and then tightend down until I felt like the gaskets were squishing out.
Logged
Of all the things I've lost, I miss my mind the most.

"Shot up the alley and then cut across the street" - now that's some violence you can appreciate!

Offline cougar

  • Hot Shot
  • ***
  • Posts: 410
  • Stamping Ground, Kentucky U.S.A.
Re: #2 & #4 pipes turned blue
« Reply #8 on: October 18, 2012, 02:59:12 PM »
Jiminy ; From the charts I've got the 1977F carbs (PD41B) runs 105 mains, 35 idle/slow jet and 1 turn out on the mixture screw. As far as measuring with a temp gun, a lot of times that is difficult because most guns (non-touch) will not read correctly because the sensor has difficulty because of the reflective nature of the chrome. If 2 pipes are getting hotter than the other 2 then I would be inclined to go with some obstruction on the mains on the hot pipe carbs. Or another possibility of the carb to engine boots are leaking causing a lean mixture.   ...cougar...
Logged
I'm not prejudice, I'll weld anything that pays! Knowledge that is shared is Never Lost!!   Right is right, wrong is wrong! The truth is the truth and a lie is a lie! DEAL WITH IT ACCORDINGLY !!!   I HATE "DIAL-UP"

Offline iron_worker

  • Master
  • *****
  • Posts: 2,081
Re: #2 & #4 pipes turned blue
« Reply #9 on: October 19, 2012, 09:23:46 AM »
The holes "drilled in the side" of the pilot jet are part of the emulsion system. It allows air to mix in with the fuel stream and turn it into an easier to burn fine mist. The pilot jet has the emulsion tube built into it. If you pull the main jet holder out you will find an emulsion tube there too. All those tiny holes need to be there and need to be clean.

IW
Logged

Offline Jiminy Indy

  • Enthusiast
  • **
  • Posts: 131
Re: #2 & #4 pipes turned blue
« Reply #10 on: October 19, 2012, 10:38:10 AM »
I should take a picture of the idle jets I pulled out when I get home. They don't look anything like the stock jets - there really isn't too much metal left at all. It almost looks like something has attached the brass and eaten it away. Like I said - weird.
Logged
Of all the things I've lost, I miss my mind the most.

"Shot up the alley and then cut across the street" - now that's some violence you can appreciate!

Offline Jiminy Indy

  • Enthusiast
  • **
  • Posts: 131
Re: #2 & #4 pipes turned blue
« Reply #11 on: October 19, 2012, 10:42:41 AM »
Thanks all -
Cougar, good suggestion on the air leak - I'll check the boots when I get home tonight.

I did snug the pipes up after the shkedown ride and that may have been some of the problem. Weren't loose, but not tight either on all four pipes.
Logged
Of all the things I've lost, I miss my mind the most.

"Shot up the alley and then cut across the street" - now that's some violence you can appreciate!

Offline WhyNot2

  • I'm finally an
  • Master
  • *****
  • Posts: 1,844
Re: #2 & #4 pipes turned blue
« Reply #12 on: October 19, 2012, 10:43:56 AM »
watching, as my pipes are turning blue also....................
Logged
If it ain't raining, I'm riding.....~~{iii}?~~prost

If it sounds like I know what I'm talking about, it's because I cut and pasted from someone else.

Offline TwoTired

  • Really Old Timer ...
  • *******
  • Posts: 21,805
Re: #2 & #4 pipes turned blue
« Reply #13 on: October 19, 2012, 11:08:34 AM »
Almost all of the mixture ratio during cruise is supplied by the slide needle position and dimensions.  This throttle position and WOT are when the exhaust pipes encounter the most heat from the cylinders.

Are all the slide needles the same?  And, are they clipped in the same position?  Is there any evidence of wear on the needles or the orifice jet in which they operate?  The jet needle orifice is on top of the mains emulsion tube and protrudes slightly into the carb throat.

Kinda need to know what you have before making random changes.

Logged
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.
Pages: [1]   Go Up
« previous next »