Topic: Pipe blueing... and more tune-up stuff

[KB02]

Is the blueing of the exhaust pipes a sign of running rich or running lean? I can never get it straight.

[Bob Wessner]

Hot and lean.

[ProTeal55]

Lean is mean !
 

[KB02]

Thanks!

Now, one more question: What size fuel hose should I be running on 750? 1976 CB750F with a 75 K engine, only one fuel petcock. Currently I think I have 1/4". Most of my riding is slower speeds. I havn't been able to do a whole lot of higher speed runs yet. The plugs show a little on the rich side, but the pipes are starting to blue up nicely. Plus, when I do get on the highway, it seems like I am just not getting any more fuel beyond half throttle. Possible that I'm draining the bowls by not having big enough of a fuel line? (The old hose was rotted and needed to be replaced. I couldn't find any size refernce on the hose or in my clymers manual.)

At least, that's my working theory right now. I won't be able to test it for a little bit as I am still waiting for the snow to melt and I am still working on my custom seat.

[mrblasty]

I have had luck with sliding the needle clip down one notch, I'm not sure if the carbs on the '76 are the same as the set on my 73 if so this will give some improvement.

[TwoTired]

Now, one more question: What size fuel hose should I be running on 750? 1976 CB750F with a 75 K engine, only one fuel petcock. Currently I think I have 1/4". Most of my riding is slower speeds. I havn't been able to do a whole lot of higher speed runs yet. The plugs show a little on the rich side, but the pipes are starting to blue up nicely. Plus, when I do get on the highway, it seems like I am just not getting any more fuel beyond half throttle. Possible that I'm draining the bowls by not having big enough of a fuel line? (The old hose was rotted and needed to be replaced. I couldn't find any size refernce on the hose or in my clymers manual.)

The stock bike has 5.3 or 5.5 mm I.D.  If your 1/4" hose is the I.D. they supply plenty of fuel unless kinked.  Do you know your carbs have the correct float height settings?

Your carbs meter fuel based on slide or throttle position.  It is possible for it to run rich at one setting and lean in another.
Slow jets, main jets and slide needles are each used to meter fuel relative to slide position.

Are you reading the correct part of the spark plug?  The center electrode insulator is where the useful tuning information lies.  The outer ring will almost always be black unless you are running scary lean.

The head pipe bluing can be from running too lean. (But at what throttle setting?)
Also, there could have been some contamination on the chrome and the heat catalyzed a reaction with the chrome.  Some chrome polishes will do that, too, if they leave a residue behind.  I learned long ago to only use fine/clean steel wool on chromed head pipes.

What are the heat range numbers of your spark plugs?

Cheers,

[supersport_CB400F]

If the pipes are aftermarket single skin pipes blue is what they will do 

[TwoTired]

Oh, I just remembered, check your ignition timing, too!

Cheers,

[cben750f0]

i had a similar problem with feuling over half throttle on my 77.... turned out that my fuel filter wasnt flowing enough... you didnt mention if you had a filter or not.... peace

[cb650]

Wont they turn to if your  just riding it hard?   



                              Terry

[KB02]

Okay, here goes:

TwoTired - Right now I am running NGK D8EA plugs. Once I get ready to get it out again I will be buying a new set - something I do with all my bikes - Do you  think I would be better with 7's? Right now I have the main jets up to 135. The plugs (on the resistor) show that it is just a touch on the rich side. Richer than I would like it, but still within tolerable levels. And the timing is set as perfect as I can get it according to measurments and my timing light (I checked all four cylinders with the light at both idle and 3k on the tach for advance, They were all fine.) Oh and the needle is set at the second clip from the bottom (forth from the top out of five).

BIFFTA - I am running a set of stock pipes that I got off of ebay. (that was a great deal!!)

Cben - I am running a fuel filter (inline). There is so much crap in the tank that I don't dare run without one. It has been cremed once before by the PO, but there is still a bunch of rust that floats around (That may be a project for this summer).

Thanks all. Any other question, fire them off.

[KB02]

Oh, I just remembered, check your ignition timing, too!

Cheers,

One more quick clarification on this issue: Like I said in the previous post, everthing appears to be spot on, but it is spot on with the adjustment plate all the way to one side.  Part of me worries about the lack of adjustment in that one direction, but the other part of me feels that it shouldn't be a problem since the timing light shows everything to be right on the mark. Your thoughts?

Kinda going away from just blued pipes now, isn't it?   

[TwoTired]

1) If you are running stock pipes and air filter, why aren't you using the stock carburetor settings and jetting?  What do you know that Honda didn't?

2) The timing plate adjustment range is there for a reason.  If you can get the timing on within the range, woopee.

3) You are using the correct plugs that Honda specified, stick with those numbers.  An NGK 7 is a hotter plug that should self clean better with a rich mixture than an 8.  However, when the engine is at higher temps in the summer, there is risk of temps getting too high.  Better to correct mixture issues with carb adjustments than spark plug changes.

4) If you have fuel filter, it blocks crud coming from the tank.  The action of blocking crud reduces the flow capacity of the filter and restricts flow capacity.  How do you know it it isn't blocked with crud from the tank and starving the motor at speed?

5) If you compare your spark plug deposits to these pics:
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html
How do yours compare?

6) Have you done any "plug chops" while the engine is behaving badly on the highway?

7) Head pipe bluing of the stock pipes is possibly a sign that combustion temps are not as intended or there is some combustion going on in the head pipes that overheats them.  (or, surface contamination, etc).  You wouldn't happen to know the actual head pipe temps, would you?  Do they glow in the dark?

Cheers,

[KB02]

1) If you are running stock pipes and air filter, why aren't you using the stock carburetor settings and jetting?  What do you know that Honda didn't?

Actually I am running pod filters. When I bought the bike the stock air box came with it, but that was pretty much the PO's way of cleaning the junk out of his shed. It is basically unusable. I bought the pods since they were cheaper and easier to get (perhaps not better...)

4) If you have fuel filter, it blocks crud coming from the tank.  The action of blocking crud reduces the flow capacity of the filter and restricts flow capacity.  How do you know it it isn't blocked with crud from the tank and starving the motor at speed?

The fuel filter I have is see through. It's not too bad right now, but I do plan on replacing it once spring officialy hits and I get the bike going again. Would it be possible that a clog could be in the fuel petcock?

5) If you compare your spark plug deposits to these pics:
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html
How do yours compare?

They're a combination of pics #5 and 7. One side of the electrode is a little lighter (like #7) with the rest of it being darker (like #5).

6) Have you done any "plug chops" while the engine is behaving badly on the highway?

Not yet.

7) Head pipe bluing of the stock pipes is possibly a sign that combustion temps are not as intended or there is some combustion going on in the head pipes that overheats them.  (or, surface contamination, etc).  You wouldn't happen to know the actual head pipe temps, would you?  Do they glow in the dark?

Not a whole lot or riding in the dark, but they don't feel like they are getting that hot.

I've got a day off coming up (finally yay!!! I hate working retail), I may pul the carbs an check a few things in the fuel system. I've got to do some brake work anyway and get that new MC on. I'll let you know what I find.

[TwoTired]

You know even pod filters have to be cleaned and replaced at some service interval.  You could try a short run with them removed as a diagnostic technique.  If your performance improves, you have a suspect.  But, even with pods, it seems like your jetting and carb setup should be closer to stock, if the rest of the bike is.  I would expect to twiddle the idle screws or idle jets for a bit more juice in that regime.  But, the main jet is for WOT and part of top midrange.  Seems like the exhaust restriction pressure buildup would dictate those settings.  Perhaps not?  Maybe more expert tuners have better insight.

4) If you have a fuel filter, it blocks crud coming from the tank.  The action of blocking crud reduces the flow capacity of the filter and restricts flow capacity.  How do you know it it isn't blocked with crud from the tank and starving the motor at speed?

The fuel filter I have is see through. It's not too bad right now, but I do plan on replacing it once spring officialy hits and I get the bike going again. Would it be possible that a clog could be in the fuel petcock?

Dunno, simple to check for, though.  Back of the envelope math...  If the bike gets 30 MPG at 60 MPH, it will take 2 hrs to consume a gallon of fuel.  Drain your petcock into a quart jar and time how long it takes to fill it.  Even if it takes 5 minutes to fill that quart jar, that's a 1 gallon in 20 minute rate, or six times the amount of consumption.

They're a combination of pics #5 and 7. One side of the electrode is a little lighter (like #7) with the rest of it being darker (like #5).

Okay, you're running a bit rich, perhaps.  How many miles on the plugs?

Oh, and are you familiar with a product called "Blue Away"?  Supposed to remove blueing from chrome.  No first hand experience though.

Cheers,

[hopterfixer]

Speaking of pipe blueing..... I came across a product just yesterday at the local Honda Shop called Blue Job (be careful with that name).  It was highly recommended by the guy at the shop so I tried it.  It worked amazingly well.  I have a '80 Kawasaki with a pipe that was so blued it was black, purple and gold too (part of the reason I got the bike so cheap, the guy did NOT know what he was doing trying to tune carbs).  The stuff took away all of the colors and it does not dull or scratch.  I have heard that the Blue Away product takes the blue away but leaves the pipe a dull color.  It comes in a little can (.5 oz) of powder that looks like an illicit drug, and costs $15.  I can post some photos if anyone is interested. 
http://www.blue-job.com/     

[KB02]

Okay, so I had the day off the other day (and it was a nice day) so I was able to get out to the garage and do a little work on the bike. I pulled off the carbs and checked the needles (I had a nagging thought in my head that I had set the slide needles incorrectly.. but all was the way it should have been). I checked the fuel line and fuel filter. Here is what I found, and I wonder how it is effecting my problem:

#1.) The fuel line is 3/16" ID and not 1/4" like I thought it was (4.75 mm vs 5.5 mm stock, right?). So, when I buy a new fuel filter (boy, that was nasty) I am going to get some new fuel line, too.

#2.) The Carb boots are all old and starting to harden up (read: leaking air). I know the best option would be to replace them with new, but would trying to seal them up with some silicone sealant (form-a-gasket stuff) work for the mean time? I know that I would have to be careful about making sure I didn't get any globs in the air pathway that might dislodge and go into the cylinders, but would a liberal amount around the mounting flange help create enough of a seal to hold it for the mean time? I will also be getting new clamps when I buy the fuel line.

#3.) Would that extra air getting in be part of my problem? I now know, from reading other posts, that it is not helping my starting issues (having to turn up Idle screw to get it to idle cold, but once it warm up that jupms the idle up to about 3k or so and I have to turn it back down). But once the bike is warm, it kinda seals itself up and the leak goes away? So it shouldn't be a part of THIS problem, right?

[byidesign]

Air leaking will cause quite a few problems
    your,start/idle rpm, issues , and not returning to idlewhen
   the throttle is closed. I have used black high temp RTV
    silicone sealer with good results, when needing a temporary fix.
         {ran my cm400 for two months, while I scrounged parts up}
     you don't need much of it for sealing surfaces.
        then make sure you allow it to cure,before using the bike.
        Note: Be sure all the work on the carbs is good before you
         put them on,{you don't want to have to remove them}


 until  you get your parts.

           then you will
          have to remove the RTV. it can be a painin the a@#....to scrape off.
           Hope it helps
                   Bruce

[KB02]

... the RTV ...can be a painin the a@#....to scrape off.
           Hope it helps
                   Bruce

Don't I know it. The PO was a big fan of the stuff when he tried to rebuild the engine. AND he was sloppy with it, which is a HUGE pet peave of mine.
The RVT is on. Unfortunetly, the next day I have off that I will be able to work on it is Friday of next week (I hate working retail). The bonus is that the RVT will have plenty of time to cure.

[crazypj]

I think I already posted this some where (I have an issue since I got hit on the head with a 25lbs bottle jack, suffer from 'CRAFT')
You want to go up about 10% on main jets, DROP the needle 1 groove (leaner) and find some way to support the rear of the carbs when using pod filters. I can explain why but would prefer not to peck it out
PJ

[needswork]

I'm glad I read this. My headers are blueing in a big way and I couldn't understand why. I changed the main jets to 125 (larger than previous) and the bike is running a whole lot better.  Twotired mentioned chrome polish and I did use some over the winter that left a residue AND it is an aftermarket pipe. I'm not concerned anymore. I'll have to find some of that blue-job stuff.
This site is soooo helpful. 

[WHALEMAN]

twotired, Get your envelope back out. Bike going 60 MPH will go 60 miles in one hour. Bike getting 30 miles per gallon will burn 2 gallons in one hour going the 60 miles.

[TwoTired]

#3.) Would that extra air getting in be part of my problem? I now know, from reading other posts, that it is not helping my starting issues (having to turn up Idle screw to get it to idle cold, but once it warm up that jupms the idle up to about 3k or so and I have to turn it back down). But once the bike is warm, it kinda seals itself up and the leak goes away? So it shouldn't be a part of THIS problem, right?

This is one of the bike's characteristics, and not a problem you are likely to ever completely solve, and part of a basic nature of carburetted engines.  A cold engine doesn't atomize fuel as readily as a warm one.  This makes cold running very inefficient.  Choke application enriches the mixture so the cylinders will fire.  However, unlike later choke systems, it does not have a separate fast idle cam coupled with the choke linkage to bump up the idle speed.  For your machine, the operator is expected to hold the throttle open with the twist grip during engine warm up.  Without changing to newer carburetors, I think your options are to routinely twiddle the idle knob settings during warm up, or purchase a bar mount throttle friction device for holding the twist grip open while the engine is warming.  Cursing, of course, is optional.

Cheers,

[TwoTired]

twotired, Get your envelope back out. Bike going 60 MPH will go 60 miles in one hour. Bike getting 30 miles per gallon will burn 2 gallons in one hour going the 60 miles.

True, should have used a clean envelope, I guess.  Anyway, it would use a quart every 7.5 minutes.  So, if your fuel line will drain your fuel tank and fill a quart jar in under 5 mins, fuel starvation shouldn't be an issue.

Thanks for helping solve the problem.

Cheers,