CB400T Overheating....

Hi Teazer, thanks for the comments...I did take the rocker cover off and plenty of oil in the top end, so no problem with circulation...
below are the temps...what do you think...are these normal?

Left head temp beside spark plug 130 degrees, right side same place 140 degrees, under transmission/sump 90 degrees,
exhaust headers 300/320 degrees
 
If the engine is running rich and the ignition timing is correct, I can't think of how the bike would actually be overheating.

And those temps look pretty good. I don't think the engine is overheating at all.
 
Thanks Sonreir....maybe all is okay...and its just the header wraps, it just seemed all round very hot...I will keep a eye on it
and see how it progresses with more miles on the engine, and hopefully the wrap will bed in okay.

Thanks to all for comments.
 
.
your temps actually look low so i would question as to whether the gauge is accurate.

most engine oil boils above 500 degrees so yours is not boiling.

its impossible for your header pipe t only be 300 if you hold the throttle at around 2000 rpm and take the temp . . it will be lowest at idle.

if you are testing the temp of the header wrap, it will read low.

your plugs definitely show a blatantly obvious rich condition, especially if they only have 100 miles on them.

as i said, i would lean it put and maybe your miss that occurs when it gets hot will go away . . also, a rich condition like you obviously have can damage piston rings causing them to not seal properly.

the noise you occasionally hear when you turn it off might be compression leaking past the rings.

your plugs are not dark and have some carbon because its too lean.

most the plug color comes from cruise not idle which means that it is at least rich at mid throttle.

.
 
Here's oil temps
oil-temp-chart.jpg


and
Sparkp1.jpg



plugcolorchart2_html_6084a1d3.jpg



What that shows is that at less than say 1/2 throttle a plug is not hot enough to burn off deposits, so it looks rich even if it is not. Plugs read at mid range tell very little about the engine temps or air: fuel ratios.
 
Good interesting information many thanks Teaser...hence why you need to do a plug chop at full throttle to really see
what's going on....
 
drduke said:
Good interesting information many thanks Teaser...hence why you need to do a plug chop at full throttle to really see
what's going on....
Click to expand...

nope, not at all, however, that certainly is one test you can do but nothing is going to change the fact that your plugs clearly show that you are rich on the main jet unless you never rev your engine past around 3500 rpm.
 
not so...main jets need to be read a full throttle settimg,or have I got that wrong also.
 
Looks like you're running aftermarket carbs (Mikuni VMs?). In this case, yes. WOT is necessary to get a decent plug reading for your main jet.
 
drduke said:
not so...main jets need to be read a full throttle settimg,or have I got that wrong also.
Click to expand...

yes, you do have that wrong to some degree as i mentioned, but its a bit complicated and few are aware of this.

the other difficulty is reading the plug properly with todays fuel because it is in fact a bit different than the old method.

if you really want to do a PROPER full throttle plug reading do the following.

1. warm bike up.

2. install new plugs.

3. get in third gear quickly then hold the throttle wide open until it reaches very close to max rpm.

4. just before it reaches max rpm, instantly shut the throttle off as you pull in the clutch and turn the bike off.

5. coast to a stop and install the old plugs.

6. go home and take a photo of the end of the plug.

7. cut the threads off of the plug with something.

8. post a photo of the porcelain from the side.

9. re-jet as necessary then repeat the test until you think it is correct.


...or just install one size smaller main and lower the needle and install two new plugs then call me in the morning.


This plug is shows the jetting is RICH.

plugchop.jpg
 
drduke said:
not so...main jets need to be read a full throttle settimg,or have I got that wrong also.
Click to expand...

Correct. To read plugs you really need to be wide open etc.

Plugs don't tell us as much as we might think at lower revs unless there is something really wrong. An A:F meter is a much better way than plug reading for lower loads. At lower load conditions the plugs will get lighter if you lean things out, but that doesn't necessarily mean that it is better.

And keep in mind that peak power is at an A:F of closer to 13:1 and peak economy is at around 16:1 and not at 14.7:1 that we all learned about as the perfect number. Where people frequently go astray is that they lean out part throttle until plugs look clean and then running on a wisp of throttle on the street and find that they are way too lean. That is one great attraction of EFI, you can set a table up for different throttle positions.

But the easiest way is to get idle right and off idle pickup and then main jet and then work on driveability in the midrange.

Barnett is right that there is more to getting fueling correct than just a plug chop or one A:F ratio. It's a little more complex. If you can do a wide open plug chop safely it might be a good idea. Don't bother cutting the plugs up unless you want to do it just to say you did it. A Spark Plug light/reader is good enough or a jewelers loupe and flashlight usually work OK to see the electrodes and the mixture ring clearly enough, but the picture shows it pretty well.
 
Thanks Guys..I think that just about covers the plug chop...I appreciate all input, it have been very helpful.
 
You must log in or register to reply here.

DTT Light or Dark

  • DTT Light

    • Spread the Love

    Back
    Top Bottom