Exhaust Temps

[n0lan]

Hi Guys,

New to the site, looks like there is a great wealth of info here.

I done some searching but couldnt quite come up with what I was looking for.

My bro-inlaw came by this afternoon on his 79 XS11 Special claiming that it was only running on 2 cyl's. I took teh seat off to take a look at the wiring to the coils and found a scary mess. The PO must have really hacked this thing up. bare wires all over the place. anyway, I broke out my trusty laser pointer temp gauge and hit the exhaust pipe coming right outta the head and it showed like 700^ F or 2 of the pipes, 1 other was 250^F and the other 350^F. I thought those reading were pretty high. Is this thing overheating? It was only running for approx 3 - 4 minutes. My honda CB750 only runs about 300^F after a long ride on a hot day.

Also, I was wondering if you can power the coils directly from the battery? with a fuse and relay of course. Its a trick commonly used on older honda CB bikes. Does anyone know if this would be a BAD idea? I done it to my 79 CB750K and the improvemnt was huge thru out the RPM range. starts easier too.


Any and all help is greatly appreciated!
Nolan

[3Phase]

Hi Guys,

Hello, Nolan, welcome to the forums!

It seems the bike is running on two cylinders. Starting from the left side of the bike as you sit on it, #1 is first on the left. Which pipes were hot and which were cooler?

... I was wondering if you can power the coils directly from the battery? with a fuse and relay of course. Its a trick commonly used on older honda CB bikes. Does anyone know if this would be a BAD idea? I done it to my 79 CB750K and the improvemnt was huge thru out the RPM range. starts easier too.

It's a BAD idea. Unless someone has put aftermarket coils on that '79 the power has to run through a ballast resistor. The ballast resistor is a small rectangular metal box on the left side of the frame next to the coils. The two Red/White-stripe primary wires from the coils will be plugged into the ballast resistor.

The two Red/White-stripe wires are always hot when the key is on and go to the coils, the Orange and Gray wires go from the coils to the ignition module, the TCI (Transistor Controlled Ignition).

Make sure both Red/White coil primary wires are connected to the ballast resistor or only one coil will work. If someone has messed up the wiring you'll need a schematic to sort it out.


One of the moderators, TopCatGr58, has a link to some colored schematics.

Member CatatonicBug has electronic copies of the manuals available for download at his web site.


Take your time and don't get frustrated, these old bikes are worth the effort to fix!


Regards,

Scott

[n0lan]

3Phase,

Thanks for teh quick response.


I cant remember which pipes were "hot". truthfully, all 4 seemed hot to me. just some were hotter than others (700^F). Do these bikes typically have exhaust temps that high? seems like teh coldest was 250ish and warmest was above 700. i should have checked the temp at the head near the plugs but wasnt thinking at the moment.

thanks also for the advise on powering the coils. I did notice that ballast resistor and remember wondering what that was, didnt pay much attention to what was wired to it etc etc. I'll definetly check it out when I get home.

I've also printed the wiring diagrams you linked for me.

I printed all 279 pages of teh service manual last night. from work
also most of the tips n tricks for repairing teh coils, adding new wires to old coils etc etc.

I'll update this thread as I make more progress. I'm sure I'll have more questions.


Thanks Again!
Nolan.

[dbeardslee]

700 sounds way hot. When I measure my header pipes at the turndown I usually get a reading around 250 degrees F across the board, depending on the ambient temp. The highest I've ever measured it was less than 300 degrees. I've never checked right at the flange, but I can't imagine there being a 450 degree difference from one to the other, but who knows.

[Brad]

Just something you have probally checked already, oil full? That could lead to higher temps....

[n0lan]

Just something you have probally checked already, oil full? That could lead to higher temps....

yep,oil level looked good thru the sightglass. I assume thats how you checkthe level? It seem like I unscrewed the fill tube and it didnt have a stem to measure the oil level.

I was curiuos if maybe something has clogged an oilport somewhere restricting oil flow to the head thus causing it to run extremely hot. I'm not really familar with the yamahas specifically but have limited knowledge of other inline 4cyc bikes or that era.

I'll know more hopefully this weekend when I can try to diagnose it a lil further.

I apprciate all the help and suggestions thus far. Keep em coming


Nolan

[n0lan]

Now that I'm kinda going over everything in my head, im hoping its not like a locked up valve or pistoin or something. would that cause exxessive temps?

He (my broinlaw) said it was running on two cyl, thats why I broke out the temp gun to try to determine which ones werent firing. well, all were warm, 2 extremely warm, and two about normal temps based on what dbeardslee describe on his readings for his bike. to me, that suggest that all 4 were firing, 2 were just extremely hot. (which is why I mentioned in my previous post about something blocking something in the head restricting oil flow and thus the high temps)

I dunno, I'm probably just overthing all of this stuff, I just need to dig into it

You guys have any thoughts?


Nolan.

[XS1100 Newbie]

Is it maybe running wy lean on the two cylinders? Lean burn ill increase heat.

[oldyam80sg]

I sold an XS400 to a friend in high school and he touched the idle screws in the carbs and don't know what the temp was but both pipes were glowing an orange color very scary to look at -700 seems very hot to me.Also did you check the spark plugs?If the temp was actually that hot i would hate to see what they look like.

[dbeardslee]

If your timing is retarded too far it can cause a motor to run hot. You really need to check which cylinders were doing what. Your ignition system works in pairs - 1&4 and 2&3, so if you're seeing these pairings as it relates to heat suspect your pickup coils or wiring.

[n0lan]

I sold an XS400 to a friend in high school and he touched the idle screws in the carbs and don't know what the temp was but both pipes were glowing an orange color very scary to look at -700 seems very hot to me.Also did you check the spark plugs?If the temp was actually that hot i would hate to see what they look like.

I didnt personally look at them. he had just put new plugs in it the day before trying to cure his two cycl running problem.

I forgot to mention it earlier but, I pulled each plug one and a time and cranked her over, had fire on all 4 plugs. it wasnt a fat blue spark or anything, but it did have spark. but on a side note, I know coils can work intermittily, like once they get hot they can quit working, then when they cool down, they will work again.

Thanks for all the help thus far guys!

Nolan

[dbeardslee]

If you're running the stock coils, chances are good that the high tension wires are shot. You can graft new wires into them, but I doubt that's what's causing the problem. The pickup coils signal the TCI to send power to the ignition coils, so again depending on which cylinders are cold, they're probably the more likely culprit. If the cylinders that are cold don't match the pairings previously mentioned, I'd be looking to carbs. Not sure if out of sync carbs could cause overheating, but I wouldn't be surprised.

[DGXSER]

Thes bikes run on what is called a "wasted spark" system. The coils run 2 cylinders each, 2&3 and 1&4 as Doug (Dbeardslee) stated. When the coil sens a spark it sends the spark to both plugs and both fire, just one is on an exhaust stroke so nothing really happens, while the other is on combustion stoke and ignites the fuel air mixture. So if you check the temps again and see 1 & 2 cold while 3 & 4 are warmer. Then the sparks are all working most likely.

I would look at a kinked fuel line or a messed up vacuum valve (better known as the "Octy"). It resides on top of carb no 2 and should have a vacuum line attached to the no 2 carb intake boot vacuum nipple. This valve controls fuel flow to the carbs when the petcock is in the ON or RESERVE position. It is possible one side is plugged and only feeding one set of carbs, or brely dribbling fuel to them so they are running lean, and intermittently. Try putting the petcocks in the PRIME position and see how it runs.

Now, if it runs nice at idle and then starts cutting out or missing or intermittently missing at RPMS above say 2500, this would tend to indicate a broken wire at the pickup coils under the timing plate.

[3Phase]

You guys have any thoughts?

Sure, don't get paranoid or you'll start tearing into things and break some perfectly good 30-year-old parts!


Easy things to check:

There's a squirrel in the air box.

A fuel line is blocked or kinked.

The rubber intake boots, vacuum plugs/lines are loose or cracked.

The carburetors are loose and air is leaking into the engine around the rubber boots or they're dirty/out of adjustment.

There's a potato in one of the exhaust pipes.

The vacuum advance line from the #2 carburetor is loose or cracked.


No? Okay, you have a new old bike that's running hot on a couple of cylinders. You think it's running on all four cylinders and it's not fuel, air leaks, potatoes, or squirrels. It would be nice if you could find out which cylinders are too hot!

Start with the basics and check the mechanical condition since you just got the bike. You can more or less choose the order since some checks are done with the engine hot and some cold but they should all be checked or you'll wind up angrily spinning yourself into the ground like a Looney Tune Tazmanian Devil:

Check the spark plugs with the engine cold to see how they look and ensure they're the correct plugs with the correct gap. You can check them hot if you insist but I don't like holding hot spark plugs and trying to set the gap. You can drop a plug on the floor while you're fooling with it in your hand, then you have to run to the store to buy a new spark plug -- not that I've ever done anything like that mind you but it did happen to a friend... once.

Start and run the engine. When the engine is hot, remove the spark plugs and check the cranking compression with the battery fully charged and the throttle held wide open. Write down the result for each cylinder.

Check the valve clearance with the engine cold. Write down the clearance on each valve. If you have to change any shims write down the number of the shim you removed, the final valve clearance after adding the shim and the number of the shim you added.
Example: #2 Exh 0.12mm 300 --> 0.22mm 290

Check the ignition timing.

Check the pickup coil wires.

Clean the carburetors and check the float height.

Synchronize the carburetors.


Take your time and don't get paranoid!


Regards,

Scott

[n0lan]

ok, got it fired up agian just to check the temps.

here is what I got:

cyl1



cyl2



cyl3



cyl4



So, just then all 4 were obiously hitting b/c of the temp readings. but if i would have run it up the road i would have experienced the 2 cyl loss at some point. temps still seem extremely high tho.

next question:

The vacuum advance line from the #2 carburetor is loose or cracked.

would that be this in the pic?





Its plugged off with a bolt by the PO. maybe the 2 cyl loss i'm experiencing is b/c of loss of fuel and not loss of fire.



a fwe other mystery items I came across that someone may be able to help me identify.

here is where the fuse box should be. not sure what the PO had attempted.
What are the 3 wires that I have circled for?





how bout this one:






This looks like some sort of realy or something, not really sure. (red arrow)





notice the white arrow in the pic above. That was the PO briiliant idea to hold the battery in there. Is these any suspposed to be a batery box to hold it?

under seat wiring:





Sideview of bike 1



Sideview of bike 2





Nolan