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Old 04-21-2015, 12:33 AM   #1
DK Dan OP
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Question Left cylinder running VERY hot - Advice needed!

Recently finished a frame off refresh on my R80 G/S and I'm now doing some small runs in order to tune and adjust the Bing carbs, clutch etc.
The bike just got some nice new stainless Keihan header pipes and after a few runs I noticed that the left header pipe fitted had discoloured to a yellowish color.
The right side header has only a very small discolouring.
After a small ride I can hold my hand on the right cylinder for some seconds but on the left cylinder I can barely touch it without getting burned. So something is very wrong.

Right side spark plug is dark brownish. Left Spark plug is light grey. Mixture screws on both carbs are now set between 3/4 to 1 turn out. I tried to run the bike with the left side
mixture screw much further out in order to enrichen the mix but nothing changed.
I still need to get the carbs balanced properly but the engine is already running quite good without much vibration. It pulls strong up until 105-110 km/h then it sort of hesitate but
will keep increasing speed in small steps between the hesitations.

Other details that may be of importance; bike is fitted with 1000 cc Siebenrock kit and Silent Hektik dual spark system. These mods were already fitted when I bought the bike
and the bike ran fine before.
I did'nt rebuild the carbs since they have not caused any trouble during my ownership.
I set the timing according to the instructions from Silent Hektik but have not checked with a timing gun.

I have the left side carb off now and will disassemble it tonight in order to check that the various nozzles are free from particles. I don't have a complete carb gasket/diaphragm kit but I do have most of the o-rings.
So I will not open and inspect the diaphragm before I have a new one available.

Double checked valve clearances and they are ok. Checked oil flow to the heads when engine is running and all is ok.
Tightened all rubber booth between cylinder head - carb - air filter house.
Checked that the carb float can move freely. Didn't adjust it since it has not caused any trouble before.

Really need to get the issue sorted out before this Saturday where I'm entering a roadbook rally. So advice on what to look for would really be very much appreciated.
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Old 04-21-2015, 04:36 AM   #2
190e
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Hot cylinder sounds to be running weak, The first thing to check before doing anything else to the carbs is that the float levels are equal otherwise there is no chance of them being truly balanced. That's not as easy as it sounds because most all methods only infer the operational fuel level rather than actually measure it. Setting the floats parallel infers it. Measuring depth of fuel in a removed bowl infers it and neither will necessarily give equal operational levels unless the floats have the same weight and buoyancy. So the No1 step for me is to install new floats or accurately weigh the ones you have to check they are the same. Or perhaps do a buoyancy comparison by suspending the floats in a jar of fuel. If either of them floats as low as this they are too heavy. There should be more like 1/3rd of the float above the surface.

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190e screwed with this post 04-21-2015 at 04:44 AM
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Old 04-21-2015, 04:54 AM   #3
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Quote:
Originally Posted by DK Dan View Post
I still need to get the carbs balanced properly
this
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Old 04-21-2015, 06:41 AM   #4
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The left and the right carbs are DIFFERENT!
Do NOT just assume that the settings will be the same for each side.
Adjust them accordingly, so that the bike runs WELL.
Do NOT dwell upon each carb having SLIGHTLY different settings.
Otherwise, perhaps the left carb does have some blockages, to be attended to.
Please do report back, after you make some tweaks.
'Thanks
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Old 04-21-2015, 07:56 AM   #5
disston
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To properly balance the carbs you must first set the valve lash and check the timing.

A bad vacuum leak can cause lean burning and overheating. Check condition of the rubber sleeves between the carbs and the heads.

The gasket for the enrichner can leak badly and this causes problems when the enrichner isn't even on.
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Old 04-21-2015, 08:35 AM   #6
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Hello Dan, hope you'll make it for the weekend..!

I'm trying with my limited diagnostic experience to think what might cause this. I think it's unlikely to be things you've not disassembled, like the carbs, if they were really fine before. Maybe a clearance is too tight somewhere.

Your push rod tube seals were in a much worse condition on the left side before. May be nothing or it may be a symptom of something correlated to what you're seeing now.
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Old 04-22-2015, 06:30 AM   #7
DK Dan OP
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Thanks for the feedback guys!

Anders: You may have a point regarding the previous condition and it may actually be that the cylinder has been running hot before. I just didn't notice it due to the rusty header pipes I had not showing any visible discoloring.

Disston: The enrichner gasket will be an easy check since I have a new one at hand and will try to fit this.

Last night I took out the various jets and checked for impurities. All jets were fine but there was a lot of fine sand-like particles build up in the areas where the atomizer sits. I think that the side holes in the atomizer must have been blocked. Cleaned it all out and took a test ride but the cylinder is still running hot.


Will continue the search based on all of your feed back.
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Old 04-22-2015, 11:14 AM   #8
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Carbs are synched?
Both plugs are firing?
Both cylinders are working?

Early on the sorting out of my machine, one cylinder was intermittently doing all of the work as the other one was both fuel starved and the plug wire was failing. The fully operating cylinder was *much* hotter.
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Old 04-22-2015, 11:31 AM   #9
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Quote:
Originally Posted by DK Dan View Post
...All jets were fine but there was a lot of fine sand-like particles build up in the areas where the atomizer sits. I think that the side holes in the atomizer must have been blocked. Cleaned it all out and took a test ride but the cylinder is still running hot.
A blocked atomiser would have made that cylinder run richer so now it will be running weaker than it was before.

Floats are looking old and possibly suspect.
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Old 04-22-2015, 12:30 PM   #10
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Regarding those floats, I wonder about a simple float hight adjustment. Just about every airhead I've tinkered with has had mal adjusted float hights. Once you have mounted your cleaned up carbs on the bike, remove float bowls on one carb, turn on gas, and while lying on the ground lift and lower the float by hand to see when the needle valve shuts the flow off/ turns it on. The valve should shut the fuel off when the floats bottom is parallel to the ground. Adjust the float/needle relationship by carefully bending the tab of the float that holds the needle. I do adjust both carbs separately. Basically I set the float to shut off gas flow to float bowl when the floats are 'level' or horizontal to ground as a standard setting. Fuel must run along your arm inside your sleeve or you are not doing it correctly...

If your left hand cylinder is running lean due to fuel starvation due to float hight being set to low, ie. Not enough fuel, adjust the tab controlling the needle valve so that the float is just a tich higher than the 'level' position when the valve shuts off the gas.

Of course check for vaccume leaks, switch plugs and leads etc as well.
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Old 04-22-2015, 02:17 PM   #11
190e
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The parallel setting of the floats is perfectly valid for new floats or for floats known to weigh the same or very close to new.

Although most everyone employs this method, it is not valid for old floats that are heavier than new. It will produce a different operational fuel level and more important if one float is heavier than the other, which is not uncommon on old floats, it will produce different operational fuel levels on each carb. Same goes for measuring fuel level in a removed bowl.

Floats should ideally be the correct weight and weigh the same on both carbs but up to a point heavier floats can be made to work just fine provided allowances are made to the setting method used. E.G. for heavy floats set them lower than parallel or aim for less fuel height in the bowl.

This is simple Archemedes in the bath principle.
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Old 04-23-2015, 01:39 PM   #12
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Quote:
Originally Posted by Dreossi View Post
Regarding those floats, I wonder about a simple float hight adjustment. Just about every airhead I've tinkered with has had mal adjusted float hights. Once you have mounted your cleaned up carbs on the bike, remove float bowls on one carb, turn on gas, and while lying on the ground lift and lower the float by hand to see when the needle valve shuts the flow off/ turns it on. The valve should shut the fuel off when the floats bottom is parallel to the ground. Adjust the float/needle relationship by carefully bending the tab of the float that holds the needle. I do adjust both carbs separately. Basically I set the float to shut off gas flow to float bowl when the floats are 'level' or horizontal to ground as a standard setting. Fuel must run along your arm inside your sleeve or you are not doing it correctly...

If your left hand cylinder is running lean due to fuel starvation due to float hight being set to low, ie. Not enough fuel, adjust the tab controlling the needle valve so that the float is just a tich higher than the 'level' position when the valve shuts off the gas.

Of course check for vaccume leaks, switch plugs and leads etc as well.
Quote:
Originally Posted by 190e View Post

This is simple Archemedes in the bath principle.
Good points about the float height adjustment and old vs. new floats! Will certainly investigate this further when I find the time. And slightly off topic; regarding Archimedes principle...we once had a Danish innovative guy/artist called Storm P. who made his own version of the principle saying "When a body is immersed in water.....the phone rings"

Quote:
Originally Posted by knary View Post
Carbs are synched?
Both plugs are firing?
Both cylinders are working?

Early on the sorting out of my machine, one cylinder was intermittently doing all of the work as the other one was both fuel starved and the plug wire was failing. The fully operating cylinder was *much* hotter.
All four plugs are firing but I didn't do a proper carb sync and I think that's one of the things causing the trouble. This evening I tried to follow the instruction on the last page of this pdf. It's the best single source I've found about Bing carb adjustments.

I borrowed an infrared temperature gun and before doing any adjustments the left hand cylinder head temp read a little above 130 degrees Celsius (266 degrees Fahrenheit) and the right cylinder head was about 95 degrees Celcius (203 degrees Fahrenheit). Both temperatures were taken after a 25 minute "medium-fast" ride. The photo below (with cold engine) shows where I measured the temperature on both heads.



After doing the adjustments in the above mentioned pdf I had the following measurements after a similar type of ride:

Left head = a little above 120 degrees Celcius (248 degrees Fahrenheit)
Right head = about 115 degrees Celcius (239 degrees Fahrenheit)

So I guess that the left cylinder had been doing most of the work prior to the adjustments.

So far both the mixture screw and idle has been difficult for me to adjust. Still need to work a lot more with the this. But the best thing to do will probably be to overhaul both carbs and get the timing checked before spending a lot of time on adjustments.
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Old 04-23-2015, 02:54 PM   #13
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Does anybody have ideal temperatures for a warmed up engine and where to take the measurements? I expect the temperatures are going to fluctuate pretty wildly depending on ambient temps, but is there a "hmm, that sounds awful toasty" reading we wouldn't want to be near?
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Old 04-24-2015, 06:31 PM   #14
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Measuring engine temperature using infrared thermometer.

It would be worthwhile having a standard measure point. I'd suggest the exhaust stub that the nut attaches to. The surface there is flat and not interrupted by the fins.

Are there specific guidelines on how to point and shoot the thermometer?
eg distance, angle etc?
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