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Gummed up Carbs and modern fuel

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exvalvesetdabbler:
Best grab a mug of coffee - this is a bit of a long post.

Two years ago, after my 400/4 had been laid up for a couple or more years, I have had to jump through all of the usual hoops to get the carbs cleaned up and working again.

On opening them up I was faced with a solid coating of brown varnish and the floats stuck solid on their pivots.

I completely stripped them and soaked everything in methylated spirit for a couple of days. Most of the varnish turned to a brown powder which came off easily with a tooth brush and soapy water. I found that the usual carb cleaners evaporated too quickly to be of any use. After an initial clean up I could remove the main jet , emulsion tube and pilot jet.  I was still left with the stuck floats. After mangling one float trying to work it loose by spraying carb cleaner over the pivot and wiggling it, I eventually had some success with using a gas soldering iron with the miniature hot air attachment to locally heat up the pivot enough to soften the varnish and was then able to push out the pin.

The whole lot was soaked again in jam jars of methylated spirit and the jars were dropped into an ultrasonic bath in the hope of cleaning the hard to reach places.  After rinsing off and blowing through with an air line the small passages were treated to a blast of carb cleaner, and catching what came put on some paper to make sure it was clean.

Main jet, float valve and pilot jet were replaced with genuine Honda items together with all of the O rings. Float heights set. After statically balancing the carbs everything seemed to be in order apart from one incontinent carb. As I have since found out this was the float that was mangled during disassembly. Basically the pivot and tang was out of alignment causing the tang to press on the needle at an odd angle and also the float was able to jam in the fully open position, hence the need to tap the bowl with a screwdriver handle when first switching on the fuel.


Fast Forward 2 years.

I finally got around to pulling off the carbs and sorting out the float problem by swapping all of them for a spare set. Reset the float heights again.  Just for good measure I put an airline on the fuel feed pipe at a very low pressure and was able to verify that the needles were sealing properly and at the right height. Once again, I checked all of the small passages were clear.

After all of this I am still left with a richness problem at low to medium throttle settings. After a few days in 30-40 mph limits the plugs are black with dry soot.  After wringing it's neck down the dual carriageway the plugs are a dark brown. Sometimes when sitting at traffic lights the pong from the exhaust makes your eyes water.

Also adjusting the pilot air screw does not change the engine speed.  I haven't balanced the carbs properly, there seems no point yet if the idle mixture is off.

Other symptoms - runs better from  idle to 3000 rpm when half warmed up, stumbles a little 2000-3500 when gently on/off the throttle when up to temperature.

Other snippets that I have found courtesy of google.

The black plastic float material can absorb fuel as the plastic ages and so give an artificially higher than normal fuel level
Modern fuels are more dense and rely on complex injection systems to correctly atomise the fuel
Modern fuels atomise poorly in carbs- droplets too big giving the symptom of running rich wheras the mixture is actually lean (?? )
Continued flooding of carbs can cause fuel in the oil which then gets recycled back to the air box causing over rich mixture
Some people have drilled extra cross feed holes in the emulsion tubes to improve matters

Also see this
 http://www.ksrc-au.com/Bike_Optimax.pdf

So, does any one believe any of the 5 snippets above or had experience of them?


By the way I am using the bog standard Shell unleaded and have used unleaded since it was first on the forecourts, prior to that I always ran on 3 star leaded.

Airbox , filter  jet sizes -  in fact everything is as Mr Honda intended.

Other sites recommend checking the needles again and oval wear to the top of the emulsion tubes, but at low throttle settings there shouldn't be any thing coming from them any way - or should there be?

I'm now just starting to add a fuel stabiliser so that I don't have to put up with gum and varnish again, Never had any problems like this with the good old leaded stuff.

Perhaps we could have a poll on here - how black are your plugs after pottering around town

One thing I do know that  causes problems is the tool tray cover migrating towards the air inlet and nudging up to the cut away in the inlet rubber.

My next move is to try a hotter plug for local riding, this is what Shell in Australia advised their customers to do
I'm clean out of ideas now - any suggestions?

Regards
Dave

PatM:
Hello Dave

A very informative post and something most of us know a little about but to me, you

K2-K6:
That's a lot of work done to get it cleaned up and a pain if you can't get it up to scratch.

Hotter plugs in my opinion shouldn't correct anything but may give better running if they are fouling? as PatM says, you are probably looking at changing the jets to get more accurate delivery

My understanding of hotter plugs is that they have less of their ceramic insulator that is around the tip touching the plug body, the effect being to retain more heat at the tip and so prevent the spark area from fouling and producing no spark. The limit comes if the engine gets too hot and the plug tip then goes over temp and sarts to melt or cause pre-ignition / pinking.

The big risk for me in overfueling is that given sufficient over fueling the neat petrol will wash the cylinder bores free of oil causing high wear of bore and rings. Also dilution of the oil which leads to both cam and plain bearing wear ( basically it breaks down the lubrication film the oil is supposed to maintain during bearing loading) if the oil smells of petrol at all it needs replacing. It's this process that has accounted for a lot of engine wear over the years especially with manually operated chokes and one of the benefits of modern lean burn engines with accurate fueling is enhanced oil and thus material life in general use.

Anybody trying to clean carb components of gum may find it worthwhile soaking in neat diesel for a while to help  start of with.

exvalvesetdabbler:
Thanks guys.

There is only the needles and emulsion tubes left that hasn't been changed. The thing I can't figure out is that at idle and small throttle openings, the main jet and needle shouldn't be doing anything towards fuel delivery. What I am finding is that the plugs do start to clean up a bit with sustained higher throttle openings. If fuel was getting past the main jet o ring the problem should be worse at high throttle settings when the main jet comes into play.

So this leaves the idle circuit. From what I traced through, the small hole on the choke flap side is where the air goes in, the pilot air screw controls the air flow and it comes out of the small hole just in front of the needle on the engine side. This points to there being reduced air flow coming in and past the air screw.

I think I need to examine the small passages again and check for wear on the needles/emulsion tubes.

PatM:
Dave

-or try another set of carbs off ebay.
the airflow will pull pule up any passage from the floatbowl. As Ive said- you are overfuelling and my guess is main jet seal or position.
If you were closer- Id say pop round and pick up my spare set

PatM

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