1975 Cota 247 - Flooding Chronically.

[handmadematt]

The saga continues.

Essentially the bike runs very well but is just hard to start, especially when warm. (Very hard to start... Making her un-usable.)

Having bought a flywheel puller and re-adjusted the timing to be spot on, replaced the plug and condensor and consistently observe a good spark I am happy that my problem is not the ignition.

The air filter is also in good order.

The only remaining problem is fuel, I believe the engine to be flooding itself, the plug is very wet upon inspection after trying to start her. Could this because the mixture's too rich? Can I resolve this by lowering the needle on the throttle slide? Or am I barking up the wrong tree do you think?

Cheers and Happy Christmas.

[ikb]

Check the choke isn't sticking but is most likely the float height is too hi letting too much fuel into the float bowl, if you have a look on the beta forum there is loads of info about float setting!!

Ian

[woody]

Raising or lowering the needle in the slide will have no affect, it only controls the fuel / air mixture passing from carb to engine when the engine is running.

If the bike isn't firing when you are trying to start it, the plug will be wet. It doesn't mean a flooded carburettor.

If the carb was flooding the engine wouldn't run smoothly. You would also have fuel running out of the carb.

A strong spark visually doesn't mean it can't be extinguished under compression if there is an electrical problem.

You haven't yet eliminated the kill button, at least disconnect it and see if the symptoms persist, if you don't want to replace it.

Are you sure there are no breaks in the wire from stator to coil

Also earth the HT coil directly to the frame by rubbing the powder coating off the coil mounting bracket completely until you see shiny metal on the entire mounting face of the bracket. Earthing it to the engine may not be a good idea as the engine mounts are also powder coated and if these haven't been cleaned off thoroughly you will have a bad earth.

Until you are certain of these things, you haven't yet eliminated the electrics entirely as a source of the problem

[handmadematt]

...have a look on the beta forum there is loads of info about float setting!!

Ian

Thanks mate. What is the Beta forum? Can you link me?

If the carb was flooding the engine wouldn't run smoothly. You would also have fuel running out of the carb.

It's the cylinder that's flooding I think, not the carb... It could be fouling the plug and prohibiting starting. It could be because of a rich mixture? (Too much fuel not enough air.)

A strong spark visually doesn't mean it can't be extinguished under compression if there is an electrical problem.

You haven't yet eliminated the kill button, at least disconnect it and see if the symptoms persist, if you don't want to replace it.

In all my testings so far I have not once witnessed "no spark," so the only electrical cause of my problem would be as you say, the spark failing under compression. I can't see anyway that this could be caused by a faulty switch, there's just no way that the switch would "know" (or be affected by) the plug being installed in the cylinder.

Also earth the HT coil directly to the frame by rubbing the powder coating off the coil mounting bracket completely until you see shiny metal on the entire mounting face of the bracket. Earthing it to the engine may not be a good idea as the engine mounts are also powder coated and if these haven't been cleaned off thoroughly you will have a bad earth.

Until you are certain of these things, you haven't yet eliminated the electrics entirely as a source of the problem

The coil is earthed to the engine casing not an engine mountain point. The engine casing is not painted or powder coated at all.

Thanks for the suggestions though. It is really appreciated.

[fantnick]

Hi Matt, have you tried a replacement coil? they can break down when warm, I had a similar problem on ty and new coil cured it. Nick.

[lineaway]

Do not worry about the beta forum, that is a different issue. Does the petcock actually turn off the fuel? Do you turn off the petcock when not riding? Is the carb really clean and you checked the needle and seat is clear and shuts off the fuel? Woody is correct on having a good earth. If the plug is real wet it will not spark. If you have a puddle of fuel in the crank it will always be hard to start.

[tony283]

This seems to be going down the "red herring" road ! ...and equally the "little knowledge dangerous route" Lets get back to the basics that the panel of real experts have been advising and that so far have not been followed.

First lets establish that all is well on the electrical side which means following their advise re contacts and earthing....... and disconnect that kill switch which the bike never had when new!

You say you have fitted a new plug ? Presumably the correct type ? Plugs of course come not only for our trials applications but a host of others. A new plug invariably comes with a huge gap ! This needs to be reset to 70's era gaps which is 22THOU. I trust the points gap has been correctly set at 15THOU. Common problems with wiring are where others have mentioned where the cabling gets hot and brittle. Also have a look at the plug lead by removing the cap, and check the wiring is not rusty ? .....if so cut back a little to new bright wiring.

You say you have a Mikuni fitted, what model and when ? Ideal Mikuni for this application is a VM26 with about 155 main jet and 35 pilot. Set needle clip to middle groove, airscrew at around 1.75 turns out. Basic info for carburation, Main jet controls flat out performance. Needle and clip control mid range performance. Pilot jet controls pick up off idle.

If you decide to keep the current carb check the jetting numbers and keep us informed.

Good luck and Happy Christmas

Tony

[handmadematt]

Hi Matt, have you tried a replacement coil? they can break down when warm, I had a similar problem on ty and new coil cured it. Nick.

It has had a new one fitted by the previous owner, it looks all nice and new in good order. I was thinking about getting a replacement though but in the end I thought it's not necessary. Maybe I should.

Does the petcock actually turn off the fuel? Do you turn off the petcock when not riding? Is the carb really clean and you checked the needle and seat is clear and shuts off the fuel?

The carb is immaculate. The fuel tap works flawlessly and it's always turned off.

If you have a puddle of fuel in the crank it will always be hard to start.

Maybe I do..? I'd not thought of that. It would certainly change the volume of the space. I'll think about that some more, thanks.

If the plug is real wet it will not spark.

I think that's what's happening once I've kicked it a couple of times. (I also have experienced it firing up and revving up nicely, then it will just die from a high rev and just drop out, during wich time if I blip the throttle I just get aspiration noises and no more firing.

Have a great Christmas guys.

If you have a puddle of fuel in the crank it will always be hard to start.

[handmadematt]

Wow, thanks mate. I appreciate your thorough reply.

You say you have fitted a new plug ? Presumably the correct type ? Plugs of course come not only for our trials applications but a host of others. A new plug invariably comes with a huge gap ! This needs to be reset to 70's era gaps which is 22THOU.

I bought the plug from Dave at Inmotion, I was there in person with my engine number getting a number of items so I am confident the plug is correct although I haven't checked. I just checked the gap and it is indeed 22thou.

I trust the points gap has been correctly set at 15THOU. Common problems with wiring are where others have mentioned where the cabling gets hot and brittle. Also have a look at the plug lead by removing the cap, and check the wiring is not rusty ? .....if so cut back a little to new bright wiring.

I did the points today and then timed it to fire at 2.5mm before TDC. All the wiring is relatively new by the last owner, the plug lead is great and I get a good spark through maybe 5mm of air to the barrel when I test it, and the barrel's painted.

You say you have a Mikuni fitted, what model and when ? Ideal Mikuni for this application is a VM26 with about 155 main jet and 35 pilot. Set needle clip to middle groove, airscrew at around 1.75 turns out.

It was fitted by the last owner who said it's been great. He was confident that it's always run seamlessly. I don't know what model it is, the only thing I can see on it is "ISO" and "Made in Japan." I've not recorded the numbers of any jets when I cleaned them. The needle clip is on the second groove from the top, by airscrew do you mean the slide adjuster/ tick over screw?

If you decide to keep the current carb check the jetting numbers and keep us informed.

Good luck and Happy Christmas

I will do. Thanks again and have a great Christmas yourself.

[lineaway]

Sounds like the electrics are working. (bad earth is still a possibility) Not sure on jets.(Did you actually remove the pilot and blow the circuit out?) Not sure if the needle and seat have been removed and cleaned. I finally read the first post.( the lighter was amusing, been about ten years since I saw a nice 348 tank on fire). Will not start plug wet, plug has been dry and not started, bike idled high and stalled.

I would closely look at the floats. Bent, crooked, loose, bent pin, wrong pin, damaged pin hole( have seen them cracked) any evidence of sticking to the walls. Full of gas on one side. Something odd is going on. By the way the pilot jet always flows.

[tony283]

Airscrew and Idle Screw. Two completely different screws with two entirely different functions. The Idle Screw gently raises the slide in the carb body when screwed in allowing more fuel/air to be let into the engine thereby increasing RPM. The Airscrew on a Mikuni is located to the rear of the carb body and allows air to combine with fuel which gives instant pick up from idle when set correctly. If you slam the throttle wide open from idle and pick up is not instant, or the engine dies then this circuit is either not cleaned/partially blocked or incorrectly set.

When the carb has been cleaned correctly, pilot jet and circuit blown through, located to the rear of the main jet down a rabbit hole, (no poking around with wires please) Start as you have been doing, adjust idle or tickover screw for about 800-1000 rpm with the idle screw. Now turn Airscrew 1.5 turns out from full in. Now adjust the airscrew in 1/4 turns until you achieve the fastest tickover....... if you are not around the 1.5 to 1,75 turns then you need to change the pilot jet. With experience you will be able to skip this step by just opening the throttle quickly and getting the desired results with minor screw adjustments. With all this done lower the rpm with the idle screw to your desired tickover if thats what you want.

Tony

[handmadematt]

If you have a puddle of fuel in the crank it will always be hard to start.

I have read more about this phenomenon having never heard of it before. It does seem to happen sometimes. I removed the tank and carb and turned the whole bike upside down and then propped the rear mud guard up on a stool so that the engine was horizontal. I then removed the plug and spun it over fast several times by hand with the kick start. Petrol was dripping out the inlet manifold and being spurted all over the frame and the floor from the plug hole, quiet a lot. I wouldn't say 100's of ml's or anything but certainly enough to make everything wet and cause for me to clean up.

Let's see how I get on after doing this. It's too late now to be starting her up but over Christmas I'll give it a go.

Edited December 24, 2012 by handmadematt

[woody]

I have read more about this phenomenon having never heard of it before.

Perfectly normal if you've kicked hell out of a bike and it isn't firing. That puddle of fuel in the crank is only there because you have been continually drawing fuel in when trying to start it, some gets pushed out the exhaust, some stays in the engine. When the bike is running, that puddle of fuel will get burnt off, it doesn't stay there permanently, so isn't the immediate cause of the bike not restating after you have stopped it. This is where a decompressor is handy, if you kick the engine over repeatedly using the decompressor, it will help get rid of the fuel and help get it started.

The only other way fuel can get into the crank is if the petrol is left on and the carb floods. Fuel will then overflow into the inlet and down into the cylinder. This will involve a lot more fuel in the engine than you describe.

Why are you so reluctant to eliminate the kill button from the list of possible causes? Electrical problems defy all logic and sometimes you just have to employ trial and error. Disconnect it - at least it will prove whether it is at fault or not.

I would also earth the coil direct to the frame and get rid of the wire to the engine - it's not how they are meant to be earthed, no bike left the factory like that.

The point I was making earlier about a weak spark is that although the spark looks strong, that may not necessarily be the case and when under compression, the pressure inside the cylinder is enough to snuff out the spark. It has nothing to do with the kill switch knowing the plug is in the cylinder - it's simply that the spark isn't strong enough under compression to fire the mixture - despite it looking fine when you test it

As I said, it's trial and error and you need to eliminate all possible electrical causes - including a nick in the wire from stator to HT coil, especially where it leaves the stator as they can always get pinched here when fitting the stator - just because it has been renewed at some time doesn't mean it's not at fault.

Also, as someone else mentioned, cut a piece off the HT lead and refit the plug cap - even if the end of the HT lead looks in good order, just do it.

The way you say your bike performs when it is running doesn't suggest anything wrong with carburation.

Concentrate on the electrics until you have eliminated all that has been suggested.

[handmadematt]

Happy Christmas.

...if you kick the engine over repeatedly using the decompressor, it will help get rid of the fuel and help get it started.

Would that also work if I just took the plug out and spun it over? (I've not noticed any mess when I've done this to check the spark (which has been many many times now! Ha.)

Why are you so reluctant to eliminate the kill button from the list of possible causes? Electrical problems defy all logic and sometimes you just have to employ trial and error. Disconnect it - at least it will prove whether it is at fault or not. ...The pressure inside the cylinder is enough to snuff out the spark (if it's weak.)

I guess my reluctance is that it just doesn't sound feasible to me. A faulty switch can't create a weak spark in my head, it's either on or off. I also disagree with the statement that "electrical problems defy all logic." However, you are right, in the name of good science I will disconnect it and see if it makes a change. Thanks.

I would also earth the coil direct to the frame and get rid of the wire to the engine - it's not how they are meant to be earthed, no bike left the factory like that.

Again, to me it doesn't make sense but I'll do it. (It is apparently a common mod when a frame is powder coated though.)

As I said, it's trial and error and you need to eliminate all possible electrical causes - including a nick in the wire from stator to HT coil, especially where it leaves the stator as they can always get pinched here when fitting the stator.

Agreed.

The way you say your bike performs when it is running doesn't suggest anything wrong with carburation.

Concentrate on the electrics until you have eliminated all that has been suggested.

It does run beautifully. It's a shame there's no window into the cylinder to observe the spark hey?

I guess I'll be rebuilding the whole wiring loom then! Ha. So, in short, at the moment the only un-proved systems (which are all observed to be functioning) are the switch, the wiring itself and the coil. The plug's new, the condensor's new, the points are new and the timing is perfect.

I just hope in doing all this I'm not barking up the wrong tree...

Thanks again and have a great Christmas.

[naichuff]

Try useing a Gunson tuner It is a spark plug where the body is brass with a clear center with the elctrode down the middle You can see the spark under load and set the carb up as you can see the fuel burning through the range I have set up several bikes this is the way and use it to balance the carbs on my Guzzi V50