[Dimitri]

Hi Guys,

I have a problem. I recently bought a Harris T140. 95% stock and never messed with. It did had an idle problem and the carbs flooded the firt time i went for a drive due to some dirt particles.

I took apart the carbs, bought some major rebuild kits from Amal, including stay up floats. cleaned them in my ultrasonic cleaner and got everything together again. I also cleaned the petcocks and tank, replaced fuel lines etc.

The bike fired up right away and after some basic tuning it ran pretty good. Exept for idle. After a run and stopping at a stoplight it dies.

Now, i tried to check my float level again, and i can see the fuel does not get the needle valves lifted to fill the bowls. even with the light aluminum ones. Does anybody else have this problem? I must say, the fuel tank level is low at the moment (on reserve). It can't be that there is to little pressure to lift the valves?

My test setup is: bowles attached to a horizontal plate, with their fuel lines attached, and the tank above. I can shut off the fuel supply just by inserting the needle valves in their seats, Gravity does the rest.

My carb is a concentric 930 MK1,5. It uses the larger needle valves from the MK2, but i also tried to use the smaller MK1 valves in combination with a custom valve seat. Without any luck.

The only solution i can think of is to eliminate the backlash of the needle valve somehow, so the needle opens immediately when the float lowers.

I assume there is no problem with a full tank, but i want my bike to idle smooth with a low fuel level too.

similar problems out there?

thanks,

dimitri

 

[Mr.Pete]

I find this hard to believe.The seats in the float bowls should be 0.100",and it only takes about 6" head of fuel to overcome the weight of the aluminium needle.That's close to an empty tank.
Caulky did some thorough testing about this;it should be easy to find if you do a search.

I don't believe "stay-up" floats are necessary,they're just easier to adjust.You need to set the fuel level in the bowl to 0.170"-0.240" below the top of the bowl,with fuel pressure equal to about a 1/2 full tank (preferably with the engine running).The old 0.080" below top of bowl setting may not work,because of different float weight.

After that,you could test fuel flow.Take the drain plugs out and turn on the fuel.You should get 300ml/minute out of each float bowl.

 

[Dimitri]

I did read the tread about the brass and aluminium needles. twice

The only thing it could be would indeed be a low fuel pressure.
I tested it this morning (sitting at my desk now with a smell of petrol around me)

When everything in place, both fuel taps open, both drain plugs removed > 275ml/minute
Same test, gas cap open > 275ml/minute
Same test, gas cap open and banjo bolt screen filters removed > 275ml/minute
Same test, Banjo bolts removed and both banjo's free > 1000ml/minute
Banjo's removed (just fuel line attached to taps) > 1500ml/minute

So fuel pressure is to low. Even though i read somewhere 150ml/minute should be sufficient. It is clearly not a good fuel pressure.

A second test i did was to blow with compressed air into the fuel tap, with both taps in reserve. That gave an interesting result. When i blow for 2 seconds, the pressure builds up in the tank and it takes 2 or 3 seconds of blowing through both taps and gas cap vent in reverse direction for the pressure to become normal again. That seems uncommon to me.

Does anyone have an idea of a normal amount of fuel flow per minute for these taps? 750ml per tap seems sufficient, but maybe it is way to low.

 

[Dimitri]

somewhere in the deep dark backside of my brain, there seems to be a memory of 'maybe' having used non-petrol-resistant o-rings between taps and tank as temporarily solution for testing when i installed them. And forgot to replace them because they were leak-free.
Could also be a memory i made up because i want it to be that way. Happens all the time. But if so, the o-rings could have swollen by the petrol causing a restriction in the taps. I can check tonight.

 

[Dimitri]

No luck. I did replace the o-ring and there was nothing abnormal about the fuel taps. They seem to flow good, are not dirty... cleaned the filter screens again, but still no lifting needles.

Can't really think of anything else causing a bad fuel flow. Had anybody tested this on his bonnie with a nearly empty tank? I'm beginning to think it was like this from the beginning.

 

[DAVE M]

for peace of mind, just buy new taps.

i don't see that lack of head pressure will make a bike stop.
I (unfortunately) ran right out years ago, the tank waqs dry enough to need to be shaken to get every last drop out, then we had to improvise to get enough petrol into a condom that a mate had to get me home.

i was lucky that my mate seldom got laid.

You have checked that the gasket isn't fouling the float?

 

[Dimitri]

for peace of mind, just buy new taps.

i don't see that lack of head pressure will make a bike stop.
I (unfortunately) ran right out years ago, the tank waqs dry enough to need to be shaken to get every last drop out, then we had to improvise to get enough petrol into a condom that a mate had to get me home.

i was lucky that my mate seldom got laid.

You have checked that the gasket isn't fouling the float?

Everything is free, and as long as the float will open the needle valve when the level lowers, it will run. But the float level will never be correct.

I have now a test setup with a tank (open gas cap) at 50cm above the bowls. The taps are replaced by straight fittings with an internal diameter of 6mm. From there on a straight fuel line from both taps to their bowls. And just the needles in the seats (no floats in the bowls) Even this way, the needles do not rise from fuel pressure. There are no restrictions. And i used different sets of needle valves to test. When i blow through the fuel line, i definately have to blow too hard to let the needles move. Everything is cleaned with carb cleaner and the needles are not a tight fit in the seats.

They are like magnets stucking in the bowls.

Spooky....

 

[DAVE M]

the only other thing that I can think of is that either the shaft that the float runs on is rough/distorted, or there is a bit of flash on the float mouldings.

or that your float (s) both leak?

 

[Old Cafe Racer]

Try your test again with some Triumph engine vibration.. I'm sure fuel will flow.

.

 

[Mr.Pete]

I have now a test setup with a tank (open gas cap) at 50cm above the bowls. . . . . And just the needles in the seats (no floats in the bowls)

Even this way, the needles do not rise from fuel pressure. There are no restrictions.

The fuel pressure in this test only depends upon the height of fuel above the needle (at its seat).Even the size of the hose doesn't matter until flow commences.

That's a high fuel head.I would have expected fuel pressure to overcome the needle weight,once the fuel head reaches about 150-200 mm.The size of the seat has an effect.That's why I mentioned the standard 0.100" seat.The hole through that seat is 0.100" diameter.

Float bowl 622/057 has 0.062" seat;fuel pump pressure required.
Float bowl 622/055 has 0.100" seat,gravity fed.
Float bowl 622/056 has 0.125" seat,gravity fed.
Float bowl 622/054 has 0.156" seat,gravity fed for alcohol use only.

057 requires 2.6 times the fuel pressure,compared to the standard 055.
056 only requires 64% of the fuel pressure,compared to the standard 055,to lift the needle off its seat.

Check the size of the seat in the bowl.

750 ml/minute through each tap (and hose) sounds like enough.That's not causing a restriction.The banjo filter made no difference;that's not causing a restriction.500 ml/minute could still flow through each banjo;some restriction,but still plenty of flow.

Any restriction would have to be in the banjo bolt or the seat in the float bowl.Even chamfering some holes could help.I've sometimes drilled a hole just above the seat,so fuel can flow sideways from the needle-tip instead of up along the needle.Some people mill a slot there,beside the needle-tip,to increase flow.

Your flow isn't really terrible,at 275 ml/bowl/minute.Less fuel flow just means a bigger change in fuel level,as the float has to open the needle more under full power.

 

[nhwally]

Dimitri said:

"The bike fired up right away and after some basic tuning it ran pretty good. Exept for idle. After a run and stopping at a stoplight it dies."

This seems to preclude low fuel flow as a problem ... Why would it run fast, but not idle??

I'll bet the low speed jet is still clogged.

 

[Dimitri]

Try your test again with some Triumph engine vibration.. I'm sure fuel will flow.

.

Thanks for all the suggestions.

As for clogged jets and sticking floats.. I narrowed down the problem to needle valves not lifting under pressure. I have my float bowls attached to the workbench, without the carb body or floats attached.

You've got a point with the engine vibration. But that is not how i want my float bowl to fill. the fuel level would never be correct when shutting the engine off, so i would never know what the best way for cold starting is.

I tested a little bit further. I modified a set of needle valves so they are even lighter than stock (i have the thick MK2 needles, and i drilled a 5mm hole in the 3 sides so all the aluminum in the centre of the needle is gone). First result was the same.
Then i tried a spare petcock i had. And now, for the first time, in this combination the float bowls started to fill very slowly. Not as it should be, but it's a start.

I think, with the superlight needles and replacing both taps by high flow taps, the problem will be solved.

I have a harris t140, and it uses the italian Paioli taps. They seem to be in good shape, so buying clones (the originals are not available anymore) would be no improvement. Are there any sugestions for taps with better flow but not the price of pingel taps?

 

[Mr.Pete]

The amount of flow you get through the taps won't affect how much head of fuel you need to overcome needle weight.If the through-hole in the taps is small,it will only affect the maximum flow you get when the needle is open.I agree that relying on engine vibration to unseat the needle is dodgy.Still,the best fuel level is 0.170"-0.240" below the top of the bowl when the engine is idling.

I use 1/4" BSP teflon-seated ball valves on everything.They are cheap and give a high flow rate.You need separate filters in the hoses (good filters),because they have no filter or any option of reserve fuel.If you wanted reserve fuel,you could make something to do it.

Needle weights:
nylon= 0.3 gm
aluminium Mk 1 needle= 0.5 gm
brass Mk1 needle=1.7 gm

Did you measure the seat orifice?Was it 0.100"?

 

[Dimitri]

The amount of flow you get through the taps won't affect how much head of fuel you need to overcome needle weight.If the through-hole in the taps is small,it will only affect the maximum flow you get when the needle is open.I agree that relying on engine vibration to unseat the needle is dodgy.Still,the best fuel level is 0.170"-0.240" below the top of the bowl when the engine is idling.

I use 1/4" BSP teflon-seated ball valves on everything.They are cheap and give a high flow rate.You need separate filters in the hoses (good filters),because they have no filter or any option of reserve fuel.If you wanted reserve fuel,you could make something to do it.

Needle weights:
nylon= 0.3 gm
aluminium Mk 1 needle= 0.5 gm
brass Mk1 needle=1.7 gm

Did you measure the seat orifice?Was it 0.100"?

Yeah, those where the classes i missed... so i'm up to the job by trial and error.

But, there is improvement.
First of all, i'm convinced the harris bonneville paioli fuel taps/MK2 float needles are a terrible combination, and if left stock don't seem to be able to work properly.

Lowering the weight of the needles (lightening the aluminum ones by removing mass) will fasten the time for the bowls to fill big time. But this mod alone is not enough to make the needles lift at a low fuel tank level.
i agree that the amount of flow won't affect pressure, but... the design of the fuel taps do. When the paioli tap is replaced by a straight tap (push pull type). The problem is solved. The routing of the originals seem to restrict a fair amount of pressure.

To be sure of the result, i replaced the taps 3 times (old - new - old - new - old -new). The straight tap is always lifting the needle, and the original never.

The new combination seems perfect. The fuel bowls fill very quick, from empty to full in less than 10 sec. and lifting the needle untill the tank is empty

But... there is a new problem:
When setting the float level, there is no possibility to set it at the correct height. With the floats level with the gasket (and just above), the fuel level sits at 8mm from the edge. It should be somewhere between 4,3mm and 6,3mm. If i bend the tangs more, the float will hit the carb body and not closing the needle anymore.
It seems that the new amal floats (stay up float) are floating too good, so they are lying on, instead of in the fuel.
I read somewhere about a guy who cut a part of his stay-up float to overcome this problem. It seems like a good solution to me. I don't like the idea of the float nearly touching the body when closing.
Does anybody know what the material of the floats is? If they are hollow, it is not possible. If they are made from some sort of foam, and not absorbing fuel when cut to pieces, it can be done.

 

[Mr.Pete]

So far,you've done well.You only have a problem with the float getting too close to the body,if the fuel level is right.
Amal claim the stay-up float is "Closed cell construction".That would mean a scratch or cut on the float would still not allow it to become saturated with fuel.Some automotive solid floats can become saturated,if the outer surface is scratched.

Rather than cut a piece off the float,it may be better and easier to add some weight to it.You could screw a small grub screw into it,on the toe side opposite the needle.I'd fit it in the top or bottom of the float.Personally,I would still use a sealant around the screw.Loctite 567 seems to work well in this application.

The float will sit lower above the fuel level,when it is heavier.In other words,the fuel level will rise even without adjusting the float tangs.

 

[Dimitri]

Good tip Pete, thanks,

I was thinking of a combination (adding weight/removing material) by drilling a hole in the top and filling it with epoxy. But it would make it more complicated than it should be.

I can try the weight of a few screws upside down on the float to see which one would suit best for this purpose.


By the way, i am reading a lot of stories about flooding Amals when the stay up float is installed. I wouldn't be surprised if these installations suffered from the same problem. If i would set the fuel level (fuel level, not float level) correct, mine would flood also.

 

[Dimitri]

a step further....


the longer i spend looking at the concentric, the longer i am convinced my bike will run like new when i am ready sorting these problems.

The added weight seems to work. At least, i can now adjust the fuel level to any desired setting easily and without risking the float touching the underside of the body. I screwed and sealed a 3x15mm screw from the underside in each float. The floats dropped a few mmand are floating at 4-5mm above the fuel level. Thus floating as supposed even with the upper side of the bowl.

However, this mod brought a new problem. I made a 'before and after' sketch.

In the new situation, there is the free play of the float axle that is working in the wrong direction. Normally, the fuel would push the float up, which would get restricted by the axle and creating a downward force on the needle valve.
The weight causes the float to 'hang' on the axle, and it still does when the needle valve shuts off. No force is applied on the valve, other than the weight of the float itself. As if the axle wasn't there.
It is causing no problems now, but it could when fuel pressure is higher (full tank maybe) or with the engine running (vibration)

 

[Dimitri]

thinking now of going back to the beginning for a different approach. I will eventually get there this way. But maybe it could be done easyer.

i'm going to try to find a very soft spring to put between the needle valve and the seat (just enough to carry it's weight). I think it would be difficult withe the MK1 needle, but with the MK2 needle, there is plenty of space. That way, a standard or even brass needle could be used without the needle closing under it's own weight. Float chambers would fill significally faster and i would be able to use my original taps. I don't think there will be an issue for the float to overcome the spring tension.

Now only finding such a light duty spring. I know they exist, but where

 

[Mr.Pete]

I can see what you mean about the clearance between the float and the pin,but it really won't change the fuel level much.It could change by about 3 times the clearance between the float and pin.

The fuel level only has to be 0.170"-0.240" below the top of the bowl,when the engine is running (0.205" +/- 0.035").It would still run OK +/- 0.060",and a lot of bikes still run OK when the error is more than that.

I reckon adjust the level to somewhere between 0.205"-0.240" when the tank is full.You should have no problem.The fuel level may drop a little when the tank is almost empty,but probably less than 0.040" change.

In any case,everything changes at full power.If you make 40 bhp with a twin-carb engine,the toe of the float must drop must drop approx 2.2 mm from the closed position to allow enough fuel past the needle.That will drop the fuel level about 0.040" lower than when you make no horsepower.

It's all allowed for,and the main jet is sized for the "low-fuel-level" condition.It would only become a problem when you can't get adequate fuel flow and the needle has to open even further.

Run what you have.It should be fine if the fuel level is about 0.205" with the engine running.You could have the best float level in the world.

 

[Dimitri]

the only problem is, when i adjust the fuel level at the correct height, the float will still touch the carb body before the needle is shut of mechanically (by the float/axle/valve). It closes, but by the weight of the float. It can still flood this way. Unless i adjust the fuel level too low. But i don't like the idea of that.

You are right though... it's about time to reassemble the carbs and see what they do on the road. Will do that this weekend ;-)