more 2stroke 2.5hp problems

[nyx2k]

the carb float bowl level seems to be ok whilst in the wheelie bin testing but when out on the water it keeps overflowing and of course wont start.

when im home later i will dig out the sheets on carb stuff and reset float height but is this the only thing it can be as the needle thing above the bowl that stops the fuel flow seems fine or shall i replace anyway.

 

[misterg]

Not sure what engine you have:

Check that there isn't any rubbish in the top half of the float needle seat. Anything that's gone down the petrol pipe, but is too big to fit through the float valve stops here, and can prevent the needle seating intermittently.

If it's a Mariner / Mercury, check that the little conical fuel filter is still in place at the fuel outlet. It's held in by some Mickey-Mouse arrangement involving the fuel tap clamp. If it's come loose, everything it collected will now be sitting in the float valve seat. You might have to unscrew the float valve and/or the petrol pipe fitting on the carb to get at it.


Andy

 

[nyx2k]

thanks for that. i didnt know they had a filter.
its a 2.5hp 2st mercuryy of mid 90's vintage.
when it runs it runs for hrs at full ish throttle and has never missed a beat but the last week the fule levelhas been intermittent and has been difficult to restart.
if i mess about with the idle screw it will then restart but the idle screw doesnt seem to make any difference to the engine speed just the smooth running of it.

 

[VicS]

Check the float adjustment and condition .
check the needle valve

Check out that filter ... but I cannot see it mentioned on the parts breakdown

That adjustment screw is supposed to be the idle speed adjustment!

 

[nyx2k]

the adjustment screw makes next to no difference tot he running speed and in fact i can take it out completely and it sucks air through the hole but makes no difference to the running spped at all.
ive checked the needle valve on top is correct for the mixture ratio and the adjustment screw only seems to make a difference when restarting it whether hot or cold.

 

[nyx2k]

on the drawings i have the float hinge says 2.0mm for magneto and 3.0mm clearance for cdi.

excuse my ignorance but which do i have and how do i tell.
the pictures are a bit ambiguous but i presume the distance is measured with the carb upside down so float is in fully closed postition and the bend in the hinge is measured at 2.0 or 3.0 mm if that makes sense

 

[nyx2k]

also the gasket that is supposed to be arounfd the foat bowl is no longer there but still seals properly so is the gasket thickness anything to do with the maesuring aswell

 

[VicS]

As far as I can discover all the 2.5 Mercs have CD ignition. I'd be surprised to find a 1990s outboard with points ignition anyway.

I do not think you would measure from the gasket. Normally you would set it all up before fitting the gasket I'd think.

As a general rule if you turn a carb body upside down the float will be parallel with the joint face with the bowl if it is adjusted properly.

 

[nyx2k]

the pics i have were posted on here last week from either you or another kind person.

they are pretty clear and detailed except ther line drawing of the float bowl assembly procedure.

 

[Lakesailor]

I think I posted a pic of the float level adjustment.
Get the whole .pdf file from this address. It gives you all the procedures.

http://www.lakelandimages.co.uk/For...u/Section 3 - FUEL SYSTEM AND CARBURETION.pdf

 

[VicS]

That clears that up then.
Disregard my comments about being parallel with the joint face. That applies to hinged floats .

3.0mm measured from the gasket!

Need a new gasket then!

I knew I'd seen that diagram before ... I've even down loaded the file!

 

[misterg]

Check out that filter ... but I cannot see it mentioned on the parts breakdown

It's the sticky-up bit on part 21 in this diagram:

It was rattling around loose in the fuel tank on our 2.2 for a while. It should be wedged into the short section of rubber hose that connects the fuel tap to the tank.

Andy


Ooh Err! it's gone big, and it's not my picture - sorry.

 

[nyx2k]

yes it was you. thats such a useful file.
will get to grips with the carb on friday but i think this will go as a spare engine and ill get myself a much newer 3.5hp or 4hp 2 stroke

 

[nyx2k]

this carb thing is a pita.

im reasembleing the carb. im describing the procedure with the carb inverted from its normal operating position

is the order of assembly float needle in fuel line then float hinge then float on top and then bowl.

the float hinge has been bent a lot but dont know how much to flatten it ( if thats wata i do)

also which way does the float hinge go on

does the hinge go on the holes for the hinge pin upper most or inverted.
cant find bloomin camera

 

[VicS]

Valve seat/fuel connector fitted first.

Invert

Fit the new gasket

Fit needle pointed end first, and then the float hinge and pin with the pin uppermost ( as you now look at it.)

The flat part rests on the needle, the two fingers curve up and down again so that they will touch the float either side of the main nozzle.

Check the measurement according to the diagram Lakesailor gave. Adjust fingers so that the clearance measured from the gasket is 3mm.

Make sure the fingers are level and that they will contact the float either side of the nozzle

Drop the float on

Fit the bowl.

The diagrams in Lakesailors link show every thing clearly.

 

[nyx2k]

i was getting confused because what i took off whas not how it was in the diaggram.
the hinge was in upside down and fingers bent the wrong way. as im an idiot i was trying to make that order of things work without looking at the diagram properly.
all rebuilt now and running much faster and no hesitation like before at high throttle openings.

will leave in wheeline bin with fuel taps open to see if cured and then ill remeasure the gap when new gasket arrives as local havent got them.
if the gasket whas not replaced before and fingers are wrong no wonder it was flooding as soon as the engine was moved from house to car to boat.

as an aside what is the name of the clips that hold the petrol hose to the valve one end and the carb intake at the other. and are they just chandlers bits or can be got from motor factor.

 

[nyx2k]

i fitted the gasket today and measured the 3mm needed for the gap and put it all back together and it ran well under medium load but is now hesitant under full load so i presume the problem now is under fueling.

do i move the gap now to 2mm above gasket height.
obviously i can fiddle about with it but need to know that the hinge finger height is causing the problem

 

[Lakesailor]

Before undoing the good you may have done so far, try adjusting the needle level in the throttle slide. If you move the E ring down to the next slot that will richen the mixture a bit.
It shouldn't need richening really once set, except that various little air leaks in the carb which may have developed through wear may have had the effect of weakening the mixture (talking air/fuel here not the fuel/oil ratio).
It's worth a try as you easily return it to the current slot on the needle and get back to ground zero if it didn't have any effect.

 

[VicS]

Was about to suggest the same as LS, but he beat me to it by a few seconds.

But note they do say that an over rich mixture will cause a drop in RPM above 2/3 throttle.

 

[nyx2k]

ive tried that and it ran like a old 1980's lada riva.
no power after 1/3rd throttle so put it back in ring place and just moved the hinge fingers to 2mm so slightly overfueling and at just above tick over is good enough and 3/4 throttle is now spot on with a slight hesitancy at full trottle but all seems fine now.

thanks to all for so much genoruos help but a special mention as always to lakesailer and vics.

if i go and buy the 3.5hp later ive been told it runs like new so hopefully wont be posting about that tonight.

regards Nick