suzi 2.5 tuning

ShipsWoofy

ShipsWoofy

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It has been so long since I adjusted the mixture on a petrol engine that I have forgotten how to do it..

Last weekend I started the o/b which had been warm (i.e. not outside, from conservatory to boot to boat). I rather stupidly let go the choke to soon and stalled it.. from then I flooded it. We paddled after much shouting and bleating from the winging skipper (me), sorry Porthmadog if I disturbed the peace, I was in a right old mood by then.

Coming home while tied alongside the boat I started the engine well enough but again was too fast off the choke and stalled-flooded-cursed. I took the plug out and heated it with my flame proof lighter, but this did not help, it had on arrival the day before.

I did notice that the plug was building up with carbon which means it is running too rich (AFAIR). Now this engine is just over a year old and has fresh petrol, I have never been overly confident that the mixture is correct, choke required even on a warm day, it does normally start first pull but keeping it going can be a delicate operation before it is up to temp.

When choked it really wont throttle up at all, hence my rush to ease out the choke and maintain the revs, if I ease the choke the motor will really begin to rev up, so I drop off the throttle and... well, if it is as cold as this weekend, stall the piece of Nipponese junk /forums/images/graemlins/shocked.gif

Before I start contacting suzi I would like to have a try at making it run a little bit leaner (unless someone says I have it the wrong way about). But as I started, I have forgotten how to do this (too spoiled with fuel injection since the 90's).

Let's say I am there, engine running in a bucket, screwdriver in hand, what am I trying to achieve? Should I also be looking at the timing, I am unsure if the flywheel is marked and if my old strobe still works.

well, I guess I have waffled a bit, but basically, how do you tune up a single 'pot' 4st o/b with basic home tools?
 
Needing choke when warm is not consistent with running rich.
These carbs have very small jets that easily block with the merest speck of dirt or water.
I would start by cleaning the carb to a spotless standard, empty the carb into a tray and look for water in the fuel, dismantle carefully, lay out all the parts on white paper before re-assembling, blow through all the jets, use solvent/carb cleaner to remove any gunge.
Then start with a new plug. Set any bypass/mixture screws to the settings in the manual, warm the engine up and adjust mixture for smoothest tickover.
The carbon on the plug could be from oil if you are tilting the engine too much or the sump is overfilled.
The mixture screws on these carbs don't usually do anything except at small throttle openings.
Thats all general advice, don't know the exact model, but it should get you started.
Also worth checking the ignition side, no dodgy connections!
Good luck.
 
Jools
my 2.5 (which to my great regret went with Sonsy Lass to Finland) was superb at starting etc etc, there is no mixture screw as I remember, something to do with california where they dont have them to stop yankee doodles from fekking up the atmosphere!
What I did find was that the spark plugs were very sensitive and once it had fouled, it became very iffy at starting no matter how much I cleaned the plug. Only answer was a new plug, I bought a pile off ebay at not swindlery prices, thought afterwards I should have bought some softer ones so they got hotter better to burn off crap.
As far as I can remember there is a set of points in the thing so timing is fixed within the parameters allowed by the points gap.
PS I found it upside down on the dinghy in the marina one day, sloshed fresh water all over it, then a can of wd40 everywhere then it started up and was fine!!
Stu
 
thank you, and I agree that I should give the carb a good clean.

re. the oil, I did put a bit more than I meant to, it is within the window (sight glass on this little motor) but is at the top of the range. We are very careful about locking it tilted and not putting it down badly, so I don't think it is seepage, but worth being aware of.

I will try and find a new chicken tooth, er, spark plug for it while I am fiddling.
 
lucky you, every time I have been in a swindlery or motor factors I have asked if they have any plugs, they seem to be very very rare.

There is a lawnmower outfit near me, I might try there as it is a mini plug, I don't have the number to hand.

If you have any over and not needed I will buy them from you if you like.
 
Jools
my apologies, I thought you were referring to the old 2 stroke one, I have one of the new 4 stroke ones as well, same thing ref the carb, no adjustment, was shown at the boat show to lie it on the handle so that the oil doesnt go in to the crank breather, however even then several times at the slip have had to pull a few times and then got a cloud of smoke until it cleared itself, quite obviously the oil gets in to the intake system even if laid down properly, the oil level should be spot on the line when not running when on the transom to get the spirit level effect, when it is running it is quite a way down the window, if you have too much oil in the crank case that wil explain the fouling.
Stu
 
Jools,

Are you aware of this place ? Seem to be reasonable prices and P&P. (I gave up trying to find anyone local who stocked plugs for my old Honda 8HP - Best I got was Dickies had one, but I needed two...)

I'm not sure if you really have a problem, but if you do, I agree with the others that you should be looking at cleaning the carb out first.

FWIW, I would adjust the mixture on small engines like this as follows:

1) Set it up as per manual.
2) Make small adjustments to mixture screw either way until it idles happily. (Reduce idle speed to spec. if necessary)
3) Open the throttle smartly:

-If the revs pick up (maybe after a slight hesitation) then it's fine.
-If the engine makes a sneeze/cough noise, it's running too rich at idle - screw the *air* screw out a bit, or the *fuel* screw in a bit (not sure which your engine has).
-If it makes noise like one would make after being punched firmly in the stomach, then it's running too lean - screw the *air* screw in a bit / *fuel* screw out a bit.

Let the throttle go, and see how it comes back to idle

- If it takes a long time for the revs to drop, or if it dies completely, it's probably still running a bit lean.
- If it drops to idle pretty smartly (and maybe undershoots a bit) it's probably OK.

You need to let it get up to full temperature and run for a while at a particular rev range to get a useful pointer from the plug colour. With the choke on/off as you've had it, I don't think you could make any firm diagnosis from the plug.

Have you tried 'edging' the choke off a fraction at a time?

0.02p

Andy
 
Thank you for the link, have ordered a few so I have some spares. Also bookmarked as they appear to hold a vast stock, will report back once I receive them..

Thank you for taking the time to write out that for me, reading through a few things came flooding back others new and I have learnt a few tricks there. I used to be quite good at this stuff and it was earlier on when I was thinking about how to approach this, that I realised I have forgotten some real basics on simple engine maintenance.

As much of the running and setting up will have to be done outside, I might opt for waiting a few days... /forums/images/graemlins/frown.gif


<span class="small">EDIT==></span> I found a parts breakout for the df2.5 in pdf, from this page here
 
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