Saving Old Seagulls

hello all, i have had 2 seagulls one i traded in for a ****** and the one I have now. I thought that with all the hate 2 stroke brigade it would pay to have something a little lighter than a 4 stroke which would last a lifetime.
The 40 featherweight starts fine and runs well, however it tends to 4 stroke at low throttle openings ( new filter, full tank), If i increase the revs it runs for a while then cuts out, and will start again with no problems until it cuts out again. If however i run it at 1/2 throttle it tends to 4 stroke but runs without stopping. This I can live with. but would like to get it a little better, I was thinking of raising the needle a tad, that would I think give it a little more fuel, and run it a little cooler.
The motorcycle forums seem to think its a weak mixture that creates 4 stroking, I was just wondering if anyone thinks the same. I run on 25 to 1 and the motor is not seizing up, any ideas please
best regards

What year is it? Does it have a 25:1 carb [Bing] or a Villiers carb, if it has the Villiers carb, does it have the 25:1 needle installed?

Difficult to give a proper answer if those details are not given.

Sorry I should have put all that in. its a late one with electronic ignition, an Amal carb and I was told that it was converted to 25 to 1. And Or I have read that the late ones can run on 25 to 1 with no mods.
If I run it at the revs that it does not 4 stroke, it runs very well (fast) for 2 minutes, and starts straight afterwards. If I run it so it 4 strokes a little it runs for 15 minutes, If I run it at a speed that cooling water flows through it, (minimum safe speed?) it runs for 20 minutes, when it runs at max fuel comes out of the carb tickler, so there is fuel in the carb. I normally dont run at max. I did think that it may be running too hot but its certainly not siezing. Or the float sticking but the things vibrate so much that should not happen! The other thing I thought of is the plug the wrong heat range but it has the correct plug, unless thats changed for 25 to 1. And it starts up straight away, no problem. Again generally 4 stroking is generally a mixture problem but then it should run somewhere in the rev range ok and the faster a 2 stroke runs the more oil it gets. Should I try it at 16 to 1 I do have a colour tune plug so I should be able to see the mixture is ok or not. But as to why it stops then starts with no problem rather suggests fuel. ugh
best regards
john

Will have to wait for someone familiar with the later Seagulls, I don't have any Amal carbed 40 series motors. If the plug shows the correct color after a full throttle run, I don't think you need to worry. The motor is not very stressed at idle and low speed so I would not be concerned about a little 4 stroking.

The excessive vibration may be due to some problem [ slightly bent crankshaft, driveshaft damaged]. Some definitely vibrate more than others, I find the pre 1965 motors to be smoother running. Depends on what motor you are comparing it to.

Maybe I'm way out on this but, I was taught when tuning chainsaws at full revs to turn the high speed needle to richen the mix till it 4 strokes, then lean it a tiny bit from there. This says to me that 4 stroking is a rich, not lean condition.

If fuel is coming out of the carb overflow while running, it sounds like you need to check that the carb float needle is operating properly. Has the fuel system been thoroughly cleaned and fresh fuel mix used? Any sign of rust or other deposits in the fuel tank? Tank, fuel tap, fuel line, carb float bowl, carb all spotless? Most of the problems described could be caused by dirt in the fuel system.

many thanks for the help so far, since this morning I have taken the carb off checked out the float and valve all working perhaps the final shut off is slightly high, but it does shut off when the float is at the top, I raised the jet needle from the mid position to the lower raising the fuel air ratio. and checked the plug which is a straw colour, about right. Again from what I read in SOS the engine should be able to run fine on 25 to 1 and there does not appear to be a cylinder head leak, well it does not loose compression and it starts directly afterwards, I had a johnson once that was always getting cylinder head leaks. Later today i ran it at about 1/3 throttle and it ran the tank out of fuel about 30 or so minutes, the tank was not full when I started. Cooling water is pencil thick and fuel has stopped coming out of the tickler, when on max revs. If I close the choke as its failing it should richen up the mixture but effectively nothing happens it still fails yet will restart immediatley, all rather strange. It all points to no fuel, yet choking it should give it plenty. I have an additional filter in the fuel line so I can see fuel is there and the filter is not empty. I may just try and open up the plug, some people say that has the same effect as retarding the ignition unless anyone has any better ideas.
regards
john

Just put a post up and its dissappeared

Changed the needle position its better it 2 strokes
I think theres not enough fuel getting through as it starts up as soon as it stops I have had the carb apart again and the float and valve seem to work fine , with a mark one blow!
I think the problem is not enough fuel, the symptons are the same as shutting off the fuel valve, i am tempted to remove the filter in the Amal carb and fit an inline one, the filter seems or rather the casting has 1 small hole just at the bottom even though the filter is quite large only a little bit of it seems to be used.
anyone any Ideas the motor starts easily and starts straight away when it stops so it surely should be fuel?

Your symptom of cutting out whilst capable of an immediate restart remind me of a problem with a KIngfisher a year or so ago. I know, different motor!

But it's a very similar carburettor if it's the later model Amal. In my case it was cracking around the plastic banjo fitting where the fuel enters the carburettor. The banjo is a plastic component, and it's very easy to overtighten - hence the cracking. A new fitting cured the problem - John has a few in stock.

Hi, apologies for a really dumb suggestion:

Did you open the air intake screw in the filler cap of the fuel tank? The only reason I ask is that I did just that last summer. The only way I could get my 40+ to run that day was by shutting the choke half-way. Next day when I remembered the air intake it ran much, much better.

Best regards,

Henrik

cleaned out the new filter (about 2 hours old) noticed it was a slightly different colour in one place. the filter only seems to work over a very small part of its area, like where the hole into the float chamber is, anyway blew it and cleaned it , checked out the float , valve, and jets. all fine. Started the little darling up and at 3/4 throttle lasted 5 minutes, started right up and reduced throttle to, well enough so that it was not 4 stroking, motor did not stop, ran for 30 minutes then was out of fuel.
I deduce that the problem is not electrical either in the magneto or the plug but in the fuel supply.
I do have an inline filter in the fuel line. And maybe the extra pressure drop in this extra filter is doing it.
Now unless I am doing something drastically wrong I think the filter in the carb is a problem as its not working over its surface area, just a small part of it. I shall remove it and use the inline see through filter.
Unless any of the learned folk on the forum have any other ideas.
Thank god its easy working on seagulls.
regards
john
the colortune didnt fit its for 14 mm plugs