sealine 218 planing problems

[robmatheson]

Hello,

I have a Sealine 218 with a VP 205A petrol engine on the Clyde. It had been running perfectly. Then I noticed the power died away when I planed for more than five minutes. First I thought it was fuel starvation, but checked the lines and filters and they were fine. The fuel's got no water in it. The points, cables and plugs have all been renewed. The thermostat's been replaced. I seatrialled her after the plugs etc were changed and she planed comfortably without using the trim tabs at all. Second go, she got onto the plane but started to falter very slightly. Third go, same thing: she planes around 12 mph, then starts to stutter very slightly and then you can feel the power drifting away.

An experienced engineer friend has suggested carburettor icing.

Any suggestions?

Many thanks,

Rob

 

[duncan]

I've only ever had carb icing when the power was off and the air temperature very low eg plane gliding with engine at idle. power on no problems.

overall you seem to be loosing power as the engine gets hot - what are your temperature readings (and are you happy your gauge is reading correctly?)

you have changed the plugs to is less likely to be plug insulation breaking down when hot - but can't be ruled out.

as it's producing power cold it's unlikely to be a bent cam, or valve clearances etc

I am aware of a slightly larger Sealine with twins of the same engines that had similar issue on one of the engines - but they never found the solution.

carbs wouldn't be the first place I looked when the engine is running fine before it gets fully hot, unless it's still running on some form of choke mechanism until the problem arises.

 

[rafiki_]

Check the simple issues first. Is there an issue with the disctributor tracking? Can you see any sparking around the distributor cap or HT leads?

If no fuel starvation, then it is more likely to be an electrical issue.

 

[robmatheson]

thanks for this

this is all very helpful.

Will check the electrics again. Temperature gauge is fine - showing first quarter green when running hot. New thermostat is calibrated correctly.

Strangely, when thermostat was duff and engine ran cold constantly, she planed no problem. But then the power dropped off after about five minutes. Hence possible carb icing under those circumstances.

However thermostat has been replaced and engine now runs hot. She planes, but feels like she starts to miss and power drops away.

She runs beautifully at slower speeds.

Hmmmm. Don't like the sound of the phrase 'similar problem but they never got to the bottom of it.'

 

[tinkicker0]

If it has an auto choke, check it is coming off fully.

Carb icing usually only occurs at low manifold pressures in high humidity conditions, it is possible in the right circumstances to occur up to 25 C.

Unlikely to ice up on an open throttle in summer.

 

[burgundyben]

Check the engine running at night, if its an HT problem you may well be able to see it arcing.