Looks like...

[Ianfs]

I might need a new Carburetor.

I spent ages looking for a power piston, found one, shipped it, popped it in and ran it. Engine great with lots of power but very rich at idle, smoke and very rough. Stripped the carb again, greased the piston popped it back on. Started last week to recommission and it was perfect, idled better than ever, started a treat. Revved her and got hesitation, so Revved again and perfect. Except the roughness at idle has returned.
I suspect the piston is stuck again, wish I had a mobile xray. lol.
I've read that Rochester are better cards. Any thoughts?

[shibbs]

Ian, PM sent.
I only know what I've learnt by what stripping my Rochester down over the last year has taught me, and most of that was with direction by yourself so can't offer too much assistance tbh.
Rochester must be the way ahead though if I can manage to strip, rebuild and set up and have it still working at the end!

[BruceK]

I don't know what carb you have in but it shouldn't be doing that, obviously, so it may be worthwhile getting an engineer to give it a once over. However I second a Rochester for ease of use and simplicity and may work out cheaper if it's an exact match to the header plate. Did a rebuild in an hour on one and it ran as sweet as a nut off standard settings. No fettling necessary

[Ianfs]

Thanks guys. Stu pm returned.

Bruce, its a Mercarb 2B BL and I'm told they were troublesome. I think its a new Rochester then, although I have sent Jamie, one of our new members who is a Marine Mechanic/Engineer an e-mail. He was recommended by Matt and antlouhay so must be ok.

[BruceK]

The 2BBL. I also had one of those on a Mercruiser 3.0GL and it also ran rough. You can get a complete rebuild kit for them for peanuts. I rebuilt one after a hard starting and flooding issue and although it ran smoother and started easier it still wasn't right. Turned out it's the autochoke. I turned mine right down rather than faff about with it. Made hot starts brilliant but cold starts a bugger. You had to be careful in priming it but not flooding it. Have a look at the autochoke, see if it's sticking and causing the issue.

[Ianfs]

Ed helped me rebuild it with a Sierra kit. It was only after I had used it a few times I thought there wasn't much improvement to power, idle was fine, but it baulked a little on heavy throttle opening and max revs were not attainable. Looking at the photos of the rebuild I realised that there was something missing and it was the power piston which activates the power valve. I put one in which I got from a guy in the States and she runs great high speed but no good pottering or at idle.

The choke is fine and works ok, I mostly do my checking with the flame arrestor off so the choke is clearly visible.

Consequently I think the piston is not operating as it should.

[BruceK]

Silly question but did you get the right or full kit because the power piston comes with it.

http://m.ebay.co.uk/itm/Carb-Rebuild-Ki ... 1076420461

[Ianfs]

Silly question but did you get the right or full kit because the power piston comes with it

Bruce, it is absolutely not a silly question and I think you would be very surprised at how many marine engineers and parts dealers and even, including those clever yanks, also thought the "power valve" (which is included in the kits) was a "power piston". Included in the above is my ignorance of the part since when Ed and I (more Ed than I) fitted the bits we both thought that it was odd that the power valve had nothing to operate it. Ed's of the modern world and an excellent mechanic but more of a genius with fuel injection and control unit programming, carbs to him are potatoes, sugar etc.

I found out that in some cases its called a Power Valve Actuator, however on a Rochester Carb, its a Power Piston. What I then discovered, is that it is not always shown in some of the diagrams and certainly was not shown in the kit diagram. In fact I also found out it is supposed to be part of the Air Horn Assembly and on searching for the part found out that the assembly was no longer available as a single part but only as a whole new carburetor. Part of my research led me to Nikki Carburetors in Japan who made them. I faxed them and e-mailed them several times for sizes to have one made but they never replied, not even a "thank you but we cannot help".

So I think its Rochester for me, unless someone round here can sort it out, even Rochester have them separately for a few bob.

http://quadrajetparts.com/power-piston-rochester-7006011-7009718-p-498.html?osCsid=5a33f751b0e6571a9aec36dd19e49f68

[Ianfs]

I got in touch with Jamie Fordham who runs RPM Marine Services. Jamie offered some very sound advice by suggesting I first of all test the needle valve is seating properly. The carb had a rebuild and has not done many hours since so this didn't seem obvious. Jamie asked if i had checked the float height to which I had, several times. He then suggested I disconnect the fuel line and try to prime the carb. This puts the valve under pressure and he said that if it was faulty I would see fuel dripping from the venturi's.
The fuel line is a metal pipe bolted to the side of the carb. I bought a cheap priming bulb from a local outboard specialist in Christchurch and adapted a pipe to fit snuggly into the fuel line receiver hole. I pumped fuel from a jerry can and the bulb went hard but no fuel was dripping so thought the valve was OK. After about a minute though it started to drip. I waited and after a while did the test again but with less pressure in order to verify my findings. Same again, after about a minute it dripped.
I managed to find a needle valve and gasket from Trickett Marine in Poole so ordered a float as well in case the old one was porous.
Needless to say she works fine now and for 40quid I now have a carb which works fine.
Thanks to Jamie, I'd better give him a call today to let him know, she runs well, tick over is very smooth.
Jamie Fordham, RPM Marine Services (boatbanter member name). Jamie does a lot of work for Sea Start and operates along the South Coast so if you are looking for a reliable Marine Engineer pm or mail him.