Thanks for your replies Adrian and T-man. I always lusted after a VT-240, as I used to own several Enya 4-strokes and really liked them a lot. But I wasn't into large scale models back then.

It's unfortunate that the Walbro WT-456 and the Zama C1Q P8 8YA carbs are both discontinued. I've asked the UK distributor of both makes to see if they can find any, but don't hold any hope of success. After attempting to search through the huge Walbro WT- carb list, and not having a similar Zama list, I gave up and decided to try a different route.

As long as the Laser carbs receive a constant fuel supply they idle, throttle smoothly and give good max revs. The carb throat diameter is 8.34mm, which is significantly larger than that of the WT-456 and is probably why the engine is short of suck on petrol. If anyone can advise me of a Walbro or Zama 4-stroke carb with accelerator pump and around 8.4mm throat dia, and which is still available, I'd be very grateful.

Given that the Laser carbs seem to work on gas, I decided to investigate ways of providing a constant fuel pressure for the existing carbs. First I looked into chicken hopper and uniflow tanks, but they didn't seem to offer what was needed for an R/C aerobatic job.

Next I looked at Cline http://www.billsroom.com/pcfs/ and Iron Bay http://www.ironbaymodelcompany.com/i...es/Page438.htm regulators and the Perry VP40-SG Pump regulator http://www.perrypumps.com/prod02.htm

The Cline and Iron Bay regs need the tank pressurising, and quite honestly I don't want to mess about with muffler pressure. If there is space inside a model, one idea would be to pressurise the tank via a pressure reservoir which could comprise a plastic 10oz fizzy drink bottle pumped to about 10psi. A check valve would stop fuel entering the air reservoir during fuelling.

The Perry gas pump-regulator might be the best thing to try initially, though I don't know if the regulator is a demand-type like the Cline and Iron Bay, or just a needle valve. The Perry website says that it will pump up to a max of 3.5 oz/minute, which is well in excess of what even a 40cc petrol engine needs. I found this page http://saito-engines.info/pumps.html which describes the glow version's use with a large Saito 4-stroke. The same page also describes an interesting Saito system for pressurising a tank from the crankcase, with an extra crankcase vent nipple, and a needle valve and oil vent.

So besides the pumper carb route, there appear to be a number of avenues to investigate which have the advantages of retaining the existing twin carbs and not having to make new intake piping, the configuration of which could be difficult for a Laser vee because of the non-parallel orientation of the intake bores in the head, and the peculiar carb mounting arrangement.