Having problems with a Walbro carb mounted on a modified 25cc 2-stroke brushcutter engine. Due to space constraints the 25mm thick hard plastic carb adaptor won't fit so the carb is mounted on a 10mm thick aluminium adaptor with thin paper gaskets. After about 2-3 minutes running the engine dies and will not re-start, but once it cools down a bit it restarts no problem. I'm guessing vapour-lock due to heat transfer from the cylinder to the carb through the aluminium adaptor. Looking for suggestions on a suitable type of plastic or similar material that will provide more insulation so the carb does not get as hot. It needs to be something of similar strength as aluminium because the adaptor is bolted to the barrel and the carb is then bolted to the adaptor. The bolt holes for carb and adaptor are not aligned. Any ideas?
Carburetor mounting
- Thread starter perko7
- Start date
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Can you not just cut the 25mm one in half and mill it down to 10mm thick
danallen
Well-Known Member
If you can get your hands on some how about some sort of phenolic material? Strong and heat resistant and not too bad to machine.
ruzzie
Well-Known Member
Is the hole that operates the walbro's diaphragm pump in the aluminium. It may be starving for fuel
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No, the piece is moulded to incorporate a transition from the round carby throat to the oblong intake port. Trimming down the existing would upset this. Also the threaded holes for the mounting bolts do not go all the way through so cutting it back would reduce the thread engagement too much to be reliable.
Phenolic material would be ideal but hard to get at a reasonable price. Smallest piece in 10mm thick would be 300mm square at about $60.
The hole for the pump pulse is there and operates well. Not starved for fuel while cold, runs up to full revs no problem.
Timber no good, needs to be threaded M5 for the carby mounting bolts. Thought about Corian, also looking at polycarbonate which may have sufficient heat resistance for the temperatures likely to be experienced.
Thanks for all the responses, decided to try with a slab of polycarbonate first, see how it goes and if the problem still exists then further options will need to be explored. Chatted to a friend who experienced similar problems with a 1/2 scale Onan flat twin he built, he used polycarbonate and his seems to be holding up ok.
I don't suppose a few layers of Polyimide Kapton Tape would be of any assistance with your original adaptor...???
Not heard of that before, will look it up. Thanks for the suggestion.
