Saturday, August 10, 2019

Will It Run - 10.1 Details

One of my friends mentioned that I had left out the steps between step 8 and step 10. Not so, step 9 was back in early July featuring me bitching about the stock carbs being really bunged up. Step 1 involved me throwing up the hands and fabricating an intake manifold to accept a single side draft carb of the same size as the originals.

Found a Mikuni knock-off that came with 2 spare jets and a rubber adapter to attach it to whatever engine you want. This thing also came with a page of instructions written in Chinese with translations that sometimes resembled English.
Click to enlarge. From what was readable, the jetting that came with the carb was the richest and was intended to work on a 125cc 2-stroke. Swapping to the smaller jets and dropping the needle one notch has the 535 running like a normal motor and the plugs show no soot deposits any more.

The carb has a raised lip that attaches firmly to the rubber adapter provided, which BTW has a spacer feature in the middle that reduces the port from 32mm to 28mm. The adapter was replaced with a piece of radiator hose with an Oring spacer that has no restrictions at all. The manifold has no engagement features so the hose needed to be as long as I could make it and some punch dimples added to the manifold spigot for traction. This works.
The engine is a 90 degree twin. There's a fellow selling a cast Aluminum manifold with gentle curves and a real Mikuni carb for about $600 which I'm sure works a treat. This one cost $28 for the carb plus some sweat. The perfect is the enemy of the good enough as they say.

The ChiCom carb was intended to work from a gravity feed fuel tank, so reducing the fuel pump pressure seemed prudent. The above Delrin block has a hole thru it on the bottom from fuel pump on the right to the carb on the left. The passage in the middle is drilled about halfway through and is connected back to the fuel tank. Down from the top is a small hole through to the lower passage with a check ball and spring. Excess fuel is passed up to the return line and the pressure is adjusted with the set screw at the top, barely visible. This reduces the delivered fuel pressure to 2 psi which the carb can handle. Crude, but effective.

Meantime I had a pair of carbs from a newer 535 fall into my lap from an unlikely source. They seem to be all there and not bunged up. The only thing holding me back is that the aft carb has coagulated gas holding the float needle in to the seat with the tenacity of Super Glue. At some point the  needle will loosen up and I'll finish the cleaning and try them out. Who knows, they may work. 6 years, a model change and 3-6 revisions so they must be better, no?

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