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Yamaha Star 650 Carburetor Test & Adjustments - Floats, TPS, Heaters, Solenoids, PMS

Today begins the first in a two part series where we go into specific detain with regard to specific testing of the Star 650 carburetor and its components to ensure that it is working within operating parameters. This is not a rebuild video. I have made those already. This could be considered a post rebuild exercise to determine good working order before installation. Another thing to consider is the screws that had to be torn up in order to take the carb apart. The original screws are terrible!!!

The first task is a trip to Ace Hardware where the original screws will be swapped out for better quality hex screws for both the carb and the air box and associated housing. Though not exhaustive I came up with:

2X M4 .70x20
2X M4 .70x25
2X M4 .80x10
2X M4 .80x12
2X M4 .70x14
8x M4 .70x various

These are swapped out on the carbs, pipes and airbox before I continue.

All of the required parts and tools are gathered for this project before we begin, its better than stopping to hunt for stuff mid-test. Amongst these would also be a rebuild kit.

The first test will be blowing air into the fuel line and turning the carbs over to see if it is blocked. A failure of this test would mean immediate attention to the float needles and or seats to resolve this issue. Though fine here we assume everything fails and replace everything later.

Next, the bowl is marked for the positions where the fuel level should be using the calipers and a razor blade to leave light marks as demonstrated. That would be 8mm below the line. and .5mm above and below that line.

Its worth pointing out that the carbs are not level in the bike when the bike is level, they are cantered to the low side 13 degrees, so a structure is assembled to pitch the carbs 13 degrees for the level testing. This is critical. With the carbs in position we set up the second test which is the hose and funnel on a scaffold filled with gas to see if the level holds. This proves out the float needles as liquid tight.

With that next test passed, we move to the float level hight test. using the translucent hose the bowl drain is opened to reveal the level within the carb. Mine are adjusted higher, but demonstrates how the position can be measured. I conduct this on both carbs. We can see the level on mine are the same on both.

We continue with the second video in this two part series. Here we will look at the carbs as if all sorts of problems were found so each issue can be addressed. The first step being to drain out the whole system through the bowls back into a gas can so that the fuel line can be detached and the bowl cover removed.

The first step will be the replacement of the float needle and seat from the carb with the ones from the kit. My kit required swapping the screen from the old one after cleaning to the new seat before installing. I further take this opportunity to demonstrate float level height adjustment before reintroducing the float into the carb.

I then assume that the bowl cover seal is also bad, though it probably isn't far off from bad anyway, and demonstrate replacing that as well before closing up the float cover. This would be the time to do float measurements and leak rechecks.

Having moved past the floats I move onto the heaters and their resistance testing, though noting that the readings off of the cable can be deceiving as two are in parallel, so its best to check each one for about 8 ohms, and then continuity through the harness. The solenoids should be about 12 ohms. When they break, put a 12 ohm resistor off the cable connection to ground and forget about them.

TPS is just a spring loaded pot. The first measurement across is the total resistance, the next measurement tests the sweep. It will never start at 0 ohms installed in the bike. So long as its between 650 and 750 ohms in the closed position its ok.

A requirement for a deep ultrasonic cleaning allows for a demonstration of TPS removal as well as the drilling out of the PMS needle plug. An account is made of the turns of the PMS needle to full seat and recorded. The carb is submerged in solution to about 60degC simple green and distilled water until it comes to temperature and then two sessions of twenty minutes with the oscillation. After this the carb is cleaned in distilled water, blown out with compressed air and reassembled.

The PMS needle is screwed in to full seat and then dialed out to the appropriate turns. This is followed by the TPS which is installed and then calibrated to 700ohms at closed plates with the meter as shown in the video.

Having completed all tasks, the other pieces for idle are re-added to the carb. Also the wire looms are added for the cables. This carb is now tested and ready for installation into the bike.

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