1994 Yamaha 225 TXRS misses midrange rpm?

Hi all,

Recently I purchased a 1981 20' whaler revenge powered with a 1994 225HP txrs yamaha (3.1L carberated). I had all 6 carberators rebuilt last spring along with new plugs (all gaped to spec).

The motor starts and idles fine (around 750 rpm) but does blow some smoke for the first few minutes of run before clearing. As I throttle up underway, the rpms pick up fine until about 1500. After 1500 rpm more throttle does nothing until the arm is 3/4 way down. Then it suddenly jumps to 3200 rpm and picks up speed rapidly. From 3200 to 5100 rpm (WOT) it accelerates and deccelerates fine? Once you get below 3000 it drops back to 1500, nothing in the middle??

I have been told it could be the TPS, TSAT, Knock sensoor, fuel enrichment controls or fuel pumps? I dont have a diagnostic test lamp on hand and dont have the cash to buy one. After speakign with my mechanic, and several hours of blogging, it seems like the obvious choice is the TPS. Im not 100% confident however and would like to get more opinions before I move forward with purchase and swap out.

Also an an FYI - I typically run 89-90 grade octane stabilized gas and am running a 13 3/4" x 21" black steel yami prop. New water seperator, new gas tank, lines, primer bulb and clean filter as well.

Feedback would be appreciated mates!

Thanks

Nick

You can test the TPS for smooth voltage increase with a digital volt ohm meter.

If there is a dead spot it will not advance timing.

Thanks!

What type of values should I be reading on the voltmeter? Im assuming as I throttle up the voltage values should climb smoothly and continuously. Also this should be doen while underway correct. Not in netural on the trailer at the ramp?

Dont remember the colors of the wires but there are three. One is ground, one is your reference voltage from the YMIS which should be around 5.0 volts, and one is the signal voltage from the tps which should be between .60 and .70 volts with the throttle plate closed and the key on.

You can check this with the boat on the trailer KOEO (Key on Engine off)

DO NOT POKE HOLES IN THE WIRE INSULATION! Slide a paper clip into the plug along side the wire into the weather connector to get your readings.

You are going to probe the wire that has .60/.70 volts. You will open the throttle plate very slow and watch for jumps in voltage or for a complete loss of voltage or for intermittent voltage.

WOT(Wide open throttle) voltage will not match reference voltage exactly. No worries.

Thanks so much! I will give it a shot