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Yamaha 40TLRZ 2 stroke - rebuilt carbs idles great but no longer get high RPM

J

jkorten

New member
Hello everybody, first time poster here. Thanks in advance for any advice.

I have a 1999 or 2000 Yamaha 40TLRZ (low hours, I can get maybe 10-20 hours on the water a year). I recently had to rebuild the carburetors, middle one was full of crystalline stuff (salt?) anyhow - new floats, new float valves, needles, valve seats, seals etc. Also replaced the fuel pump and made sure the fuel filter was clean (did not replace).

Engine started like a dream. Adjusted needles for fastest idle (around one turn open or so). And off we went. But ran great for about a half an hour planning at high speed going to our favorite fishing spot. Bluefish hitting the surface, casting and able to bring one aboard, then off to the place where my brother can spear fish and I'm telling him "come on let's go!" and he says he's got the throttle full on. (travelling at a fast idle at this point with motor sounding like it was bogging). In fact the vent on the gas tank was closed. I opened it. Still no joy.

I powered off. Took of the hood, checked throttle linkage - seems well adjusted (made sure this was the case before hand). Manually manipulated the butterfly linkage and saw all was moving as it should. Timing adjustment moves from idle point to high RPM point just fine as it is supposed to.

I then started it up, moved the idle speed to fast, motor revved up fine, then put the motor in gear and moved the throttle forward and it sort of punched up a couple of times (zing.. zing..) and up we went to full speed. So I thought the engine must have sucked itself into some kind of locked closed situation when the vent was closed. We motored back home after landing a striper and a blue, and then again, after a half hour at high speed. Slowed down, then tried to speed up and it bogged down again! Could not get it to go fast anymore. Moved the throttle to full on and every once in a while a zing up to full RPM for a fraction of a second, but no more.

Seems like a fuel issue. If anybody has seen this before, would be much obliged for your guidance.

Again thanks in advance.

Jerry
 
Oh also, before we put it in the water we also replaced the impeller.

When the throttle cable gave out I wasn't even touching it which is interesting to me. We just made it out of deeper water and I could see it was a bit shallower but I highly doubt we hit anything. Maybe sucked something up and its still there? Engine still spits out water but could it be partly clogged causing a lack of power?
 
I've flushed the engine with a hose after every use since I'm on saltwater. When connecting with that hose adapter is shoots the water through quite strong so that doesn't seem clogged at that point. Maybe clogged down lower?

(Forgive my ignorance, I'm learning)
 
schreck425 said:
I've flushed the engine with a hose after every use since I'm on saltwater. When connecting with that hose adapter is shoots the water through quite strong so that doesn't seem clogged at that point. Maybe clogged down lower?

(Forgive my ignorance, I'm learning)
Click to expand...


You are in the wrong thread. This is my thread! ;)
 
jkorten said:
Hello everybody, first time poster here. Thanks in advance for any advice.

I have a 1999 or 2000 Yamaha 40TLRZ (low hours, I can get maybe 10-20 hours on the water a year). I recently had to rebuild the carburetors, middle one was full of crystalline stuff (salt?) anyhow - new floats, new float valves, needles, valve seats, seals etc. Also replaced the fuel pump and made sure the fuel filter was clean (did not replace).

Engine started like a dream. Adjusted needles for fastest idle (around one turn open or so). And off we went. But ran great for about a half an hour planning at high speed going to our favorite fishing spot. Bluefish hitting the surface, casting and able to bring one aboard, then off to the place where my brother can spear fish and I'm telling him "come on let's go!" and he says he's got the throttle full on. (travelling at a fast idle at this point with motor sounding like it was bogging). In fact the vent on the gas tank was closed. I opened it. Still no joy.

I powered off. Took of the hood, checked throttle linkage - seems well adjusted (made sure this was the case before hand). Manually manipulated the butterfly linkage and saw all was moving as it should. Timing adjustment moves from idle point to high RPM point just fine as it is supposed to.

I then started it up, moved the idle speed to fast, motor revved up fine, then put the motor in gear and moved the throttle forward and it sort of punched up a couple of times (zing.. zing..) and up we went to full speed. So I thought the engine must have sucked itself into some kind of locked closed situation when the vent was closed. We motored back home after landing a striper and a blue, and then again, after a half hour at high speed. Slowed down, then tried to speed up and it bogged down again! Could not get it to go fast anymore. Moved the throttle to full on and every once in a while a zing up to full RPM for a fraction of a second, but no more.

Seems like a fuel issue. If anybody has seen this before, would be much obliged for your guidance.

Again thanks in advance.

Jerry
Click to expand...

Any chance water had got into fuel tank? Old fuel, or often replaced? Did you notice what the status of the primer bulb was during the time the engine was bogging down?..collapsed, full, normal?

When you cleaned the carbs, did you also pull jets from each carb and clear each of debris?
 
ClassicAQ said:
Any chance water had got into fuel tank? Old fuel, or often replaced? Did you notice what the status of the primer bulb was during the time the engine was bogging down?..collapsed, full, normal?

When you cleaned the carbs, did you also pull jets from each carb and clear each of debris?
Click to expand...

Thank you - Perhaps a chance. I temporarily bypassed my water filter before rebuilding the carbs, perhaps I put this back in. Primer bulb was stiff. Indeed I did replace the jets and there was a brass insert (the jet seat) that I also pulled and replaced with new O-rings below.

But I will put the water filter back in line and swap out the gas tank thanks for the suggestion.

Jerry
 
jkorten said:
Thank you - Perhaps a chance. I temporarily bypassed my water filter before rebuilding the carbs, perhaps I put this back in. Primer bulb was stiff. Indeed I did replace the jets and there was a brass insert (the jet seat) that I also pulled and replaced with new O-rings below.

But I will put the water filter back in line and swap out the gas tank thanks for the suggestion.

Jerry
Click to expand...

So an update - the engine mostly will work at high RPM but occasionally I go through this phase where you advance the throttle full on, the engine goes brrrrr at a low RPM and suddently VROOOM then brrrrr then VROOOM then brrrr. Switching between the two RPM way to fast to be a fuel issue. Seems electrical. Do I just replace the solid state ignition module and spark plug wiring harness?

Thanks

Jerry
 
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