2007 Yamaha 70TLR PrimeStart Issue

[Whaler94]

Hi everyone, I've been following this forum as a ghost for a little while now, but have had this long going issue I was hoping I could get a little help on. A few months ago I purchased a 2007 Yamaha 70TLR outboard from the original owner. When I first got the engine, it ran fine on the muffs at first but then began to run rough. When I would start the engine, it would idle very rough and want to stall out unless I revved the throttle. My friend and I took the boat to the dock and a test run and had the same issue. The engine was idling rough at the dock and wanted to stall. However, once we got it into gear and got it above idle, it began to run great. It ran great all the way up to WOT so we bombed around in it for a bit to just get some gas through it. But when we brought it back down to idle (or tried) it began to get rough and want to stall out again. So we took it home and most of the research I did pointed to dirty carbs. However, I've been doing a lot of research on the PrimeStart enrichment system and began to suspect that as the culprit.

So Saturday, after lots of research on the PrimeStart, we took the boat back to the water. The beginning was the same as the last test ride, it ran rough at first and then cleared up after getting it passed idle in gear. Then is ran great. After running it for a while and burning that extra gas up, we removed the cowling and turned the red PrimeStart valve behind the sound deadener from normal position to totally closed off. I ran it around for another couple minutes and then tried to bring it down to idle again. This time it got down to idle beautifully, both in gear and in neutral. The engine was willing to start and restart freely and was idling great. So (I thought) I had my answer. I went home and took the whole PrimeStart system off yesterday. I bench tested the actual electro thermal valve and it was heating up and moving fine when connected to a battery. As well, the diaphragm and all other internal guts looked clean as a whistle.

Since the PrimeStarter works when hooked up to a battery and everything else is clean in there, is this some kind of electrical problem? Could the PrimeStart be getting no power and therefore just dumping fuel into the engine? I haven't done any cleaning or adjustment to the carbs and nor did the original owner, but it seems odd that that would be an issue since the engine idles beautifully when this PrimeStart system is closed off and very rough when it is in the normal position. Any help or insight would be terrific. Thanks very much in advance.

[99yam40]

are you sure it was in the normal position, and not the on position when running rough?

Yes it could be possible that the wiring to the prime start is not connected properly keeping power from getting to it.
easy to trace out and test while motor is running for power

[Whaler94]

are you sure it was in the normal position, and not the on position when running rough?

Yes it could be possible that the wiring to the prime start is not connected properly keeping power from getting to it.
easy to trace out and test while motor is running for power

I'm sure it was in the open position when running rough from both looking at the diagram on the sound deadener and then this was confirmed by looking at the actual openings on the rod that let the fuel through when I took the unit off. What components would I want to test and is there any specific order they should be tested in?

[boscoe99]

If the valve is in the open position then the motor will run excessivley rich when it is warmed up. Possibly run ruff. Normal position is fully counter clock wise. The automatic position.

To check for voltage simply put a volt meter on the blue wire that runs to the PS device when the motor is running. Other meter lead to ground. If you measure AC voltage there when the motor is running that means the PS device is being powered electrically. In which case the pin will extend to close off the valve as the motor warms up.

[Whaler94]

If the valve is in the open position then the motor will run excessivley rich when it is warmed up. Possibly run ruff. Normal position is fully counter clock wise. The automatic position.

To check for voltage simply put a volt meter on the blue wire that runs to the PS device when the motor is running. Other meter lead to ground. If you measure AC voltage there when the motor is running that means the PS device is being powered electrically. In which case the pin will extend to close off the valve as the motor warms up.

Sorry, I should have specified better. I had the red lever fully counter clockwise in the normal/automatic position like you said when it was running rough. I never ran it in the fully open position because I figured it would only make it worse. I didn't switch it to the off position until I got plenty of gas through it to burn off the extra fuel. When testing the voltage, should it read 12V if it's being powered properly? Sorry if that's a dumb question, electric work is not my best area.

[99yam40]

the power comes from the lighting coil and is AC not DC
It is tapped in before the Rectifier/regulator.
so voltage will not be 12 , it should be higher depending on how fast the motor is turning

[Whaler94]

the power comes from the lighting coil and is AC not DC
It is tapped in before the Rectifier/regulator.
so voltage will not be 12 , it should be higher depending on how fast the motor is turning

Ok great. So if I'm getting low voltage, would that mean that the lighting coil is the culprit? Or do I need to then check other parts as well?

[boscoe99]

If the PrimeStart manual valve is fully closed and the automatic valve is fully closed, and the motor is running ruff at idle when fully warmed up, I would hazard a guess that there is something amiss in the carburetor. Dirty carbs would be my guess. I does not take much crap to seal off a gnat's arse.

[Whaler94]

If the PrimeStart manual valve is fully closed and the automatic valve is fully closed, and the motor is running ruff at idle when fully warmed up, I would hazard a guess that there is something amiss in the carburetor. Dirty carbs would be my guess. I does not take much crap to seal off a gnat's arse.

The engine ran rough / stalled with the valves in the automatic position and great with them fully closed. Once they were closed and plenty of gas was ran through, the engine both idled well and restarted without issue after being shut off. It was not willing to either idle well or keep idling with the valve in the automatic position. Wouldn't dirty carbs cause an engine to run rough all of the time?

[boscoe99]

The Prime Start system is part of carburetor number two is it not?

[Whaler94]

The Prime Start system is part of carburetor number two is it not?

It's attached to the #2 carb, but from a post I read by Rodbolt, I believe it enriches all three carbs.

[99yam40]

On my C40 the line from the enrichment system runs to one spot on manifold, but yes it enriched all 3 cylinders through passages in manifold

the service manual gives procedures and specs for testing the charging system.

measure and report back what voltage you are seeing at the thermal valve heater connection .
if low check it at the connection coming from lighting coil also

[99yam40]

If the PrimeStart manual valve is fully closed and the automatic valve is fully closed, and the motor is running ruff at idle when fully warmed up, I would hazard a guess that there is something amiss in the carburetor. Dirty carbs would be my guess. I does not take much crap to seal off a gnat's arse.

Boscoe you need to re read his posts, motor runs well with manually shut off

[Whaler94]

On my C40 the line from the enrichment system runs to one spot on manifold, but yes it enriched all 3 cylinders through passages in manifold

the service manual gives procedures and specs for testing the charging system.

measure and report back what voltage you are seeing at the thermal valve heater connection .
if low check it at the connection coming from lighting coil also

Awesome, thanks very much. I have a factory service manual for the motor that I'll look through for the testing instructions when I get home from work. From reading through a decent bit of it already, I was surprised how little information there is about the PrimeStart system in there. When I looked through the wiring diagram, it appears that the only two things that feed power to the PrimeStart are the lighting coil and the rectifier regulator. Is this correct? I know that you said the lighting coil is it's power supply, but would the rectifier be the next place to check after that? Also, does the lighting coil supply power to just the PrimeStart or other components as well?

[boscoe99]

Boscoe you need to re read his posts, motor runs well with manually shut off

I just did. Which leads me to believe that maybe, just maybe, too much fuel is getting through the system when the valve is in the automatic position. Maybe there is debris on the needle seat that is preventing the needle from fully seating and closing off the flow of fuel when the motor is warm. Allowing too much fuel and resulting in an excessively rich mixture.

OP says the Primestart heater and needle valve are working. For some reason it seems to not be getting the job done. If indeed too much fuel is flowing and causing the ruff running issue.

OP might want to go and review the dangar prime start video.

Heck I don't know. Just guessing. Hard to trouble shoot in person. Harder still to do it from a distance.