Low Idle speed question

H

Halfhitch

GreatGrady Captain
Joined
Nov 11, 2017
Messages
1,536
Reaction score
500
Points
113
Location
Venice, Florida
I have two 115hp four stroke Yamahas. 2003 year model. Both motors start up fine but want to idle at 600 rpm. The Yamaha specs call for 750(50+ or -). Not a huge deal except that when cold at start-up when launching and manuevering to the dock, the port engine will occasionally die. It starts right back up but I'm sure if it was clicking just a little faster that wouldn't happen. Each engine has just over 1000 hrs.
I haven't checked fuel pressures yet. I'm just wondering if, on reading those symptoms, what would be your first guess about to investigate to get the idle where Yamaha says it belongs?
 
I’d get the Ydis software and cable to troubleshoot. Not expensive. Look for TPS (throttle position sensor) setting/voltage. If this started all at once or over time, look at rigging as well. The YDIS can tell you a lot and test several components. Not likely to be a major issue on both engines, did they both show the lower idle at the same time? If they run good at higher power, not likely fuel.
 
Thanks for that Bill. They have been that way since I bought the boat. I see in the paperwork that the previous owner had the injectors cleaned and a couple replaced at one time, but it was several years back. Both engines run good from idle on up. It's just the idle itself.
 
Ekea said:
do those engines have idle air control valves?
Click to expand...
They have an idle speed control assembly. There is also a throttle position sensor. Before messing with them I am trying to figure out why both engines would get a slow idle symptom at the same time.
 
Just for giggles, open the fuel cap and see if it changes anything. If not, remove and clean the AS valve. While it's off, blow through the tank fitting to ensure no blockage.
 
You can't assume that both engines had the problem at the same time since it is possible that the previous owner had the problem at different times and didn't fix the motors, just lived with it. When you got the boat, you 'inherited' the problems
Measuring the fuel pressure is a good start. The idle air valve is also a good place to look. I doubt the TPS is the issue. If the problem only occurs on cold motors, that is a clue that the air control valve may be bad. I am not sure how the 'choke' works on that model. I would research the internet for info on low idle when cold.
 
DennisG01 said:
Just for giggles, open the fuel cap and see if it changes anything. If not, remove and clean the AS valve. While it's off, blow through the tank fitting to ensure no blockage.
Click to expand...
I will check the anti-siphon valves(i hate those things) and ensure no restriction, although I have run it full throttle on both engines for 10 minutes straight, just to see if there was a flow problem and it showed that my wallet was getting depleted rapidly enough to make me think all is well there.
 
seasick said:
You can't assume that both engines had the problem at the same time since it is possible that the previous owner had the problem at different times and didn't fix the motors, just lived with it. When you got the boat, you 'inherited' the problems
Measuring the fuel pressure is a good start. The idle air valve is also a good place to look. I doubt the TPS is the issue. If the problem only occurs on cold motors, that is a clue that the air control valve may be bad. I am not sure how the 'choke' works on that model. I would research the internet for info on low idle when cold.
Click to expand...
You are right about the timing of the beginning of the low idle condition. It idles at 600rpm whether cold or warm but usually only dies when I first start and am maneuvering back to the dock after launching. As you well know Murphy likes to present you with challenges when there are people watching. :) I don't know if that idle air valve is something that can be or needs to be cleaned or if it is just a replace as needed type thing. Any idea? It's kind of a pain to get at, or I would just pull it off and mess with it.
 
Halfhitch said:
I will check the anti-siphon valves(i hate those things) and ensure no restriction, although I have run it full throttle on both engines for 10 minutes straight, just to see if there was a flow problem and it showed that my wallet was getting depleted rapidly enough to make me think all is well there.
Click to expand...
Yeah, and on top of that the fuel prices are crazy!

But, yes, I understand what you're saying. Sometimes, there just isn't enough pull/vacuum at low RPM's to get enough fuel. BUT... I overlooked that you probably have a fuel injected engine and that is probably less likely the issue.

To 100% eliminate the whole fuel supply to the engine system.... borrow a portable tank and plumb it to your engine. Run it on that. If you still have the issue, look at the engine and idle adjustments. IF the issue goes away, now look at the supply.

In the end, AS valves are good thing, though!
 
DennisG01 said:
Yeah, and on top of that the fuel prices are crazy!

But, yes, I understand what you're saying. Sometimes, there just isn't enough pull/vacuum at low RPM's to get enough fuel. BUT... I overlooked that you probably have a fuel injected engine and that is probably less likely the issue.

To 100% eliminate the whole fuel supply to the engine system.... borrow a portable tank and plumb it to your engine. Run it on that. If you still have the issue, look at the engine and idle adjustments. IF the issue goes away, now look at the supply.

In the end, AS valves are good thing, though!
Click to expand...
Yeah, I know the smart money is on the AS valves. That's a good plan for eliminating all that below the deck stuff. I do have four stroke fuel injected motors.
 
You must log in or register to reply here.