PDA

View Full Version : 91 ProStar: Engine Over Revving in Neutral


TonyB
05-26-2012, 09:16 PM
After a great day on the boat with friends I headed back to the launch to call it a day. When I approached the launch and reduced the throttle it would not come back to normal. In neutral it was over 2200 rpm. I backed the idle screw all the way out and that reduced the rpms to around 1500. I've looked at everything on my Holley 4160; I've checked and lubed the throttle linkage and every other moving part on the exterior of the carb. Still, it over revs.

Suggestions?

1redTA
05-26-2012, 09:26 PM
choke out of whack?

Cloaked
05-26-2012, 09:29 PM
Check the return spring on the throttle cable linkage. To troubleshoot, take your hand and push forward (or down) on the throttle linkage at the carb. right where the throttle cable attaches. See if that idles it down. If so. your spring needs to be adjusted, replaced, or unsprung, or something similar.

.

Jerseydave
05-26-2012, 09:32 PM
After checking to make sure your throttle plates close all the way, start looking for a vacuum leak. Check all vacuum hoses including your PCV hose (if you have one)
You can also spray 2+2 around the intake gasket if you find no other vacuum leaks. If there is a vac leak the idle will increase when you spray near the leak.

Cloaked
05-26-2012, 09:39 PM
After checking to make sure your throttle plates close all the way, start looking for a vacuum leak. Check all vacuum hoses including your PCV hose (if you have one)
You can also spray 2+2 around the intake gasket if you find no other vacuum leaks. If there is a vac leak the idle will increase when you spray near the leak.I think that is the only vaccum hose on the 91 carb. model. The hose should run from the starboard valve cover via PCV back to the spacer plate or base of the carb (for newer 4160s). The hose should not connect into a port on the intake manifold. The gasket at the base of the carb (and / or the spacer plate, either side) can also have deterioriated. Throttle cable could have gone south but that is the long shot.

.

TonyB
05-26-2012, 09:49 PM
After checking to make sure your throttle plates close all the way, start looking for a vacuum leak. Check all vacuum hoses including your PCV hose (if you have one)
You can also spray 2+2 around the intake gasket if you find no other vacuum leaks. If there is a vac leak the idle will increase when you spray near the leak.

I've had vacuum leaks. They are only an issue at low idle rpms (i.e. rough idle). Once the rpms get above a certain level the amount of fuel overcomes any "vacuum" that may exist.

Ive Checked the springs, the plates, etc. Everything is going through its full range of motion. But the rpms remain unbearably high.

Boat had been running great all day. On the way home I did come out of the hole somewhat hot and then proceeded to the launch at around 35mph till stop.

Anything else?

Cloaked
05-26-2012, 09:57 PM
I've had vacuum leaks. They are only an issue at low idle rpms (i.e. rough idle). Once the rpms get above a certain level the amount of fuel overcomes any "vacuum" that may exist.

Ive Checked the springs, the plates, etc. Everything is going through its full range of motion. But the rpms remain unbearably high.

Boat had been running great all day. On the way home I did come out of the hole somewhat hot and then proceeded to the launch at around 35mph till stop.

Anything else?If the linkage is free and clear, the next place up the line is the accelerator pump. The lnkage may be riding it hard (a slip of adjustment) to make the carb think the throttle is calling for acceleration. There should be minimal clearance between the linkage and the pump lever, just enough to allow it to close when the throttle is in neutral or backing down. Something in that area or an associated componet almost has to be thr culprit. Beyond that, you would then be looking at floats, fuel bowl, etc, but would then be getting excessive fuel and not necessarily a high RPM. That's about all I know on this subject. :D

.

.

TonyB
05-29-2012, 10:24 AM
Inexplicably, all is back to normal.

Carry on.