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Engines do not want to slow down 1991 454

S

s_williams

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I have 1991 454 xlt crusaders when running for a while at 3200 rpms when I throttle down they do not return to idle one might stay at 1800 rpms the other at 1200. If I turn the engine off and restart it will return to idle
 
Re: Engines do not want to slow down

It sounds like you may have cables or throttle plate hanging up somewhere keeping them revving. Worn cables can cause this. Years ago I had a high performance carb on a 327 Chevy in my Toyota Land Cruiser and it always failed to return to idle. I added helper return springs to the linkage and it worked well until I fixed it with the proper set up. It will be a bit stiffer to advance the throttles until

You may also have a leak ... air or fuel
 
Re: Engines do not want to slow down

I first added extra springs no help.Removed cable from carb linkage and worked the throttle by hand after I reached 2200 rpms and I returned the throttle back to idle it stayed at 1800 rpms until I turned it off.Another thing is that I have noticed the last couple of times when I return to the dock and power down after around 20 minutes or so the cabin smells like gas real stong
 
Re: Engines do not want to slow down

Well, you seem to have ruled out the cables. Do you know which carbs you have on the engine? How long have you owned the boat and have they been rebuilt at all, especially on your watch. Not that I discount what any previous owner says but..............
 
Re: Engines do not want to slow down

Well, the engine NEEDS air to run, so if, in fact, the throttle butterflies close completely, air is getting around them. Are the secondaries also fully closed? Actuate the choke to full choke when the engine idles high and see if the rpm drops. If not, look elsewhere around the intake manifold besides the carb. Is there a stray vacuum hose somewhere loose? Also, if the rpm does go up with an air leak, then it's liable to be running rich without the leak.
 
Re: Engines do not want to slow down

Holly carbs 5years and i have not done anything but clean and per the records I have from the original owner nothing done to them
 
Re: Engines do not want to slow down

If you come back to cables, I've had great success with a procedure I found online using a tire valve, hose and Marvel Mystery oil with a compressor.

Basically you use low pressure to blow the oil completely through the cable and out the other end. It takes about 5 mins to work all the way through and will make a stiff cable feel like new.

I can dig it up, it was a guy who owned a houseboat who posted it, I remember that.

Bob
 
Re: Engines do not want to slow down

Like DD said, an elevated idle RPM with the throttle plates closed means air is entering via another path (aka a vacuum leak). if the factory intakes are still on, check the adapter plate and the interleaved gaskets, too.
 
Re: Engines do not want to slow down

I had a similar problem, one engine was racing. It ended up that the carb's secondary was not closing completely- it wasn't the top "butterfly" but the one down inside the carb. Try spraying both carbs with some good lubricant.
 
Re: Engines do not want to slow down

Thanks that is what it turned out to be. I cleaned real good and no more problem
vikingtime said:
I had a similar problem, one engine was racing. It ended up that the carb's secondary was not closing completely- it wasn't the top "butterfly" but the one down inside the carb. Try spraying both carbs with some good lubricant.
Click to expand...
 
Re: Engines do not want to slow down

Ahah... beat me to it. Had the same problem one time on our boat. Port engine stuck arouind 1800 RPM's. The secondaries did not close completely. Flicked it with my finger, lubed it, and no problem since. Glad you got it figured out.
 
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