Can't get RPM up

[mmcdjs]

Hello everyone and thanks in advance for any help!

I have a 1982 Century 5000 23' w/5.7L engine. I am having a problem when I'm under load, I can't get RPM above 2400 most of the time. I have had the carb rebuilt, and checked timing. I watched the carb while running WOT and it looks like there is a huge amount of fuel being dumped in (oh 4bl rochester carb), but no increase in RPM. Bogs down considerably when i turn, below 2000 rpm, and chugs/backfires sometimes when I push it to WOT. Any ideas?

Thanks!

 

[Bt Doctur]

Re: Can't get RPM up

We`ll need some basic information first
Compression readings
Spark plug wiring confirmed as correct 1,8,4,3,6,5,7,2
You could try a "cyliner balance test" by pulling off 1 wire at a time from the cap and checking the amount of rpm drop. no drop= a non-firing cylinder
use a laser temp gun on the spark plugs,no heat reading=no fire
spark plug wires were changed when?

 

[mmcdjs]

Re: Can't get RPM up

The compression was about 135 average for all 8 cylinders. Plug wires, plugs cap and rotor were replaced at the end of last year, around October I think. I am not misfiring or have a rough idle. It only chugs when I go from 1000 rpm to WOT quickly.

Thanks for the quick reply. I love this site!

 

[Bt Doctur]

Re: Can't get RPM up

Assuming the wires are in the proper order and those compression readings are accurate ,try a cylinder balance test to make sure all 8 are operating.
you don`t list the type of drive ,could it have been switched to one with a different ratio? Other than that a fuel delivery problem in the carb.
Was it ever running at the correct WOT

 

[mmcdjs]

Re: Can't get RPM up

Yes, it was running ok before I did some other work to stop an oil leak. I removed the intake and replaced the gaskets. Cap, rotor, plugs and wires were replaced and had the carb rebuilt while I had it apart. Since putting the pieces back together, it won't go above 3000 rpm at WOT and sometimes won't even make it to 2500 rpm.

 

[mmcdjs]

Re: Can't get RPM up

hey, I've also got a 16 x 16 prop if that helps any. A few dings but nothing too bad. Even at 2400 RPM my stern is down and the bow is way up. I'm churning lots of water, but not picking up any speed. If you trim up, doesn't that lower the stern? I've tried trimming it in different positions too, still no luck.

 

[v1_0]

Re: Can't get RPM up

Yes, it was running ok before I did some other work to stop an oil leak. I removed the intake and replaced the gaskets. Cap, rotor, plugs and wires were replaced and had the carb rebuilt while I had it apart. Since putting the pieces back together, it won't go above 3000 rpm at WOT and sometimes won't even make it to 2500 rpm.

Working ok + changes = not working ok = suspect one/all of your changes. That gives you a starting point to work from.

I like to work from "low to higher" cost diagnoses (in both time and money categories). I'm not good enough to work from most probable to least...

I'd pull the plugs and take a look at them. Dark/fouled plugs = too rich a mixture = carb adjustment. Wet (fuel) plugs = not firing.

Regap the spark plugs at this point since you have them out.

Next, I'd confirm or re-re-re confirm that the wires are correctly hooked up between the distributor and the correct spark plug. And that they are firmly seated at both ends.

If that checks out, I'd get one of those inline spark plug testers and confirm that all the plugs are firing.

If that looks ok - I'd look at the timing.

After that, I'd shift suspicion to the carb rebuild. Did you do the rebuild yourself, send it out, or bring it to someone local? How did they adjust the mixture?

 

[v1_0]

Re: Can't get RPM up

hey, I've also got a 16 x 16 prop if that helps any. A few dings but nothing too bad. Even at 2400 RPM my stern is down and the bow is way up. I'm churning lots of water, but not picking up any speed. If you trim up, doesn't that lower the stern? I've tried trimming it in different positions too, still no luck.

You didn't list changing the prop in your first post - is this the same prop you were running 'before'.?

 

[mmcdjs]

Re: Can't get RPM up

Same prop as before, elephant ears 16 x 16. I'll go back and check the plugs and wires etc. I'll let you know what I find.

 

[mmcdjs]

Re: Can't get RPM up

I checked the plugs. all of them looked really good. Checked firing order and wires, also good.

 

[Bondo]

Re: Can't get RPM up

Ayuh,... Don has a List of Causes for a lack of RPMs up in the Adults Only section,....
Start at the Top of Don's list,+ work your way down...

 

[mmcdjs]

Re: Can't get RPM up

Ok. I'll go there and start at the top and work my way down!