1983 regal 18' only 25mph

[eedwards]

I have a 1983 regal 18' open bow with a mercruiser 120 and only getting 25mph and 3500 rpm seems to me boat should go a lot faster.Have no clue what prop is on the boat the one that came with it has no size stamp.

 

[Don S]

Re: 1983 regal 18' only 25mph

Here is a list of possible causes of low WOT (Wide Open Throttle) rpm.

In no particular order

Engine Won't Reach Operating RPM. Check

1. Fuel condition. Type and Octane possibly old fuel
2. Propeller pitch or diameter, damaged blades
3. Restricted fuel pickup tube or anti siphon valve Fuel System Test
4. Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
5. Marine growth on hull and outdrive
6. Wrong gear ratio in outdrive
7. Restricted carburetor air intake (clogged flame arrestor)
8. Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
9. Poor cylinder compression Compression Test
10. Carburetor defective, or wrong type.
11. Fuel pump pressure and vacuum
12. Boat overloaded, improperly loaded, or improperly trimmed.
13. Engine Overheating
14. Engine timing and ignition system operation
15. Remote control cables and linkage for proper travel to open throttle plates fully.

 

[eedwards]

Re: 1983 regal 18' only 25mph

Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
Where are these and how do i check?
I'm new to I/O and what a pain it has been with bellows and gimbel bearings after i figure this out i'm selling it and going back to outboards

 

[cr2k]

Re: 1983 regal 18' only 25mph

Regal is a heavy boat. I have an '84 19' with a 3.8 and it only gets up to about 36-38 MPH. Well built but heavy. Funny thing is it runs the same with a 17p or a 19p only difference is fuel consumption is noticeably higher with the 17p.

 

[eedwards]

Re: 1983 regal 18' only 25mph

Is 3500-3800 to low of rpm's?

 

[Don S]

Re: 1983 regal 18' only 25mph

Is 3500-3800 to low of rpm's?

Yes, you should be seeing between 3900 and 4300.
Just out of curiosity, when you were running the boat, did you trim the drive up while you were running, or leave it all the way down?

 

[eedwards]

Re: 1983 regal 18' only 25mph

Trimmed up to where i get the max rpm's.
The boat had a oil change before i got it, but i just checked it now and it is way over filled about two inches above the full line.So im wonder if it blowing back into the carb from the breather tube.

 

[Don S]

Re: 1983 regal 18' only 25mph

The boat had a oil change before i got it, but i just checked it now and it is way over filled about two inches above the full line.

Was the oil milky colored? Or did it look like normal oil.

Being overfilled like that will cause the crankshaft to aireate the oil and cause the lifters to partally collaps. That would sure kill rpm.
Time to fix your oil problem then do a retest.

 

[eedwards]

Re: 1983 regal 18' only 25mph

Well i was changing engine oil and saw the back ignition wire had came off.Now running 4500 rpm.The oil smells strong of gas can that be from the cylinder not firing?

 

[muc]

Re: 1983 regal 18' only 25mph

Yes that might cause it. Change the oil run it some more and keep an eye --- I mean nose --- on it.
Good Luck Muc

 

[eedwards]

Re: 1983 regal 18' only 25mph

Still can't believe i didn't notice the wire had come off.

 

[Joshua Nichols]

Re: 1983 regal 18' only 25mph

Sometimes a bad fuel pump will cause gas to enter the oil sump. But it would be a noticeable amount.. Like said before, just watch it.. Seems like you found your problem

 

[slag]

Re: 1983 regal 18' only 25mph

wish that was the cause of my issue. I'm going to do a compression test tonight and go from there. Mine wont go over 3100 rpms when trimmed up. but is around 30 mph according to the dream o meter.