Not reaching max RPM!!!

[ddbyrd3]

I have a 1981 Johnny 140 V4 J140TXCIM.<br /><br />Compression is 109 - 115 on all 4 cylinders, I have great spark, carbs were rebuilt last month, Butterflies are at full horizontal position full throttle)fuel pump was rebuilt, and all lines were changed. Coils and power packs are all new. Static timing is set at 24* (tested on the trailer in the water, per DHadley's instruction) and the timing base is moving free to the stop.<br /><br />My question is this, The motor (prior to rebuild in "01") use to run at 6000 RPM running a 13 1/4 x 19 SST prop. I had it out again yesterday (same prop) and at full trim it will only pull 4800 - 5000 RPM full fuel, myself and 2 of my boys. (standard load)<br /><br />My tach is a teleflex set on the proper setting (per instructions)the motor location on the transum did not change, I am scratching my head as to why I cant get it to pull in the 5500 - 6000 RPM range. <br /><br />I do intend on taking it out again this weekend using my 13 1/4 x 17 Aluminum Hustler prop to compare RPM. <br /><br />Any ideas???? Sorry for the long post....

 

[ddbyrd3]

Re: Not reaching max RPM!!!

I was thinking that since the motor was rebuilt in "01" and the compression numbers are in the low 100's that the builder might have used the Low Compression head gaskets.<br /><br />Is that a viable place to begin?? I have seen other post of compression numbers being as high as 125 - 130. That would have an over all effect on performance right????<br /><br />DHadley had walked me thru a TON of steps to check in a previous thread "engine swap" and it is alot better than it was then, but it still isnt quite right..... please help..............

 

[ddbyrd3]

Re: Not reaching max RPM!!!

DHadley where are uuuuuuuu?????????? help me....

 

[ddbyrd3]

Re: Not reaching max RPM!!!

OK, I installed my 13 1/4 x 17 aluminum prop and was only able to pull 4800 - 5000 RPM....<br /><br />There is NO change in engine RPM from my 19 SST to my 17 aluminum......<br /><br />Any ideas......

 

[wilde1j]

Re: Not reaching max RPM!!!

I would carefully check the timing again. If nothing else has changed, the rebuilt PH should turn close to what you had before the rebuild.<br /><br />BTW, what was the reason for the rebuild? If it was lean running, I would consider rebuilding the carbs. PH failures usually have a reson, unless you just wore it out (which is not to common, since most engines in pleasure use don't see 100 hrs per year.)

 

[ddbyrd3]

Re: Not reaching max RPM!!!

Thanks for your reply, the top ring land on #1 cylinder came apart. the reason was the previous owner took it in the ocean and never flushed it out. Calcium built up in the cylinder head cover blocking the water passages that cooled the top of the combustion chamber, hense overheating #1 cylinder...<br /><br />As far as a carb rebuild, I did that last month, I know for a fact they are good to go..... <br /><br />The motor will not pull more than 5000 RPM regardless of the prop I install.... The hull is dry (not saturated) motor position hasnt changed, no hull damage I am trully stumped....<br /><br />and I did verify timing, it is still at 24* static..

 

[Basscat 1]

Re: Not reaching max RPM!!!

and I did verify timing, it is still at 24* static..

Have you checked the timing in the water with boat turning 5000 rpms? You can do this by backing the boat into the water and leaving it on the trailor. If the motor dont reach 5000, try pulling the trailor foward, but keep the AV plate still under water, or trim up if needed.

 

[ddbyrd3]

Re: Not reaching max RPM!!!

Yes.... I have done that as well, timing is at 24* although I cant get it to pull 5k on the trailer, the max it will pull is 4200 - 4500 RPM regardless of the depth the prop is in the water...<br /><br />Correct me if I am wrong, even if the timing is close, which I am positive it is, the fact that the RPM's dont change between the 19 and 17 pitch prop is a concern, as well as I cant pull beyond 5k with either.....

 

[Basscat 1]

Re: Not reaching max RPM!!!

You need to set the timing to 28* at WOT.

 

[ddbyrd3]

Re: Not reaching max RPM!!!

I was told by DHadley to set it at 24* and the packs (ignition) do the rest bringing the total advance to 28*.

 

[Basscat 1]

Re: Not reaching max RPM!!!

That is an initial setting. You have to set it at 28* at WOT.<br />Go back an read this thread again. web page <br />___________________________________________________<br /><br />Dhadley <br />Fleet Admiral <br />Member # 685 <br /><br /> posted June 08, 2005 02:41 PM <br />--------------------------------------------------------------------------------<br />Thats correct. No matter how you set the timing for starters it needs to be checked under a load. The service manual doesnt refer to it because they instruct it to be set under a load using a test wheel. In the field we just figured out what worked, in a general way. <br /><br />And yes, the timer base must be aginst the stop. Thats what determines the total timing.

 

[ddbyrd3]

Re: Not reaching max RPM!!!

Thanks Cat, I did what was described by DHadley in that thread.... The most I could ever see was 24* regardless of RPM.... <br /><br />Now again this was done on the trailer..<br /><br />I have not tide it up in a slip and tried it as of yet, maybe thats what I need to do next.....<br /><br />But in my "not to experienced mind" regardless of the timing, the motor should carry a different RPM based on the prop installed and it isnt....<br /><br />Again, I know I am at least in the ball park in reference to timing.....<br /><br />Its as if the motor WILL NOT exceed 5k RPM, I have (not recently) installed my 13 1/4 x 15 Hustler aluminum prop and I only saw a 100 RPM gain, but a major loss of top end speed (as expected)

 

[wilde1j]

Re: Not reaching max RPM!!!

Have you checked the whole fuel system out for air leaks, vacuum due to clogged vent, fuel pump delivery, etc.?

 

[ddbyrd3]

Re: Not reaching max RPM!!!

Yes too all of those...the primer ball pumps up hard and stays hard all day.... And the vent is clear....

 

[Boilermaker]

Re: Not reaching max RPM!!!

You may have dropped a cylinder>>>try pulling the plug wires off and back on, one at a time (use well insulated pliers!) while the engine is running. If you pull one off, and the engine doesn't change rpms>>>you found a dead cylinder. Then you need to figure if its Ignition or Fuel delivery. <br />I had a similar problem with my 115>>>sounded OK, but was down aprox 800 rpm from normal. Turned out that I broke a wire leading to an ignition coil!<br />GOOD LUCK<br />

 

[ddbyrd3]

Re: Not reaching max RPM!!!

Thanks, I just installed new power pack and performed that very test after the install.... I have great spark on all 4 cylinders..... <br /><br />The only thing I havent checked, or changed is the head gaskets.... I am beginning to think the builder installed low compression head gaskets...

 

[jack7771]

Re: Not reaching max RPM!!!

"use to run at 6000 RPM ... yesterday ... only pull 4800 - 5000 RPM"<br /><br />Just curious -- did you notice a commensurate drop in speed per the speedometer?

 

[ddbyrd3]

Re: Not reaching max RPM!!!

Yes, it use to pull 50+ mph, now it barely pulls 38 mph...

 

[Boilermaker]

Re: Not reaching max RPM!!!

Just so that we are sure on this>>>The loss in RPM came directly after the rebuild in 2001??? OR did the loss of power come more recently???<br /><br /> I was wondering if it came directly after rebuild>did you ask the mechanic why the drop in power???<br /> <br /> I was wondering>>>>If it has been since the rebuild, is there any chance the pistons were installed incorrectly??? I have heard the pistons can be installed backwards & the engine still runs, has good compression ect.., but it is way down in power!!!<br /><br />I think you need someone more experianced with these engines>>>such as DHADLEY, JB, OBJ ect....<br /><br />

 

[Boilermaker]

Re: Not reaching max RPM!!!

One other thing>>>I was just wondering what type of boat this is on, because I have a '78 115 ( very similar engines)& can bearly turn 5100 with a 13.75 x 17 S.S. prop???<br /><br />Thanks