Cant get high rpms

[lennygilbert]

Here are some details..<br />78 Chrysler 75HP on 16ft boat<br />Compression check is 150psi in all 3 cylinders.<br />Carbs rebuilt last yr<br />Tune up done last week by shop<br />new fuel pump kit<br />new plugs<br />new fuel line and fresh gas/oil mixed at 50:1<br /><br /><br />Here is the problem.<br />I cant get anything over 3k rpms. I took it into the shop last week to have it tuned up thinking that was the issue.The mech found that the fulepump diaprham had a big hole in it so he replaced it,tuned the carbs,set idle,timing.<br />I took it to the lake today and backed the rear into the water and started it up.I gave it full throttle and noticed that the rpms jumped up quicker than normal,so i launched the boat.I still had the same issue of not being able to get over 3k rpms.After pulling the boat out i noticed that the prop had two of the blade chewed up kinda good.I guess i had the motor down to low when i was first testing it.<br />Could a prop with some blades thatare bent and chewed up cause rpm issues??<br />I have a brand new prop to install but dont have time today.<br />Any other ideas on what could be causing my rpm issue?? Thanks...

 

[lennygilbert]

Re: Cant get high rpms

I think tonight I will goahead and warm up the engine on mufs then spray some deep creep into each carb, and then into each cyl and let it sit over night before heading back to the lake tomorrow..for another test with the new prop.

 

[eurolarva]

Re: Cant get high rpms

Before you do the decarb pull and examine all three of the spark plug tips. Do they all appear to have the same amount of grime on them, or the same type of burn pattern? Prop could be the issue but a cylinder not firing will give you the same results. A clean spark plug tip could be a blown head gasket or a cylinder not firing.

 

[lennygilbert]

Re: Cant get high rpms

cant tell on the plug since this is the first time they have been run.<br />A freidn of mine mentioned the following..The boat originaly came with a Force engine.The engine that is on it now is a Chrysler.(boat is 1988 Renken,Engine is 78 chrysler) He thought maybe I was getting the correct Rpm's but that the tach currently on it is not compatible or set correctly to work with the chrysler.And since the prop has some small cracks,and ruff edges that the prop could be what is keeping the speed slow.He had this happen on one of his boats when he changed over to another outboard.He thought he was not getting the correct rpm's according to the tach but in reality he was but his prop was slowing him down.I've got a brand new prop in the garage..I am not able to let the cyl's soak over night with deep creep,so I will spray them down 1st thing in the morning,then wait a cpl of hrs and head out to the lake.for a "smoke session".Plus since its monday the lake ramp should be wide open..

 

[lennygilbert]

Re: Cant get high rpms

here is some more information...'<br /><br />MODEL-757H8D<br /><br />I also found that the tach is not connected to the "tach" connection on the wiring block.The block shows that the WHITE wire is for the TACH.The way it is connected now is the tach wire is going to the PURPLE GENERATOR wire.<br />I think tomorrow I will either go buy a new tach or run a Wire from the tach connection to the tach and see if that changes anything..<br />I also couldnt find any place on the rear of the tach where you could change and of the settings like pole,# of cyl,ect..

 

[lennygilbert]

Re: Cant get high rpms

given my model number listed above. can anyone tell me what kind of tach I need to have??<br />Do I need to find one that works on 20 pole?

 

[roscoe]

Re: Cant get high rpms

Should be a 12 pole.<br />See chart at the bottom of this page:<br /> http://ww2.tflx.com/PDF/99320.pdf