Motor not hitting max RPM range

[Quadruplecccc]

Picked up a merc. 233hp (1976) that was rebuilt and cammed up a bit .PO had all sorts of stuff messed up and have been trying to get all the bugs worked out.

I'm now on what I believe to be the last and final thing to adjust. The carb.

Had the 76' cresttliner crusader 24' out yesterday for a good run and discovered that with a 19 pitch prop on her , she won't climb above 3000 rpms. Not blaming the prop as I believe It's not over pitched.

Smells like it's running rich at idle but have a good brown look to the plugs. If it were running rich plugs would be on the black side. Running lean I would expect to see a white look to the plugs.

Using a marine holley 2bbl carb and have size 78 jets in . Last motor carb was on had no trouble goin over 3000rpms. Should be able to hit a max rpm at 4400rpm.

Its kind of wierd that the motor flattens out at 3k rpms. I'm thinkin I have to jet it up even more. My 2nd option is to go back to using a 4bbl carb. This one has size 66 jets in. This one worked on this motor until the carb to intake adapter plate started to leak vacuum. So I switched back to my other carb (2bbl) that I used on my old motor.

Timing is set at 8* bftdc and advances to 20 or 22*bftdc @ 3000rpms. Runs very smooth but I'm a little stumped. Any suggestions? sorry soooo long!

 

[180shabah]

Re: Motor not hitting max RPM range

Read #13

 

[bakerjet]

Re: Motor not hitting max RPM range

if your running a holly carb and have to go up more than 4 sizes from stock on the jets then the carb is to small, if i were you id get some one to drive and get in the back and make sure your getting full travel on your carb linkage and then check your fuel psi 5# at the least and fuel psi is a good place to start if your chasing WOT problems unless its bad fuel it will elminate anything from the carb back. hope this helps.

hey i read your post again i dont think you have enough advance it should be closer to 34* at full and i think at 3000r's it should be all in, but maybe someone with more know how will chime in.

 

[Quadruplecccc]

Re: Motor not hitting max RPM range

Hmmm I thought 26* was max advance, Will have to investigate that.

Today I tried size 80 jets and put my 17pitch prop on. Got 3200rpms with prop. Don't think jets helped. Advanced the timing by 4* and got up to 3500 rpms. After that she falls on her face again.

Is it possible that I'm going the wrong way with the jets causing the motor to run too rich and crap out at WOT??

I'm thinkin when I pull the plugs Sat. ,,They're gonna be black as black can be.

What will the motor generally do as I lean it out. Will RPMs climb ?

 

[180shabah]

Re: Motor not hitting max RPM range

What will the motor generally do as I lean it out. Will RPMs climb ?

yes - 'till it grenades....

If you are not sure what you are doing here, this is NOT the time for trial and error.

 

[bakerjet]

Re: Motor not hitting max RPM range

i dont think a 2bbl running rich will flood out a v8 what engine do you have? as you lean it out the rpms wont climb much it will just burn a hole in you piston. im gonna guess that your running out of fuel at WOT which is leaning it out! CHECK YOUR FUEL PSI! You can not read plugs if you idle around!! it takes a full throttle run and kill it coasting in and then read'm. hope this helps.

 

[Lucky 1]

Re: Motor not hitting max RPM range

This may not be the problem in your case but I have to add this. I had a similar problem for 7 years and not a single mechanic could figure it out. I did just yesterday. The barbed coupling at my pick up tube was loose causing a leak. Taped and tightened. Good to go. And I have spent a lot of money trying to get this fixed

 

[Quadruplecccc]

Re: Motor not hitting max RPM range

It's a 351 windsor and just inspected the plugs . Very black and some are more wet with unburned fuel. Way too rich. That much fuel going in there , how's it gonna burn correctly???

 

[180shabah]

Re: Motor not hitting max RPM range

Sounds like you are narrowing it down.