engine won't rev above 3k?

Posted By: Anonymous

engine won't rev above 3k? - 10/29/08 12:07 PM

Thought I would post a message here to see if anyone had any ideas... I just put in a 408 stroker in my dart... runs well up to 3,000 rpm but after that it kind of hesitates, and rpms fall. I have a 727 and it's shifting at 2000-2500? I'm not sure what's going on!

the carb is a edelbrock avs 800, when should the seondaries be opening? I'm not sure that they are... but supposedly adjustable.

I'm using a standard mopar distributer.. set about 15 degress initial.. not sure how much mechanical advance is built in, is it hard to change the springs to adjust this?

anyway... any ideas you guys might have would be appreciated greatly!!

-j

some details
Mopar electronic ign.
carter mech. fuel pump
cam: 474 Int / .474 Exh & 233 Int / 240 Exh duration @ .050 - 110 degree lobe sep
magnum heads.. 9.8:1 compression
edl. mag. air-gap intake
edl. avs 800cfm carb (have not changed jets/rods)..

Posted By: 540challenger

Re: engine won't rev above 3k? - 10/29/08 12:16 PM

Quote:

Thought I would post a message here to see if anyone had any ideas... I just put in a 408 stroker in my dart... runs well up to 3,000 rpm but after that it kind of hesitates, and rpms fall. I have a 727 and it's shifting at 2000-2500? I'm not sure what's going on!

the carb is a edelbrock avs 800, when should the seondaries be opening? I'm not sure that they are... but supposedly adjustable.

I'm using a standard mopar distributer.. set about 15 degress initial.. not sure how much mechanical advance is built in, is it hard to change the springs to adjust this?

anyway... any ideas you guys might have would be appreciated greatly!!

-j

some details
Mopar electronic ign.
carter mech. fuel pump
cam: 474 Int / .474 Exh & 233 Int / 240 Exh duration @ .050 - 110 degree lobe sep
magnum heads.. 9.8:1 compression
edl. mag. air-gap intake
edl. avs 800cfm carb (have not changed jets/rods)..

Ok one check your total timing stock distrubtor has alot of mech timing built in. i think mine was around 25 mech

i little much i liked my timing set around 34*total.

Also when does it bog full throttle or just crusing. with part throttle???

Also is this the blue printed 408 crate engine. if so check out this thread.

Posted By: Anonymous

Re: engine won't rev above 3k? - 10/29/08 12:38 PM

Yes it's a blueprint 408.. It hesitates when I am just crusing... maybe 50% throttle...

I'll check the timing later this afternoon...

if anyone else has any suggestions of what to try, I would love it! I want to get this figured out before the snow comes

I should add that I have highway gears on the car... 2.something.. and I'm getting pretty awful milage.. less than 10 mpg

-j

Posted By: 540challenger

Re: engine won't rev above 3k? - 10/29/08 12:43 PM

Quote:

Yes it's a blueprint 408.. It hesitates when I am just crusing... maybe 50% throttle...

I'll check the timing later this afternoon...

if anyone else has any suggestions of what to try, I would love it! I want to get this figured out before the snow comes

did you take the carb apart to check where the floats were every eddy i had the floats where never set right out of the box.

Also i purchased that same motor check out my thread i having not too good of a time with it right now.

-j

Posted By: RapidRobert

Re: engine won't rev above 3k? - 10/29/08 02:35 PM

some thoughts, check total timing w vac dissconnected, pull plugs & see what they look like & check rotor phasing at the offending rpm. EDIT retard your initial from 15 back to 5 & take it out for a quick spin.

Posted By: 68LAR

Re: engine won't rev above 3k? - 10/29/08 03:16 PM

.
A few places to start looking.
1. Make sure that you have the coil wires properly hooked up. + gets battery voltage - goes to distributor.
2. Make sure that the secondaries are opening all the way. Don't look at the air valve just the secondary butterflies.
3. Make sure you are getting fuel. Check pressure.
4. Check total timing. Without the vacuum advance connected you should be at least at 35*.

Good luck.

Posted By: Anonymous

Re: engine won't rev above 3k? - 10/29/08 04:00 PM

i doubt total timing would stop it from reving over 3 k. my total on my 416 was pretty darn high before I fixed it and I reved up to 6500 quite often.

Id say you need to look at carb first, check the plugs and see if your lean (maye major vacuum leak), valve float. valves not closing. cam timing WAY off

Posted By: 68LAR

Re: engine won't rev above 3k? - 10/29/08 04:28 PM

Quote:

doubt total timing would stop it from reving over 3 k. my total on my 416 was pretty darn high before I fixed it and I reved up to 6500 quite often.

If it was advanced too much, but what if the mechanical advance was retarded too far and the only advance was from the vacuum advance side? There would be no advance when the gas pedal was pushed thus retarding total timing.
I'm just throwing noodles at the wall to see what sticks. I also believe that the problem is with the carb, but I have also seen the coil wires reversed having the same effect.

Posted By: 70challrtse

Re: engine won't rev above 3k? - 10/29/08 04:29 PM

Is there a rev limiter on your tach?

Posted By: 68LAR

Re: engine won't rev above 3k? - 10/29/08 04:36 PM

Quote:

Is there a rev limiter on your tach?

Wouldn't it be ironick if it was the tach?????

Posted By: kenworth_goose

Re: engine won't rev above 3k? - 10/29/08 05:27 PM

My 68 dart did the same thing. It was a ground strap that I forgot to put on it. Make sure you have a good engine to body ground. A good battery to body ground.

Posted By: B G Racing

Re: engine won't rev above 3k? - 10/29/08 05:27 PM

Cam timing or distributer out of phase with the cam.Recheck you distributer for correct location at TDC of #1 on compression and make sure you have enough movement for correct timing.Set total at 38 degrees 3000 rpm.

Posted By: MoparforLife

Re: engine won't rev above 3k? - 10/29/08 06:12 PM

How is your cam installed?? Put one on the wrong keyway once and that is exactly the way it ran.

Posted By: Anonymous

Re: engine won't rev above 3k? - 10/29/08 07:32 PM

Quote:

My 68 dart did the same thing. It was a ground strap that I forgot to put on it. Make sure you have a good engine to body ground. A good battery to body ground.

I would look for a bad ground. A buddy had same thing. box wasn't well grounded.

Posted By: 70challrtse

Re: engine won't rev above 3k? - 10/29/08 08:26 PM

Quote:

Quote:

Is there a rev limiter on your tach?

Wouldn't it be ironick if it was the tach?????

Don't ask me how I came up with that suggestion.

Posted By: RapidRobert

Re: engine won't rev above 3k? - 10/29/08 08:37 PM

I bet ya had a smile on your face when you caught it.

Posted By: 70challrtse

Re: engine won't rev above 3k? - 10/29/08 09:24 PM

Quote:

I bet ya had a smile on your face when you caught it.

Actually another member here suggested that I check my tach, when I made a similar post. I had numerous serious gearheads work on the problem, but to no avail, then a member here asked if it had an aftermarket tach and asked if the rev limiter had been turned down. Sure enough it was turned down to about 2500.

Posted By: Anonymous

Re: engine won't rev above 3k? - 10/30/08 06:35 AM

Thanks for all of your help guys... old harness, wire colors were too similiar... had the coil hooked up backwards! suprised it ran at all...

-j

Posted By: 68LAR

Re: engine won't rev above 3k? - 10/30/08 10:40 AM

Quote:

A few places to start looking.
1. Make sure that you have the coil wires properly hooked up. + gets battery voltage - goes to distributor.

Quote:

had the coil hooked up backwards! suprised it ran at all...

Good Job.

Posted By: Anonymous

Re: engine won't rev above 3k? - 10/30/08 12:55 PM

Thanks bud! You win the diagnostician award of greatness!

-j

Posted By: 1974Cuda360

Re: engine won't rev above 3k? - 10/31/08 07:45 AM

I has a machine shop put together one of my older 360 motors, and it also wouldn't rev over 3k. After a ton of trouble shooting and discussions with other mechanics, I discovered that they installed the cam wrong. It was not installed dot to dot. One tooth off caused all my problems.