I have a 78 400 that I had rebuilt last July of 03. I have a 1406 edlebrock 600 carb. Performer intake. MSD 6A Ignition. Comp cam 255. 45 thousanth shaved of the heads, stock dist. with springs change to the lighter side. The sticker says to set timing at 12 degrees btc. I tried that, and had little performance. I set the timing by using a vaccum gauge and getting the highest vaccum right when it dropped off, I locked it down. I am at the ''c'' in btc. I have tried every combo of jets and metering rods, I had the best results with .101 in the primaries and .092 in the secondaries. But the MPG is at about 4. I have had such a hard time with this engine sinse it was rebuilt. I wonder if it wasn't better as a 2bbl motor craft. Any one had simular problems with their rebuilds that could shed some light. It flutter pulling hills if I go leaner on the Primaries than .095 and the secondaries are richer than .095. I only get good power mode response with rich primaries. I can't afford the fuel though. I have talked to several people who say they get 15 loaded or empty.------- PLEASE HELP!!!

 

"I am at the ''c'' in btc." -What does this mean?

Which cam?

 

4 MPG? Sounds like a 400 to me.....guess you already knew what size it was though. :sarcastic

Cody

 

way over advanced, setting for highest vacuum is for the idle mixture on the carb. bring the ignition base setting back down onto the scale and you'll get some MPG back too. if your base timing is off the scale, where do you think your total timing is?

 

so you are running.101 jets on the primary, what rod are you running with this?

 

are we talking about comp cams 255DEH? there's no mention of performance in the description, and in a 400 rather than a 351, makes the cam smaller yet. you can't put more cam in the engine with your right foot.

 

quote "45 thousanth shaved of the heads,"

I thought .020" - .025" was a safe limit on this. or is it off the deck and and the heads?

.045" should be enough to make a transition in the intake ports from the manifold to the heads reducing air flow? unless ordy had anything milled off the intake?

 

You could have a vacuum leak from the manifold to head surfaces (underneath most likely) due to the heavy milling. I'm a little confused on your base timing. With the vacuum hooked up you will need to see around 20 at idle.

 

I have almost the same setup on my 400. I have a high energy 260H cam,peformer intake, 1406 600 carb. The heads are stock and I have a factory ignition box with blaster coil. My timing is set at 12btdc on the money with a light. The carb still has the factory rods and jets in it I get 10 mpg out of it on the highway. The truck has plenty of power I run 36" swampers with 4.10 gears and a c6 auto. With my smaller 33" tires it will just smoke em no problem.

 

sorry, it was late when I wrote that. I had 30 thousandths shaved off the heads. I Had no milling done elsewhere. I have checked for vaccum leaks on all the exterenal surfaces. I have the timing set at the c on before top dead center. I think that must make my initial timing at around 36 degrees. That is with out vaccum. I have already checked the harmonic ballancer and timing mark for accuracy. By timing by the Vaccum I am trying to set it to just before the valves open. I went to when the vaccum just droped and then backed the timing down 2 degrees. If i set the initial timing at 10 or 12 it doesn't react or perform half as much as up at 36. I have watch for predetination, haven't had eny signs yet.
As far as the carb goes I have the richest rods and the richest jet they make for the 600 in the primaries and almost the leanest they make in secondairies, If eny more changes were made I would have to use 650 or 700 jets. I am running it this way because using the scale in the book for the 1406 isn't working. I tried every combination and had little change in performance. I'm talking about the cruise mode. Several situations changed the take-off power but then the cruising power isn't there The richer I go on the primaries the more power I have before using the secondaries. That what I have found this far.

 

I only got a Few of the cam specs. Does enyone know where to go on the internet to look up cam specs for a MC 650 cam. I'm curious if I'm running out of the RPM range of this cam. The lift is 481-490 and the overlap is 120-110 Loap center. The sheet says at 50 and I don't know what this pertains to but at 50 it's 206-221. This was all the machine shop had for me. They ordered the cam off the Internet and The place they got it from had no more in stock to check the specs on.

 

I am surprised that the motor even starts up with that much advance as your base timing. Your having to run so much extra fuel into the motor because you have the timing advanced off the charts. Set the timing with the vaccum advanced unplugged and the vacuum line plugged. Set it at 8 BTDC with a timing light.(4-6 BTDC should be stock) Then plug your vaccum back in to the canister. Next use the vacuum gauge to set your idle to the highest vaccum it can obtain and then 1/8th turn back in. Set the idleto 750 or so. The problem you are experiencing with the performance at the lower timing is an overly rich condition. If the motor is properly timed you will not need these huge primaries and secondaries and can go back to stock to gain some performance back. One other thing that hit me is your cam may not be degreed in the correct location, if the shop can verify for you that they did this, it could put your mind at ease. If not, you may have to pull a valve cover and do this while it is in the truck. Also, by going to lighter springs you may be pegging your mechanical advance too early for the cam you have. It is not much more than a stocker and by letting the advance come on too quick you will loose power at cruise speeds. You want all you timing in by 2000rpoms not 1000rpms.
Good Luck,
Brian
PS: I have a 400 with a Eldebrock 1406 with a comp Cams 268H and it screams on 8 BTDC and gets 9 mpg in the city and 12.5 on the road, all day and at any speeds.

 

I have tried timing at 8,10,2,4,6,12,14,16,18,20ect... This was all with the carb stock and still no performance. At 8 degrees it takes about 5 miles to get up to 70 miles per hour. Last night I switched to a richer secondary. The elevation I am at is 3500 feet and I should have to go leaner, but everything I've found shows me richer. I would like to have economy but most of all power. I still have the timing at 34 and is really seams to react fast and have even acculuration. The cruise power is constant as well. This might be the jet combo I want. The only other question would be is the 1406 giving me enough fuel to air. Maybe I need a larger carb,.

 

I didn't read all of the post here but if you put in a new cam you might want to recheck the cam timing.

 

Are you sure the MSD is wired correctly or is working properly I had troubles with my MSD it started to act weird it would idle rough and lost power. I pulled it out and installed the factory duraspark and it idled smoother and gained power. I really dont even notice any performance loss from going from the MSD to factory I just still use the blaster coil so I get the high voltage I want all the MSD gives is multiple spark so it makes sure you have spark at the top of the stroke. So if the box it working fine I would say the cam wasnt timed right. Take the engine to TDC on #1 and pull the distributer cap and make sure the rotor is pointing at #1 plug wire. I know this is all basic but usually it comes down to the easy things that are missed. It took me 6 months to run the bugs out of mine from the previous owner. Sorry about the long wind.