CJ Brando
I rebuilt the 304 in my 1978 CJ7 and have the following. I had it bored .030 and the heads fully redone and new pistons ring bearings and everything is new. I put an Edelbrock performer intake and performer camshaft in. I put an HEI distributor and a 670 cfm Holley Truck Avenger carburetor on it. I set the initial timing with the vacuum advance unhooked to 12 degrees BTDC.
I checked all of the obvious stuff on the carburetor like the float level and check for accelerator pump squirt and am getting good squirt. The engine runs and sound like a champ at idle no missfires or any indication of anything wrong. When I step on the gas fast it will bog down and die if I keep the gas to the floor with an occasional carb backfire. If I push the gas down slowly from idle it will keep going doggishly until the RPMs get up. Then on the highway when I step on the gas to accelerate there is no power at all it falls on its face. I have had problems keeping it cool also it likes to run between 210 and 230 with an aluminum radiator. I don't have enough experience with carburated engines to know what to do, especially with a Holley which are foreign to me. I did change the jets from 68 to 72 primaries to see if it cured it, but it did nothing. I am not sure if it is timing or carburetor problems. I have been chasing my tail and refuse to give up, so if somebody could maybe help me it would be appreciated
ironman_gq
put a vacuum gauge on it and see what the readings are you should have at least 15in at idle and much more at anything above idle. look for a steady reading that doesnt wander when you keep a steady rpm. I would suspect that you are running very lean in the transfer and low speed circuits.
JERSEYJOE
I would bet that the cam has been installed in a retarded position. I have found that the Edelbrock cam needs to be advanced 4 degrees to run decent. Classis symptom is low steady vacuum. Did you degree the cam or just install with a stock gear set? If I recall correctly the stock replacement gears will set the position retarded.
CJ Brando
I installed the cam with a stock gearset. I just lined the to marks up on the cam gear and crank gear when I assembled it. I di have someone ask me if I had them off, but I told I lined up the marks so it should be good. Is that really true? It will be retarded 4 degrees if the marks are set? When I tried to tune the idle mixture screws on the carb I would put a vacuum gauge on to pull as much vacuum as I could and I only remember getting a little above 10 inches, and is was really erratic, but I thought this was from the bumped up cam.
Thanks for the replies, I hope that I can figure this out with all of your help.
JERSEYJOE
NOT SAYING IT IS BUT I INSTALLED THAT ON A 360 I BUILT A FEW YEARS AGO AND ENDED UP PULLING THE COVER AND ADVANCING THE CAM 4 DEGREES. NOW DAYS I SPEND THE TIME AND DEGREE IT. THAT CAM SHOULD PULL 16 INCHES OF VACUUM AT 800 RPM WITH 12 DEGREES INITIAL TIMING.
ANY ONE ELSE AGREE?
CJ Brando
Joe,
I tested it tonight again and I was only able to pull about 12.5 inches of vacuum from adjusting the idle mixture screws on the carburetor. You probably have a good point there Joe. If the cam was retarded 4 degrees would that cause what I am experiencing? Also is degreeing a cam very hard? I know that I have to buy a degree wheel. Could I get away with pulling the timing cover and keeping the cylinder heads on if I knew where #1 cylinder was at? Thanks for the help I really appreciate it. I hope that I can get this thing running good since I have a lot of time and money into it and I want to feel the power.
JERSEYJOE
I SUPPOSE YOU COULD DO IT WITH THE HEAD ON BUT FINDING TOP DEAD CENTER IS NOT AS ACCURATE, AND YOU NEED TDC. NORMALLY I WOULD NOT DO THIS BUT I WOULD BUY AN ADJUSTABLE TIMING GEAR SET AND INSTALL IT AT 4 DEG ADVANCED AND TRY IT. THE ONES ON EBAY ARE DECENT AND THEY COME WITH 3 SETTINGS: 4 DEG RETARDED, O, AND 4 DEG ADVANCED.
ironman_gq
really erratic vacuum could be a vacuum leak in the manifold or a misfiring cylinder or a sticking valve. I would check for leaks before tearing into the motor. Im not 100% about this but I think that only later motors came with the retarded cam to help them meet emissions
CJ Brando
Ironman,
When I checked the vacuum yesterday, it was pretty stable, but I do remember it being erratic. I did test for vacuum leaks using a propane torch bottle with a hose and also sprayed carb cleaner around the intake and carb to see if the engine would pick up. It didn't respond to either, so I think that everything is good in the vacuum leak department. It doesn't misfire at all which is a good thing, I just have no power. Thanks for the reply.
CJ Brando
Joe,
So if I get an adjustable timing set from ebay, I can install it and run it 4 degrees advanced and hopefully it solves the problem? Would this be the same as degreeing the cam to 4 degrees advanced?
JERSEYJOE
WELL TO BE HONEST IT'S LIKE SHOOTING FROM THE HIP BUT IT'S WORTH A SHOT. I BELIEVE THAT YOU WILL SEE A DIFFERENCE. MAKE SURE THAT YOU INSTALL THE LOWER GEAR AT THE ADVANCED POSITION . JUST REMEMBER THAT NORMALLY YOU NEED TO DEGREE THE CAM TO SEE WHERE THE INSTALLED TIMING IS BEFORE YOU ADJUST IT. I AM SUGGESTING THAT YOU ADVANCE IT SINCE EXPERIENCE HAS SHOWN THAT MOST OF THE AFTERMARKET GRINDS WILL SHOW UP AS RETARDED WHEN USING THE STOCK REPLACEMENT GEARS, AND I HAVE USED THE EDELBROCK CAM AND HAD TO DO EXACTLY WHAT YOU ARE ABOUT TO DO AND IT WORKED FOR ME.
CJ Brando
Thanks Joe,
I will have to tear it apart and get the parts, it might take a little while to find the time between work, but I will post again and let you know how it worked out. Thanks again everybody who posted for the knowledge I do appreciate it!
One quick question, do the adjustable timing sets just have different keyway positions for the crankshaft? I have never dealt with an adjustable timing set. Thanks
JERSEYJOE
THERE ARE 3 SLOTS ON THE CRANKSHAFT GEAR. THEY CAN HAVE A VARIETY OF MARKINGS. COULD BE LIKE THIS:
A FOR ADVANCED
R FOR RETARD
0 FOR STRAIGHT UP
COULD ALSO BE
+ FOR ADVANCED
- FOR RETARD
0 FOR STRAIGHT UP
THE PAPER WORK IN THE SET SHOULD TELL YOU.
GOOD LUCK, LET ME KNOW
ironman_gq
you could have a leak under the intake manifold that will draw air from the lifter valley. but if it has no misfire go ahead and try the cam. Also how did you break in the new cam?
AMX69PHATTY
What rocker arms are on it ?
Could it just be that the rockers are too tight and the lifters over pre-loaded ?
Too much lifter preload can prevent valves from wanting to close
and cause errattic idle vacuum and low power.
Triple check the plug wires and firing order.
Would check all the simple got-chas first.
CJ Brando
The cam was already broke in 7,000 miles ago. I had to rebuild the engine because of a knock and tore it down and found a scored piston. The cam only had 7,000 miles on it before the teardown. I took it to my machine shop and had it checked and it passed. I kept track of all the lifters very good. The stock rocker arms are on the heads. I torqued them to spec. I am pretty sure that Joe is right about the camshaft timing set. Not saying I know a whole lot but I used to be a mechanic and checked all of the things that I could check for simple solutions.
The firing order is 18436572 and everything matches. When I put the engine together I was ignorant of the cam timing set. I just had all of these new parts that I got in the rebuild kit and slapped them on. I didn't even take notice of the three key ways in the timing set. I threw it away and put on the brand new stock timing chain and gears. When Joe brought this to my attention I checked the Edelbrock site and sure enough the camshaft I have requires part# 7818 timing gear set and cannot be used with late model timing sets because camshaft will run in a retarded position.
JERSEYJOE
OK NOW GET OUT INTO THE GARAGE AND SWITCH THAT TIMING GEAR SET.
BY THE WAY I AM NOT SHOUTING USING ALL CAPS. I FIND IT A LOT EASIER TO SEE WHAT I AM TYPING.. CAN'T SEE CLOSE NOW THAT I AM OLD...
CJ Brando
I ordered the timing set from Edelbrock and it shipped from Pennsylvania and the dang thing was supposed to be here yesterday and never showed up. I was banking on doing it this weekend. I have everything apart and ready to replace it. I even bought a degree wheel so I can learn how to do it for future knowledge. Thanks again for the replies. I can't wait to feel the power that it is supposed to have!
JERSEYJOE
SORRY TO HEAR. KEEP US POSTED.
CJ Brando
Well, I got the new timing set in and dialed in the cam with a degree wheel to make sure the timing was on. I did have a dead spot when I drove it for the first time with the new timing set. So I undid everything I did to the carburetor when I thought my original problem was the carburetor. It now runs great with lots of power and I can't complain one bit. Oh yeah it also runs about 30 degrees cooler now with the valve timing right. Thanks again to all of the people who lent me their knowledge in finding the problem. A big thanks goes out to Jersey Joe for really helping me and diagnosing the problem.
