Hemi Tuning

[2059]

Finished up the install of the crossram in the '64 yesterday and I want to throw this out there as a refresher for me.

I am still struggling with getting it to idle below 1200 without oscillation. in other words, the engine will idle up then down, back and forth between ~1300 and 900 rpm. the only way to get it to smooth out is idle it up, out the idle circuit.

I'm running about 34* initial and 9* mechanical for a total of about 43-44*. I've heard somewhere that I should set initial at about 43* and 9 mechanical for about 52* total which will allow lower Idle; and then balance the Idle screws, then the mixture screws, starting with the Drivers side carb.


Opinions/input/observations and questions welcomed and encouraged....

Thanks,

Mike

 

[Richard Cranium]

I don't think that you are ever going to get a crossram equipped Hemi to idle that well at all.

 

[Sonny Black]

hemi guys are always "looking" for the right carbs.....but it's worth the fun!

 

[2059]

I don't think that you are ever going to get a crossram equipped Hemi to idle that well at all.

Honestly, you're probably right... When I had the manual trans it didn't matter tat much to me. Now with the auto is does...

 

[Hemirunner]

What carbs are on it?

 

[snakeoil24]

Are you using the cross ram just for the great look? I f you are then you can weld in baffels to shut down some of the plenum area to help the low end. But like crack head said these manifolds just hate idiling.. If you have a 2 piece cross ram you can mill the top plate down to reduce chamber volume and this will help alot.. Switch to Holly old style 550 cfm carbs will make it more driveable..

 

[lewtot184]

your ignition timing is all screwed up.

 

[2059]

What carbs are on it?

They're Edlebrocks, I'll get the numbers when I get home today...

 

[2059]

your ignition timing is all screwed up.

Elaborate Please... How would you set it?

 

[lewtot184]

Elaborate Please... How would you set it?

if you have 9 degrees in the distributor that's 18 crankshaft degrees. if you want 36 crankshaft degrees total (hemi's generally don't need a bunch of timing) then set the total timing at 36 degrees (18 initial) and let it go at that. if you have a fast centrifugal advance then you'll have to set the total timing only and not worry about the initial. disconnect any vacuum advance until your comfortable that the total mechanical advance is where it should be. carbs will probably need to be recalibrated.

 

[2059]

Thanks Lewtot! I don't run a vacuum advance, one less variable. I'll head out to the shop shortly and start from scratch. I'll shoot for 36 total.

 

[HEMI-ITIS]

Also keep in mind that more timing increases the idle.

 

[Hemirunner]

A good possibility is not enough vacuum to hold the metering rods down at idle. They bounce up, engine goes rich, rpm decreases vacuum goes up, rods come down, engine leans, rpm drops, vacuum drops and the cycle repeats. Or some variation of this. Beer has clouded my tuning ability right now, lol.

 

[coloradodave]

Hemirunner makes a good point about vacuum and the power pistons. Worth checking.
I disagree that a motor can't be tuned to idle at a steady RPM with a factory crossram. I base my opinion on my own experience. I run 2 Edelbrock #1404 500 CFM carburetors with stock jets and metering rods, after trying various other combinations. Using a Uni-Syn idle speed synchronizer and a wide band air/fuel meter helped immensely to get the carburetors on the money. Of course, idle speed will depend on several variables, including camshaft used and timing set-up. My motor has 10:1 compression,runs on 91 octane gas and idles at 950 RPM. I run 16* initial with 20* mechanical advance, all in by 3,000 RPM. If I try to run more initial, hot starting becomes an issue and if I try to bring the mechanical in sooner, the motor pings. My car is only driven on the street; but driven a lot. I used to run Edelbrock 750s with good results but like the better throttle response from the smaller carburetors.

 

[2059]

A good possibility is not enough vacuum to hold the metering rods down at idle. They bounce up, engine goes rich, rpm decreases vacuum goes up, rods come down, engine leans, rpm drops, vacuum drops and the cycle repeats. Or some variation of this. Beer has clouded my tuning ability right now, lol.

Good point! I remember reading something about that a while back... Heck, I t might have been from you on this forum!!

 

[2059]

Hemirunner makes a good point about vacuum and the power pistons. Worth checking.
I disagree that a motor can't be tuned to idle at a steady RPM with a factory crossram. I base my opinion on my own experience. I run 2 Edelbrock #1404 500 CFM carburetors with stock jets and metering rods, after trying various other combinations. Using a Uni-Syn idle speed synchronizer and a wide band air/fuel meter helped immensely to get the carburetors on the money. Of course, idle speed will depend on several variables, including camshaft used and timing set-up. My motor has 10:1 compression,runs on 91 octane gas and idles at 950 RPM. I run 16* initial with 20* mechanical advance, all in by 3,000 RPM. If I try to run more initial, hot starting becomes an issue and if I try to bring the mechanical in sooner, the motor pings. My car is only driven on the street; but driven a lot. I used to run Edelbrock 750s with good results but like the better throttle response from the smaller carburetors.

I got sidetracked yesterday afternoon and didn't get a chance to tune. I had the hot starting problem a year or so ago and reduced the initial. I can easily open up the mechanical advance. If memory serves, I have a very similar set up here as you do Dave. At the very latest I'll have time this Saturday to work on it.

thanks guys!

Mike

 

[super-bee_ski]

Again, sounds to me like a vacuum leak
BUT: I ALWAYS listen to lewotot184, Hemirunner, Colorado Dave and the gang.

 

[2059]

Again, sounds to me like a vacuum leak
BUT: I ALWAYS listen to lewotot184, Hemirunner, Colorado Dave and the gang.

Another good point... Rule #1 Check the easy stuff first!!

 

[2059]

After work I had about an hour or so to tune. Got it to operating temp. Set it so I had a steady idle, about 1300. Checked for vac leaks with carb cleaner. All good. Harnessed it up. Set initial at about 24 wick gave me About 35 total. Set idle screws to get smooth idle at 1100. Hooked up the two vac gauges to the carbs, one each. Set the mixture screws at highes vacuum. 13-15. When I drop it in gear it pulls down to 950ish and because of the stall the car doesn't pull at all. Took it for a short test. Runs good, pulls hard, easily light em from dead idle through 2nd.. Still need to get alignment before too much more driving... Call it good for today!! Time for a beer!!