66 Hemi jetting

[RJRENTON]

Pulled of the carbs on my engine today to check how the are set up. Only pulled the top on the front carb before quitting for the day but didn’t find stock jets in it so probably need to make some changes, These are correct number 66 carbs and look to be in really nice shape.

I know the stock jetting specs but wanted to see if most owners are sticking with that or some slight modification. The engine seems pretty stock although I’m not sure what camshaft is in it - I suspect a later hydraulic one as it seems too quiet for solids.

I found .083 jets in 3 bores and a single .101 jet in the left secondary bore. Stock is .089 and .1065 so someone in the past has leaned it down. I’ll find out in the morning if this holds the same for the rear carb. My theory on ethanol fuel is that due to its less efficiency as compares to non-ethanol fuel, at least stock jetting or one size richer is generally good. Not sure that’s completely correct or valid but everyone has to have a theory. The car has seemed to idle rich (smelly) but now I wonder if it’s just too lean to burn efficiently.

Curious what other early Hemi owners are running for jets in stock engines - staying with stock jets or something else.

IMO....ethanol blended fuels are troublesome at best. Ethanol has approximately half the heating value or energy of gasoline. It depends of percentage of ethanol is in the blend you are using....as it depends on brand and octane rating. Therefore, it generally requires a richer fuel mix, based on percentage of ethanol. To me, its easier to change primary step up rods than jets. Sometimes, the jets can become frozen and VERY difficult to remove, especially the primary jets, as they are in a "nich area" and almost flush with the bottom of the casting and unless a proper size straight blade screwdriver is used, the jet can be chewed up and will need to be drilled out. Perhaps an impact screwdriver can help with removal. Since you know what the origional jets and rods are, consider making the rods ~ 0.002" diameter smaller on the intermediate step and ~ 0.002" smaller diameter on the power step. The Edelbrock kit uses 2 step rods, which are shorter than the OEM rods, step up pistons are different as well. Perhaps 0.003" larger secondary jets should help but can be to remove. Remember to calculate the AREA differences from the jet diameter and rod diameter when the rod is in the jet as fuel flow is based on area presented. I'm sure others will have their own preferences and opinions and recommendations.
BOB RENTON

 

[AR67GTX]

I had to remove the jets. The existing arrangement was totally screwed up from what I see - I think they got left and right switched as well as front and rear. Either that or they had some really strange theory worked out. I’m going back with stock jets per the FSM and rods with stock cruise diameter but the power tip reduced by a size (4 or 5 thousands smaller). See how that works.

 

[Dragon Slayer]

What rod numbers did you have?

 

[AR67GTX]

What rod numbers did you have?

the rear carb had 16-440 stock rods (.057/.065). (Corrected/edited post)

The front carb had some gawd awful mess - 16-691 (.055/.078) on the right and 16-205 (.063/.071) on the left in .101 and .089 jets respectively. It’s possible I lost track of which rod was on which side on the front carb. I was not expecting to find two different rods.

 

[Dragon Slayer]

I guess they were trying to compensate for not having 440 rods, but the 136 should be in the front carbs with .089 jets.

The 205 is actually a .069 x .056 rod, and the 691 is a strip kit rod and .076 x .055. With the correct rear rods being 440 at .0665 x .058 you need to find different rods especially if you go back to .089 pri in the rear carb. The 201 strip kit includes 98 at .068 x .0555 or the 485 is .065 x .052.

Now when you look at this closely compare your length and transition point to the hemi 136 rod. You can shorten a longer rod, but you can't change the transition spot and hemi rods are different than other AFBs. (Unless you are going to use a lathe or some creative sanding/filing)

Looks like someone leaned the carb out, which is what occurred for the later 68 up cap emission carbs; with timing going down to TDC and distributor adding 32 crank degrees at full throttle. Hemi can load up at idle low speed, so getting hotter plugs, making sure you know what cam stop is in the distributor, what initial timing is will affect all of this for drivability.

 

[mrhemi]

Remember the front carb is high speed high throttle open only. Progressive linkage. So getting your rear carb dialed in for idle cruise. Since your jets do not have orig numbers they clearly were changed at some point. My L5 66 carbs had original jet numbers in them.

While this is true, also keep in mind the the engine idles on the front carb as well, for a '69 Hemi anyway. There is a detailed procedure in the '69 FSM to set up the idle balance between the two carbs. I have found (on a stock Hemi) that having this set correctly greatly improves off idle and low speed operation.

 

[AR67GTX]

Your right - must have been distracted by the AR/Alabama game when typing - 440 rods in rear.

Some of my dimensions on my existing rods were my own with a caliper - could be a thou or maybe two off as I ran through them quickly.

I have ordered new rods from Mikes Carburetors - .065/.052 for the rear and .070/.057 for the front. Not sure of their origin - supposed to be for the AFB - I’ll check them out on receipt.

Right now I have initial timing at 15 deg and total looked like it was topping out at 32 deg but once I get it back on the road and good and warmed up I need to double check the 32 total again with my dial back light.

I’ll double check the 66 supplement on carb idle adjustments. I have another car with 2x4 bbls and typically I tune the idle mixture screws (all 4) for rpm roll off and then back off a 1/4 turn approximately and go back and forth a couple of times. Then I turn the idle speed out an equal number of turns from contact with the throttle shaft cam (but on the Hemi I turn the idle air adjustment bolt out an equal number of turns from bottomed out). These are 4139 and 4140 cabs with the center bolt for adjusting idle speed.

thanks

 

[Dragon Slayer]

Yes I agree to an extent, but I would say the FSM is poorly written. Also, the 68 up carbs have sealed hidden idle mixture screws on the front carb so you can't adjust them without removing the lead plug (set at factory for emissions). So the only real adjustment of idle mixture is on the rear carb for 68 up. By the way 68 up rear carbs have a non adjustable idle contributing port in the secondary venturis. So while 66-67 carbs can be balanced both in idle mixture and idle contribution especially since they are bypass carbs, the 68 and up can't.

How the vehicle transitions from idle to mid throttle is really on the rear carb since the primary's of the front will remain closed other than idle contribution. If you balanced them the rear car pri blades will be closed more and the time to uncover transition port goes up. If you let the front carb contribute less (maybe 50-100 rpm of idle) to help prevent any front lean cylinder conditions, the rear carb will get on the transition slot sooner (pri blades already open more for idle).

66-67 carbs can be balanced better because primary blades closed. Idle is an air bypass valve which can be closed and both carbs have idle mixture screws. But ultimately same affect. The Rear transitions to mid throttle and cruise and the front is still on idle with pri blades closed. At WOT the front carb moves through the transition much faster (blades open progressively faster) so that both carb have wide open throttle blades at full throttle. By that time the rear carb already had primary and secondaries open feeding the manifold.

 

[AR67GTX]

Received my rods and jets from Mikes Carburetors and they seem to check out fine - couldn’t find any dimensional differences between them and the original rods.

The jets check out right on the money too. Only problem is stamping on the jets is very hard to read, to impossible to read on some of them so have to keep them tagged or check orfice with a pin drill.

Now if I can figure out which specs to go with for float and accelerator pump settings. Every manual and the FSM have different specs. I think the guy who last rebuilt these decided to use a different chart for each float and each carb.

 

[Runcharger]

I've had good luck with the FSM for adjustments.

 

[AR67GTX]

Guess I’ll go with them for now but I dropped their float level 1/32” because it was so high. I also used the accelerator pump height but it’s a lot lower than you find in most publications. But I figure (or at least hope) Plymouth knew what they were doing.

 

[Dragon Slayer]

What rod did you get? What is the old one?

 

[AR67GTX]

.65/.52 for the rear carb and .70/.57 for the front. Stock dia was listed as .65/.57(or.58) and .71/.61 for rear/front. I tried to stay as close as possible to the FSM with the cruise portion and go down one step from stock on the power portion to richen it slightly.

That 678 Venturi does go in the front carb - is that correct? I think I got my secondary ventures back into the wrong baggies after I sprayed them out with carb cleaner. My notes when I took it apart says it goes in the front carb on the right side.

 

[Dragon Slayer]

Not at home to help. Did you compare new rod to the 440?

 

[AR67GTX]

The .65/.57 (might be .65/.58) are the 440 rods. I used .65/.52 in their place.

It’s amazing what some people do to these old cars. The rear carb had some sort of dried out milky white, thick deposits inside the upper air horn, cluster and air valve. The residue cleaned off OK with carb cleaner and a tooth brush but their origin stumped me. Today it dawned on me what it was - dried white lithium lubricant. I think someone must have tried to lube the air valve shaft for mysterious reasons. It swings easily. They probably tried to rotate it in the wrong direction and thought it was stuck.

 

[Dragon Slayer]

Compare your new rods to the 440 for the length and location of transition points on rod. Step. I am thinking 678 on rear carb but again that is memory. Think front had the 347 and 348.

 

[AR67GTX]

I mentioned that in #29 above. The rods measure the same - no difference on length, position of steps. Diameters all check out. I’m using the rod sizes from the 66 FSM supplement - 136 & 440 - but the 136 rods could not be found anywhere so I got new rods from Mikes Carburetors all around - just a bit richer on power than stock.

 

[AR67GTX]

I guess I really need to get this #678 cluster figured out as right now it’s on my front carb. I’m waiting on a choke baffle plate though so they are just sitting with the top plates on loose for now.

 

[Dragon Slayer]

Back home now. Front carb have the 942/943 Primary and the 347/348 Secondary. Rear carb has the 946/947 Primary and 348/678 Secondary venturis.

On the rod question I had was making sure you checked against the hemi 440 rod. Not the non hemi ones that were installed. I need to go back and look at mine. I do know the later carb had a different step position and the carter charter on rod mentions the length difference.

 

[Fran Blacker]

That's depressing, checked my carbs. Whar is the difference? I type this so it was easy to read but site removed the spaces.