Attention MoparHeads ! 72 Dodge B300 Carb/ 360 cid

[P. Vallerie]

It,s a balmy 3 degrees!! Time to start doing the heavy mechanic's on the "Queen". She's a Class C, 1 ton duelly, all butt 20' bumper to bumper @ 8,000 lbs. Carburetion on this olde gal... I am ready to yank this Holley H2 2210 and throw it against the wall!! We knew when we bought her that the carb needed work. The right carb & it's settings are the heart of any engine. Here's my dilemma. Do I rebuild or replace with new and improved. I would really like an electric choke - cold starts suck. Fuel economy, ease of tune ability, settings; that will hold. 2 barrel 500 cfm square bore vs a 4 barrel spread bore @ 600 cfm. She has a 3 speed automatic transmission. Here's another thing to put in our bonnets. We live @ an altitude of 5,500 ft. above sea level. We do a lot of mountain camping typically @ 9'000 ft. above sea level & would like to take her along. It's the age old fight between Holley vs Carter (Edelbrock now a days). It's all about air or lack of it.
Mmmmmm.. Do I keep the old and rebuild/remanufactured? OR Do I replace with a new Holley 500 cfm - electric choke (bypass the heat/vacuum auto business). OR Change the input manifold to a spread bore configuration add a 600 cfm Edelbrock electric choke. I really would like to keep a cast iron manifold..........
What do....What to do? Any suggestions? Do and don'ts from experience?

[P. Vallerie]

Will do. Thanks for all you support and suggestions.

[John Demarrais]

[John Demarrais]

I suspect when you get done swapping carbs - you'll see little to no difference in fuel mileage.  I've had two Class As with Mopar drive-trains.  One had a 318 and the other a 360.   I reworked both a lot.   Different  small chamber heads, higher compression pistons, special RV Crane camshaft, headers, Edlebrock Performer intake manifold, etc.  Several Holley and Carter carbs and also a Rochester Quadrajet (known for an efficient two-barrel half).    Both got 7-8 MPG before the work and when all done? Both got 7-8 MPG.   Seems there's no work-around for a big non-aerodynamic body, a Torqueflite auto trans with no converter lockup and very high RPMs at cruising speed.   After getting rid of them I changed to a Dodge diesel truck with a slide-on camper and got a consistent 17 MPGs doing 65-70 MPH. That was fantastic when diesel fuel was cheaper then gas.  Now with silly diesel prices? I'm driving a 20 foot Toyota RV with a 2.4 liter gas engine.   Gets 14-16 MPG at 55 MPH and really doesn't want to go much faster.  

[P. Vallerie]

Thanks John. You have verified my suspicions with practical experience. You have tried all types of combinations especially with carburation. Helps me simplify my decisions. Put a new - well tuned carb with an electric choke. Improve the air intake & exhaust and call it good.
Do you remember what the vehicle weight of those older rigs of yours were?

[John Demarrais]

I don't recall the weight on either but - the smallest was a 1973 Champion on a Dodge dually chassis.  Flat front and 21 feet long. Probably one of the smallest Class As made. Has a 318 commercial engine, Torqueflite 3 speed auto trans and a 4.33 rear.  Besides being a gas hog - it also had cold starting issues.  The choke never quite did the job needed. Seems the gas-charge always got lost on its way to the cylinder heads. The other was a 24 footer with a 360 and slightly rounder front.  Both ran fine although at very high RPMs and both were extreme gas hogs.  

A friend of mine from Florida has a 80s Transvan dually with a 360 2 barrel and he claims that on a flat highway  will get 14 MPG at 50-60 MPH.  He left it up in a rural area of NY and has tried to get me to take it.  It's long and more of a Class B type.  I drove it locally on our mountain hills and it got 9 MPG.

Note that in regard to the two I reworked that only got 7-8 MPG.  I test both on long highway trips from NY through Canada to Michigan, and back.   So, even on a long highway cruise - 8 MPG was the absolute best they ever got.

I worked as a mechanic most of my life. Auto, farm, heavy equipment, diesel, etc.  Back in the 80s during one of the big fuel crunches - just about every person in our shop tried modifying their rigs. At the time many aftermarket companies were promoting "fuel saving" camshafts, cylinder heads, intake manifolds, exhaust systems, ignition systems, carbs, EFI systems, etc.  I can fairly state I've either tried them all  - or at least watched many others do it. I even built one of the those magical Pogue "vaporizing" carbs claimed to yield 90 MPG.    Out of all the things we tried - I never saw anything give any sort of substantial gain. I DID get near 40 MPG with a vaporzing carb on a slant-six Dodge - but it ran lousy and too lean to last.  Even car and truck engines today are not way more efficient then in the past.  Much of the gains made in MPGs comes from aerodynamics and lower RPMs along with properly placed torque-curves. Yes new engines burn a lot cleaner but few exceed 25% efficiency. Some new diesels are reaching 40% efficiency.

My last effort to gain MPGs in an RV was also a failure.   I have a 1986 diesel min-RV with 4WD on a Chevy K5 Blazer chassis with a pop-up roof.  Weighs 6800 lbs.   When I started - it had a non-turbo 379 cubic inch V8 diesel, a TH400 auto trans (no lockup or OD), and 3.08 axles.  Got a best of 16 MPG at highway speeds.  I installed a tuirbo and tweaked the ignition/injection advance curve.  Also added a 4L60 overdrive trans with a HD lockup converter.  Also changed the axle ratios to 3.73 so when in 4th OD at 65 MPH - the RPMs would be perfect for optimum fuel mileage.  Also made a custom free-flow exhaust system.  Got all done and it has more power and drives better.   And fuel mileage now??   16 MPG, just like before.  To be fair, I am climbing hills faster so there's a little gain.   My stock 1992 Dodge 4WD extended cab truck with a 5.9 tubo-intercooled Cummins and a pop-up roof truck camper on back consistently gets 17 MPG at 65-75 MPH - even in the mountains.  So far, nothing else I've driven has beat that combo. Not even my 20 Toyota Minicruiser RV with a 2.4 gasser.

[P. Vallerie]

Thanks Again John. This all great information!! I am by no means a master heavy duty mechanic but I figured there are a few out there on this site. Sharing info like this is paramount with the younger generation who is just getting started in the strange world of vintage engines and body designs.
I currently don't know what our gas mileage is because this old gal has never work well since we acquired it a year ago. I've been focused on repairing exterior and H20 damage. Now it's time to focus on making it a safe driving machine. Most of the rubber - gaskets are tied and dry. Drain the fluids put new in. We are restoring the front end & brake system as we speak. Next is the piece of crap carb that is on this rig.
I fully understand & have experienced the cold choke syndrome. I am hopeful with an electric choke it it help. As far as all the rest of the modifications to the engine I would be in agreement it not worth the expense or time. These older rigs if you get 8 to 9 mpg you are doing great. They are not really designed to do long cross country hauls. They are perfect for local long weekend excursions.
With your infinite wisdom any suggestions on Holley model # for a replacement for a h2 2210 that can accommodate an electric choke?

[John "T" Nordhoff]

  Very fun chat, its dear to my heart because in the 80's and 90's I was buying and selling and using old motor homes (lots of Mopar in those days)  out the ying yang lol and carb work or even letting Gerharty Automotive (RV Performance Expert in the day) rebuild and tweak them for improved MPG it still didn't make any huge difference. WHAT DID IMPROVE MPG as I mentioned earlier, was oversize dual exhaust,,,,,,,,shorter exhaust pipes like running them out the sides versus alllllllll the way back,,,,,,,,,,,,Improved air intake flow (like the poor mans supercharger I mentioned) ,,,,,,,,,,,,,Toying with the distributor advance curve and timing,,,,,,,,,,,,,,,,,,,,Driving 60 MPH and under,,,,,,,,, Perhaps an overdrive tranny or auxiliary overdrive gear box, but those aren't cheap. The 360 or 413 Truck Engine and that Torqueflite 727 tranny all performed greattttttttttttttt.

 Keep us posted, this is fun spending your money lol

 John T  RV user and past dealer of over 40 years. 

[P. Vallerie]

That's the whole idea. Having fun. It's OK for spending our $$ because your helping us save $$ & aspirin for our head aches. I have every intention of taking photos of the transformation. Yes to larger exhaust pipe diameter. Yes to a poor mans air intake.
A quick update to the intake; my little 92 Isuzu pick up gave me an idea. I'm going to the local junk yard and find a clamp on intake extension that fits on to the air filter horn then add a 4" metal flex hose to the front for fresh air. I want two oh my god handles and shoulder harness seat belts for the front cab - simple safety updates. The 70's were not known for good safety features. I am having a blast!

[John Demarrais]

I may of missed something in this discussion -but why do you think an electric choke is going to improve your drivability?   If anything, it might make things worse (as compared to a properly working mechanical choke).   When it comes to cold starting and half-way decent cold running - it goes like this (for a carbed engine.   You stomp on the gas pedal before starting to activate the choke. It is supposed to close all the way.  You pump the pedal a few times so the accelerator pump squirts raw gas out of the bottom of the carb. Note that this is essential and some engines need a lot of pumping. Much depends on how much volume per stroke you get in raw gas coming out.   Then you crank the engine. If it starts - a well designed engine has part of the engine exhaust running through through the middle of the intake manifold and under the carb. A heat activated valve at the end of one exhaust manifold  is closed when cold and blocks off the exhaust leaving the engine partially so it travels under the carb instead.  This hopefully heats up the metal fast so atomized gas and air mixture does not condense and stick to the walls of the intake manifold.  Note that in 1972- many US auto makers started plugging up that heat path and it made cold running miserable. The second the engine starts - the "choke break" partially forces open the choke with vacuum.  If not adjusted properly  and opening too far and again - cold running is awful.   As the engine runs and warms up - a bi-metal coil opens the choke up slowly.  Electric models use a electric heater to speed up that opening.    These are all things that need to happen in sequence to have a decent cold running and starting engine.  Note that electric chokes will often open the choke regardless if the engine is really warmed up enough or not. This was done to keep down emissions. 

Before you start swapping carbs - it would behoove you to explore the functions I mentioned.   Since your's is a 1973 - it's possible the heat ports for the exhaust to travel through the intake manifold were blocked at the factory with steel block-off plates (many were). On those that were not blocked from the factory - many get plugged up with carbon stopping the heat from working.  Does your engine have an operating heat-riser valve on the end of one of the exhaust manifolds?  Also, when stone cold - have you looked down the carb with a flashlight while working the throttle to see how much raw gas is squirting into the intake?

When Throttle-Body EFI came out in the mid 80s - this all got simpler and often  less fuel efficient.   With a Throttle-Body EFI, you just crank the engine.  The raw gas automatically squirts into the intake manifold just like it does when you "pump" a carb.  Instead of needing a choke - the TBI unit just sends in a huge amount of atomized gas and cuts back as the engine warms up. That's why EFI units tend to drive much better when cold. No vacuum is needed to "draw" an atomized gas-air mixture from the carb. 

[John "T" Nordhoff]

You have to be somewhat careful with  a ram air sort of forced air intake that it does not draw in or accumulate excess moisture and I had a fine brass mesh screen over any I fabricated to keep bugs etc out.  Some of the after market performance air filters can also aid in fresh air intake. The fact remains a carb engine, regardless what carb you use or type of choke etc.,, (insure she opens full once warmed up!!!) is only going to get reach a certain efficiency and MPG which is why I concentrated in the air flow and exhaust and  timing and overdrive areas, yet still 8 to 9 was about all I could get out of them in those days. With fuel injection and overdrive trannys I can get better now. Weight and weight distribution and aerodynamics and keep tires properly aired and keep her to 60 mph are, of course, other considerations.

 Best wishes and Merry Christmas

 John T 

[P. Vallerie]

Had to take a break from our conversation. This is helping us in doing our homework before we really start tearing into the engine. Today we are going to start. Will take photo's and post.
To answer your question. Yes there is gas coming out of the ports in the throat at dead cold start when I pump the pedal. Accelerator pump is working some what it did not work at all when we first got it. Squirted cleaner up its nostrils seemed to get it loosened up on the inside and started to work. It was always flooding with gas at first - did a slight adjustment on the float. Got that squared away. The heat riser valve seems to be working as the engine warms up the butterfly valve slowly opens.
The reasoning with an electric choke or a manual choke is to possibly making the cold start a little easier then relying on the heat of the engine to do its thing. We had 3 other mechanics take a look and all of them said "oh just replace it with something new". My gut is saying let's rebuilt it. It is gummed up from sitting for years. Pull the intake and have it hot dipped. Those Chrysler's have a horrible reputation of getting carbon fouled. It may be preventing the heat to really do what it is designed to do in a timely manner. We went and talked to a performance shop yesterday they wanted $35 to hot tank it. Not bad. Hopefully today we will pull the carb, intake manifold and valve cover (they are leaky - no surprise). Oh by the way Happy Holidays!

[John Demarrais]

Hot tanking is more for "show' then "go."  If the intake heat runner is plugged with carbon -it's no big deal to unplug without special tools once the intake manifold is off.  On both the Mopars I had - I installed manual chokes. I prefer them and like having full control. I.e I know when the choke is closed and also know when it's fully open.  But I had installed aftermarket aluminum dual-plane intake manifolds on them (Wiand and Edlebrock) and neither came with any heat-riser port like the OEM manifold does.

In regard to flooding when first starting?  Having a high float setting being the cause does not make sense to me. If it was too high - it would give problems all the time.  Flooding at cold start with a carb is usually caused by a bad "choke break" and/or a bad choke "unloader."   Flooding - i.e. running too rich after first start and still cold is usually doe to a bad "vacuum break", bad "choke coil", or lack of heat to the "choke coil" if fully mechanical.  If the mechanical choke coil has an electric heater assist - that needs to work as well.

In regard to the accelerator pump - being gummed up or plugged is rarely the issue. I have never seen one plugged in 50 years of working on them. The pumps are major wear areas and they simply wear out or dry out.  On most carbs you can install a new one without even removing the carb.  Rochester and Carter carbs use a plunger with a rubber/viton seal at the end that goes bad.  Holley and Ford carbs have a square diaphram on the OD of the carb that is easily replaced via four little screws.

Note also that some carbs have adjustable accelerator pumps.   If they squirt too much gas then can be adjusted to squirt less, and vice-versa.

Did you check your choke's vacuum break and verify it's still good and adjusted properly? They go bad very often.  It's job is to pull the choke partially open the moment the engine starts.  If not working - the engine runs way too rich, fouls spark plugs, smokes, etc. until it gets warm.