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MG MGB Technical - Off Topic, 46 Chevy, But I Bet Someone Knows

I know this is way off base from MGs, but I know people here have wide-ranging knowledge. So, I bet someone knows something about my problem. Sorry if straying so wide from MGs is inappropriate.

Iíve got a 46 Chevy 2-ton truck that has been resting outside for the last 4 years. A couple of days ago I went out to fire it up to press it back into service to do some work on the house I grew up in.

It idled like a sewing machine, but when I tried to drive it, it bogged when I gave it the throttle. I managed the 10 or so mile trip with it, but it was not running correctly. I made the trip by continuously pumping the throttle to drive it on the accelerator pump, and using about half choke.

I removed the Rochester B single barrel carburetor, and freed the float before the initial trip. After the trip, I pulled more of the carb apart, and found a stuck power valve. Thinking that was the problem, I freed the power valve, cleaned some more stuff, and put it back together. I tried it again, and it still bogs when you kept your foot in it. I did not put a kit in it. I just cleaned and freed it and put it back together.

Although this is a 1946 Chev, in about 1975 I cooked the 216 cu in engine and I replaced it with a 1953 or 1954 235 cu in engine. In about 1977 I bought a brand new carburetor for it, and have rebuilt it once since then in about 1994.

There are some issues with the heat riser system between the exhaust and intake manifolds, but I donít think those issues have changed since the time when it ran well about 4 years ago. I think my vacuum advance canister is leaking, but I tried blocking the vac line and the symptoms did not change.

So, any suggestions? It idles sweetly, but you can only cruise if you keep pumping your foot to activate the accelerator pump. It will even bog sitting still if you try to hold it at high rpm with the throttle in a constant position.

A pic of the sweetheart is below.

Thanks,
Charley

C R Huff

Charley -
Classic fuel starvation, caused by something blocked other than the idle circuit. And even more so since you seem to have found two stuck things in the carb. My first line is always to dump some "Fuel injection system cleaner" in it, at about double dose. Run it enough to suck some through the system and go away for a day or so. Then fire it up and apply my standard treatment for water in carbs: get it up to about 2000 and full choke it with your hand until it almost stalls, do that a few times. That puts a lot of vacuum on passages that see very little normally, very good for sucking water and crap out. Might repeat this for a few days to let the cleaner act.

This problem is usually a blockage of either the main jet- usually easy to find and fix, or the mid range emulsion tube system, which involves air and fuel passages that wind around the innards - not so clear! Sometimes those passages have little check balls in them. A favorite is the very tiny mudwasps (or spiders) that like to block the little holes in the carb with eggs & mud! Those little holes in the venturi area (some on the underside of any spraybars that cross the throat) are the beginning and end of the midrange circuits.

Also worth checking fuel delivery from the pump, as low delivery is equivalent to very low float level, which also screws up mid & top end.

FRM
FR Millmore

Hello FRM,

I had a feeling that you would be the first to help me confront this problem.

I have not yet put any fuel injection system cleaner in it, and I guess I should have mentioned that there are about 5 gallons of 4-year old gasoline in the tank, into which I dumped 7 gallons of new high test. I did start it on the 4-year old gasoline and drove it a couple miles to the gas station on only the old gas. And, there was no difference with the 7 gallons of new dumped in.

There is no actual water in the carb, as I have disassembled it and it has been sitting on my desk for the past few days. However, the rev and choke treatment couldn't hurt to try to clear something out. When I dissembled it, I removed the horn (float bowl top) from the carb, but I did not remove the throttle body from the bottom of the float section.

The Rochester B has two ball and spring valves, and I removed and cleaned them both. There are two little holes on the top of the tube that crosses the venturi, and they seem to be clear (judged by feeding them with a spray can of cleaner).

Regarding delivery from the pump, when I first started it up, the float valve was stuck open, and the carb gave a good geyser of gas out of the overflow tube. So, I don't think that is too likely, though I have not done a pressure/flow check on it. But, because it will bog at higher revs just parked in the driveway doing no work, I don't think it is a fuel delivery proplem from the pump. Then again, I've been wrong a few times before.

Thanks,
Charley
C R Huff

Charley -
Those two holes are the beginning of the mid range circuit, you need to follow them around the carb. Usually you can do this by looking at cast lumps that are drilled, with punched in plugs at passage corners. Since you have it off and dry, take it apart. Very likely there is a hole or two blocked up in the bottom of the carb, which feeds that circuit. Air goes in the holes, down and picks up fuel which it then "emulsifies" aka turns to froth, and it goes back up and comes out usually on the bottom side of that bar or somewhere on the bottom of the venturi. With the bottom off you will also be able to verify that the main jet is clear. That is generally removable. Some carbs feed the mid range from the main, others have separate feed. I had thought that you had the bottom off to clean the power jet, since the olde tyme carbs I knew (Ford/Stromberg) had the powerjet in the bottom section. I probably have a book with that in, but it is very cold and dark and I'm askeert to go out to find it!

FRM
FR Millmore

FRM,

The Rochester B has three main body pieces. The upper is the air horn section, next is the float bowl section, and the lowest section is the throttle plate body. So, you can get to most of the business without removing the throttle section. I think there is only one hole in the bottom section, and it feeds manifold vacuum up to the power valve, which is in the air horn section. That hole is open, but I suppose it is possible that there is another hole in the bottom section that I canít see without taking it off.

The carb is back on the truck now because I thought I had fixed it with partial disassembly and spray cans of cleaner. But, as you know, it is about a 5-minute job to get it off again and it looks like thatís what I need to do today. A friend has a bucket of Gunk carb soaker so I guess Iíll do a full disassembly and put a kit in it and see what happens.

Iíve always had a pipe dream about putting an SU on the Chev with a curved tube sandwiched between two adapter plates. The Rochester is a 1.55 inch carb. Do you suppose an HS-4 would be enough or would an HS-6 would be better. I think I have both and suspect the 6 would be the better choice. Alternatively, do you think the whole idea is nuts.

By Brit car norms either seems kind of small for a single carb application since 235 cu in is about 3.85 liters, but the HS-6 is bigger than what is on it now. I think the engine power peaks at 105 hp at 3000 rpm. I'm guessing I might need a stiffer dash pot spring to keep it from going to full top too early with that much air going through it. My HS-6 is from a Volvo B-18 or B-20, and the HS-4 is from an MGB.

Thanks, Charley
C R Huff

The 235 is not one of my favorite power plants. Just pull off the oil pan and you will see why. The main oiling system is a series of jets that spray the crank and cam. If these jet tubes are not perfectly set up, you will spin a bearing in short order. I agree with the probability that the low or high speed jet has become clogged with old gas. They should be removed, cleaned and the passage ways blown out with compressed air. RAY
rjm RAY

RAY,

I think you are confusing the 235 with the 216 that had poured bearings, dippers on the rod caps, and shims between the cap and rod. The early 235s might have been a similar construction, but I believe that by 1953 they had a pressure fed crank. The 235 that I put in is one that I pulled from a 53 or 54 Chevy sedan. It was just dumb luck. I didn't know the difference at the time.

The pressure fed 235s are a highly respected engine. Many say that it was the best 6-cylinder that Chevy ever built.

Back around 1976 I did an in frame rebuild that included main brgs, rod brgs, rings, and a valve job. It's run pretty sweet ever since except when I neglect if for long periods.

I pulled the carb back off today and plan to get it soaking in Gunk tomorrow. Then I'll kit it, and hopefully it will run like new again.

Thanks, Charley
C R Huff

Hi Charley,

I had a similar problem with a VW Golf (Rabbit?) years ago. Idled fine, could drive it very conservatively, but try to get any power and it died.

The problem turned out to be a plug, covering an access hole, had fallen out, and, when the butterfly passed the opening, heaps of air was sucked in.

Herb
Herb Adler

Most of my experience has been with Solex twin chokes as fitted to Opels and Citroens. I always liked them, long lasting easy to service and good performance or economy, your choice with the right foot. Some things are constant in all fixed jet designs, usually there is an idling jet located so it works with the butterfly closed, as the butterfy open the main running jet takes over, so if that is blocked you will idle fine but have no power. The emulsifier tube does a similar job to the throttle pump, the fuel is half way to vapour and a sudden drop in choke pressure forces its contents into the engine. If the truck wont respond as you open the throttle, or on a constant open throttle it is either fuel supply, which seems OK from disconnecting or blocked jets/passages in the carb. If cleaning the carb thouroghly doesnt work then maybe looking at the condition of the fuel supply including gunge in the tank is needed. I guess you have the air filter off to elimate it, prolly an oil bath on a truck of that age.
Stan Best

Charley, I installed a rebuilt '54 235 ci engine into a friends '54 Chevy sedan a couple of years ago. It was a complete nightmare. A DPO had cut a hole, in the exhaust manifold, to run a second down pipe for a dual exhaust setup. Needless to say, it got in the way of everything. They had also installed a twin carb inlet manifold, that came with a "rebuilt" carb. It was a dog to get it running right. The throttle shaft was so worn, I was amazed it worked all. They did clean it up very nicely, though. When I got the engine installed, I cranked it over on starter motor power with the spark plugs removed. The dash gauge read 40 lbs., but no oil was getting to the rocker assembly. I removed the tappet cover internal oil feed line only to discover that it was plugged solid. When i removed the oil restrictor, from the block, it too was clogged solid. When I checked its size, in comparison to the old engine's restrictor, it was 1/3 the size. When I finally got the engine running to where I was satisfied, one of the lifters started to make a lot of noise. After adjusting the #1 exhaust rocker several times, I came to the realization that the cam wasn't properly hardened. The owner called the company, located in Texas, that had supplied the engine and told them his tale of woe. They said that a new cam and lifters were in the mail. They never arrived and the company seems to have disappeared. The car is just sitting in his backyard now. I simply can't bear to work on it anymore. RAY
rjm RAY

Hey Charlie: You may want to check the distributor. Remove the points plate and look at the advance mechanism. Sometimes that gets frozen over time. Also check the secondary coil wire as that has a habit of building up resistance over the years. If the advance is not working properly, your power curve will flatten out as the revs increase thus giving you the feeling of fuel starvation.. If it starts to break up and the plugs and points are good the secondary coil wire may have built up too much resistance and start to fail.

Love the old stuff!!! Let us know what happens

Cheers

Gary

PS When are you going to get that old Aeronca fired up??
gary hansen

Herb,

I took it apart today and dropped in a gallon of carb cleaner. I didn't see that any of the plugs looked loose or missing, but I'll look more when I remove it from the cleaner.

Stan,

Yes, it bogs on constant throttle. I think the fuel supply to the carb is sufficient because when I first started it the float was stuck open and it was putting a good stream out the overflow. I have tried it with and without the air cleaner, and yes it is an oil bath. Yes, it does have an inline settling bowl and filter. The main jet is clear, but there may be a partial blockage between the jet and the venturi.

These Rochesters have a power valve, which I don't fully understand, but it seems that it feeds extra fuel at low vacuum, and reduces fuel flow at high vacuum. I think it opens up another jet in addition to the main jet when under low vacuum. It was stuck, but freeing it did not solve the problem. Half of the fuel is 4 years old, but I don't think that is the problem because you can drive it by slowly and continuously pumping the throttle to activate accelerator pump. As I mentioned above, it is now soaking in carb cleaner. I should have a new rebuild kit tomorrow.

RAY,

I can understand how you got soured on the 235, but I think the fault was that particular one rather than the 235 in general. I have never played with the split exhaust manifold and twin carbs, but I have read about it. From reading, it seemed like a path full of pitfalls.

These engines do not operate well without intake manifold heat, which is supplied by the exhaust manifold. I think when you do the split exhaust you loose the heat to the intake. If you go to twin carbs, the heat source is not at the base of the carb anymore. When you do both, and make no arrangements for intake manifold heat, you are asking for trouble. The other problems sound like it was down to a bad rebuild.

I mentioned in an earlier post in this thread that I have toyed with the idea of putting an SU on it. In the past I imagined twins, but after reading up on these engines, if I ever do it I think I will go with a single, or else I would have to have entirely new manifolds and go with triples. Triples are probably more than I would want to get into.

My thanks to everyone for pitching in with help on a non-MG issue.

Charley
C R Huff

Hello Gary,

I think we were typing at the same time.

I do need to go through the ignition. I think my advance canister is leaking and the distributor doesn't seem to be turning enough. If you remember these, the whole distributor turns in response to the advance mechanism.

While that needs to be done, I don't think it is causing the bog because I can drive it if I keep pumping the throttle.

Yes, I do need to get the Aeronca back in the air. It seems I don't get the combination of time and money that I need to do it. Worst part is I have no one to blame but my self.

I will report back with any progress (or setbacks)

Thanks,
Charley
C R Huff

Charley -
Once I was afflicted with a 454 pickup, 2wd slushomatic, that was a true pig, Quadrajet that everybody in town had been into over the years. {People would laugh at me when I pulled in anywhere in town - "You bought THAT truck?!") Wouldn't go up a hill or past a gas station, so after rebuilding it a couple times I thought about replacing it with a suitable adaptor to mount 2xHS2 and 2xHS8 with progressive linkage to function as the QJ was supposed to. Hated the rest of the truck so much I gave it away instead.
You could certainly fit a single HS6 with suitable spring/jet/needle and it could be made to work at least as well as the Rochester. American design uses twice the pressure drop as typical UK design, so the size difference is not much, with the advantage to the HS6. The only advantage of triples over twins is straighter manifold runners. The firing order of straight sixes is such that twins feed three evenly spaced cylinders per carb, which is why any but all out sixes use two carbs. For instance, a dual carb 4.2 Jag as fitted to sedans is only about 20bhp short of the three carb E type, and that is just on the top end - not where you'd run your truck.

FRM
FR Millmore

Oh FRM, a 454, well you have all of my sympathy. Give it all the fuel you own and it repays you with spun bearings. Hated it so much you gave it away? Smart move. We used to have a saying among my trucking buddies called the "Ohio River Syndrome" whereby you would have been better off if someone had stolen your truck and run it into the Ohio River before you did all the work on it.

I'm not sure what you are trying to tell me about the pressure drop design of US vs UK engines. Are you saying that if the UK used two 1-1/2 inch SUs for 1800 cc, that I might get by with one 1-1/2 inch carb on an American 3600 cc engine?

If the answer is easy, I would like to know. But, don't make it your life's work trying to explain it to me. The reason I would like an SU on the Chev is because everything I ever had with an SU got good fuel mileage, but these days I put so few miles on the Chev that it is not so much of an issue. Years ago, I routinely drove it from Louisville to eastern and western KY, and I have driven it up to northeastern PA. I got about 15 mpg in general use, and got 10 mpg with the house on the back of it going to PA and back when I had a lot of wind resistance.

Thanks,
Charley
C R Huff

The Zenith has a similar richening jet arrangement called the econostat. An engine runs 10% lean for best economy and 10% rich for best power. The econostat is a jet and spring loaded diaphragm arrangement. The main jet supplies 90% of stochiometric at cruising depression, when the the butterfly is fully open the spring can overcome the pressure and the econostat jet supplies 20% of stohiumetric. It worked brilliantly in the Citroen which pulled like a train but gave excellent mileage.
After using some dirty fuel once I did have borrow an airline to blow out the carb. I drove it there, took out all ther available jets one by one soaked them in carb cleaner (can you still buy it?) then blew through. Car was back to its old self on the way home. You could see the crud in the choke when this happened. The oil bath air cleaner is a rugged and simple system, most unlkely to cause a problem so long as it is intact has some oil in it and the filter mesh is still there, plus you had to use choke anyway. I agree its time to move onto igntion soon
Stan Best

The Rochester Quadrajet carb, when tuned properly, can actually be a very good carb. Unfortunately, many of the castings were porous and allowed fuel to seep into the engine unchecked. I've rebuilt at least 1,000 of these little darlings and the beat of the lot were actually made by Carter, when Rochester was on strike. I still come across them and I haven't forgotten the little tricks to get them to perform up to their potential. As to the 454, they do like to spin bearings. I had one customer, whose 454 spun a main bearing, broke the crankshaft in 2 and cracked the block in half as well. RAY
rjm RAY

Stan,
I didn't know that about the Zenith. It does sound similar to the vacuum and spring loaded ball/check valve in the Rochester.

RAY,
I only recently learned about the 454 spinning the bearings. I was called out to offer an opinion on a failure of a marine engine, and it just left me scratching my head until I took the crank and bearings to someone who knew that particular engine.


I have rebuilt and installed the carb onto the 46 Chev, but I haven't been able to start it yet because I need to come up with a filter/sediment bowl first. It turns out the old style, or parts for them, aren't just sitting around on the shelves of auto parts stores these days.

Charley
C R Huff

Amazingly, the twin carb intake manifold still incorporated the exhaust manifold's heat riser control valve on the 235. After all these years it still operated like new. RAY
rjm RAY

Well, it looks like the carb rebuild solved the problem. I got the filter issue solved yesterday, and it started up and ran well. I haven't driven it yet, but prior to the rebuild it would not hold higher RPM even sitting in neutral.

I still have to sort out the vacuum advance system and do some electric work to it, but it's good to have it up and running again.

RAY, the twin intake / twin exhaust that I have seen for the 235 uses tubes from the exhaust to heat the intake, but it only heats the center of the intake. I guess the homemade double drop exhaust works differently because the aftermarket factory version doesnít have the door and bimetallic strip.

Thanks to all for the help.
Charley
C R Huff

Charley, getting that vacuum advance to work properly is going to be a whole different task. Most of the parts are NLA and the entire plate, inside the distributor, rotates with the advance mechanism. The available rebuilt units rarely come with all of the needed components. RAY
rjm RAY

RAY,

I see the vac adv unit advertised for sale on most of the old Chev parts sites for about $40. I don't know if they actually have them or not.

On this model, the whole distributor turns, not jut he plate in the distributor. If they are NLA, I put very few miles on this truck, so the loss of fuel economy would not kill me. I anticipate maybe 150 miles this year. It's still a work truck, so it needs to make a few trips to the lumber yard and a trip or two to the dump.

I used to work it harder back in the 70s. When I hauled these loads uphill, I could judge the work by how red the exhaust pipe was by viewing it through the holes in the floorboard. See pic below.

Thanks,
Charley



C R Huff

Charley, I used to have a 53 chevy 5 window PU w/235.

If your truck had been sitting for a long time without running or simply a long time with the same old fuel pump, consider that the diaphram could very well be so tired that it is not pumping you enough gas. Lots of movement of the mechanical arm, etc, but little real movement of the worn out ol' diaphragm. I would put a new pump on it.

Also, you may need a new vac advance unit for the same reason. FWIW.

Oh, and the pic is of my old truck - thought you might enjoy.

BobMunchausen

Hello Bob,

I'm delighted to hear from you. I know you by your MG fame, and have saved many of your MG tips.

Yes, you are right, I did enjoy the pic of your "Advance Design" Chev. Mine is the earlier "Victory" model.

I can't explain why, but I think my fuel pump is still working fine. It is the same one that was on the engine of the 54 sedan that I pulled out of a junkyard in about 1976.

The truck is running well now, plenty of fuel being pumped, so who am I to argue with success?

Charley
C R Huff

A great tail guys. I am working on a 1950 GMC 1/2 ton I inherited from my father in law when he passed. Along with the '65B Iam restoring and the '69B that developed a sever misfire.
Cheers

Geoff
Geoff Kimler

Goeff,

That's a nice piece to have. In those days, the GMC was a heavy duty version of the Chevy rather than just a different name plate. I put a 2-ton 2-speed GMC rear end in mine, and I have a 5-speed overdrive gearbox from a GMC that I have been threatening to put in since about 1977.

What, no photo?

Charley
C R Huff

Charley, It would seem that you invented the pyrometer by judging the color of your exhaust pipe through the holes in your floor. I had a '62 Chevy 1/2 ton throw a rod through the block, somewhere in the middle of South Carolina, while towing my MG back from Florida in the late '70s. The oil, gushing out of the engine, covered the hood and windshield of the MG. Of course, I had the MG's driveshaft disconnected at the time and it was pouring rain to boot. A day to remember. RAY
rjm RAY

Indeed, RAY, that sounds like a day to remember.

Hopefully we will meet up in CA some day, and I can tell you about the time I invented beef stew.

I also invented ear plugs when the whole exhaust system fell off at the manifold one night when it was 17F below zero. I shoved cigarette butts in my ears, and kept on trucking.

Charley
C R Huff

This thread was discussed between 26/03/2011 and 06/04/2011

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