Marvel problems

[Guest cardinal905]

I have a problem with my Marvel carb on my 26 Standard Six. I have had the car 6 weeks or so, it ran like a top the 1st 2 times I drove it---on the 3rd start it ran like crap, sooting up--would not idle etc. I have taken the carb apart and cleaned and checked for obvious defects---found none. I thought maybe the float was sticking but verified it is where it should be (I think) It seems to run good for the 1st 10 seconds then goes bad. I have read that long Marvel post previous, and set the adjustments to those mentioned, but the screws dont seem to change anything---that I can hear anyway. What are my options ? Any help for this rookie would be greatly appreciated.

[bubba]

If you are using a vacuum tank it sounds like the float in the tank has a pin hole in it. Remove the vacuum line from the intake manifold and plug it at the tank and see how it runs. Look up in the history for vacuum tank troubles as this has been written about before. I had a 27 Standard that did the same thing and the tank was the problem.

bubba

[Mark Shaw]

Cardinal,

Since you already have the carb off, check the carb float to make sure it still floats and is not saturated. Dry it out in the sun & re-coat the float with model airplane dope or Crazy Glue to prevent saturation.

Also, Check your heat riser tube for leaks. The internal tube is prone to rusting out and allowing exhaust into the intake manifold.

Check for any other gasket leaks too.

[Guest cardinal905]

I have put the carb back on, the float looked kinda worn in places so I sealed with Kwik-Poly. May be a dumb question, but am I looking up the riser from the inside---or will I tell from the outside. Also, after a few minutes of running the crankcase vent and the oil filler cap start fuming a little, is that normal ? or an indication we may be looking for ?

[Mark Shaw]

Check inside the heat riser to make sure the steel tube is not perforated.

[1940_Buick]

Just a dumb question, but one that got me on my 1926 Master 6... are you sure the choke plate is open when you think it is? The spring fell off mine and the choke wasn't opening, making it run way too rich.

[Guest 2827buick]

Try disconecting the vacum line to the vacum fuel pump. The seat on the float droped down in mine and I was pulling gas into the manifold thru the vacum line.

Herb

[Guest cardinal905]

Ok, last nite I pulled the heat riser off----had to pull all the way back to the exhaust manifold as that crossover tube was frozen in. The inner tube looks ok I guess, had some rough parts but looks intact. The crossover tube has a hole in the bottom, but was plugged at the exhaust end however was open to the intake manifold---would that suck air and screw up the mixture? Also there was a bunch of carbon that fell out when I shook it. I will check the choke once I patch the crossover tube and make a blocking gasket for the intake manifold end. Mr 2827 Buick, when you say disconnect the vacuum line---how will the car run, or am I just looking for gas in that line? Remember I am a dumb rookie.

[Mark Shaw]

Having no leaks in your heat riser tube is very important. Even a pin hole will cause real problems.

I suggest you block one end and apply air pressure to the other end of the heat riser to test the internal tube for leaks. If you hear air leaking between the tube and the cast iron heat riser, you need to replace the internal tube.

[Guest cardinal905]

How do you replace that ? Is the part available ?

[Mark Shaw]

Cardinal,

I replaced the 1 1/2" ID tube in my 24 Buick at a local Midas Muffler shop during the BCA National Meet in Rochester MN. I was lucky that the tube was the same size as a standard exhaust pipe. There are replacement tubes available on Ebay and other Buick sites, but see if you can match the size with standard aluminized exhaust tubing first. (Local muffler shops usually have several scrap pieces you can get free.)

The replacement tube was measured and cut with a tubing cutter that slightly beveled the end so it slipped into the cast iron heat riser without catching an edge. We lubed the OD of the tube and used a small arbor press to push it straight down into the riser body. The shop even had the right size gaskets for re-installation.

My buddy Rob was there to watch the process and brought his car to the same shop the next day to have his done.

[Guest cardinal905]

Sounds good, I assume the old tube pulls out? I did not see a way to grab the tube, or did they press it in without taking out the old one. What is your opinion of the fuming of the crankcase vents mentioned earlier, is that normal ?

[Mark Shaw]

Getting out the old tube is not easy. We used a big screw driver and a chisel to bend the ends of the tube inside itself; and to collapse the tube and make it small enough to remove. Be very careful not to crack the cast iron riser.

The fuming from the oil breather and crankcase vent is probably just "blow-by" from worn piston rings. You should do a compression test to see if all cylinders are within 5-10 lbs of each other. If not, you may have one or two cylinders with broken or badly worn rings.

[Guest cardinal905]

I have determined the inner tube is still good, I JB welded the rusted part of that crossover tube last nite and reinstalled it. Tonite I hope to reinstall the carb and start it to see if anything has changed, then I supposed I will pull the top off the vacuum tank to see if the float is ok. Thanks for all your advice, I suppose I would have a for sale sign on my cars if it were not for this forum.

[Mark Shaw]

Cardinal,

Part of the fun is learning how to make them run...

You might try testing the vacuum tank before you disassemble it. The lid is pot metal and subject to tiny cracks that you cannot see. Close the valves and put a little air pressure (less than 5 lbs) in it to see if it leaks down over a few minutes. This may save you some time and the cost of a new top gasket. Pay particular attention to the areas around the threaded connections as they tend to crack when fittings are overtightened.

If it does leak down, you can use your JB Weld or Crazy Glue to seal any cracks. While it is open, use carb cleaner to get all the varnish off the "teeter totter" valve mechanism so it works without sticking. There is also a small screen at the outlet that will need to be cleaned.

[carbking]

The surest way to remove the tube from the heat riser is to take the heat riser to a machine shop with a small engine boring bar. The tube may then be machined until paper thin, at which time it will collapse, and can be removed.

WHEN PRESSING IN THE NEW TUBE BE CAREFUL NOT TO DAMAGE THE LATTICEWORK OF THE RISER HOUSING!!!!!!

Jon.

[Guest cardinal905]

I know, but I thought I had a good driver and have done no driving----ITS ALL WORK! I will get over it, I am not by the car--but I dont remember any valves other than the on/off by the glass bowl. How do I pressurize it, do I put a schrader in the top plug with a guage tee incorporated?

[Mark Shaw]

Yes, exactly. See..., you are learning....

[Guest cardinal905]

Gotcha, have a great weekend.

[Dave_B]

At this point I agree with bubba, 2827, and Mark. Take a good look at the vacuum fuel pump. I had a similar problem with my '28. It turned out there was a stuck valve in the vacuum tank. The tank fills up using manifold vacuum. When the inner tank fills and the float gets to the top it closes a valve that connects the tank to the intake manifold. If that valve does not close it will suck raw gas into directly into the intake. To test for this condition start the engine when it starts running rough disconnect the vacuum line. Hold your finger over the open end so no air goes into the intake manifold. If condition clears up you will need to remove the top of the vacuum tank and check all the linkage, the valve and seat for dirt etc, or the float has a hole and has gas in it.

Dave

[garnetkid]

I agree with Dave B as well. I had the same problem with my car a few years ago and it was the vacuum tank with perforations in the lower tank causing fuel to be sucked into the intake manifold. Take your vacuum tank apart and check it closely. they are not complicated.

[Guest cardinal905]

I limped it onto a trailer Sunday and went to a car show--one fella said that my in-line filter is not supossed to be there and may be causing back pressure, he said eliminate the whole fuel system (blocking the vacuum line to tank) and run it on a can to see if that solves the problem. That is my next step--then I can troubleshoot from there. I will keep ya posted, I really appreciate the concern from you guys. ML

[Guest cardinal905]

Here is the car, thought some may like to see.

[Fred Rawling]

One important thing to know is that you should not use teflon tape to seal any of the pipes going into a die cast part on these old cars. The teflon is a lubricant as well as a sealer and you will probably overtighten the fitting because you do not feel the resistance and that will break you diecast part. I use permatex #2.

There is or was a filter screen in the top of the vacuum tank wher the gas goes in. Check that. There is also a screen or supposed to be a screen on the pick up tube from the gas tank that may be pluged up. I found that some permatex on the copper gaskets works as well as getting a new gasket for these 2 fittings.

The blow by may clear up after a few miles. I would not worry about it now.

Do not be surprised if your JB weld burns off.

The measurements for the heat pipe from the exhaust manifold to the heat riser for all 1926 to 1928 Standard or 116" wheel base cars is:

1 1/4 inch O.D. and 10 1/32 inches long. I bought the correct O.D. seamless tube from a pipe supply house. Also try a muffler shop.

Removing the stuck tube from the exhaust manifold and heat riser is a bit difficult and the compression collar that holds the packing in will probably have to be sacraficed (cut on the inside of the collar and twisted out). Save it for a pattern. Be careful not to break the heatriser or manifold valve.

I made the new collars out of a piece of black pipe or out of a black pipe coupling, I do not remember which. I used round teflon or round rope graphite packing in the opening after the tube was inserted into the heat riser and before the collart was taped gently in.

The axel for the flaper in the exhaust manifold valve has a line scribed on the end of the axel that indicates the orientation of the flaper.

Check to be sure that the flaper is open. This has nothing to do with the problem you are having now, just a precaution to prevent overheating of the exhaust manifold.

So far, nothing that you have asked about is covered in the shop manuel but you should get one when you have a chance. There is a reprint of the 1927 shop manuel. 1926 and 1927 are almost identical cars.

Call or e-mail me if you have any questions or just want to talk about it. frawling@bristolhomeloans.com 562 644-4670

[Guest cardinal905]

Thanks, more good tips---I have figured out that exhaust flapper deal, I found it worked closed on me--that may be why I could not run it with the bypass gasket closed off, although I cant verify that it was closed when I ran it (sounded like a tractor with straight headers) It may be a week or two before I can get back to this problem, I will keep you guys posted.

[Guest cardinal905]

Back at it, I tried filling the vacuum tank with gas like we talked about at Flint--still runs bad, even got a good backfire out of the exhaust. I decided to just pull the gas tank and take to my radiator shop for a boil job, once that is back I will remove the in-line filter and pull apart the vacuum tank for inspection. A question on running on a remote gas tank---do I just have to block the vacuum lines from the manifold and hang a gravity tank ???

[Mark Shaw]

Cardinal,

Yes, you can hang a gravity tank. Just make sure it is vented. I suggest you check the main jet and readjust it to provide enough gas for high speed operation.

Two weeks ago, my son asked for help in adjusting his 29 Buick carb. I removed the carb. from the car, removed the three bottom screws that attach the float bowl to the venturi and removed & cleaned all three jets.

The longer jets are idle and accellerator pump jets that are not adjustable, but they do require the correct setting for the big air control knob. (The spring inside the knob should have a fat spot in the middle). Start with the big knob even with the end of the stop tang and adjust it in and out until the engine idles smoothly in between.

Only the shorter larger diameter high speed jet is adjustable via a needle valve under the venturi. (The needle adjustment knob is the disc with holes in it). Make sure the needle is straight and the leather seal is in place before assembly. It should be about three turns out to test run. Adjust it out until it runs at high speed without backfire. It will take several tries to get it right.

[Guest cardinal905]

Thanks, yeah I have been thru all that previous---nothing seems to help. I am gonna have the carb rebuilt. I am trying to get the name of a guy a fellow clubmember used for his Marvel, he has had no problems since. Does anyone have a name for me ?

[carbking]

Going back to the beginning of this thread, the original problem was "sooting up" and running poorly. It appears that many of the responses are geared toward too little fuel rather than too much.

"Sooting up" can occur because of three conditions:

(1) Too much fuel supplied to engine (3 percent of time)

(2) Low compression (2 percent of time)

AND

(3) Defective ignition (95 percent of the time!).

I would suggest, in order:

(1) compression test - this will eliminate item 2 above

(2) checking the vacuum control valve for the vacuum tank (most likely culprit in the fuel system, even if you do have a Marvel). A failed vacuum valve will allow fuel to be drawn directly from the vacuum tank into the intake manifold, completely bypassing the carburetor.

If both of the above are good, start on the ignition system, and check it out completely. The easy way is to hook up a diagnostic oscilloscope, use the "parade" setting, and observe the firing voltages at the plugs.

Jon.

[Guest cardinal905]

Wow, you are in Missouri--what part? Good advice, a couple questions though, I am a rookie. #1 What will I expect to see as a compression reading, and do I need a special compression tester or adapters for plug holes #2 How do I check that vacuum control, could I eliminate that as a problem by running on a hanging remote gas tank #3 The ignition diagnostic is way over my head but want to learn--where should I buy the ocilliscope, and will the directions from that instrument tell me what I need to know? I appreciate all the help I get here. Mike

[Dave_B]

I agree with Jon. I also like to do the easy and cheap things first. So I suggest you make sure the vacuum tank is not leaking into the intake manifold. As was discussed earlier in this thread.....To test for this condition start the engine when it starts running rough disconnect the vacuum line between the intake manifold and the vacuum tank. Hold your finger over the open end so no air goes into the intake manifold. If condition clears up you will know the problem lies with the vacuum tank. You will need to remove the vacuum tank, disassemble it and check all the linkage, the valves and seats for dirt etc, or the float has a hole and has gas in it, or some other problem.

Start with this simple test so you can eliminate the vacuum fuel pump as the source of the problem. This is a good place to start. It should take less than an hour.

Dave

[Guest cardinal905]

Well I finally got around to trying a remote gas tank---no change, spitting and sputtering. I guess its time to order the rebuild kit for the carb---then I can go thru some of the directions above.