Carb. question

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Model T Ford Forum: Forum 2005: Carb. question
Top of pagePrevious messageNext messageBottom of page Link to this message  By Ruth on Sunday, November 11, 2007 - 12:05 pm:

We are in the final stages of restoration on our 26TT. Thank you for the tips on starting it for the first time the other day. Unfortunately we have a few more questions. We put fuel mixture needle 1/2 turn open from closed postion. The carburetor, which is an NH swivel top, wanted to spew gas out port, under ID tag. After cranking for an hour or so. We managed to get it running breifly. Only to have it die after a few seconds. Carb was taken apart and cleaned, new gaskets installed. We did not install new valves. Question is, do you think we should purchase all possible replacement parts for carb and rebuild it (mechanically inclined, but have never rebuilt a carb before) Or should we purchase a rebuilt one from a pro? One more thing, when truck was running for those 3-5 seconds. It appeared to be firing on 3 cyl. Front plug looked like it had not fired. Truck has new valves.
Ruth


Top of pagePrevious messageNext messageBottom of page Link to this message  By jack daron-Indy. on Sunday, November 11, 2007 - 12:22 pm:

Sounds like your float is either set to high or it has a leak allowing gas to overflow out the vent. Try resetting it 1/4 inch above the gasket flange on carb. open your fuel mixture up to 1 1/4 turns. (it will start easier and can be adjusted later while running)If it doesn't idle good,chances are you will have to overhaul it. If float has gas in it,you will have to replace the float. Check the wiring for your plug missfireing. HTH.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave_Sosnoski on Sunday, November 11, 2007 - 12:47 pm:

Gas leaking out the vent hole is an indication that the bowl is being overfilled with gas. The amount of gas in the bowl is controlled by the float and the needle and seat. When the gas level rises, the float rises and pushes the needle valve closed to shut off the fuel. As the gas is used up in the bowl, the float lowers and lets in more gas. None of the other parts of the carb. have anything to do with this so concentrate your troubleshooting to this area.

The first thing to do is tap the top of the carb and see if that stops the leak. If there is any dirt or crud in the gas tank it could become jammed in the needle valve causing the leak. This is probably the #1 cause of leaks. If that doesn't stop it, then it's time to remove the carb. and open up the bowl.

Check the float to be sure it doesn't have any leaks. Get a pan of hot water and submerge the float in it for a few minutes. The hot water will heat the air in the float causing it to expand. If there are any holes you will see little bubbles come out. If no bubbles come out, remove it and shake it. If there is no water inside then it is probably good.

Next, check the needle and seat. The needle should be a smooth taper with no groove. With the needle and seat installed, and the float in place, turn the carb upside down, suck on the inlet and put your tongue over it to seal it. You should be able to create a suction and feel it against your tongue. If the suction doesn't last, then there is a leak somewhere and that's your problem.

If there is a leak there, I would remove the seat and make sure there is a gasket installed under the seat for the needle valve . The seat screws in and there should be a little gasket between the seat and the body. If it's not there it will leak gas into the bowl even though the valve is closed. Also, make sure that there is only 1 gasket installed there. Sometimes people remove the seat and install the new one with the new gasket, but never remove the old gasket from down inside the hole! If there is a gasket there, then I would replace the needle and seat using the neoprene tipped needle. Install it with the gasket and do the suction test again. If it still leaks, then there could be a crack in the casting or something else going on.

Once it passes the suction test, then go ahead and set the float level as Jack mentioned above. Reassemble the bowl and give it a try.

Good Luck,
Dave S.


Top of pagePrevious messageNext messageBottom of page Link to this message  By David_Cockey on Sunday, November 11, 2007 - 01:10 pm:

1/2 turn open from closed is not open enough unless the needle valve and/or seat are worn. Trying to start with the needle valve closed too far which results in the engine being very hard to start, and then if it starts it will quickly die. The Ford Service Manual specifies opening the needle valve 7/8 to 1 turn as the intial position. Starting with a cold engine is likely to need an ADDITIONAL 1/4 to 1/2 turn from the usual running position (unless the engine is run with carb set rich).

Our T has an NH carb (condition of needle valve and seat not known) and it usual running position once the engine is warm is 5/8 to 3/4 open from closed. If I try to start it with the mixture set that lean it will not start even when warm hot unless it's cranked a nuimber of times and heavily choked. Then if it starts it will only run for a few seconds. However, with the mixture open another 1/4 to 1/2 turn the engine starts right up.

I suspect some folks were mislead by an earlier discussion where myself and others said we opened the mixture (needle valve) for starting. One person emailed me asking if that was opened from closed postion. It is open from normal running position.


Top of pagePrevious messageNext messageBottom of page Link to this message  By David_Cockey on Sunday, November 11, 2007 - 01:14 pm:

Does the carburetor leak fuel just sitting without the engine running, but fuel to the carbuertor turned on? If it does then either dirt is blocking the float valve from closing, or the float valve is bad.

Drain some fuel from the carb using the valve on the bottom - how clean is it? You might also pull the bowl off the bottom of the carb and look for any residue in the bottom of the bowl.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John T. Tannehill III on Monday, November 12, 2007 - 01:31 pm:

I would also be sure that the 2 small holes in the throttle portion of the NH are clear. These holes are evident when the throttle is open, when closed you should only be able to see the 1st hole. A paper clip will help you clean out any crud that may be in them and then air clean or liquid clean them to be sure they are open. Those two holes help the engine Idle.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Stan Howe on Monday, November 12, 2007 - 01:36 pm:

Send me your address off the forum and I will send you an NH to install that I know will run OK. Then you can send me yours back and I will clean it, set it right and send it back to you. Stanhowemt@aol.com Put "T Carb" in the subject line so I don't delete it as spam.


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