Carby Problems (still)

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Model T Ford Forum: Forum 2012: Carby Problems (still)
Top of pagePrevious messageNext messageBottom of page Link to this message  By Liam Cox on Sunday, July 01, 2012 - 06:22 am:

Hey guys :-)
Last year I asked some questions about a flooding problem I am having with my NH carby. Here is the thread: http://www.mtfca.com/discus/messages/179374/254361.html?1324502921

Since then, I have drilled out the brass plugs (which were blocked), and also checked for cracks.. although the flooding problem is still there. I have set the float to what the workshop manual suggests (for memory it is 1/4 - 5/16), which works out to be 5.95mm - 6.35mm. I screwed the spray needle down until it just started to get some resistence. Do I then screw it out 1.5 turns? It is flooding the bad that fuel is even coming out of the fuel bowl gasket. I have done some tests to make sure the seat is actually sealing, which it is. The fuel delivery is from gravity.. there isn't a pump. Can someone please offer some more advice!! I am running out of ideas :-(

Many thanks :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Weir on Sunday, July 01, 2012 - 07:01 am:

Liam; First things first.
The spray needle has nothing to do with the float bowl overflowing.

If there are no cracks or pin holes in the housing, the gas must be passing the the needle valve.

I would suggest replacing the valve with a rubber tipped one.

I would suggest you make sure the float has free motion, not dragging on the bowl. Also make sure the float actually does float in gasoline. Most of the float should be above the fluid line.

If these suggestions do not work, make a test stand that would hold a reservoir about 3' ( a meter) above your work bench with some flexible tubing and a shut-off valve. Use a fluid like paint thinner as a test fluid and test the unit with and with out the float bowl on both upside down and correct position.

Cheers

Jim Weir


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bud Holzschuh - Panama City, FL on Sunday, July 01, 2012 - 08:35 am:

i think Jim's summed it up well. Another test I use is to blow into the inlet. With the carb upright you should pass plenty of air. With the carb exactly inverted and level, you shouldn't be able to blow hard enough to pass any air.

Cheers
schuh


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ed in California on Sunday, July 01, 2012 - 08:42 am:

I had the same problem. I put the rubber tipped float needle on, and switched out the float. The float was not leaking, however, it appears that it was re-soldered at some point, and did not have the same buoyancy as another float I had. By using the stock float setting height, the repaired float was not shutting off the gas as it should, resulting in flooding. Another known good float cured the problem.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Charlie B actually in Toms River N.J. on Sunday, July 01, 2012 - 09:10 am:

The guys are right about the needle/seat. If it's metal tipped or the ball type replace it with a viton tipped needle. As to the float what I usually do is submerge it in a small container of fuel or lacquer thinner. Weigh it down and let it sit a few hours. Remove it and shake it vigourously. If you hear noise the floats taken on fuel through a pinhole. Provided there's no body damage one of these things is your problem. Set the float so that it's level with the bowl mounting land.(holding the carb upside down). Close enough.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Erich Bruckner, Vancouver, WA on Sunday, July 01, 2012 - 01:31 pm:

One other issue could be unseen buildup on the sealing surface of the inlet seat. I have had good luck cleaning and polishing these by using a bamboo skewer or bamboo sharpened chop stick and inserting the end into the seat. Spin it with a drill or better yet, with your hands. Use some solvent on the end to help clean off any build up and soon the seat should be clean. If you are using the original type inlet needle, you may need to carefully mate it to the seat by giving a few gentle taps with a small hammer. Easy does it. Rotate it between taps.

One other issue that helps on some stubborn floats is to polish the back end of the inlet needle, the hinge pivot pin, and the contacting surface of the float arm that pushes up on the back end of the needle.

Let us know what you find.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Stan Howe Helena, Montana on Sunday, July 01, 2012 - 02:24 pm:

Many of the NH's have a bad seating surface where the brass seat screws in. It can be re-machined with an end mill if you have those kinds of tools, if not, a dremel tool with a 5/16's square end stone on it will clean it up. Many times the needle and seat is sealing fine, the gas is coming around the base of the seat. Many are also cracked in that area.

Buy a new float if the old one has been soldered on. Lead is heavy.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf, Parkerfield KS on Sunday, July 01, 2012 - 02:42 pm:

Is there a gasket behind the seat?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Erich Bruckner, Vancouver, WA on Sunday, July 01, 2012 - 04:20 pm:

yes, and a new one come in the rebuild kits.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Liam Cox on Sunday, July 01, 2012 - 05:53 pm:

Thanks heaps everyone, heaps of interesting advice! I will play with the float level, inspect the float for leaks, and check the weight of the float. I have a spare float at home, i will compare this one against the spare one.
When I turn the carb upside down, I can't blow through the inlet - suggesting that the needle and seat is working correctly. The new needle that I got with the kit has a blackish tip on it, is this one of the rubber tipped needles that you guys are referring to?

Thanks again :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Erich Bruckner, Vancouver, WA on Sunday, July 01, 2012 - 07:02 pm:

that sounds like the viton tip type.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Peter Kable on Sunday, July 01, 2012 - 11:35 pm:

A quick test I always do is
with the bowl removed turn the carby upside down so the float rests on the needle and suck on the end of the inlet elbow. If the needle is seating and the actual seat is not leaking around the end where it is screwed into the body of the carby you should be able to get a vacuum. Put your tongue over the end of the fuel line connection, if its seating properly you should be able to hold the vacuum for a few seconds or longer if you can't the leak is at that needle/seat area.

Put the carby under water upside down with the float pushing down the needle but not in the water with a tube attached where the fuel line is connected and gently blow into the tube. Air bubbles from the leak should tell you what actually is not sealing.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Liam Cox on Friday, July 06, 2012 - 05:37 am:

Argh, still no luck!!
I have tried adjusting the float level to a much wider gap.. this was done by "guessing" compared with the previous gaps that I have actually been measuring using the workshop manual.

This has no stopped the fuel from leaking out around the bowl gasket, although she still won't fire and run.

However, I now have fuel coming out of this hole when ever the engine fires. Any more suggestions please?! I have almost had enough :-(

[IMG]http://i293.photobucket.com/albums/mm42/getitupthere/IMG_4438.jpg[/IMG]


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Friday, July 06, 2012 - 06:52 am:

Liam,

Could be the needle seat assembly is not sealing to the carburetor body properly. The condition you describe can only happen if the float is not shutting off fuel at the right level. So perhaps there is an uneven surface for the gasket to seal against, or part of an old gasket stuck in there, or the carburetor was very rusty and pitted in that area?

Occasionally we run into an NH that won't act right for what ever reason. They are cheap and easy to find. Let me know if you need another one, I have many in stock, or you may have a local source, or you can buy a new reproduction from Lang's.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Stan Howe Helena, Montana on Saturday, July 07, 2012 - 09:37 pm:

I dunno. Did you do what several people have suggested, check the casting where the seat screws in? It is possible you have drilled through something that is letting gas come into the bowl from somewhere other than the brass seat.

There is a reason Russ Potter has rebuilt over 5,000 NH's and I have rebuilt a bunch & Jack Daron has rebuilt far more than I have and lots of other people rebuild them, too.

If you don't follow the advice of the people who have done hundreds of NH's, checking the float to make sure it is not too heavy, checking the casting where the seat screws in, turning it upside down and checking by sucking on it, etc., etc. you are not going to make much progress.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Brian Healey on Saturday, July 07, 2012 - 10:01 pm:

I had similar issue. Real easy way to narrow down or rule out the needle/seat is to install carb without bowl on the carb. Turn on gas. When gas starts spilling out lift the float. If the gas stops spilling out the needle is working and floats neds to be adjusted.

I just rebuilt my carb and adjusted float as the carb book stated at this adjustment it continued to pass by the needle. Adjusted a little further by doing this test and all is well.

Hope this helps


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf, Parkerfield KS on Saturday, July 07, 2012 - 11:58 pm:

I agree with Royce about NH bodies being plentiful and cheap. I think the most I ever paid for one was $20, but I usually pick them up at swap meets and auctions for $5 to $10. If the one you have refuses to work, try another one. Fixing an NH ain't brain surgery. Even I have done it a few times.


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