Pitted Carburetor Repair

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Model T Ford Forum: Forum 2018: Pitted Carburetor Repair
Top of pagePrevious messageNext messageBottom of page Link to this message  By Rich Chillingworth on Thursday, December 27, 2018 - 04:40 pm:

We are looking down the barrel of a straight-through Holley NH carburetor in an ďas foundĒ condition. The pitted bore might enhance air flow at speed, think golf ball aerodynamics, however, Iím rather sure idle performance will be adversely affected due to air leakage around the throttle plate. What materials and/or methods have you used to rebuild and smooth the interior surface back to spec?

I appreciate your input Ė thanks!

Rich C.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Cascisa - Poulsbo, Washington on Thursday, December 27, 2018 - 04:49 pm:

Brake cylinder hone might clean that up.

Be_Zero_Be


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger - Wyoming on Thursday, December 27, 2018 - 05:00 pm:

By looking at the location of the idle bypass plug relative to the bore, the bore is massively eroded oversize. And based on the pitting, a brake hone will not clean this up in a couple of lifetimes. Additionally, the pitting will impede airflow, through turbulence. What you want here is laminar flow, not turbulent. You want the bore smoooooooth.

Sorry about that, but your casting is toast.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank van Ekeren (Australia) on Thursday, December 27, 2018 - 05:00 pm:

I run a S/T that is reamed out an 1/8" so that end is no problem to clean up. As for the throttle plate end, maybe with the help from someone that re-sleeves brake wheel & master cylinders.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger - Wyoming on Thursday, December 27, 2018 - 05:06 pm:

I do agree with Frank that the inlet could be sleeved, but you have to precisely locate and replicate the air bleed holes past the throttle plate. This work will exceed the value of the carb. While they are not super common, in my opinion, their value is less than the machine work contemplated. Thus, my opinion is to look for a better straight-through to start with.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger - Wyoming on Thursday, December 27, 2018 - 05:16 pm:

One of the clubs had an article on a really thoroughly documented test of carburetors...I cannot recall the issue. I remember being struck by the unimpressive improvement in stats on the straight through, vs the swayback NH. I'm including a link to previous discussions on "best carb" and you can see the CFM of straight vs humpback. Again...not that impressive.

http://www.mtfca.com/discus/messages/411944/499552.html?1417925977


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank van Ekeren (Australia) on Thursday, December 27, 2018 - 05:16 pm:

Air bleed holes shouldn't be a problem Scott, the holes are drilled from the out side and then plugged.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger - Wyoming on Thursday, December 27, 2018 - 05:17 pm:

Frank

not the two around the throttle plate...those are done through the mouth opening


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank van Ekeren (Australia) on Thursday, December 27, 2018 - 05:45 pm:

Thanks Scott checked one and you are right, but I don't see it being a challenge to line up and drill.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger - Wyoming on Thursday, December 27, 2018 - 06:47 pm:

The nearest one to the "mouth" is the critical one. It is (as I recall) about 25% covered with the butterfly closed, so it needs to be very carefully located and drilled. I don't think it is too difficult of a job for someone used to this work, but believe it is not an easy task for the uninitiated. Maybe I'm wrong and we'll see this carb supporting the next Pike's Peak hillclimber...(but I kind of doubt it :-))


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank van Ekeren (Australia) on Thursday, December 27, 2018 - 07:26 pm:

We are speculating that to bring it back to stock, is a big job, what about machining the venturi and throttle body, as long as not hitting any of the drilled passages in the body, just make a bigger brass butterfly.
My reamed S/T gives me at least another 5 mph but does bring my fuel consumption back to about 16 mpg.


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Menzies on Thursday, December 27, 2018 - 07:28 pm:

You might find a brass sleeve (pipe) at your local hardware store. I sleeved a side lamp part with a brass pipe from a sink component. If you are lucky enough to find something that would be a press fit you could epoxy the sleeve to the carb wall. For a perfect fit, it may need some machine work for a press fit.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Anderson on Thursday, December 27, 2018 - 07:33 pm:

JB Weld sand it smoothe. Did that to a carb on a John Deere tractor.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bruce Compton on Thursday, December 27, 2018 - 09:41 pm:

Hey Rich : I agree with Scott. You can spend weeks on this and still not accomplish much. If you get one of the RFs working properly, you will never mess with an NH ever again, even if it is a straight through. Keep in touch. Cheers : Bruce


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dean Yoder, Iowa City IA. on Thursday, December 27, 2018 - 09:52 pm:

I agree with Mark. JB weld & sand.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bruce Compton on Thursday, December 27, 2018 - 10:27 pm:

No matter how precise you are with either a sleeve or J.B.Weld, you still need to have the exact location and size for the idle mixture holes in the bore by the throttle butterfly. A few thou off here and you've wasted a lot of time and efort. Rich, put it on the back burner and spend your time getting an RF to work.They are the ultimate best. Bruce


Top of pagePrevious messageNext messageBottom of page Link to this message  By kep on Friday, December 28, 2018 - 02:38 am:

I would just clean it & use it. But then I don't care for much other than making the machine work again.

People I know have sleeved carbs. I'm not sold on the JB weld idea but i'm sure it'll work for a while.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Charlie B actually in Toms River N.J. on Friday, December 28, 2018 - 08:22 am:

Toss it Bro.


Top of pagePrevious messageNext messageBottom of page Link to this message  By john kuehn on Friday, December 28, 2018 - 10:17 am:

If it were a really rare carb a rebore and resleeving might be OK . This one isnít really rare and another can be had for less than time and money than would be spent on this one.
Clean it up in the condition that itís in, put a kit in it and use it.
You might be surprised that it works OK.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Larry Smith, Lomita, California on Friday, December 28, 2018 - 11:14 am:

You should forget that carburetor! Buy one that doesn't need that kind of repair.


Top of pagePrevious messageNext messageBottom of page Link to this message  By kep on Friday, December 28, 2018 - 02:03 pm:

Haha, some of you think other carb's exist. It's 2018, there are none out there Get with the times.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Don - Conroe, TX on Friday, December 28, 2018 - 02:32 pm:

Back when I was a poor high school science teacher, I had a slant-six Plymouth Valiant with a carb that look like that. I smeared an oversized amount of JB Weld on it then sanded it smooth on the mounting surface and left the bore alone.

I ran it like that as my daily driver for three years then sold it to a guy who I'm pretty sure was a drug dealer. I saw it running around for a few more years after I sold it.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Don Kirtley on Friday, December 28, 2018 - 03:06 pm:

Rich. PM me I think I can help out. I have a few extra cores. Don


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger - Wyoming on Friday, December 28, 2018 - 03:07 pm:

I could make a dozen arguments to slather on JB Weld on a carb where it wouldn't make any difference. This matter is quite different: The bore past the throttle plate is in terrible shape and oversize; The idle bypass circuit is involved in the damage as well; upper and lower throttle shaft bushings must surely be eroded oversize. Any one of these troubles could stump the average owner. Model T's can and should idle and run like a fine watch. This carb will be a huge amount of work for even a specialist, and short of that, will unlikely perform to any degree of usefulness. That said, I've been on many tours and there has not been a single tour where there were not multiple vehicles that ran horribly, yet owners just loved them and and despite evidence to the contrary all around them, proclaimed that all T's are cantankerous. This carb may well end up on one of those T's.

As an aside, if you were by any chance to get a cash offer from Kep, I'd take it


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Leffler on Friday, December 28, 2018 - 03:47 pm:

With it being a Holly NH you can get a new one at a reasonable price from one of the T parts supplier.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank van Ekeren (Australia) on Friday, December 28, 2018 - 04:06 pm:

John, who's got new straight through NH's??


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tony Howard ( Australia) on Friday, December 28, 2018 - 04:08 pm:

Before the Cameron Corner run I fitted one of these to my '26. Spent an hour or so with the brake cylinder hone and really cleaned up the passage getting rid of the pits. Made the car feel stronger and for the trip, carrying 2 x 200+ pound individual and all the camping gear, spare parts,
5 gallons of water and 2 gallons fuel oil etc, returned 18 1/2 miles per gallon for the trip.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bruce Compton on Friday, December 28, 2018 - 09:44 pm:

Rich : Take Scott's advice and toss it. There are rebuilt and re-buildable straight throughs on ebay every day. You can't just hog it out to get rid of the pitting without building an oversize throttle plate and insuring that the idle mix holes are proper, and re-sleeving introduces another host of problems(and cost). Scott's comment on poor running Model T's is also right on. So many T owners accept and even praise their poor running cars claiming that they always ran "cantankerous", sort of part of the folklore that surrounds all Model T's. Trouble is that most will never know just how nice a T can run with an excellent carb, or at least an original that has been rebuilt correctly. Anyone that has tried a Stromberg OF or RF, knows what I mean by "excellent", and I already know that Larry will be screaming that they aren't original LOL (but they sure run nice)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dennis Brown on Friday, December 28, 2018 - 11:19 pm:

Would you mind posting a picture of the carb as I would like to see what a straight thru NH looks like. Thanks


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tim Eckensviller - Thunder Bay, ON on Saturday, December 29, 2018 - 12:35 am:

Do you have the rest of that carb? How far gone are those parts? Looks to me like it could be a fun winter project to get it back together and run it but if every other piece needs to be replaced you may as well start with something better.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger - Wyoming on Saturday, December 29, 2018 - 10:43 am:

For Dennis:

I do not recall the source, so cannot give credit, but I do know they made it into one of the national magazines...


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Tomaso - Longbranch,WA on Saturday, December 29, 2018 - 11:13 am:

The above photo - top left is not an original straight bore NH - they originally had cast throttle & choke levers !


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger - Wyoming on Saturday, December 29, 2018 - 11:26 am:

Yes, Steve, but I believe it does justice to the feature that everyone seems to covet.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Rich Chillingworth on Saturday, December 29, 2018 - 05:25 pm:

Gents Ė thank you for the many responses to my straight-through Holley NH basket case. I understand all the thoughtful advice and, nonetheless, have decided to see what I can do with this piece. Iíve removed the spray nozzle and float valve seat with the help of some heat, drilled out all the internal passageways, wire brushed the casting, and gave it a long bath in EvapoRust. Next Iíll coat the worst sections of the bore with JB Weld making sure to place oil coated 1/16Ē brazing rods in the two idle bypass holes to preserve their placement and diameter. An alternative to JB Weld will be the metal repair composite called Belzona 1111. Iím lucky to have Mike Bender only 6 miles away and I believe he has some. Being a straight-through carb, a small half round file can fairly easily be worked inside the bore to get things smoothed out. Fitting the throttle plate to have a tight fit w/o binding will be a trial and error process.

The air flow through a carburetor is anything but steady state. As the flow pulses on and off with each piston intake stroke, I would imagine there is both laminar and turbulent flow regimes at one point or another. I guess I could calculate the Reynolds number and see if thatís true. The point is Iím not too concerned if the bore isnít completely smooth. This is meant to be a fun project on my part - there are no immediate plans for this carburetor. I actually do have the early cast choke and throttle levers to go on this piece if successful. I will post more pics as I proceed.

Cheers,

Rich C.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Terry Horlick in Penn Valley, CA on Sunday, December 30, 2018 - 01:04 pm:

I don't know a lot about NH carbs, but I agree with Steve. There is something fishy about that NH.

The one on the left has an interesting data plate. I have never seen an original with the plate upside down... maybe it happened though. I suspect a rebuild has been done and perhaps some changes made.



I show the two plates side by side and then inverted the straight-through's plate for easier inspection in the lower photo.

I would like to see the data plate on Rich's carb.

TH


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger - Wyoming on Sunday, December 30, 2018 - 01:20 pm:

I have seen several upside down ID tags. Not uncommon on these carbs. I own one of them. As for cast vs built up throttle shaft, there is no reason to expect that the one on top left was not rebuilt with reproduction parts rather than repair the original shaft. In fact it is quite common to see early or later NH's rebuilt with the entirely wrong throttle shaft...short vs. long, etc.

Dennis wanted to see the difference in straight through vs sway-back. I believe the photos illustrated those differences.

Courtesy of Dennis Sanford in 2015, here are two more straight-through carbs, one of earier vintage with the air bleed hole and one with the air bleed hole covered with an ID plate. Note that both have upside down plates and throttle shafts that have some age but are not cast:


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Tomaso - Longbranch,WA on Sunday, December 30, 2018 - 01:22 pm:

The first straight bores also didn't use the plate over the vent - they had a small brass screw-in vent.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger - Wyoming on Sunday, December 30, 2018 - 01:26 pm:

I have seen several upside down ID tags. Not uncommon on these carbs. I own one of them. As for cast vs built up throttle shaft, there is no reason to expect that the one on top left was not rebuilt with reproduction parts rather than repair the original shaft. In fact it is quite common to see early or later NH's rebuilt with the entirely wrong throttle shaft...short vs. long, etc.

Dennis wanted to see the difference in straight through vs sway-back. I believe the photos illustrated those differences.

Courtesy of Dennis Sanford in 2015, here are two more straight-through carbs, one of earier vintage with the air bleed hole and one with the air bleed hole covered with an ID plate. Note that both have upside down plates and throttle shafts that have some age but are not cast:


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger - Wyoming on Sunday, December 30, 2018 - 01:28 pm:

oops
so sorry for double post


Top of pagePrevious messageNext messageBottom of page Link to this message  By Rich Chillingworth on Sunday, December 30, 2018 - 02:23 pm:

The data plate on my rough straight-through NH is almost illegible, but is of this type.

It was mounted in the upside down orientation. I too have seen NH's with the data plate mounted both ways, however, all Kingston L4's I've seen have the plate upside down. I believe the reason is that when the carburetor is attached to the intake manifold the view you'd have of the data plate is then right side up.

Rich C.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Cameron Smythe - Australia on Sunday, December 30, 2018 - 07:06 pm:

Hi fellas as for the straight through carbs I'm running these and finding better pull and less fuel going through
i love the straight through
but i am running a standard scat crank , Z head high intake manifold!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Cameron Smythe - Australia on Sunday, December 30, 2018 - 07:10 pm:


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Tomaso - Longbranch,WA on Sunday, December 30, 2018 - 07:44 pm:

Thanks for the photo of the early style vent, Cameron - saved me a trip out to the shop !


Top of pagePrevious messageNext messageBottom of page Link to this message  By Cameron Smythe - Australia on Sunday, December 30, 2018 - 09:29 pm:


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