Projects Giant speedster project

as a word of caution, i once had a similar problem and was checking for a
vacuum leak with acetylene, i was moving it all around the intake and got a little to close to the distributer and BANG it blew the cap off, sounded like a gun shot.

 

Cars are dangerous, no doubt. I had a battery blow up in my face. My ears rang for a few days after that.

Jerry
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That emulsion tube in pic #5 looks nasty enough that it might have some of the holes plugged, but I assume you've made sure that they're all clear. Good to hear you're zeroing in on the backfiring problem.

 

Is the carburetor marked so you know what manufacturer and model you have? Someone may make an adjustable setup for it already. You should also be able to vary the mixture while running by using the choke. How does this affect things?

 

The carb is a Bendix/Zenith, not sure of the exact number. If I choked the carb while it was running the engine just wanted to die. I also had another flash--what if the feed tube I was using was too small and the engine emptied the bowl before it could refill. Then the engine would only be able to run on whatever ran into the bowl. More things to check before I start hogging out the jets.

Jerry
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You may be on to something. My 1090 cubic inch Hall-Scott 400, straight six engine goes thru two or three times that much in 10 minutes. Was it originally gravity fed or did it have a fuel pump?

 

I love those Hall Scott engines! As you see in the picture Seagrave had a big fuel tank mounted way up high and a carb mounted way down low. Tomorrow I'm hooking up a fuel pump and a big hose and giving the engine a test run.

Jerry
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Jerry,

Here are some pictures of the original carb on my model F engine. It looks like you have the correct one.
You may be onto something with the size of the fuel line, as you can see the original was quite large .

Forgive the snow.

Jack

 

The F6 can really suck in the gas. Today's test is big line and fuel pump. I'm glad you posted those pictures because I wasn't sure I had the right carb. The pictures I'd seen before were of a beautiful brass carb. Your carb looks pretty close to mine. You can also see in the pictures, I had to loose the extension tube and turn the carb backwards to clear the steering box. That's because I moved the engine back a foot. I think I paid $80 for the carb on ebay. I just found another on ebay for $21.

Jerry
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I hooked up a fuel pump and gave cranked it up. No change. I'm back to hogging out the carb jet--although I might wait until my new ebay carb shows up. It might have a bigger jet in it.

Jerry
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Jerry,
Not familiar with you're particular carburetor but most carbs have an idle circuit, mid range circuit, and hi-speed circuit.
Drilling out the main jet will probably have no effect on the idle mixture.

What do the plugs look like? White? Tan? Sooty?

 

Maybe a sum of several things, though I wouldn't doubt the jet size is probably the real key.



That inlet looks like maybe a 1/4" nipple or smaller? Seems really really small. Maybe you are emptying the bowl?

You say it just idles when you choke it? Any possible vacuum leaks?

 

Halftime. I downloaded a Zenith manual from the Carburetor Doctor. I'm not sure what's going on with this carb I'm going to get to the bottom of it. A carb idles on the idle circuit but if you open the throttle slightly you should get it to run on the main jet. This carb does neither. I'm going to study the manual and tomorrow tear into things.

Jerry

 

Good thought, but I replaced that fitting with a larger one when I put on the electric pump--no change.

Jerry
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When you open the throttle, you are running on both the main jet and the idle circuit.
I had similar problems when i put my falcon on the road a few months ago. The idle adjustment is an air metering screw. I could back mine all the way out and it wouldn't quite run rich enough. I ended up having to bore out the hole where the idle circuit sucks in it's gas. Once i did that it idled fantastic, but hesitated in the mid range. I bored out my main jet a few thousandths and the plugs read an even tan under all loads.
I would be hesitant to bore out the throat

 

New Carburetor

My new ebay carb arrived today. Fast shipping! It looked like the exact model as the old one. I had a lot to do but I found time to dismantle it. Upon examination it looked like a rebuild that someone put on the shelf and forgot about until the roof started leaking. The needle and seat, the floats and all the valves looked perfect. The jets were bigger too. The old main jet was a 25 the new is 39. The idle jet was bigger too. What does all this mean? It means I'm going to give it a quick clean up and bolt-er-up. With a little luck my engine problems may be solved.

Jerry
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Jerry,

I can hardly wait for the next video, showing it purring like a (really loud and really big) kitten! My Chris Craft KCL had that same carb (or at least a really big old Zenith which looks exactly like yours), on which the floats had been crushed by water freezing in the bowl after it'd been sunk by the PO. They leaked, and would fill up with fuel after half an hour or so of running. Then, when it sat, they'd leak back down to the seam, float, and it'd run great. This lead to some real frustration, and smokey runs back to the dock, the transom covered with soot.

I know you'll get it!

Brian

 

New Carburetor

I bolted on the new carburetor, hit the starter and lost my spark. Searched around for a new coil, found one, hit the starter again and guess what? No backfiring. Funny how things work out. The idle screw adjustment even worked. But when I jazzed the throttle I got a some black smoke so I think the idle circuit is good but the main jet might be a bit too large. I think I'm going to build an adjustable main. If there's time I'll post a video tomorrow.

Jerry

 

Great to hear that it's getting better. I like the adjustable main jet idea. It will save you a lot of time and effort dealing with various modern gas blends. That's the reason Henry had a main jet adjuster on the T's and A's. To acomodate whatever fuel got bought.

I think that the black cloud, or haze is common and normal for such a huge engine. Once the engine speed catches up it should clear up. Go for driveability, however it looks.

Frank

 

Looking forward to new video, are you going to be able to pull that thing outside for some wide angle views of it?

 

I dying to get the Seagrave outside, but I've got to get the fuel tank installed and the pedals and steering tied down. It won't be too much longer. I need a few dry days too. The beast might sink into the muck outside my shop and never be seen again.

Jerry
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Glad to hear its running better, looking forward to more videos.

 

I likey! Thanks for the photos. Keep us updated on the build.

 

Jerry, glad it was one of the easy fixes, beats the heck our of having to deal with tight valve clearances or something like that. Off the subject, but what's the story behind "yonahrr"? Acronym for something?

 

Yonahrr stands for Yonah Railroad. Back before the down turn, my retirement and my new crop of children I used to build commercial buildings on the side. One day I caught the steam bug and wanted a locomotive. I finally found one in South Carolina, a 1904 ALCO 0-4-0. To justify buying it I built a recreated train depot for a commercial rental. Yonah Station has had a shaky rental history but it's been fun. If I ever get some more money I'm going to build a dream shop at the back. Out of 150,000 or so steam locomotives that once chugged through the US, only about 1500 remain. Sad. You can Google Yonah Station to see some more. One more thing, Yonah is the tallest mountain the county and unique for it's rock face. They say in another million years Yonah will look like Stone Mountain in Atlanta. Yonah means "bear" in Cherokee and curiously ""Dove" in Hebrew. Did someone say, Lost Tribe?

Jerry
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Adjustable Main Jet

Since I couldn't find one on the net, I spent the day building an adjustable main jet out of hardware store plumbing. I used a 1/4-1/8 reducer, a 1/8 compression fitting, a phillips screw from an old Honda motorbike and a tiny o-ring. I rethreaded the reducer to 1/2-20 and screwed in the compression fitting. I cut off the phillips screw and ground the end to a point. Then I drilled a hole in the shaft and drove in a small rod. After that I brazed up a wee hole in the brass cooling tee I made previously. Tomorrow I fill the engine up with water and see if the jet works and the tee quit leaking. My 12 volt non external resister coil should be in at NAPA too. $11.95 MP IC277SB if you need one. Video to follow.

Jerry
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i have seen a few high speed needles and i would of made mine more needle like.

 

Funny, that looks like a Briggs setup for the old updraft carbs. They do have more taper to them like budd said. Also looks similar to the Tecumseh style.

 

C'mon guys, don't "needle" him. If it doesn't work like it is, it won't take a government initiative to decrease the taper on it. I think he has the skills to accomplish it..........

 

lets not forget this thing requires alot of fuel. It may be perfect in this application, if not easy enough to change