Eliminator carb

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Miles
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Eliminator carb

#1

Post by Miles »

G'day,
I have an eliminator carb on my 51 FL which I am trying to tune. I have the neele size close but feel I have to get a lighter spring as I get a slight spit out the aircleaner when I open the throtle with the clutch disingaged while gearing down. The instructions say a stronger spring will result in a richer mixture. That doesn't make sense to me as the spring resists the movement of the piston and thus the needle up into the dome. The more the needle stays in the jet the leaner the mixture.
Anyone have experience with the eliminator carb that can shed some light for me?
Al
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Re: Eliminator carb

#2

Post by Bigincher »

I can't answer your question, but something you said made me curious. It sounds like you rev the motor and downshift, similar to the way truck drivers do?
I'm not one to criticize another mans habits, but I think that's a poor method- except for extreme situations such as emergencies. When I downshift, I do something similar, but on the very low end of the scale, if you know what I mean.
And maybe you do the same thing and I'm merely misinterpreting what you describe. If so, I apologize in advance.

One other question, what do you mean by "eliminator" carburetor?
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Re: Eliminator carb

#3

Post by panhead »

I think he means the SU Eliminator.
Miles
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Re: Eliminator carb

#4

Post by Miles »

Bigincher, no apologies necessary.

Panhead, I tried to open the thread you posted but for some reason I get 'not authorized to view'

Yes I disingage the clutch, rev the engine to what it will be in the lower gear, shift and let the clutch out. That way the engine is running at or near to the rpm it needs to be at before the clutch is engaged. Reduces clutch wear. Just a habit from my Norton Commando days, been driving like that for the last fifty years.

When running at low rpm and I twist the grip it sometimes spits out through the carb, lean off-idle.

Yes I meant SU Eliminator carb, I put one on in 1982, worked well for years but developed a crack. I bought a new Eliminator II to replace it. The II has a leaner needle than the I but a weaker piston spring, I have to lean it beyond limits to run at idle and to start. The I has a richer needle but a stiffer spring. I can swap the dome, piston needle and spring from one to the other but not the springs alone as the II has a wider piston shaft and spring.

I just wonder if anyone out there is familiar enough with these carbs know if a lighter spring will give a richer off-idle setting than the stiff spring. One has to know how these operate before buying springs and needles. They are altitude sensitive, I used to live at 3800 feet and now I'm at sea level.

Al
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Re: Eliminator carb

#5

Post by panhead »

here is the info:
SU Eliminator.pdf
(406.71 KiB) Downloaded 206 times
Miles
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Re: Eliminator carb

#6

Post by Miles »

Thanks Panhead,
That's the same instructions that came with the carb, telling me to put on a stronger spring to richen the mixture. I couldn't figure out how holding the piston/needle down would cause that.
I contacted Rivera Engineering today and got the answer. The spring holds the piston down causing less air flow, but the open throttle results in higher velocity of the air going under the piston and over the bridge drawing more fuel through the jet. I'll have to get some springs and trial and error until good.
Thanks again.
Al
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Re: Eliminator carb

#7

Post by Excalibur »

Miles wrote:G'day,
I have an eliminator carb on my 51 FL which I am trying to tune. I have the neele size close but feel I have to get a lighter spring as I get a slight spit out the aircleaner when I open the throtle with the clutch disingaged while gearing down. The instructions say a stronger spring will result in a richer mixture. That doesn't make sense to me as the spring resists the movement of the piston and thus the needle up into the dome. The more the needle stays in the jet the leaner the mixture.
Anyone have experience with the eliminator carb that can shed some light for me?
Al
It's been quite a few years since I had a S.U. on my Shovel. I had a head start setting up these carbs because I worked on cars factory fitted with them in the 70's. I can still remember a number of the details.
Make sure there is no air leakage at the manifold. The dashpot needs to be absolutely spotless, no grit, buildup etc. The dashpot stem should be perfectly rust free. To test, raise the dashpot by hand, it should fall with a 'metallic click' as it bottoms out. Do a proper tuneup on the plugs and points because the spark NEEDS to as good as it can else you chase your tail with mixture setting. Unlike on the cars, Harleys use no oil in the dashpot damper. A stronger spring will result in richer mixture because the dashpot piston with be more closed allowing less air past. Mixture screw should be set with engine hot and at a RPM where the dashpot is not bouncing up and down. Always err toward rich perhaps 1/8 turn. Avoid restrictive air cleaners. BTW, these S.U.'s should be fitted with a proper high flow needle valve called a gross jet because car type needle valves don't flow enough from gravity feed.

My Shovel (daily rider) won a number of drag race events using a S.U with velocity stack., 'A' grind cam and straight headers. Memory says it did 13.1 sec.

Even on the cars S.U.'s receive a mixed response from people. When set up properly, the carbs were known for exceptional economy and good power. Some folks swore by them, while others swore at them. Get the basics right first..

Hope this helps
Miles
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Re: Eliminator carb

#8

Post by Miles »

Excalibur,
Thank you,
You are correct, air leaks and dirt are an SU's enemies. I have been running one for quite a few years and I also had them on my Land Rover, Triumph and Austin Healey. They do require attention and I also know folks who swear at them, but I also know folks who swear at Quadrajets. I just couldn't grasp the needle buried in the jet and still having a rich mixture. Got it now.
Al
For what it's worth, they paid more attention to detail with the Eliminator II over the I. All the flashing is ground off and the interior is polished for better air flow. The I looks pretty ugly, internally, compared to the II.
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Re: Eliminator carb

#9

Post by Huck »

I oil mine regularly with wd-40 or like wise. The slide needs to work like butter, be oiled & and cleaned every now & then.
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Re: Eliminator carb

#10

Post by Panacea »

My 49 chop had an SU, also with an andrews A cam. That was my best starting panhead, the only problem I ever had was coming home late one night, she started bogging, I pulled up to a street light to look it over and noticed the carb had sucked the foam from the air cleaned down it's throat! Pulled it out and went on my way...
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Re: Eliminator carb

#11

Post by Miles »

Been a long time since I was here.
Two more issues with the SU I wanted to share.
First is the Eliminator II. Bike just started to run like heck, I got it home and after taking the carburetor apart I found the screw that holds the jet in place, called the 'bi-metallic screw' in the parts list, had broken, the top half was in the bottom of the bowl. The threaded portion was still in the body. Maybe it was over torqued. Anyone know the size and threads of this screw?

I have the eliminator I on the bike now with some of the eliminator II parts in it. I was having trouble with surging rpm, at idle and in cruise. At idle it would pick up about 1000 rpm then slowly drop back. Sounded like a vacuum leak so I removed the carb, checked the gaskets, cleaned it out and tightened all screws. Ran the same. I removed the carburetor and the intake manifold, replaced the manifold O rings, reinstalled the manifold and carb. Problem solved. O rings I removed looked good but must have been leaking. Just thought I would pass this on in case someone else is having the same problem.
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Re: Eliminator carb

#12

Post by Bosheff »

For a reasonably stock panhead use a BBX needle, a .100 pick-up tube, and a silver spring. Vacuum leaks and dirt are an SU's worst enemies. Initial adjustment for the main jet (pick-up tube) should be approx. 4 turns out. If you have to go more than 2 turns in either direction you need to change the pick-up tube, the needle or the spring....bosheff
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Re: Eliminator carb

#13

Post by Excalibur »

Miles wrote: Thu Aug 02, 2018 5:59 pm I found the screw that holds the jet in place, called the 'bi-metallic screw' in the parts list, had broken, the top half was in the bottom of the bowl. The threaded portion was still in the body. Maybe it was over torqued. Anyone know the size and threads of this screw?
Some thoughts:
A screw replacement could be obtained from SUcarb.co.uk
http://sucarb.co.uk/hif-bi-metal-assembly.html
It appears the bi-metal assembly needs to be purchased as a kit.

Otherwise if no luck from Rivera, Bob at thegoodoldmotorcyclepartscompany.com mentioned he had some SU parts including oddball stuff.

Failing all that, a screw could be made. In the images from Sucarb.co.uk, it appears as though the screw has a stepped shoulder. I bet it's broken right at the step. You could find a regular screw of the same length and thread, then slide a tube onto it. I say this having a lathe at my disposal.
Either way you go, the broken piece of screw needs to be extracted. At this stage you'll be able to measure tpi. I have 2 SU HIF's in the shed at the moment so I could open one up for tpi measure if it helps.
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Re: Eliminator carb

#14

Post by Robert Luland »

Have no fear! I ran out of that screw but have more on order. Should be in in under a couple of weeks in I will post them on my site. Bob L
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Re: Eliminator carb

#15

Post by Excalibur »

Update:

I found the part number for that screw: AUD 3584 ...and it's available on its' own: http://sucarb.co.uk/screw-23849.html (2.39 pounds sterling)
It looks like their minimum "rest of world" shipping is 12.50 pounds sterling! :evil:

I opened up one of the carbs and the screw thread is 32tpi so if BSW it must be 5/32". A quick look in my stash of random screws and almost immediately found a possible donor.

Ok, making one would be possible but for 2.39 pounds sterling you'd just buy it. Shame about the postage. Maybe wait for Bob to get some in, then you'd only need to get it up to Canada?

Hope this helps.
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