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Discussion Starter · #1 ·
Greeting
I'm hoping someone else has had this issue with their carb. and came up with a solution. Then it would be cool if they read this thread and posted their solution so that I too can share the joy of happier days of riding.
I'm running an SU Eliminator on my 71 XLCH hardtail Ironhead and the idle screw has a mind of it's own. I bought the bike as is, and it didn't have a tension spring on the idle screw. I bought a tension spring from a Harley dealership, but it's useless. The spring has made no affect and the screw keeps moving around. I'm getting pretty good at readjusting it at every traffic light, but when I ride for 20 or more miles, it gets so bad that I have to pull over, turn the bike off and reset it. I think it's going to blow the engine, if I don't figure out a way to prevent this screw from moving. Other times, it backs itself off and it wants to stall when I come to a stop. I end up keeping my right hand on the throttle, giving it gas, while reaching over with my left arm and trying to readjust the screw. Any ideas on how I can fix this problem? :confused:
 

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You said you got a spring but didn't say if it was the correct spring. Where you got it is irrelevant. WHAT did you use? Always try to be precise. Rivera can sell you a spring or direct you to a seller.

Parts list with numbers:

http://www.riveraengineering.com/SUInstructions1108-0001LORES.pdf

Rebuild with pics and thread sizes. Remember they are a mix of US, Metric and Whitworth.

http://www.riveraengineering.com/SU-Rebuild-Disassembly-LORES.pdf
M4 x 0.7is the listed thread pitch.

If the hole in the aluminum body is loose, Loctite as suggested can prevent further wallowing of the threaded hole.

If the hole ever strips out you might be able to use a barrel-type insert (not a coiled insert) to repair the hole.
 

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try using ''BLUE HYLOMAR'' instant gasket on the screw threads,...it's fuel resistant and never sets solid,
I have used it to keep adjuster screws in one place, but still able to do adjustments without having to repeat the process.
being sort of ruberised it absorbs vibrations and prevents screws undoing themselves,
or if ya want it solidly held in one place try a Blob of ya old ladys Nail Polish between the screw and the body of the carb,...like a factory sealed set screw...
 

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3# - 6# mono filament fishing like works like lock tight, without the locking to tight. Run in with a impact will make it lock as it melts it some. But the correct spring is best.
 

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Are you sure the idle screw is the issue? I don't know squat about an iron head ignition but I had nearly the same idle issues you are describing when the advance unit and springs were shot on my 76 FLH.
 

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Are you sure the idle screw is the issue? I don't know squat about an iron head ignition but I had nearly the same idle issues you are describing when the advance unit and springs were shot on my 76 FLH.
you came on and asked = the guys who answered have more experience then you have years lived

before you question - try the examples
 

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If the threads are good in the body, maybe you could use a jam nut. If there are enough exposed threads on the screw then maybe a nut on each side of the body would work. I've never had an SU, so I'm just guessing.
 

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The guys above have suggested pretty much everything, you could also drill a hole and wire thread it around another bolt which will mean it cannot move. That way you can guarantee it'll stay seated where you require.
 

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Discussion Starter · #10 ·
I appreciate all the responses I've received with the awesome solutions to my problem. I left one thing out though.

When I tried to install the new spring, I discovered that this screw only backs out so far and then it just spins. This is why I ended up threading the new spring onto it. I am unable to remove the screw to add locktite to the threads, as it does not back out far enough.

I've considered many options, but with my very limited knowledge of any side effects, (so to speak), I haven't tried anything yet. Other than keep my rides short and filled with re-adjusting the screw at every traffic light/stop sign.

This is my SU carb. w/Idle-Adjuster screw

This is me pointing to the screw in question:
 

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cant see them pictures of yours less we have an account with cyclefish... just post them here direct from ya computer... real easy if ya go ''advanced''
 

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Choose from the below "screw scenarios" since I'm not quite sure which screw you mean after considering your "spring". Your, and perhaps the Harley parts counter guys, confusion may have been because most carbs use a spring under the idle fuel mixture screw in the body. A Harley mechanic might expect such a screw, AND expect one under any screw on the linkage.

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When a male threaded fastener unscrews then spins in a threaded hole without further progress, that's usually due to stripped threads on a portion of the screw.

I'd take the few minutes to unbolt the carb and inspect the area on the bench under BRIGHT light. Stuff a clean, lint-free rag into the open intake manifold after removing the carb.

Do you mean the screw in the Idle Stop Lever Assembly, reference pics 34 35 on page 3 this .pdf? (It's really a small hex bolt.) Zoom in closely if needed:

That does not show a spring.

If the threads are trashed you can check with Rivera for that part, which in the photo in their parts breakdown does NOT show a separate bolt and arm. The orientation in the photo is deceptive and the color pics are much better in this .pdf.

http://www.riveraengineering.com/SU-Rebuild-Disassembly-LORES.pdf

I would replace both bolt and arm because both male and female threads are likely worn.

IF there's enough space all round I'd consider drilling out the remaining threads in the arm (so they are no obstacle to the new screw) , obtaining a suitable screw and nut, and tack welding the nut to the arm to provide threads. That's only worth doing if you can EASILY do it right and know what right looks like.

Either way you get working threads.

Inspect the carb while you have it off. SUs are good carbs but complex, and old carbs are often worn in more than one place.
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If the screw you mean is (49/50/51) the Idle Speed Screw that doesn't show a spring. Many other carbs provide one but the photo shows an O-ring. That ring is all you have to provide friction to keep the screw from both moving and leaking. Leaky O-rings can cause hunting idle speed. Idle Speed Screw is 47 in the parts illustration, Page 8 of the Instructions .pdf. Its O-ring is 34.

Such screws can sit and spin instead of coming out once they are past their threads. That does NOT indicate damage. They are usually clinging to the O-ring. They aren't designed to be removed with the carb on the motorcycle. I'd screw it a couple threads in so it doesn't fall out, remove the carb, then unscrew the screw and invert the carb over a tub or tray on the work bench.

Inspect hole threads, screw threads etc under BRIGHT light, install a new CORRECT O-ring (hardware store rings may not be Viton), reinstall carb and press on.

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Assumption is the mother of all phuqueups, so unless the parts breakdown shows a spring don't expect one to exist.
 

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Discussion Starter · #14 ·
I see now that I installed a spring where there was none from the factory. Chalk up another mistake for my side, but reduce it by half, since I learned something from it.

Farmall is corrrect. It is an Idle Speed Screw. Part 47 in the parts illustration of the "Instructions.pdf".

http://www.jockeyjournal.com/forum/album.php?albumid=4186&pictureid=35666

The only reason I have not taken the carb off and inspected it, is because I have no access to a replacement gasket or gasket material to make my own. But, here again I've made a mistake in not checking Rivera Primo for one.

Like I said, I'm very green when it comes to motorcycle mechanics, and I really appreciate the more experienced taking the time to offer assistance.
 

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Any US auto store should carry gasket material. It usually comes in rolls so I often lay a book on top to flatten it.

If your gasket doesn't tear when you remove it I've reused many after a light wipe of grease or vaseline on each side. If gaskets are very crushed and brittle, replace them.

If you want to copy a gasket, scan it and save the image. You can print it out as a template later. Of course you can scan a damaged gasket and tidy up the print before tracing then cutting a new one.

Fel-Pro and Mr. Gasket materials are available online. It's worth keeping in stock.

When you get your new O-ring, measure it before you install it. You can measure the inside using the shank of a drill bit. I like calipers for the outside and thickness. (Harbor Freight cheap digital calipers are decent.) When you get an O-ring note any identifying data on the package.

For example S&S use a small blue fuel resistant O-ring that's often lost. I matched up my last new one then got a matching bag of 100 for about nine bucks.

Any time I take a carb apart I save all the gaskets and seals until I'm sure I've their match to install.

Walmart carry US-made clear plastic boxes in the sporting goods section. They have removable dividers and are outstanding for carb parts. Less than ten bucks and totally worth it.
 

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Discussion Starter · #16 ·
Thank you for the tips and tricks Farmall. I'll be sure to incorporate them into my future endeavors.
 

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Discussion Starter · #18 ·
Okay. New question.

I read that "Red Line" tranny oil, will remove the clunking sound from the tranny when down shifting. Has anyone used Red Line or Lucas and had it remove or reduce the clunking sound, or is this just a spin on reality?
 

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4 speed sporty trans fluid is more or less 50W type gear oil that works with clutches

if the clunk is looseness no oil will take that away
 

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Discussion Starter · #20 ·
I was told by a friend named Jack in Illinois that 60wt was best for my bike. His family has owned and operated the Harley Repair in Effingham, Ill. since the late 1960s. He only works on the older Harleys, so I figured he knew what he was talking about. Do you think that my using 60wt is why my tranny is making that clunking noise?
 
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