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Discussion Starter · #1 ·
So...I picked up a 98 from my buddy for $800. It had been sitting for just under a year but put some gas in and it started, ran a little rough, but not horrible. The idle fluctuated up and down and around 40 mph and above it would seem to sputter or jerk while maintaining speed. So I said screw it and decided to rejet, ear shave, and coaster the reed valves since I was pulling the carbs anyway, as well as standard stuff like an oil change and new spark plugs. Now once I got every all squared away and figured out she fired up better and no longer had the sputter/jerk while maintaining crusing speed, however the idle was sporadic still, so I ordered brand new OEM boots for the carbs. Installed them correctly, lined up the nibs, everything is tightened up good but now it's the same sporadic idle and sometimes the RPMs are hanging (I'll pull on the clutch and my RPMs spike to 3-4 k until I'll adjust the idle nob, and that will work...until it doesn't.)

I live in Carroll County Maryland, the only shop remotely close that works on metrics is 6 weeks backed up on work but at this point I almost feel like I should just accept the down time and let them try and fix it. I've pulled those carbs so many times now checking and double checking that I can pretty much have them out, checked and back in in under an hour. I feel like I'm so close to finding the problem but I just don't quite know enough and I've exhausted everything option I've researched.
 

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how about the idle adjustment air/fuel screws? They’re normally plugged with lead from the factory but if someone screwed with them that could cause funky behavior. But your problem of the idle hanging sounds like air getting in there or something sticking in motion
 

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Discussion Starter · #4 ·
Have you checked the diaphragms and checked the slide action? Diaphragms installed correctly?
Oh yeah, I was really worried about reinstalling those correctly and had seen in researching the carb disassembly/reassembly to manually check the slide action through the intakes and they move like they are supposed to.
 

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Discussion Starter · #5 ·
how about the idle adjustment air/fuel screws? They’re normally plugged with lead from the factory but if someone screwed with them that could cause funky behavior. But your problem of the idle hanging sounds like air getting in there or something sticking in motion

Oh the lead plugs were not present so I know someone had worked on the carbs before, and I pulled those when I cleaned the carbs and reinstalled everything in the correct order. I screwed them down then backed them out 2 1/2 turns.

I keep going back to vacuum leak because the throttle cables and assembly snap back as they should. The whole issues is so headache inducing lol.
 

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Oh the lead plugs were not present so I know someone had worked on the carbs before, and I pulled those when I cleaned the carbs and reinstalled everything in the correct order. I screwed them down then backed them out 2 1/2 turns.

I keep going back to vacuum leak because the throttle cables and assembly snap back as they should. The whole issues is so headache inducing lol.
Hi vkng, I feel your pain. I have done complete fuel system rejuvenation, from fuel tank cleanout to petcock to carb rebuild to air filters. I ran into issues here and there. The petcock was a disaster and needed replacing. The pilot jet was clogged solid and needed replacing (might as well replace everything when rebuilding carbs!) One coasting enrichment valve was stuck.

Anyway, there are three flow circuits in the carb: pilot, mid range, and high. Make sure those three holes are clear in the carb throat. The first hole is the idle and the butterfly valve should just touch it.

If the butterfly valve is positioned properly and moving properly, then your problem is often a vacuum leak, which does cause the idle issues. Here is a Youtube video about that.

The choke should be clear and not sticking.

The idle knob just moves the butterfly valve. Make sure the butterflys are moving freely and don't bind up on the rotation pivot. When you close the throttle the return cable should force the butterfly fully closed so the idle stop bracket hits up against the idle adjustment screw.

When you have the intake boots off (big pain I know), you can look in the carb throat and see the sliders. Move them all the way to the top feeling for binding, and make sure you hear a nice whoosh sound. Then when you release them they should drop down smoothly and quickly. Do both at the same time and they should hit bottom at same time when you release them.

Use carb cleaner and silicon lube on the butterfly pivots and choke linkage if necessary. Replace the choke plunger if necessary. And pull off the carbs and use 2500+ sandpaper to smooth the bores and slides if necessary.
 

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What brand of pod filters?

You can use an unlit torch to shoot propane to check around the leak points, starting fluid works too, just be aware of anything getting into the air filter that would give a false reading.

Sometimes a boot will only leak when it's hot. Does the idle change all the time?
 

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Discussion Starter · #8 ·
What brand of pod filters?

You can use an unlit torch to shoot propane to check around the leak points, starting fluid works too, just be aware of anything getting into the air filter that would give a false reading.

Sometimes a boot will only leak when it's hot. Does the idle change all the time?

I used the K&N RC 2340's (I followed the ear shave guide to a T)

It does it while hot or cold. I don't get any reaction when I spray the boots with carb cleaner or starter. But I'll have to go over it all again with a fine toothed comb.
 

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Can you post a video of it idling?

A leak can cause a hanging idle but I'm not convinced an air leak is causing it to fluctuate up and down.

Could it be loading up with fuel, and the idle drops when it's too rich, then bounces back up? What size jets?
 

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Discussion Starter · #10 ·
Can you post a video of it idling?

A leak can cause a hanging idle but I'm not convinced an air leak is causing it to fluctuate up and down.

Could it be loading up with fuel, and the idle drops when it's too rich, then bounces back up? What size jets?
I'll have to get a video when I get home from work in a bit.

I've got 142 main jets and 42 slow jets. 2 shims on each of my needles.
 

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I'll have to get a video when I get home from work in a bit.

I've got 142 main jets and 42 slow jets. 2 shims on each of my needles.

That's usually a very rich setup. Stock pipes, or something else?

Any bad fumes when it's idling? Black smoke at all, especially when you first rev it?
 

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Discussion Starter · #12 ·
That's usually a very rich setup. Stock pipes, or something else?

Any bad fumes when it's idling? Black smoke at all, especially when you first rev it?

Stock pipes
That's usually a very rich setup. Stock pipes, or something else?

Any bad fumes when it's idling? Black smoke at all, especially when you first rev it?
I had been thinking it was running a bit rich, just checked the new spark plugs that I put in the other day and they are black.

Stock pipes, goats belly intact.

I'm not getting any black smoke, no. But I have from time to time caught a bit of a gas scent.
 

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Stock pipes


I had been thinking it was running a bit rich, just checked the new spark plugs that I put in the other day and they are black.

Stock pipes, goats belly intact.

I'm not getting any black smoke, no. But I have from time to time caught a bit of a gas scent.

So possibly then the carb is just too rich.

Another possibility is float height or a leaking float, but I lean more toward jetting being too rich.
 
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