Float height/fuel level

[schpiff]

Hi All,
I am a new owner of 81 special (complete with a couple years of cobwebs). The previous owner said it ran great, parked it cuz he bought a new bike.
I have cleaned the carbs every way I can think of, but am having what appears to be a lean condition on cyl. 1 and 2.(when cold it only runs on 3 and 4 till it starts to warm a bit). They will fire with some throttle, but at idle or just off do not. Let me add that it is pretty cold here in Wis. right now and maybe thats a factor....?
The carbs have been worked on before( boot clamps swithched around etc.) I am thinking that fuel level is coming into play but cant seem to find a common spec for fuel height or float level....
I am hopin that someone can help. (judging by the posts here I am sure someone can).
Thanks in advance

[skids]

Re: Float height/fuel level

It seems like a fuel delivery problem, but if they start firing after it warms up, you are probably right about the pilot circuit. The pilot jets probably need some attention. Did you spray carb cleaner through them when they were removed? I used a guitar string to clean a set out -- contrary to warnings that I could change the oriface characteristics. I was careful and it worked out OK.

Originally posted by schpiff
Hi All,
I am a new owner of 81 special (complete with a couple years of cobwebs). The previous owner said it ran great, parked it cuz he bought a new bike.
I have cleaned the carbs every way I can think of, but am having what appears to be a lean condition on cyl. 1 and 2.(when cold it only runs on 3 and 4 till it starts to warm a bit). They will fire with some throttle, but at idle or just off do not. Let me add that it is pretty cold here in Wis. right now and maybe thats a factor....?
The carbs have been worked on before( boot clamps swithched around etc.) I am thinking that fuel level is coming into play but cant seem to find a common spec for fuel height or float level....
I am hopin that someone can help. (judging by the posts here I am sure someone can).
Thanks in advance

[schpiff]

Thanks skids I will give that a try.
Tonite i went thru and reset float heights at 25mm, (thats about the middle ground of the specs i can find. Started as usual but cyl. #1 started tryin right away..2 was still dead. When i cleaned pilot jets I used a a tooth brush and crammed a couple bristles thru the jet (took some tryin as they were really plugged). Maybe I missed some crud..I dunno..I think that 3x clean thing is comin into play... As for the floats ..they were all set different..from 23mm to 26. The idle mixture screws were all out about 4 1/2 turns and at idle the throttle plates were open just to the start of the first transition hole..
Thanks again

[TopCatGr58]

Hey there Schpiff,
Are you very familiar with the Special's fuel delivery system?? They have an Octopus and it's vacuum controlled. Could be some sludge in it, the petcocks, etc. since the bike sat for several years. With the hoses off the petcocks, do the petcocks flow in Run position? You can try turning the petcocks to PRIME, and start the bike and see if it hits on all four almost immediately. If it does, then your Octopus isn't working right, cause the PRIME bypasses it and sends fuel directly to the carbs without any vacuum control required. Just an idea!?

[stevec5000]

Speaking of pilot jets, the manual shows they should have a plug screwed into the hole covering the jet, #21 on the carb drawing in the Haynes manual. My carbs do not have any plugs over the pilot jets! Are those really needed, should I replace them? What problems will be caused by the plugs being missing? Thanks.

[nashville_bill]

The plugs are on older style carbs. Your '81 special, and mine, don't have them.

Check your fuel level using the test described in the manual using a piece of clear 1/4" tubing connected to the float bowl. I had to set my floats at much less than the 25mm listed to achieve the correct fuel level.

[schpiff]

Could one of you guys give me the fuel height spec from the clymer or haynes manual..I ordered one but it hasnt arrived as of yet. I did check out the spider and petcocks, fuel will flow in the on position on the left side, but I have been using the prime position and all carbs seem to be getting fuel ok. I will look into that prob after I get this one ironed out.

[skids]

OK, I think I see the problem...
You have 81 carbs. Just like the 80 carbs.
The float "height" is supposed to be 23 +/- 0.5 mm (see clymers page 255).
These are different than older carbs which bring all fuel through the main jet. If your "height" is excessive, your fuel surfaces will too low.
You might need to readjust the pilot screws tighter (like 1.75 turns out from lightly seated) after your float levels are fixed!

Originally posted by schpiff
Thanks skids I will give that a try.
Tonite i went thru and reset float heights at 25mm, (thats about the middle ground of the specs i can find. (snip)
..from 23mm to 26. The idle mixture screws were all out about 4 1/2 turns and at idle the throttle plates were open just to the start of the first transition hole..
Thanks again

[nashville_bill]

Check out the maintenance section of this forum.


Go to: Setting Carburator Float Height

Then go to: How high is the fuel?

It even has great pictures. I didn't make the test jig but I did use the clear tube to check it.