1980 rebuild and stumped

[BigalG]

80 special starting rehab , carbs are clean and rebuilt, air mixtures drilled out and new sets put in, new battery, plugs, so far.
will start with choke in full open position , will race up to 4 to 5 k rms then drop down and hunt floating between 1500 and 2000 rpm. if i drop the choke down to the second position it kills the engine. Start it back up on full choke and it races back up to 5000 or better for a bit then comes back down. pick up wires look ok and resistance at the cdi plug looks good. Where would you go from here? Thanks for any advice

[oldyam80sg]

Did you check the vacuum caps? They can crack and cause all sorts of issues. Are you sure the carbs are clean? I have sworn in the past they were only to find dirt in them. Even though I run fuel filters on the lines, gum and varnish in todays fuels can cause issues.

[Bax]

Hey, BigalG nice to see another New Englander on the board. Okay first step would be to get the idle down to a workable rpm. When it's running on full richening position try and turn down the idle stop screw (bottom of carb array) until 2k rpm or so and then try to hit half rich position. Do you have the vac advance ported to the carb or is it in the boot? Carb is correct placement.

-Bax

[Bax]

What you are referring to "air mixture" is spring loaded screw on engine side, top of carb body? Or fixed air jet pressed into the mouth of the carb?

----Bax

[BigalG]

Thanks guys, the carbs are sparkling, i recently finished a 79 special so i know how many times you have to clean them to be sure.... vacume advance is on the carb body, vac caps are solid. Air mixture screws on the 80 are under caps that had to be drilled out, replaced all of those with new orings and screws, no broken tips....

[Radioguylogs]

Did you, by any chance, replace the pilot jets with the parts in the K&L carb kit?

The pilot jets in those kits are the wrong size, and I had similar symptoms until I figured it out by reading old posts on this forum.

[BigalG]

these were the specs on the carb kit
Float bowl gasket
2.0 Float needle and seat
#110 & #42.5 jets
Mixture screw, o-ring, washer

I saw an old post from TC that said some of the 80's carbs did not use the rubber pilot jet caps because they were built different and drew from the maine bowl. When i opened up the carbs for the first time i thought the po forgot to replace them and so i orderd a set ant put them in . ??
Thanks for the help
winters comming

[jetmechmarty]

When i opened up the carbs for the first time i thought the po forgot to replace them and so i orderd a set ant put them in . ??
Thanks for the help
winters comming

Bingo! Up to the last post it read like clogged pilot jets. That's exactly what you have. Remove the plugs. Also, you'll have a much easier time with genuine Mikuni jets.

[Bonz]

Good work BigalG.

[BigalG]

Yes that was it, runs like a champ, rode it up and down the street , tomorrow carb tune. fork seals are leaking though, how much do i worry about that

[Bonz]

Besides the inconvenience of adding fluid eventually and the mess of leaky fork seals, if left alone and it gets worse it can eventually contaminate the brake pads.

[bikerphil]

fork seals are leaking though

Nine times out of ten it is just dirt lodged in the fork seal, I would try the 35mm film cleaning trick first. I have fixed many seals this way so I know it works most of the time, YMMV. Here is a link to a You Tube video if you are unfamiliar with the process...

https://www.youtube.com/watch?v=niYSt1oyzKA

[Bonz]

I’ve cut a piece from a plastic H2O bottle, maybe easier to find than 35mm film... In this digital age, doncha know.

[2WheelFun]

Cut one from a 1/2 gallon milk jug. Make sure your not running any air pressure or more oil will come out than you expect.