’88 XLH1200 – Bad Carb swap out.

[cyclobutch]

This bike is an original 1200 running Screaming Eagle pipes and air cleaner. Still on the original carb, but jetted to suit. That carb is the OE item, a CV type – I presume a Keihin, though with the HD logos cast in. It does not have the accelerator pump of those fitted on later models. The bike has a 4 speed transmission, and I suspect it has been geared up a little – I've never counted teeth, but it is quite tall geared in first and can be a bit lumpy at lower speeds leading to a lot of clutch work in traffic.

I figured a later carb with the pump might improve this. So I bought one from an '04 model. Looks the same, but has the pump. I figured if I just compared the jets and then swapped any in from the old carb where they differed then it should be good to go. They looked OK though. The main jet was 10 out, and is a different fitment between the carbs, and so I figured that wouldn't matter for now – I'd road test that. I tried looking at the needle, but that's all wrapped up with the diaphragm and I found no markings.

Fitted to the bike it's pretty disastrous. Not so bad on the choke, but once that is backed off it is banging and popping real bad at low revs and on the overrun. Kind of driveable, but not like you'd want to. Swapped back to the old carb and all was as good as it ever was. I don't think that I'd introduced an air leak whilst it was fitted. I did confirm that the accelerator pump was working.

So what is the problem ... ? Is there some mis-compatibility fitting an '04 carb to an '88 bike? Is there something wrong with the carb I've bought?

Thanks

[rigidthumper]

The pilot jet on the 04 is probably 2 or 3 sizes too small. Replace it with a 46 or 48 pilot, shim the needle .025"-.040", & verify the idle air mix passages are open, and retest.

[guppymech]

My '02 was very lean in the low speed ranges with stock jetting. The later needles have a slightly larger diameter straight part of the needle and that combined with a smallish pilot jet cause bad running,  Make sure you remove the tamper proof plug over the idle mixture screw and set it to 2 to 2 1/2 turns out baseline.  You should try swapping over your jets and especially the N65C needle (known to be one of the best) from your '88 carb.
Have a look at this carb tuning stickie from over a XLF.
http://xlforum.net/vbportal/forums/showthread.php?t=642408

[cyclobutch]

Thanks for that input folks. I've since talked to my friendly on line parts supplier and they've wizzed me over a 45 pilot jet, a 180 main (which would have nothing to do with my problem anyway) and what they call an 88 Sportster needle.

It will be some weeks now before I will have time to fit these parts and then swap the carb back in. I will report back.

  B

[cyclobutch]

Update - been looking at a potential starter issue (separate thread hereabouts) so have still to get back to this one.

[Carl 1969]

Thanks for that input folks. I've since talked to my friendly on line parts supplier and they've wizzed me over a 45 pilot jet, a 180 main (which would have nothing to do with my problem anyway) and what they call an 88 Sportster needle.

It will be some weeks now before I will have time to fit these parts and then swap the carb back in. I will report back.

  B

I've had good luck with that '88/'89 Sportster needle in a '94 883/1200, a '99 FLTR & now my '02 FXD.