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Ironhead Sportster Motorcycle Talk (1957-1985) For all those that wanna talk about Ironhead Sportster Motorcycles

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  #11  
Old 7th December 2011
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hmiller hmiller is offline
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All of what I say is for an '88 converted to 1200 and was figured out using a bunch of online searches and the stickies here. I've found that Wedge (member here) know more about carbs than I ever will. Hopefully he'll chime in here.

This is what I've found:

Jet: 42 or 45 with a 175 or 180 will usually be good, as bobber58 said, some have better results with a 48. Once you start fine tuning you may find you need a different jet. You may want to start with a 45 and decide if you want to go up or down from there. The jets are pretty inexpensive so you won't break the bank doing this.

Needle: I haven't tried anything other than the 65C but a lot of people are using the adjustable ones. I can't comment on any of those. You can do a search and decide for yourself. Since you already have the kit with the adjustable just play with that before spending any money on another.

Slide: Make sure the diaphram is good no pinholes or tears. Mine had a pinhole that drove me crazy. You can polish the slide to make it move more smoothly. Some people drill the hole out on the bottom of the slide, half of the websites say to do it the other half say not to. I didn't and am happy with it. Check the spring, you may want to replace it since you have the top cover open anyway.

Clean the carb really well. Soak it or spray the heck out of it. Blow air through all the orifices. Check the main jet (where the fuel comes in), Check the holes in the emulsion tube and jets. Check the needle jet (small peice above the emulsion tube) for wear and make sure it goes in the right way. I think the beleved edge points into the carb throat but I haven't looked at mine in a while. I put mine in wrong the first time and gas spewed out the carb. It was basically the same symptom as a bad diaphram. Check the float level, that can make it run rich or lean too.

Once you've cleaned it, get new gaskets. Check them for leaks with wd-40 or starter fluid, if you have any change in idle you have a leak. Just make sure you're not getting any in the carb throat or the idle will change then too.

Start with the air mixture screw out about 2 1/2 turns. Adjust the idle so it's just barely running and warmed up. Adjust the mixture screw in until the idle stumbles then turn it out until it stumbles (count the turns), turn it back in half the amount. If you're out more than 3 1/2 turns get a bigger jet, if the idle doesn't change when you turn it in you probably need a smaller jet.

I picked up a easy adjust idle screw and mixture screw from CVP to help with adjustments.

I'm sure I forgot something, someone will chime in.

Edit: Also take the choke apart and clean and inspect that, if it's worn it will let too much air in. BTW, I don't have experience with the accel pump models, but It's basically just another diaphram and linkage I think.
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  #12  
Old 14th October 2018
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I have an 82 XLS with 'Q' cams. At the moment the bike has a Mikuni VM38 set up as a -9 carb. The jetting is generally too rich on this and I'm slowly zeroing in on a decent set up. As I have a CVK carb ready adapted for the Iron head with a VOES nad Dynotech igniton I intend installing the CVK in an attempt to get more range from the standard tank. Has anybody fitted a CVK to a standard bike with 'Q' cams and would like to share what jets they ended up with?
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Old 9th August 2020
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I bought a cv carb on the cheap that looked as though it had been through the war....more than once....all kinds of crude and garbage built up on the outside and grunge everywhere....the carb cleaner Advance and other sell cleaned it like new.....I let it sit for a week and checked every evening....it came out without any junk on it..
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Old 9th August 2020
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Here's the Sportsterpedia section on tuning the CV40 carb:
http://sportsterpedia.com/doku.php/techtalk:evo:carb02

The extensive information there should get you 99% set for a well-running engine/carb.

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  #15  
Old 11th August 2020
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I've a 1980 Ironhead with standard'ish exhausts and completley standard engine and run a 42 pilot jet. No idea what the main size is or the needle. Runs very slightly rich but rather that than too lean as was the carb it came with. (standard Keihn butterfly)The 45 pilot made it run very rich.
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Old 12th August 2020
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Quote:
Originally Posted by redironhead View Post
I've a 1980 Ironhead with standard'ish exhausts and completley standard engine and run a 42 pilot jet. No idea what the main size is or the needle. Runs very slightly rich but rather that than too lean as was the carb it came with. (standard Keihn butterfly)The 45 pilot made it run very rich.
Every engine is different - and many CV carbs have been bastardized with aftermarket parts - that often makes the carb run rich or lean in various parts of its operational range.

The 42 Slow Jet can be the right one for engines less than 1200 size, but on 1200/1250/1275 engines, they usually want a 44, 45 or 46 to create the right operation of the Transfer Ports. The entire tuning function is a bit of a balancing act - That's why using the original Keihin jets, needle & emulsion tube will often be needed to get the right balance throughout the full range of the carb operation.


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  #17  
Old 12th August 2020
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Quote:
Originally Posted by IXL2Relax View Post
Every engine is different - and many CV carbs have been bastardized with aftermarket parts - that often makes the carb run rich or lean in various parts of its operational range.

The 42 Slow Jet can be the right one for engines less than 1200 size, but on 1200/1250/1275 engines, they usually want a 44, 45 or 46 to create the right operation of the Transfer Ports. The entire tuning function is a bit of a balancing act - That's why using the original Keihin jets, needle & emulsion tube will often be needed to get the right balance throughout the full range of the carb operation.


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I just ordered a standard needle to match a 45/175 jetted 40mm
Stock spring (6") is still available
DJ spring is 5.75"
If a 7/64th drill will not go in the vacumm port in the slide it is still stock
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