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

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  #1  
Old 8th August 2012
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Default Carb issues not starting again

Ok so my 72 xlh, no electric start, started right up after the new coil. It was spitting gas out the carb and overflow. So I cleaned the carb, it was dirty and there was junk on the rubber tipped needle preventing it from seating properly, hence the excess gas.

Oh yeah it's got a later model 76 keihin carb.

Put it back and it would not start. So I pulled it again and read the post here on these carbs. Here's what I found:

No rubber plug at all over the slow jet. Slow jet is a 100. Main is a 145.

I'm thinking the lack of a rubber plug is preventing fuel from passing from the main to slow, no gas no start. It kind of coughs but will not stay started.

I think my main will be too small, but should be adequate to start it. Slow seems big, but I'm bored out .020 over so we'll see.

I also noticed my new coil gets hot, just trying to start it.

What do you guys think .."..lack of rubber stopper is the issue here, hot coil a problem.....main will be at Wot??
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Old 8th August 2012
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Ok so my 72 xlh, no electric start, started right up after the new coil.
did you mean XLCH?
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  #3  
Old 8th August 2012
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Don't know what way to tell you to go, I'm tweakin on mine to right now too, but just a tip if your workin on it and your bowl gasket starts to strech out leave it on the bowl and put it in the freezer for about 20 mins, pull it out, slap the gasket in the groove and slam it on the carb as quick as you can. (putting the bowl and the gasket in the freezer together the gasket will shrink up)

This kinda crap always happens to me on a sunday or on a gasket that you have to buy a whole kit to get one gasket.

B
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Old 8th August 2012
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Quote:
Originally Posted by nickleuci View Post
Ok so my 72 xlh, no electric start, started right up after the new coil. It was spitting gas out the carb and overflow. So I cleaned the carb, it was dirty and there was junk on the rubber tipped needle preventing it from seating properly, hence the excess gas.

Oh yeah it's got a later model 76 keihin carb.

No rubber plug at all over the slow jet. Slow jet is a 100. Main is a 145.

I also noticed my new coil gets hot, just trying to start it.

What do you guys think .."..lack of rubber stopper is the issue here, hot coil a problem.....main will be at Wot??
Yes to start with you nead that plug. Then you can see if your jets nead changing.

coils do get warm. If your just sitting at idle not rideing it. If it's excessive find out why.

And after (there was junk on the rubber tipped needle ) it may nead replaceing. I'm not a big fan of the rubber tipped ones. The all metal ones seam to work better for me. they don't seam to stick as easy. witch wont let the gas in.
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Old 8th August 2012
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Xlh. Kickstart removed.

Will get plug and some jets. Stay tuned.
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Old 8th August 2012
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Quote:
Originally Posted by Beavis View Post
... but just a tip if your workin on it and your bowl gasket starts to strech out leave it on the bowl and put it in the freezer for about 20 mins, pull it out, slap the gasket in the groove and slam it on the carb as quick as you can. (putting the bowl and the gasket in the freezer together the gasket will shrink up) ...
An alternative, use a little of this on a stretched float bowl o-ring ...

http://www.permatex.com/resource_aut...08222008_2.htm
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Old 9th August 2012
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OK I put in a rubber plug over the slow jet. Changed the slow jet to a 70 and the main is now a 165. I wanted an 85/175 but I took what my parts guy had that was as close as possible. Figured it had to be a better starting point than 100/145. I also put in a new fuel valve/needle and a carb isolator.

The slow needle screw is at about 4/5-1 turn out.

The good news is it starts again. The bad news is it's spitting gas out of the carb again. I'm baffled. The float is adjusted, carb is clean. Looks like the gas is coming from the main jet nozzle just behind the choke butterfly.

Anybody have any suggestions on next steps?
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  #8  
Old 9th August 2012
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Do you have stock cams??
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Old 9th August 2012
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Is gas coming up the main jet nozzle at idle? or under some [how much?] throttle?

Gas come up thru jets in response to low presure in the venturi compared to atmospheric pressure in the float bowl. The bowl gets atmospheric pressure thru the hole at 1:00 o'clock of the face of the carb that faces the air cleaner. The low pressure in the venturi is a result of air being sucked thru the venturi as the piston goes down.

I am wondering if the throttle plate is too much open when the throttle is closed - it should be open just enough to result in enough air flow to suck up enough fuel for idle.
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Old 9th August 2012
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This was discussed on here a little while back: the very first 1976 Keihins do not use the rubber plug beneath the slow jet. They do not have the tiny hole drilled from the slow jet area of the carb body to the main jet area, so need to suck gas up direct from the float bowl though the exposed slow jet.

Check if your carb has that small hole drilled in the body, if you look down into the hole where the slow jet sits it will be visible in the wall on the side where it can lead to the main jet. If it does not have that hole, take the plug out.

That is probably why you now need to screw your idle mix so far open.

As far as spitting goes, main causes of carb farts are lean mixture, retarded spark and tight pushrod clearances.
Lean mixture can be too small jets, too low float level, leaking intake manifold, gunk in the carb.
Retarded spark is usually from a worn out auto advance unit in the ignition allowing too much retard at idle.
Pushrod adjustment is what I would check first - it is easy.

EDIT: some earlier discussion on that plug here, with some pics of the hole.
http://xlforum.net/vbportal/forums/a...t-1423900.html

If you look carefully at the Keihin carb diagram in the 70-78 manual, it shows no plug in place, so it must have been something they added later during 76.

Some other discussion about it over on the JJ board here
http://www.jockeyjournal.com/forum/s...ht=keihin+plug
See the last post in that thread. According to him, stock low jet without the plug would have been a 100, so if you run plug free, but have free flow air filter and exhuast, you will probably need to go a size or two bigger to richen up the mixture.
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