Ironhead 27494-81 carb on an ironhead 1979

[chaz]

Im getting the Ironhead running again, but think Ive got fuelling problems.
Its got a 27494-81 carb, I think from a Big Twin which is 38mm. the stock Iron uses a 36mm one I think.
is there any way to work out jetting for the carb? want to keep it as its fairly new not worn.
current jets are 80 on the bottom float , 170 main and 88 pilot.
the other marking on the carb is B78KVJ28

[rokytnji]

I'd keep the main and go down on the pilot.
68 instead of 88 on the pilot.
Jet set helps.

What kind of pipes we talking here? If drags. I use lollipops for back pressure.

There are other ways to tune in pipes. Like baffles or slip on mufflers.
So that is why I ask.

[rejeanprimeau]

Does the old jet from the removed carb fit your new ones? Try that first.

[80HDXLS]

If I am reading Sportsterpedia correctly the 27494-81A was used on a FLH 80 classic.
Sportsterpedia listed the jets as 165 and 70.
What kind of fueling problems are you having?

[chaz]

thanks for the replies, Im using a different browser as Chrome wont allow access to the forum??
its on standard Harley pipes with the name stamped into them, its the only carb I have at the moment so will look at my spare jets and see if anything useful.

the only problem at the moment is it wont keep running, IT was ok but developed a mis/spit back a few months ago. Ive checked valves, and a complete rewire as old loom had burnt parts and a relay had gone bad. Now I use an easy start to get running but thats all it will do, possibly due to not being used for months and bad ethanol based fuel its using.

[80HDXLS]

There are some really smart guys on this forum who know more about carburetor diagnostics than I do. For what its worth I would clean the carburetor if it has been sitting a long time, and change the jets to 165 and 70 and see what happens.

[Ferrous Head]

You can chase your own tail for months with these things if you just guess at solutions.

So often the real problem with your carb is in the electrics. Or something else.

Break it down and approach it systematically. Do the simple cheap diagnostics first.

1. Compression
2. Ignition and timing
3. Carburetor.

You need a couple of cheap tools to do the basic diagnostics. Buy, beg, borrow or steal them. Guessing is not a plan.

1. Compression gauge. Under 50 bucks, learn how to use it properly.

2. Normally I would say check this next. But with an engine that has electronic ignition and doesn't run this gets difficult to do. So maybe 3 first.

3. "Fakes S&S Super E from eBay (under 50 bucks) order one pre jetted for your engine (year of the bike and model eg, 81 Sportster.

If the compression is ok and the bike still won't run with the fake S&S you know the ignition unit is the problem area.

You now have $100 worth of diagnostic tools and the typical mechanic would have charged you that much to tell you as much as you now know.
(You also have a better carb to run on your bike.)

[chaz]

Ive got more tools than Im ever going to need, I even made my own plate for holding the gearbox on the 1988 evo sportster, only used once.
compression test both cyls at 140psi, yes Ive got two testers.
Its currently got points fitted, just the single setup.

will look for jets, not easy to find here

[John Harper]

You might try a squirt of starting fluid to check for ignition. If there is spark, it should be apparent. That's a quick way I check my friend's dirtbikes if they have a starting issue. But, since you say it starts, seems like ignition is at least working.

John

[Ferrous Head]

the only problem at the moment is it wont keep running, IT was ok but developed a mis/spit back a few months ago

OK, Compression is ok, that's good.

Now I use an easy start to get running but thats all it will do,

By "easy start" I'm assuming you mean something like Aerostart, ether.

And by "that's all it will do" are you saying it will sit and idle until the cows come home ? Or it dies as soon as you open the throttle ?

Have you checked for intake manifold leaks ?

Are you sure the advance mechanism is working correctly ?

Does the carb use a VOES ?

Have you checked fuel flow through the carby ?

It sounds as if the carby has been on for a while and you recently started having problems. If thst's true I would do the fuel flow test first. Simply pull the drain from the float bowl and measure how much fuel flows through in 1 minute.

If the carb has been on the bike and working until recently jet changes are unlikely to affect this. Unless of course the inter is blocked.