Need your help again guys.
My 74 xlh has been fitted with a very good condition Bendix carb with what looks like an adjustable main jet. I put it on the bike and the engine started bogging down when the throttle was opened wide, losing all power. This morning I took the baffles out of the drag pipes and took it for a spin and it flew like a good un. The problem I have is that while tuning the idle no matter what I do it runs rich often fouling the front plug. Compression is good.
Can anyone tell me what size jets were fitted as stock to a 74 xlh ? Also does anyone have any suggestions on tuning the carb ? Does screwing the idle mixture screw inwards weaken or richen the mixture ? And finally, does the main jet have any bearing on the mixture at idle/low throttle or does it only start affecting the mixture at mid to high rpm ?
Thanks in advance, sorry for the daft questions but I'm new to Harleys (been running Kawasaki turbos for the last 20 years)
Pasc.

 

Can't help you with the adjustable main jeet as I've never messed with one.

The low speed mixture screw should be lightly seated, then backed out about 1/2 turn. This'll be too rich, but will allow easy starting. It turns clockwise, or in, to richen the mixture. Make sure the cable allows the throttle plate to completely close. Start the engine and let it warm completely. Set the throttle screw for correct idle rpm: 700 - 900 rpm. With the engine at idle, readjust the low speed mixture screw for smoothest operation and highest rpm. Reset the idle to 700 - 900 rpm. The main jet doesn't have any effest on operation until well off idle. Before that the fuel is drawn up through the tube screwed in from the top of the carb just in front of the low speed mixture screw, and expelled into the carb throat through the series of small holes located below the mixture screw. As the throttle plate is opened it uncovers these holes to allow more fuel in.

It sounds like you have the main jet adjusted close to right for running without baffles. It might be a tad lean, but you can sort that out after getting the low speed mixture correct. If after following the idle mixture adjustment procedure it still wants to run too rich, the needle and/or seat may be damaged. If the seat is trashed, the whole carb is usually good for a paper weight. Also check the float height. If it is too high, it'll cause a too-rich condition, especially at lower speeds. Float height is checked with a 3/16 inch drill bit between the float and carb body. You can drop it to 1/8 inch if needed, though this might cause it to run out of fuel at very high speed ops.

 

Hi Skip, thanks again for the help. One of my plugs went bad yesterday so off I went to the local Harley shop for 2 more. Turned out the previous owner had put the wrong plugs in. They were quite a bit shorter than the correct ones. Replaced them, carb tuned very easy and now the bike ticks over and accelerates like a good un. Just need to sort out my genny now. I'm running a CC solid state regulator (the one with the green and red led's on it. At low revs the red led is lit indicating no output but as the revs get higher both led's light indicating that the genny is putting out but not the correct amount. Any suggestions ?
Thanks again for sharing your info.
Pasc.
Ps. love the photo of your dad on your avatar. Oozing nostalgia.

 

I've never seen one of those particular regulators. I think the first thing I'd do would be to check the connections at the battery and the generator. If they are clean and tight, pull the cover off the generator and check the condition of the brushes and commutator. If they look OK, then the hard stuff starts. Pull the brushes and insulate them from the commutator. With an ohm meter, touch one lead to a generator terminal and the other lead to the generator frame. Resistance should be near infinity. Do the same for the other terminal; again, the resistance should be infinity. There are several more tests but I can't remember the methods and values off the top of my head. Basically, they involve checking for shorted or open field coils and armature windings. If you have access to a 0-20 ammeter, you can hook it in series between the regulator and the battery. With the engine at about 2000 rpm, temporarily ground the field (F) terminal. The ammeter should read about 18 amps minimum. If it is OK, it's probably a bad regulator. If it is low, the problem is usually in the generator. DO NOT leave the field (F) terminal grounded longer than 10 seconds max! It'll fry the generator if you do.

If you think the generator is OK, and suspect the regulator, the MoCo uses the tried & true regulator testing method: Install a "known good" regulator and see if everything is OK! Brilliant, huh?

Almost forgot; do you have the generator idiot light still connected? Is it lit up when the generator LEDs say the output is too low? If it isn't lit up, it may be the regulator's acting weird. If the regulator is bad, try getting an Accel unit. I've found they are generally of better quality than the Custom Chrome stuff. Accel also makes complete generators, and repair kits.

 

I had the same problems on my 74 Sporty, ended up ditching the adjustable main jet and installing a .156 fixed jet...still runs a little rich but better than being too lean. I went to an AC45S plug, they burn fairly hot for a single fire plug and they're half the cost of HD. Fixed the generator problem by cleaning the armature and commutator, and put in some new brushes since I had it open anyway.

 

I recently replaced my S&S Carb for a Bendix and my Ironhead runs a lot smoother at low speeds. However I was also running rich and it would sputter at high RPM. I got my carb new and the main jet is probably a little too big. I had to adjust the high speed screw almost all the way in to get the proper mixture. To answer your question on adjusting the Bendix carb, I will tell you how I adjusted it for my '75 XLCH. The procedure for adjusting the idle is just as Skip described it. The idle mixture screw is the innermost screw. After you gain a smooth idle, the high speed mixture is adjusted by running the engine up through 1st or second gear to 4500 RPM or above. If the mixture is too rich it will sputter or run rough at those speeds. To lean the high speed jet (outermost screw), turn clockwise or in, counter clockwise or out to enrichen. Once your high speed jets are running smooth in all gears and RPMs, you may need to readjust your idle setting. I like this Bendix carb because it allows for easy adjustments for a variety of riding conditions which may be a drawback for people who dont like to tinker with their bikes. Hope this helps.