76' ironhead problems...!

[desertratguy2001]

Hope someone can help. I recently, finally, picked up my '76 Ironhead Sportster project bike. Drove it home, about 45 miles. I knew there was a timing issue, so after I got it home, I checked out the points, etc., and found the springs off the advance were missing. I got a new unit, replaved it, and it ran again. It was a bit rough, so I thought I'd tweak the carb adjustment.Big mistake. After putting in many hours with it, I barely got it running again. Now, I was told by the previous owner that the carb was touchy. You can't give it ANY throttle until you start it with the choke, and let it warm up a bit. The carb is a Mikuni. Not sure of the model, but I haven't been able to dig up any info on it yet. It has a round cylinder between the air filter and the intake, one small screw (idle mixture?) near the air intake, and a larger srew (idle adj.?) next to it near the center - these are facing towards the front of the bike. The larger screw actually raises that cylinder slightly as you turn it in, increasing the air intake. Also, the engine was supposedly bored and stroked as much as possible, now between 1100 and 1200cc. My questions are, doesn't anyone have any suggestion on how to make this thing run again? Some insight on the carb itself? Maybe even a starting point on where these screws should be set at? It seemed like it ran rich from the get go, not sure if that's normal. One other quick question. The gap on the plugs was a good bit less than the spec gap when I checked them (HD 3-4 plugs), should the gap be the same spec gap if the engine was bored and stroked?? Thanks in advance for any input!

[flathead45]

I got the whole mikuni pdf file on my computer if ya pm me your e-mail I'll sed it to ya

and plug gap is not as big a deal as some might think , if its close , its good enuff

[Y2K]

I'll add that 1100 to 1200cc in not the max,my '75 was taken out to 86cid(a bit over 1400cc) via axtell barrels and truet & osborn stroker kit.
Others of the ironhead persuasion may gasp but I'd get rid of the points ignition and switch over to a high performance electronic ignition.

Y2K :smoke

[desertratguy2001]

Yeah, I thought about doing away with the points, eventually. It's a little pricey, and there's other things I need to do first with it.
ALSO, I forgot one thing I need to add to that first qustion. The point it's at right now, it only runs with the choke on at this point, take it off, and it dies...

[Y2K]

ALSO, I forgot one thing I need to add to that first qustion. The point it's at right now, it only runs with the choke on at this point, take it off, and it dies...
How long was the bike sitting without being run? carbs tend to get plugged up when gas is left to go bad in the carb.
These days with the poor quality of fuel it can happen in just a few months.
If it only runs with the choke(enrichener) on it leads me to think you have a carb that needs to be disasembled and cleaned out real good.
That would include cleaning the jets with welding torch tip cleaners and blowing compressed air through the carb body fuel passages.
I would recomend soaking first with carb cleaner in a coffee can and the carb being submerged in it for a day or two.
Also check the tank for rust and other debris that may be clogging up the screen in the fuel petcock.A rusty tank can be a real PITA and may require a good sealent on the inside to get rid of the problem.
Lots of luck and let us know how ya come out on this.
Y2K :smoke

[dabronco]

I would say the primary jet is clogged. It is very small and if the bike sat for any time at all, it will gum up. Choking it will draw fuel through the main jet. And yes you are correct, the small screw is the idle mixture, the larger one is the stop for the throttle slide, (idle speed). You can try all sorts of things but the only way to really clean the primary jet is to remove the carb, the float bowl, and the jet. When removing the jet, don't just assume that the first brass jet closest to the manifold side is it. after removing that one, look very closely into the hole and see if there's another jet deeper in the hole. THAT is usually it. Spraying carb cleaner into all the orafices thinking that will do the job, is not a good idea as it will usually eat the o-rings and other rubber parts and that's not good. Disassemble the carb and THEN you can spray out the passages. Also when you set the idle jet, seat the needle GENTLY so as to not jam it in the seat and snap it off, then back it out 1 1/2 - 2 turns to start with. You may want to look at the idle adjust screw first and make sure it comes to a nice point and hasn't been snapped off in the seat already.

[flathead45]

did ya get it ????? I sent it out for ya , hope it helps

[desertratguy2001]

Thanks for all the tips, I'll keep you posted on it. (got it, flathead45 - thanks!)

[desertratguy2001]

SUCCESS! Thank you. The specs and info really helped, and the tip about a blocked jet led me to actually find a semi-blocked jet. thanks again, and I'm sure I'll be back soon with many more questions on this scoot!

[72 Ironhead XLH]

I still prefer a "Tillotson",easier to service and maintain.A 40 micron filter is what all carbs should be using,not something that only strains out gravel sized debris.

[desertratguy2001]

I stand corrected. It ran for 5 min. off the choke. After that, no way. I found gas bubbling up as I removed the air filter and looked in. I found that a "fuel retaining cup" that goes around the main jet is missing. Seems like that was it, huh? Well, I put the original carb back on (Keihin - came with the bike in a box), and I've spent many hours trying to get it to run at least with that till I can track down that part. Problem is, I'm getting the same kind of problem!!! Not giving it ANY throttle, I get nothing without any choke, and the middle postion or full choke I get about 3 seconds then it dies. Looking in the throat, I see plenty of gas, and pulling out the plugs, they are plenty wet with gas. What the hell is going on here?? The float is at the correct level, I got a kit for the carb, and there's no overflow form the tube either, just very wet inside - using absolutely no throttle. I'm at the point now that I don't even want to see this son of a bitch ever again...!!!!

[Irondrake77]

Just a suggestion, maybe go for the S&S super E carb. I know it get's talked up alot on here, but it's becuase it works really well, and with very few to no headaches.

[desertratguy2001]

Any idea why this is happening, or where all this gas is coming from? (I've been toying with that S&S carb too, just wondering if I'll have the same problem, or if this bike is even worth it...)

[Irondrake77]

I had the same problem with mine when I first got my bike, but after the carb got a good scrubbing, it worked fine, and if that's the only thing thta's giving you a problem, then your in good shape just be persistent, eliminate the small problems one at a time, and you will eventually all add up to a well tuned carb and bike

[desertratguy2001]

Thanks, man. I appreciate the suuport - just gets a BIT frustrating when you try for hours and hours and end up where you started! Take care, I'll drop a line when I square this pblem for good!

[Sleevedfreak]

DUDE DONT GIVE UP! I have chased my tail around for a few months with a starter problem, and just when I think I got it bam it acts up again...before that it was a carb problem...I got out the S&S E shorty carb and runs like a champ....(well when I jump the starter with a screwdriver) but in any case you will overcome this "hickup"

[dabronco]

Mine runs a Keihin butterfly carb and works fine. When you had the bowl off, did you see a black plug in the hole where the pilot jet is? It needs to be there. In the idle circuit the fuel is drawn from the main jet siphon through a bypass hole,(above that plug), and thru the pilot jet. Also check right next to the idle mixture screw, (toward the a/c) and make sure the 1/2'' disc plug is there and you don't see exposed fuel passages. They drill the fuel passages thru that opening and then seal it. One good backfire with the throttle or choke closed will blow that plug out and it will do EXACTLY what you are saying. It happened to me...at night. Luckily I found the cap and pressed it back in, then permatexed it so it wouldn't (hopefully) come out again!

[rob76xl]

have you checked the plug wires and coil? lack of voltage at the coil or crappy old plug wires can seem like a carb problem. old coils can go bad too. i had an accel on mine from a previous owner, and after replacing it with a stock replacement (and wires) it ran better than ever before. when a coil is going south, engine heat (and it's own heat ) will allow it to work for a while and make for really hard starts after the engine heats it up. same for the wires from the timing assembly, heat up and old wire that has been fried before, and the spark can dissapear. sounds funky, but if the plugs have gas on them, maybe the spark isn't lighting up your fire.
just throwing out another possibility

[desertratguy2001]

Yep, both plugs are in place. And Rob, I did check for spark - looks good on the plugs, I also changed out the pionts (regapped) and advance unit (one spring was missing when I got it, and it was a little worn...). I also tested the coil with an ohms meter, and it matched the specs in the book. I'm really at a loss here...

[75oldschool]

sell the peace of s--t and get a new one.fourth time on rebuild not this time sits in back of garage and thats were it will stay untill i find an as is buyer for down payment on a new bike no riding this summer a bunch of bulls--t! just watch others as they go by. old is good but learning new is better.:bump

[rob76xl]

ok, how about these ideas.
your idle mixture screw was tightened down to the point that it was totally distorted. it pours gas into your engine like a bucket. adjustment is not an option if the needle does not seat.

or... as dabronco said, there is a plug on the underside of your secondary system that isn't in place. so it is sucking straight from the fuel bowl again drowning the engine.
Though, i have an early keihin that has no plug, but also has no feed hole from the main jet draw either. they took a long time to sort those carbs out.

somebody did a "bubba" on your main/secondary or idle circuit. dirlled it out so they could use it as a drag bike, or something like that. you can't put it past Bubba to try to retrofit a holley carb jet into just about anything

last idea in this vein, you bought the bike from iowa and brought to your mountain hideaway. increase the altitude by 5000 ft and the thing will be jetted so very wrong.

just ideas. hope they help.
rob