Ironhead Sportster Harley Engine Discuss Ironhead Sportster in the Harley Tech & Harley How-to forums; I have a stock 1980 sporty which I recently installed a 38mm Bendix carb with an adjustable main jet. The only mods to the engine are a Dyna single fire ...

I have a stock 1980 sporty which I recently installed a 38mm Bendix carb with an adjustable main jet. The only mods to the engine are a Dyna single fire electrionic ignition and cycle shack muffer pipes. The main problem is plug fouling, mostly on the front cylinder. Both plugs are burning about the same, the rear burning a little better than the front but the front is fouling first. I am currently running NGK B6HS. I have a pair of Harley plugs 4R5 and 4R which I have not tried yet. Both heads were rebuilt about 100 miles ago and installed new stock pistons and rings about 2000 miles ago. I am hopeful the Harley plugs, especially the 4R will solve the problem since it is a hotter plug but looking for some advice. Should I be checking something else? Thanks

Dave

[83XLX]

What sort of fouling do you have - oil or gas? Assuming it's gas, it's running rich for some reason. If both plugs are dark, could be that the choke plate isn't fully open, or the carb jetting/adjustment is wrong, or the air filter is dirty. For the front only, the accelerator pump nozzle might be aimed toward the front cyl instead of toward the center of the intake. Could also be a weak plug wire on that cylinder. Since it's mainly on the front cyl, I'd check the accelerator pump aim and the plug wire first. If there's no problem you can easily identify, I've had good luck with the 4R5G plugs H-D sells. They are much more resistant to fouling.

If it's oil fouling, you probably have a worn valve guide or worn rings. If so, you should see smoke - mainly on startup with a worn guide, and constantly while riding with worn rings. Hopefully, it isn't either of these since your top end was just rebuilt.

Thanks for the response. My fouling is gas. I am not seeing any smoke on start up or while riding. Yes my choke plate is fully open, air filter is clean and the adjustable main jet is open around 3/4 - 1 turn. Good suggestion on the accelator pump, I will check. I believe it is in the center but how do you adjust if it not? Good suggestion on the plug wire, that makes sense. Will install a new set before I install the HD plugs.

Dave

[83XLX]

I'm not that familiar with the Bendix carb, but if it's like the Keihin, the spray tube has a hex bottom on it you can access when the float bowl is off. A small wrench can be used to twist it to aim it correctly. I had a similar problem with my '83, but it was the rear cylinder that was too rich, especially when just riding around town. While installing an Andrews accelerator pump kit, I noticed the pump nozzle shot a stream of gas straight down the rear side of the intake manifold. I re-aimed it to the center and never had another rear-fouling problem. Sounds like you may have an overall slightly rich problem, too. I'd do some throttle-chop plug reading tests to determine which circuits are rich, and make whatever adjustments are necessary. If this happened after a carb switch, it's probably a carb adjustment problem. Good luck with it.

[evoKENevo]

Something else to consider is that if your choke/enrichener and air filter check out O.K. and you're sure your plugs are gas-fouling vs oil-fouling check your initial ign.timing and the advance curve you've selected (if your Dyna ign. provides for that) before you go any further...noting that a slightly retarded ignition will queer your burn time...and if you just lean out your carb to compensate you're just losing power as a result.

As far as spark plugs go...no magic in any of them...however what I've found is that one spark plug brand with the same heat range of another brand (cross indexed) may run slightly hotter or colder due to minor differences in manufacturing. So the only "tuning-secret" I can give you in that sense is to select a brand (any major brand) tune/adjust everything running those plugs...and stick to running with that brand.

Personaly...I've run Champions in just about everything I've owned (right down to lawnmowers & weedwhackers) for decades, simply because they've "been around" so long...I've had no problems with them...a spark plug is JUST a spark plug...and they're readilly available most anywhere.

[frisco-rigid]

Hey Dave

Came back to edit a wee bit..
A 38mm Butterfly carb is on the upper end of Venturi size for a 61" (1000cc) mostly stock motor like yours..
I'm not sure if the OEM Keihin for your motor was 38mm or 36mm but at least it had more adjustability with an inter/low-spd jet..

My early 70's 36mm Bendix, that I ran back then, Does Not appear to have an adjustable position Accel Pump nozzel.. It appears to be pressed in and it's been soo long since I ran it I simply do recall if I ever even tried change it's "shot" position.. But yes, best performance is if it squirts over the Dis-charge Nozzel to mix with the In-coming float bowl charge..
However,, remember,, the Accel Pump Nozzel shoots from Off-Center Rear of the Discharge Nozzel so it just Naturally aims toward the front Cyl..
If your newer 38mm model Accel Pump nozzel also apears to be Pressed in,, be very careful if you attempt to turn it..

I am not a believer in adjustable main jets..

There's only 2 circuits in a Bendix----Idle and Main..
The ONE jet that the Bendix uses runs from Off-Idle to Full-Tilt Boogie..
The Idle mix is most important for starting and Take-off and Tooooo Much pump will give Diminishing returns..

The Bendix was Never a Hi-Perf carb but it is a "workhorse".. I ran mine on shovels and at least one Pan back then..

A slightly rich Idle mix was always preferred in those units..

Be sure the AC backing plate doesn't obstruct the carb breather hole..

Have you checked and corrected the float.? Do you have instructions for this carb.?

Doing a hi-spd plug test will show you a snap-shot of the mix at that particular Rpm.. Tannish in color is a good thing..

Like Ken says,, there is No magic in Plugs,, but diff heat ranges are sometimes necessary..
Especially back in those days,, we Often ran a hotter plug in one or the other cylinder..
And I second comfirming timing,, it must be correct Before A/F adjust..

Just my curiosity----
What carb did you remove and why did you install a Bendix.?
AND-----
Are you running the Dyna S with weights & springs..??
What is your Idle and final timing..
You can adjust both idle timing and curve, regardless of final timing,, in case ya didn't know..