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Old 04-14-2017, 07:26 AM   #1
70FLH
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Default Sportster running hot - Zenith carb

1963 Sportster with a Zenith carb nearly holed a piston and scuffed the skirts badly after a heat seize. Now it is seriously burning oil on the rear cylinder. Of course I suspect ignition timing (not magneto, thankfully) but I want to make sure the carb isn't the culprit. What jetting and settings are correct?

Any input for ignition settings is also very welcome since the manual probably only covers magnetos. Thank you.



Note: Yes, it has been converted to electric start. Case half transplant?
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Old 04-14-2017, 12:35 PM   #2
CookieMonster
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Default Sportster running hot - Zenith carb

Fitting an adjustable main jet seems to be the way to go, mine came with one and it looks like it saved a lot of ball ache.

https://www.ebay.com/itm/172566905285

I referred to this for tweaks:





Which manual do you have?
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Old 04-14-2017, 02:17 PM   #3
joe49
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Default Re: Sportster running hot - Zenith carb

Any cleaned Bendix with out drag pipes won't hurt your pistons, the last ones are the leanest ones. Timing is likely retarded or advance isn't working.
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Old 04-14-2017, 04:04 PM   #4
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Default Re: Sportster running hot - Zenith carb

electric start 63 Sporty? Just curious.
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Old 04-15-2017, 12:28 PM   #5
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Default Re: Sportster running hot - Zenith carb

I have ran Bendix carbs since the early 70's, and never seen one jetted to melt pistons. That don't mean that it has never happened, but the more common problem with the early bikes, and mainly the ones up to the flat band intakes, were the incorrect installation, or weathered old orings leaking at the intake manifold. With both pistons damaged, it is very likely. Did you see the orings when you pulled the intake, or did you just take them off and throw in a box. And, it will make them run hot as yours looks like it ran.
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Old 04-15-2017, 02:42 PM   #6
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Default Re: Sportster running hot - Zenith carb

Quote:
Originally Posted by CookieMonster View Post
Which manual do you have?
I have just gotten hold of the '1959 -1976 V-Twins XL XLH XLCH 900 & 1000 service manual' so it should cover all the different kinds of ignition types.

Quote:
Originally Posted by dbkp View Post
electric start 63 Sporty? Just curious.
Yeah that is strange. What I've been able to gather so far is that this must have been a difficult and costly modification if it is legit.

Quote:
Originally Posted by shovithead View Post
Did you see the orings when you pulled the intake, or did you just take them off and throw in a box. And, it will make them run hot as yours looks like it ran.
Foolishly I didn't check for intake leaks when I took it apart since I was told it was using oil and the valve guides were likely bad (not my bike). Now it is pretty obvious the guides are not the cause. I'll make sure to check the state of the O-rings.
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Old 04-16-2017, 11:43 AM   #7
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Default Re: Sportster running hot - Zenith carb

Whenever diagnosing heat related failures I suspect (and inspect) in this order:

1) intake seals - leaking will hole a piston fast. Were you getting any popping or hard starting

2) main jet obstruction - i've seen more than enough cases of main jet partial clog from tank sealer chips, rust chips, paint, red rag lint (HATE those shitty red rags), etc

3) ignition timing incorrect - if you have points and you don't service them regularly or the position screw doesn't grip nicely the gap and timing can change significantly. If the wiper wears down, the point opens later and your timing is late. Timing weight issues are another common contributor. Service regularly or you *will* have problems. I've had close fitting timing covers and slightly worn travel limit pins result in weights hanging open keeping timing too far advanced. I've also see weights that hadn't been lubed since new that were frozen in position giving incorrect timing. Electronic ignitions area whole other story . . .

4) Valve adjustment - If lash is not set correctly you can have valves hanging open which builds heat in the head fast and can burn valves. Slightly bent or binding valve stems will do the same.

5) lack of oil - makes things run hot REAL fast. Usually will see skirt failure rather than piston top holes. Clean your tappet screen every time you change the oil.

Just some things to think about.

The order of likelihood isn't set in stone, it's just the way I look at it. Checking all of them is the important part.

Jason
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Old 04-16-2017, 04:24 PM   #8
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Default Re: Sportster running hot - Zenith carb

Jason nailed the whole thing up. And in pretty close order of accuracy. Looking at that one piston, it looks like a bad oring, because they almost always eat the rear of the front, and front of the rear piston, due to the direction of the intake into the cylinder, and if one or both of them are bad. Lack of fuel, is usually noticed more on the tops, and sometimes a hole, and others the ring journals disinagrate. But, with motors, and all the little things that can be wrong, it could be any of the things Jason mentioned. And pretty much in that order.....
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Old 04-17-2017, 07:46 AM   #9
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Default Re: Sportster running hot - Zenith carb

Great tips. Thank you all very much! This morning I got around to checking the timing. It was set so that the points started opening (without touching the auto advance) exactly at the full advance mark (line mark) on the crank. Guess that would explain it. I've now gapped it to 0.020" and set it as the manual explains so the points starts to open at the line mark while twisting the timing cam to full advance.

O-rings are looking fine but they could of course still have been installed wrong.

Another thing. When I looked in the crankcase it was nearly 1/3 filled with oil yet the dipstick in the oil tank is halfway between refill and full. Am I looking at wetsumping or is it simply overfilled? Any ideas what the brass valve looking thingy on the oil line is for? Some sort of one way valve?


Last edited by 70FLH; 04-17-2017 at 01:16 PM.
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Old 04-17-2017, 02:42 PM   #10
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Default Re: Sportster running hot - Zenith carb

For the timing being set so wrong, it explains why they converted it to electric start. That thing must have been a real ass to start.

On the oil, it may be over filled, or it may be filled correctly, and just looks like more than it is. When you start the bike, I am sure that you plan on changing the oil. So, drain the tank, and clean it thoroughly. Then, when you start the motor, leave the return line(the one we are about to talk about) unhooked so the oil in the crank case returns to a waste container, as the new oil is pumped into the case. You will see a clear difference, when it old oil is gone, and the new oil starts to hit the waste tank. Then shut it down. Hook up the return line and fill the tank. Constantly keep your eyes looking in the tank, so it does not get empty.

The line in the photo, with the "whatever the yellow thing is". So, with so little to see of what it is, I can say that it is not supposed to be there, if it is a filter, or a one way valve. And that line, in its stock configuration, should come up behind the tank and the battery, and come in from under the seat. It was probably rerouted, because those lines can get real close to the drive chain. But, it will sure look better, and you won't need that piece of leather or what ever that is keeping the line from rubbing on the cap.
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72 XLH
70 XLH
69 XLH
68 XLCH *project*
66 FLH *Daily Rider*
66 Shovel/Pan/Pan
65 XLCH *project*
60 XLCH Doc Dytch*project*
51 FL *project*
42 UL*project*
Non Dated, S&S Panhead with 65 swingarm *project*
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Old 04-17-2017, 03:55 PM   #11
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Default Re: Sportster running hot - Zenith carb

Two more things . . .

1) You can't assess whether you had (or still have) an intake leak by looking at the o-rings. Manifold must be assembled to the heads and tested. Easy enough to do. Make a little block-off plate for the manifold (where the carb would attach) and connect some sort of air nipple or even just plain hole. Get a spray bottle with a little soapy water (not too soapy) and spray the area around the manifold-to-head joints. Apply a stream of air at LOW PRESSURE to the nipple/hole and look for bubbles. Low pressure means around 2-5psi. You could rig something together out of a bicycle pump and an old piece of scrap wood. Seriously. It's worth doing.

2) Those ironhead cases have a transfer valve between the primary chamber and the crankcase. Stock, they have a thin spring steel diaphragm valve covered by a screen. They ALWAYS get stuck open eventually. If your motor is wet sumping, the oil will "disappear" into the primary case. Symptoms are as you describe: Look in the oil tank, low. Run bike for ten minutes and look again, still low. WTF did my oil go? Others symptoms are shitty clutch action, dragging, slipping (yeah, I know, standard sportster clutch issues), etc. Open the clutch adjustment plug over a drop pan. Oil may come gushing out if your bike has been sitting a while.

The fix for #2 is to plug that useless valve. Dig the spring out with a pick. Tap the orifice (think it's somewhere around 1/8" ... been a while since I did one) and install a set screw with red loctite. They sell replacement valves but getting the old one out is beyond a bitch and case damage is a real possibility. It's located near the front sprocket below the center line. You'll need to take the clutch shell, sprocket, and primary chain out to get to it. Fun!

All this is making me weepy and nostalgic for my ironhead. Well, just a little maybe.

Have fun. Always.

Jason
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