Engine missing

[RobW96]

This is for my 48 fully restored Chief.



Earlier this year, The bike started running rough to find that the rear cylinder was not getting hot, so I changed the rear plug. This corrected the problem for the 5 mile ride I took. Later that day I tried to start the bike and couldn't. With some help come to find that the coil has very low spark, and the high speed needle had separated from the adjustment knob. Replaced the coil and the needle and got it running pretty well that day. I rode it again a few days later for a 20 mile ride (still breaking in) and it would backfire and surge a little bit. Maybe better described as missing. But thought maybe it was from the carbon buildup from the rear cylinder problem. Yesterday tried to go for a ride and the bike was missing and had an sporadic visual exhaust a darker color. Riding it turned into a bucking bronco ride. I have tried adjusting the needles to the point that the high speed was less than a full turn out without improvement, and the low speed leaned to 3 turns out without improvement.



I returned to the garage and started checking it over. Low speed needle at 4 turns out. High speed needle at 1.5 turns out. All wires are good. replaced dist cap condenser and rotor. Pulled both plugs to find them covered in black soot. Replaced the plugs and it ran well for a short time and then started missing again.



The fuel is 87 octane and new.



I am at a loss as to what to do. the bike has less than 250 break in miles on it. I am a backyard tinkerer, so any advice is appreciated, but a good mechanic would be appreciated. I am in Ashtabula county, Ohio.



Thanks.

[pisten-bully]

Rob, part of what you describe sounds like a timing issue, or another part sounds like a bad plug wire. If it were me I'd recheck and/or reset engine timing before going any further.

[T. Cotten]

Rob!

Never does only one thing go wrong at a time, but...

I always suspect an evil manifold leak anyway.

Please bubble-test your assembly as discussed at httpl://virtualindian.org/11techleaktest.html

If you do not get bubbles with a regulated air supply, then we can go on to other things.

Although I am not a gambler, I would wager that you would find a leak to the front cylinder, and over-enrichening the carb to accomodate it fouls the rear.

Good luck!

....Cotten

[RobW96]

Sorry, forgot to mention replacing both spark plug wires.

[RobW96]

Cotton,
Thanks for the info. I will try this the next time I get to work on the bike.

The leak you talk about will foul both cylinders or just the one that doesn't leak?

[T. Cotten]

Rob!

Vacuum leaks are evil.
The only leaks that behave the same are the ones that keep the motor from starting at all.
Some go totally un-noticed until they burn a hole in a piston (and then folks blame the piston...)

No leak, no matter how small, is an acceptible leak.

Once the bubble-testing diagnostic shows the manifold assembly is air-tight, we can go on to other things; As I posted, never does only one thing go wrong at a time.

....Cotten

[RobW96]

I must be out of town for the next week but will try the test after I return and will post the results on this chat. Thanks.

[cdf6333]

A manifold leak is about the last place I'd look. I'd look for a plug wire touching and grounding on a head fin---been there done that. Usually a manifold leak will cause total non-control or idle, stalling and then racing, not a miss. Plan on replacing the wires and run them outside the frame as a test, before going nuts with complicated stuff. The majotity of the time it turns out to be s simple Homer Simpson duuuuh problem.

[T. Cotten]

The fix is always the last place you look.

(Duh.)

....Cotten

[Skirted]

Is whoever restored the bike available? A competant shop would want to know whats going on and take responsibility to fix the problem as it sounds like something wasn't right from the get-go with so few miles. If contacting those who did the work is not an option, As mentioned I'd start from scratch by setting the timing, points and carb mixture by the book as well as checking integrity of primary and secondary ignition wiring. Costs you nothing then at least you can rule that out. You do have a confirmed good charging system and battery right?

The difficulty in troubleshooting a problem on a freshly restored machine is that instead of troubleshooting with the mindset of something wearing out, you also have to be in the mindset to look for the endless possibilities human error. If you don't have a Repair and Overhaul manual may as well order one now....you'll need it. You should be able to download it free on the AMCA Virtual Library website. Great benefit of membership.

I stumbled on intake leaks at both cylinders on my 48 last year from Cotten's suggestion to check for them. It wasn't the root cause of my problem but after correcting the leak I was finally able to fine tune the engine to the sweet spot. For a quicky check with engine running you can spray some Gumout around the large gland nuts. Any change in rpm means you have a leak which must be corrected. I routinely check mine now at every 500 mi oil change just for peace of mind.

[RobW96]

Skirted,

The shop who restored the bike is more than willing to take it back, and if I don't find the problem will be getting it back. Problem is they are more than a days travel away, so I am trying to eliminate the small stuff on my own.
As stated in the post, carb adjusted to book, filters clean, new wires and plugs, plugs and points gapped correctly. and so forth.

I will try pressure test hopefully tomorrow.

[RobW96]

Thanks for all the advice. I took the bike back to the restorer and discovered that somehow I got E85 gas. Drained the tanks, put in New 91 and it runs great. Don't know how we got E85 as the local brand names only sell "up to 10% ethanol" as labeled on the pumps. Ethanol must go.

[cdf6333]

Great news! I don't think 91 octane is helping you though. Remember that the higher the octane the slower the flame burn. THe purpose of high octane is to allow higher and more efficient compression ratios.

[RobW96]

Cdf, thanks. I will be looking for local stations that offer non ethanol gas in the 87 to 89 octane rating. 91 was what I could get with the least ethanol in it.

[cdf6333]

I've been running the 10% gas in my Chief for quite a few years and haven't noticed any issues. Still a first kick starter, even though I stroked it last year. The only thing I tell people is to not use additives without a lot of positive feedback about the additive. some of that crap gums up your valves in an air cooled engine. And Marvel will constantly remind all your pals riding behind you that you don't care-----mile after mile!