Sudden Poor Running

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My '72 has been running very nicely over the last 5-6 months and started 1st kick. Other than a Pazon ignition module failure that was fixed with a replacement box, the bike has ran really strong. I started using non-ethanol 94 octane gas about 5 months ago which improved the bike's performance as well. The last few time I rode I noticed the bike would cough and stumble in the first quarter mile then clear up and run really well. Yesterday I was riding and at a stop I noticed the idle started to get a little rough and the RPMs started to drop a little. I looked in the tank, my gas was low so I put on the reserve and all was fine. I made my turn and approx. 1/2 mile from my house the bike started to studder, stumble, and felt like the right cylinder stopped firing or was only firing intermittently. I limped it home. Once home I found the bike would idle without issue but at low throttle opening there was a really bad studder and the bike would bog. Once above 3000 RPM the bike would run better and above 3500 RPM it was like nothing happened. I pulled the plugs (BP7ES) and found them to be heavily sooted but dry. I changed plugs with the same results as before, shortly thereafter these plugs appeared much the same as the set before. I started checking the carbs, doing a quick cleaning of the right hand side and went for a ride. Same result. The bike will respond to air screw adjustments but not enough to make any difference in off throttle performance. From there the bike has only gotten worse and now will not idle below 1500 RPM and will develop a stumble at speeds over 3000 RPM. The symptoms are worse the warmer the engine is and will have occasional hiccups through the carbs. There is no exhaust smoke noted (no white, blue, or black). In neutral with a blip of the throttle the bike will want to die. A moderate roll of the throttle makes the engine very hesitant and bog with a slow rise in RPM, under a load at launch it will stumble and try to die. Above 3000 or so RPM in neutral it revs appropriately and briskly. The bike still starts but it takes a few kicks to get it there. Here is a list of what I have done:

Cleaned both carbs - pilot jets are free and open, carbs synced, float levels checked (~3mm below), all joints in manifolds sealed, flange o-rings replaced, no gas leaks, tickles fine. The needles and needle jets have about 2500 miles on them. The slides appear to be some kind of chrome sleeved type. All jetting and needle positions are stock. The bike itself has 3300 miles since a total rebuild

Changed plugs x3 - all sooted but fire good

Checked ignition timing - Sits at ~30* at 4000 RPM, checked the Pazon magnetic rotor and is still in the correct compression stroke location. Bypassed ignition switch and directly wired the battery to the ignition module with no change. Did the Pazon trigger test with no issues.

Battery - charge 12.3v at rest, 11.9v at idle and increases over 13v with RPM climb above 2000 RPM

Coils - Resistance measured at 2 to both coils

Valves - Clearances in spec for a Combat, new gaskets placed on rocker covers

Timing - Strobbed at 28* 4000 RPM initially, advanced to ~30* 4000 RPM with no change noted. Currently at ~30*

Gas - Different can of non-ethanol 94 octane with seafoam added


I tried going through previous threads and have noticed others with some of the same issues. However, most people do not return to tell what they found to be the issue and what was done to fix the bike. I have ran out of ideas and here I am.

What am I missing?

Scott
 
Wire from the ignition to the pick-up, near the engine. The varying RPM can cause intermittent open/short. Rule it out with a jumper.
 
concours said:
Wire from the ignition to the pick-up, near the engine. The varying RPM can cause intermittent open/short. Rule it out with a jumper.


I did bypass everything with a jumper. I think I took that tip from you a while back as a matter of fact.
 
while the old saying that what is initially suspected as being carburation is resolved through electrical solution should always be first respected, the fact that the plugs return to sooty even after replacement makes me suspect that this IS a carb problem

so a question, do the poor running symptoms improve upon immediate plug replacement even if only for a little while?

if so then it has to be a too rich carb mixture problem, no?

if not then I don't know and back to electrical

but if so then attack the plug loading as prime suspect, you have verified the needles are indeed held securely in their cir clips?

so start by backing out the mixture screws some more and lower the needles one notch, so we get leaner and stop the sooty fouling?

if plugs clean up after some runs but poor running remains then back to electrical for selection of final door, intermittent grounds?
 
1up3down said:
so a question, do the poor running symptoms improve upon immediate plug replacement even if only for a little while?

if so then it has to be a too rich carb mixture problem, no?

if not then I don't know and back to electrical

but if so then attack the plug loading as prime suspect, you have verified the needles are indeed held securely in their cir clips?

so start by backing out the mixture screws some more and lower the needles one notch, so we get leaner and stop the sooty fouling?

if plugs clean up after some runs but poor running remains then back to electrical for selection of final door, intermittent grounds?


Will symptoms improve? Marginally. With new plugs it is still hard to start with normal tickling (8-10 kicks with belches and backfires). After warming up I was able to get it to idle near the "normal" air screw settings (1/8th leaner) but it will eventually fade and die. Still slow with throttle response and idles best above 1500 RPM. After 5 minutes of run time the brand new plugs are dry-black soot. I have not intensely checked the needles, but did give them a tug to check seating. Of note: the bike symptoms are still present but not as severe without the K&N air filter.

I'm thinking carb issue with some reassurance from your input, but I don't know how exactly. These are not complicated carbs in all honesty. I hate throwing money and parts at the issue but maybe it's the needle jets/needles? That really crappy response is up to about half-throttle or so. If you want to rev the piss out of it above 3500 RPMs it will do as you please (as much as concentrics will allow that is) and track straight back down without hesitation.

I haven't lowered the needles yet but will do so and report back.

Scott
 
I dropped the needles one notch (only has three) and noted a little improvement in throttle response but not much. Bike will not idle by itself now but will while holding the throttle so it rests at about 1100 RPM. I did notice one of the needles had some pitting/plating loss and both had some witness marks. Nothing to catch a finger nail in though. I did not change plugs for this attempt. I don't have an endless supply and have bought up most that are around at the local auto parts stores.

I ran it without the air filter which resulted in a crack/backfire when blipping the throttle. I put the air filter back on and ran better without the backfire but still has no throttle response. When allowed to idle then die it finishes with a back fire out of the carbs.

Ideas?

Scott
 
Ok Scott,
So what is your present air screws setting out from seated? 1 1/2 turns is stock setting

Next let us maybe verify fuel flow be unscrewing bottom bowls big nuts off with petcocks on, do they pour gas out into wife's coffee cup?

With air screws at 1 1/2 and gas flow verified if issues still persist thinking you ought to take bottoms of both carb off to verify the float spindles are fully seated under the gaskets?
 
Also Scott
Open the gas cap and start and run
Possible air hole is plugged and not allowing gas flow?
 
I had a brain fart and lowered the clip making it richer. I corrected this by taking the clip to the top position making it leaner.

No change. Still won't idle now that the engine is warmed up and the plugs are sooted. Still coughs out the carbs as it dies.

No gas flow issues. Spindles are fine, etc. I did check all of this when I had the carbs disassembled, cleaned, and float height checked. Tickles like a champ.
 
Air screws are 1 1/4 out. 1 1/2 will raise the idle to around 1200 RPM which is the lowest it now wants to go without nose diving and dying.
 
What you haven't told us is if you have since filled up the tank with gas.
And if you have fuel filter(s) of any sort fitted.

If there is not sufficient fuel in the tank, or the filters are blocking the flow,
it may not run well at all.

Its also likely that going onto reserve flushed a whole mess of gunge into the carbs,
which are still blocking a fuel passage or 2 there. Any water in the bottom of the floatbowls
can also make it run like a dog, and this is hard to pick, until you drain it out....
 
I would like to see 13.7 to 14 volts above 2000 RPM. Some of the electronic ignitions can be sensitive to low voltage. Try a stator test.

Slick
 
You checked the float level (dry), but perhaps a failed float is at play here. When you tickle it, how many seconds till it spills over? A sight tube rigged from the bowl plug would tell the story.
 
It is KEY when cleaning the carb and the air circuit that you flush with carb cleaner and compressed air from all directions. This include the pin hole in the throat (critical), the threaded orifice under the body in the float bowl (although this is for gas, it gets gunked up in there), the pilot air intakes around the face of the throat, the airscrew orifice. Blow carb cleaner every which way and witness its discharge throughout the circuits.

Just clearing the air jet hole with a #72 drill or piano wire isn't good enough and can prove to only cause more problems and confusion by loosening debris which will re-lodge itself in a short time. Don't assume its open just because you poked something in it.
 
Duhhh, ever since no lead lean burn gasolines with or w/o booze hit the pumps, there is hardly any tendency to varnish up anything anymore but higher oxygen radical content does tend to react with the zinc in carb metal to create whitish, same as on coaches noses, so no organic solvent will touch this so only acid boil or pure physical poking & scratching can remove the zinic oxide crust. Crust can be stained off white by gasoline dyes and rust and such.
 
I found the problem. But will answer questions folks mentioned.


Rohan:
I did fill the tank with newly bought (who knows how old though) non-ethanol gas and added Seafoam, didn't make a difference I could tell. I don't run an in-line filter but thought maybe my tank liner could be coming loose. Unfortunately my take is a steel '73 model with a baffle type plate just behind the fill neck. I can partially see the petcock stem sticking up but that is as far as I can visualize inside the tank for debris, etc.

1up:
Tried the open gas tank trick, no change.

Slick:
A little low on the charge, has the original alternator so that could be a future project.

Concours:
I did a version of the DogT method using gas to measure the float height. Not as precise but got me in the neighborhood. Tickling takes about 3-4 seconds per side.

Pete:
Hit the passages from all angles as suggested and watched for spray. Assuming it's open just because I poked something into it is good to remember.

Hobot:
Good point, I noticed the threads in one of the jet holders getting as you described with deterioration of the threads. Another future project...

Now for the rest of the story:

The problem were the COILS

After going through everything I went back to electrical on a whim. I had tested the coils free of wires and found resistance to be 2.0 initially. That's within spec, right? Well the bike continuously got worse and I figured what the hell, I had an extra set of coils so I put them on. Bike fired right up, holds idle, revs without stumble, and now runs fine. I retested the coils and they now test at 1.8 each.

I thought coils were either good or bad with no in-between? Thanks everyone for the help.

Scott
 
just bored procrastinating before labor chores and glad it ain't mine this time but have ya checked the sealing of the carb manifold head tightness while always keeping electrical gremlin in mind?
 
Finally a thread where someone reports back on the fix. Scott, as you mentioned, most often the thread is started andpeople respond with all sorts of good ideas. The OP usually keeps reporting while the problem persists, then when finally fixed, rides off into the sunset without ever adding to the data base by telling us what made it go again.

I believe the score for electrical over Carb problems is something like 9,057 to 8 :mrgreen:
Coils can also be OK cold and go bad as things warm up.
Glen
 
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