backfiring through carbs

OK, I'm about to get the parts to fabricate a yics tool and make a mamometer to adj the carbs. The carbs have been ultrasound cleaned and all the jets removed and checked for patency. The float bowls all check via clear tube. Last night it ran pretty well although there has always been a stumble when I roll the throttle but then it accelerates nicely. I've always felt it runs too rich at operating speed.

I pulled the plugs and all looked brown. I then put in Iridium plugs that were black from before the rebuild and drove 1/2 mile. When I turned around to come back and do a plug chop, the bike stalled and would backfire through the carbs on both sides; no fire, just vapor thrown back through the intake (I had not yet put on the boots to the airbox so I could see this happening). It would idle but any gas or load and it would immediately crumble and stall. I had to push the bike home.

Back home, all 4 NGK Iridium plugs were carboned badly. I put the regular NGK in and it again runs pretty well, acting las well as it did last night but there still is backfiring, only to a much lesser extent and the bike does run pretty well. It does run better if I don't give it a lot of gas at once.

With luck I'll have the yics tool and the manomemeter fabricated today. I have the colortune plug and idle jet screwdriver via Len. What I'm not sure is what would be causing the backfire & why the iridium plugs carbon up so fast.

Any suggestions?

Thanks

de ka1j

 

I'm not a fan of NGK's, but you really should put the aribox boots on for your testing, it does make a difference.

 

davstarks is right - with the airbox boots off, your engine is sucking a lot more unrestricted air than normal which really throws off your air fuel mixture.

With the boots off, my thinking is you should have a lean mixture (possibly why you need to give it a lot of gas to get it going).

 

Make sure the spark plugs are the right heat range. The "backfiring through the carbs" sounds like pre-ignition, or knocking. This can be caused by the wrong spark plug, and is very very bad. Use BP7ES. No "R", and no number on NGK other than 7.

Once you put the boots back on, and ensure the right spark plugs are in, let us know how she runs.

 

Thanks for the replies!

While I've been dealing with the carbs I haven't put the inlet boots on because they're a bear to get in just right. I did though put them on and checked how it ran. I'd say it ran better. I'm using a K&N air filter so the flow is pretty good anyway but it's in place.

I used the colortune to adjust the idle and all 4 settings were too rich although #4 was almost OK. I do though need to get the carbs properly balanced. Looks like today has run out of time, Barn Swallows are nesting right beside where I'd work on the bike inside & I don't want to scare them off their eggs so I can only work outside, in the day & it's going to be dusk soon.

As to the plugs, what is in there are the NGK BP7ES The Iridium version does not seem to work so well, at least as well as described in my above post. The Iridium plug number is NGK BPR7EIX.

Perhaps now that the idle is not so rich I can use those Iridium, I thought they were supposed to be better.

But now I'm wondering if the R in the Iridium means it's a resistor plug & if so, I believe I read these boots have a resistor in them... Two resistors in series adds to the resistance so perhaps that is an issue. This # was what several places came up with as the proper Iridium plug.

Hmmm....

 

Yes. The R does mean they have resistors. They are nice plugs, but using those plugs year old on a 20+ is kind of like having a high definition tv with basic cable, at least that's my take on them. I would be interested to know if you notice any real difference.

That is the proper plug. I don't know the effects of the resistor. I know my po had BPR5ES and no boots, and it ran like crap. Easy fix for a bike that cost $600. Changing to BP7ES stopped the knocking immediately and allowed it to start to idle right. The boots made it idle good. I need to adjust the shims before I sync and then it will idle perfect. *knock on wood

Also out of curiosity, did you rejet? This is the first instance I've heard of here of a bike running rich with more airflow. Generally we have the opposite problem. Of course, when I got my bike the plugs were black with no airbox also. I chalked it up to the enrichment circuit needing to be on to make it run better, but now I have my doubts. Now with the boots on and a good idle, my plugs are white but the thing runs like its rich, after experimentation with the pilot valve I have determined this.

Time to do a plug chop, but where to do it in busy SoCal?

 

IF the R means it's a resistor plug AND I have a resistor boot, that's pure ugly. That would explain why I have had so much trouble with these plugs although they are what are called for in the Iridium line. That would cut the available current and volts to the plugs and of course they would carbon up & bog the engine.

At this point since I bought the plugs (Iridium = pricey) I have two choices, ditch the plugs or keep the plugs & ditch the boots & go with after-market.

I do need to check the shims & did buy the shim removal tool from Len as I know I'll eventually need it but at 13K the shims are probably still pretty good.

I took it out this evening to gas up and was able to have no difficulty going up a steep hill in 5th with solid acceleration so it's definitely better than earlier with the Iridium plugs. Again, it might could be that double resistor in series issue that was the bog-down earlier today.

My KA1J name is my Ham Radio call and I so well understand the realities of excessive resistance in a properly engineered circuit...

Double Hmmm...

 

service manual calls for checking them every 5k.

 

Hey!!! I didn't write that!

 

does it backfire anymore?

 

Not after the last 3 days efforts...

I'm pretty compulsive about getting the details right and then following through as best I can. I am though finding new things daily about the XJ that make me question what is the best idea to follow. One thing for sure, using a resistor plug and a resistor boot are not the way to go.

I found three of the the NGK Iridium plugs I mentioned above read 4.5 ohms and one reads 4.8K ohms according to my Fluke multimeter.

Removing the caps and checking them #1 & #4 caps read around 5K ohms and #2 & #3 caps read around 8K ohms. This is the cap alone, removed from the plug wire.

I plugged YICS port, made a mercury manometer and synced the carbs then re-adjusted with the colortune plug.

I went for a 20 mile ride and checked the plugs; all the carbon from before has burned off. I wouldn't say the plugs are bone white but it's closer to that than brown. Zero backfire and it's running really great.

I'll go into some detail in a separate topic.

It was backfiring badly; too much resistance is not a good thing...

 

IGNITION SYSTEM OVERVIEW:

Before we get into the list of components within your ignition system, it may be useful to explore the basics of the ignition design used on these bikes, as this knowledge may help you to better recognize, troubleshoot, and repair performance problems with your engine that you think may be due to these components.

The ignition system actually begins at the left end of your CRANKSHAFT, since the rotational position of the crankshaft determines the position of the pistons and of the camshafts. Obviously, since the purpose of the entire ignition system is to deliver a high-voltage spark at the plugs at exactly the proper instant----meaning, as the piston approaches Top Dead Center of the compression stroke----then the ignition system must "know" what the position of the crankshaft is in order to transfer that information (via electrical signals) to the major components: the PICK-UP COILS, then onto the TCI UNIT, to the IGNITION COILS, via the PLUG WIRES and through the PLUG CAPS and finally, onto the SPARK PLUGS.

But it all begins at the crankshaft, which has a flat metal ROTOR DISC bolted onto the left side snout, and which hides under the left side, round "Oil Pump Cover" (also called a "YICS" cover on YICS-equipped engines). This spinning rotor disc has a small magnet embedded within it's outer tip, and as that outer tip rotates past the fixed magnets within the PICK-UP COILS, the interaction of magnetic fields triggers a small voltage in the pick-up coil wires that lead to the TCI UNIT.

Note that since the rotor disc is fixed in position and spins along with the crankshaft, this rotor disc "knows" the position of the crankshaft at all times. And since the pick-up coils are bolted in place, and are thus stationary, whenever the spinning rotor passes by a fixed pick-up coil, and thus triggers it to send a voltage signal to the TCI, in this way the TCI unit thus also "knows" where the crankshaft is, rotationally-speaking, and thus where the pistons are in relation to Top Dead Center and when their spark plugs need to be fired.......

Also note that since there are only two pick-up coils for your four-cylinder engine, that each pick-up coil is actually providing the "firing signal" to the TCI unit for two different cylinders. In these engines, one pick-up coil is responsible for sending the signal to the TCI that eventually leads to the spark plugs firing off for cylinders #1 and #4 at the same time, and the other pick-up coil sends the message to the TCI unit to fire off spark plugs #2 and #3, again, at the same time.


Although this may seem odd at first, the mechanical arrangement within the engine of the crank throws, and thus the rods and pistons, as well as the camshaft timing, allow this situation to proceed without a problem; in fact, when one of these "paired" cylinders (for example, #1) is approaching Top Dead Center of it compression stroke----and thus is in need of a spark from its spark plug----it's "mated" cylinder (#4) is also approaching Top Dead Center, too.........but on its exhaust stroke.......and so even though cylinder #4 gets a spark at its spark plug, there's nothing in the cylinder to combust, and thus it's a "wasted" (yet harmless) spark that occurs in cylinder #4.

Obviously, the exact same situation occurs in the mated pair of cylinders #2 and #3.

In fact, the whole system is known as the "wasted spark" system, since one of the two sparks that always occur at the same time is "wasted" on a cylinder that is on its exhaust stroke............


Anyway, to continue our journey: when a pick-up coil is energized by the passing magnetic field of the spinning rotor disc, it send an electrical impulse signal to the TCI. Therefore, the TCI unit now also "knows" the position of the crankshaft (and thus of the piston). Using other sensor information.....primarily, the rotational speed (RPM's) of the engine......the computer chip in the TCI is then responsible for calculating exactly when to send a "message" to the proper IGNITION COIL to release it's energy to the proper cylinders. And note that we said "cylinders" (plural), since just like the pick-up coils, one ignition coil also sparks two cylinders at once (part of the same "wasted spark" method discussed above).


The ignition coils use a rather small (12V) input on their primary side to product a large (20,000V +) amount of electrical energy on their discharge (spark plug wires). When the TCI unit determines that "the time is right" for a particular coil to fire, it grounds that coil, which collapses the small magnetic field inside the primary side of the coil, which thus induces a large electrical field in the secondary (plug wires) side of the coil, which then rushes to ground (the plugs are grounded to the head). This electrical energy rushes down the non-resistive PLUG WIRES, through a resistor in the SPARK PLUG CAP, and finally jumps a small gap in the spark plug electrode on it's way to ground, and thus the spark occurs that fires the air-fuel mixture (in one of the two cylinders being sparked at the same time), things go boom, power gets produced, and you're on the way down the road........


Now, What Could Go Wrong?:

Well, remember, all of these components are basically used to transmit knowledge of where the piston is within it's four-stroke cycle, and to be able to deliver a spark at the appropriate time to each cylinder to take advantage of the compressed air-fuel mixture in the cylinder (during the compression stroke). So it sometimes help to understand these component pieces as being mainly responsible for providing this stream of precise information, and the electrical-spark making (at the spark plug gap) as merely being the natural (according to the laws of physics and electricity) end-result of all this information handling and processing.


Now, unless your crankshaft was installed backwards (an impossibility, by the way!) or the camshaft was installed improperly (or if the camshaft drive chain has skipped a tooth----not a common occurrence, at all), then we can safely ignore all of these issues. And since the spinning rotor disc used to trigger the pick-up coils is bolted firmly in place at the end of the crankshaft, it can be ignored for troubleshooting issues.


But the pick-up coils themselves can go bad over time, and even though it's rare, it can happen. No pick-up coil signal out----along their wires to the TCI unit-----means no signal into the TCI unit, and the whole system breaks down. Which means the small wires from the pick-up coils to the TCI had better not be pinched, shorted to ground, or broken internally, or the message just won't get through.


Of course, if the TCI unit itself is defective, then even if it is getting a signal from the pick-up coils, it is unable or unwilling to process the signal, or the signal gets processed incorrectly, and either the signal doesn't get sent to the ignition coils at the proper time, or doesn't get sent at all.


But even if the pick-up coils and the TCI are performing flawlessly---which they usually are----if the ignition coils are not getting enough voltage input to them, or, if they are not able to multiply the small incoming voltage into a much higher output voltage (that is, after all, their main purpose in life), then we have a problem.

Worn-out ignition coils, or coils that perform poorly or get cracks in their outer cases (and thus short out when moisture enters their internal shells), are a common cause of ignition system problems.


And even if the coils are performing properly, if the spark plug wires have an internal break, or an external break, and thus prevent the coil electrical output from reaching the plugs, then nothing good is going to come from all this activity.


Of course, the spark plug Resistor Caps also play a role. They have a tiny resistor embedded within them, and the purpose of the resistor is to provide, of course, electrical resistance to the flow of electrical energy. There are a couple of reasons why some resistance is necessary-----it helps eliminate electrically-generated Radio Frequency Interference "noise" (RFI), it provides a "cushion" against instantaneous electrical energy pulses (which is really hard on small, fragile electrical components, such as the capacitors and transistors in the TCI unit), and it "slows down" the passage of the electricity through the spark plug, thus providing a sort of "electrical Viagra" to spark at the plugs, allowing the electrical discharge (and thus the spark) to last a bit longer (instead of being instantaneous), thus promoting more-better and fuller combustion of the air-fuel mixture.

In fact, outside of the RFI suppression issues, it is the control of this "spark burn time" that is really the most critical issue, especially on bikes that are jetted a bit lean to begin with........as increased electrical resistance in the secondary circuit will increase the spark firing or "burn" time, and that longer burning spark assists in the more complete combustion of harder-to-fire lean fuel mixtures.


But those resistors in the spark plug caps........or in the spark plugs themselves, for those engines that use resistor plugs........do wear out over time. And when they do, their resistance increases, which means that they provide more resistance to the flow of electricity than is needed. So that 20,000 volts of electrical energy, instead of being discharged at the spark plug gap in a rather short (10 milliseconds) amount of time, gets "spread out" over a much longer period of time, and gets reduced in voltage, too. So when plug caps or plugs "go bad", they rarely fail to the point where no spark occurs at all, it's just that the electrical output is being "spread out" over such a long period of time that the energy being created in the spark plug gap is so low that it's not enough to fire the fuel mixture completely (or at all)........and that's what leads to hard starts and poor performance (and reduced gas mileage, too).

By the way, as you may have figured out by now, a spark plug that is contaminated ("fouled") by carbon or oil deposits, or one which has too large of a gap, fail to operate properly mainly because such situation can greatly increase the electrical resistance characteristics of such a plug.........and now you know why that's not a good thing.


A very good review of the issue of electrical resistance in ignition systems can be found at:

http://www.ultralightnews.com/enginetro ... dplugs.htm

Although the above article references the ignition systems in ultra-light aircraft, the same concepts apply to all ignition systems.

 

Thanks for the info!

Seeing as there's 3K or so difference between cap 1&4 And 2&3, it seems as if the caps are degenerating and the resistance is increasing. Seeing as the Iridium plugs are resistor and new, It seems to me like the right choice is to get some non-resistor caps and use those Iridium resistor plugs.

I'm really having fun getting this bike to run as it should!

 

Makes me want to get new caps. They tested within specs, but...for the price...

Does that mean one could get non-resistive caps and use BPR7EIX Plugs? And In Your Opinion, would the plugs make any real difference?

 

If you're asking my opinion (chacal would have a better opinion than mine), I think using the non resistive caps with the Iridium plug would work very nicely; the ignition system would see the required resistance and the plug would disperse the energy well.

Also, I'm thinking that there wouldn't be any noticeable improvement over new but standard plugs. What I would expect is with the iridium plugs, they would last probably for the lifetime of the bike and... I suspect they are less prone to fouling.

Since all of the NGK Iridium plugs are resistor, it seems the use of a resistor plug and cap combo is a bad combo as evidenced by my bike carboning up shortly after putting them in and nothing else being done other than that.

 

I read in a service manual that 1&4 are 5K and 2&3 are supposed to be 10-11K for plug caps. So it's possible that 2&3 aren't good anymore 8k not 10k.

I know i'm going to be dumping my 5k caps in the near future, as it's getting impossible to find non resistive spark plugs in my area. D8EA as opposed to D8REA

 

Typically, as electrical circuit components wear out, they increase their resistance......so those caps probably started out at 5K and have "worn" to the 8K (higher) readings. Some original caps can be taken apart, and the resistors replaced (we stock them) or the small spacer discs cleaned, and that will get them back into spec.