Ignition problems?

[Anonymous]

After tuning the slide carbs on my 79 550 (again,long story :twisted: ) I went for a test.Above 3/4 throttle I experienced surging so hit the kill switch and checked the plugs.1 & 4 are lean and 2 & 3 are fairly rich.I'm using points & condensers and pod filters.The carbs have been jetted with a LEDAR kit,but the needles are still at the stock setting.The mixture screws have been set with Colortune and she runs fine from tickover (110 rpm) to 3/4 throttle.Could this be caused by the timing and/or points gap being wrongly set?If all four plugs were the same (rich or lean) I'd have an idea,but............ :? :? :?

[lhanscom]

I know very little about points, but it sounds like the issue is either an adjustment in the points (check them against the stock settings) or a coil is having issues. If it's the coil it could be voltage to the coil, or the coil itself. You can check that by swapping the coils, and seeing if the problem follows the coils, or the cylinders.

[Anonymous]

Thanks Luke.I was going to check the ignition with feeler guage and timing light to eliminate that,then start swapping things round.You've pretty much confirmed what I thought.If I get all plugs looking the same then I can worry about the carbs. 8O

[KEITH KRAUSE]

It could also be the carbs are out of synch. These VM carbs are VERY sensitive to a poor synch. This would explain the uneven plug reads. Hook up a vacuum tool and if # 2/3 levels are higher than 1/4, that's probably the reason or certainly contributing to the darker plugs.
It can also be a weak spark as you guys have discussed.
With pod filters, YOU MUST raise the jet needles. Surging is the classic lean condition. I'm not familiar with the LEDAR kit you mentioned, but there's no way the stock needles, in their stock position, will be the correct jetting. Even with a stock exhaust, the needles have to be raised at least 1 position for pods. Test the bike at 1/3 to 1/2 throttle and see what the plugs say.
The VM carbs must be re-synched whenever the needles are moved.

[Anonymous]

Thanks Keith.I got a PM from Earl this morning with much the same advice.The LEDAR kit is a British kit designed for running pods,but the instructions never mentioned raising the needles.By swapping the coils & condensers and checking points gaps & timing settings I've ruled out ignition probs.As I told Earl the bike lives outside and I don't have access to a garage or shed so I'm at the mercy of the weather and daylight,so this could take a while.My next step will be to check the float levels (just to be sure) then raise the needles and balance the carbs,Earl suggested running 1 & 4 at slightly higher vacuum than 3 & 4.If that gets the plugs looking the same then I know where to go from there.This really is a black art!
Thanks again,I'll let you know how I get on.

[KEITH KRAUSE]

You say the carbs have been jetted with a "LEDAR" jet kit, but the needles are still at the stock setting. So what is in this kit, just main jets and possibly pilot jets? Did they give you jet needles? Are they tapered differently than the stock needles? Just wondering so we can get your jetting RIGHT. What exhaust do you run?
Be sure to remove the two floatbowl vent lines. Installing pods on these carbs increases the intake and the floatbowl venting can't keep up. The jets can't draw fuel easily. This creates fuel starvation. The increase also creates a vortex in the vent lines which makes more resistance to proper venting. The only practical way to help the venting is by removing some of the resistance. Removing the lines decreases the resistance and of course eliminates the vortex. Removing the lines is a requirement with Dynojet jet kits. Just be careful if you wash the bike.

Earl, what's with the PM stuff ? Someone with your knowledge should share what they have to say so everyone benefits. Are you getting shy or did Dougie PM you first? I get PM's but I always tell the person to keep it public because more minds usually helps.
You know I mean this in a good way.

[Anonymous]

Keith,
The LEDAR kit is new main jets and air jets for pods,and the exhaust is a Motad 4 into 1 that is supposed to need no rejetting which is generally the case.I've used Motads for the last 10 years.I removed the floatbowl vent lines after reading a post here.The needles and needle jets are stock.
Thanks again.

[Anonymous]

Dougie, I sell and repair carburetors for a living. Nothing is more a waste of time than working on carburetors when you have an electrical problem. I suggest you first tune the bike prior to adjusting carburetors. This means set point gap and replace the condensors (hard to diagnose bad condensors). After you have the timing sorted, based on your symptoms, I suggest you may have weak spark on two of the plugs rather than jetting issues (you may have jetting issues but more likely spark). This is because the 2&3 plugs look "rich". What you are seeing on the 2&3 plugs is soot. Since these plugs are fired by the same coil, I suggest you might want to look at the coil as the culprit. First check primary/secondary impedence of this coil and measure it against the other or just swap the coils to see if the problem moves. I suggest that you will probably find nothing wrong with the coil except it has perhaps too little power going to it. The path of electricity to the coils goes through a lot of wire, connectors, the ignition switch and then the kill switch. A dirty connection or switch can degrade the amount of voltage powering the coil. See this mod as a possible fix: http://www.kzrider.com/ignition_upgrade.shtml

Now, if the coils check out, look to the carburetors. It is critical to synchronize the carburetors to the same vacuum height using a manometer. I don't agree that they should be set to different vacuum levels as the bike will run roughly. Find out what you base OEM jetting should have been and your "jet kit" (not familiar with the one you are using) should recommend moving the clip on your jet needle to the 4th position, using one size larger pilot jet and 3 steps up on the main jet... Main jet step sizes go in 2.5 increments so if your stock main jet is a 90 you should be using a 97.5 main jet... the pilot is probably a #15 and you should have used a 17.5... this is my recommendation for pods/free flowing 4 into 1 exhaust.

[Anonymous]

Well,the saga continues.Thanks for the input,Wiredgeorge.First thing I did was to check points gap and the timing,no probs there.I then swapped the coils and condensers,problem remained the same.The connections should be okay as I did a total rewire last year (no problems with charging I'm glad to say),but I cleaned them anyway.However,in one of those 'Eureka' moments I remembered today that I didn't replace the wires from the points to the coils,as they looked fine (famous last words!) 8O .I'll change them the first chance I get as they may be breaking down and affecting the spark at high revs.Following Earl's advice I balanced the carbs with a higher vacuum on 1 & 4 than 2 & 3 without moving the needles,this had the effect of richening up 1 & 4 at high revs but didn't lean out 2 & 3 as expected.So,I'll replace these wires and take it from there.
Once again,thanks for all your help guys.If this tale helps some other poor sod (as well as me,of course!) it'll be worth it.

[KEITH KRAUSE]

There is always the chance that the wires you plan to replace are causing a weaker spark to #2/3. I hope replacing them helps you.
I've never seen a bike run right that has pod filters and the jet needle in the stock position. That's what's causing your surging. Surging is a lean condition and the only way your plugs will read rich at 3/4 throttle,(with your latest synch) is if the mains are too big and you're getting an overlap read.
Mark your throttle and grip and go out and run the bike at a true 1/2 throttle for a few miles if you can. The plugs should read lean. Raise the needles, re-synch and test. Get the performance/color just right and then install the largest main you can, without creating a bog during a 5th gear roll on from about 60 mph.
Because you're using the stock jet needles, you'll probably have to go up to a #17.5 pilot jet and then fine tune the pilot screws (underneath) and then set the side air screws for the highest idle and re-set the idle to 1,100 rpm's with the idle adjuster knob.
Just a thought, are you certain that all four carbs have the same jetting components? Any chance someone installed larger needle jets or?

[earlfor]

Wasnt any great display of knowledge. :-) Just a couple brief comments.

Earl

Earl, what's with the PM stuff ? Someone with your knowledge should share what they have to say so everyone benefits. Are you getting shy or did Dougie PM you first? I get PM's but I always tell the person to keep it public because more minds usually helps.
You know I mean this in a good way.

[Anonymous]

Success! I was right about weak spark,I replaced the wires from the points to the coils and got an immediate improvement.Following Earl's and Keith's advice I raised the needles 1 notch and balanced the carbs.After a 8-9000 rev run for 1/2 to 3/4 of a mile with no problems the plug check showed 1 & 4 as a nice brown and 2 & 3 to be a touch rich,but nothing to worry about.A bit of fine tuning is required but I can handle that at my leisure,the big problem is now out of the way!
Once again,many many thanks to Keith & Earl,without their help I'd still be banging my head off the wall! ](*,) ](*,)

[KEITH KRAUSE]

Success! I was right about weak spark,I replaced the wires from the points to the coils and got an immediate improvement.Following Earl's and Keith's advice I raised the needles 1 notch and balanced the carbs.After a 8-9000 rev run for 1/2 to 3/4 of a mile with no problems the plug check showed 1 & 4 as a nice brown and 2 & 3 to be a touch rich,but nothing to worry about.A bit of fine tuning is required but I can handle that at my leisure,the big problem is now out of the way!
Once again,many many thanks to Keith & Earl,without their help I'd still be banging my head off the wall! ](*,) ](*,)

Glad to hear it!
With several more miles, those slightly rich 2/3 plugs may burn off a bit and look better. Also, when you accelerate hard on a rich plug, the sudden change in temperature can glaze the plug and the previous rich mixture gets glazed on. This can take a lot of miles to burn off before you get a true read of how the mixture really is.
If you still run a tad rich on 2/3 you can try adjusting the side air screws out an additional 1/4 turn. If your filters are K&N ovals you can rotate the 2/3 filters "up" and get a little more air flow. Raising the float height, thus lowering the fuel level, say .02" may help, as long as you're still in the correct range (.90 to .98") I set mine to .94/95" with no problems.

[Anonymous]

Cheers Keith,thanks again!

[earlfor]

I'm happy to hear you're back on the road with a running scooter. :-) :-)
CHEERS!!!! :-)

Earl