Poor sparks on front cylinders

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MadDogRoger
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Poor sparks on front cylinders

#1 Post by MadDogRoger » Fri May 07, 2021 8:34 pm

Hi all,

I have a problem with my '85 RD500. I have poor sparks on the two front cylinders. Poor meaning, the left one will fire probably 50% and the right one about 10%. The left exhaust pipe will get warm (not hot) relatively quick, but the right one will take a long time to get only luke warm.
What have I done so far?
- changed the ignition coil (including leads) on the front cylinders with new aftermarket one: no change.
- new spark plugs: no change.
- new spark plug caps: no change.
- measured the pickup coil, at 127 Ohms it is within spec: 112 Ohms ±20%.
- measured first source coil, spot on at 127 Ohms.
- measured second source coil, also spot on at 18.6 Ohms.

The bike will start and run. If I pull off the spark plug cap, while the bike is running, from either one of the front cylinders, I hear a change in note from the engine. Clicking it back, engine note changes back. Riding the bike is possible but I'm lacking power (obviously). Also on the exhaust from the front right cylinder there will be moisture (gas and oil) coming from the exhaust after a ride. It is wet. The left one not.
If I go by the book it's a faulty CDI.
Thinking logically about the problem: two cylinders are running fine, so the "common" parts are working, meaning pickup coil and source coil. The fault has to be after where there is a split between front and rear. This is in the CDI: one cable goes in and two come out. One for each ignition coil. So starting from those two cables there could be a problem or inside the CDI itself.
With the engine running, I have the impression that fiddling with the wires coming out of the CDI until the connector, influences the running of the engine (better or worse). I just can't seem to find a position where it's all good and keep it there. So maybe a bad wiring connection. Measuring the wire from the connector to the ignition coil gives met 0 Ohms, no matter how I wiggle it, so that seems good.
What I could do is strip the orange wire for the front cylinders immediately at the exit of the CDI and run a new wire to the ignition coil and see if this helps.

What I would like to know: is there a way to check/measure the CDI? I don't mind replacing a faulty CDI, it's just a lot of money to spent if it wasn't faulty after all.
What also puzzles me is that the front cylinders don't behave the same. They both get the spark from the same "path". If I switch left and right spark caps, the right exhaust will get warmer. So it follows the lead. Why aren't the sparks similar, they come from the same CDI, through the same, new ignition coil


If you have any other ideas, I'm open to suggestions.
Any help is greatly appreciated.

Thanks in advance,
MadDogRoger

silverstrom
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Re: Poor sparks on front cylinders

#2 Post by silverstrom » Fri May 07, 2021 10:05 pm

I've heard of problems like this when the gap between the pickup coil and rotor is too large. You can try reducing that gap a bit and see if spark quality improves.

The standard theory on the CDI is that it works or it doesn't. Weak spark to half of the cylinders would be an unusual CDI fault.

I am not aware of any way to test the CDI other than swapping in another one.

We recommend putting your location in your profile. Doing so may help you find a donor CDI in your area that you can borrow. Either 47X or 1GE CDI will suffice for testing.

MadDogRoger
Posts: 33
Joined: Thu Oct 09, 2014 6:47 pm
Location: Belgium

Re: Poor sparks on front cylinders

#3 Post by MadDogRoger » Sat May 08, 2021 8:03 am

Thanks Silverstorm for the suggestions. I've added my location to my profile (Belgium).
I'll have a look at the gap between pickup coil and rotor.
This morning I checked the ground cable from the ignition coil but it also read 0 Ohms, so that isn't the issue.

"Weak spark to half of the cylinders would be an unusual CDI fault." I know, that's what's puzzling me. I'm not an electrical guy, so I'm having a hard time understanding the problem.

MK
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Re: Poor sparks on front cylinders

#4 Post by MK » Sat May 08, 2021 12:05 pm

To debug whether it's the CDI or something else you could swap the orange cables between front and rear HT coil (just build some connections with additional cables and crimped connectors)
If that makes the effect wander to the rear cylinders, it's really the CDI.
If not, you need to carefully check the ground connection of the front HT coil (maybe even manufacture a new cable and attach it to a thread on the frame that you freshly re-cut)
Otherwise you could also swap front/rear HT coil to check if it's the coil.

And there's an easy solution that involves the same amount of time / work, but with adding some 10HP:
Get a Zeeltronic ignition and PV controller, preferably the PDCI type which solely runs on 12V and does not need the source coils.
With that 250 Eur box you eliminate generator, CDI and PV controller as a source of trouble AND you gain more performance than with a decent set of pipes.
Bye
Martin

MadDogRoger
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Re: Poor sparks on front cylinders

#5 Post by MadDogRoger » Sat May 08, 2021 8:48 pm

Hello MK,

Thanks for posting a reply.
You said: To debug whether it's the CDI or something else you could swap the orange cables between front and rear HT coil (just build some connections with additional cables and crimped connectors)
If that makes the effect wander to the rear cylinders, it's really the CDI.
I thought about this. Is it actually possible to swap the two orange wires, I mean will the engine still run. Won't it spark at bottom dead center? Do all pistons go up simultaneously? Don't they alternate?

Then about the grounding of the HT coil: If not, you need to carefully check the ground connection of the front HT coil (maybe even manufacture a new cable and attach it to a thread on the frame that you freshly re-cut)
Otherwise you could also swap front/rear HT coil to check if it's the coil.
The front has a new aftermarket ignition coil. When taking off the bracket from the old one, it turned out to be broken so I had to weld it back together. Cleaning all the parts and grinding back the weld I made sure there's good contact there.

silverstrom
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Re: Poor sparks on front cylinders

#6 Post by silverstrom » Sun May 09, 2021 12:58 am

MadDogRoger wrote: Sat May 08, 2021 8:48 pm Won't it spark at bottom dead center? Do all pistons go up simultaneously? Don't they alternate?
Wasted spark system. All 4 plugs fire at the same time, every 180 degrees. 1 and 4 fire at TDC while 2 and 3 fire and are wasted at BDC. Then 2 and 3 fire at TDC while 1 and 4 fire and are wasted at BDC.

When checking for spark you should have all 4 plugs grounded.

MadDogRoger
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Location: Belgium

Re: Poor sparks on front cylinders

#7 Post by MadDogRoger » Sun May 09, 2021 5:04 pm

Hi all,

An update to the story. Beautiful weather today so a great day for testing. What did I do? I disconnected the multi-connector that comes from the CDI. It has nine connections so I made nine "jumpercables". Connected all the 9 pins except I switched the two orange ones. So the orange one that went to the rear cylinders would now go to the front cylinders and visa versa. Start her up: no change, front cylinders still running poorly and not heating up (right one). Great, this means the CDI is OK! This means the short piece of cable coming from the CDI is OK!. This means the fault must be somewhere from the multi-connector to the spark plugs.
So I made a cable from the CDI end of the multi-connector to the ignition coil (so instead of the orange cable) and a cable from the frame to the ground side of the ignition coil. Start her up: no change. Scratch my head. The only thing remaining is the ground from the ignition coil HT side so made a cable from the frame to the ground of the ignition coil HT side. Start her up: no change.
Like I sad before, I'm not an electrical guy but I think I checked everything electrical: changed "good" side of CDI to "bad side" replaced every component after that in the system and still no solution. Maybe the problem is not electrical.
What if the fuel air mixture is way of because there is an air leak somewhere or if a reed valve isn't working properly or a seal isn't working properly?
What other issues could cause poor running on two cylinders?

Thanks in advance.
MadDogRoger

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phildu31
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Re: Poor sparks on front cylinders

#8 Post by phildu31 » Sun May 09, 2021 5:37 pm

Most probably, you have a carb issue : blocked idle jets.
What happens with choke on ?
To check if there is an air leak, you can do a leak down test.

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Re: Poor sparks on front cylinders

#9 Post by MK » Mon May 10, 2021 5:30 am

As fouled plugs are common, I'd have changed to a fresh set of plugs or at least exchanged front/rear.
And you didn't mention, if you exchanged the HT coils between front & rear.

Concerning the term "possible causes" you'll hear a lot of things, that are possible, but extremely rare (like crank seals on the RD350).
I'd like to enhance that with the likelihood of occurrence and rather call it typical.

Surely removing, disassembling and cleaning the carbs is not a bad idea as this is a typical issue on RD500's.

Other typical causes on the RD500 would be piston damages like broken rings, seizures, carbon build up that lower compression. Have you measured that on all 4 cylinders?
Bye
Martin

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Jeff B
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Re: Poor sparks on front cylinders

#10 Post by Jeff B » Mon May 10, 2021 2:20 pm

I had ignition issues that turned out to be a bad ground. Leaky check valves in the oil injection can fill the pipes with oil when it's not running. This is common and can cause the lower cylinders to run poorly.

MadDogRoger
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Re: Poor sparks on front cylinders

#11 Post by MadDogRoger » Mon May 10, 2021 6:02 pm

Hi guys,

another update. Today I measured compression on all cylinders. Every cylinder measured 6.0 bar. All the same within a couple of tenths of a bar. That doesn't look bad to me, does it?

"Most probably, you have a carb issue : blocked idle jets."
I can't imagine that there's anything blocked. When I take out the spark plugs, they are soaking. This time I blew them off with air, cleaned them, dried them and checked again for spark. With the spark plug out, in the cap, against ground, kicking the starter, the bike started and the plug sparked! This was for both front cylinders. The bike actually started with the spark plug out (so on 3 cylinders). The amount of mixture spurting out of the spark plug hole is not normal. In no time the front fender is absolutely soaking. So I think it's getting too much fuel rather than not enough (blocked idle jets).


"What happens with choke on ?"
When I start the bike cold with choke, it starts runs briefly to 3000 rpm then quickly (5-10s) settles at 1000-1200 rpm and choke can be closed.
Reopening the choke causes a change in engine note but not significantly in idle speed.

"To check if there is an air leak, you can do a leak down test."
I ordered a leak down test yesterday and tried it today but I can't measure because applying the pressure (some 2 bars) to the piston at top dead centre, causes the piston to go down and lets the air escape through the exhaust, thus giving me a 100% leakage. Should I put in 6th gear to prevent the engine rotating?

"As fouled plugs are common, I'd have changed to a fresh set of plugs or at least exchanged front/rear."
As mentioned above, cleaning the spark plug indeed helps. It seems they are so wet that sparking is an issue.

"And you didn't mention, if you exchanged the HT coils between front & rear."
The front got a brand new HT coil. Yes aftermarket but the chances of it being bad and replacing it with a new one that also happens to be bad, are very slim.
Besides, with the spark plugs, cleaned, dried, they spark.

"Concerning the term "possible causes" you'll hear a lot of things, that are possible, but extremely rare (like crank seals on the RD350).
I'd like to enhance that with the likelihood of occurrence and rather call it typical.
Surely removing, disassembling and cleaning the carbs is not a bad idea as this is a typical issue on RD500's."
I did a rebuild of the carbs, using original Yamaha-kits. Did have some problems getting the carbs to seal properly (leaking), but they have remained dry for the last year. There's a thread on this:
http://www.rzrd500.com/500phpBB3/viewto ... ab90fc68d5
However there is another thing I would like to mention: fuel consumption. I know, I know, RD's do use a lot of fuel. And I'm not complaining BUT I've never managed to get 10km/l (or 23.5 mpg). Always just below that. The odd thing here is, my first bike was a RD350FII, also known for heavy drinking. I could ride that bike with 10km/l (23.5 mpg in lunatic mode), but also at 25km/l (58 mpg in grandma mode) if I kept it below 6000 rpm, easy cruising, short shifting at 4000 or 5000 rpm. Now I've tried this with the RD500. Filled her up and kept it below 5000rpm but even then: no 10km/l (23.5 mpg). No matter how I ride it, fuel consumption stays the same. Is this normal or is this an indication of carbs not set up right. I used the manual to set up the carbs. All the jets are standard sized. Balancing was also done by the book.

"Other typical causes on the RD500 would be piston damages like broken rings, seizures, carbon build up that lower compression. Have you measured that on all 4 cylinders?"
Yep, see above, measured compression, all the same, all around 6.0 bar.

"I had ignition issues that turned out to be a bad ground. Leaky check valves in the oil injection can fill the pipes with oil when it's not running. This is common and can cause the lower cylinders to run poorly."
Does every RD500 have check valves mounted as standard? If yes where are they mounted. If you say oil injection can fill the pipes, do you mean the exhaust pipes? Shouldn't this burn off after a run? Should the pipes otherwise be drained??
As far as the ground thing is concerned, I checked this by running a new ground directly to the frame but with no difference. Also the bracket of the ignition coil was broken. So I had to weld it and ground the weld flat creating a brand new, clean ground point (haven't painted it yet).

Sorry about the long story. I do appreciate you guys helping me think through this.

Greetz,
MadDogRoger

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Jeff B
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Re: Poor sparks on front cylinders

#12 Post by Jeff B » Mon May 10, 2021 7:16 pm

If you think the plugs are wet with oil you should pull one of the exhaust pipes off (left lower is typically worse than right. See if you can dump any oil out. These bikes all have check valves screwed right into the injection pump.

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phildu31
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Re: Poor sparks on front cylinders

#13 Post by phildu31 » Mon May 10, 2021 7:22 pm

The check valves are in the oil pump, output side.
Seems like ignition system is ok.

To do a leak down test, you must remove carbs and exhausts, close the openings, apply some pressure ( 0,5 bar typically ) and wait a dozen minutes to see if pressure remains.
There must be some threads around about this.
In your case, I don't think this is an issue.

I still suspect that it is a carb issue, but possibly on the rich side.
After checking the carbs, what you may do is to swap the idle jets side by side : swap right front and right rear idle jets, and same thing for the left side.
If you still have the same issue on the front cylinders : well I have no more ideas !!

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Re: Poor sparks on front cylinders

#14 Post by MK » Tue May 11, 2021 6:25 am

When you rebuild the carbs, what float height did you set?
There's an error in the first Yamaha RD500 manuals that was later corrected.
Can't remember 100%, but I think it was 21, later corrected to 24 mm.
21 is richer than 24 which will affect fuel consumption as well as plug fouling.

Same applies for the idle air jets :
The early models had 1.1mm air jets. This is usually overly rich and they had 1.4 mm in the later models.
For my bike I found 1.3 to be optimal.

And then the main jets : Are they new #195 and original Mikuni? If yes that's likely too rich and you need #165's.
Why? Check out my measurements
http://rd500lc.free.fr/technics/jet_size_en.htm
Bye
Martin

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Re: Poor sparks on front cylinders

#15 Post by silverstrom » Tue May 11, 2021 3:36 pm

I thought the poor spark issue still existed. Or has that been ruled out?

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