Spark Plug

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  #1  
Old 04-23-10, 09:19 PM
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Spark Plug

1982 400 Maxim.Right cylinder continues to soot up and foul plug after about 1 minute of riding. I Have: 1- Removed and cleaned carbs throughly 2 times. 2- Put in Seafoam 3- Checked and replaced plugs, plug wires and caps 4-Checked OHMS on coils (they were fine) and even swapped the coils, but the problem remained on the right cylinder.
4- I have replaced the little fuel pump diaphram at the petcock and cleaned the petcock.
5- Fresh fuel

Info: 1-Bike has different sized main jets, apparently this is factory.
2- Bike has idle jets that are different, one has multiple holes, the other has just the one hole, apparently this is O.K. also.
3- I am running NGK D8EA plugs. (per specs).
What should I do?
Change to hotter plug? If so, what number and to both cylinders or just the one that is fouling?
I know very little about this bikes type of ignition system. Points? If so how to check and where are they? It does not appear it has points.
 
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  #2  
Old 04-24-10, 07:21 AM
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I think what you have done diagnostically narrows it down to the carburetor.

A varnished carb more often leads to a lean running condition. A schematic of an '82 400 shows the different sized jets. I can't believe that was on the drawing board for that engine, but an after thought during testing to correct a heatup of the left side. I say left side since it shows that jet with the larger number = interpreting that as being the larger jet.

With this being the case and the right side is the smaller jet, I would look at the fit of the jet, the float (if fibrous for ability to float) and the float valve for that carb. If you are riding it a lot and plan on keeping, I would put floats and float valves on both sides.

As far as the ignition, you already did what I would do in swapping the coils. That has a pickup coil = no points and with an electronic job of some type. You can't rule a wiring or connector fault out of it altogether, but I would suspect the carburetor.

All this is assuming the compression is good and you don't have a cylinder burning oil. An oil burner would put a lot of blue smoke out the exhaust.

Also could you post the complete model. Are there letters after the "Maxim".

Keep us posted.
 
  #3  
Old 04-24-10, 08:13 AM
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Thank you a marbobj! I just have few questions.
I think what you have done diagnostically narrows it down to the carburetor.
Hows that ??
to date we are not informed if the engine is in a working state, to wit, an over tight valve clearance will cause a cylinder to stop working without much white smoke from the exhaust?
I am going to change out the jets and floats. I was reading about putting in the same size jets in both carbs. Any suggestions on what size and where to buy them?
 

Last edited by clavis; 04-24-10 at 08:39 AM. Reason: +thanks note
  #4  
Old 04-24-10, 12:51 PM
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The big thing in an electronic ignition usually falls on the coil or pickup. The coil takes the beating since that's where the high voltage comes from to fire the plug. The stuff, like plugs and wires you have changed out, with new, I assume. You have swapped, side to side, the coil and still have the problem on the same side.

Now, if the compression was bad you could get a sooty plug from lack of compression = the exhaust valve not closing fully. If the intake didn't close the backwash of the compression through the intake would kill the vacuum and the bike would lose that side altogether.

With that said, you still have a sooty plug, and the carbs have been cleaned. Varnish in the jets won't give you a sooty plug, but a malfunctioning float valve will. If the run time on the foul out is one minute, you have a lot of extra fuel going through that side.

As far as jet sizing, if the left side is showing a light brown coloration after a couple of hours of running time, I wouldn't change that jet.

I would check to make sure you have the OEM fitted jets in both carbs and stay there. Normally you jet heavier to performance tune an engine and often that is done with a change in the exhaust or intake = more air flow. Things like compression increases or timing advances, where you can do so, will benefit from richer jets.

If the right side has the OEM jet, that jet shouldn't be the cause of the problem, unless it's gotten loose in its mounting point. The cause is more likely to be the float valve or on a lesser chance, something in the ignition.

*** The different size jets, back to an OEM schematic, I can't account for, except maybe as an overheating remedy.
 
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Old 04-24-10, 03:42 PM
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Thank you! I am going back to the floats. I will put in new factory size jets. I think it must be carbs. It sat for a long time at the guys house, but ran perfectly before that. Really makes you think carbs. They are just so clean. I know the carbs are spotless, but without putting in new components, I can't be sure the carbs are not to blame.
 
  #6  
Old 05-05-10, 07:35 PM
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These are all good leads to follow, but nobody mentioned your "choke" circuit. I believe your carbs have an "enrichening" circuit that adds fuel when activated by the choke lever. That plunger is kept closed by a spring and when you push/pull the choke lever, it lifts it and allows more fuel to flow. You have to unscrew that fitting and make sure it is closing off the fuel flow when the choke is not applied. Good luck!
 
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