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98 MXZ wont run - Carb Settings - Any other ideas?


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#1

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Posted 02 December 2007 - 11:23 AM

Does anyone know the factory settings for the Carbs on a 1998 MXZ 500?
Air Screw, Jets, Needle Position, etc

I have been have trouble with this sled for ayear and need to get it back to a good starting point.


Here is the issue...

It starts fine when I install new plugs. The issues arises after the sled cools down and I try to start it again. It will run for about 2-3 minutes then one cyclinder drops and it dies. Then I cannot get it started unless I replace the plugs. Recently I have checked the carbs (cleaned them).

Cleaning didnt help.

Still the same issues. Today replaced both plugs... Ran for 3 minutes.. One cyclinder dropped... I checked to see which cylinder (covered the carb)... was the PTO side. Then I switched plugs from side to side and fired it back up... the dead cylinder moved with the plug... Go figure.. (The plug is still silver nothing build up on it - only ran 3 minutes).

I could see getting 1 plug that had issues... this is the 5 set that I have replaced and always the same results...

Any ideas?

At the moment. I just want to get the carbs back to "factory settings". I apologize if this seems scattered... Just frustrated with this.. Been trying to get it corrected for a while.



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#2

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Posted 02 December 2007 - 01:39 PM

http://www.dootalk.c...p;#entry1444228

I have had some issues with my 98 mxz 500 as well. the above link is to the topic and responses i had. Hope this helps. It sounds like there are still carb issues causing plug to foul.

#3

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Posted 02 December 2007 - 04:03 PM

http://www.dootalk.c...p;#entry1444228

I have had some issues with my 98 mxz 500 as well. the above link is to the topic and responses i had. Hope this helps. It sounds like there are still carb issues causing plug to foul.



Thanks for the link...

Been plaing with the machine for a while today. I found something else that dont make a whole lot of sense.

I set both carbs back to where they should be... Started with new plugs ran fine, got back let it idle for 2 minutes (needed to re adjust idle). It dropped a cylinder so I pulled the plug cap off to see which cylinder dropped and it started to fire on both. What I found and it makes no sense to me is that if I place the cap on the plug (or the wire directly) it does not fire. If I hold it away so that it arcs (about 1/2") it starts firing again on that cylinder (Both cylinders).

Anyone heard of this? Is it the coil? The wires? (Don't make sense that it would fire if it arcs and not direct contact)

#4 L.R.TnT

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Posted 02 December 2007 - 05:23 PM

Thanks for the link...

Been plaing with the machine for a while today. I found something else that dont make a whole lot of sense.

I set both carbs back to where they should be... Started with new plugs ran fine, got back let it idle for 2 minutes (needed to re adjust idle). It dropped a cylinder so I pulled the plug cap off to see which cylinder dropped and it started to fire on both. What I found and it makes no sense to me is that if I place the cap on the plug (or the wire directly) it does not fire. If I hold it away so that it arcs (about 1/2") it starts firing again on that cylinder (Both cylinders).

Anyone heard of this? Is it the coil? The wires? (Don't make sense that it would fire if it arcs and not direct contact)

Thats goofy, Well I would change the plug boots. Just keep screwing the air-fuel screws in untill it stops fouling plugs, if that doesnt work bring down the needle 1/2 a clip. you should have a spacer underneath your clip, pull it off and stick it on top of the clip and put it back together.

#5

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Posted 02 December 2007 - 05:26 PM

u know that both carbs are set dif? there suposed to be...

try new coil wires, if that dont work try coil, if that dont work cdi

#6 L.R.TnT

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Posted 02 December 2007 - 05:32 PM

u know that both carbs are set dif? there suposed to be...

try new coil wires, if that dont work try coil, if that dont work cdi

Only the Main jets are differ, the mag side (nearest the pipe) is a little leaner because it runs hotter because of the heat on both sides. Needle settings, pilot jets, and air-fuel screws are set the same because they are used at lower RPM which means less heat, they are only differ when the carbs are drawing off of the mains at high RPM.

#7

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Posted 02 December 2007 - 05:46 PM

Thanks all for the suggestions.
I will have to get new caps and wires.


Here is a pic of the sled.
Posted Image

#8 est142

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Posted 04 December 2007 - 04:43 PM

stop moving plugs from one cylinder to another.keep using new plugs on the cyl in question. check compression. i would say either bad crank seal on pto side cylinder, or bad secondary coil. when the pto side starts to drop out, try spraying some starting fluid between the back of the clutch and the crankshaft output area. if the motor picks up, the seal and bearing are probably done. If not, I would try a new secondary coil.

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Posted 05 December 2007 - 10:42 PM

This problem is exactly the same as i'm faceing right now. It just happend. when i pulled the plugs off the pto side that is black "too rich" and my mag side was rich but not nearly as bad. i will be pulling it apart in a few days.

#10 mustardbucket1

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Posted 05 December 2007 - 11:32 PM

Pulling the cap off partially is an old trick used to clean out a fuel fouled cylinder that my uncle showed me back in the 70's. What this does is drastically increases voltage to the plug, forcing it to fire where it normally wouldn't. I would think if the plug in the cylinder in question is wet, it's a carb issue (perhaps leaking needle/seat or plugged air jet) or a low coil output to that plug. <_<
'03 Spring MXZ REV X 800-45th production REV made
'97 MXZ 670
'80 SRX 440
'80 TX-L Indy340
'74 SM 292
'68 Super Olympique
if it ain't broke, Richard around with it long enough and it will be

#11

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Posted 06 December 2007 - 12:12 PM

do these carbs have an air jet?

#12

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Posted 06 December 2007 - 08:10 PM

do these carbs have an air jet?


I am not sure I know what you are asking about. There is an air screw on them for adjusting low 0 - 1/4 throttle air/fuel mix.
They are 38mm Mikuni VM carbs.


Here is an update for what I have found:

1) I did get a new cap for the plug... didn't help.
2) It is the Mag side and not the PTO.
3) the plug(s) are not black at all when I pull them out. Just wet. (Typically)

Is it possible that one side of the coil could not be producing a high enough voltage?
I'll have to check compression on the cyclinders.

I am begining to think that I should just take it in to get looked at by a dealer... Just kills me to pay $$$$ especially when I think it is probably something simple enough to fix on my own.


Again thanks for the info and ideas...

#13 700ditchbanger

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Posted 06 December 2007 - 10:26 PM

Try the trick that est142 suggested with the starting fluid. Compression test won't tell much for a seal problem. I currently have a 99GT500 in pieces after a pto bearing went. A slow death, not putting out full potential, fouling plugs, occasional strange sound from pto side of engine. Looking on ebay for cranks or crankcases for this engine, you will find it is always a pto bearing that went.

#14 ~~XpS~~

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Posted 06 December 2007 - 10:49 PM

Check the needle and seat in the carbs....

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#15 mustardbucket1

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Posted 06 December 2007 - 11:56 PM

do these carbs have an air jet?

Sorry............ it's still early in the season and it was late in the night when I pondered your inquiry. I meant air screw. These can get glazed over if the carbs dry out repeatedly.
How does it run outside the idle circuit? If it cleans out above that it's most likely in the idle circuit of that carb. Did you clean out the .020" or so dia. passage at the bottom of the bore of the carb near the slide? This tiny, easily contaminated hole activates the idle circuit. I always pass a stripped twist tie through them followed with aerosol carb cleaner with the straw extension when I'm going through a set of carbs.
'03 Spring MXZ REV X 800-45th production REV made
'97 MXZ 670
'80 SRX 440
'80 TX-L Indy340
'74 SM 292
'68 Super Olympique
if it ain't broke, Richard around with it long enough and it will be