Sport Bikes banner

1 - 17 of 17 Posts

·
Registered
Joined
·
1,070 Posts
Discussion Starter #1
So I've been working on this '91 zx7 since february, and I had it running yestarday after putting the new sprockets/chain on, and man that thing is fast. I am leaving the shop, its screaming, hit the interstate, and it seems like it lost a little power, Get home, chill, go back out, take a nice little ride around my town, and then I really notice a loss in power, pull over, spray some water on all my headers, and two of them are cold. At least, not hot, they are warm to the touch, but the other two steam the water right off.

Okay, so I have known about the problem. I believe I am getting oil from the valves to my number 1 and 4 cylinders(plugs are oil fouled), but I can't do that repair yet, so I follow the manuals instructions, and put a hotter plug in both, and lean them out a tad, this was last week. Didn't get to ride much, was waiting on new chain, but it was screaming, then last night, it happened again, except this time, it was cylinders 3 and 4 that weren't firing.

I didn't have time to pull the plugs, i will today, but I would bet money #4 is oil fouled again. Before #3 was overheated(i was running a cr8e plug) so I put the original cr9e plug back in.

Summary:
All 4 cylinders had cr9e's, NGK-R
_____#1 and #4 oil fouled, #2 and #3 weren't bad

So I put cr8e's, NGK-R in all 4 cyl's, leaned #1 and #4 by 1/4 turn
_____#1 and #4 still oil fouled, #2 and #3 were overheated
_____So I lost #1 and #4 again, after about 50-60 miles

So I put cr7e's, NGK-R in #1 and #4, leaned those out another 1/4 turn and placed the cr9e's back into #2 and #3
_____So I lost #3 and #4 last night, after 60 miles maybe

Carbs have been cleaned twice since march, the last time was last week. Fuel is getting to the cylinder, and I have compression(can't tell you how much, just using the dowel/plunger thingy). Am I missing something here? Obviously Spark! But I was getting spark for at least 30 miles, probably more like 45, and then I lose power. As soon as I replace the plugs, I am back on all 4's. Like I said I am willing to be money that #4 is oil fouled again, not sure how much more I can lean that biotch out. But #3??? I dont know why it isn't firing, maybe it is oil fouled too, that would be the easy fix(for now).

I will pull the plugs today, and post up my findings, but I am hoping somebody sees something in this long-ass post that is so freaking obvious I will slap myself :bitchslap and yes the plug gap is set appropriately

Thanks for reading all this if you made it this far :cheers
 

·
Registered
Joined
·
487 Posts
now that i read your post a little closer could be lots of things if your getting oil fowled plugs on a 4 stroke engine. maybe valves are not seated properly ????? sounds like a trial error project
 

·
Registered
Joined
·
1,070 Posts
Discussion Starter #5
jim schmidt said:
Aren't those cylinders on the same coil?

Nah, coils are 1+4, 2+3. But, when I got the bike, both coils were bad, but I still got spark on 3+4??? I didn't think that was possible, so I replaced them(with used coils :rolleyes ) and I got spark on all four.

Is there any way the coils on these bikes can stop working after 50 miles, then work again when the bike is cold again? If not, then I don't think they are suspect, because I can put a fresh plug in and the thing fires.

I am about to pull the plugs right now, maybe that will help somewhat.
 

·
second chimp in space
Joined
·
3,344 Posts
You can have the wire/boot fail and the coil still be fine. I've had that happen. Then you can loose individual cylinders. But mine would be worst when cold and moist, and usually the bad cylinder would come back on once the wire dried out from the heat of the motor.

So why are you leaning out the idle mixture? Is that supposed to help the oil burning somehow? It won't do jack at more than 1/4 throttle anyway.

It seems like the problem is oil fouling the plugs. If so, the first thing I'd try is an oil/oil additive that's supposed to help rejuvinate seals. Sure, it's a patch, but it's easier than tearning the top end apart.
 

·
Registered
Joined
·
1,070 Posts
Discussion Starter #7
enos said:
So why are you leaning out the idle mixture? Is that supposed to help the oil burning somehow? It won't do jack at more than 1/4 throttle anyway.

It seems like the problem is oil fouling the plugs. If so, the first thing I'd try is an oil/oil additive that's supposed to help rejuvinate seals. Sure, it's a patch, but it's easier than tearning the top end apart.

Idle Mixture? Not that I am aware of. I was told the screw on the bottom of the carbs(bottom when still on engine) is the Fuel Mixture Screw, and that it controls the mixture throughout the throttle range. Is this wrong?

Anyways, just as I suspected, #4 was oil fouled again, and #3 seemed about the same(overheated) as when I put it in. Will a slightly overheated plug still work?

I am guessing #4 has a whole lot of oil leaking in, cuz #1 is running fine with the hotter plug. I don't know what is wrong with #3, and I checked the coils, they seem fine.
 

·
second chimp in space
Joined
·
3,344 Posts
That is the idle mixture screw, it adjusts the mixture at idle only. Since you've taken the carbs apart, you're probably familiar with the needle/needle jet and main jet, which do 1/4-3/4 and 3/4-full, respectively.

The overheated one might be because it's too lean at idle now.

I'd set the idle mixture back (unless somebody else knows that leaning it out is a patch for burning oil? I never heard of that), and put a new plug in #3. Then see if it's overheated again.
 

·
Registered
Joined
·
1,070 Posts
Discussion Starter #9
enos said:
That is the idle mixture screw, it adjusts the mixture at idle only. Since you've taken the carbs apart, you're probably familiar with the needle/needle jet and main jet, which do 1/4-3/4 and 3/4-full, respectively.

The overheated one might be because it's too lean at idle now.
I never leaned #2 and #3 out, but they might need some "richening".

I checked the book, and it doesn't say lean it out??? Just put in a hotter plug. I will run that my by my friend again.

How hot can you go on the plug? I got 7's in there now. I might pick up a 6 tomorrow.
 

·
King of Oilernation
Joined
·
1,237 Posts
I would start looking a little harder at the ignition/electrical system.
 

·
second chimp in space
Joined
·
3,344 Posts
Have you looked at the spark? Is it nice and bright?

Is it burning oil? Do you see smoke?

If the hotter plug is needed it's just a sign of engine problems. I think you can just keep running it if you don't notice any detonation, if it's too expensive to fix.
 

·
Registered
Joined
·
1,070 Posts
Discussion Starter #12
YammyR1 said:
I would start looking a little harder at the ignition/electrical system.

Thanks for all the advice. I am going through all the components now. Hopefully #3 is bad from something easy(boot). As for #4, i guess im looking at the valvetrain job. I talked to a guy today and said he wouldn't go any further than 1 heat rating away from stock for the plugs. Ive already got 7's in #1 and #4, and stock plugs are 9's, so I guess i better fix the real problem.

Anybody got any good places to buy the stuff i need for the valves? im probly gonna go with stock stuff, I found some performance springs and things, but they are ridiculous $$ wise.
 

·
second chimp in space
Joined
·
3,344 Posts
Depends. If you just want it to run, you only need new seals. There are gasket kits you can buy for around $90 that have every gasket and seal on the engine. Might be cheaper if you find one for just the top end. It's a good deal, since just the head gasket can cost close to that. You shouldn't NEED anything else. If you want to get some extra performance while you're in there, go ahead and get some trick parts, but it's purely optional.

And don't forget to check all components in there to make sure they're still in spec. Like the cam lobes, valve springs, valves. Get new ones if they're out of spec.
 

·
Registered
Joined
·
1,070 Posts
Discussion Starter #15
enos said:
Depends. If you just want it to run, you only need new seals. There are gasket kits you can buy for around $90 that have every gasket and seal on the engine.
That is what I am looking to do for now. I want to ride it, but I dont want to damage the engine. Next year I will be able to add the performance parts, but for now I just want to get some seat time on it.

When i searched for the valve stuff, all I could find was expensive performance stuff, cam for about $700, valves for $300, plus all the other stuff. Where can I find a set of seals? I already have the valve cover gasket.

DissT said:
Had a valve job done lately?
No.
 

·
second chimp in space
Joined
·
3,344 Posts
look for gasket sets.
here's one:
http://www.bikebandit.com/partsbandit/productlist~section_dept_id~1170244~terrain_dept_id~1176461~cat_dept_id~1176704~product_dept_id~1176778~selection_Path~3.asp

though it's a bit expensive and i'm not sure if it's exactly for your bike. Be careful which one you get, because kawi likes to have multiple versions. make sure the number of Rs matches.. I've had that when there were two different zx-750s in 1989...

check ronayers and ebay too. you might get away with just getting each seal and gasket individually.

You shouldn't need any new cams, springs, or valves unless yours are too worn out. Even then, stock replacements aren't too bad.
 

·
Registered
Joined
·
1,070 Posts
Discussion Starter #17
Thanks alot for all the help, hopefully you wont hear much from me while i tear it apart :bitchslap
 
1 - 17 of 17 Posts
Top