New Plugs

[CEPMAN]

Ok, here's the deal.

I have a '92 750, and I was getting horrible gas mileage. The shops around here wanted to charge me a million bucks to look at it, so I decided to get the manual and take a crack at it myself. I took out the old plugs, and they were all loosely screwed in with black tips.

I put in new plugs (I'm proud of myself - the whole idea of removing a gas tank really freaked me out) and now I get better gas mileage, but I've noticed a few negative side effects.

1) The idle is lower, which should be a good thing, but now when coming to a stop light if I don't downshift perfectly, the bike will cut off on me. This kinda sucks if the light all of a sudden changes to green and there are cars behind you.

2) At first I didn't know what 'flat-spots' were. Now I do, because I have them. Mostly in the lower RPM range. It seems like if I have the throttle fully open or close to it that they kinda go away, but if I have the throttle partially open (like I do most of the time while riding) the flat spots are there.

3) Sputtering - low RPM's in low gears cause the bike to sputter. Like if I'm in 1st or 2nd gear getting ready to pull into a driveway or a parking spot.

Does anyone have any ideas?

Nothing was changed except the spark plugs, and all the wires were put back properly. I took the air cleaner out to inspect it, but I didn't change it.

Thanks for any help

[mharrison]

Did you set the gap on the plugs?

[CEPMAN]

i got the plugs from the dealer, and I was told that they were pre-gapped

[GregS]

Did you inadvertently knock off a vacuum line or forget to put one back on from having the tank off?
It kinda sounds like you created a lean condition.

[reconstyle]

Carbs may need to be synced...

[arsenic]

negative, if it ran good before and you just changed the plugs, the carbs don't just go out of sync. You can easily turn up the idel with the adjustment screw. The dealer will tell you the plugs are pre gapped, so will the manufacturer, check them anyway, they are rarley right even if they are pre gapped.

[CEPMAN]

*SIGH*


two days later, and I'm back to where I started.
My other car is a full size SUV (I have 4 kids), and I'm getting about the same fricken gas mileage on the bike as I am in the truck.

When i'm riding, it kinda feels like the engine is either not getting enough gas (which it obviously is with the amount of gas it's using) or not getting enough air or SOMETHING!

I pulled the plugs this morning and they're just as bad as before. Starting with the '1' plug being the darkest, they gradually get ligher as they go to the '4' plug, which is still bad, but is more like a dark brown than a black.

When I took off the tank, I took off three lines from the gas tank and two electrical wires. Is there supposed to be anything else under there connected?

I'm kinda nervous about having to tinker with the carbs. Is there any special tools I would need? If I end up working on the carbs, about how long can I expect it to take for my first time?

[CEPMAN]

oh yeah, and there's a ton of black soot in the exhaust pipe (muffler) if that means anything. It's an aftermarket vance & hines exhaust.

You guys think maybe the previous owner had a jet kit put in that's messing things up? If so, would it be easier to just get another carb to put in?

[md86]

So you're running rich for some reason . You can either get a manual and some tools and get to tinkering , or take it to a shop and let it languish and be charged insane amounts of money for not much .
Basically , you gotta find out WHY it's running rich . I would tend to lean towards worn carb parts . Hey , it's old , and rubber and soft metal don't last indefinately .

[CEPMAN]

I've been looking at the carbs, and everything looks good. Nothing looks worn or bent or dirty or anything like that. There were two rubber seals that weren't seated properly at the top, but would that be enough to cause this much of a problem? I guess my next step is to make sure the pulg gaps are right and try messing with the fuel screws

[87vert]

oh yeah, and there's a ton of black soot in the exhaust pipe (muffler) if that means anything. It's an aftermarket vance & hines exhaust.

You guys think maybe the previous owner had a jet kit put in that's messing things up? If so, would it be easier to just get another carb to put in?

that was my problem, pull the carbs for a cleaning and check the needles to see if they are the shim type (this can be done without removing the carbs if you want, just remove the tank and take off one of the black vaccum cap covers)

replace the jets with the correct jets for your mods (if any)

[GregS]

Your first post sounded like you have owned the bike for a while but a later post seems like you haven't. Some history is in order here. How long have you owned the bike and has it always run this way or when did it start running this way?

[CEPMAN]

GregS
PostPosted: Sun Sep 23, 2007 10:12 am Post subject:
Your first post sounded like you have owned the bike for a while but a later post seems like you haven't. Some history is in order here. How long have you owned the bike and has it always run this way or when did it start running this way?

I got the bike around mid August. It's my first bike. When I got it and started riding, it had some issues, and I took it back to the guy I got it from and he changed the alternator. The only mods I know of is a Vance and Hines exhaust.
the bike was running ok, but getting horrible gas mileage. When i got it, the guy said that he'd just cleaned the carbs, and after taking them off and having a look, I at least know that part is right. The carbs are almost spotless (well, I guess as spotless as you can expect carbs to be)

Everything appears to be in tact. Nothing is bent, loose, torn, broken or anything else that I can see. Could the number of turns for the jets cause this much of a problem? Or is it the jets themselves that need to be replaced with a different size?

The bike was slowly losing performance before changing the plugs, and after changing the plugs, mileage went up very briefly (for about 50 miles) and then went right back to crap. After changing the plugs, I didn't really have any performance gains, other than the idle dropping, but after the mileage went back to crap, that lower idle was causing the bike to cut off on me every time I down shifted and came to a stop unless I kept revving the engine.

[gaillarry]

With poor gas mileage and black soot its time to pull the carbs and tell us what jets they're running and where the needle is set. Also verify the air screw settings.

[CEPMAN]

With poor gas mileage and black soot its time to pull the carbs and tell us what jets they're running and where the needle is set. Also verify the air screw settings.

uhh.....how do you tell what jets are in there? This might be a dumb question for those of you with experience, but I'm just starting out. I've pulled the carbs already, and right now they're sitting in the garage. How do you identify what specific jets are in there?