hi, this is for a 99 CBR900RR, with stage 1 jet kit, K&N filter, and Yoshimura RS-3.
this bike, blew 3 different set spark plugs in the last 6 month.
is it because my carb is outa sync? if so, how do you sync it, or, where can you get the vacum meter?
or I should just lean it out?

 

What do you mean by "blew". Do you mean burn them out or literally the spark plug comes out of the block. The latter problem is nothing to do with your carburation.

 

the sparks got burnt out, totally.
if the sparks flew out of the engine, then I am in big trouble.

 

Are the plugs black and fouled?

If so, your mixture is too rich.

Bike carbs are a PITA to diagnose sometimes, I don't think being out of sync would foul plugs.

Here is some good info on Carb tuning. It's not difficult, but tedious and messy. All of my Bikes will be fuel injected from now on.


Carb Tuning

George

 

The carbs on a Honda sportbike are usually pretty foolproof. As long as they are set up according to the factory specs (which I think pretty much all you can mess with is the pilot screws (which the setting is listed in the factory manual and the dynojet kit instructions) and carb sync screws - the float bowl levels on my Honda sport bikes have been non-adjustable), all jets and needles are clean and don't have any nicks or scratches, and the right jets are in the bike, you should be fine. Neither Honda nor DynoJet recommend deviating from their spec'd jets and needles, unless there is a serious problem which resulted from some other extensive modification. The mods you have done sound like the factory Honda jetting and recommended DynoJet jetting should be just fine.

A few questions:

1. With all the parts on the bike now, did it ever run well? If it did, than the carb is dirty or a tiny part got wrecked. Take it apart and clean it and inspect every jet and needle.

2. a) Who did the jet kit install?
b) was it done right? My F2 required (among other things) a few holes plugged, a jet swap, a needle swap, and a pilot screw adjustment

3. When was the last time you took the carb apart and cleaned it with a good solvent and put it back together? A good cleaning can do wonders for a carb. I had to do my F2 just this last weekend (thanks to some crap race gas that sat in it for a few months - never again race gas...). The bike has never run so well.

4. Do you have a factory service manual with all the jet part numbers in it? If the above suggestions don't work, I would start checking to make sure the right jets are actually in the bike. Honda's factory jetting (and DynoJet's jetting) are actually really good and you shouldn't have to screw with it at all. Newer sport bike carbs are no where near as finicky as dirtbike carbs (there's something I hate having to adjust...)

And yeah, you're going to have to better describe exactly what is happening to your sparkplugs, cause the last two descriptions you gave make no sense at all.

EDIT: for reference, I'm running a '92 CBR600F2 with a Stage 1 kit, K&N direct replacement filter, and a full Two Bro's exhaust. The kit went in as recommended by DynoJet and has run great since the spring of 2000 when I did the work (except for that damned race gas... Ohh race gas... ). The bike saw two years of street riding and a year of hard track use set up like this.

Chris.

 

Carb tuning is not that hard . . . . IMO

I did it on my '95 900RR and on a friends '96 GSX-R 750. My 3rd bike was a '97 GSX-R 750 and was fuel injected.

Anyway, it is not so much that it is hard to do, but hard to get the tools. You need a vacuum gauge for inline 4 cylinders. The vacuum gauge is connected to the vacuum lines of the 4 carbs and then you roll the throttle on (obviously the bike is on a wheel stand). As the carbs and jets open the vacuum across the 4 should be even. If not one cylinder may be too lean and another too rich.

CHRISSA is right on with his symptom diagnosis, IMO.

If you have a Factory Brand Jet Kit, you will definitely need to plug a port in each carb (see #2 above)

Hope you get it STR8

happy canyon carving ;p)

 

Yeah, ACLR8 is right that a carb sync is easy to do. A vacuum gauge shouldn't cost too much. I think I spent something like $50 to $60 CDN for my cheap one? Any parts counter at your local shop will sell one to you. I found that a carb sync helped mostly with the throttle response right off idle. The transition from fully closed to partially open becomes super smooth.

Usually the carbs are pretty good at holding their sync. Back in '92, Honda recommended re-sync'ing every 8000 miles. When I did a friend's bike at 12,000 miles, the sync was still really good. If you clean out the carb, I would definately recommend re-sync'ing them. I would recommend a re-sync after installing a jet kit too. It can turn a bike that runs well into a bike that runs like it's absolute perfection!

Chris.

 

Spend a little extra ($100) and get the Morgan Carbtune II. No mercury, not fragile, and very accurate.

 

problem solved, the jet kit was not installed right
Now, this thing pulls really hard
thanks guys.

 

GR8 to hear brutha!!