Question about 1994 Suzuki RF 600 R

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Rf has race can K&N and dyno jet fitted when i got it, but terrible flat spots all over the place. can you give me a clue what size of main jet to use

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No one can tell you what jet size to use unless they know exactly what exhaust and jets you have now. The best thing for you to do is go back to a known good configuration. If it has never run right since you had it, go back to stock (make sure it runs right with stock settings now!) and start your adjustments from there. Change one thing at a time and do performance testing between each change. Dyno runs are best, but timed runs might work too, depending on your application.

Posted on Jun 30, 2009


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Gtr 1000 losing power I have to keep changing down gears to get top end back up I have stage 3 jet kit and separate aftermarket air filters could this be a vacuum problem?

go back to basics with the carby/s
they are designed to give top performance at all rpms and torque settings for the engine
accordingly the jet sizing has been carefully set to give that performance
if you alter that sizing believing that bigger jets means more power , then you are altering the air/fuel ratio
it is all well and good if you have fitted a real lumpy cam as that gets extra air for the bigger jets
if you want better power at top end then spend a dollar in a bike shop that has a dyno so that the jets sizes can be selected and tested in a running engine under load

Sep 11, 2015 | Power Motorcycles

1 Answer

2004 Kawasaki ZX-12R Motorcycles bad flat spot

Hi, Jonathan if you have changed your engine size, fuel delivery system, air filter size or flow rate, mufflers or exhaust system or a significant change in altitude your carburetors need re-tuning and if your fuel system (gas tank, filters, fuel valve and carburetor) is contaminated with ethanol sludge, varnish, rust, dirt, water etc. or your bike has been sitting for months or years without running these components must be "PROPERLY" cleaned and reassembled "CORRECTLY" before any adjustments can be made. Tuning your carburetor is fairly simple once you understand the basic principals. You engine is a simple airbox sucking air in and blowing it out, it is finely tuned at the factory for maximum performance once you upset that delicate balance by changing air filters, camshafts or exhaust systems your performance may go down the and the engine may run poorly, you need to compensate the air-fuel mixture in the carburetor in order for the engine to run smoothly and at peak performance. If you are running multi carburetors you need to sync them first and make sure your air cleaner element is clean and dry for paper elements or lightly oiled for foam and meshed elements and properly installed. Here is how and where you compensate trouble: "TIP" if your engine "BOGS" you're not getting enough fuel.
1. Close to 1/8 throttle is managed by the air screw and pilot/slow jet.
2. 1/8 to 1/4 throttle is managed by the air-screw, pilot/slow jet, and throttle slide.
3. 1/4 to 1/2 throttle is managed by the throttle slide and jet needle.
4. 1/2 to 3/4 throttle is managed by the jet needle, needle jet, main jet, and air jet.
5. 3/4 to wide open throttle is managed by the main jet and air jet.
6. A wide open throttle is managed by the main jet.
If you are running lean, spark plug electrode color is white, engine runs hot and feels like it is starving for fuel you need to go up on the jet size or move the c-clip down one notch. If you are running rich, spark plug color is black or dark gray, the engine runs cool, and bogs down when accelerating you need to go down on jet size or move the c-clip up one notch. When your carburetor is properly tuned for maximum performance your spark plug electrode will be a light tan color like coffee with cream. If you prefer fuel economy over performance you can go down on main jet sizes until a satisfactory level of lower performance is acceptable versus MPH, your spark plug color will be whiter and your engine will run warmer. These tuning adjustments will only make improvements if your intake and exhaust system have no air leaks or sealing issues and the entire electrical system is in proper working order and you have no mechanical issues.
For more information about your issue and valuable "FREE" downloads that you will need for viewing or printing please click on the blue links below. Good luck and have a wonderful day.
How to fix the Muzzy Flat Spot
Flat spot 2000 3000 rpm
Kawasaki NINJA ZX 12R Service Manual
Carburator Theory and Tuning
OEM Parts for Kawasaki
2004 Kawasaki NINJA ZX 12R Owner Manual

Btw, I’m available to help over the phone in case u need at

Dec 20, 2017 | kawasaki ZX-12R Motorcycles

1 Answer

Hi , I fitted a race exhaust on my x8r-s , and wanted to put a bigger main jet on it ... the problem is : I'm not sure which number it is right now , cause it looks like a 68 one way , but also 88 if you...

dont Change the you need to Change your afr air fuel mix to work with the new pipe changing the main will be to much of a change but first see how it rides but if your doing it for more power or speed the best size main jet is the right one ether the one from the dealer if in your area or u need to find the right one for your area

Jan 07, 2011 | 1972 Honda CB 250

1 Answer

I have a stock 1989 600xr. I have noticed tha it has a flat spot in the carberation from off idle to full throttle. If I put the choke on this goes away. Temp is around 80 and alltitude is 4000 feet. I...

They often had a flat spot from new, once the restricters were removed.
and there was a performance jet kit at the time.
Stock would mean it has a very restrictive end cap in the muffler, it may not still be there after 20 years, most were removed in the first few days.

you could try raising the needle a notch or two, then maybe a larger main jet.

Make sure it has a good air cleaner first.
Take notes about changes made and improvements.
adjust one thing at a time
dyno jet will have a kit I imagine.

Jun 27, 2010 | 1989 Honda XR 600 R

1 Answer

1100 Dragstar Fitting Straight Pipes

We have changed a few bikes from standard pipes to drag pipes. Their is a few considerations here, sea level or at what altitude, how much back pressure. so my suggestion rather take it before fitting the pipes to someone with a dyno, run and record the test, then have the pipes fitted, and let the same shop to the test again on there dyno, they will then know what to do with the jetting, because you should achieve better results with your new pipes.

Jun 15, 2010 | 2002 Yamaha XVS 1100 Dragstar Classic

1 Answer

Fouling plugs

This can be caused by all sorts of things.There is no real order of probability so I'll just list them.Your oil/fuel ratio could be rich depending on what oil you use,your powervalve could be stuck closed(pop off the plastic cover over the actuator located at the front of the clutch cover,its held in place by 3 screws attached to the barrel,start the bike and give it a big blat on the throttle and see if the lever moves)it could have a blown crank seal(the symptom displayed by this fault is that you will be using gearbox oil),the expansion chamber could be carboned up,or the piston and/or rings could be worn.If all these things check out ok I suggest either raising the clip on the needle(which drops the needle causing the mixture to run slightly leaner) If this does not have enough effect go down one size in the main jet.Adjusting the main jet size will require you initally to very frequently remove the spark plug to check that you haven't gone too lean. The plug should not be wet and oily,the perfect colour is a tan colour and not wet.I must stress that jetting a 2 stroke if you lack experience can be tricky in that if you go too lean you can seize the engine so if you do reduce the size of your main jet frequent initall inspections of the plug is highly recommended.As a final note,if you are using a standard plug and not a racing plug(ie gold paladnium or irridium)thay are inherently more susseptable to fouling & changing to a "racing plug" may help to reduce your plug fouling.Hope this was helpfull

Nov 22, 2009 | Yamaha YZ 125 Motorcycles

1 Answer

Carburation for road racing

buy a dyno jet kit from dyno jet should make some diffrance

Oct 29, 2009 | 1993 Honda CBR 250 RR

1 Answer

Changed the pipe to a 4 to 1 and added pod filters now bike runs out of gas at hard acceleration..what jets should i use and will a hi flow gas valve solve this

you dont need more gas through the valve. unless all out racing, that shouldn't be a problem. you definately need rejetting. the proper jet size can only be determined by trial and era. you need a dyno to tune properly. but of the head I would say start with 10 sizes over what you had. say if they were #120's, go with #130's. this should get you in the right direction.

Oct 20, 2009 | 1989 Suzuki GSX-R 750 K

1 Answer


1. Install a larger main jet to your standard fxr150 cabrurettor. We suggest fitting a 117.5 main jet, also remove the airbox and replace with an appropriate pod type airfilter. you will notice a gain in power and also a cool induction noise! 2. Fit a new aftermarket carb like a Keihin PE28 this is a chrome round slide carb which has the advantage over the stock carb that while still being 28mm there is no butterfly and shaft obstructing the airflow. 3. Another easy option is a GN250 carb, it’s a CV type of about 33mm, you can fit this with stock GN jetting and the engine will run GREAT and give quite a noticeable gain in power all over the rev range. 4. Try a flatslide carb from a DR200 if you can find one that is! I have one fitted to my race bike (see projects section) and i'm now looking for the best jetting options, but for now with the jetting i have made it looks to be a very promising carb for the fxr150, check back soon! 5. Honda XL250 carb, this so far has worked by far the best with my race engine and also very good with the std engine, but i did have to make a new throttle cable. For my standard road engine i used a 140mains jet, for my race engine with cams i had to drop the size and use a 130 main jet.

Nov 10, 2008 | 2001 Suzuki FXR 150

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