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Ways to identify jetting? FCR39 help...

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Hello all,

My bike runs great and pulls hard. It has an old style FCR39 from what I can tell from the pictures I searched for. Ive been inside the carb but have never actually screwed with the jetting short of adjusting the air and fuel screw. Right now I go about 60 miles before I hit reserve. How could I figure out what jets and jet kit I have if any at all? I bought the bike built since It was a good deal but now I have no idea what is going on when I maintain it. Thanks.

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You need to remove them to see. The main, starter and pilot are in the float bowl, they will have numbers stamped on them. The needle has numbers too in addition make note of what groove the clip is on (count from the top). Also, if there are no numbers on the needle, on the top/flat, it may be painted a color.

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You need to remove them to see. The main, starter and pilot are in the float bowl, they will have numbers stamped on them. The needle has numbers too in addition make note of what groove the clip is on (count from the top). Also, if there are no numbers on the needle, on the top/flat, it may be painted a color.

will do that, last I had them off I didnt see any colors on the needle. I have a feeling the owner just threw the carb in without jetting it. The bike pulls hard and runs nice but it feels like I am running rich. Heres a picture. Anyone know what it is off of, I want to order a JD jet kit for it and make it run better.

100_4434.jpg

shameless plug for my toy:ride:

101_4417.jpg

Much mahalos willliam1

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It's not an FCR39MX (I have one) so that would lend more weight to your suggestion that it's an original FCR39.

Can you take it to a dyno shop with EGA and get a run done? That will tell you exactly what you need to do.

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if you think its running rich,take the airbox door off and go for a rip.if your running rich it should rip a little better with the airbox door off.

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if you think its running rich,take the airbox door off and go for a rip.if your running rich it should rip a little better with the airbox door off.

IVe done that and it does run better. Im just trying to figure out why I get 35 mpg

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If you're getting 35 mpg (like I was), you need to pull the carb and double check the jetting. My carb was set up all wrong by the prev owner.

IVe done that and it does run better. Im just trying to figure out why I get 35 mpg

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If you're getting 35 mpg (like I was), you need to pull the carb and double check the jetting. My carb was set up all wrong by the prev owner.

update guys. I pulled the carb off and the jet in the float bowl is a 160. The needle was at the 4th from the top position. The needle says OCEM M on it. It has black deposit marks near the clip. Can anyone help explain this and what route I should take?

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If it ran better with the airbox door, the main is too latgre. I will assume the cork/spark arrestor is in your pipe. I'd put a 155 in. Also, was the 3X3 done? If not, it is a 'must do' first and retest. Here is the skinny on testing for the correct main jet.

Starting with the recommended main, remove the airbox door and go for a ride (bike fully warmed up). Is it better or worse?

If it is better, you need a smaller main.

Go down one size, replace the airbox door, ride. Remove the airbox door and test again. Better or worse? If better, go down a size again. Keep repeating this till the test with the airbox door is worse.

If it was worse with the airbox door removed, tape over 1/3 of your 3X3, test.

If it is worse now with the tape and was worse with the airbox door off, your main is just right. You are done!

If it seems better, you need to go up a size in main jet. Test it again (remove the tape). Replace the tape, test again. If with the tape on it is better, go up another size in main. Keep repeating this till having the tape on is worse than with it off.

To finish up and ensure you are set accurately, retest the bike with the tape off, ride it, then remove the airbox door. Best performance should be with the airbox untapped, airbox door on.

Remember, the main only operates at WOT. Ideally, you want to be in 3rd or 4th gear doing the tests, hitting max revs (just shy of the limiter) for at least 10 seconds to get an accurate representation of the jet status.

Be sure to keep notes of your settings. You may find you need to make a change, say if you're riding in the mountains, down at the beach or mess the 'cork'. Returning home, it is a simple matter of referring to your notes to restore things.

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the cork is not in my yosh, I took it out because it robs the power. Also, if I was to order a JD jet kit would it make a big difference and what model would I order it for? Thanks guys.

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For sea level with uncorked exhaust, the recommended jetting is a 160 main. I've got a corked exhaust and a 155 main is still a little rich for me. You might try a 155.

Your mileage is mostly going to be affected by pilot jet. What's the current size? I'm running a 45 pilot and found it to be still too rich based on a dyno run. I'm moving down to a 42.

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For sea level with uncorked exhaust, the recommended jetting is a 160 main. I've got a corked exhaust and a 155 main is still a little rich for me. You might try a 155.

Your mileage is mostly going to be affected by pilot jet. What's the current size? I'm running a 45 pilot and found it to be still too rich based on a dyno run. I'm moving down to a 42.

Im running a 40 pilot. I guess the bike was jetted correctly. Im still trying to figure why my MPG would be so low. Would a needle running to rich cause this?

This may be a dumb question, but what is the two screws in the intake bell? What do they do.

Im thinking the needle was just a bit rich, so I moved it to the number 3 position. Im going to try it like this and see what it does.

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