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I seem to have a problem going lean on top. I have verified this with wideband o2 and top speed runs. Maybe it's running out of fuel? I have tried to fatten the MJ and lower the needle without success. It runs perfect anywhere but at the top of the speed run.

The bike is being used for drag racing.

This is a 07 engine with a ported head. Running stock needle NJYR 3rd clip, 158MJ @ 12.8, sea level. It runs well with this jetting. However, top speed is not achieved. The O2 curve slowly goes lean at WOT dropping power.

The speed difference is about 6MPH (98MPH with good jetting and 92 lean)

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I seem to have a problem going lean on top. I have verified this with wideband o2 and top speed runs. Maybe it's running out of fuel? I have tried to fatten the MJ and lower the needle without success. It runs perfect anywhere but at the top of the speed run.

The bike is being used for drag racing.

This is a 07 engine with a ported head. Running stock needle NJYR 3rd clip, 158MJ @ 12.8, sea level. It runs well with this jetting. However, top speed is not achieved. The O2 curve slowly goes lean at WOT dropping power.

The speed difference is about 6MPH (98MPH with good jetting and 92 lean)

If you are talking about a CRF450R as in your signiture, a 158 main jet is WAY too small. I run a 178 with an '02 R cam and stage III porting. Some SM guys run as high as a 185. You should also try the NCVS needle, as it is richer earlier. Oh, and lowering the needle makes it leaner, unless you mean lowering the clip....

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If you are talking about a CRF450R as in your signiture, a 158 main jet is WAY too small. I run a 178 with an '02 R cam and stage III porting. Some SM guys run as high as a 185. You should also try the NCVS needle, as it is richer earlier. Oh, and lowering the needle makes it leaner, unless you mean lowering the clip....

When I jet higher I lose midrange (to fat). I try to compensate by leaning out the needle. It does not work very well in the low midrange when I do it.

Typically in hot weather I need to run a 155 to maintain a 12.5-13.1 A/F.

I ran last weekend with a 158 and it was still a tad rich in 70 deg weather. The port job is a RH port job. It has a high vacuum signal to the carb requiring less MJ. Many people on this board with the same head run 155.

I started with a 175MJ and was running in the 9.xx:1 A/F range.(low 9's)

160 netted a 11.5:1

158 netted 12-12.5 or less.

doing the math based on the above trend equates to somewhere in the 150 range is where I need to be to be at 13:1 for short bursts and 158 for prime jetting WOT.

I have read about the sump cavity on the bottom of the carb running out of fuel at high speeds. I think this may be an issue but wanted to confirm.

Tests were done on the 07 model trying to achieve max speed at the salt flats to break the current record. They ran into the same problem.

The O2 shows the mix creeping up at the end of the run but spot on in the mid and top... until the last 1000RPM or so.

I don't have the logs to post them right now. I will do some testing this weekend with a friends longer bowl sump bolt and see if it cures the problem.

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When I jet higher I lose midrange (to fat). I try to compensate by leaning out the needle. It does not work very well in the low midrange when I do it.

Typically in hot weather I need to run a 155 to maintain a 12.5-13.1 A/F.

I ran last weekend with a 158 and it was still a tad rich in 70 deg weather. The port job is a RH port job. It has a high vacuum signal to the carb requiring less MJ. Many people on this board with the same head run 155.

I started with a 175MJ and was running in the 9.xx:1 A/F range.(low 9's)

160 netted a 11.5:1

158 netted 12-12.5 or less.

doing the math based on the above trend equates to somewhere in the 150 range is where I need to be to be at 13:1 for short bursts and 158 for prime jetting WOT.

I have read about the sump cavity on the bottom of the carb running out of fuel at high speeds. I think this may be an issue but wanted to confirm.

Tests were done on the 07 model trying to achieve max speed at the salt flats to break the current record. They ran into the same problem.

The O2 shows the mix creeping up at the end of the run but spot on in the mid and top... until the last 1000RPM or so.

I don't have the logs to post them right now. I will do some testing this weekend with a friends longer bowl sump bolt and see if it cures the problem.

The R&D Powerbowl II ends the cavitation/starvation issues.

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