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jetting and valves

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James -we have been working hard here (in oz) to try and cure the valve issues on the crf and rmz's. One theory which is bearing fruit is that stock the rmz runs very lean on the needle. As we know, lean = heat and ti doesn't like heat.

I had no problems with my CRF until I put your needle in(not blaming the needle at all as there were a fair few hours b4 the valves went, but second set did not last long at all) but was wondering if it is possible that the needle is too lean which is increasing heat at the valve face. Could just be Oz fuel enhancing this problem as well.

Our real world experience behind this is that we have two RMZ's with stock jetting, but which run at altitude, which have both dropped valves (three times) but one KXF which is set at the richest needle setting (still stock needle) and is ridden same spot by a state pro and has not budged valve clearances all year.

Honda also seem to have admitted to this a little by the large increase in stock jetting 04-05.

Your thoughts/ experience. I am running recomended settings for crf kit as well.

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Running a KXF at the richest clip setting is certainly going to run cooler than everyone else's bikes. The RMZ/KXF250's are VERY lean near idle and at risk of overheating and causing problems with stock jetting. The CRF is less likely to run as hot, and even less yet with the kit as long as the ('04 models with #40 PJ) fuel screw is out at 2 1/4 turns. When the valves went, the guides may have deteriorated too, making a shorter life for the new parts.

I have not had any problems... --yet.

James

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The seats were recut by Honda, but I reckon the springs are shagged hence why they didn't last real long.

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