intra Posted February 7, 2010 Report Share Posted February 7, 2010 One of my mates has been having trouble with his zxr400 racebike (my old bike). The bike runs fine above 3000rpm but that is where the revs will sit at idle and when you try to adjust the idle below that mark the engine just dies. You can catch it with the throttle and it will splutter and then jump back to 3000rpm. The bike starts fine but just will not idle. We tried adjusting the fuel screw from where I had it set, and where the manual says to set it, at 3/4 of a turn out, down to 1/2 a turn and up to 1 and 3/4 turns but the exact same problem happened. That has me thinking that it isn't a carburation problem, and we've checked that the spark is still good, so the next thing I can think of is balancing the carbs. I've never done this with a set of fcr's though and they have no little spout to attach a manometer to like a cv carb does so I was hoping some of the knowledgeable lads on here would be able to point us in the right direction. He's supposed to be racing it this weekend so here's hoping. They're 33mm Keihin FCR's. Cheers. Link to comment Share on other sites More sharing options...
lorenzo Posted February 7, 2010 Report Share Posted February 7, 2010 Air leak on the inlets? Link to comment Share on other sites More sharing options...
intra Posted February 7, 2010 Author Report Share Posted February 7, 2010 They're brand new rubbers and sealing well. Link to comment Share on other sites More sharing options...
spacemonkey Posted February 7, 2010 Report Share Posted February 7, 2010 One of my mates has been having trouble with his zxr400 racebike (my old bike). The bike runs fine above 3000rpm but that is where the revs will sit at idle and when you try to adjust the idle below that mark the engine just dies. You can catch it with the throttle and it will splutter and then jump back to 3000rpm. The bike starts fine but just will not idle. We tried adjusting the fuel screw from where I had it set, and where the manual says to set it, at 3/4 of a turn out, down to 1/2 a turn and up to 1 and 3/4 turns but the exact same problem happened. That has me thinking that it isn't a carburation problem, and we've checked that the spark is still good, so the next thing I can think of is balancing the carbs. I've never done this with a set of fcr's though and they have no little spout to attach a manometer to like a cv carb does so I was hoping some of the knowledgeable lads on here would be able to point us in the right direction. He's supposed to be racing it this weekend so here's hoping. They're 33mm Keihin FCR's. Cheers. When did it start to get problems? Was it working right at some stage? - For balance get them off the bike and check that the slides are all sitting at the same height and that they lift together. That should get you close enough. Link to comment Share on other sites More sharing options...
Gregorious77 Posted February 7, 2010 Report Share Posted February 7, 2010 Could be the pilot circuit. take the float bowls off and clean out all the jets. Link to comment Share on other sites More sharing options...
will#224 Posted February 7, 2010 Report Share Posted February 7, 2010 Does it seal through an air box? Mine has a carbon ram air set up and the carbs sit on the rubbers that then compress between the carbon airbox and the head. If i dont have any gasket under the carbon that sits on the head i dont get a seal and have the same problem. Link to comment Share on other sites More sharing options...
suspensionsmith Posted February 11, 2010 Report Share Posted February 11, 2010 Try this for lots of useful info http://www.factorypro.com/tech/carbkei.html Link to comment Share on other sites More sharing options...
intra Posted February 11, 2010 Author Report Share Posted February 11, 2010 I balanced them as best as I could and replaced the o-rings around the bowls. She's now idling at 1200rpm. WIN. Link to comment Share on other sites More sharing options...
suspensionsmith Posted February 11, 2010 Report Share Posted February 11, 2010 Something to be aware of on high mileage FCRs. You know how they have the cool trademark rattle at idle,well those rattling slides have a tendancy to wear indentations in the aluminium body where the little slide wheels run. Makes it hard to smoothly balance the bike midcorner with the throttle as the throttle wants to surge as the slide wheels climb in and out of those little indentations. People tend to think its a jetting problem. I have rebuilt three sets successfully so its fixable. Link to comment Share on other sites More sharing options...
spacemonkey Posted February 11, 2010 Report Share Posted February 11, 2010 Something to be aware of on high mileage FCRs. You know how they have the cool trademark rattle at idle,well those rattling slides have a tendancy to wear indentations in the aluminium body where the little slide wheels run. Makes it hard to smoothly balance the bike midcorner with the throttle as the throttle wants to surge as the slide wheels climb in and out of those little indentations. People tend to think its a jetting problem. I have rebuilt three sets successfully so its fixable. I've seen this before too. What did they do? Fill 'em and scrape 'em? Link to comment Share on other sites More sharing options...
suspensionsmith Posted February 12, 2010 Report Share Posted February 12, 2010 I've seen this before too. What did they do? Fill 'em and scrape 'em? Yep I prep the surface and fill with epoxy then carefully sand it back. Link to comment Share on other sites More sharing options...
spacemonkey Posted February 12, 2010 Report Share Posted February 12, 2010 Yep I prep the surface and fill with epoxy then carefully sand it back. Yeah, I did that once but scraped instead of sanded. It worked OK..... Link to comment Share on other sites More sharing options...
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