Member Contributer tomk1960 Posted July 3, 2013 Member Contributer Share Posted July 3, 2013 As of today, my VF1000F is registered and inspected. It starts right up and accelerates nicely. Around town and on country roads, it runs great. Then I took it up on the highway and REALLY twisted the throttle. It pulled hard up to 6000 RPM and then stumbled like it was gasping for fuel or air. If I backed off a bit on the throttle, it accelerates fine. When I got home I installed the new air filter that arrived today. I was hoping that maybe the old one was partially clogged and causing the problem. Back on the highway and at 6K, it felt like it was being held back. Otherwise, it runs great, but I know with a much higher redline, 6K should not be an issue. The carbs were professionally overhauled by Mike Nixon, so I have no doubt that they were done correctly. I'm wondering if the OEM coils might be showing their age and should be replaced. Other thoughts are a partial clog in the tank's fuel line or in the fuel filter. Any ideas? Anyone else had a similar issue and fixed it? Thanks, Link to comment Share on other sites More sharing options...
Member Contributer Switchblade Posted July 3, 2013 Member Contributer Share Posted July 3, 2013 Kinda sounds like the slides are not opening quick enough . Link to comment Share on other sites More sharing options...
Guest Posted July 3, 2013 Share Posted July 3, 2013 Nixon is indeed a competent builder. The VERY first thing to do is check your compression and valve clearances, and of course the cams. As for carburetion, in the most general of terms if you have difficulty asking for horsepower you're rich, if you surge at constant speed you're lean. Try running for a short spell, very short, without the air cleaner element installed. V4 carbs have a reputation for a flat spot right about where you're seeing it but we need to know what all's happening elsewhere in order to narrow down the list of variables. Jack http://www.oldschoolcarbs.com Two of my V4's: Link to comment Share on other sites More sharing options...
Member Contributer tomk1960 Posted July 3, 2013 Author Member Contributer Share Posted July 3, 2013 Nixon is indeed a competent builder. The VERY first thing to do is check your compression and valve clearances, and of course the cams. As for carburetion, in the most general of terms if you have difficulty asking for horsepower you're rich, if you surge at constant speed you're lean. Try running for a short spell, very short, without the air cleaner element installed. V4 carbs have a reputation for a flat spot right about where you're seeing it but we need to know what all's happening elsewhere in order to narrow down the list of variables. Jack http://www.oldschoolcarbs.com Two of my V4's: Valve clearances were all checked and adjusted a couple of weeks ago when I was finishing up the bike, so they're good. Compression is yet to be checked. I just double checked and readusted the choke cable to make sure that in the off position, the chokes are fully open. If they were still slightly closed, that could cause the issue. Mike suggested the air filter test as did you, so that's next on my list if the choke cable adjustment doesn't help. Is everyone running these on stock jets nowadays? Some carbs like different jetting based on today's poor gasoline. And speaking of gas, am I ok to be running on 87 octane? I always run my bikes on regular and just realized that maybe this engine calls for high test. More to come on this, and thanks. Very nice bikes, BTW. Link to comment Share on other sites More sharing options...
Guest Posted July 3, 2013 Share Posted July 3, 2013 Premium only!!! LOL. Do a google search for ethanol-free gas in your area. I have to drive a few miles out of my way but boy does it make a difference. The lines on Sunday morning are around the block. We just shot a video where Nila talks at length about the whole ethanol business. I'll post a link when it's up. Jack Link to comment Share on other sites More sharing options...
Lobotomy Posted July 3, 2013 Share Posted July 3, 2013 Possibly fuel filter getting blocked? Link to comment Share on other sites More sharing options...
Member Contributer tomk1960 Posted July 3, 2013 Author Member Contributer Share Posted July 3, 2013 Possibly fuel filter getting blocked? Definitely possible and a cheap thing to try with nothing to lose. I'm also very suspcious of the 29 year old coils. I may try to adapt a set of CBR600 coils to see if they'll make a difference. Are you all running stock jets on your Interceptors? I'm wondering if today's gas calls for different jetting. Link to comment Share on other sites More sharing options...
Guest Posted July 4, 2013 Share Posted July 4, 2013 Ugh, ethanol. Don't get me started. We just shot a video where Nila talks about the subject at length. I'll post a link once it's up. The prognosis is all bad. The short answer is yes, we rejet—not just because of ethanol but we as a matter of simple course preemptively bump you up a size in all our builds. This takes care of the annoying flat spot in one simple operation. Honda tells us on the very first page of the common service reference manual that their EPA compliance consists of lean carburetor settings. The mandate was to starve them and make the fuel mix screw inaccessible. This, however, is a wink and a nod to everyone downstream that richening is in order. You'll run cooler and, somewhat counterintuitively, you may experience better fuel economy. Go figger. There are other things to consider where it comes to V4 carbs. The forward and rear pairs of carbs employ different needle jets, emulsion tubes, slide springs, and in many cases slide needles—the forward pair being set up leaner. The parts may look identical at a glance but if they get mixed up during assembly you'll wind up with anomalous problems that are near-impossible to pinpoint. Really the only things they all have in common are the slides themselves, slow jets, fuel mix screws, and bystart (choke) plungers. I'm not even remotely suggesting that Mr. Nixon made this most amateurish of errors, but I've seen carbs off of professional racing V4's where they were mixed up by otherwise extremely, incredibly competent bona fide engine experts. We also want to differentiate between California and 49-state models, the CA ones being equipped with a vapor scavenging system---and much smaller needle jets. If you have thin black tubes running every which way, you've got a CA model. We delete the entire system, which on the carbs involves knowing which vent nipples to close off. One in particular is hidden, thus easy to miss. This together with proper jets and you're off to the races. You can also safely get rid of the crankcase breather snorkel and close it off securely at the airbox. You'll immediately hear increased intake sounds because you're no longer pumping oil-laden crankcase vapor into the airbox. Route new hose from the engine breather nipple down under the swingarm and attach a small paper filter, which you can replace when and if it loads up with oil. Be a pro and use strategically placed zip ties and it'll be both secure and invisible. OSC http://www.oldschoolcarbs.com Link to comment Share on other sites More sharing options...
Member Contributer tomk1960 Posted July 4, 2013 Author Member Contributer Share Posted July 4, 2013 I just got back from a little "experimental" ride back and forth on some highway stretches. I removed the spring from the air filter housing and just left the filter in there "ajar," allowing more air to get to the carbs. It seemed to help, but not cure the issue. There was noticeably less stumble in the 5500-6000RPM range and then it seemed to be even better at the higher RPM's, indicating the flat spot that you mentioned. If the carbs have to come off for rejetting, sobeit, but I wasn't planning on it. Perhaps the gas is just that bad and even Mike's best efforts can no longer counteract the negative effects of ethanol-laden fuel. I haven't been able to find any ethanol-free gas stations within a reasonable riding distance, so I'm stuck with what's offered locally. Link to comment Share on other sites More sharing options...
Member Contributer tomk1960 Posted July 7, 2013 Author Member Contributer Share Posted July 7, 2013 After several different experiments to try to find the cause of the issue, I decided to pull the carbs and see if I missed something. The bowl vent tubes looked like they were partially pinched during the installation, so I straightened them out and carefully reinstalled the carbs. The bike started right up, so I took it for a ride. Once on the highway, it ran a LOT better - very good throttle response all the way through the RPMs and no more bogging, no flat spots, nothing. Looks like that was the problem and now it runs GREAT! My only problem now is going to be keeping it close to the speed limit. :) Link to comment Share on other sites More sharing options...
Member Contributer Switchblade Posted July 7, 2013 Member Contributer Share Posted July 7, 2013 YEY !!!!! Link to comment Share on other sites More sharing options...
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