Hi Guys, New the boards and Interceptors. I bought an '86 VFR750 that had been sitting for a long time. Pulled the carbs, cleaned them thoroughly, ran brass wire through all the idle holes, washed and blew everything out, replaced the bowl gaskets and o-rings around the bowl drain screws and idle mixture screws. The bike was originally a California machine, and had an emissions canister and other items on it, that I decided to remove since emissions tests are not required here in Tucson. I ran hoses off the carb vent tees to open air, and put a cap on the vacuum feed nipple on the #3 intake. I also fattened up the main jets while the carbs were apart, since the bike has a Yoshi exhaust and K&N filter, and no "door" in the air box, and set the mixture screws an extra 1/2 turn out. Anyways, I got it back together and it is a bear to get started, and is only running on 2 holes. If you rev it up, one more seems to comes alive, but it's obviously lean. Are any of you guys familiar with making these types of changes? Is there another vacuum port that I missed? How about any guys with intricate knowledge of the carb circuits? Is it possible the pull air in around the mixture screws? It did seem that the o-rings around those screws were kinda small.... Any other thoughts? I sure want to get this thing going an take her for a ride! Thanks!
Maybe SOME of this will help ... Hello: I just had a huge response to this go “poof.” (Damn!) It is late, so here is a much more brief, and less detailed response. First, understand that I don’t have a CA bike, so, I am not completely familiar with some of the things you are handling. For now, I’ll just ask questions: Did you push some crud back into the jets when you ran the brass wire through them? What do you mean by “door” in the air box? On my carbs there is ONLY ONE hose to the atmosphere, and you are saying “hoses,” plural. Hard to visualize. Maybe the prior owner had already backed-out the air screws, and your “extra” ½ turn is too much? Did you calibrate/re-set the linkage, which operates the four “starter valves?” (The choke valves.) On a similar note, are you sure the throttle linkage is installed correctly? Or, in other words, how do you KNOW the butterflies are all opening at the same time? When you say “fattened up” the main jets, you got proper (larger) main jets, right? I assume you had the vacuum tubes out. Are you SURE they are seated properly? It is a bit difficult to put the tops back on the carbs and manage that "slinky-like" spring at the same time. I don’t quite understand why you capped-off ONLY ONE carb (#3). Again, hard to visualize. The idle (pilot) jet does the first 25% of the “work,” the needle jet the next 50% (that is 25% to 75%) and the main jet does the last 25%. On my bike, the threaded access ports for an adapter that would be used when using a manometer to sync the carbs are located just under the rubber carb attachment rings in the cylinder heads. Same on your bike? If so, are they all closed-off properly? Gotta go … it is late. (Updated a bit the next a.m.) Gray Market
If it's only the front two or the rear two carbs, then you probably have spark box / coil issues. Swap them around and see if the two carbs change.
Thanks for your responses guys. First, it does have spark on all the holes. That's how I figure out which cylinders are running is by pulling the wires using a pair of grounding pliers. Spark was jumping all over the place on all cylinders. When I ran wire through the jets and emulsion tubes, they were out of the carbs in my hand, then got rinsed and blown out, and reinstalled. The "door" thing I could be wrong about. I was under the assumption that these bikes had a vacuum operated "air door" in the air box, and that mine had been removed. I could be thinking of a different generation or model I thought I had read something about it....:unsure: On my carbs, there are two separate series of plastic tubes/hoses that connect the four carbs, and then come to a tee. The hoses from these tees originally went through vacuum operated control valves and then to the charcoal canister, for evaporative emissions control. There is also a fitting just above the left side of the bowl on the #1 carb that appears to be a bowl vent. I think when the tank goes back on, it connects to the gas cap vent. Right now, I have all three vented to open air. Definitely not a :treehugger: On the mixture screws, I removed them when the carbs were off, rinsed out their holes, ran brass wire down into them and blew them out, then put the new o-rings on them and reinstalled them. The specs (from the dealer) call for 2 turns out in California, and 2 1/2 in the other 49 states. I did not fully disassemble the rack of carbs, so I did not mess with the choke linkages themselves. Just removed and reinstalled the cable. I did verify that they all open and close fully though. The new main jets are Keihin slotted type, and looked identical to the originals except the numbers are on the top instead of the side. I beleive stock is 118's and I put in 125's The vacuum feed port below the #3 intake is the only one I saw when removing the emissions crap, so I capped it. I will try to take a more in-depth look at it tonight and see if there are more. I will also look closely for the sync ports. Are they supposed to be small hose nipples or just screws? I'll work on it some more tonight. Thanks Again!
Limited help ... Hello: Where this is gonig to break down for me is the fact that I do not have a CA bike, so, I can't visualize some of this stuff. No, there is no "door" in the air box on these bikes. You mentioned the two sets of plastic tubes. The brown ones are fuel, the black ones air. Glad to hear you got proper jets. (I had visions of you drilling-out the old jets.) As to the "manometer access holes" (don't really know what to call 'em), just make certain they are sealed off. They are 5mm threads. My bike had little brass fittings, but one was missing. IF they are open, just cap 'em off with a short (5mm?) 5mm screw. However, you might want to balance the carbs after all this. Actually, it sounds like you are getting close here. Just make certain you have capped-off any holes left behind due to the removal of the CA smog crap. Gray Market
If you count the fuel tubes, then I have three sets. 2 separate air, that tie the four carbs together in different locations, then the brown fuel tubes... I must have a vacuum leak(s) somewhere. The finnicky starting makes me think so. It will try with the throttle completely closed but won't light. If you give it any throttle, it stops trying. If you choke it just so that you are richening the mixture without opening the butterflies, or give it a shot of carb cleaner it starts and will stay running if you have the idle cranked way up. It seems #'s 1 & 2 are running, but 3 & 4 aren't. If you spray a little fuel towards 3&4, it picks up RPM, but it pops and snorts like it's lean. It's gotta be getting a foreign source of air.....
I got home last night and verified that all the sync ports were closed, and that I had no other open vacuum ports. I figured I must have missed something in the carbs so I pulled them back off, and dropped the bowls. There is a brass "tube" next to the pilot jet that I had tried to fish wire down before and it wouldn't go very far. I just thought that's how they were, but I tried again. On the cylinders that had been running, I was able to get the wire in now. So I fished down all of them again and got all four of them cleared out, and re-washed and blew things out again. Put the carbs back on and the bike immediately started easier, and would almost idle. It was still running on only two holes, but it used to be #'s 1 and 3, and now it's #'s 2 and 4, and #3 is almost running on it's own, and the bike sounds almost normal when you rev on it. I think I've got it down to a synchronization problem. I will work on it some more tonight. PS, to GrayMarket, I read over you updated post. I did find all the sync ports and they were closed except for the one that had the nipple on it for operating the emissions valves. I pulled the nipple out and installed a screw (yes, the proper thread) in it to eliminate any future issues with vacuum caps. On the air cut-offs, I did have them out. Mine seemed to fall right back into place upon re-assembly, but I will re-check them to be sure. One of the lids has a dent in it, and it is the #3 cylinder, so maybe I should pull it off and make sure that the flange is still flat and that it seals up. I guess that could be a vacuum leak.....
If you had to push wire through the jets, then you most likely need a full-on carb cleaning: where you pull everything off the carb, dunk in in carb cleaner for awhile, and then blow out the passages with compressed air. Shooting carb cleaner into the passages won't do it. Carburetors - SabMagFAQ
