jet needles and springs

i have an 85 vf700f with 8k miles that had the wrong carbs on it when i got it, i believe they were off of a magna. it came with 2 other sets of carbs which had been disassembled, i determined from the carb numbers which set belonged on the bike and which jets were correct. it runs pretty good now except lower and midrange it feels lean and lugs shakes at lower rpms. can anyone tell me how to identify which needles it should have by the letter codes on them. also what should the free length of the slide springs be? some of the slides have a red plastic ring on the top where the diaphram attaches to the slide and some are white or yellow.does this matter?
i know that the needles and springs are different between cyl #1 3 and 2 4, are the slides also different? any help with this would be greatly appreciated. also what is the proper way to set idle mixture and sync, do i set them at the same time or do i set mixture on all of them and than sync them?

 

I'll try and help a little. The books say that 1&3 have shorter springs and thinner needles. I've mic'd several sets of needles for these carbs and they all come out the same size up and down the taper/shank. All slides are the same with in a set. You can raise the needles .020 at a time with mic'd washers if need be.

The idle mixture screws you may or may not see. They could have the alum plugs in them. Which need to be taken out for adjustment. To adjust turn in until it seats. Count your turns and keep for referrence. Then back out 2 1/2 turns for each for a base setting. You should really take each one out and look at the tip. They could be eaten away some what or damaged by the last guy cranking them down. (if plugs are out) Careful though there's a very small washer and o-ring on them or stuck in the hole.

Now at this point I would hook up the gauges to the carbs and check the sync between carbs. Remember bring the motor up to operating temp. If they are way out(i'd expect them to be) sync them then finish the idle screw adjustment.

Adjust your throtlle to 1000rpms =/-. Start with #1 carb and turn the screw out untill the motor increases by 50 rpm or more. Turn the others the same amount. Adj throttle stop/idle speed to 1krpms. Start w/#1 again and turn in until rpms drop by 50 or so. Then turn screw 1 turn out. Adj idle again. Repeat for the other three.

"it runs pretty good now except lower and midrange it feels lean and lugs shakes at lower rpms."

That could be a slide not working freely/properly. They may need cleaning w/brake cleaner. Or the rubber seal on top of the diaphragm is not in correctly,vac hole plug etc. Your low speed jet/circuit could be gummed up. Floats not set correct. You never said they were clean thoroughly and rebuilt properly. So there could be a number of reasons for it not running well.

The slides have to work FREELY no stickyness at all for proper operation and performance. If the small hole at the edge of the diaphragm is not line up with the vac hole in the carb it won't work right or may not pull up with slight throttle opening. Make sure all your rubber manifolds are tight too.

Good luck, let us know how you make out.

 

thanks for the advice, i took the carbs back off and found the float bowls full of rust so i cleaned the tank and carbs. i found a pair of needles that were thinner than the rest in my spare carb parts and i installed them in carbs 1 & 3, i also found a matching set of needle jets and installed them in all 4 carbs. i synced and adjusted them the way you suggested and now the bike runs smoother and pulls harder through midrange, but i had to adjust idle mixture screws on 2&4 out 6.5 turns , 1&3 out 3.5 turns. the bike feels rich at light throttle low rpms, i can hear it sputtering a little from the exhaust. it does idle smoothly and starts easily, any suggestions? thanks

 

The pilot jets (idle mixture screws) should be pretty close to the same for all four carbs. If not, then something is not right. Remove them and make sure no "extra" washers or O-rings are in the bore.

After doing a valve adjust & carb sync, adjust the pilot jets...

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Idle Drop Method of adjusting pilot screws

1. Open the pilots to 3.0 turns. Set idle to 1100.
2. Start with #1(really don't matter what number you start at) and turn OUT the pilot until the idle drops. You can hear as well as see the idle drop on the tach.
3. Then turn in the pilot slowly until the idle picks back up. You want the highest idle, smoothest running engine.
4. If the idle increased past 1100 for this procedure twist the idle screw to back it down to 1100.
5. Goto #2 and repeat
6. Goto #3 and repeat
7. Goto #4 and repeat.
8. Doing this will get the most efficient burn at idle. Oh... if you didn't mercury synk the carbs then proceed to step 10(shut off bike and go play golf) WHY? Cause you are wasting your time.

After you do the idle drop method, the pilots should be close to the same turns out. The reason they might be different could be many variables: Compression, dirty carbs/pilot circuit, un-even throttle plates, valve lash different between cylinders, cam lobe center different between front and rear, dirty intake valves, FLOAT level different between carbs. I am sure there are more but these are the most common.
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Balance carbs before adjusting pilot screws ? doesn't that throw off the mixture at idle ?

does a carbtune tool help ? worth the money ?

 

Make your own monometer

Make your own, posted this before look for it.:biggrin: