Carb Balancing

I purchased a lovelly example of a VF1000F a few months ago…the bike has had a lot of work done and whilst trying to balance the carbs with my carb tune kit i noticed the rear two cylinders at the top of the scale whilst the two front cylinders down near the bottom…have tried to adjust but doesent seem to do much…im sure this problem has popped up before with someone…any ideas?

ps…have fitted a new spark unit recently as the rear were not firing…John

Got some balancing gauges a few weeks ago to do the carbs but haven’t sused out how.

Can a member explain on a post how its done please

we would be most grateful[:)]

Well I do it like this,As you sit on the bike the cylinders are rear left no1,rear right no3,front left no2 and front right is no4.The base carb is no4 all others are altered to match no4.I first adjust no3 to match no4 then no2 and finaly no1.If 1and3 are both similar but miles away from 2and4,it may be worth checking the cam timing on front and rear cylinders is correct.Regards BIF

just balanced carbs on my fe before my mechanical malfunction, as i remember it,

  1. warm bike up.
  2. remove the vacuum screws from the cylinder inlets and screw attach your gauges as per instructions.
    3)start the bike.(i normally increase the tick over to about 1500/2000 revs for balancing purposes )
    4)number 4 cylinder/carb(front right) is factory set and cannot be adjusted, (you adjust the other 3 to match this one.
    5)from the right hand side of the bike adjust the adjusting screw for no 2 cylinder/carb (front left cylinder)this screw is located just behind the tick over screw. (clockwise to decrease, anti clock wise to increase gauge)adjust till it matches no 4 cylinder.
    6)from the left hand side of the bike adjust the two rear cylinders one at a time till they all match number 4 cylinder.

foot note… as these bike tend to get hot when idling when stud i often switch the bike off if i have to make big adjustments, then start up and look at gauges…last time i did them i set some desk fans up to blow some cool air on the engine, which helped. the screws are awkward to get to, best thing i have used to date is a socket on the short end of a allen key… (ITS A FOOOOKING FIDDLY JOB but should only take a couple of hours if you get organised…

john, there is a throtle linkage that links the front and back carbs, if this has got bent it could hold the rear carbs slightly open, and no amount of adjustment on the screws would compensate for this, also there is a choke linkage that runs around all the carbs, make sure this is working. also check for air leaks between the rear carbs and the alluminium base of the air box,and also between cylinder and carb

oops… bif posted while i was one finger typing.

Hi Pete…thanks for all that really useful info…as the bike has been rebuilt after having all the engine coated etc i recon it could be something like badly refitted carbs …will check all the linkage, air leaks …and keep you posted on what i find…im just checking the valve clearances as well but the timing is another story as that would be a major job…cant see why that would be out and ive had the bike up to 110 mph…wouldnt it have damaged engine by now if timing is out?..bought a special tool from carbtune to reach the adjusting screws…really useful.

ps read somewere about the front carb slider springs being a different size to the rear…maybe i will check that to just incase someone mixed them up…

Hi Bif thanks for your reply…how would i check the cam timing without the special honda clear casing?

quote:
Originally posted by bif

Well I do it like this,As you sit on the bike the cylinders are rear left no1,rear right no3,front left no2 and front right is no4.The base carb is no4 all others are altered to match no4.I first adjust no3 to match no4 then no2 and finaly no1.If 1and3 are both similar but miles away from 2and4,it may be worth checking the cam timing on front and rear cylinders is correct.Regards BIF


Sorry for the blond moment…forgot this was a forum with lots of other info so found the thread on cam timing…[:)]

quote:
Originally posted by John Hartland

Hi Bif thanks for your reply…how would i check the cam timing without the special honda clear casing?

quote:
Originally posted by bif

Well I do it like this,As you sit on the bike the cylinders are rear left no1,rear right no3,front left no2 and front right is no4.The base carb is no4 all others are altered to match no4.I first adjust no3 to match no4 then no2 and finaly no1.If 1and3 are both similar but miles away from 2and4,it may be worth checking the cam timing on front and rear cylinders is correct.Regards BIF



Hi John,the cam timing is checked static with the flywheel set to TDC for cylinders 1+3.In this position the cam sprockets index marks,lines either side of the camshaft,must align with the top of the cylinder heads and all camshaft marks must face either up or down.this is easy to do if you have the covers off to check the tappets.The bike will run with no engine damage a tooth or so out on the cmshaft.Well worth checking the carbs are fitted properly as you suggest,if they are not it may be worth removing them and setting all throttle valves to the edge of the bypass hole on the throttle body.

Hi John,
The ‘HO’ i got off my brother had similar issues and thats half the reason he gave it to me, I.E. couldn’t get the vacumes right.
There was no. 3 carby gromet to the head folded over creating air leak, the carby trumpets were not fitted properly and shrank (check post on ‘carby trumpets’) there was a spark plug lead faulty, so i made new leads and replaced all spark plug caps and 3 out of 4 cams were one tooth out.
After all this was done and double checked everything the thing goes like a rocket. check some of my other posts for more details.
double check to make sure all the small springs are in place on the adjusters for the carbies as the may have fallen out.

cheers.

Thanks for all your help guys…will keep you posted

Update…took carbs off and found manifold rubbers split so ordered new ones from http://www.ajsutton.co.uk/ cost £46.58 this includes postage took three days for delivery…checked valve timing and found front two cylinders in perfect alignment but rear two are one tooth out of line…now for another question can i adjust the rear two on there own? and what is the best way of doing this…

I found it pretty easy to do John.Set crank to TDC 1-3,remove the cam chain guide on the top of the cylinder head.Now back the cam chain tensioner right off and lock in place with a piece of thick wire through the hole at the top of the mechanism.Now skip the chain over the sprockets to line timing marks up.Good luck BIF

Thanks Bif…sounds straight forward…let you know how i get on.

quote:
Originally posted by bif

I found it pretty easy to do John.Set crank to TDC 1-3,remove the cam chain guide on the top of the cylinder head.Now back the cam chain tensioner right off and lock in place with a piece of thick wire through the hole at the top of the mechanism.Now skip the chain over the sprockets to line timing marks up.Good luck BIF


Ok Guys…bike is all put back together and carbs balanced…runs sweet…took her out for a blast and she is smooth up the revs but wont go over 6000rpm…in all the gears…she doesent hesitate…just seems to stop wanting to progress up the revs…ive read somewere that pick up coils could be the problem…what do you think?
John

Hi John,did the bike rev past 6000rpm before you started work on it?I have come across this problem on bikes that have been parked up for a while.The solution was a session in the ultrasonic cleaner for the carbs.Regards BIF

Thanks Bif…will run them through my ultrasonic cleaner and see if that helps…cant remember if they went past 6000 revs before…

its worth a double check on the float height too.7.5mm from the carb base

A Quick note to say whilst the bike is stationary it revs all the way up so only whilst riding it the revs wont go over 6000 revs

hi john, with the bike reving ok while there is no load on the engine, then bogging down when the engine is under load,sounds like some of the jets are clogged, i would go with what bif says about giving the carbs a good clean, i did mine a while back, striped each carb down and gave it plenty of “zap” then re-assembled making sure not to mix parts up between carbs,
The only other things i could think of would be if the mixture screws are set wrong making the mixture too lean, off hand i think they should be 2.25 or 2.5 turns out, or maybe petrol pump not working ?. but i would defo clean carbs first though.

Thanks Pete…will keep you all updated