Fuel in vacuum take off stubs

[Z.O.A]

Hey all, the vacuum stubs on intakes #3 and #4 keep filling with fuel and there seems to be a fair bit of blowback through the throat of the carb to the filters (pods).

The carbs are spotless inside and out, new keystar kits to all of them, (now thinking these may be the problem , although all the part numbers were correct). My other guess was that maybe the valves needed to be re-shimmed, would that cause this problem

The carbs are vm26sc's fitted to an otherwise finished '76 A4
Needle position is standard at pos. 3
Main jets, mikuni 120 for use with k&n filters
Pilot jets are standard 17.5
The idle mix is set perfectly.
The fuel levels in the bowls are spot on according to the clymer manual I have, I even tried it a bit lower just to see but no change.

There are no leaks at the intake rubbers and the engine runs sweet as a nut with all cylinders making good compression

Problem starts from idle, the bike idles perfect and revs cleanly but rides like it's being smothered with too much juice on a couple of cylinders.
Any insight or ideas much appreciated.

[Al]

What were that valve shim clearances last time they were measured and how many miles since then.

What is the Dynamic fuel level for 3 and 4 compared to 1 and 2?
Measured when the engine is running (on centre stand for example) with the service tool or equivalent.

Did you dislodge any smolge when servicing the carbs?

How is your fuel tap flowing?

You mentioned that the fuel mix is set perfectly..... by what method and if colourtune what colour did you set it to.
If by spark plug colour....... what colour are you getting?


AL

[Z.O.A]

Hi Al,

I set up the idle mix both by ear and by using the gunson colortune till I got as blue a flame as I could and by adjusting each one to the point where revs were highest.

The motor has just over 26,000 miles on it, I have'nt done the valve clearences yet, I'm just waiting on a shim tool to arrive and that will be a job I will be doing then.

The fuel level, with the bike as close to level with the ground as I can get it is the same for all carbs at 3.5 -4mm below float bowl mating surface, this is with engine running. I bought measuring tools from a guy in the states for checking the fuel level on these carbs with the small drain screw, I bought two so I could check two carbs at once.

The fuel tap is a dual outlet pingel tap, two inline filters, I've done all I can think of with carbs, thinking of trying to get hold of another set just to see.
Plug colour was a bit darker on 3&4 but not what I would call fouled.

[Al]

I set up the idle mix both by ear and

Any hint of any carb 'stuttering if done by ear??

using the gunson colortune till I got as blue a flame as I could and by adjusting each one to the point where revs were highest.

Cant remember whether it blue to yellow or yellow to blue but at the margin i would definately elect for the weak side or the flame because;

EDIT; its yellow(rich) to blue(weak) just looked it up and i would go for the blue (bunsen blue) end of the scale and not just at the point where it changes over.

although these engines need a rich setup at idle this causes a number of idiosyncrasies under modern conditions (meaning modern fuels and modern plugs)
and

I dont believe the accuracy of the colourtune which i recently used which i believe gave an under- rich (weak0 reading when it was in fact richer than it needed to be.

Suggestion; run it down to the local MOT garage and get them to run the exhaust hydrocarbons test on the exhaust. Cost you a drink.

The motor has just over 26,000 miles on it, I have'nt done the valve clearences yet,

Is this the mileage you have done since it was last checked??

The fuel level, with the bike as close to level with the ground as I can get it is the same for all carbs at 3.5 -4mm below float bowl mating surface, this is with engine running. I bought measuring tools from a guy in the states for checking the fuel level on these carbs with the small drain screw, I bought two so I could check two carbs at once.

A man after e own heart!!

Plug colour was a bit darker on 3&4 but not what I would call fouled.

What colour would that have been???

Almost any hint of colour it seems and youre already too rich or approaching it with modern fuels!!

Any signs or fuel washing on the 3 and 4 plugs.

There should be the appearance of dryness which is difficult to define but if you look at the plugs in raw daylight (difficult i know) there should be no signs or iridescence on the central insulator.

This would suggest incomplete combustion or an over-rich condition.
In this case plugs although new should be regarded as dead and replaced.

What starts out as a rich or flooding problem then fans out into plugs then bore washing and terminally crankcase combustion

Questions; are any of the pods fouled / dirty?
Do the carbs flood the pod filters too?
is it possible for rain water to have blocked the pods?
What type are they K&N or S&B and have you tried swapping them round?

Just as a reality check; what were the settings of the screws when you tuned in in the way that you did?
Broadly in agreement or noticeable differences anywhere??



AL

[Z.O.A]

I think it's from yellow to blue on these older engines with the colortune although I did prefer doing it by small adjustments and listening to the engine for best combustion.

26,463 miles is the total mileage on the engine, I brought her in from new jersey, she was a solid but sadly neglected bike. It's also older than me which is probably why it's seen fit to give me grief when I'm so near to finishing it .

Anyway, all is new on her, genuine k&n filters fitted, they do'nt flood the filters as such but there is petrol being blown back through them and soaking the oil in the elements, I have a stack of spare plugs here both NGK and DENSO, they were'nt soaked in fuel when I checked them, no's 1&2 were good light tan colour, 3&4 were darker around the insulator and electrode but the combustion sounds good and strong still.

I am going to borrow another set of vacuum gauges tomorrow and try setting the slides again, my gauges gave the proper reading of 23cm but maybe there is something wrong there, can't hurt to check with another set, and if all is right fuel wise with the carbs then maybe it is a vacuum/vapourisation problem
I will give an update and let you know if it makes a difference.

[Al]

Had another thought but clutching at straws really; when i had after-market filters on mine it would practically rattle the fuel out of the float bowls. With no airbox to support the carbs at the rear they were bouncing around like i dont know what. Ended up making a flattened 'S' shaped strap from top of carbs to cam box screw.

If youre going to take the cam cover off to have a check on the shim clearances it might be worth having a count up on the cam timing. Though to be fair it will effect 'all the same' if incorrect. That said; with marginal clearances on some...... it may make that difference.
Also might be worth taking a view on the cam wheels too. If there's a chance that slotted ones have been fitted,. timing of cams may count up correctly but the cams can be rotated in the wheels.


What were the air screw settings after adjustment?

Do you need choke to start it?

How long does it need choke from cold if you do use it?

If you need choke to start, does it take full choke or 'bog down' if you do?

Does it tend to start on two cylinders and the others chime in as it gets going a bit?





AL

[Z.O.A]

Thanks for all the advice Al, I did a bit more fiddling with the slide settings, I even took carbs off and set them mechanically first using a .7mm steel wire between the notch in the slider and the bottom of the carb throat.

I should mention that these carbs, although the right ones with all the right part numbers are not the original ones from this bike, I did notice that the notches on the slides on the intake side do have some slight uneven wear, the bike originally came with what I believe were GPZ carbs????

I put them back in and adjusted vacuum with another set of gauges, it does make a difference but they're still not right.

I am convinced it is still a carb problem, but I will whip off cam cover and get the feeler gauges out anyhow as I know valve clearence will effect setting up the carbs if bad enough.

I am going to leave the carbs for a day or two at this point because I found this morning that two of them suddenly started pissing fuel from the overflow without the bike being moved at all, ( an aux fuel tank is rigged up) if I do'nt walk away for a while I'll end up taking them out and f*****g them at the wall

I will update as soon as I get sorted with either more new carb parts or a spare set to try out.
Cheers.

[KWACKERZ1]

I assume that the new kits came with float valves and needles, so was it the same two that were p----ing out fuel that you were having problems with?

It could be float levels on those carbs or the new float needles not sealing properly.

If it were me I might be tempted to swap needles float and float jet between say 1 and 3 to see if 1 then fouled up.?

Or double check you got the same stuff in all four kits, you never know.

Cheers
Phil

[Z.O.A]

The kits I put in already were only for the needles and needle jets, I now have new float valve assy's (seats and needles x4) ordered to hopefully solve the intermittent fuel level problem.

Have cam cover off and have checked valve clearances, the only ones out of tolerance are the exhaust valves on cylinders #1 & #2, they do'nt have the minimum clearance of .05mm, that's as small as my gauges go so will have to get another set to see exactly what they are and then order a couple of shims.

[PAULJAC47]

Just A thought check seats on choke sliders you can pull them out one at a time found two of the seats were perished on my A4 letting fuel through when i thought choke was fully off,Cheers Paul Jac..

[02GF74]

it all seems to point to the carbs overfilling.

the fact that they share the same feed is probably a clue .

you have checked that the floats are not holed?

[Z.O.A]

I will check the choke plungers one by one, certainly a possibility that something is stopping it seating perfectly even tho it operates smoothly.

No holes in the floats, they're good, should have the new parts before the week is out.

I took the shims out from the two ex valves that were out of limits 275 A and 280 A were the sizes, the price for shims was ridiculous from Z-POWER at £9 a pop and WEMOTO were £8.50, adding postal strikes to the equation, I decided to order a few different sizes from Z1ENTERPRISES in the states at $5 each and $7 to post, big difference, hopefully they won't be too long getting here.

[000zeds]

Z.O.A are you a member of the club ?

Jerry does a free exchange for members only !

[paul doran]

Z.O.A are you a member of the club ?

Jerry does a free exchange for members only !

I have an extensive range of shim's which are available to anybody over here

[Z.O.A]

Ta for offers, had em ordered anyway and put in for a few different sizes just in case.