vacuum on #4 when trying to sync


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bradmonkey
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vacuum on #4 when trying to sync

Postby bradmonkey » Mon Feb 04, 2013 12:56 pm



my 1986 1200i wing will not pull out of a vacuum on #4 cylinder when I try to sync the carbs,I took off the carbs, had honda clean them,put them back on and still have the same problem.The compression is 150 but #4 is at 170.I'm getting fire on the plug but if I pull the wire off #4 while running it' makes no difference--its running on three.I even squirted gas down the vacuum port and it still won't fire.I sprayed under the carbs for vac leaks--no change in speed.Whats next--help



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virgilmobile
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Re: vacuum on #4 when trying to sync

Postby virgilmobile » Mon Feb 04, 2013 1:15 pm

That you have good compression would indicate that the cylinder MUST draw air....and if the throttle valve is closed....it must create a vacuum in it's tube.

So I can only guess that that cylinder is operating wide open throttle...Bad for fuel mixture..it will never fire.

You can test one thing for curiosity sake.Attach the compression gauge to the matching cylinder and crank it for 3 seconds with the throttle closed and read the compression.
Reset and crank it again for 3 seconds with the throttle wide open...It should be higher.

Do the same test on the dead cylinder...I'll bet a nickel there won't be any change.

Look between the carb body..there is a coupler shaft for the throttle valve...it may be missing.
You could also remove the downtubes,leaving the carbs on the bike and visually inspect the throttle valve while operating the throttle..being sure it's firmly coupled to the matching carb and closing at the same time.

Also...I'm not positive but one of the tubes has a vacuum port on the inside for the electronic ignition module...It goes to a "T" ,the module and the extra hose is plugged off.

bradmonkey
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Re: vacuum on #4 when trying to sync

Postby bradmonkey » Mon Feb 04, 2013 3:22 pm

back again,I tried a compression check with throttle closed and open,I got 90 closed and @ 175 open ,rt bank #1 was165 closed @170 open,#3 was 140 @175 ,there is a vacuum hose under the carbs that no one at honda new where it went,kinda scary when you give em $200 to clean them

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virgilmobile
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Re: vacuum on #4 when trying to sync

Postby virgilmobile » Mon Feb 04, 2013 4:55 pm

Your surprised????
When you say to "clean the carbs"...that's just what they did....no more.
Nothing was mentioned about testing them or even a pre-adjustment of the throttle plate so don't expect a plug and play.
You may have to take those steps yourself.
My 84 had a vacuum line on the back side of the left rear carb runner tube.It goes to the ignition module.I don't recall any hose on the carb body tho.At least any need for a vacuum line.

You will need to manually inspect each throttle valve as the throttle is moved.A pre-adjustment is started on the right rear carb.Get that one closed and adjust the others to match.Check after all adjustments that all close exactly at the same time.
Adjust the idle screw up a little and look at the throttle plate.All 4 carbs need to have the same gap.

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virgilmobile
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Re: vacuum on #4 when trying to sync

Postby virgilmobile » Mon Feb 04, 2013 5:10 pm

bradmonkey wrote:back again,I tried a compression check with throttle closed and open,I got 90 closed and @ 175 open ,rt bank #1 was165 closed @170 open,#3 was 140 @175 ,there is a vacuum hose under the carbs that no one at honda new where it went,kinda scary when you give em $200 to clean them


The first line....was that on the offending cylinder?(90 and 175)

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virgilmobile
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Re: vacuum on #4 when trying to sync

Postby virgilmobile » Mon Feb 04, 2013 5:15 pm

Just curious...90/175 would indicate that the throttle plate is closing tight and should pull a high vacuum....maybe too tight compared to the other 3.
#1 seems to be off too...kinda like it's open too far.
#3 sounds about right.

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SteveB123
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Re: vacuum on #4 when trying to sync

Postby SteveB123 » Mon Feb 04, 2013 5:56 pm

bradmonkey wrote:back again,I tried a compression check with throttle closed and open,I got 90 closed and @ 175 open ,rt bank #1 was165 closed @170 open,#3 was 140 @175 ,there is a vacuum hose under the carbs that no one at honda new where it went,kinda scary when you give em $200 to clean them


$200 is maybe two hours of shop time at a dealer. Pretty tough to do a decent job cleaning four carbs in that time, particulary if you don't do it often.
And they don't.
Current:82 GL1100 Interstate, 60 Amp Poorboy, MSD coil
Previous: 93 GSX1100F Katana
82 GL500 Silverwing

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thrasherg
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Re: vacuum on #4 when trying to sync

Postby thrasherg » Mon Feb 04, 2013 7:49 pm

I think we may be jumping the gun here, regardless of whether the carbs are clean or not, it would NOT effect the vacuum on number 4.. We need to find why there is no vacuum first, then if there is rough running we can say the carbs need extra cleaning, but you need to find why there is no vacuum.. As stated I can only think of the throttle slide being stuck in the wide open position or a massive air leak (Which would be highly visible) or the cam is timed completely wrong, but then the other cylinders on that side would have the same problem!! Have you tried rotating the camshaft with the rocker cover off and made sure the inlet valve is actually being opened? I would suspect a broken rocker arm or something which is preventing the inlet valve from being opened. That would cause no vacuum on that cylinder..

Gary

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Re: vacuum on #4 when trying to sync

Postby bradmonkey » Tue Feb 05, 2013 9:11 am

Hi gary, Thanks for the input--the #4 is in a big vacuum and the other cylinders I can sync pretty close,Virgilmobile thinks since I had the carbs cleaned at Honda they did'nt bother checking the butterflies to see if they opened in sync.Thats my mission this a.m---I'll keep you posted. Thanks again BILL

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Re: vacuum on #4 when trying to sync

Postby virgilmobile » Tue Feb 05, 2013 9:30 am

This is a afterthought.....Does the gauge work???
Can you verify by swapping with another vacuum port.

Something about seeing the forrest through the trees.
We might be overthinking this.
I guess the point is if a cylinder has compression and the throttle valve is closed it must create a vacuum in the connecting tube if all is sealed up.

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Re: vacuum on #4 when trying to sync

Postby bradmonkey » Tue Feb 05, 2013 10:27 am

Yep, I switched guages--same thing,I'm going to do the basic adjustment like you told me but not quite sure how to adjust them,do you loosen the nut on the side of #3 and adjust to #1?

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virgilmobile
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Re: vacuum on #4 when trying to sync

Postby virgilmobile » Tue Feb 05, 2013 11:33 am

bradmonkey wrote:Yep, I switched guages--same thing,I'm going to do the basic adjustment like you told me but not quite sure how to adjust them,do you loosen the nut on the side of #3 and adjust to #1?


When I pre-set mine,I did it on the bench,but it can be done on the bike too.

Loosen all the adjustment screws till they no longer move the throttle control arms.
loosen the main idle screw till it doesn't touch,this should set the right rear carb closed.
On the right side,loosen the nut between the 2 carbs and start turning the screw.At some point it too will loosen and a with a little pressure you can see the arm move against the spring.Push gently down and see the free play.
Turn the screw slowly back and push it a little till the free play is gone.Snug the nut there.This sets the throttle plate closed.
Move to the left rear adjuster and do the same ,then the center one.
You'll see when you start turning the screw.There comes a time when it doesn't move the throttle plate arm.That's it's closed position
PM me if you get lost.It's easier to convey on the phone than trying to describe it in text.
When your confident all are closed the same,turn the idle screw back up and test.

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thrasherg
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Re: vacuum on #4 when trying to sync

Postby thrasherg » Tue Feb 05, 2013 1:31 pm

bradmonkey wrote:Hi gary, Thanks for the input--the #4 is in a big vacuum and the other cylinders I can sync pretty close,Virgilmobile thinks since I had the carbs cleaned at Honda they did'nt bother checking the butterflies to see if they opened in sync.Thats my mission this a.m---I'll keep you posted. Thanks again BILL


I thought you said there was no vacuum on Number 4? If there is a big vacuum then it would imply that the throttle valve is not opening. Can you clarify for me, do you have a big vacuum (Lots of suck) or no vacuum (No suck :lol: )? As stated if there is no vacuum, I would be concerned the inlet valve is NOT being opened, but if there is a lot of vacuum then I would suspect the throttle valve was not opening (Incorrectly assembled by your mechanic after cleaning being the most likely cause).

Gary

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Re: vacuum on #4 when trying to sync

Postby bradmonkey » Tue Feb 05, 2013 4:49 pm

I checked with my Honda tech and he's scratching his head too,so I went home and fired it up with the guages on it --same thing big vacuum on #4,so I got missed off and really started cranking in on the adjusting screw,suddenly #4 started coming out of a vac and #2 went into a vac,looks like the butterflies are way off,going to give it try after it cool off.Thanks, Bill

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virgilmobile
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Re: vacuum on #4 when trying to sync

Postby virgilmobile » Tue Feb 05, 2013 5:17 pm

Ahhh....The very first post...."#4 will not pull out of a vacuum".....what you say and what I understood were 2 different things...altho it's the same problem.
So it was stuck pulling a high vacuum compared to the others...meaning the throttle valve was closed further than the others.

Should be easy to get it from here....Get all the throttle valves to open and close the same... :D

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Re: vacuum on #4 when trying to sync

Postby thrasherg » Tue Feb 05, 2013 5:39 pm

virgilmobile wrote:Ahhh....The very first post...."#4 will not pull out of a vacuum".....what you say and what I understood were 2 different things...altho it's the same problem.
So it was stuck pulling a high vacuum compared to the others...meaning the throttle valve was closed further than the others.

Should be easy to get it from here....Get all the throttle valves to open and close the same... :D


I had the same misunderstanding!! Tricky thing this English language!! :lol:

Gary

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Re: vacuum on #4 when trying to sync

Postby bradmonkey » Thu Feb 07, 2013 1:09 pm

Thanks again guys I did the butterfly adjust but now I find out after firing it up she won't idle down even with the idle screw backed out all the way--somebody was really screwing this thing up before I bought it.The amazing thing about it is it didn't run that bad even as messed up as it is !

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Re: vacuum on #4 when trying to sync

Postby thrasherg » Thu Feb 07, 2013 3:03 pm

If it will not idle (reving too high) then something is stopping the throttle slides/valves from fully closing. I would be taking the carbs out again and giving a good look over them. I suspect something has not been re-assembled correctly. Once they are all out you can check that every carb does fully close. An air leak between the carb and the inlet valve can also cause this problem, have you checked that each carb is correctly seated in its rubber inlet manifold and that the rubbers are not cracked?

Gary

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Re: vacuum on #4 when trying to sync

Postby bradmonkey » Sat Feb 09, 2013 5:43 pm

gary, the reason it would'nt idle down was because dumb ass forgot to hook the vac line to #4--the good news is after taking off the intakes ,again I set the openings with a feeler guage like I had done before,this time I shot wd 40 down the butterfly shafts,fired her up and whalla' no vacuum in #4,although my barracuda guages are only reading about 10 they are even.Most of the web sites seem to show those gauges fluttering around 5,should the lower reading make a difference?---again your the MAN!

Bill

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virgilmobile
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Re: vacuum on #4 when trying to sync

Postby virgilmobile » Sat Feb 09, 2013 8:46 pm

ignore the numbers.
your only concern is that they pull the same vacuum at 1000 rpm.




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