#4 cyl.only 30 lbs. compression

[slyone]

Got it a month ago, been doing all the routine stuff (valve adj., carb overhaul etc. been bombing around a few days when weather was nice- no problems like this. I "thought" it may have dropped a cyl. the other day when tinkering with gas leak/carbs right before I shut it down to redo carbs and reseal cam chain tensioner. Finished both yesterday and it wasn't firing on #4. I tried switching coils this morning and it began firing on all cylinders..? Tried again this afternoon and #4 not firing again so I pulled plugs and checked compression; 110 psi on 1,2&3 but sadly..30psi on #4 cyl. I did not try putting any oil down cylinder and left throttle closed when checking compression. I can see valves thru plug hole operating. Thinking my next step might "have to be" pulling cam cover and checking cam timing and valve adjustment? When I resealed tensioner I did put #1 at tdc so I can't believe chain skipped a tooth-wouldn't it effect more than 1 cyl. anyways?

Update: I just went out and rechecked #4 with throttle 1/2 open and it pumped right up to 125psi..WTF! I guess...that should be considered a good thing..lol..
why do the others have 110psi/closed throttle and #4 has only 30psi?
I did install an inline simple clear screen fuel filter?

[tkent02]

Look elsewhere, but rechecking the valves after a few miles is always a good idea.

[Mekanix]

1 get rid of the filter if you have starvation issues. sounds like the last cylinder didn't get any gas until after and then it fired but the next time it was empty again.
2 always do compression checks wide open throttle.
3 always test a warm engine.

leakdown test would tell you more.

[slyone]

OK I'll remove the filter. Ya know, I read where everyone "sync's" their carbs, I have not done that before..BUT, I don't see how they could have ever changed because I did not loosen those tappet adjusters on top of the sliders, I simply removed the bolt and shaft that is deadlocked in 1 position. Just trying to come up with possibilties?

[tkent02]

The synch will change slightly from valve adjustments, or even carb tuning.

You don't know what the PO did either.

[hjfisk]

Did you even try the bench sync as I suggested earlier in your other thread short cuts are long cuts they don't work

[slyone]

I've never tried syncing carbs, the PO of 10 yrs just changed oil and stuff. I just removed that inline fuel filter and set the coils back to original and it ran on all 4 nicely! yeah! but it definitely needs alot of fine tuning that's for sure. Though the way it's gone..this thing "could" act up next time I start it!

Isn't bench syncing just to get all the slides operating uniformly to the eye? I mean, I did "look" at them and see they were ok? just wondering..so bear with me..lol

[SqDancerLynn1]

TO do a compression test The throttle needs to be fully open

[Mekanix]

Yup that is what a bench sync is. Its setting them in the closed position for a good baseline to start with. Some people set the idle high and use a small precise drill bit to measure the slide height in each one to see if they are all the same height. Same idea as the valve adjustment.

The proper way all depends on the engine and will vary with how the engine is performing cylinder to cylinder.

There's only so much preparation you can do before you have to adjust in the moment things are happening.

[hampshirehog]

TO do a compression test The throttle needs to be fully open

And the engine hot.

....

[tkent02]

And the engine hot.

....

If it runs.

[slyone]

If it runs.

lol, so true! I gotta pull them carbs to do the sync

[hampshirehog]

lol, so true! I gotta pull them carbs to do the sync

No you don't - there is another way.

Remove the tops of the carbs and measure down to the tops of the slides. As long as you line up with the seam on the back of the carbs so you're measuring in the same place each time and measure very accurately (caliper gauge will be fine) you'll be as close as you are doing it 'the proper way'.

[azr]

TO do a compression test The throttle needs to be fully open

Not sure if you noticed Lynn's post here or not. A cold compression test isn't as accurate as a warm one but it's fairly close.

"Remove the tops of the carbs and measure down to the tops of the slides. As long as you line up with the seam on the back of the carbs so you're measuring in the same place each time and measure very accurately (caliper gauge will be fine) you'll be as close as you are doing it 'the proper way'. "

Hey 'hampshirehog' that's a great tip to remember in the future. I've done some carb synch's where I've started dicking around with things so much I put everything out and needed to bench synch again. Great tip, thanks.

[slyone]

I pulled the carbs-like 10 min. no biggie. I'm just getting mentally exhausted! lol Anyways, wow bench sync is so easy & quick and yes, sliders were off. So I get it all back, fire it up, guess what? Yup #4 not firing at all-cold pipe! WTF! I hope I stumble upon the failure/culprit soon.... So to me it appears to be intermittent, and difficult to isolate into a basic category too! I think I can set mechanical on the back burner since it does and always has run great. So either secondary ignition or air/fuel...carbs are done..synced and floats done, no more fuel leaks with the new gaskets and fuel rails/tubes. Think I'll try swapping boots/coils again New points and condensors static timed last week too.