Backfiring out of carb with 1982 140 mercruiser

[THEWHORULZ]

Recently I had the heads redone on my boat because it seemed the no 2 cylinder valve was not opening and closing as much as the other valves. I also had backfiring out of the carb at the time. After getting the heads redone, it is still backfiring out of the carb. Would there be another reason why the no 2 cylinder valve would not be opening and closing? The reason I dont think its the cam is because I've never had metal in my oil and the backfiring came on suddenly. We drove the boat for 2 days and in the middle of the 3rd day it started backfiring out of the carb. I rebuilt the carb, redone the heads and cannot figure whats going on. If the cam was the problem, wouldn't this be something gradual instead of sudden. Also wouldnt there be a lot of metal in the oil? Is it possible the hydraulic lifter is bad and is it hard to replace.... Is there anything else it could be? I know this is long but I would appreciate any help. Thanks

 

[dubs283]

Re: Backfiring out of carb with 1982 140 mercruiser

carb set too lean??

timing correct??

valve lash adjusted properly??

 

[THEWHORULZ]

Re: Backfiring out of carb with 1982 140 mercruiser

Ive checked all that...Could it be the hydraulic lifter is bad?

 

[Bondo]

Re: Backfiring out of carb with 1982 140 mercruiser

Ive checked all that...Could it be the hydraulic lifter is bad?

Ayuh,... How did you determine the carb ain't going Lean,..??

 

[Bt Doctur]

Re: Backfiring out of carb with 1982 140 mercruiser

You could remove the rockers and using a dial indicator determine the lift of the push rod.This would tell you the cam lobes are ok.Lifter replacement is as easy as removing the side cover and pulling the lifters.
I`d be betting on a weak/broken valve spring or carbon track in the dist cap.A compression test would be helpful too.

 

[THEWHORULZ]

Re: Backfiring out of carb with 1982 140 mercruiser

I'll check the compression later today. I just had the head redone so the valve springs are all new they are OK. I didnt know if a hydraulic lifter could malfunction to where it wouldnt move the valve enough. I can pretty much look at the valve and tell its not moving as much as the others. The weird thing about the backfiring is that it came on suddenly and not gradual.

 

[THEWHORULZ]

Re: Backfiring out of carb with 1982 140 mercruiser

Here are my compression reading 1st cylinder 132 2nd cylinder120 3rd cylinder 135 4th cylinder 120. Does that sound OK? Thanks

 

[dubs283]

Re: Backfiring out of carb with 1982 140 mercruiser

sounds okay

if you had a valve hanging open you would expect to see a zero reading on one of the cylinders

 

[THEWHORULZ]

Re: Backfiring out of carb with 1982 140 mercruiser

Is it normal for one of the valves to barely move?... When I take the valve cover off, the intake valve on the 2nd cylinder barely moves up and down unlike the other valves...Could the hydraulic lifter cause this or is it for sure a camshaft?...It does a lot of backfiring out of the carb when it runs....I have never seen metal in all the oil changes I have done thats why I was reluctant to think its a cam. Thanks

 

[Bondo]

Re: Backfiring out of carb with 1982 140 mercruiser

Ayuh,... Did you adjust the valves when you replaced the head,..??

How,..??

 

[THEWHORULZ]

Re: Backfiring out of carb with 1982 140 mercruiser

I adjusted the valves but even before that I noticed the hydraulic lifter not moving as much as the others. I noticed it also when I put the push rods on. The number 2 intake cylinder barely moving up and down. I didnt know if it was the cam or the lifter. Is it even possible for the lifter to do this? Thanks

 

[Bondo]

Re: Backfiring out of carb with 1982 140 mercruiser

Is it even possible for the lifter to do this?

Not really, No...

Meassure the difference...

I still wanta know HOW ya adjusted 'em...

Btw,... Cam dust may not show up as obviously as ya think...

 

[THEWHORULZ]

Re: Backfiring out of carb with 1982 140 mercruiser

I adjusted them by rotating the timing marks to the NO 1 cylinder then adjusted the valves according to the manual zero lash then 3/4 turn. Then I rotated it 360 degrees and had it on the NO 4 cylinder and adjusted the valves according to the manual. Then I ran it, took off the valve cover and checked the valves to make sure they werent loose. Also if a cam was going out wouldnt it be a gradual process instead of sudden?

 

[THEWHORULZ]

Re: Backfiring out of carb with 1982 140 mercruiser

bump

 

[Joshua Nichols]

Re: Backfiring out of carb with 1982 140 mercruiser

checked for a bad gasket? Around carb?.. Around the manifold?.. Good way to test is carb cleaner.. Engine speed will increase will you spray the faulty area..

 

[fishrdan]

Re: Backfiring out of carb with 1982 140 mercruiser

Also if a cam was going out wouldnt it be a gradual process instead of sudden?

When I rebuilt my 140 the cam had a couple of lobes that were really worn, probably 1/2 of the lobe gone, yet it still ran OK and I didn't know the cam was worn. It's possible that the cam has been wearing without showing any signs of running problems and now it's to the point where it's causing problems.

Have you done the dial indicator test to measure the push rod lift as BT suggested? You could also remove the side cover (behind distributor) and see how high the lifter is moving, compared to the other lifters, less accurate and more of a pain removing parts, but if it's really worn you should be able to see it.

 

[THEWHORULZ]

Re: Backfiring out of carb with 1982 140 mercruiser

I had the cover removed and its moving half as much as the others...I will check for a bad gasket with the carb cleaner...good idea. Is the camshaft hard to replace and does the engine have to be out of the boat? Thanks for everyones help.