2.8 won't start

[daron]

My 86 mj with a 2.8 died while idling and now wont start. I changed the plugs, wires, distributor cap and rotor, coil and fuel pump. all with no help. I rebuilt the carb and even put a new carb on it still with no help. The motor turns over nicely and has good spark. once in a while it will try to start and idle for about a second but then dies again. I've even tried rotating the distributor to adjust the timing but nothing works!!!!! Does anyone have any ideas. I hate watching my toy just sit there and not be able to go play.

 

[Eagle]

Start with the basics --

Do you have compression?

You have spark -- is it pumping fuel? When you manually flip the throttle linkage, can you see it squirting gas onto the carb throat?

Have you set the timing accurately, or did you just turn the distributor at random and hope for the best?

Are the plug wires installed in the correct order? Last time I changed wires on a 4-banger, I managed to get two of them crossed. It happens.

 

[daron]

I worked it some more today. I've got good compression and the I set the timing. There is plenty of fuel being supplied by the pump and you can see it squirt into the carb when you work the linkage. I think I may have a really bad vacuum leak around the carb or intake. I put a vacuum gauge on it and when cranking you only get about 1 pound of vacuum. I was thinking that it should be around 5 to 10 poundds while cranking.

 

[CheapXJ]

is the intake manifold torqued down properly?

one of my 2.8s, the intake manifold loosened up somehow and it would do basically what you described (and the low vacuum)

those motors are such a pain in the ass...

if ya don't get the float JUST RIGHT in the carb, they won't run either. had a hell of a time gettin it in a workable state, and it ALWAYS died in left hand turns, up until the day i got rid of it...

I hate 2.8s... HATE 2.8s

 

[Eagle]

Could also be the carb itself. The hold-down screws tended to loosen themselves from vibration. 4-bangers did the same -- I pulled the carb off one to check for tightness and found that not only were the hold-down nuts loose, the screws holding the carb body to the sub-base were also loose. Small wonder the darned thing wouldn't run.

 

[daron]

I figured it out. The back end of the intake manifold gasket was blown out. That accounts for the no vacuum and no start. Now its just a matter of tuning the carb and timing. Thanks for your help!