I partly rebuilt my engine but haven't been able to get it to start since
I put it back in the car. I took a plug out and turned it over and it
was making a spark. Also, I can see the fuel thru the little windows
on the PMO carbs so it should be getting gas. What could be preventing
it from starting given that seems to be getting gas and spark?
Assuming the cams and piston relationships weren't disturbed, it's could be a matter of making sure the spark occurs at the right time.
No. 1 cylinder should be at TDC, end of compression stroke and the distributor rotor should point to the number 1 spark plug position on the cap. Make sure the piston position isn't at TDC, end of exhaust stroke. If so, you installed the distributor 180º out of synch.
As for fuel, remove the air filter housings, then peak into the throats with a flashlight. Work the throttle. You should be able to see a squirt from the accelerator pump into each throttle bore. If so, you have plenty of fuel for starting.
Hoe this helps,
Sherwood
I looked down the carbs and can see the gas squirting. To test if
I had the cam timing wrong I reversed the wiring on the distributor.
It still would not start. Am I going to have to take the chainbox
covers off so I can see the position of the dots on the end of the
cams?
So your previous engine work involved the camshafts?
If so, before you take anything apart, check to see if you have compression at no. 1 cylinder while traveling towards TDC. The timing mark on the pulley should confirm this as well. You can check this by fitting just the hose from a compression tester (or equivalent) into the spark plug hole, then feel for compression as the engine rotates toward TDC.
Reinstalling the distributor shaft/rotor 180º only corrects the relationship between distributor and camshaft, not the basic camshaft timing.
Sherwood
Thanks for the advice. I will do as you suggest. But at TDC for #1 aren't both the intake and exhaust valves supposed to overlap and both be open?
If you've got fuel and spark, I'd check for compression and timing. Timing of both the ignition and cams. Checking the compr. and ignition timing are probably the easiest, so start there. Distributor correctly installed, firing order correct, and so on. It might help to know what kind of work you did on the motor?
Ok. I checked the compression on #1 and it does go up every 2 revolutions when the rotor is pointing to the notch on the dizzy. As to the work I did, I took off the chainbox, removed the cams, and heads. I put on updated tensioners, set the cam timing, and resealed the cyc./head interface, and resealed the chainbox. I also replaced the MFI with PMOs. I did not remove the dizzy.
Yes. That's correct for cam timing purposes. However, in the 4-stroke cycle, each stroke requires 180º, thus 720º for one complete cycle. That means for each 4-stroke cycle, each piston will approach TDC twice; once for compression, once for exhaust.Originally Posted by dhopkins
If you disturbed the cams, there's a chance the cam timing is off.
As JHunter suggests, perform the easy stuff first.
Sherwood
Ok. The intake valve opens and the piston sucks in the fuel/air mix, then the piston travels up with valves closed causing compression, the plug fires causing the power stroke, and finally the piston travels up with the exhaust valve open, right? Thus TDC occurs twice but compression should occur only once every 720 degrees. Since that is what happened when I checked #1, the left cam should be Ok, right? I guess the next step would be to test #4 and expect compression to occur every other time that the rotor is pointing to the #4 ignition wire, right?
After that I am not sure what other easy tests are left. The static ignition timing seems to be correct in that the Z1 mark is lined up with the mark on the engine at the same time the rotor is pointing at the notch in the dizzy. I already checked the compression in #1 as I mentioned. I guess the next thing would be to double check to make sure the cam timing is correct by removing the upper valve covers and using a dial indicator. Does that make sense?
Yes, all is correct. However, just to confirm: With piston at TDC, compression stroke, the rotor must point to number one plug wire in dist. and Z1 mark is aligned with mark on crankcase. Merely having the rotor point to number 1 at TDC doesn't confirm TDC is at end of compression (correct) or end of exhaust (not correct) since the installed orientation of the distributor is independent of the piston and camshaft relationship.
As a next step, I would remove both lower valve covers and observe the position of no. 1 and no. 4 exhaust valves and cam lobes. When no. 1 is @TDC compression, the ex. and in. valves should be closed and no. 4 cyl. should be @ TDC in the overlap position, end of exhaust, beginning of intake (both partially open or on the ramp of the cams).
Hope this process minimizes the troubleshooting process.
Sherwood
Posting Permissions
Reply With Quote