Setting Base timing?

[toyotaspeed90]

How does one set "base" timing on these since there's no vacuum advance nor (that I know of... nor mention of it in the Clymers book) any ports to jumper to set base timing?

Tried to time it via light and it's jumping a good 5-10* back and forth at idle...

4.3L alpha 1, Thunderbolt IV ignition

 

[sickwilly]

Re: Setting Base timing?

I know how to do it on a thunderbolt V, but I don't think you do it on a IV

http://forums.iboats.com/showthread.php?t=313279

 

[John_S]

Re: Setting Base timing?

If you have confirmed you have T4, there is not a base mode. Some people think they have T4 because they don't have a knock module, which is not the case with a number of models.

If you have T4, and its jumping around, it could be play in distributer, rotor, sensor, corroaded dist cap, bad connection to coil, and hopefully not the expensive ICM module.

 

[toyotaspeed90]

Re: Setting Base timing?

If you have confirmed you have T4, there is not a base mode. Some people think they have T4 because they don't have a knock module, which is not the case with a number of models.

If you have T4, and its jumping around, it could be play in distributer, rotor, sensor, corroaded dist cap, bad connection to coil, and hopefully not the expensive ICM module.

well there should be advance built into the system... there isn't play in anything and it states "Thunderbolt IV" on the module.... rpm's at idle at this point aren't 100% steady but trying to knock down the basics first.

 

[Don S]

Re: Setting Base timing?

rpm's at idle at this point aren't 100% steady but trying to knock down the basics first.

Until you get the idle steady, you will not see the timing stay steady. If you are between 5 and 10? BTDC with it surging, the surge is not caused by timing. I would suspect idle mixture on the carb, or maybe vacuum leaks causing the problem.

 

[toyotaspeed90]

Re: Setting Base timing?

don't know how there could be a vacuum leak.... new intake gaskets, no ports on the manifold nor the carb..... most likely fuel... as the carb is acting up a bit. I think the previous owner had the carb rebuilt, but the choke plate was somehow stuck and literally wedged in the carb... cutting up the sides of the carb... I "fixed" that issue but the rod it's on is probably bent as it is a bit rough to turn.

 

[RogersJetboat454]

Re: Setting Base timing?

Did you spray carb cleaner around the carb gaskets and the throttle blade shafts? A re-builder who didn't make sure the carb parts didn't seat correctly, or didn't check for excessive play in the throttle shafts may have made an air leak.