[1970SS454TH400]

Good evening,

I had some carb issues that were corrected "running rich". I did not change the plugs as they did not have 50 miles on them. Well after the carb was fixed the car has some small misfires at idle and high RPM a little hesitation not the smoothest. Should I change the plugs? They are R42TS, I got R45TS from Napa today. The car engine specs as I bought it 770 Holley vacuum secondaries, Eldebrock intake, Headman long tubes and slight cam, HEI distributor. Gapped at .040.... So basically I messed up by not changing the plugs after the carb ???

 

[japete92]

Recommend checking the ignition timing. The 'Ignition 101' sticky in the ignition section of this forum is recommend reading.

Pete

 

[427L88]

plugs can foul up pretty easily, there have been times I ought have changed them out. . Did you mean to deliberately change heat ranges?

 

[modern malibu]

R45ts is 3 heat rages hotter than R42ts is more likely to burn cleaner in your engine setup. R42ts is usually only used for racing applications,where compression ratios are extremely high

 

[Aaron]

There is no way to tell with what you said. Get the basics out of the way first. Looks like your first post. You have a lot to learn I would guess about those things. There are books and or etc you can get or good comments here. Sort out the basics of ignition first. Tuning is not a issue until the misfire is gone.

 

[1970SS454TH400]

There is no way to tell with what you said. Get the basics out of the way first. Looks like your first post. You have a lot to learn I would guess about those things. There are books and or etc you can get or good comments here. Sort out the basics of ignition first. Tuning is not a issue until the misfire is gone.

Thanks

 

[1970SS454TH400]

R45ts is 3 heat rages hotter than R42ts is more likely to burn cleaner in your engine setup. R42ts is usually only used for racing applications,where compression ratios are extremely high

So you suggest running the R45TS over the R42TS ?

 

[billdini]

So you suggest running the R45TS over the R42TS ?

Plug heat range is determined by compression. For instance and as mentioned extremely high compression needs a very cold plug to avoid preignition that can sound like a misfire firing before it should. My 11 to 1 compression L79 327 used R44 heat range. Studies showed later that even with high compression a R45 is a better match then the 44 and I have been running them for a couple years now. BTW a plug that is too cold like a R42 can cause plug fouling. Are you sure your carb needed to be modified. What was done?

 

[modern malibu]

Yes I suggest running a R45ts in a street car and monitoring the engine for any knock under cruise and full throttle conditions.

 

[1970SS454TH400]

Plug heat range is determined by compression. For instance and as mentioned extremely high compression needs a very cold plug to avoid preignition that can sound like a misfire firing before it should. My 11 to 1 compression L79 327 used R44 heat range. Studies showed later that even with high compression a R45 is a better match then the 44 and I have been running them for a couple years now. BTW a plug that is too cold like a R42 can cause plug fouling. Are you sure your carb needed to be modified. What was done?

Power valve was shot, bad needle and seat and wrapped accelerator pump. Prefect storm to run rich. The carb shop suggested to change out plugs. I didn't since less than 50 miles on them. I changed to thr 45 this morning runs better

 

[Aaron]

Dont worry about range until you solve the other issue.

The heat range issue you are not going doing anything with until you go to the track or get on a chassis dyno.

Its hard to read plugs on pump gas these days.

Take your car to a chassis dyno and dial it in there. Then you get a LM2 or a monitoring system to tune for the street. The chassis dyno will be provide WOT tuning only, unless they more for you.

Once you get it running, just back timing off and only baby the car around. You will not hurt anything.

 

[DUTCH MAX HEADWORK]

If the misfire comes back, check the terminals inside the cap and rotor. You can check your plug wires by doing a resistance test on them. Also, pop the hood in a dark place and look for arch over.

 

[Aaron]

Look also can take a infrared temp gun, if you have one, and shoot the header tubes. May or may not indicate a misfire. A squirt body will do the same thing.

You can also do a screw driver test to see if you have spark at each plug.

If your having a stinky smell when your first crank the engine, don't really worry about setting the timing. The fumes will burn your eyes and you will need to take a vacuum gauge and tune the carb for highest vacuum to get the tears out of your eyes. You then can set the timing.