My Tuning Adventures

[Cudajason]

When @Chryco Psycho looked at my car last week, we pulled couple of plugs and they were reading very lean!

So I switched out the main jets to a pair I had on hand...70s to 75s.

Here is what the plugs looks liek after a quick / short highway run.

I think she is too rich now, so I plan to drop down to 73s, once I go buy some.

The problem I am having, is after I switched the jets, I found the idle got a little choppy, and the engine started to surge at idel.  I am not sure it comes across in the video, but please let me know if you hear it.

Before the jet change, the idle seemed smooth and I no surge...thoughts?

Jason

[70 Challenger Lover]

Five jet sizes richer is a massive change. The plugs look good but did you pull a plug after prolonged idling? That can give you a different reading. If 70 was too lean, I'd go no more than 72 and run it through it's paces for a while to see how it performs.

[70 Challenger Lover]

I don't detect any surge in the video. A tach and vacuum gauge might make a surge more noticeable.

[GoodysGotaCuda]

I'd suggest spending $150 or so and getting a wideband o2 sensor for tuning. Takes the guesswork out!

[RUNCHARGER]

Try 72's. I usually jump 2 at a time as well. At least you know you're close.

[HP_Cuda]

I agree AFR takes all the guesswork out.

When playing with jets I try and limit my increment/decrement by 2 sizes - mostly 1 size at a time.

[70 Challenger Lover]

Another thing to consider is that surging is often a lean condition. It is possible to have the idle mixture screws to far in making it lean at idle and at the same time have main jets too big making it too rich for cruising down the highway.

A lot of 750 cfm Holleys come with 72 primary main jets and putting those back in may be perfect.

[Chryco Psycho]

I agree that the idle mixture needs to be adjusted , you should be able tofeel a power increase with the correct jets in there ,
Jason has an O2 sensor but has not welded the bung into the new exhaust yet

[Cudajason]

Hey guys,

Thanks for all the responses.

Yeah I know 5 jets up is a big leap...I had the 75s on hand and was bored so I switched them to see what would happen. 

I am going to pick up some 72s and see what that does. 

As CP mentioned, I have a Wideband O2, but need to weld in the bung to my new exhaust.  I will get to it eventually.

I will also adjust the idle mixture screws again one I put in the proper jets.

Jason

[RUNCHARGER]

I know a lot of people will tell you the jets don't affect the idle but I readjust them anyway. When I was tuning my orange car I finally went and bought a wideband and threw it in, turns out my tuning was pretty much dead on without it, however you will get there a lot faster using one.

[70 Challenger Lover]

I have found that a decent underhood tach and a vacuum gauge will get you pretty darn close.

[Cudajason]

I know a lot of people will tell you the jets don't affect the idle but I readjust them anyway. When I was tuning my orange car I finally went and bought a wideband and threw it in, turns out my tuning was pretty much dead on without it, however you will get there a lot faster using one.

I am starting to believe they do....I made not other changes and the engine doe not idle the same.

I have found that a decent underhood tach and a vacuum gauge will get you pretty darn close.

I have both and will use them next time.

I have a pair of 72s and 73s on order for the weekend.

Its supposed to rain all weekend...oh well, I can get it apart and back together and see what happens.

Jason

[Chryco Psycho]

My guess is the 73s
Jetting does affect idle

[Cudajason]

July is always a crazy month for me at work...and this year did not disappoint.  I have not had a lot of time to spend on the car.

I managed to get the 73 jets installed a few weeks ago, but have been dealing with a fuel leak in the carb feed line since then.  It seems like what ever time I could find I spent trying to get the lien to seal up.  So last week I just gave up and bought a new feed line.  Looks like it solved the problem.

Next step is to take it for a spin and see how it runs...that and change the valve covers and see if that fixes my oil leak.

My only concern at this point is that the valve train seems to make a lot of noise on initial start up after the car has sat for a day or two?

Are Hughes Cam savers lifters know for being noisy?  I don't think its an issue, because it quiets down fairly quickly...but once you kill a cam you get a bit jumpy!!!

Jason

[70 Challenger Lover]

I've always found that once hydraulic lifters pump up, they stay that way so I'm surprised you're getting noise at start up as if they are bleeding down after shut off.

On a car I recently bought, I noticed a little rocker noise on one side and initially I was worried. It went away after warm up and I thought that was unusual so I pulled the cover to inspect. I noticed that the rockers at two cylinders didn't have quite as much side to side clearance as the others so I pulled the hold down spacer only and swapped it out with one a little bit narrower to provide a bit more clearance. Problem went away and has never reappeared.