Help reading plugs after rejetting (5.7 v8)

[mtb_prodigy]

I recently rejetted my carb, the original jets were size 58 but I put in a pair of 61's due to the engine running lean. I also adjusted the float to the correct specifications and had a mechanic mess with the idle mixture screws. I did notice that one of the mixture screws is out about 3 mm more than the other one. This must be at least a couple whole turns. Here is what the plug looks like after 2 days out and about 3 hours of total run time after putting in new spark plugs. Thanks in advance!

 

[alldodge]

I see still a bit lean and plug may be a bit cold or timing is not correct. Just initial guess right now, would like to see them after some more time.

What carb do you have?

 

[Leardriver]

After years of racing MX, operating a dyno, and tuning engines, I am scared to try to read plugs with modern additives in fuel. Having said that, I agree with AllDodge that those plugs look a tad lean with the limited time that they have on them.

 

[mtb_prodigy]

I have the Rochester 2 barrel gv. Will I be causing damage to the engine running it this way or will I be ok with the current condition?

 

[alldodge]

Unable to say right now because the plugs are not showing enough to say. If anything is going on it will be at high rpms. To get a good read the motor needs to run some at high, then stop quickly, shut it down and pull the plugs. If much idling is done the idle can hide what is going on. Only other way is with O2 sensors in the exhaust.

I think the 61 jet size is a good choice. Check your fuel pump pressure to make sure your pump is keeping up (4-7 psi)

 

[achris]

It would be nice to know what year (or better, engine serial number) we are dealing with.

Chris.......

EDIT: I found your engine serial number on a different thread. Interesting that you have a Rochester carb, since Merc only used MerCarbs on the 5.7 since the mid 80s. And both the serive manual and the parts diagrams for that engine also only show a MerCarb. I suspect the carb may have been changed in the past.

The Merc spec for the main jet on the MerCarb (which is very similar to the Rochester anyway) is 1.65mm

 

[alldodge]

1.65mm

That would put it at 0.0649 or a 65 so bit larger