Misfiring and sluggish acceleration when exiting traffic jam

[Mark Maras]

 Don't richen it up yet. Refresh my memory please. What needles are you running? Meanwhile, just drive it for a week, pull the plugs and send pics.

[jalexquijano]

SM needles provided by Ztherapy when the 3 screws carbs where restored by them. Ill drive it today and take a picture of the plugs. Should i just race the car for 10 mins and then shut the engine off or normal driving on traffic jam and then shut the car down?

[Mark Maras]

IMO, drive it normally before checking plug color. General opinion, that I've read, is the SM's are a bit richer a low RPM's. 

[jalexquijano]

Mark,

Just be advised that my car has a schneider 274f cam and not the stock cam as my car was overhauled to 2.6L with oversized pistons. Could this affect? What needles may be recommended better than sm needles for this upgrade.

 

[Mark Maras]

 First things first. I still would like to know if the difference in color between #4 & #5 plugs is normally what you find when you pull the plugs and I'd still like to see the compression test readings. I know very little about the cam you selected and how "hot" it is but I'm beginning to believe that dealing with traffic and warm temperatures you may be better off with a cam closer to, if not, OEM and OEM needles. Keep in mind this is only one opinion. Other's may differ. The over-sized pistons will make little to no difference when it comes to the carbs. OEM Hitachi's work just fine on 2.8s. Taking a trip on the "WayBack Machine", this reminds of fooling around with small block Fords and Chevy's in the late 1960's. It was common to stuff a bigger cam into them and usually over carb them too. The result was similar to the symptoms you're experiencing. Lousy response at low RPMs. Loaded up plugs. Poor all around driveability on the street. Not saying that you won't get it running well, but the changes from stock aren't an asset at this point in time. Now back to # 4 & #5 plug colors. Is that normal?

[jalexquijano]

THis is the cam i have installed:

http://schneidercams.com/274FL6.aspx

Sincé my engine was overhauled due to wear of the original engine by DATSUN LLC increased to 2.6L, i was recommended to buy this camshaft. If replacing the needles with another type will compensate and solve the driveability issue at low rpms while mantaining the same response over 3000 rpms, i guess that is something that will need to be considered. I will drive the car today after increasing both mixture knobs to 2.65 as i need more power but not too much that will foul the plugs during long idle time in traffic.

 

Edited October 10, 2017 by jalexquijano

[Mark Maras]

 Your cam appears to be fairly mild grind. Been looking back in older CZCC threads concerning SM needles. The consensus of opinion (curiously except Bruce Palmer) was that the SM's were too rich for a stock engine or a mild build. An interesting suggestion to lean rich mixture needles was to physically lower them (pull them out) .020" from the standard position. You might try that and see if the over-rich condition improves.

[jalexquijano]

OK. We´ve got a point!! SM´s were too rich for stock engine or mild build (my case). What i want to achieve is the following: Good and fast response on 1st gear when speeding and good acceleration over 4K

[jalexquijano]

On 9/10/2017 at 3:43 PM, Mark Maras said:

IMO, drive it normally before checking plug color. General opinion, that I've read, is the SM's are a bit richer a low RPM's. 

I dialed both carbs to 2.70 turns clockwise. Drove it for 30 mins yesterday night including a couple of street light no longer than 30 second stops. Response at 1st gear got better. Once at the parking, i took all the 6 spark plugs out and this was the result

[Mark Maras]

Congratulations. Looks like progress. Now drive it normal for a week and take another look at the plugs.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[jalexquijano]

On ‎10‎/‎11‎/‎2017 at 8:18 AM, Mark Maras said:

Congratulations. Looks like progress. Now drive it normal for a week and take another look at the plugs.

 

Still driving it but only during sundays and no traffic situations.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[jalexquijano]

On 11/10/2017 at 8:18 AM, Mark Maras said:

Congratulations. Looks like progress. Now drive it normal for a week and take another look at the plugs.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2.75 clockwise