Newly purchased GT350 flawless 150 miles. Now sputters out every few miles.

[zray]

"........What is the best way to brake in a fresh rebuilt motor?

put in some good synthetic oil, I like Mobil 1 15w-50, 1300 ppm zinc / 1200 ppm phosphorus. But any good synthetic oil with over 1000 ppm ZDDP will be fine, and drive it all over the rpm range. Don't neglect the 4,000 to 6,000 rpm area.  You aren't hurting the engine, you are exercising it.

after  500 miles change the oil and filter. 

There are a lot of varying opinions regards using a synthetic oil for break in . I am in the camp that uses synthetic oil for break-in and thereafter as well. Aside from the fact that numerous  new car manufacturers use synthetic from the git-go, I've been using it during break-in for 20 years in numerous classics with zero ill effects. Synthetic is superior in regards to reducing friction related wear, & at break in this becomes even more important.  Some say it reduces friction too much and rings don't seat. Personally I've never encountered this issue, and neither do the millions of new cars that come from the factory with synthetic in the crankcase.


Z

Put in a new fuel filter. It takes 5 minutes, and you'll know at once if that's the issue.

[2112]

Am I the only person who wants a photo posted of your new baby, broken down on the road side or not

Hope you get your issue sorted soon.

Peter

Second the motion.

Richard E.

Dilly Dilly 🍻🍺

[2112]

"........What is the best way to brake in a fresh rebuilt motor?

put in some good synthetic oil, I like Mobil 1 15w-50, 1300 ppm zinc / 1200 ppm phosphorus. But any good synthetic oil with over 1000 ppm ZDDP will be fine, and drive it all over the rpm range. Don't neglect the 4,000 to 6,000 rpm area.  You aren't hurting the engine, you are exercising it.

after  500 miles change the oil and filter. 

There are a lot of varying opinions regards using a synthetic oil for break in . I am in the camp that uses synthetic oil for break-in and thereafter as well. Aside from the fact that numerous  new car manufacturers use synthetic from the git-go, I've been using it during break-in for 20 years in numerous classics with zero ill effects. Synthetic is superior in regards to reducing friction related wear, & at break in this becomes even more important.  Some say it reduces friction too much and rings don't seat. Personally I've never encountered this issue, and neither do the millions of new cars that come from the factory with synthetic in the crankcase.


Z

Put in a new fuel filter. It takes 5 minutes, and you'll know at once if that's the issue.

Aren't modern engines built much tighter than old pushrod engines?

I use Joe Gibbs break-in oil to seat rings (Roller valve trains).  It is Dino oil.

[jerry merrill]

Check for vacuum leaks

[Dynomax]

+ 1 for non venting fuel cap causing vacuum in the fuel tank. Easily eliminated as a symptom.

[gt350hr]

    Mostly Mustangs in Oakland is owned by Jack Schroll and is an excellent place to use . Jack is a long time SAAC member and former owner of 6S001. He can make your car run like it should.

[J_Speegle]

+ 1 for non venting fuel cap causing vacuum in the fuel tank. Easily eliminated as a symptom.

Easy enough to remove the gas cap and try it.

[Tinface]

Wow. I just want to say thank you so much for each and every one of you really helpful posts to my problem.

What oil to use in a new engine, how to brake in a new engine, what issues are causing my problem, gas cap, fuel filter, floats, the various carb issues.

Also, the Mostly Mustang referral helps. When I was considering purchasing two of the gt350s Fantacy Junction cars but passed, they mentioned Mostly Mustangs. If anyone has had dealings with them that were great or moe private—not so great—I sure would appreciate a private and confidential message. I don't want to entrust my assets to someone unless they are really competent.

Thank you so much all

By the way, I had a well funded  silicon valley friend with me when the car died on the freeway the first time. I've been trying to show him reasons why these cars are sooo much cooler than a new McLaren— which we went into the local dealer a few weeks ago, and put a deposit on. "One shot fired." One shot ..MISSED". No photos of the brakedown will be posted here. However, if interested, check out the Jaguar clubs in the SF areas. A nice series 1 rag top E-Type with a blonde woman in the passenger seat purred by—a wry smile on the driver's face. He didn't bother to stop...

[6s2020]

I know you said your car has had a thorough restoration , but have you replaced the short fuel hose between the sender unit and hard line?
These tend to constrict with age and have seen first hand a mustang run fine, then under load or up hill cough and splutter then die, will start back up again and repeat. He replaced this hose and all good.

Darryll

[Tinface]

Daryl, that is an interesting point thank you very much for that.

[zray]

"........What is the best way to brake in a fresh rebuilt motor?

put in some good synthetic oil, I like Mobil 1 15w-50, 1300 ppm zinc / 1200 ppm phosphorus. But any good synthetic oil with over 1000 ppm ZDDP will be fine, and drive it all over the rpm range. Don't neglect the 4,000 to 6,000 rpm area.  You aren't hurting the engine, you are exercising it.

after  500 miles change the oil and filter. 

There are a lot of varying opinions regards using a synthetic oil for break in . I am in the camp that uses synthetic oil for break-in and thereafter as well. Aside from the fact that numerous  new car manufacturers use synthetic from the git-go, I've been using it during break-in for 20 years in numerous classics with zero ill effects. Synthetic is superior in regards to reducing friction related wear, & at break in this becomes even more important.  Some say it reduces friction too much and rings don't seat. Personally I've never encountered this issue, and neither do the millions of new cars that come from the factory with synthetic in the crankcase.


Z

Put in a new fuel filter. It takes 5 minutes, and you'll know at once if that's the issue.

Aren't modern engines built much tighter than old pushrod engines?

I use Joe Gibbs break-in oil to seat rings (Roller valve trains).  It is Dino oil.

I do imagine there are major differences in piston and piston ring materials and design.  How that translates to a reluctant use of synthetic oil,  that is something  I question as being reasonable.

not sure what the low end of the rod and main bearing clearances are for modern engines. But the low end of desired clearance for  '65/'66 Ford 289's are pretty tight.  re the Ford shop manual: Mains:  0.0005"  Rod big end: 0.0008".  non HiPo piston clearance low end : 0.0014" HiPo piston clearance low end: 0.003".   I still build engines using this  low end of the desired tolerances for the bearings and the pistons too.  Very long lasting, and just as durable as setting them up loose, when the right lubrication is maintained.

When I was first learning the insides of Ford engines in the mid 1960's , my job at uncles shop was to tear down engines from crashed cars for cannibalizing of the parts. These newish engines routinely had clearances  on the low end of the published specifications.

Z

[J_Speegle]

What is the best way to brake in a fresh rebuilt motor?

IMHO I and many others just install Brad Penn brake in oil and be done with it.  Run it up and down the rpm with a slight load in both directions  - up and down the rpm range.  Yes this can be seen as old fashion but has served many well for 60 plus years

[1967 eight barrel]

I realize that this is a "new restoration" but I was curious if you know what it has for an ignition system? If they have replaced the points with a Pertronix unit, there may be an issue. I'll be glad to explain in PM. I have also seen faulty condensers cause similar issues. I had just this issue on my Harley. I ran a direct ignition sourced 12V for my Shelby and it stopped hard starts and rough idling post warm up.
                                                                                                             -Keith

[98SVT - was 06GT]

Another vote against synthetic oil for break-in. Run regular 30 weight for first 100 miles. Drain and 30 weight again to 1000 miles. Then Mobil 1 forever. With a flat tappet cam you'll feel better if you add some zinc too but I've found Mobil 1 is a good enough lubricant not to need it with stock valve spring rates. New cars come with semi-synthetic oil not full synthetic. I also use a filter designed to work with synthetic oil.

[Stubee]

No Photo of the. ..Breakdown at the side of the road? 
No problem.. I would get some friends and do a recreation of sorts... Get a Jag as you had mentioned earlier and have the Jag parked in front of your Shelby at the side of the road. Only change is this time, have him abandoned and sitting in his car, with the blonde under the Shelby hood and you both looking for the problem...
You have the smirk, she has the smile and he has the scowl..

Sorry, back to the technical issues at hand.

Stubee