Need Help With New Motor
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Joined: Aug 2000
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From: Lewisberry PA
Need Help With New Motor
I'm trying to get a few more things done to my '68 before winter, but can't get the motor to run well enough to drive out of the neighborhood. I put a new 385 fast burn rate motor with a Mallory Electronic distributor (w/mechanical tach) and a 750 Speed Demon carb. We roughed in the timing and it has always started perfectly. The motor did not come with a timing tab, which is now on order, so I don't know where my timing is set. My problem is a lot of blue smoke coming out of the exhaust and my spark plugs immediately getting very black (dry, not oily).
I had it at a shop when we first got it running and they changed the primary jet settings from 76 to 71 to try and lean it out. It helped just a little. I went through the Demon setup and made sure the idle mixture screws were about 1.5 turns out. I checked the other setting. I put a fuel pressure regulator on to make sure I wasn’t putting to much fuel into the carb.
What is a reasonable jet setting for a 750 carb on this motor? Am I looking in the wrong direction, I never had a carb that was so far off from the factory. Demon is not open on the weekend for technical help.
Any suggestions would be greatly appreciated!
Jeff Reed
I had it at a shop when we first got it running and they changed the primary jet settings from 76 to 71 to try and lean it out. It helped just a little. I went through the Demon setup and made sure the idle mixture screws were about 1.5 turns out. I checked the other setting. I put a fuel pressure regulator on to make sure I wasn’t putting to much fuel into the carb.
What is a reasonable jet setting for a 750 carb on this motor? Am I looking in the wrong direction, I never had a carb that was so far off from the factory. Demon is not open on the weekend for technical help.
Any suggestions would be greatly appreciated!
Jeff Reed
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From: Semper ubi, sub ubi
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Re: Need Help With New Motor (JeffReed)
Jeff,
It looks to me like you are still rich. I would suggest changing the jets to the next two steps down and trying it again with a fresh set of plugs.
It looks to me like you are still rich. I would suggest changing the jets to the next two steps down and trying it again with a fresh set of plugs.
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From: Bloomington MN
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Re: Need Help With New Motor (JeffReed)
Have you been driving it much, or is it the idle setting that is fouling your plugs? I have found that the best tuning tool seems to be a vacuum guage for me. Set the idle mixture screws to what gives you the best vacuum. The vacuum guage is also a good tool to adjust your base timing when a timing pointer isn't on. Ultimately, an air/fuel ratio meter would be the best tuning tool, but most C3 guys have a vacuum guage laying around (helps to troubleshoot for vacuum leaks too :smash: ) .
AC
AC
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Joined: Aug 2000
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From: Lewisberry PA
Re: Need Help With New Motor (A C)
It fouls on idle. There's a lot of blue smoke coming out the back at idle. I do have a vacumn guage, haven't used it in years, but it sounds like a good idea.
Thanks!!
Jeff Reed
Thanks!!
Jeff Reed
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From: Raleigh North Carolina
Re: Need Help With New Motor (JeffReed)
Blue smoke is oil.
Some people have this problem after installing the intake... the ports sometimes do not seal at the bottom edge because of a port mis-match. The engine sucks oil from the lifter valley. The solution is to use a good (usually GM) intake gasket set and to re-install the manifold being very careful about dropping it straight down and making sure the bolts are torqued to spec and then retorqued 2 more times after running. Just a possibility. Also, make sure your PC valve is working properly. It can suck oil as well. Lastly (not likely) the valve seals were not installed properly (or at all).
Some people have this problem after installing the intake... the ports sometimes do not seal at the bottom edge because of a port mis-match. The engine sucks oil from the lifter valley. The solution is to use a good (usually GM) intake gasket set and to re-install the manifold being very careful about dropping it straight down and making sure the bolts are torqued to spec and then retorqued 2 more times after running. Just a possibility. Also, make sure your PC valve is working properly. It can suck oil as well. Lastly (not likely) the valve seals were not installed properly (or at all).
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From: kennett square,pa,us
Re: Need Help With New Motor (JeffReed)
Jeff,
Try calling Jones Pontiac down in Lancaster and ask Don which jets they use on the 385? GM uses Holley, but they should be very close to Demon. Their number is (717) 394-0711.
If worst comes to worst I will loan you a Holley 650 you can try. We are only about 75 miles apart.
That 750 seems like a lot of carb for that engine. I use a 650 Demon on my 355 with fast burns and I have a little more cam (XE274) than you do.
Good Luck!
Try calling Jones Pontiac down in Lancaster and ask Don which jets they use on the 385? GM uses Holley, but they should be very close to Demon. Their number is (717) 394-0711.
If worst comes to worst I will loan you a Holley 650 you can try. We are only about 75 miles apart.
That 750 seems like a lot of carb for that engine. I use a 650 Demon on my 355 with fast burns and I have a little more cam (XE274) than you do.
Good Luck!
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From: Lewisberry PA
Re: Need Help With New Motor (bud snyder)
Bud, thanks for the info. I will call Don tomorrow. I only picked the 750 based upon information from Demon's literature. They say the 750 Speed Demon for 350-427 hi performance 350+ horse powered engines.
I'll start with Don and see if he can help me out. I appreciate the information!
Jeff Reed
I'll start with Don and see if he can help me out. I appreciate the information!
Jeff Reed
