small block diagnosis - Pirate4x4.Com : 4x4 and Off-Road Forum

Jason E · 10-31-2007, 08:45 PM

Im finishing up my buggy build and am having trouble getting my motor running. I bought the small block 350 quite some time ago and it has alot of unknown internals. what i do know is it has a cam (unknown type), 1.5 ratio rocker arms, stock cast iron heads, gear drive, holley 650 carb (carb is temporary as I am going to run fuel injection once I get the motor running, as not to complicate things anymore than they already are.) bran new msd distributer w blaster coil and block hugger headers.

ok here are the symptoms: the motor will start but runs very poorly and just after a few minutes the exaust just past the headers gets cherry red hot!!! the motor will only run in the low rpm range, wont idle at all, and back fires through the carb when i goose it.

I have set the timing at several different deg. from 4 to 12 advanced. I know the firing order is correct and I get spark on all cyl. in fact I know it is firing on all cylinders as my headers are discolored right at the first bend off the head at all cylinders. i also checked compression and have 140 to 150 at every cylinder. seem like i have raw fuel or flame going out exaust valves? any help is much appreciated!!!!!!

Grumpy_old_fart · 10-31-2007, 08:50 PM

what year is the timing cover/timing pointer/balancer? are they all from the same year?

they need to be... there are different setups. this will change the timing.

Find TDC on the PISTON. then, find it on the balancer.

once you get the engine TIMED Correctly, you can tune the carb/injection system.

Jason E · 10-31-2007, 09:00 PM

good point, the motor did not have a pointer on it when i got it. i picked up a pointer at parts store and was told they were all the same as long as i got the one for the right size harmonic balancer. ill do some reserch on that. thanks

BumpyDodge · 10-31-2007, 10:39 PM

Sounds like retarded ign timing or lean A/F mixture to me. Check for Vaccuum leaks? Is your Vacuum Advance working? Compression readings pretty much rule out valves not fully seating.

P.S. Backfiring thrugh carb will ruin the Power valve in "old style" Holleys, so even if you fix timing, you could have another problem on your hands with the carb.

Jason E · 11-01-2007, 06:04 AM

I was thinking that I had a vacume leak as well so I replaced carb flange gasket and made shure all ports were pluged. it runs too bad to get an acurate vacume reading as i have to open throttle to keep it running. I'll check the vac advance but I don't think thats the problem as I ran a different distributer in the begining, unless the vac port on the holley is bad. Thanks for input. mabey I should have got a crate motor instead of an atlas!!!

riddler28 · 11-07-2007, 01:13 AM

It really sounds like timming!!!
Like Grumpy said find #1 tdc and mark it.
A trick ..... pull #1 plug have a buddy bump engine in VERY small increments while you hold thumb over spark plug hole once air is excaping "by blowing finger out of way" you know that is #1 compression stroke.
Then turn engine over by hand with flywheel wrench. I like to use the engine oil dipstick put that down #1 hole ontop of piston. while buddy turns engine over with wrench watch the stick come up then when it stops just b-4 going down that is your #1 tdc. Put your marks there. Now pull dist. cap your rotor should be pointing right at #1 hole. If not adjust it.
Good luck.

florida4x4 · 11-07-2007, 05:34 AM

note that once you get the piston at TDC there will be a few degrees of crank rotation that the piston will stay at TDC. Mark TDC on the flywheel in the middle of this flat spot.

10-31-2007, 08:45 PM	#1 (permalink)
Jason E Registered User Join Date: Oct 2007 Member # 102035 Location: Fremont, CA Posts: 46	small block diagnosis Im finishing up my buggy build and am having trouble getting my motor running. I bought the small block 350 quite some time ago and it has alot of unknown internals. what i do know is it has a cam (unknown type), 1.5 ratio rocker arms, stock cast iron heads, gear drive, holley 650 carb (carb is temporary as I am going to run fuel injection once I get the motor running, as not to complicate things anymore than they already are.) bran new msd distributer w blaster coil and block hugger headers. ok here are the symptoms: the motor will start but runs very poorly and just after a few minutes the exaust just past the headers gets cherry red hot!!! the motor will only run in the low rpm range, wont idle at all, and back fires through the carb when i goose it. I have set the timing at several different deg. from 4 to 12 advanced. I know the firing order is correct and I get spark on all cyl. in fact I know it is firing on all cylinders as my headers are discolored right at the first bend off the head at all cylinders. i also checked compression and have 140 to 150 at every cylinder. seem like i have raw fuel or flame going out exaust valves? any help is much appreciated!!!!!!

10-31-2007, 08:50 PM	#2 (permalink)
Grumpy_old_fart Devout Newbie Hater Join Date: Jun 2003 Member # 20147 Location: Oakland Orygun Posts: 6,482	what year is the timing cover/timing pointer/balancer? are they all from the same year? they need to be... there are different setups. this will change the timing. Find TDC on the PISTON. then, find it on the balancer. once you get the engine TIMED Correctly, you can tune the carb/injection system. __________________ sympathy, empathy and apathy... i dont know which one is which.... But i know you can find sympathy between shit and syphilis in the dictionary. Win this car for a whole BUCK!

11-07-2007, 01:13 AM	#6 (permalink)
riddler28 Registered User Join Date: Nov 2007 Member # 102385 Location: alaska Posts: 10	It really sounds like timming!!! Like Grumpy said find #1 tdc and mark it. A trick ..... pull #1 plug have a buddy bump engine in VERY small increments while you hold thumb over spark plug hole once air is excaping "by blowing finger out of way" you know that is #1 compression stroke. Then turn engine over by hand with flywheel wrench. I like to use the engine oil dipstick put that down #1 hole ontop of piston. while buddy turns engine over with wrench watch the stick come up then when it stops just b-4 going down that is your #1 tdc. Put your marks there. Now pull dist. cap your rotor should be pointing right at #1 hole. If not adjust it. Good luck. __________________ 77 chevy 427bbc th400 np205 14bolt dana60

11-07-2007, 05:34 AM	#7 (permalink)
florida4x4 Beaver Pleaser Join Date: Sep 2002 Member # 13645 Location: home of the wayward dirt bike Posts: 1,434 Blog Entries: 1	note that once you get the piston at TDC there will be a few degrees of crank rotation that the piston will stay at TDC. Mark TDC on the flywheel in the middle of this flat spot. __________________ 1972 GMC Submarine 383 / TH350 / 203D-NP205 / D60 / 14FF / 42's on Stazworks / heavy foote / four eyez Inclined to brute force attack a 70* incline with a Quadrajet 1997 GMC K3500 Suburban Turbo 5.3 in the works / 4L80E / HP60 SAS / PROJECT TOWHOE

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10-31-2007, 09:00 PM	#3 (permalink)
Jason E Registered User Join Date: Oct 2007 Member # 102035 Location: Fremont, CA Posts: 46	good point, the motor did not have a pointer on it when i got it. i picked up a pointer at parts store and was told they were all the same as long as i got the one for the right size harmonic balancer. ill do some reserch on that. thanks

10-31-2007, 10:39 PM	#4 (permalink)
BumpyDodge Registered User Join Date: Jun 2005 Member # 48682 Location: ATL GA Posts: 1,386	Sounds like retarded ign timing or lean A/F mixture to me. Check for Vaccuum leaks? Is your Vacuum Advance working? Compression readings pretty much rule out valves not fully seating. P.S. Backfiring thrugh carb will ruin the Power valve in "old style" Holleys, so even if you fix timing, you could have another problem on your hands with the carb.

11-01-2007, 06:04 AM	#5 (permalink)
Jason E Registered User Join Date: Oct 2007 Member # 102035 Location: Fremont, CA Posts: 46	I was thinking that I had a vacume leak as well so I replaced carb flange gasket and made shure all ports were pluged. it runs too bad to get an acurate vacume reading as i have to open throttle to keep it running. I'll check the vac advance but I don't think thats the problem as I ran a different distributer in the begining, unless the vac port on the holley is bad. Thanks for input. mabey I should have got a crate motor instead of an atlas!!!