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06-12-2006, 01:48 PM | #26 | |
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Re: New crate 350, backfires...stumbles...
Quote:
Just make sure that it don't ping under load. If you have to much advance it will ping usually in third gear at slower speeds with light acceleration. That's a sure way to blow a hole in a piston, or blow out a head gasket. I normally time engines by ear, advance a little at a time until I hear it ping then back it down a little. This is usually were I find the "sweet" spot in any motor.
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Clif '68 C/10 LWB, 327, TH400, 12 bolt |
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06-12-2006, 02:06 PM | #27 | |
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Re: New crate 350, backfires...stumbles...
Quote:
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1971 GMC K1500 SWB Fleetside, 4" skyjacker softride and, 14 Bolt FF, HD Dana 44 4.10's 1970 K5 TBI conversion lifted etc SOLD 1968 C20 camper truck SOLD “To ban guns because criminals use them is to tell the innocent and law-abiding that their rights and liberties depend not on their own conduct, but on the conduct of the guilty and the lawless.” Jeff Snyder |
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06-12-2006, 02:35 PM | #28 | |
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Re: New crate 350, backfires...stumbles...
Quote:
The only reason EVER to use ported vacuum is for an emissions controlled engine where the designers wanted very little, if any advance at idle. In fact, some engines built in the 70s were retarded at idle. For a non-emissions, performance engine you want the FULL-TIME vacuum port connected to the distributor advance canister. (That's the driver side port on an Edelbrock Performer carb.) And yes, that means full vacuum advance at idle and "nearly full" vacuum advance under light-load conditions, such as cruising on a level highway. On the other hand, you should have NO mechanical advance at idle. It should start kicking in just above idle. There's an article on the Internet by a former GM engineer who does a great job of explaining vacuum advance as well as ported vacuum vs. full-time vacuum. I will post it if I can find it. I leave you with this: Why do you think the shop manuals always said something like, "Plug distributor vacuum advance line when setting timing." It was so you could set the initial timing w/o interference of vacuum advance.
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Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then! Last edited by MikeB; 06-12-2006 at 02:46 PM. |
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06-12-2006, 03:01 PM | #29 |
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Re: New crate 350, backfires...stumbles...
MikeB, I do agree with you, engines with radical cams can use manifold vacuum to gain additional timing advance at idle. Mild performance or stock cams do not need this.
http://home.comcast.net/~chadwick.robert/distributor.pdf#search='vacuum%20advance'
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Clif '68 C/10 LWB, 327, TH400, 12 bolt |
06-12-2006, 03:16 PM | #30 |
Hittin E-Z Street on Mud Tires
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Re: New crate 350, backfires...stumbles...
Dang it, now I'm confused. This is straight from Edelbrocks Q and A page:
Q:Which side of the carburetor do I put my dist vacuum line to? A: Generally the distributor vacuum line goes to the timed (passenger side of carburetor) port. This is mandatory on emission controlled applications. http://www.edelbrock.com/automotive_...f/carb_faq.pdf Mines on the pass side with .45 NGK plugs, 8 degrees timing with no pings... I'm gonna leave her alone
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Jesse James 1967 C10 SWB Stepside: 350/700R4/3.73 1965 Ford Mustang: 289/T5-5spd/3.25 Trac-Loc 1968 Pontiac Firebird: Project Fire Chicken! 2015 Silverado Double Cab 5.3L Z71 2001 Jeep Wrangler Sport 4.0L 5spd 2020 Chevrolet Equinox Premium 2.0L Turbo 2011 Mustang V6 ~ Wife's ride American Born, Country by the Grace of God 1967 CST Shop Truck Rebuild! My 1967 C-10 Build Thread My Vintage Air A/C Install Project "On a Dime" Trying my hand at Home Renovation! 1965 Mustang Modifications! Last edited by 67ChevyRedneck; 06-12-2006 at 03:17 PM. |
06-12-2006, 03:34 PM | #31 |
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Re: New crate 350, backfires...stumbles...
I run full advance at idle and agree the reason you would want no advance at idle is for lower emissions at idle. mine runs much better and smoother with the vaccum advance hooked up to full vac.
This topic is discussed and debated often I tried it both ways and would not go back to ported or spark vac.
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1968 c10 lowered 3" 4" 355/Th400 built by Hatfield racing in joplin MO |
06-12-2006, 03:55 PM | #32 |
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Re: New crate 350, backfires...stumbles...
Cliff,
Excellent article. Please note the author didn't say to use ported vacuum ONLY on race engines. He simply suggested using a modified vacuum advance canister as means to smooth out a radical idle w/o changing the initial or mechanical advance. (Normally, vacuum advance is not used at all on a race engine.) You can get an engine to run OK using ported vacuum, but you will need more initial advance to compensate. Otherwise you will get a hesitation on light acceleration coming off idle. And compensating with more initial advance means you'll have to limit mechanical advance such that initial + mechanical = no more than 36. If you have a Chevy V-8 with no vacuum advance at idle and it's set to 10-12 degrees inital advance, you have something unusual there if it: 1) idles smoothly, 2) doesn't heat up at idle, and 3) doesn't stumble off-idle. Unlike some of my ramblings, this stuff isn't my opinion, it's simply fact.
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Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then! Last edited by MikeB; 06-12-2006 at 03:56 PM. |
06-12-2006, 04:04 PM | #33 | |
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Re: New crate 350, backfires...stumbles...
Quote:
I wonder how many "my engine stumbles off-idle" tech support calls they get because of this?
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Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then! Last edited by MikeB; 06-12-2006 at 04:06 PM. |
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06-12-2006, 04:19 PM | #34 |
Hittin E-Z Street on Mud Tires
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Location: Greenville, SC
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Re: New crate 350, backfires...stumbles...
Hmmmmm, interesting info MikeB. My truck doesn't idle "prefectly smooth" at idle, but it's not what I would call rough either, this may be due to my adjustment of my idle mixture screws. I've never noticed a "stumble" on take-off, but if I try to hammer it from idle it will "hesitate," AND it ALWAYS went up to about 205 degrees after startup and stayed there for a few mins before dropping to 190 degrees. It would also climb to 200 on a hot summer day in traffic, but never overheated (I'm talking 103 degree Columbia SC summer days.) I think I'll try it on the other port (what could it hurt?) What would you recommend as a start for degrees BTDC with the full ported vacuum so I have something to shoot for? (I have a timing light and I fully understand what pinging and a bad idle sound like.) With my current set-up I was getting about 14mpg city and 16-17mpg hwy with a 700R4/3.73 rear. Thanks all, I hope daubs gets his problem fixed too
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Jesse James 1967 C10 SWB Stepside: 350/700R4/3.73 1965 Ford Mustang: 289/T5-5spd/3.25 Trac-Loc 1968 Pontiac Firebird: Project Fire Chicken! 2015 Silverado Double Cab 5.3L Z71 2001 Jeep Wrangler Sport 4.0L 5spd 2020 Chevrolet Equinox Premium 2.0L Turbo 2011 Mustang V6 ~ Wife's ride American Born, Country by the Grace of God 1967 CST Shop Truck Rebuild! My 1967 C-10 Build Thread My Vintage Air A/C Install Project "On a Dime" Trying my hand at Home Renovation! 1965 Mustang Modifications! |
06-12-2006, 05:41 PM | #35 | |
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Re: New crate 350, backfires...stumbles...
Quote:
Well, obviously there are different veiws on this issue. I've been turnin' wrenches on SBC engines for 20+ years, there are many ways to tighten a bolt, but the end result is always the same.
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Clif '68 C/10 LWB, 327, TH400, 12 bolt Last edited by clif1968; 06-12-2006 at 05:43 PM. |
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06-14-2006, 04:57 PM | #36 |
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Re: New crate 350, backfires...stumbles...
I have always gone by the rule of less timming during load for less chance of detonation and that is why I use the ported vacuum thinking that when vacuum is low then timming is retarded. Interesting, now my Grandma's 79 C20 with a 350 has the vacuum advance pulled at idle and I always thought that was just a wierd emissions deal.
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1971 GMC K1500 SWB Fleetside, 4" skyjacker softride and, 14 Bolt FF, HD Dana 44 4.10's 1970 K5 TBI conversion lifted etc SOLD 1968 C20 camper truck SOLD “To ban guns because criminals use them is to tell the innocent and law-abiding that their rights and liberties depend not on their own conduct, but on the conduct of the guilty and the lawless.” Jeff Snyder |
06-15-2006, 08:27 AM | #37 | |
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Re: New crate 350, backfires...stumbles...
Quote:
Shane
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1993 K1500 350 5 speed 1985 K10 Silverado Vortec 406 5 speed (in body shop) "I been drivin' this '85 pickup truck Them buddies of mine call it a bucket of rust She's a little beat up but she still runs like the wind Yeah, kinda like me I been banged and bruisedBeen around the block a time or two But I'm runnin' like new goin' places I never been No, I ain't broke I'm just broken in" 1963 Dodge Townwagon(its amazng what 30 years and zero miles will do to a vehicle ) Member#20327 |
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06-17-2006, 05:26 PM | #38 |
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Re: New crate 350, backfires...stumbles...
I have a timing issue as well. Here's my post in the tech forum
Today, I reset the timing to 12deg BTDC and retarded the adjustable vac advance completely counter clockwise. With this setting the engine starts fine, idles smootly, but drives like a complete dog - very little acceleration. I checked total advance at 3000rpm which was 22deg. Isn't it supposed to be more like 36deg? I tried connecting to the unported vac port on the carb. But the engine runs like it's being rev limited at idle, if I advance the vac. adv at all, the engine won't idle or start. I ordered the HEI from Summit Racing, it comes with medium weights and adjustable vacuum advance. The best way I have the engine running is to adjust timing by vacuum gauge to highest vac ( 15"HG @ idle ) and back it off 2", this gives me approx. 16deg BTDC.
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___________ Greubin '71 C20 custom - GM Crate 350CI/290HP, BTO 700R4 level II, Qjet, and HEI |
06-17-2006, 07:26 PM | #39 |
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Re: New crate 350, backfires...stumbles...
Howdy;
when I first got to working on my truck after limping it home after buying it, I got one of those Mr Gasket advance curve kits for around $9, with the new weights and three sets of springs, for my HEI. I ended up using the lightest set of springs, initial advance of 12 degrees, and a plug gap of .060" For whatever reason, my engine liked .060 better, and it was inexpensive to try. Went from stumbling hesitation to ,well, really decent! Just my 0.02 cowboy33713 |
06-17-2006, 10:53 PM | #40 |
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Re: New crate 350, backfires...stumbles...
Thanks Cowboy - I'll look into the recurve kit
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___________ Greubin '71 C20 custom - GM Crate 350CI/290HP, BTO 700R4 level II, Qjet, and HEI |
06-17-2006, 11:50 PM | #41 |
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Re: New crate 350, backfires...stumbles...
Yea, guy at Autozone recommended .060 gap on my plugs. I thought he was a little crazy cause he sold me some "it will do" parts in the past. I might have to open up those gaps and give her a try. They are @ .045 right now.
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'72 Chevy K-20 Crate 350, SM465, 4.10's |
06-19-2006, 12:33 AM | #42 |
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Re: New crate 350, backfires...stumbles...
I regapped at .060" and that made an improvement. I gave up on running the vac. advance, truck runs like crap with it connected. I guess I'll call Summit and have them send me a replacement HEI dist.
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___________ Greubin '71 C20 custom - GM Crate 350CI/290HP, BTO 700R4 level II, Qjet, and HEI |
06-21-2006, 10:17 PM | #43 |
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Re: New crate 350, backfires...stumbles...
might as well bump this thread to the top...
I've got a question. I've been toying around with my truck lately, and since a few days ago, on my 600cfm E-Choke Edelbrock Carb, the High-Idle Cam has seemed like it's been loose and fallen back in a way that the adjusting-screw on the throttle plate there isn't contacting any of the notches on the Cam. Anyways, this isn't such a big deal now that she idles at that, but now around ~2000+/- RPM she'll pop like a Civil War battlefield. I've played with the timing a bit, but she's still doing it. I still need to get a timing light on her, but til then, anybody got suggestions? Is this timing, or am I off on that too? Could it be something in the carb, too?
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Mark 1997 K1500 Z71, 14 bolt SF 3.73 posi, Bright Blue Metallic. 6" Superlift 1972 C-10, toolbox, p/s, 350/TH350/3.73 open, black int., bronze 2008 Dodge MegaCab. H&S tuned 6.7 Cummins. Fast Four Tons Some of my pics http://s107.photobucket.com/albums/m294/69-350/ |
06-21-2006, 11:34 PM | #44 | |
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Re: New crate 350, backfires...stumbles...
Quote:
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___________ Greubin '71 C20 custom - GM Crate 350CI/290HP, BTO 700R4 level II, Qjet, and HEI |
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07-06-2006, 02:46 PM | #45 |
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Re: New crate 350, backfires...stumbles...
Problem solved! Turned out to be carb problems.
When I pulled the Holley from the old engine I tried to clean her up as best I could. Engine cleaner to get all the gunk off. I probably got some grime down in the carb, etc. After initial start up and break in, we drove the truck around the block. She sputtered and backfired off idle, but seemed to run good once you built RPM's. Just never did well off idle. I posted another question here on the board and asked if I should ditch the Holley. Some suggested going with an Edelbrock...which I did. And boy am I glad. Went with the Edelbrock 1405, 600 CFM manual choke carb. After re-routing the fuel line, getting a spacer for the air filter and getting her all hooked up, she fired righ away. Re-set the timing and took her around the block. Wow! Amazing difference. Super strong off idle and power all the way up. Carb really woke up that motor! I still got some tweaking to do, but I can spin the tires turning a corner in second gear (right off idle). I like. Many thanks to all who helped me trouble shoot this new engine. Running great now. This is what I expected when I opted for the new crate over a rebuild. Thanks, thanks, thanks!!!
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'72 Chevy K-20 Crate 350, SM465, 4.10's |
07-06-2006, 03:08 PM | #46 | |
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Re: New crate 350, backfires...stumbles...
i had the same problem with my q-jet when i put it on the my new 305 in my '69. just drove the haeck out of it from a few days and problem solved. chris.
Quote:
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its a work in progess. 71 c-10 lwb, in the middle of frame off restoration. 69 c-10 swb, drag truck, 406 sbc, balanced, comp 292 cam, ported, polished, gasket matched, and bowl blended pro comp 210cc heads, 2.02/1.60 ferrea valves,1.6 roller rockers, re curved hei with msd 6al box, 2-step rev limter, accel 300+ wires, ported victor jr intake, holley 750 double pumper carb, dynomax 1 5/8 headers, 4 spd munci m-20 with super case and iron midplate, mr. gasket vertigate shifter, 5.38 pro gears with full spool, 33 spline moser axles and c-clip elimators, line-loc, 5 gal fuel cell, holley blue pump. 7.807 @ 88.37mph 1.60 60FT 80 g-20 van, tow rig, cammed 305, th350, 10 bolt 88 jeep wrangler, dd, 258, ax-15 swap, 4.5" lift, 33x12.50's, lockers, 3.55's |
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12-12-2006, 01:07 AM | #47 |
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Re: New crate 350, backfires...stumbles...
I'm still tuning the engine, looking to get best possible MPG with reasonable performance. Getting back to the vacuum advance discussion...
My engine specs GM GoodWrench 350 / 290HP, HEI, eddy 1406 ( primary jets 1426 / rod 1456: secondary jet 1425 ) 700R4 w4.10 I recently rejetted my 1406 carb to the aforementioned specs and achieved 15mpg, up from 12mpg thru tuning of the carb alone, vac. adv connected to the non-ported vacuum connection ( drivers side ). My initial timing was set to 12*BTDC and I experienced that off idle hesitation that MikeB mentioned ( full time vacuum ). After reading several articles about vac. advance, most of the articles argued that an increase in MPG would be seen from running "ported vacuum" on the vac. advance. I switched the hose back to ported vacuum, MPG dropped to 11.5MPG, but the off-idle hesitation went away. Today, I moved the initial timing up to 16*BTDC and left the vac. advance connected to ported vacuum. Truck ran great on the way into work, I'm hoping to see an MPG increase. I have yet to check full advance, perhaps tomorrow. I'll post my MPG once I fill 'er up in a few days.
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___________ Greubin '71 C20 custom - GM Crate 350CI/290HP, BTO 700R4 level II, Qjet, and HEI |
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