The 1947 - Present Chevrolet & GMC Truck Message Board Network







Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > 47 - Current classic GM Trucks > The 1967 - 1972 Chevrolet & GMC Pickups Message Board

Web 67-72chevytrucks.com


Reply
 
Thread Tools Display Modes
Old 03-13-2011, 08:40 PM   #1
Steve Van Gent
Registered User
 
Steve Van Gent's Avatar
 
Join Date: Feb 2009
Location: Redding, Ca
Posts: 229
250 straight six starving?

Trying to get my sons 71 stepside with 250 straight six running. Here is thread to see truck - http://67-72chevytrucks.com/vboard/s...d.php?t=427824

Last owner had 6 in poor condition, bad fuel pump, mating gasket on intake/exhaust burnt out, bad alternator, greasy mess. We started working on this weekend, got running ok, found coolant leaks every where. Bad one, rear freeze plug. So we pulled motor, trying to replace plug-also degreasing motor and compartment.

Here is question- While motor was running, motor idles great, timing is correct, plenty of fuel, new inline fuel filters for catching rust, etc. Motor hesitates and backfires when I try to accelerate. Once I get motor past 2000 RPMS, runs fine. BUt the initial acceleration always results in backfire, trying to stall, hesitation. I pulled carb, it looks fairly recent manufactured carb, and is labeled as a Napa reman carb. Looked clean inside. Now I am stumped, not sure why it is stumbling....any ideas? Seems to have good spark, lots of fuel, no vacuuum leaks, new gaskets on all manifolds.

????
Steve Van Gent is offline   Reply With Quote
Old 03-13-2011, 09:02 PM   #2
LandonL
Registered User
 
LandonL's Avatar
 
Join Date: Nov 2009
Location: Georgia
Posts: 440
Re: 250 straight six starving?

I know you said the timing was fine, but I had a very similar issue with my 250 six. It would run barely and stumble pop and backfire, found out that the distributor hold down clamp bolt had loosened up and the dist was moving however it pleased. To me it just sounds like a timing issue.. always could be wrong though lol. Usually am
__________________

---| 1967 GMC Stepside |--
250 L6 .030 over

---| 1985 Porsche 944/1 |---

Build Thread: '67 GMC
http://67-72chevytrucks.com/vboard/s...d.php?t=378640
LandonL is offline   Reply With Quote
Old 03-13-2011, 09:22 PM   #3
orangek5
Senior Member
 
orangek5's Avatar
 
Join Date: Nov 2008
Location: Rose Hill Ks
Posts: 224
Re: 250 straight six starving?

Quote:
Originally Posted by LandonL View Post
I know you said the timing was fine, but I had a very similar issue with my 250 six. It would run barely and stumble pop and backfire, found out that the distributor hold down clamp bolt had loosened up and the dist was moving however it pleased. To me it just sounds like a timing issue.. always could be wrong though lol. Usually am
I agree. sounds like a worn timing chain.
__________________
70 Jimmy 4x4 IL6
71 Jimmy 4x4 350ci v8
72 Short Stepside 305ci v8
72 Blazer 2WD CST LS9 350ci 4sp
99 GMC 4 Door Long Bed 1 Ton Old Body Style 5.7 v8
orangek5 is offline   Reply With Quote
Old 03-13-2011, 10:34 PM   #4
Shyguy
Junior Member
 
Shyguy's Avatar
 
Join Date: Dec 2006
Location: Southeast Missouri
Posts: 2,433
Re: 250 straight six starving?

I don't think a L6 has timing chain, pretty sure it is gear drive.
__________________
'67 Chevy C-20 short stepper - build complete, 454/SM-465.
'75 C-30 Single Cab DRW-350 small block/NP-435.
'77 GMC-6500 Dump Truck, 427 Tall Deck.
'92 GMC K-3500 Duallie, 454/4L80E.
Shyguy is offline   Reply With Quote
Old 03-13-2011, 10:47 PM   #5
mr48chev
Registered User
 
mr48chev's Avatar
 
Join Date: Jul 2007
Location: Toppenish, WA
Posts: 6,430
Re: 250 straight six starving?

A 250 has timing gears and no chain. Have you checked the accelerator pump to make sure it is working right?

One of the thinks that throws guys is the new, just replaced, rebuilt thing.
just because it had been rebuilt at one time doesn't mean it's working right.

Along with that check for kinked, flattened or twisted fuel lines and if any brass fittings
appear to have been change check them to make sure that they are the correct size.

Back in the early 70's I bought a 57 Panel with a built 327 with a dual 4 early Corvette intake on it. The thing would run like crazy for 50 ft and fall on it's face and the go again after I let off the gas. Turns out that the guy who put it together used a natural gas fitting with a 1/8 inch orifice in the line.

My guess is still that your accelerator pump isn't working right.
mr48chev is offline   Reply With Quote
Old 03-13-2011, 10:54 PM   #6
oldgold70c10
Who's got steelies?
 
oldgold70c10's Avatar
 
Join Date: Feb 2006
Location: Morrison, Oklahoma
Posts: 972
Re: 250 straight six starving?

x2 for the accelerator pump.
__________________
1970 C10 with '67 small window cab, 68 front end, blue; 305/TH350, 3.08 limited slip rear end, manual brakes, power steering; & 4-wheel drums-My daily driver.
1975 Chevelle Malibu Classic Coupe 350/th350 mint green
1970 C20 Suburban 350/700R4 4.10 gearing green & white

How to add a trip odometer to your 67-72 stock speedometer

How to rebuild your Q-Jet

My Truck Page
The "real" reason I bought a truck.
oldgold70c10 is offline   Reply With Quote
Old 03-13-2011, 11:24 PM   #7
Dark Knight
Registered User
 
Dark Knight's Avatar
 
Join Date: Dec 2008
Location: Pleak, Texas
Posts: 418
Re: 250 straight six starving?

I also blame the accelerator pump. Depending on when it was re-built, the ethanol in today's gas might have eaten up the rubber flap on the plunger.
__________________
-1967 Chevrolet Fleetside LWB- 350 V8 w/thumpr cam, NV3500, 3.08 gears, A/C, PS
-1989 Chevy Silverado K1500 SWB- 5.3L swap, 700R4, 3.42 gears

"The only thing we have to fear is fear itself." -FDR (and maybe rust too)

You've gotta be able to stop and steer before you can go fast!
Dark Knight is offline   Reply With Quote
Old 03-13-2011, 11:43 PM   #8
mrsmothers
Registered User
 
Join Date: Oct 2010
Location: ruston la
Posts: 169
Re: 250 straight six starving?

3x the accelerator pump I had an f150 that did the same thing.
mrsmothers is offline   Reply With Quote
Old 03-14-2011, 01:11 AM   #9
Steve Van Gent
Registered User
 
Steve Van Gent's Avatar
 
Join Date: Feb 2009
Location: Redding, Ca
Posts: 229
Re: 250 straight six starving?

Thanks guys. Will find out soon, I have installed new accel pump while I had apart. I doubt timing, I have it slightly loose, turning it while it running...makes no difference. It runs fine at low speed, runs fine at high speed, just has problem getting from low to high....
Steve Van Gent is offline   Reply With Quote
Old 03-14-2011, 01:12 AM   #10
Steve Van Gent
Registered User
 
Steve Van Gent's Avatar
 
Join Date: Feb 2009
Location: Redding, Ca
Posts: 229
Re: 250 straight six starving?

I should note, must wait til next weekend, motor is out right now, I am replacing rear freeze plug-what a pain...!
Steve Van Gent is offline   Reply With Quote
Old 03-14-2011, 08:00 AM   #11
cdowns
Senior Member
 
cdowns's Avatar
 
Join Date: Jan 2003
Location: daytonabeach
Posts: 21,785
Re: 250 straight six starving?

i'd replace all freeze plugs if i had the engine out//preventive maintenance
__________________
71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane

MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF

DONT BELIEVE EVERYTHING YOU THINK

TAKE MY ADVISE;I DON'T USE IT ANYWAY
cdowns is online now   Reply With Quote
Old 03-14-2011, 09:37 AM   #12
Wrenchbender Ret
Registered User
 
Join Date: Oct 2005
Location: Lenexa, Kansas
Posts: 3,655
Re: 250 straight six starving?

Did you check the float level while the carb was down. I agree because it was a reman doesn't mean it is right.
Wrenchbender Ret is offline   Reply With Quote
Old 03-14-2011, 01:01 PM   #13
70STOVEBOLT
Broke
 
70STOVEBOLT's Avatar
 
Join Date: Jun 2005
Location: Winona Lake, IN
Posts: 2,145
Re: 250 straight six starving?

I had an issue similar to this recently. I have a manual choke and it would run fine with the choke pulled out about 3/4, but with the choke pushed in it would hesitate and backfire through the carb. I could not find a vacuum leak anywhere on the intake or carb,
so I pulled the pcv valve hose off and plugged it and it ran better. So I replaced the pcv valve and now it runs fine. You might check your pcv valve also, could be a vacuum leak there.
__________________
70 SWB 250 TH400 "The Needy Beast"
200,000 Mile Club
Drum Brake Club
Daily Driver Club
Owner installed options:
Front Sway Bar
Power Steering
Power Brakes
Cigar Lighter
Courtesy Lights
Deluxe Side Markers
Wiper Delay
70STOVEBOLT is offline   Reply With Quote
Old 03-14-2011, 02:43 PM   #14
PanelDeland
I am a Referee of life.
 
PanelDeland's Avatar
 
Join Date: Jun 2000
Location: Greensboro N.C.
Posts: 13,543
Re: 250 straight six starving?

Might also check the vacuum advance.Mine did the same thing but quit when I replaced the vacuum actuator in the dist.
__________________
The 47-present Chevrolet and GMC Truck Message Board Network,it's owners,moderators,members,and associates of any type should not be held responsible for my opinion.
You can't fix stupid,not even with duct tape.
"My appearance is due to the fact that "GOD" does punish you for having too much fun!"
Barrett-Jackson has perfected alchemy,they make rust into gold!
"You can lead a horse to water but you can't saddle a duck"
"Cleverly disguised as a 'Responsible Adult'
"Sometimes your Knight in shining armor is just a retard in tinfoil"
PanelDeland is offline   Reply With Quote
Old 03-15-2011, 03:31 PM   #15
stsalvage
Scrapper 1
 
stsalvage's Avatar
 
Join Date: Jan 2007
Location: Riverside Calif
Posts: 955
Re: 250 straight six starving?

Quote:
Originally Posted by Steve Van Gent View Post
I should note, must wait til next weekend, motor is out right now, I am replacing rear freeze plug-what a pain...!

I hear that from a lot of guys trying to put freeze plugs in while the engine is in the truck Trust me the inline 6 is so easy to take out and put in spend the weekend and do it right and you even get to clean and paint it while its out and check to see if you need to change the pan gasket the inline 6 engines i hated for the longest time until i found a 1971 with a 250 with a 700R4 with the 4 bb intake with a edalbrock on it and man it runs super
stsalvage is offline   Reply With Quote
Old 03-15-2011, 08:59 PM   #16
Roadmarks
Registered User
 
Roadmarks's Avatar
 
Join Date: Apr 2010
Location: Raleigh NC
Posts: 157
Re: 250 straight six starving?

What Panel Deland said! What I would do , however is to hit a local salvage yard and pick up a nice HEI for cheap and toss the point set-up all together. That one change alone will make more difference than you will believe. HEI is THE way to go. 1976 up Chevy car or truck L6 is where you get the distributor. New plug wires and plugs for HEI set to .045. Then look over the gaskets on the intake /exhaust and you'll be good to go!

Later,

Les
Roadmarks is offline   Reply With Quote
Old 06-14-2011, 09:51 AM   #17
70STOVEBOLT
Broke
 
70STOVEBOLT's Avatar
 
Join Date: Jun 2005
Location: Winona Lake, IN
Posts: 2,145
Re: 250 straight six starving?

What was the outcome on this?
__________________
70 SWB 250 TH400 "The Needy Beast"
200,000 Mile Club
Drum Brake Club
Daily Driver Club
Owner installed options:
Front Sway Bar
Power Steering
Power Brakes
Cigar Lighter
Courtesy Lights
Deluxe Side Markers
Wiper Delay
70STOVEBOLT is offline   Reply With Quote
Old 06-14-2011, 11:06 AM   #18
Steve Van Gent
Registered User
 
Steve Van Gent's Avatar
 
Join Date: Feb 2009
Location: Redding, Ca
Posts: 229
Re: 250 straight six starving?

Well, the outcome was that I never reinstalled motor after rebuilding carb and replacing freeze plug. Instead I have been spending time building up a Firebird Gen3 TPI V8 and 700R4 to replace old power plant....My bad....
Steve Van Gent is offline   Reply With Quote
Old 06-14-2011, 11:32 AM   #19
70STOVEBOLT
Broke
 
70STOVEBOLT's Avatar
 
Join Date: Jun 2005
Location: Winona Lake, IN
Posts: 2,145
Re: 250 straight six starving?

Oh, cool, good luck with the repower.
__________________
70 SWB 250 TH400 "The Needy Beast"
200,000 Mile Club
Drum Brake Club
Daily Driver Club
Owner installed options:
Front Sway Bar
Power Steering
Power Brakes
Cigar Lighter
Courtesy Lights
Deluxe Side Markers
Wiper Delay
70STOVEBOLT is offline   Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 08:15 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Copyright 1997-2013 67-72chevytrucks.com