Carburation mystery

Tech tips and how to's

Moderators: notoptoy, garth, S Allen

User avatar
RBMann
Roadster Fanatic
Posts: 475
Joined: Mon Jan 05, 2015 8:37 pm
Location: Kenmore, WA

Carburation mystery

Post by RBMann »

I am having an issue with our '69 1600. The whole car will start lurching/bucking/surging after the transition from light or no throttle to very slight acceleration in 1st or 2nd gear. When I let off the gas coming down my street then turn into the driveway and roll into the gas to start the climb it will lurch so bad that it starts chirping the tires. That is the worst case and requires either full throttle or stop and try again. It makes low speed light throttle driving very difficult. It's as if the pistons in the SUs are flopping up and down without any damping.

This behavior started a couple months ago but seems to be getting worst. I have checked the carb tuning, float level, checked the timing and have played with the mixture. I used ATF in the pistons, I tried straight 30W to slow things down and I have tried driving without the plungers in the pistons. It performs the same in all three cases.

As I am writing this I remembered the electric fuel pump was changed but to a new one that was supposed to have the specs. as the one that has been in the car for ten years. Maybe I'll switch it back as it is the only thing I can think of at this point.

Thanks for any ideas/tips.
RBMann

mechanic on '69-1600(not mine)
User avatar
Nissanman
Roadster Fanatic-Site Supporter
Posts: 3129
Joined: Mon Apr 16, 2007 8:07 pm
Location: Adelaide, South Australia
Model: 1500/1600
Year: Low Windshield-64-67.5

Re: Carburation mystery

Post by Nissanman »

Just maybe it is spark not fuel.
Run the engine in the dark and look for any lightning display.
Check the points, if you have points, for correct gap and function.
As the saying goes, when your sure it is a fuel problem check the ignition and vice versa :idea:
Nissanman, just trying to help.
1965 SP310 Engine No. G-93326 Car No. SP310-10817
http://nissanman.shutterfly.com/117
McQueen!
He's on the road again!
User avatar
spl310
Roadster Guru
Posts: 12416
Joined: Sun Dec 29, 2002 10:38 pm
Location: In front of this keyboard... in Jacksonville, Florida!

Re: Carburation mystery

Post by spl310 »

Carb problems are often ignition problems and vice versa. I'm betting that the springs or posts for them on the mechanical advance in the distributor has a problem. They are under the breaker plate
"Wow, a Roadster!" Stuart Little

1967.5 2000
1967.5 2000
1964 1500
1964 1500
1967.5 1600
1968 chassis
2000 Durango
1995 F350 Powerstroke!
More...
User avatar
jrusso07
Roadsteraholic
Posts: 1481
Joined: Sat Aug 02, 2008 9:02 am
Location: Penn Yan, NY
Model: 2000
Year: High Windshield-68-70

Re: Carburation mystery

Post by jrusso07 »

i had a very similar problem years ago - it was caused by the little graphite button on the center contact (coil voltage contact) in the distributor cap had broke and fallen out so the coil voltage to the rotor was through the spring and spark was intermittent but car would run, but not well. (so spark was the problem). Not sure how the button broke - found pieces of it inside the distributor.
Joe

1969 SRL311 - Solex
1970 SPL311 - U20 mod
1970 SRL311
User avatar
redroadster
Roadsteraholic
Posts: 1599
Joined: Tue Mar 12, 2013 10:58 am
Location: KCMO
Model: 1500/1600
Year: High Windshield-68-70

Re: Carburation mystery

Post by redroadster »

You are in need of the old sun machine oscilloscope
Are the carb pistons slides moving smooth and free when you push them up ....maybe one is froze and your running on 1 carb
A spark plugs fuel fowled , or a plug wire arcing very possible too....carbon tracking in distr.
Check for vacuum leak , ign timing cetrifical adv
Last edited by redroadster on Mon Apr 12, 2021 6:17 pm, edited 5 times in total.
User avatar
keith0alan
Roadsteraholic
Posts: 824
Joined: Wed Sep 22, 2004 10:07 am

Re: Carburation mystery

Post by keith0alan »

It may be a carb problem but I have never seen this.
User avatar
Gregs672000
Roadster Fanatic-Site Supporter
Posts: 7558
Joined: Fri Aug 07, 2009 11:47 pm
Location: Tacoma, WA

Re: Carburation mystery

Post by Gregs672000 »

I would agree that on and off, lurching etc suggests more of an electrical issue than carbs. Usually if it's lean it will backfire through the carbs, and an overly rich condition will just make it boggy and slow.
Greg Burrows
'67 2000 #588
Tacoma, WA
User avatar
rwmann
Roadster Fanatic-Site Supporter
Posts: 327
Joined: Wed Aug 20, 2008 6:11 am
Location: Port Washington, NY
Model: 2000
Year: High Windshield-68-70

Re: Carburation mystery

Post by rwmann »

Broken throttle return spring?
User avatar
notoptoy
Vendor-Site Supporter
Posts: 9372
Joined: Fri Oct 02, 2009 2:55 pm
Location: Winston-Salem, NC and Ocala, FL

Re: Carburation mystery

Post by notoptoy »

I'm with electrical as well, look for arcing at the coil, cracked cap, loose or broken lead or ground wires.
"When all else fails, force prevails!" Ummm, we're gonna need a bigger hammer here.

67.5 SPL311 H20 w/5 speed
65 Impala Convertible
2017 C43 AMG
User avatar
RBMann
Roadster Fanatic
Posts: 475
Joined: Mon Jan 05, 2015 8:37 pm
Location: Kenmore, WA

Re: Carburation mystery

Post by RBMann »

Thanks for the suggestions. Looks like I'll be going into the distributor.

It's that thing over on the other side of the engine right? :wink:

Image
RBMann

mechanic on '69-1600(not mine)
User avatar
notoptoy
Vendor-Site Supporter
Posts: 9372
Joined: Fri Oct 02, 2009 2:55 pm
Location: Winston-Salem, NC and Ocala, FL

Re: Carburation mystery

Post by notoptoy »

I can see how you would be distracted by this side of the engine - looks good!
"When all else fails, force prevails!" Ummm, we're gonna need a bigger hammer here.

67.5 SPL311 H20 w/5 speed
65 Impala Convertible
2017 C43 AMG
todd lorber
Roadster Fanatic
Posts: 453
Joined: Sun Dec 09, 2007 5:58 pm
Location: Los Angeles

Re: Carburation mystery

Post by todd lorber »

The problem is that your engine is too clean. No car can run properly looking like that.
User avatar
itsa68
Roadsteraholic
Posts: 805
Joined: Sun Apr 18, 2004 11:24 am
Location: Winnipeg, Manitoba,Canada
Model: 1500/1600
Year: High Windshield-68-70

Re: Carburation mystery

Post by itsa68 »

A quick check of the points wire might be in order. The wire likes to break inside the covering and could be intermittently making a connection during timing advance. I have also had a brand new rotor with leak path to the distributor shaft causing an intermittent spark short.

Hope that helps.

Cheers
Ray B.
Thats not a R16 death rattle....its a dried leaf hitting my heater blower fan.
1968 SPL311 non-smog
User avatar
Gregs672000
Roadster Fanatic-Site Supporter
Posts: 7558
Joined: Fri Aug 07, 2009 11:47 pm
Location: Tacoma, WA

Re: Carburation mystery

Post by Gregs672000 »

Eye candy for sure, really really nice.
Greg Burrows
'67 2000 #588
Tacoma, WA
User avatar
redroadster
Roadsteraholic
Posts: 1599
Joined: Tue Mar 12, 2013 10:58 am
Location: KCMO
Model: 1500/1600
Year: High Windshield-68-70

Re: Carburation mystery

Post by redroadster »

todd lorber wrote: Mon Apr 12, 2021 11:55 am The problem is that your engine is too clean. No car can run properly looking like that.
Ya looks like it was wire brushed & buffed
Hope you wore a respiratory and gloves