One of those carb issues that can't really be diagnosed over the internet
02-20-19, 12:38 AM
#1
Full Member
Thread Starter
One of those carb issues that can't really be diagnosed over the internet
So, I've decided to post this question despite my best judgment. I know that these carb issues flood the forums, and are difficult to diagnose, if the issue even ends up being the carb.
First off, I'm currently in the process of replacing all vacuum hoses with silicon, all fuel lines and filters, and any other rubber component I can while lubricating anything that moves. This MAY fix this issue, but I'm a little doubtful.
I'm not quite sure of how to be sure that some of the moving parts in the vacuum I'm running into work correctly... Vacuum systems are amazing, and complex. learning as I go.
On to the issue at hand. I'm running a bone stock Nikki on my 1985 12a, with 180k on the old gal, and am having some issues with fueling right off idle. I recently posted a writeup with my clutch change, and the car has been a lot more drivable with new fluids and clutch in it (Who knew?!), but it definitely makes this issue stand out a bit more now that it's one of the last things left between this car running perfectly.
Directly after applying throttle, the engine chokes/stutters and rpms stay even, then about 1/2-1 second later the rpms catch and shoot up normally. If the clutch is let out during this time, the motor will usually stall. If the rpms are above 1600-2000 the issue never arises. The car idles at around 1000-1100 RPM, a little high, but very smoothly. The car starts easily with the choke, and once it warms up idles perfectly without it. The engine performs excellently at all rpm's above 2000ish and I drive it daily. Compression and fuel pressure are good, new spark plugs and leads, corrosion cleaned from any easily accessible terminals. seafoam ran through the gas, good quality battery, etc. I've tried everything short of tearing into the carb, and once I finish the vacuum lines that'll probably be my next step, unless one of you guys knows the answer.
Right now to drive the car the workaround I've been doing is a quick tap of the throttle peddle from a stop to bump the rpms up above 2000, then I can mostly drive normally after that. Very easy to stall it if you don't remember to bump the peddle first though, the engine has absolutely no power at all while it's stuttering right off of idle like I've been describing.
I know this was long winded. Here's 2 shot and sweet youtube videos I made trying to convey the issue I'm having.
1st video, narrated with the issue briefly.
2nd video, a bit better demonstration and you can hear the stutter in the engine better, no narration.
Thank you in advance! I don't know what I'd do without this community. I've learned so much already from the archived threads and the other guys around here on the forums.
First off, I'm currently in the process of replacing all vacuum hoses with silicon, all fuel lines and filters, and any other rubber component I can while lubricating anything that moves. This MAY fix this issue, but I'm a little doubtful.
I'm not quite sure of how to be sure that some of the moving parts in the vacuum I'm running into work correctly... Vacuum systems are amazing, and complex. learning as I go.
On to the issue at hand. I'm running a bone stock Nikki on my 1985 12a, with 180k on the old gal, and am having some issues with fueling right off idle. I recently posted a writeup with my clutch change, and the car has been a lot more drivable with new fluids and clutch in it (Who knew?!), but it definitely makes this issue stand out a bit more now that it's one of the last things left between this car running perfectly.
Directly after applying throttle, the engine chokes/stutters and rpms stay even, then about 1/2-1 second later the rpms catch and shoot up normally. If the clutch is let out during this time, the motor will usually stall. If the rpms are above 1600-2000 the issue never arises. The car idles at around 1000-1100 RPM, a little high, but very smoothly. The car starts easily with the choke, and once it warms up idles perfectly without it. The engine performs excellently at all rpm's above 2000ish and I drive it daily. Compression and fuel pressure are good, new spark plugs and leads, corrosion cleaned from any easily accessible terminals. seafoam ran through the gas, good quality battery, etc. I've tried everything short of tearing into the carb, and once I finish the vacuum lines that'll probably be my next step, unless one of you guys knows the answer.
Right now to drive the car the workaround I've been doing is a quick tap of the throttle peddle from a stop to bump the rpms up above 2000, then I can mostly drive normally after that. Very easy to stall it if you don't remember to bump the peddle first though, the engine has absolutely no power at all while it's stuttering right off of idle like I've been describing.
I know this was long winded. Here's 2 shot and sweet youtube videos I made trying to convey the issue I'm having.
1st video, narrated with the issue briefly.
Thank you in advance! I don't know what I'd do without this community. I've learned so much already from the archived threads and the other guys around here on the forums.
Last edited by M_D_H; 02-20-19 at 12:42 AM. Reason: clarification
02-20-19, 06:36 AM
#2
ancient wizard...
The carburetor has an enrichment circuit that addresses this. When throttle is opened just like you’re experiencing,an accelerator pump delivers a spray of fuel into each barrel of primary bore of carburetor.
When throttle is initially opened like starting from stop the engine has an immediate,short term need for extra fuel. Without this accelerator pump shot of raw fuel into the primary barrels of carburetor the carb goes temporarily lean as throttle is opened.
To test... run engine shortly to be certain carb bowls are full. Shut car off and remove air cleaner lid and watch while someone pushes down about 1/2 throttle,like you would starting out. If no one available,remove entire air cleaner and grab the throttle linkage by hand
As soon as you begin to move throttle from idle position you should see a steady stream of fuel squirting into throat of each primary barrel-to about 1/2 throttle..Should be a strong stream,not a dribble.
If this doesn’t occur,this is responsible for your problem. Sourcing carb overhaul kit is your next step. Napa and some other parts stores have or can get one for you.
If all other functions of carb are satisfactory,you may just want to replace accelerator pump on carb in place.
Consult Fsm(can be downloaded on(foxed.ca) and look at exploded views of carb to see what’s involved in removing/installing Accel pump.
While Accel pump diaphragm is out of carb,take a can of carb cleaner with straw tip attached and spray into pump discharge orifice and observe spray coming out of discharge nozzles. If so,install pump diaphragm and gasket from kit and start car and rev to see if you have Accel pump shot with throttle movement.
Next,lower base idle warm speed to 750-800 rpm. Likely someone previously increased idle speed in attempt to minimize stalling. Go drive it!
When throttle is initially opened like starting from stop the engine has an immediate,short term need for extra fuel. Without this accelerator pump shot of raw fuel into the primary barrels of carburetor the carb goes temporarily lean as throttle is opened.
To test... run engine shortly to be certain carb bowls are full. Shut car off and remove air cleaner lid and watch while someone pushes down about 1/2 throttle,like you would starting out. If no one available,remove entire air cleaner and grab the throttle linkage by hand
As soon as you begin to move throttle from idle position you should see a steady stream of fuel squirting into throat of each primary barrel-to about 1/2 throttle..Should be a strong stream,not a dribble.
If this doesn’t occur,this is responsible for your problem. Sourcing carb overhaul kit is your next step. Napa and some other parts stores have or can get one for you.
If all other functions of carb are satisfactory,you may just want to replace accelerator pump on carb in place.
Consult Fsm(can be downloaded on(foxed.ca) and look at exploded views of carb to see what’s involved in removing/installing Accel pump.
While Accel pump diaphragm is out of carb,take a can of carb cleaner with straw tip attached and spray into pump discharge orifice and observe spray coming out of discharge nozzles. If so,install pump diaphragm and gasket from kit and start car and rev to see if you have Accel pump shot with throttle movement.
Next,lower base idle warm speed to 750-800 rpm. Likely someone previously increased idle speed in attempt to minimize stalling. Go drive it!
Last edited by GSLSEforme; 02-20-19 at 06:56 AM. Reason: spelling,from phone,big fingers...
02-20-19, 10:26 AM
#3
Waffles - hmmm good
iTrader: (1)
Yeah, you mentioned cleanup up of line and hoses. You have to assume there may be crud in the carb as well. I agree with GSLSEforme but I would recommend a full carb dismantling and rebuild to fully eradicate any future gremlins from the carb condition as it is.
02-20-19, 10:35 AM
#4
Full Member
Thread Starter
Thanks guys, that really gives me a starting point. I'm trying to keep most of the rats nest intact on this car, so I'm just doing my best to learn everything. If I do a carb teardown and rebuild ill probably make a post about it
02-20-19, 10:53 AM
#5
ancient wizard...
When I have a situation like this on a good customers car,particularly if customer on a low budget and i’ve Driven the car and feel all other functions of carb are good,i’ll give them the option of accel pump replacement-if that is actually the problem- versus complete carb overhaul which may make the difference between them being able to afford the repair. I would more likely recommend the carb o/haul if a 1st time unknown customer.
02-20-19, 11:32 AM
#6
Full Member
Thread Starter
I'm definitely going to check out the pump before I drive into ripping the carb apart. I've read a lot about avoiding rebuilding the carb unless it's really necessary
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