Jump to content

IGNORED

Engine idling at 3k RPM, I think I’m getting too much fuel from the carbs


Recommended Posts

Hey guys so after trying to get my 260z with Weber 32/36 carbs set up(which I just rebuilt) I finally got it running today! It’s not running too good though haha. When I started it up it was idling at about 5k rpm! I tightened the idle mixture screws a bit and got it down to 3k rpm, obviously better but still really high. Another strange thing is when I turn off the car, it almost keeps running but dies slowly and starts blowing some white smoke from the top of the carbs. If I want to kill it right away as soon as I turn it off, I floor it to open the throttle valves and it shuts down smoothly. 
 

A couple things that I think may be causing these issues and wanted to get your opinions;

number 1 that the throttle valves aren’t closed completely and they are staying a bit open and letting too much gas into the engine at idle. The reason I think this is that when I filled the carbs with some gas to get it running originally I noticed that the primary valve was not holding any of the gas I was pouring 

number 2, that my floats could be too high, I switched the brass ones to plastic and reset the heigh to 35 mm, but maybe I made a mistake here? 
 

number 3 honestly not too confident in this one but it may be caused by somehow getting too much fuel from the mechanical fuel pump?

 

number 4, other possible area where the carbs could be having an air leak.

Just a quick note as well: my carbs don’t have the choke plates installed, the previous owner welded the choke shaft’s holes shut 

 

any help is greatly appreciated, and if there’s any info I can add please let me know!

Link to post
Share on other sites

Who is the resident Weber 32/36 wizard on here? 🧙‍♂️

The issue of the motor that still running after the ignition being off can be from having too much fuel in the system. This also might be linked to issue # 1 from your post.

It seems like the state of the carb might mean it needs to be repaired. For the reasons 1 and 4. (air leaks can be checked by shooting carb cleaner at the car while the motor is on, and listen for a change in RPM)

I think Weber 32/36 need 3/5 psi of fuel (from what a reference manual says online) the OEM SU carbs use 4-6 PSI if i recall correctly.

 

Link to post
Share on other sites
52 minutes ago, heyitsrama said:

Who is the resident Weber 32/36 wizard on here? 🧙‍♂️

The issue of the motor that still running after the ignition being off can be from having too much fuel in the system. This also might be linked to issue # 1 from your post.

It seems like the state of the carb might mean it needs to be repaired. For the reasons 1 and 4. (air leaks can be checked by shooting carb cleaner at the car while the motor is on, and listen for a change in RPM)

I think Weber 32/36 need 3/5 psi of fuel (from what a reference manual says online) the OEM SU carbs use 4-6 PSI if i recall correctly.

 

Thanks for answering man, there’s no way That originally pouring fuel into the carbs should be causing the motor running after turning it off right?
 

I just rebuilt the carbs and everything was functioning and sliding properly when I manually tested them

regarding the PSI, since the 260z had both an electric and mechanical pump is the system getting too much gas? And even if that Is the case, isn’t the point of the float to limit the amount of gas ? 
 

I’ll give the carb cleaner in the carb while running a shot and hope that works. I was able to get it down to about 2500 rpm after tightening the idle mixture screw down but that’s still a ridiculous idle especially with the car being manual

Link to post
Share on other sites
1 hour ago, heyitsrama said:

Who is the resident Weber 32/36 wizard on here? 🧙‍♂️

The issue of the motor that still running after the ignition being off can be from having too much fuel in the system. This also might be linked to issue # 1 from your post.

It seems like the state of the carb might mean it needs to be repaired. For the reasons 1 and 4. (air leaks can be checked by shooting carb cleaner at the car while the motor is on, and listen for a change in RPM)

I think Weber 32/36 need 3/5 psi of fuel (from what a reference manual says online) the OEM SU carbs use 4-6 PSI if i recall correctly.

 

Quick note to add that I’d love to ask you about, I don’t have a fuel return line, the previous owner removed it. Do you think this could be causing my issue??

Link to post
Share on other sites

Engine RPM is controlled by air flow.  So high RPM means that you have uncontrolled air getting in somewhere.  If it's idling at 3000 RPM and you already have extra gasoline then carb cleaner might not show you much.

Engine running after ignition off is usually from hot spots in the combustion chamber.  Often caused by carbon deposits from running rich.  When you floor it before shutting down you let a blast of cool air and gasoline in and kill the hot spots.

The throttle blades control air flow not gasoline.  They need to shut completely if you want to control your idle speed.

  • Like 1
Link to post
Share on other sites
8 minutes ago, Zed Head said:

Engine RPM is controlled by air flow.  So high RPM means that you have uncontrolled air getting in somewhere.  If it's idling at 3000 RPM and you already have extra gasoline then carb cleaner might not show you much.

Engine running after ignition off is usually from hot spots in the combustion chamber.  Often caused by carbon deposits from running rich.  When you floor it before shutting down you let a blast of cool air and gasoline in and kill the hot spots.

The throttle blades control air flow not gasoline.  They need to shut completely if you want to control your idle speed.

Thank you @Zed Head, so what do you think the problem could be? Could it be running rich due to too much fuel pressure? Should I try installing a regulator? 
 

also could the fact that I don’t have a choke be causing the issue? I’m sorry if my questions aren’t advanced,I literally just started learning about carbs and how they work about a week ago. Thanks for your time

Link to post
Share on other sites

Hey guys I also just realized that my throttle stop is sitting really far forward after installing the carbs, compared to when I had them out of the car. I wish I I had a picture right now but I work on the car at a lot an hour away. Basically even with the idle speed screw screwed in all the way it doesn’t touch the throttle stop. Could I have just bolted it down too far forward by accident?

Link to post
Share on other sites

So first thing, do not overtighten any mixture screws in a Weber carb!! You can damage the seats in the carb...

The white smoke coming out of the carb might be atomized fuel

Remove the any linkage from the gas pedal and see if the butterflies will close any more.

Also an small inline fuel pressure gage can be very helpful

Do these carbs have any electrical solenoids on them? I believe some of these carbs had anti dieseling solenoids on them

Link to post
Share on other sites
28 minutes ago, siteunseen said:

Make sure these flats are in the right order. I put mine back on wrong and it shot up to 2 or 3 thousand rpms.Screenshot_20210501-174022_Gallery.jpg

Oh crap I did it again. Y'all are talking about Webers and I started reading at the last post. I'm sorry.

  • Haha 2
Link to post
Share on other sites
34 minutes ago, Patcon said:

So first thing, do not overtighten any mixture screws in a Weber carb!! You can damage the seats in the carb...

The white smoke coming out of the carb might be atomized fuel

Remove the any linkage from the gas pedal and see if the butterflies will close any more.

Also an small inline fuel pressure gage can be very helpful

Do these carbs have any electrical solenoids on them? I believe some of these carbs had anti dieseling solenoids on them

Okay I’ll loosen up the screws to not damage the carbs, I didn’t over tighten, I had seated them and turned them two full turns out, but while adjusting I tightened it in one more term. I believe the smoke coming out is run on(dieseling) from excess fuel. I’m going to borrow a fuel pressure test from autozone and see what I can figure out tomorrow. I’ll also unhook the gas pedal linkage and see if I can get the throttle stop to sit more forward as that may be part of my problem.

no I don’t believe there’s any electrical solenoids on them

  • Like 1
Link to post
Share on other sites
25 minutes ago, Patcon said:

Let us know what you get

Quick question before I get into it tomorrow morning, I'm wondering if it could be some other issue with timing or something? This is my first time running this engine so I am not sure. The thing with the idle is, although it is high at 2500 rpm, it is not rough or jumpy at all. It holds it pretty steadily. What do you think? Also thank you so much for helping me out!

Link to post
Share on other sites

Timing might determine smoothness but Zed is right. You're very likely getting too much air. The place to start it to remove the linkage from the pedal to see if the blades can close some more

Link to post
Share on other sites

Okay I think I understand what @Zed Headbetter now, so I’m getting too much air that’s causing it to run rich, so I’m thinking that could be either a vacuum leak(but I’m not sure since it’s not running rough just idling high). The other likely culprit could be that the carb wasn’t running choke plates ? When I rebuilt the hole for the choke shaft was welded close. I’m headed out now to check the linkage 

BFB4DDF1-8D95-4C7D-AFDF-C0E1DA8570A0.jpeg

Link to post
Share on other sites

Holy crap guys it’s perfect now, it was just the linkage!! I readjusted it and now I’m idling at a smooth 800-1000. (Atleast I think so, my rpm gauge decided to stop working all of a sudden LOL). It also had a ridiculously loud exhaust for a car that’s actually pretty slow. Thank you so much for all your help!! 

  • Like 2
Link to post
Share on other sites
22 hours ago, bravemushi260z said:

I don’t have a fuel return line, the previous owner removed it. Do you think this could be causing my issue??

Well you fixed the problem, but the return lines were added because of heat soak that can occur, this causes the fuel in the fuel rail to vaporize and prevent it from getting into the carb.
 

Did they remove the whole line? It’s a bit of a pain in the arse to get to the whole thing, I’d be surprised.

Link to post
Share on other sites
1 hour ago, heyitsrama said:

Well you fixed the problem, but the return lines were added because of heat soak that can occur, this causes the fuel in the fuel rail to vaporize and prevent it from getting into the carb.
 

Did they remove the whole line? It’s a bit of a pain in the arse to get to the whole thing, I’d be surprised.

@heyitsramaI believe they did, I had bought a kit with all the fuel lines and am planning to install them, but I think I’m going to need a new fuel rail for the return, here’s a picture of the setup right now, and you may be able to see it better in the video I posted earlier.

D5166A5B-2EDD-47B6-BBDC-52887482D195.png

Link to post
Share on other sites
1 hour ago, heyitsrama said:

Some cars don’t have a fuel return line, what year is the car? 
 

dustyyyyyyyy or as some people say “patina”

I know I’m cleaning it up haha, it’s It’s been sitting outside in Colorado for years. It’s a 74, it definitely has one I see it capped off with a bolt on the passenger side. Really not sure what the previous owner was trying to do. 

B233C6D2-CEFA-4E87-9C80-CDCE6A36E1AA.jpeg

Link to post
Share on other sites
  • 4 weeks later...
On 5/2/2021 at 10:34 AM, Patcon said:

Good job

It was all going well for a while but now I have the same issue, it's not being fixed by the linkage any more. I'm thinking it might be caused by a vacuum leak but i checked everywhere and don't know what else to check to be honest. Carb adjustment doesnt make any difference. I am at a point where I might just buy some new carbs to be honest. Or just go EFI

Link to post
Share on other sites
2 hours ago, bravemushi260z said:

It was all going well for a while but now I have the same issue, it's not being fixed by the linkage any more. I'm thinking it might be caused by a vacuum leak but i checked everywhere and don't know what else to check to be honest. Carb adjustment doesnt make any difference. I am at a point where I might just buy some new carbs to be honest. Or just go EFI

Have you checked for vacuum leaks?

If so, how?

 

Changing carbs, or going EFI, is following the same route as the guy who put the Webers on did. I know, the Webers replaced those pesky flat top Hitachi things, but the flat tops can be made to operate correctly, give the proper maintenance and adjustment.

 

Your car looks like it has been neglected for a considerable amount of time. Get rebuild kits for the carbs, and replace the intake/exhaust manifold gasket. Put the fuel return back into the system. 

Then adjust and tune the carbs.

 

 

  • Like 3
Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.