Engine Won't Start - L20 w/ dual Weber 40 DCOE carbs

Engine, Transmission and related drivetrain.
sBay510
Posts: 7
Joined: 06 Jun 2016 18:19

Engine Won't Start - L20 w/ dual Weber 40 DCOE carbs

Postby sBay510 » 06 Jun 2016 22:56

Hi Guys,

Long story short, I have a 71’ 510 with a L20 w/ twin Weber 40 DCOE carbs. I didn’t have the opportunity to get it in and start it up for about a year. I did have a battery tender on the battery to keep it alive. Now that I have the chance to hop in the car, I can’t get it to start. It will turn over, but not start.

I have tried to use starting fluid and it roars to life, but then just dies out. The starter is running/turning so I do not think that’s the problem. The last time I had the engine running, I purposely used most of the fuel in the tank. I put in a fresh half tank load of fuel in it recently before trying to start it.

The car has an electric fuel pump in the trunk next to the fuel cell. It turns on when the key is put into ACC. I can hear it buzzing and working. I’m fairly new to working on carburetor engines, so I have been doing a lot of reading on this forum and online in general. I have tried leaving the pump on for about 2-3 min to fill up the fuel bowls in the carbs. Both fuel lines for each carburetor have a in-line fuel pressure gauges (under the hood – pretty close to the carbs) and are reading at approx. 3 – 3.5 psi after the bowls are full. I have taken off the fuel lines, put the open end into a bottle and turn the ignition on to ensure fuel is actually getting pumped to the carb..which it is. So I do not think fuel delivery to the carb is the issue either. I have pumped the gas pedal anywhere from 3-6 time before trying to crank the engine – as I have read to do so – but still will not start.

Since I was able to get some results with starting fluid, I then resorted to spraying some gas into each venture body. After I sprayed fuel into them, the engine started up for a few seconds (I was so happy), but then died again. I did this multiple times with varying results. Since I’m at least able to get it running for a second or two, I assume I can rule out any spark issues. After a while, I noticed the starting attempts was taking a toll on the battery, so I attached a jumper batter pack to it to charge/assist. I’ll be getting a brand new battery this week.

At this point, I’m thinking it is some type of fuel delivery problem within the carb and going into the throttle body (Accelerator pump circuit?). With the ignition and fuel pump on, I tried opening and closing the throttle plates via the linkages under the hood ( I hope that makes sense) to see if any fuel would squirt out into the venturis, but no fuel was squirting out. I checked in all 4 openings and no fuel was squirting. I should be seeing fuel squirt out at this point correct?

I have read to take the top cover of the carb off and check the needle valve since it might be stuck since the car sat for a while. I have not checked the needle valve yet. What exactly should I be testing/looking for?

I really want to fix this issue myself and get the car started. I feel like I can almost get the car started, but I need to fix a minor things. I really do not want to take it into a shop, but I’m going to have to if I can’t resolve it.

I would greatly appreciate any assistance from you guys.

Thank you in advance!

Colbino
Posts: 510
Joined: 19 Sep 2007 12:58
Location: Bellevue, WA

Re: Engine Won't Start - L20 w/ dual Weber 40 DCOE carbs

Postby Colbino » 07 Jun 2016 00:03

Maybe the carbs just need to be cleaned since old ethyonol gums up and probably have clogged the tiny jets.

User avatar
GREG510
Posts: 490
Joined: 23 Jun 2003 23:12
Location: Richmond B.C.
Contact:

Re: Engine Won't Start - L20 w/ dual Weber 40 DCOE carbs

Postby GREG510 » 07 Jun 2016 03:32

You would be surprized of the crap that can gum up the jets and passage ways.
I don't run my car nearly as much as I should and over the years (Keith you can chime in here...LOL)
I have torn my webers apart to clean them a few times.

User avatar
okayfine
Supporter
Posts: 14123
Joined: 12 Nov 2007 23:02
Location: Newbury Park, CA

Re: Engine Won't Start - L20 w/ dual Weber 40 DCOE carbs

Postby okayfine » 07 Jun 2016 05:56

Excellent troubleshooting and description. I third the suggestion that a good cleaning of your carb internals is your most likely solution. Lots of YouTube how-tos, but I'd mainly suggest cleaning one carb at a time so you have the other complete carb to reference.

You'll also likely have to balance the carbs once you've got 'em back together, so you'll need a flow meter for that.
Because when you spend a silly amount of money on a silly, trivial thing that will help you not one jot, you are demonstrating that you have a soul and a heart and that you are the sort of person who has no time for Which? magazine. – Jeremy Clarkson

User avatar
Byron510
Moderator
Posts: 11619
Joined: 01 Jul 2003 23:06
Location: Maple Ridge, BC

Re: Engine Won't Start - L20 w/ dual Weber 40 DCOE carbs

Postby Byron510 » 07 Jun 2016 07:03

On any carburetor, the fuel jets and ports lead out the bottom of the float bowl. If left to sit, fuel will slowly evaporate away - but not all of the fuel - just some of the components that make up fuel. The rest of the fuel components are left behind and can leave a gell or a dry flaky residue. If you were to look at the minute size of the jets and passageways inside the carb, it will become very clear that any of them can easily be blocked. And since pumping the pedal - which should activate the accel pump - didn't help the situation, it would seem that not only are the idle and main jets not getting fuel, your accelerator pump circuit is also not getting fuel.

All is not lost, in fact all of the side draft type carbs are very easy to get access to any of the circuits without removal of the carbs or even touching any of your throttle linkage. But you need to be methodical. First you need a good diagram of all the fuel circuits (best to purchase a good book on your specific carbs). Study them first, and then trace each system/circuit. Pulling out the emulsion tubes will get you access to the main fuel jets (bottom) and air corrector jets (top) behind this is the low speed emmultion tubes that control the idle and low speed mixture (air/fuel). These get fed from the float bowl and into the bottom of the jet wells. Fuel is dorwn up and air is pulled down, metered at the correct amounts. From either circuit, the air/fuel mixture is drawn into passages in the throttle bore. These passages, especially the low speed circuit, are small. But there are access points on the low speed circuit close to the throttle shaft where you can make sure this passage is clear – both from the jet wells to this point and from this point into the throttle bore. The main fuel circuit feeds into the booster venturi. The venturi's themselves are easily removed via a lock nut and threaded set screw under the carb. Again the passage from the emmultion tube well to this area needs to be clear. The last circuits are the accelerator pump and the choke circuit. The accel pump has a little check ball that allows fuel into the diaphram from the float bowl. Once the circuit is activated via throttle position change, this check ball moves backwards, stopping the flow of fuel back into the float bowl and fuel is injected strait into the throttle bore. Again passages into the diaphram are normally below the fuel level. If the fuel has evaporated away, all kinds of gunk will form in here. And of course the circuit after the pump needs to have a clear path.

It's a short run down of the basic circuits, but it's all certainly within the realm of someone willing to take a few hours to read up and methodically attempt a cleaning of the carbs. First you really need a good book on the carbs. This will go a long way. When getting down to it, lots of carb cleaner and compressed air wouldn't hurt. Lots of good light is in order. Meticulously clean is next in order. Label bits as you remove them.

Moral of the story, if the car is getting parked for any length of time, run the carbs completely dry of fuel by stopping the fuel supply and letting the car run. The accel pump circuit will continue to hold fuel, so in the cars last few breaths, little blips of the throttle will inject these last portions of fuel out of the carb.

It’s a hard lesson for you, but if you like playing with your car – this is a chance to get intimate in understanding carburation very well.

Hope this helps.

Byron
Love people and use things,
because the opposite never works.

User avatar
bertvorgon
Supporter
Posts: 9837
Joined: 04 Aug 2003 20:45
Location: White Rock, B.C. Canada

Re: Engine Won't Start - L20 w/ dual Weber 40 DCOE carbs

Postby bertvorgon » 07 Jun 2016 07:28

Do not know if you saw this link...but...it will help!

Thanks to Rob for posting this originally.

http://www.lainefamily.com/images/WeberTuningManual.pdf
"Racing makes heroin addiction look like a vague wish for something salty" - Peter Egan

1973 2Door Slalom/hill climb/road race / canyon carver /Giant Killer 510
1968 Vintage 3HP Mini Bike
1971 Vintage 13' BOLER trailer

sBay510
Posts: 7
Joined: 06 Jun 2016 18:19

Re: Engine Won't Start - L20 w/ dual Weber 40 DCOE carbs

Postby sBay510 » 07 Jun 2016 13:10

Hi Guys,

Thanks for the replies. Byron, thanks for the detailed flow of the circuits.

So i should be getting fuel squirting into the barrels when accelerator is activated, right?

So it sounds like I am going to have to get in and start cleaning the carbs. Can i just use some carb cleaner on the jets, valves, etc? Someone else had recommended guitar strings, which i will have to google.

User avatar
bertvorgon
Supporter
Posts: 9837
Joined: 04 Aug 2003 20:45
Location: White Rock, B.C. Canada

Re: Engine Won't Start - L20 w/ dual Weber 40 DCOE carbs

Postby bertvorgon » 07 Jun 2016 13:22

Yes, shine a nice bright light into a throttle bore and you should see a squirt of fuel when you wing the throttles.

If you do not, then that says those carb(s) are really plugged up, as the feed for the accelerator pump reservoir is kinda on the large side, so the feed is large...and if that is PLUGGED...or the check valve is STUCK...then that really says the carbs a crudded.

If when you tried to start the car and you "winged" the throttles, the engine should have maybe coughed and farted as at least the accelerator pumps got some fuel in there. As it sounds like it did not......

Have you popped the top off the float bowl/jet wells?
"Racing makes heroin addiction look like a vague wish for something salty" - Peter Egan

1973 2Door Slalom/hill climb/road race / canyon carver /Giant Killer 510
1968 Vintage 3HP Mini Bike
1971 Vintage 13' BOLER trailer

sBay510
Posts: 7
Joined: 06 Jun 2016 18:19

Re: Engine Won't Start - L20 w/ dual Weber 40 DCOE carbs

Postby sBay510 » 07 Jun 2016 13:31

bertvorgon wrote:Yes, shine a nice bright light into a throttle bore and you should see a squirt of fuel when you wing the throttles.

If you do not, then that says those carb(s) are really plugged up, as the feed for the accelerator pump reservoir is kinda on the large side, so the feed is large...and if that is PLUGGED...or the check valve is STUCK...then that really says the carbs a crudded.

If when you tried to start the car and you "winged" the throttles, the engine should have maybe coughed and farted as at least the accelerator pumps got some fuel in there. As it sounds like it did not......

Have you popped the top off the float bowl/jet wells?


OK, so I am getting no squirting of fuel. I did take a video with my phone to double check since the spaces are tight to put my whole face into. I didn’t see any squirting unfortunately.

I actually did finesse the throttle when trying to start and the engine coughed/stumble/fart sometimes, if that helps.

I haven’t take the top cover off yet, but will do so soon. Should I be looking for anything specific. Or is it a matter of taking things apart?..which I am somewhat hesitant to do.

sBay510
Posts: 7
Joined: 06 Jun 2016 18:19

Re: Engine Won't Start - L20 w/ dual Weber 40 DCOE carbs

Postby sBay510 » 07 Jun 2016 13:37

bertvorgon wrote:Do not know if you saw this link...but...it will help!

Thanks to Rob for posting this originally.

http://www.lainefamily.com/images/WeberTuningManual.pdf



Thank you and Rob for the link and PDF! I will take a thorough look!

User avatar
defdes
Supporter
Posts: 4958
Joined: 12 May 2005 14:45
Location: Vermont

Re: Engine Won't Start - L20 w/ dual Weber 40 DCOE carbs

Postby defdes » 07 Jun 2016 15:35

You'll take the top cover off first (small rectangular plate with one screw) that will expose air, idle and if you pull out the ...(are they called emulsion tubes on Weber's?) the main jets are screwed into the bottom of those. The pump jets have their own little flat head screw covers (at least they do on Mikunis) those jets have a flat section on them and only go back in one way along with a VERY small aluminum washer on the bottom of them that you don't want to lose. Pull them all out, run carb cleaner and compressed air through them and re insert. You can pull the main cover after that to pull out the float, you should check the floats for proper adjustment while they are all apart (you'll have to look at a Weber tuning sheet for that measurement).

sBay510
Posts: 7
Joined: 06 Jun 2016 18:19

Re: Engine Won't Start - L20 w/ dual Weber 40 DCOE carbs

Postby sBay510 » 08 Jun 2016 12:45

defdes wrote:You'll take the top cover off first (small rectangular plate with one screw) that will expose air, idle and if you pull out the ...(are they called emulsion tubes on Weber's?) the main jets are screwed into the bottom of those. The pump jets have their own little flat head screw covers (at least they do on Mikunis) those jets have a flat section on them and only go back in one way along with a VERY small aluminum washer on the bottom of them that you don't want to lose. Pull them all out, run carb cleaner and compressed air through them and re insert. You can pull the main cover after that to pull out the float, you should check the floats for proper adjustment while they are all apart (you'll have to look at a Weber tuning sheet for that measurement).


Thanks for the reply. Yes, emulsion tubes on Weber's. Unfortunately i dont have an air compressor at the moment, so i'll just have to rely on the compressed air in the carb cleaner can.


Return to “Powertrain”



Who is online

Users browsing this forum: No registered users and 1 guest