Why does motor stall when cold start is pushed in? - father/son project

[GeniusAndHisAssistant]

Hi,
We are again working in earnest to get our seriesII going. Prior to being given to my son it had been in a barn for 30 years without running and we are working on the motor now. We have it running ok but when the cold start is pushed in it runs very rough and then quits. I have cleaned the jets in the carb but seems unchanged. I think I may have only pulled the top half of the carb off to clean. I know I had the bowl fully opened and cleaned it out well. There are no bubbles in the fuel line. I have a temporary tank set up for clean fuel direct to the lift pump. Any thoughts on what to approach next? All the linkages on carb and choke are cleaned and slide ok. It is the Zenith carb. I don't know anything about the vacuume advance or how to check it?

Jay

[bugeye88]

As the cold start is a choke and supplies extra fuel during start up, it could be that it is not getting enough fuel even if you warm it up a bit on choke. (which you did, right?) Then what is impeding the flow of fuel is the question. Partially clogged fuel line, clogged fuel pick up screening the tank, fuel filter, some clogged jets in the carb you have missed, failed or failing fuel pump diaphragm. These are just a few things that come to mind after it had been sitting for 30 years.

Cheers,
Rob
68 2a Bugeye 88

[GeniusAndHisAssistant]

Thanks Bugeye,
We are running fuel from a jug to the lift pump. The lift pump is new and I think works well. I must have missed a jet in the carb or something. I just put in new points and condenser... zero difference. I think you are probably right, so I'll have to pull the carb again and see. I'll also check the volume flow pre-carb.
Better luck tomorrow I hope!
We are still open to suggestions if anyone has insight.

J & E

[CKubinec]

x2 Robs advice. When you push the cold start all the way in the only fuel getting into the engine is from the idle circuit until the throttle is depressed. It is possible the idle passages in the carb base is plugged or the idle mixture screw is out of adjustment. It is best to completely remove and tear down carbs completely when cleaning. There are passages that are very small and plug easily. You can also check the gasket under the carb this way. To me it sounds like a lack of fuel or maybe a vacuum leak. Good luck.

[divingmikeboats]

Does it sputter and die when you give it throttle with the choke pulled out? Either way it sounds like a plugged jet but if you can't give it throttle it's the pilot jet. Little guy next to the main jet when looking at it from the bowl side. Happens a lot with carbs that sit.

[GeniusAndHisAssistant]

When the cold start is pulled out everything seems fine. I can hit the throttle and there is no hesitation. The problem arises after it idles a few seconds... then it starts to run real rough and coughs, sputters, and quits unless I start to bring it back with the throttle. I can have the cold start most of the way in after warm up but then the last small push in and all heck starts again. I guess I'll pull it off again and take another look. Who knows. I'll look at the seals better too. Maybe the needle is sticking but it looked very clean last time through.

[GeniusAndHisAssistant]

Thanks for the help everyone. It turned out to be a split diaphragm in the vacuum system. I temporarily placed a piece of heavy mil plastic over the regular diaphragm and the problem was resolved. Only one thing though.... in the process I think I damaged the accelerator pump valves in the process... arrrgh!!

I am posting that problem now on a new thread. I think we are gaining still!

Ebben and Jay

[rbbailey]

Hey, can you take a photo of the spot you found that you then fixed. I have the exact same problem, and I didn't do anything about it earlier because I didn't know any different! The engine always idled just right with 1/4 inch of choke pull. (Engine warm.)

When I swapped engines recently, I did a basic cleaning of the carb just to be sure it went on the new engine clean. Now on the new engine, it does the same thing -- but with just a tad less carb, like 1/8 pull. So maybe the vacuum on this engine is just a bit better! I was thinking it was time to get around to asking about it when I saw your post.

If I push the choke all the way in, it sputters and wants to quit; and will quit if still not fully warmed up, or if I don't get on the gas pedal.

[GeniusAndHisAssistant]

Sounds very similar to our problem - but a difference is that no matter how long we warmed the motor the problem continued.

Our leak was in the vacuum diaphragm which is directly connected to the carb by a short hose. Look for the circular disk with a flat top that is about 4" in diameter - within 6" of the carb. There is a wire retainer across the top which holds the top down. You can pull the wire directly out on either end, and the top should just come up with some creative assistance. No threads or anything. You will see a tiny breather hole in the top (of the aluminum cap). Keep that spot in mind before you move anything - as we found the tear in the diaphragm was immediately below that. OUrs was a long tear/crack about 1" or more, right along a seam so look closely.

I simply placed the top on a sheet of heavy mill plastic and zipped around it with a razor knife. I put two layers in over the original diaphragm and the problem was solved. We'll now order a new diaphragm from RN.

Hope this helps. Look closely at all hoses of course too. I am surprised at how much a vacuum loss affected the low idle.

J & E

[PavementEnds]

Was just reading this post. I think what you are referring to is the PCV diaphragm, part of the emisions control system -- see #4 in the diagram on this screen of the RN website:

http://www.roversnorth.com/Land-Rover-Parts/28