M38A1 cold start problem

Brinken · Post by **Brinken** » Tue Jan 10, 2017 10:07 am

Hi all
My -61 M38A1 has a Solex carburettor, and now after I got the licence plates and it is legal for me to take a ride now and then, I have discovered that the engine is very hard to start when the engine is cold. but it starts easily if she gets a spray with "start-aid" in the air inlet.

I should also mention that the original fuel/vacuum pump is in place, but it is propably not giving enough as the former owner put an electric fuel pump between the tank and the original fuel/vacuum pump, accordingly both pumps are working when the engine turns around.

Then she is not running clean when the engine is cold or half-cold, but when the engine is warmed up she runs clean and nice and is easy to start.

Me myself consider this as a carburettor problem, maybe some adjustment to one or more of all the adjustable screws on the carb. My problem now is that I have no idea of which screw to adjust.

Do you know where I can find a manual for the Solex carb, or do you have any tips or trix for me?

Post by **wesk** » Tue Jan 10, 2017 11:45 am

The Solex is very sensitive to fuel delivery pressure. Most electric pumps must be accompanied with a pressure regulator to use them with the Solex.

Tech Data is here:
http://www.willysmjeeps.com/v2/modules. ... _album.php

Note the instructions for cold starting.

4x4M38 · Post by **4x4M38** » Tue Jan 10, 2017 12:23 pm

Running those two pumps in series is probably not helping either
Wes?

Brinken · Post by **Brinken** » Tue Jan 10, 2017 12:27 pm

Thanks very much for the link to your album and the info about fuel pressure for the Solex. I will print out and thouroghly read it.
What will your reccomendation be then, a pressure regulator or a refurbishment of the original fuel pump

4x4M38 · Post by **4x4M38** » Tue Jan 10, 2017 12:32 pm

The original pump puts up 4-1/2 to 5 psi per specs. From what I see
the Solex only wants 1-1/2 to 3 psi?

You do not need both pumps in series with any set up. Use one pump
or the other but it appears the stock pump puts out too much for the
Solex.

Does that sound right Guys?

Post by **wesk** » Tue Jan 10, 2017 4:16 pm

I would avoid the tendency here to assume too much. It only takes a minute to plumb a fuel pressure gauge to the system and see what you are really getting!

The delivery pressure of the stock mechanical pump can actually be adjusted by using a thinner spacer. Again this requires accurate gauging of the current pressure and time.

skyjeep50 · Post by **skyjeep50** » Wed Jan 11, 2017 9:18 am

My M38 has a Solex, rebuilt fuel pump and a pressure regulator set to 2 lbs. It starts easily when hot but does need a little more cranking when cold. Important to note the cold starting instructions with the Solex - the choke must be applied fully and to NOT touch the accelerator pedal. There is no accelerator pump and hitting the gas pedal breaks the choke circuit. When starting a warm engine - choke is applied halfway, hot engine - no choke. Note that the choke is referred to as the "progressive starter" in the Solex instructions. The carb has been working well since I rebuilt the jeep.

Brinken · Post by **Brinken** » Wed Jan 11, 2017 11:35 am

Thanks a lot gentlemen for all information, first I have to get familiar with the Solex and then tame it.

I have spent most of the day today (I am far ahaid of you time wise) asking the local garages if they have a fuel pressure gauge, but all of them have the same answer: Today's cars don't have carburetor so we don't need such a gauge. I will look further for this delicate instrument.

We are having a blizzard here this afternoon so I stay indoors this evening.

Post by **wesk** » Wed Jan 11, 2017 1:08 pm

Most automotive Vacuum measuring gauges have a low pressure scale on them for dual use. Any type pressure measuring gauge that is scaled to accurately measure pressures in a range of 0 to 20 pounds will work.

https://www.google.com/#q=low+pressure+gauge+0-20+psi

Brinken · Post by **Brinken** » Mon Jan 23, 2017 3:37 am

Hi again all
After the discussion above I ran around to the garages in the neighborhood asking for a fuel pressure gauge. The guy at the last garage said: "Why don't you go to the local auto parts store, they have a fuel pressure gauge at a reasonable price." So I did,

The bearable price was about US $10 = SEK 100. A swift fix for the provisional connections and I found out that the the fuel pressure was about 3,5 - 5 PSI, both for the original fuel pump and the electric fuel pump.

Another guy at another gararge adviced me about this combined fuel pressure regulator and fuel filter called Filter King, so I ordered one on the Internet. This one was already from the start adjusted to 0,13 BAR = about 1,8 PSI, and also preperred with an outled for a pressure gauge.

After some problems with leakage at the connections, I finally got the filter/regulator running properly. I have now taken the electric pump away and I am only running the original pump.

I have also got familiar with "the cold start problems" in my Solex carb, and almost tamed it, she will start now after the third cranking, but I still find a lot of soot in the exhaust gases when the engine is cold. Is that something I have to live with, or is it some adjustment problem, or maybe just too much choke?

skyjeep50 · Post by **skyjeep50** » Mon Jan 23, 2017 7:35 am

"after the third cranking" - if you are cranking the engine for a few seconds then letting up, then cranking again, and again - that may be your problem. just crank the engine until it starts. Black exhaust can also come from oil contamination of the cylinders - worn piston rings. You might want to do a compression test. Low cylinder compression also leads to poor starting.

Brinken · Post by **Brinken** » Mon Jan 23, 2017 7:39 am

Thanks for the advice, I will do a compression test

Brinken · Post by **Brinken** » Thu Jan 26, 2017 10:37 am

Hi again
I think I have tamed my Solex now. When the engine is cold I crank until it starts, which takes about 10-12 seconds, and then she runs. I think I was a little too considerate of the starter mortor initially, it is new you know, and I want it to last as long as I have the jeep.

I have also performed a compression test with the following result:
Cylinder 1: 6,5
Cylinder 2: 7,5
Cylinder 3: 7,3
Cylinder 4: 6,5

I really don't know the sort, maybe it is kg/cm square, but is really doesn't matter. I can see that cylinders 1 and 4 are equal, 2 and 3 are equal. They differ a little too much in my opinion, but I suppose I have to live with that, anyway until something worse is happening and I have to lift the top.

skyjeep50 · Post by **skyjeep50** » Fri Jan 27, 2017 7:16 am

Cranking for 10 seconds or so won't hurt your starter motor. 6.5 Kg/cm2 is 92.5 psi, 7.5 Kg/cm2 is 106.7 psi. Factory specification for a fresh L134 is 110 psi. The range for a normal engine would be 90 to 110 psi. Testing should follow these guidelines for the most accurate test results. (from the CJ2A page): http://www.thecj2apage.com/forums/compr ... 20282.html

It would appear that your engine is within normal parameters for compression. You may want to go through and make sure timing, points, plug wires and spark plugs are also correct and in good condition.

Brinken · Post by **Brinken** » Fri Jan 27, 2017 7:58 am

Thanks for the further advice, i'll check on that when spring is coming up, now it is too cold in the garage for these extra tests.
Thanks again