Cold start problems

[Frameman]

The float levels are set the same as you would the earlier model, except on carbs using plastic floats. As I stated earlier, the manual is incorrect on the HD8s float levels it should be 5/16ths. The reasons are :1) with the float being at 7/16ths the fuel level is lower so engine cranking is longer to pull fuel up. These cars are cold blooded and need lots of fuel on cold starts.2) with the float level set at 7/16ths, there is less fuel in the float bowl which could cause the car to run out of fuel when running at high RPM causing a lean mixture and a loss of power. I use the 5/16ths round bar to set the float . The bar goes between the float bowl cap and the float leaver arm. I believe this is what the manual shows but I don't have a manual in front of me. Remember to measure where the float hits the arm.
Elevation above sea level will change the settings required. Generally service manual instructions are based on being at sea level.

 

[steveg]

The float levels are set the same as you would the earlier model, except on carbs using plastic floats. As I stated earlier, the manual is incorrect on the HD8s float levels it should be 5/16ths. The reasons are :1) with the float being at 7/16ths the fuel level is lower so engine cranking is longer to pull fuel up. These cars are cold blooded and need lots of fuel on cold starts.2) with the float level set at 7/16ths, there is less fuel in the float bowl which could cause the car to run out of fuel when running at high RPM causing a lean mixture and a loss of power. I use the 5/16ths round bar to set the float . The bar goes between the float bowl cap and the float leaver arm. I believe this is what the manual shows but I don't have a manual in front of me. Remember to measure where the float hits the arm.
Elevation above sea level will change the settings required. Generally service manual instructions are based on being at sea level.

What source says the manual is incorrect? Is there a supplement or other authoritative source for this assertion? Where did it come from?

 

[Frameman]

I have been working on these type of carbs for over 50 years. I am a skilled license automotive mechanic. This skilled training allows me to analyse and understand the theory behind automotive mechanics. I have a complete understanding of automobile functioning. The information I provided comes from applying theory to resolve this problem, not trial and error. Without an understanding of theory, it is only luck if you happen to solve the problem as a former instructor told me.

 

[steveg]

I have been working on these type of carbs for over 50 years. I am a skilled license automotive mechanic. This skilled training allows me to analyse and understand the theory behind automotive mechanics. I have a complete understanding of automobile functioning. The information I provided comes from applying theory to resolve this problem, not trial and error. Without an understanding of theory, it is only luck if you happen to solve the problem as a former instructor told me.

Martin - Thank you for the clarification.

Raising the fuel level - is it the same as installing the UN richer needles?

I installed the richer needles in my car because I've got various speed equipment items (hotter cam, port matching, headers, DMD manifold, etc).

I live in a year-round driving climate (so calif) and have not had any cold starting problems.

 

[andrea]

I agree with Randy -
my car is reluctant to start in cold day (good in Summer day) starter spray is my solution to avoid battery and electr. start overheating-problems-counter run never happened-
gearbox in neutral position -few spray over the air filter -with the cocker in full position -few turn and it start immediately-then I must reduce the cocker for rev at +/- 2000 rpm to heat the engine-
i can make the operation with the hood opened throttling the engine with one hand and pushing the starter button with the other
after this operation car start normal overall - and the next day
Simple solution to avoid to change good road performance

 

[Bob_Spidell]

I would use starting fluid sparingly, if at all. It works--sometimes--but has potential problems (just do a search on 'downside of using starter fluid'). If you live in a really cold region and have a lot of starting issues a block or engine heater would be advisable.

 

[Michael Oritt]

Starting fluid is a bigger issue with diesel engines as combustion happens from compression, not spark ignition.

When ether is injected into a diesel combustion can happen at the wrong time in the cycle with pistons not at TDC and consequent damage to crank, connecting rods, etc.

 

[mgtf328]

An update to finish the post off. I think I solved one problem and found a bigger one! The choke wasn't opening fully. Too much free play in the cable the jet didn't start to move until the choke was a 1/4 the way out. It became very apparent when I took the pistons out. But, I noticed that the jets were set at different depressions in the bridge. It ran OK and I wouldn't have noticed if I hadn't had the cold starting problem. On closer inspection it looks like one jet has a larger diameter drilling than the other. Which is correct, can I change them without removing the carbs! It's a fast road engine with alloy head, modified cam (and who knows what else) by Rawles Motorsport so which one is correct.
Thanks for the help anyway.
AJ
AJ

 

[BJ8Healeys]

BJ8s are notoriously hard to start, especially when not started in a week or so -- and it doesn't even have to be cold weather. To minimize excessive cranking on the starter, I use starting fluid (and no, I've never had the engine start backwards in 36 years of using the fluid on my BJ8). Fluid is cheap, but rebuilding a starter not so much. Turn the key to fill up the float bowls, give a couple long shots of fluid into the carbs, jump in and pull the choke full out. This will typically start my car in a few revs of the engine.

 

[red57]

Seem like a trick lot of folks don't know on diaphragm carbs (HD) is that when you pull the choke and the jet drops, it squirts a small bit of fuel up as the jet displaces fuel. So, if you pull and release, pull and release, several times you are pumping fuel into the carb throat and starting will be easier. If you doubt this, take the chambers and pistons off and look at the jet while dropping it as the choke would, you will see the small squirt (assuming fuel is right near the top of the jet).
Dave

 

[Bob_Spidell]

... On closer inspection it looks like one jet has a larger diameter drilling than the other. Which is correct, can I change them without removing the carbs! AJ

I've not heard nor seen any jets with different opening diameters (as opposed to needles which come in several flavors). What often happens is a needle that isn't perfectly centered will wear a jet opening oblong; I think, if you look closely, that this may be the case with yours.

I don't think it's easy, or even possible, to replace the jets without removing the carburettors from the engine. It appears at least one important aspect of your carbs is incorrect, and should be remedied. Getting the jets properly installed is a bit tricky--IIRC, you have a BJ8 with HD8 carbs?--as you have to make sure the flappy diaphragm is properly seated in the bottom of the carb or it will leak profusely. It sounds to me like you need to get the carbs on the bench and go through both of them and, at the least, replace both jets (they can become brittle and crack with age, and newer ones should be more resistant to modern fuels). Also examine the needles to make sure they haven't been worn by contact with the jet. This (relatively) cheap kit has all the tools you'll need to adjust and balance the carbs, including a fitting to center the jets:

https://mossmotors.com/tool-kit-su-carburetor

 

[steveg]

An update to finish the post off. I think I solved one problem and found a bigger one! The choke wasn't opening fully. Too much free play in the cable the jet didn't start to move until the choke was a 1/4 the way out. It became very apparent when I took the pistons out. But, I noticed that the jets were set at different depressions in the bridge. It ran OK and I wouldn't have noticed if I hadn't had the cold starting problem. On closer inspection it looks like one jet has a larger diameter drilling than the other. Which is correct, can I change them without removing the carbs! It's a fast road engine with alloy head, modified cam (and who knows what else) by Rawles Motorsport so which one is correct.
Thanks for the help anyway.
AJ
AJ

HD8s use the .125" jets & needles - sounds like one of yours might be a .100" from an HD6. That needle is probably wrong, too. You can usually read the tiny letters on the shank of the needle with a magnifier or loupe.
Needles for HD8s: UL lean, UH standard, UN rich.

AJ - a smaller jet & needle would contribute to the lean symptoms including hard starting. This sounds like the root problem.

Dittos to Bob - rebuilding these carbs on the bench is easy. Might as well replace the plastic shaft bushings, too. Side note: my car would never idle - it would start off at 1200 or so then gradually die back until it would die. Replacing the plastic shaft bushings fixed all that. Might want to order a spare set of these as they're somewhat easy to bugger up on installation.

The jet centering tool is highly recommended.

 

[mgtf328]

I found out the hard way that fuel squirts out when you operate the choke! It goes a long way if you disconnect the cable and vigorously pump the lever by hand! Especially if you're watching closely!
I don't think my choke was coming out far enough for this to happen before I dismantled it. I'm thinking a few pulls of the choke should be as effective as starting spray when it's set up properly.
I'm wondering why someone would go to the trouble of fitting different size jets, I measured the needles and the diameters seem to match along the length. I've decided that it's probably an illusion caused by one being deeper than the other. Also I suspect you're right about them not being correctly centred. So, before I start tearing everything apart, I'm going to set both jets at the magic .075" starting point, put everything back together and see if I've solved the starting problem. It's been running fine all summer long, the only problem I had was that the plugs get a bit sooty unless you stop the engine before it gets down to idling revs. As the man said, don't fix it if it ain't broke.
AJ

 

[andrea]

I agree with Steve - AH gasoline engine, haven't sophisticated elements as injectors pumps are son of oldest, honest, technology, simple and rustic, as the milk truck or (gasoline) tractors, so a little quantity of vaporised starting liquid on the external faces of the air filers don't have any effect if engine are promptly turned to low rev. -are better than a long squirt of gasoline from the SU carbs, drowning
sparks and pistons, typical of the prolonged start tempts
the secrets are: first turn the engine without any help for few turning helping the oil to be ready
-and then value the little quantity of spray sufficient, to help the modern gasoline (very bad) to be ready to firing at the spark flash
The real problem of the colds stars, are the oil quality, for the lubrication in this critical moments
But this are one other argument