Dieseling

[MotorHead67]

Howdy,
Haven’t checked in for a while. The Healey has been hibernating in the garage and I’ve been occupied with other projects.
I’m back on the road with this problem: I cant figure out why she diesels. The motor in my BJ8 has had some headwork by a competent motor builder, a hotter cam, new pistons, balance etc and headers. I’ve changed up to ‘UR’ needles.
I’ve run the engine with an INOVATE air /fuel ratio meter and I can get a good idle with a reading of 12 –14 afr but as soon as I come off idle she gets rich to about 8-9 afr. I’ve checked the distributor and timing all seems well. No Gas seeping past the jets with the pump swithed on. I’ve even tried a leaner ‘UH’ needles. With the lean ‘UH’ needles she backfires through the carb but I still read rich on my meter.
There is one thing- every now and then she starts to blow white smoke from the exhaust. I’m wondering if the brake booster is failing. Would this give me a rich condition? Would this create the white smoke? I haven’t tried running without the brake booster hose connected yet. Wonder if anyone has had this type of experience.
Mike

 

[Keoke]

Howdy,
Haven’t checked in for a while. The Healey has been hibernating in the garage and I’ve been occupied with other projects.
I’m back on the road with this problem: I cant figure out why she diesels. The motor in my BJ8 has had some headwork by a competent motor builder, a hotter cam, new pistons, balance etc and headers. I’ve changed up to ‘UR’ needles.
I’ve run the engine with an INOVATE air /fuel ratio meter and I can get a good idle with a reading of 12 –14 afr but as soon as I come off idle she gets rich to about 8-9 afr. I’ve checked the distributor and timing all seems well. No Gas seeping past the jets with the pump swithed on. I’ve even tried a leaner ‘UH’ needles. With the lean ‘UH’ needles she backfires through the carb but I still read rich on my meter.

There is one thing- every now and then she starts to blow white smoke from the exhaust. I’m wondering if the brake booster is failing.
Well it just might be.


Would this give me a rich condition?
Yep it sure will. :frown:




Would this create the white smoke:

OH my goodness yes tons of it. :laugh:

That is one of the best indications that the booster is injecting brake fluid into the combustion system that I can think of.


I haven’t tried running without the brake booster hose connected yet. Wonder if anyone has had this type of experience.-- Definitely!!!!
Mike, Yep most first time owners have had the experience of dragging a cloud around behind them.----Keoke-

 

[Healey 100]

Dieseling is pretty common with Healeys. Try using premium fuel and slow down the idle speed. Make sure the timing is correct and the engine temperature is reasonable. Try a richer mixture, that lowers cylinder temperatures. Or, just leave it in gear and let out the clutch right after you turn the key off!

White smoke sounds like a water leak to me, possibly due to head gasket failure or cracks in the head. I don't think it's too likely your brake booster would produce that condition, but I am not familiar with that unit..

 

[MotorHead67]

Healey 100-thank-you. I'm running 93 Octane and already too rich.

Keoke-Wouldn’t brake fluid in the intake dilute the mixture and give me a lean condition?
Also, the white smoke comes and goes. Is that what I should expect?
Ive noticed there's not much of a vacuum at the distributor. Am I losing it to the brake booster?

 

[Bob_Spidell]

In my experience with my BJ8, run-on/dieseling is due to too fast an idle speed, high compression/low octane and/or hot engine. Hard to pinpoint with all the mods you've done--what are your compression readings? Idle speed?

The white smoke could be from burning brake fluid or coolant. Watch your hydraulic fluids closely--if the brake fluid level drops noticeably in a short period you've got a problem (it will, of course, drop slowly as your brakes run in). Only check under similar conditions--i.e. when cool after sitting on level ground for awhile--the levels rise when the car heats up. Same with your coolant level--use a dipstick for more accuracy. Look for oil in the coolant.

You can tell if your servo's working by pressing on the brake pedal (with your foot) as you start the engine. When the engine fires, the pedal should go down about an inch. The servos have a small seal called a 'gland seal' that seals the vacuum piston's shaft. Like any seal, they will wear out or get hard and brittle with age. If it fails it allows brake fluid into the vacuum piston chamber, which can get sucked into the intake manifold. You might pull the vacuum line to the servo to see if there's any fluid inside. If you're losing coolant, you probably have a problem with your head gasket like Healey_100 suggested.

Rich and lean needles have the same diameter/mixture at the first three stations (1 station = 1/8" on the needle). Thereafter, the rich needle has narrower diameters/richer mixture at all stations. How have you adjusted your mixture? Changing the mixture with the screws will affect the entire speed range.

 

[MotorHead67]

Bob,thanks for taking an interest.
Compression reads 255 in four and 260 in two cylinders. I run 93 octane and idle at 750-800rpm. The motor almost never gets hotter than 190 dgrees.
I start the jets at about .075 below the bridge. I'm probably at .090 after all the adjusting.
Re: the smoke- it only smokes on occasion and my coolant is OK.
I havent checked the brake fluid yet. The thing that makes me wonder is- it only smokes every now and then...

 

[sjuengst]

I was recently reading through a stack of old "Chatter" magazines that my dad gave me, and the December 1996 issue has an article about a run-on solution by Norman Nock. It describes a Lucas Anti Run-on Valve that creates a vacuum in the float chamber when your ignition is switched off. This stops the fuel flow into the carb. Parts cost was ~$150 (in '96).

 

[Bob_Spidell]

Wow ... that's really high compression (175lbs or so in a BJ8 is nominal). Does it ping on 93 octane? Is it 93 R+M/2 octane? 750-800rpm idle should be OK.

With that compression there's nothing wrong with your head gasket. An occasional puff of white smoke could be just a drop or two of brake fluid getting into the intake.

Lowering the jets enrichens the mixture. Where is the fuel level WRT the top of the jets?

When you come off idle you should get richer momentarily, but it should come back to around 14 I would think.

 

[Michael Oritt]

A cam with more duration will cause the engine to "lope" which is also called "dieseling".

 

[MotorHead67]

Bob,
Thats what I'm thinking. Just an occasional bit of brake fluid meaning the booster is on it's way out. Maybe a vacuum issue too.I don't know if the brake fluid would give me a rich indication on my meter.
How can I tell where the fuel level is? I've checked the float levels and they're OK.
Isn't 14 too lean?

 

[Bob_Spidell]

Bob,
How can I tell where the fuel level is? I've checked the float levels and they're OK.
Isn't 14 too lean?

Pull the carb vacuum cylinders off, then turn the key on. When the pump stops clicking look at the level of the fuel in the jets. It should be a bit below (1/16-1/8") the top of the jets.

An A/F mixture of 14 would be slightly rich of stoichiometric (about 14.7). That should be OK, I would think, not being sure how your meter(s) are set up.

 

[MotorHead67]

Well...Brake fluid IS low and I'm not losing it at the wheels. I've plugged the vacuum port at the manifold.
The fuel level in the front carb is a bit lower than 1/8". Would that make that carb leaner?
I'm wondering about the compression. The engine spec sheet says it should be 9.8:1. Is there a way to find out if that's correct? Compression is approx. 255psi.

 

[tahoe healey]

225? are you talking about the average engine compression? I've never heard of it being that high.

 

[Keoke]

. The engine spec sheet says it should be 9.8:1. Is there a way to find out if that's correct? Compression is approx. 255psi.

Yes, I suggest you get a new compression guage.---Keoke

 

[GregW]

Isn't 255PSI normal for a diesel engine? :wink:

 

[Keoke]

Dogone it ifin you aint right Greg----Keoke- :laugh:

 

[MotorHead67]

OK,OK Go easy on me... I'll do the compression test again. I let it crank and build up pressure.
Guess I should check the reading after the first revolution?

 

[Keoke]

I'll do the compression test again. I let it crank and build up pressure.


That is the right way to do it jest borrow you buddies guage-----Keoke-- :laugh:

 

[Genos2]

GregW, a diesel engine wouldn't run with 255 psi or a least not start without towing, I think min is 380-400psi for our VW diesels,like to see 450-480psi.Most of my Healeys have been 135-150psi. Did have a tri-carb that had 225psi, both head& block had been milled(alot)& block relieved for valve clearance! I blew it up in B.C., had to tow it home(long drive)w/ tow bar. I agree w/Keoke,time for new guage,eng warm, throttle open. cheers Genos2

 

[Bob_Spidell]

Well...Brake fluid IS low and I'm not losing it at the wheels. I've plugged the vacuum port at the manifold.
The fuel level in the front carb is a bit lower than 1/8". Would that make that carb leaner?
I'm wondering about the compression. The engine spec sheet says it should be 9.8:1. Is there a way to find out if that's correct? Compression is approx. 255psi.

More than 1/8" below the top of the jet? Actually, a lower fuel level will make an SU run richer (greater fuel surface at any point along the tapered needle). At any rate, both carbs should be at about the same levels.

If you have the data for your engine, you can calc static and dynamic compression ratios. See: https://www.kb-silvolite.com/calc.php?action=comp

Heat of compression also adds to the reading on your gauge; don't know if these formulas account for this or not.